It is proposed that concentration-dependent PDA film formation reflects the competition between intermolecular amine-quinone condensation processes, leading to adhesive cross-linked oligomer structures, and the intramolecular cyclization route forming little adhesive 5,6-dihydroxyindole (DHI) units. Film growth would then be sustained by dopamine and other soluble species that can be adsorbed on the surface.Despite extensive investigations over the past decade, the chemical basis of the extraordinary underwater adhesion properties of polydopamine (PDA) has remained not entirely understood. The bulk of evidence points to PDA wet adhesion as a complex process based on film deposition, and growth in which primary amine groups, besides catechol moieties, play a central role. However, the detailed interplay of chemical interactions underlying the dynamics of film formation has not yet been elucidated. Herein, we report the results of a series of experiments showing that coating formation from dopamine at pH 9.0 in carbonate buffer: (a) Requires high dopamine concentrations (>1 mM); (b) is due to species produced in the early stages of dopamine autoxidation; (c) is accelerated by equimolar amounts of periodate causing fast conversion to the  Despite extensive investigations over the past decade , the strAnother relevant issue is whether other structural units and functional groups in addition to amines, especially cyclized 5,6-dihydroxyindole (DHI) units, play a role in PDA film deposition and coating. This issue was addressed in a recent study  showing Although there is to date enough evidence indicating that primary amine groups, besides catechol moieties, play a vital role in PDA wet adhesion, the detailed interplay of chemical interactions underlying the dynamics of film formation has remained little understood. Important insights into the mechanisms underlying PDA film deposition can be obtained by studies of concentration dependence. Early studies on this aspect ,13 showeNotably, no coating formation was reported at low dopamine concentrations (<0.1 g/L) or when the substrate was immersed after the process of PDA formation was completed . It was concluded that PDA film formation follows two different mechanisms with different regimes, namely film deposition and film growth . These rThe aim of the present study is to address in a systematic manner these central issues by means of a chemical approach based on: (a) A re-examination of the dependence of film formation on dopamine concentration; (b) an analysis of the evolution of the film-forming properties of PDA with the course of dopamine oxidation; (c) the effect of the fast generation of dopamine quinone on the two phases of film deposition and growth; and (d) the effect of added amines on film deposition. Based on the preliminary results of these experiments, an improved chemical model for PDA film formation is proposed, in which the two processes relating to film deposition and growth are interpreted in terms of concentration-dependent intermolecular amine-quinone chemistry and of subsequent monomer adsorption on the deposited layers, respectively.2SO4/30% H2O2 5:1 v/v) overnight, rinsed with distilled water and dried under vacuum.All reagents were purchased from commercial sources  and used without further purification. Quartz substrates were cleaned by soaking in piranha solution  in 0.05 M carbonate buffer (pH 9.0), or 0.05 M phosphate buffer (pH 9.0), or 0.05 M Tris buffer (pH 8.5) , under vigorous strirring. v/v, and air-dried. The coated substrates thus obtained were analyzed by ultraviolet–visible (UV–vis) spectrophotometry on a Jasco V-730 instrument . When required, after 24 h the reaction mixture was acidified to pH 2 with 4 M HCl, centrifuged at 5488× g at 4 °C , and the precipitate washed three times with water and lyophilized to collect the dark pigment (45% w/w yield).Quartz substrates were dipped in the autoxidation mixtures after complete dissolution of the catechol. After 24 h, substrates were rinsed with distilled water, sonicated in methanol/water solution 1:1 In separate experiments, to investigate the evolution of film forming during PDA synthesis from 10 mM dopamine in carbonate buffer (pH 9.0), quartz substrates were dipped in the solution for the appropriate amount of time according to the experiment (between 1 and 24 h), and then rinsed and analyzed as described above. To a 1 mM solution of the appropriate amine  in 0.05 M carbonate buffer (pH 9.0), dopamine hydrochloride was added under vigorous stirring in a 1:1 molar ratio. Quartz substrates were dipped into the reaction mixture and left under stirring for 24 h, then rinsed with distilled water, sonicated, dried and analyzed as above.Dopamine hydrochloride  was dissolved in 0.05 M carbonate buffer (pH 9.0)  followed by sodium periodate in a 1:1 molar ratio. The reaction mixture was left under vigorous stirring for 24 h. The quartz substrates were dipped in the solution for the appropriate amount of time according to the experiment (between 5 min and 24 h). They were then rinsed with distilled water, sonicated, dried and analyzed as above. g at 4 °C, washed three times with water, and lyophilized (90% w/w yield).After 24 h the reaction mixture was acidified to pH 2 with 4 M HCl and the dark pigment was collected by centrifugation at 5488× Polydopamine films obtained as described above by periodate oxidation of 10 mM dopamine for 1 h were immersed into solutions of 0.1 or 1 mM dopamine in 0.05 M carbonate buffer at pH 9.0 and left under stirring for 3–6 h. The substrates were rinsed and analyzed as usual.2 (yellow square). For the micro-Raman imaging, the samples were scanned over the area of 18 × 18 μm2 indicated by the red squares. The scanning step was set at 320 nm in order to match the FWHM of the diffraction-limited focused laser spot. The Raman spectra results from 500 ms acquisition time, while the Raman images of the analyzed regions were reconstructed integrating for each scanned position the Raman signal in a spectral window of 140 cm−1 in width, centered at the 1584 cm−1 peak.The combined atomic force microscopy (AFM) and micro-Raman analysis were conducted with the integrated apparatus Alpha300 RS . The system can be switched at will between AFM and confocal micro-Raman configurations, allowing a combined topographical and spectral characterization of a specified microregion of the sample. The samples topographies were studied by AFM in intermittent contact (AC) mode using a cantilever with 75 kHz resonant frequency. For the micro-Raman analysis, a laser beam at λ = 488 nm was used as excitation light source. The beam was focused onto the sample surface by means of a 50× microscope objective  of 0.75) working in epi-illumination mode. The diffraction-limited focused spot in the objective focal plane had a full width at half-maximum (FWHM) of approximately 320 nm. The light backscattered from the sample was collected by the same objective, and sent to the spectrograph through a confocal optical collection path. The samples analysis was conducted in the microregions marked by the colored squares in the optical images of the films. The AFM images correspond to an area of 25 × 25 μm13C and 15N NMR experiments, respectively. Cross polarization (CP) spectra were recorded with a variable spin-lock sequence (ramp CP-MAS), and a relaxation delay of 4 s; a 1H π/2 pulse width of 3.0 μs was employed and high-power proton decoupling was applied during acquisition. For 13C spectra, the contact time was set to 2 ms and 20,000 scans were recorded per each sample. Spectra were referenced to external adamantane , set at 0 ppm). For 15N spectra, the contact time was set to 1.5 ms and 80,000 scans were recorded. Spectra were referenced to external glycine . Solid state nuclear magnetic resonance (NMR) spectra were recorded on a Bruker Avance II 400 spectrometer  operating at a static field of 9.4 T, equipped with a Bruker 4 mm magic angle spinning (MAS) probe. Samples were packed into Bruker 4 mm zirconia rotors sealed with Bruker Kel-F caps. The spinning speed was set at 10 and 6 kHz for In a first series of experiments the dependence of PDA film deposition on the initial dopamine concentration was re-examined using carbonate buffer at pH 9.0. For the purposes of these experiments, the final absorbance on quartz was taken as a rough index of the degree of coating deposition. The results showed that at 1 mM concentration (or lower) dopamine autoxidation in carbonate buffer does not result in ultraviolet (UV)-detectable coatings . o-quinone, was not effective in inducing UV–vis-detectable film deposition with 1 mM dopamine. Notably, however, when HMDA or other amines were added to 1 mM dopamine at pH 9.0, variable levels of coating formation were observed  and 120–170 (sp2 hybridization) ppm, are observed. The complex sp2 band, centered at 130 ppm, is compatible with indole/pyrrole-like structures, however the poor resolution prevents a detailed assignment. The sp3/sp2 intensity ratio is comparable in both samples. In a final series of experiments the mechanisms of film growth following deposition of the initial PDA coating was investigated based on changes in UV–vis absorbance. Polydopamine films obtained by periodate oxidation of 10 mM dopamine for 1 h were extensively washed, dried and immersed into solutions of 0.1 or 1 mM dopamine at pH 9.0 (under these conditions no coating was deposited in control experiments using uncoated quartz substrates). The results showed a detectable increase in the film absorbance over 6 h . This obIntense research activity into PDA film deposition over the past few years has contributed to delineate an improved picture of the underlying structural factors and features of the process, including kinetic profiles, concentration dependence, role of oxidants and amine-based additives. Very recently, a thermodynamic top-down investigation of the effects of oxidants and pH on dopamine oxidation showed that the crucial parameters in autoxidation are the pKa values of the semiquinone and the amino group in the oxidized quinone . HoweverIn addition, it was shown that: (a) The rapid oxidation of dopamine with periodate results in the rapid deposition of film which however do not attain the levels observed by autoxidation (UV–vis evidence); and (b) soluble monomers/oligomers can be physically adsorbed on the primer coating leading to a UV–vis detectable growth of pre-existing films. This process can be observed at a dopamine concentration of 1 mM, which does not lead to detectable coatings in the absence of the primer film. To put these observations into a rational framework of competing mechanisms it is necessary to look at amine-quinone reactions, mainly Michael-type and Schiff-base chemistry , as the 4/H2O2 [Although partly speculative, this scheme would well explain some observations such as the effect of periodate on thickness and roughness, the effect of long chain amines and the observed increase in film absorbance following immersion in dopamine solutions. Use of periodate ensures that all dopamine is rapidly converted to the quinone, favoring cross-linking reactions. However, while a minor amount of the material adheres to the substrate to form the primer layers, the remainder of the dopamine and other monomers would be rapidly converted to large insoluble aggregates, which would no longer contribute to the subsequent growth of the film, as observed in the slow autoxidation process. The lower roughness of the films produced by periodate oxidation compared to autoxidation is in accordance with previous findings using either higher oxygen concentration  or CuSO44/H2O2 , and canThe effect of long-chain diamines in promoting film formation at low dopamine concentrations can thus be attributed to coupling with the quinone, via e.g., addition or Schiff-base formation. Inclusion of long and flexible aliphatic chains into the main structural components of PDA via amine groups would account for: (a) The provision of a hydrophobic component, which is critical for underwater adhesion; (b) the inhibition of intramolecular cyclization by occupying critical positions or via Schiff-base formation; and (c) the inhibition of aggregate formation which is important for adhesion.Work in progress is directed to validate this scheme by isolating and characterizing the primary intermediates in dopamine oxidation at high concentration to assess their adhesion properties.


Smenospongia are a prolific source of chlorinated secondary metabolites. The use of molecular networking as a powerful dereplication tool revealed in the metabolome of S. aurea two new members of the smenamide family, namely smenamide F (1) and G (2). The structure of smenamide F (1) and G (2) was determined by spectroscopic analysis . The relative and the absolute configuration at C-13, C-15, and C-16 was determined on the basis of the conformational rigidity of a 1,3-disubstituted alkyl chain system . Smenamide F (1) and G (2) were shown to exert a selective moderate antiproliferative activity against cancer cell lines MCF-7 and MDA-MB-231, while being inactive against MG-63.Caribbean sponges of the genus  Marine organisms are a source of compounds with enormous chemical diversity, which, in turn, translates to a wide variety of biological activities. Many marine natural products show unusual and unique chemical structures, often containing halogen atoms. Halogenated natural products are widely present in nature. Currently, more than 5000 compounds are reported in the literature and most of them have a marine origin ,2. Smenospongia, which have proven to be very rich in new chlorinated secondary metabolites. Among them are smenamides  to investigate the possible antiproliferative activity of the two compounds.In this paper, we report on the use of a molecular networking dereplication strategy which resulted in the rapid detection from extracts of S. aurea collected along the coast of Little Inagua (Bahamas Islands) was extracted as described in our previous papers +) and 541.2440 ([M + Na]+). Intense (32%) M+2 isotope peaks of both ions suggested the presence of one chlorine atom in the molecule, allowing for the determination of the molecular formula C28H39ClN2O5 with 10 unsaturations. The 1H NMR spectrum of smenamide F (1) was indicative of a mixed NRPS/PKS biogenesis metabolite, in that it showed signals for five aromatic protons, suggesting a monosubstituted phenyl group, one amino acid α proton , two olefinic protons , five methyl groups , and a methine proton . The general features of the spectrum suggested compound 1 to belong to the smenamide family. A second methyl doublet  replacing the vinylic methyl singlet of smenamide A (3), the oxymethine group at C-15, and one less unsaturation showed smenamide F (1) to be a hydrated analog of smenamide A (3). The high-resolution ESI MS spectrum of smenamide F  showed a COSY correlation peak with a second methylene group  which was, in turn, J-coupled with another methylene group . This latter group showed HMBC correlation peaks with an N-methyl group  and a carbonyl carbon . The presence of correlation peaks of the N-methyl group at C-27, and an acetyl methyl group  with the carbonyl carbon atom at Cδ 173.4, established the N-methylacetamido function as the western terminus of the molecule. As a result of the E/Z conformational equilibrium at the N-methylacetamido function, most resonances in the proton NMR spectrum of compound 1 were split into two signals, with an approximate 1:1 ratio. This is quite common for cyanobacterial metabolites with a tertiary N-methyl amide function, such as kalkitoxin . The resulting l-FDAA derivative was subjected to LC-ESIMS analysis and showed the same retention time of an authentic standard prepared from l-FDAA and l-Phe, thus determining the S configuration at C-8.Smenamide F  was the foundation for determining the relative configuration at C-13, C-15, and C-16. As discussed in our previous work  present 3-17 and H-16 with H3-14 and the absence of any correlation of H-13 with H2-18, could only be accounted for by conformation d in S,15S,16R or 13R,15R,16S. Under these assumptions, the relative configurations at C-13 and C-16 could be determined based on NOESY data. The two possible diastereomers are depicted in 1) possesses the same 16R configuration as smenamide A (3) + and [M + Na]+ ions at m/z 519.2620 and 541.2440, respectively, consistent with the molecular formula C28H39ClN2O5, and suggesting that it is isomeric with smenamide F (1). The one-dimensional 1H NMR spectrum of compound 2 appeared nearly identical to that of compound 1 , with minor differences in chemical shifts for all signals. Correlation peaks in the 2D NMR spectra (including NOESY) were also very similar, and the MS/MS fragmentation pattern was identical (2) has the same relative configuration as smenamide F (1). In contrast, Marfey’s analysis showed that the l-FDAA derivative obtained from compound 2 was identical to l-FDAA-d-Phe, and therefore, that configuration at C-8 was R. Therefore, smenamide G (2) was determined as the epimer at C-8 of smenamide F (1), i.e., the 8R,13S,15S,16R,20Z stereoisomer.The high-resolution ESI mass spectrum of smenamide G  and G (2) were measured. The ECD spectrum of smenamide F (3), while the ECD spectrum of smenamide G  and G (2) were shown to exert selective moderate antiproliferative activity against both MCF-7 and MDA-MB-231 breast carcinoma cell lines , MDA-MB-231 (triple negative breast cancer) and MG-63 (osteosarcoma) cell lines. Smenamides F and G were evaluated individually against cancer cells at concentrations of 1 and 5 μM for 96 h. As previously reported  to evaluate the possible antiproliferative activity of the compounds. Data obtained showed that smenamide F (1) and G (2) exert a selective moderate antiproliferative activity against both breast carcinoma cell lines (MCF-7 and MDA-MB-231) at 5 μM, while being inactive against the MG-63 osteosarcoma cell line.The use of molecular networking as a dereplication strategy allowed for the rapid detection of two new members of the smenamide family of compounds, smenamide F (


H/ΔT = 26.9 J g−1 °C−1), the less activation energy of cyclization , and the higher extent of stabilization (sE and SI) during TOS process, which demonstrated that the AMPS comonomer improved the efficiency of the TOS process. The P(AN-co-AMPS) nanofibers had the better thermal stable structures. Moreover, the carbon nanofibers derived from P(AN-co-AMPS) precursor nanofibers had the better graphite-like structures (GX = 46.889). Therefore, the AMPS is a promising candidate comonomer to produce high performance carbon fibers.The quality of polyacrylonitrile (PAN) precursor has a great influence on the properties of the resultant carbon fibers. In this paper, a novel comonomer containing the sulfonic group, 2-acrtlamido-2-methylpropane acid (AMPS), was introduced to prepare P(AN-co-AMPS) copolymers using itaconic acid (IA) as the control. The nanofibers of PAN, P(AN-co-IA), and P(AN-co-AMPS) were prepared using the electrospinning method. The effect of AMPS comonomer on the carbon nanofibers was studied using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and Raman spectrum. The structural evolutions of PAN-based nanofibers were quantitatively tracked by FTIR and XRD during the thermal oxidative stabilization (TOS) process. The results suggested that P(AN-co-AMPS) nanofibers had the lower heat release rate (Δ Due to their high strength and modulus, low weight, and excellent heat resistance, carbon fibers have been extensively used as a versatile reinforcing material of composites applied in the fields of aerospace, automotive industries, and civil engineering ,2,3,4. PIn order to solve this problem, several acidic comonomers, such as itaconic acid (IA) , acrylicIn the present work, we have further introduced another industrial-grade, low-cost comonomer into PAN copolymer used as a carbon fiber precursor, namely, 2-acrtlamido-2-methylpropane acid (AMPS) also containing the sulfonic group. AMPS is a hydrophilic vinyl monomer which is widely used in hydrogel . To the Itaconic acid , 2,2-azobisisobutyronitrile , and analytical grade methanol were obtained from Shanghai Macklin Biochemical Co., Ltd., Shanghai, China. Analytical grade acrylonitrile (AN), AMPS and dimethyl formamide  were purchased from Sinopharm Chemical Reagent Beijing Co., Ltd., Beijing, China. Dimethyl sulfoxide  was purchased from Shanghai Aladdin Bio-Chem Technology Co., Ltd., Shanghai, China. AN was distilled under reduced pressure and restored in a freezer prior to further use. Other reagents were used without further purification.PAN homopolymer and PAN copolymers were synthesized by free-radical solution polymerization in a 100 mL three-necked flask. Briefly, by taking DMSO as a solvent and AIBN as an initiator (1 wt.% based on the monomers), the solvent concentration was 77 wt.%, and the molar ratio of AN and IA was 98:2. Next, the reaction was carried out at 60 °C at nitrogen atmosphere for 8 h with mechanical agitation. After polymerization, the substance produced was washed by deionized water and methanol to remove unreacted monomer, and then the substance was dried in a vacuum oven for 8 h. PAN homopolymer and P(AN-AMPS) were synthesized by the same method. The synthesis process of PAN homopolymer, P(AN-co-IA), and P(AN-co-AMPS) are shown in The electrospinning was performed using an electrospinning machine . The electrospinning solution was prepared by dissolving PAN (co)polymers into DMF solvent and its concentration was 10 wt.%. The solution was loaded into a horizontal syringe with a 21-G metal nozzle. The applied voltage was 12 kV and the distance from the collector to the needle was 12 cm. The feed rate was 1 mL/h and the rotation rate of the roller was 1000 rpm. The resultant nanofibers were deposited onto the aluminum foil covering the roller. After electrospinning, as-obtained nanofibers were put into a vacuum oven at 60 °C for 12 h to remove the residual solvent.In order to study structural changes of PAN and PAN copolymer nanofibers during the thermal oxidative stabilization (TOS) process, all of the nanofibers were heated by the following program, as shown in The carbonization of nanofibers was operated in a quartz tube oven at 1000 °C under a nitrogen atmosphere after TOS treatment of PAN and PAN copolymers nanofibers at 300 °C with 1 °C/min for 2 h in air condition. The nanofibers after carbonization treatment are marked as cPAN, cP(AN-co-IA), and cP(AN-co-AMPS), respectively.The processes of the polymerization, electrospinning, stabilization, and carbonization are shown in N,N′-Dimethylformamide as an eluent.Gel permeation chromatography  was used to determine the molecular weight and molecular weight distribution of PAN homopolymer and PAN copolymers equipped with a refractive index detector using Field emission scanning electron microscopy  was used to study the morphology of all the nanofibers. Before SEM observation, all of the nanofibers were sputter-coated with platinum. The diameter and distribution of each nanofiber (at least 50 measurements) were measured using the SEM software SmileView .Differential scanning calorimetry  was used to study the thermal reaction during stabilization process ramped at 10 °C/min to 400 °C under nitrogen and air atmospheres, respectively.The cyclization energy evaluation was performed using DSC  from 25 °C to 400 °C under a nitrogen atmosphere at the heating rates of 5, 10, 15, 20 °C/min, respectively.−1 with 32 scans from 4000 to 500 cm−1 at different temperatures in the thermal stabilization process with the program  with attenuated total reflection (ATR) mode was recorded with a resolution of 4 cm program .X-ray diffraction  was used to characterize the thermal stabilization process of PAN and PAN copolymers nanofibers with different temperatures, using the program . All theThermogravimetric analysis  was used to measure the weight loss of the nanofiber samples under nitrogen atmosphere ramped at 10 °C/min to 600 °C. The carbon structure of PAN-based carbon nanofiber carbonized at 1000 °C for 2 h was recorded by Raman spectrum  using 633-nm laser excitation. The peak fitting was operated using Origin Pro 9.0 software with Gaussian-LorenCross equation.w) of PAN homopolymer, P(AN-co-IA), and P(AN-co-AMPS) were 60,000 g/mol, 38,000 g/mol, and 31,000 g/mol, respectively, and their polydispersity index (PDI) values were 3.00, 2.92, and 2.58, respectively.The weight-average molecular weights , and P(AN-co-AMPS) in DMF solvent are all good. The spinnability of the three polymers was evaluated by electrospinning as follows.The incorporation of IA and AMPS comonomers into the PAN macromolecular chains reduces the values of Mw) and its distribution, electroconductibility of spinning dope, the viscoelastic force of the polymer solution, and the electrospinning conditions.2 and air atmosphere, respectively. The corresponding parameters were obtained from the thermograms, including the temperature of initiation (iT), the temperature of termination (fT), and their difference (ΔT), as well as the peak temperature (pT), the released heat (ΔH), and the rate of heat release (ΔH/ΔT). The details are listed in iT of P(AN-co-IA) and P(AN-co-AMPS) nanofibers was much lower than that of PAN nanofibers, which suggests an easier initiation of cyclization reaction in the novel P(AN-co-AMPS) nanofibers. Moreover, the ΔT and ΔH of PAN copolymers nanofibers were both larger than those of PAN homopolymer nanofibers. This means that there was a lower heat release rate (ΔH/ΔT) for PAN copolymers nanofibers during the cyclization process.iT exhibited the same tendency as the results under nitrogen atmosphere  and P(AN-co-AMPS) nanofibers were about 28.7 and 26.9 J g−1 °C−1, respectively, which are both lower than that of PAN nanofibers (103.7 J g−1 °C−1). It is noteworthy that the P(AN-co-AMPS) nanofibers had the lowest ΔH values, which is essential to avoid concentrative heat eruption and obtain a homogeneous stabilized structure. Therefore, the novel comonomer of AMPS can lower the cyclization temperature and retard the heat release during the TOS process, which is beneficial to produce high performance carbon fiber.In the actual industrial production process, PAN undergoes the thermal oxidative stabilization (TOS) process under an air atmosphere, which principally includes cyclization, oxidation, and dehydrogenation reactions . Figure mosphere . In addiaE) is an important parameter to evaluate the thermal behaviors of the PAN, P(AN-co-IA), and P(AN-co-AMPS) nanofibers [aE, the DSC curves with different heating rates  under N2 atmosphere were collected, and are shown in The apparent activation energy of cyclization reaction  and the Ozawa equation (Equation (2) as follows [The values of  follows ,31:(1)−EaE was calculated from the slope of the linear plot of the aE was calculated from the slope of the linear plot of log R is the gas constant, T is the maximum exothermic peak (absolute temperature), and aE values of PAN, P(AN-co-IA), and P(AN-co-AMPS) nanofibers obtained using the Kissinger and Ozawa methods are listed in aE1 obtained from the Kissinger method (Peak1) of PAN, P(AN-co-IA), and P(AN-co-AMPS) nanofibers were calculated as 41.2, 21.7, and 26.6 kcal/mol, respectively. The results of PAN and P(AN-co-IA) nanofibers almost agree with the values reported previously  and P(AN-co-AMPS) nanofibers were both lower than that of PAN nanofibers. This indicates that the incorporation of AMPS comonomer improves the cyclization reaction the same as the IA comonomer. Moreover, compared with the aE2 values obtained from the second exothermic peak (Peak2), the aE2 values of P(AN-co-AMPS) nanofibers  were lower than that of P(AN-co-IA) nanofibers . This demonstrates that, as a whole, the cyclization reaction of PAN is more easily initiated by the AMPS comonomer containing the sulfonic group.The  for PAN ), respec−1 is attributed to the stretching vibration of nitrile group (C≡N) [−l was assigned to the symmetrical bending vibration of C-H in a hydrocarbon backbone [−1 was assigned to carboxyl (C=O) stretching vibration of the COOH groups [−1 in the spectra of P(AN-co-AMPS) was due to S=O stretching vibration [up (C≡N) ,34. The backbone . These aH groups . The chaibration . The abo−1 was generated, which was assigned to the stretching vibration of C=C conjugated with those of C=N and N-H groups originating from cyclization, dehydrogenization, and tautomerization reactions [−1 originated from the dehydrogenation reaction [−1, assigned to C-H, N-H, and O-H in the ring, also demonstrated the occurrence of the cyclization reaction [−1 gradually appeared with thermal treatment, which was assigned to the out-of-plane bending of =C-H in saturated rings [As the stabilization temperature and time increased, the peak of stretching vibration of nitrile group gradually weakened and ultimately disappeared for all the PAN and PAN copolymer nanofibers. A new multiple and broad peak around 1590 cmeactions . The weareaction . The appreaction . A weak ed rings . All thesE) was calculated using the following equation [A1590 = absorbance intensity of C = C + C = N + N-H, A2243 = absorbance intensity of C≡N, and f is the ration of C≡N and C = C + C=N + N-H group absorptivity constants = 0.29.In order to quantitatively study the structural evolution of PAN and PAN copolymer nanofibers during the TOS process, the extent of stabilization (equation :(3)Es=f*sE of PAN, P(AN-co-IA), and P(AN-co-AMPS) nanofibers at different temperatures during the TOS process is shown in sE gradually increased for all of the nanofibers, suggesting the transformation from C≡N structure to C=C, N-H, and C=N structures. What’s more, the sE values of P(AN-co-IA) and P(AN-co-AMPS) nanofibers were higher than that of PAN in all of the temperature ranges. This demonstrates that the cyclization reaction of the C≡N group is more easily initiated by the incorporation of IA and AMPS comonomers. The sE value of P(AN-co-AMPS) nanofibers (32.1) was higher than that of P(AN-co-IA) nanofibers (12.2) at 195 °C. This indicates that the AMPS comonomer immediately triggers the cyclization reaction after heating. The TOS efficiency of P(AN-co-AMPS) nanofibers was higher than that of P(AN-co-IA) nanofibers. Those with higher sE value and less unreacted C≡N group avoided thermolysis and the forming of defects in the stage of carbonization [The plot of nization .d). This indicates that the polymer chain segments rearranged at an elevated temperature during the TOS process.I0 is the peak intensity of (100) plane from the original nanofibers and sI is the peak intensity of (100) plane from the nanofibers stabilized at different temperatures. SI of PAN, P(AN-co-IA), and P(AN-co-AMPS) nanofibers as a function of temperatures during the TOS process. As shown in SI of PAN, P(AN-co-IA), and P(AN-co-AMPS) nanofibers at 195 °C are negative. This might be because the energy supplied by heating is not enough to start the TOS process, but is enough to activate chain segment motion and further improve the recrystallization [SI of P(AN-co-IA) and P(AN-co-AMPS) nanofibers gradually increased. It means the thermal stabilization reaction accompanied by the transition from the linear structure to ladder structure. However, the SI of PAN decreased below 235 °C, which indicates that the stabilization reaction is more difficult than the recrystallization. It also demonstrates the lower initiation stabilization temperature and the higher TOS efficiency of P(AN-co-IA) and P(AN-co-AMPS) nanofibers than those of PAN. The results agree with the analyses using FTIR.As mentioned above, the TOS process converts the linear structure to a ladder structure, which can be related to the changes of peak intensity of (100) plane . Equatio2 atmosphere. The slight weight loss at temperature under 100 °C of P(AN-co-IA) and P(AN-co-AMPS) nanofibers is owing to the moisture evaporation derived from the hydrophily of IA and AMPS comonomers. Due to the absence of oxygen molecule, the weight loss at this heat treatment process can be attributed to the dehydrogenation and thermal decomposition [wT) of PAN, P(AN-co-IA), and P(AN-co-AMPS) nanofibers were about 260.8 °C, 280.5 °C, and 335.3 °C, respectively. The lowest wT of PAN nanofibers could be due to the violent free radical cyclization mechanism, which quickly releases plenty of heat and leads to thermal degradation of the PAN chains [wT suggesting the best thermal stable structures. The second wT of the three nanofibers are around 420 °C, which is due to the degradation and produces lots of volatile particles. In the end, the final weight residual at 600 °C of PAN, P(AN-co-IA), and P(AN-co-AMPS) nanofibers were about 40.3 wt.%, 45.9 wt.%, and 45.2 wt.%, respectively. This indicates that the addition of AMPS comonomer improved the cyclization of PAN under the same heating conditions, generating more heat-resistant molecular structures and favoring further carbonization.position . The temposition . As showN chains . In contD/IG), the full width at half maximum (FWHM) of the D and G peaks, the in-plane graphitic crystallite size (aL), and the mole fraction of graphite (GX) of the cPAN, cP(AN-co-IA), and cP(AN-co-AMPS) nanofibers are listed in −1 (D band) are associated with a disordered diamond-like carbon structure, while the peaks around 1580 cm−1 (G band) are attributed to an ordered carbon cluster. The ID/IG value indicates the number of defects in the ordered carbon clusters of the carbon nanofibers [D/IG values of cPAN, cP(AN-co-IA), and cP(AN-co-AMPS) nanofibers were 1.166, 1.132, and 1.133, respectively. The higher the ID/IG values, the more defects in the ordered carbon clusters [D/IG value of cPAN nanofibers was higher than those of cP(AN-co-IA) and cP(AN-co-AMPS) nanofibers. The aL value was inversely proportional to the ID/IG value. The GX values of cP(AN-co-IA) and cP(AN-co-AMPS) nanofibers were larger than that of cPAN nanofibers. The content of graphitic sp2 carbon crystal can be estimated from the FWHM of the D and G peaks. The relatively sharper D and G peaks of cP(AN-co-IA) and cP(AN-co-AMPS) nanofibers suggest the higher degrees of crystallinity [The Raman spectra of cPAN, cP(AN-co-IA), and cP(AN-co-AMPS) nanofibers carbonized at 1000 °C for 2 h are shown in nofibers ,48. The clusters ,49. The allinity . In esseH) and a lower heat release rate (ΔH/ΔT), especially, under an air atmosphere. Based on the Kissinger and Ozawa methods, the results demonstrated that the P(AN-co-AMPS) nanofibers had less activation energy of cyclization , which indicated that the cyclization reaction of PAN was more easily initiated by the AMPS comonomer containing the sulfonic group. Furthermore, P(AN-co-AMPS) nanofibers had a higher extent of stabilization (sE and SI) during the TOS process, quantitatively tracked by FTIR and XRD. TGA results showed the P(AN-co-AMPS) nanofibers had better thermal stable structures. The Raman test indicated that the carbon nanofibers derived from P(AN-co-AMPS) precursor nanofibers had better graphite-like structures (GX = 46.889). The shrinkage of the nanofiber diameters after carbonization could be due to the degradation and exclusion of non-carbon atoms. Based on the above results, AMPS is a promising comonomer to improve the TOS process of PAN. Furthermore, the P(AN-co-AMPS) copolymer could be used for the fabrication of high-performance carbon fibers in the industry.In this study, a novel PAN-based carbon fiber precursor of P(AN-co-AMPS) copolymer was prepared. Moreover, the thermal stabilization and carbonization processes of the electrospinning nanofibers were investigated. The SEM showed that all of the nanofibers had a smooth surface and uniform diameter in the nanoscale. The DSC test indicated that the P(AN-co-AMPS) nanofibers had the lowest released heat (Δ


Escherichia coli serotype O51 : H30, sequence type (ST) 38. Sequencing was performed on the MinION Flow cell MIN-106 R9.4. Nanopore raw FAST5 reads were base-called using Albacore v1.2.1, converted to FASTA and FASTQ formats using Poretools v0.6.0, and assembled using Unicycler v0.4.2, combining the long-read sequencing data with short-read data produced by Illumina sequencing. The genome was interrogated against an antimicrobial resistance (AMR) gene reference database using blast. The majority of the 12 AMR determinants identified were clustered together on the chromosome at three separate locations flanked by integrases and/or insertion elements . AMR determinants located outside these three regions were a chromosomally encoded blaCMY-16, mutations in gyrA and parC, and two plasmid-encoded AMR determinants, blaOXA-181 and qnrS1 located on the same IncX3 plasmid. Long-read analysis of whole genome sequencing data identified mobile genetic elements on which AMR determinants were located and revealed the combination of different AMR determinants co-located on the same mobile element. These data contribute to a better understanding of the transmission of co-located AMR determinants in MDR E. coli causing gastrointestinal and extra-intestinal infections.The aim of this study was to use single-molecule, nanopore sequencing to explore the genomic environment of the resistance determinants in a multidrug-resistant (MDR) strain of enteroaggregative  Long- and short-read FASTQ sequences have been deposited in the NCBI Sequence Read Archive under the BioProject PRJNA315192 (SRP071789), Sample: SRS2937479, Experiment: SRX3676443, Accession numbers Nanopore FASTQ: SRR6702264 and Illumina FASTQ: SRR5470155. Assembly accession numbers: CP026723.1 (chromosome) and CP026724.1 to CP026728.1 .Escherichia coli and provides real-time data on emerging resistance patterns nationally and internationally. Understanding the genomic environment of these AMR determinants, with respect to whether they are chromosomally encoded or plasmid-encoded, and whether they are co-located is essential for monitoring transmission of AMR and assessing the risk to public health. Short-read WGS data can identify the presence or absence of AMR determinants but not their genomic architecture. In this study, long-read analysis of WGS data enabled us to determine the mobile genetic elements on which the key AMR determinants are located, and to characterize the combination of different AMR determinants co-located on the same mobile element. A combination of short- and long-read WGS data contributes to a better understanding of the transmission of co-located AMR determinants in multidrug-resistant E. coli.The implementation of whole genome sequencing (WGS) for routine public health surveillance has enabled us to monitor trends in antimicrobial resistance (AMR) gene content in Escherichia coli (EAEC) cause a range of gastrointestinal symptoms including acute or persistent, watery or mucoid diarrhoea, often accompanied by severe abdominal pain ;parC, qnrS1, dfrA1, tetA, sul2 and catA , ciprofloxacin  and the β-lactams  at different locations in the genome in this strain of EAEC  a, b. Fur of EAEC a, b.blaCMY-16, located on the chromosome between positions 892 919 and 894 050, mutations in gyrA and parC, and two plasmid-encoded AMR determinants, the carbapenemase blaOXA-181 and the plasmid-mediated quinolone-resistant determinant (PMQR) qnrS1  qnrS1 . blaCMYeumoniae . In E. cescribed .qnrS1 and aac(6′)-Ib-cr, which exhibit the potential to induce reduced susceptibility to the fluroquinolones, EAEC O51 : H30 also had one mutation in gyrA[83 : S-L] and two in parC. The combination of all these fluroquinolone resistance determinants resulted in the isolate exhibiting an MIC>0.5 mg l−1 to ciprofloxacin.In addition to the PMQRs blaOXA-181 is a blaOXA-48-like carbapenemase conferring resistance to penicillins and carbapenems, and is commonly found on a 51 kb IncX3 plasmid .E. coli ST38 is a known cause of gastrointestinal disease and extra-intestinal infection, including sepsis and urinary tract infections, and has been associated with MDR in the UK and elsewhere [E. coli, contributing to a better understanding of the transmission of co-located AMR determinants in MDR E. coli causing gastrointestinal and extra-intestinal infections.lsewhere . Short-rlsewhere . A combiGreig DR, Dallman TJ, Jenkins C. NCBI Sequence Read Archive PRJNA315192 (2018).


In the case of square-wave voltammetry, the linear range was 2–250 μM, with a correlation coefficient of 0.9996, and the detection limit was estimated to be 0.7 μM. The effects of interferents, such as ascorbic acid (AA) and uric acid (UA), on the electrochemical detection of dopamine were also examined. The modified electrode can successfully separate the oxidation potentials for ascorbic acid and dopamine, shifting the oxidation peak potential of ascorbic acid to a more positive potential, and significantly decreasing the peak current. The presence of ascorbic acid increased the sensitivity of dopamine determination at the modified electrode, and the detection limit was estimated to be 0.5 μM with 0.1 mM ascorbic acid to imitate physiological solutions. Additionally, studies showed that the presence of uric acid does not affect the electrochemical detection of dopamine. The modified electrode can be successfully applied for the quantitative analysis of dopamine both with and without interferents.A gold electrode modified with a polypyrrole–mesoporous silica molecular sieves (polypyrrole—MCM-48) nanostructure film was used for the electrochemical determination of small concentrations of dopamine (DA) by cyclic voltammetry and square-wave voltammetry techniques. This electrode showed good electrocatalytic activity for the oxidation of dopamine. The oxidation potential of dopamine was decreased significantly compared with that obtained at the bare gold electrode. The observed linear range for the determination of the dopamine concentration, without interferents through cyclic voltammetry measurements, was from 10 μM to 1.2 mM (R Dopam2 powder . Ramanavdophenol . They obRecently, conductive polymers and their composites have been used to modify electrodes to detect dopamine ,35,36,37MCM-48 is a cubic form of mesoporous silica molecular sieves with a three-dimensional pore structure. Such a system exhibits high specific surface area, large pore volume, and high thermal stability ,47,48. TIn this paper, we report the electrochemical behavior of dopamine at the surface of a polypyrrole—MCM-48 nanostructure-modified Au electrode, both in the presence and absence of ascorbic acid and/or uric acid. The modified electrode shows electrochemical activity for the oxidation of dopamine. The nature of the polypyrrole film is also very important and affects the determination of dopamine. In addition, we discuss the suitability of these modified electrodes in the voltammetric determination of dopamine in a phosphate buffer solution.1) peak and one reduction (R1) peak. The morphology of the polypyrrole—MCM-48 composite is shown in the inset of The polypyrrole—MCM-48 nanocomposite powder was dispersed by sonication in dichloromethane solution to form a homogenous mixture. Ten microliters of a 1.5 mg/mL mixture was dropped onto the surface of the Au electrode, and the solvent was evaporated. The morphology of the gold electrode surface modified with polypyrrole—MCM-48 nanocomposite is shown in 1) dopamine is oxidized to dopaquinone (peak a1), and next, it is reduced in part to dopamine (peak b1). Part of dopaquinone undergoes a cyclization reaction to form leucodopaminechrome, which is immediately oxidized to dopaminechrome, and next, this dopaminechrome is reduced back to form leucodopaminechrome (peak b2). Therefore, in the second scan (2) an a2 peak appears, corresponding to the oxidation of leucodopaminechrome to dopaminechrome, while the dopamine oxidation peak, a1, decreases at the expense of the peak pair, a2 and b2.The cyclic voltammograms obtained for dopamine oxidation at the bare gold electrode in 0.1 M of phosphate buffer solution are shown in ond scan , curve 25 in In the case of the polypyrrole—MCM-48-modified electrode, the analyte has to enter the pores of the mesoporous material before electrochemical measurements. Therefore, the effect of the time of preconcentration was examined. The influence of the pH of the solution on dopamine oxidation was studied by cyclic voltammetry in the presence of 0.1 mM of dopamine in an aqueous buffer solution, with increasing pH values, from 4.2 to 9.0. The potential of the anodic peak shifted in the negative direction as the pH increased. The linear dependence on pH, with a slope of −0.056 V/pH, indicates that the oxidation of dopamine at the polypyrrole—MCM-48 nanocomposite-modified electrode had been inferred to be a double electron transfer reaction. It was also observed that both the oxidation and reduction peak currents obtained maximum values at a pH of 7.4. Considering the physiological environment, a phosphate buffer solution at a pH of 7.4 was chosen as the supporting electrolyte for the experiments.2) and, for comparison, on the bare gold electrode (1) in 0.1 M of phosphate buffer solution containing 1 mM of dopamine. Under these conditions, the potential of the polypyrrole oxidation peak corresponds to the potential for the oxidation of dopamine. This observation demonstrates that the polypyrrole—MCM-48 nanocomposite has high electrocatalytic activity towards the oxidation of dopamine. This peak current increased almost three-fold compared with the bare gold electrode. The increase in the sensitivity of the analytical determination of dopamine is a clear indication of the enlargement of the active surface area of the electrode modified by the polypyrrole—MCM-48 nanocomposite. The effect of the sweep rate on the anodic peak current of dopamine was also studied. As the sweep rate increased, the oxidation peak current (paI) also increased (−1 (inset of ncreased b. The oxinset of b. The re2 = 0.9989. The limit of detection (LOD) of dopamine determination was calculated from the following relationship [2 = 0.9996. The limit of detection was determined to be 0.7 μM. Thus, the prepared electrode allows for the sensitive determination of dopamine in a relatively large concentration range. The comparison of the results for the determination of dopamine using different polypyrrole composite-modified electrodes is summarized in The influence of the concentration of dopamine at the gold electrode modified with the polypyrrole—MCM-48 nanocomposite in 0.1 M of phosphate buffer solution, using cyclic voltammetry and square-wave voltammetry, is shown in tionship :LOD = 3inset of b, and thAn important property of the composite that is useful for the evaluation of high-performance sensors is its selectivity, which is a measurement of the ability to reject major interferents, such as ascorbic acid and uric acid. These compounds are presented in physiological solutions at concentrations of 0.1 mM for ascorbic acid and 0.05 mM for uric acid ,58. AddiThe cyclic voltammetric responses of dopamine, uric acid, and ascorbic acid recorded in 0.1 M of phosphate buffer solution at the bare gold electrode and the polypyrrole—MCM-48-modified gold electrode are shown in In the case of the gold electrode modified with the polypyrrole—MCM-48 b, the poThe influence of ascorbic acid and uric acid on the determination of dopamine was examined using both cyclic and square-wave voltammetry. The electrooxidation of dopamine in the presence of uric acid under similar conditions was also studied. Typical cyclic and square-wave voltammograms are shown in 1 in 2 in 3, 4, and 5 in The simultaneous determination of the mixture of dopamine, ascorbic acid, and uric acids at the bare gold electrode and modified electrode were studied by cyclic voltammetry. The electrochemical behavior of the polypyrrole—MCM-48 nanocomposite was studied in the presence of dopamine, both without and with interferents such as ascorbic acid and uric acid. The experimental results show that the oxidation of dopamine is catalyzed at the surface of the modified gold electrode. These materials have been also used to compare their abilities to detect small concentrations of dopamine, both without and with interferents. The larger oxidation peak separations, between dopamine, ascorbic acid, and uric acid, on the modified gold electrode make it suitable for the determination of dopamine in the presence interferents. The modified electrode showed good selectivity and high sensitivity, even in the presence of interferents.2PO4 and Na2HPO4. Freshly prepared solutions of dopamine were used in all experiments. Pyrrole and FeCl3 were used as received from Aldrich Inc. The n-hexadecyltrimethylammonium bromide template, tetraethyl orthosilicate, aqueous ammonia, and ethanol were used as received from the Aldrich Chemical Co. These were used for the synthesis of MCM-48 spheres. Pure deionized water, with a resistivity of 18.2 MΩ cm, was obtained from a Milli-Q Millipore system.Dopamine, ascorbic acid, and uric acid were purchased from Aldrich and were used as received. The 0.1 M phosphate buffer solution with a pH of 7.4 was prepared with KH2.Voltammetric experiments were performed on an AUTOLAB Model 283 Potentiostat/Galvanostat  with a three-electrode cell. The AUTOLAB system was controlled with GPES 4.9 software by the same manufacturer. A gold disk electrode with a diameter of 1.5 mm  was used as the working electrode. Prior to each experiment, the electrode was washed with acetone and dried. An Ag/AgCl/saturated KCl electrode was used as the reference electrode. The counter electrode was a platinum tab with an area of approximately 0.5 cmScanning electron microscopy (SEM) images were obtained using an Inspect S50 microscope . The accelerating voltage of the electron beam was either 20 or 25 kV and the average working distance was 10 mm.Transmission electron microscopy (TEM) images were recorded with a FEI Tecnai TF20  instrument using an accelerating voltage of 200 kV. The films for the TEM studies were prepared by constant potential electrodeposition on a gold grid with a diameter of 3 mm (300 square mesh).3 [3 was added and stirred for 2 h at room temperature. The composite of polypyrrole@MCM-48 was washed with pure water and methanol 4 times and dried at 80 °C. The color of the silica changed from white for pure MCM-48 to beige for the composite. Morphological parameters of these materials were obtained by nitrogen sorption measurements [−1 and 1270 m g−1, respectively. The incorporation of polypyrrole into the pores of MCM-48 resulted in a decrease in the average pore diameter, from 3.2 nm for MCM-48 to 2.7 nm for the composite. These changes in the pore diameter corresponded to changes in the pore volume, from 0.74 to 0.70 cm3 g−1, respectively. The small changes of pore volume indicated that polymer only partially fills the MCM-48 pores. Namely, this polymer is deposited only on the walls of mesopores [The mesoporous silica MCM-48 was synthesized according to the procedure proposed by Schumacher et al. . This sy3 . For thiurements . Both saesopores .


Buffered intravenous fluid preparations contain substrates to maintain acid-base status. The objective of this systematic review was to compare the effects of buffered and non-buffered fluids administered during the perioperative period on clinical and biochemical outcomes.We searched MEDLINE, EMBASE, CINAHL and the Cochrane Library until May 2017 and included all randomised controlled trials that evaluated buffered versus non-buffered fluids, whether crystalloid or colloid, administered to surgical patients. We assessed the selected studies for risk of bias and graded the level of evidence in accordance with Cochrane recommendations.I2 = 61%). This difference did not persist on postoperative day 1. Serum chloride concentration was higher in the non-buffered group at the end of surgery . This effect persisted until postoperative day 1 . Quality of this evidence was moderate. We identified variable protocols for fluid administration and total volumes of fluid administered to patients intraoperatively. Outcome data was variably reported at disparate time points and with heterogeneous patient groups. Consequently, the effect size and overall confidence interval was reduced, despite the relatively low inherent risk of bias. There was insufficient evidence on the effect of fluid composition on mortality and organ dysfunction. Confidence intervals of this outcome were wide and the quality of evidence was low  1.85, 95% CI 0.37 to 9.33; I2 = 0%).We identified 19 publications of 18 randomised controlled trials, totalling 1096 participants. Mean difference (MD) in postoperative pH was 0.05 units lower immediately following surgery in the non-buffered group  0.04 to 0.07; Small effect sizes for biochemical outcomes and lack of correlated clinical follow-up data mean that robust conclusions on major morbidity and mortality associated with buffered versus non-buffered perioperative fluid choices are still lacking. Buffered fluid may have biochemical benefits, including a significant reduction in postoperative hyperchloraemia and metabolic acidosis.The online version of this article (10.1186/s13741-018-0108-5) contains supplementary material, which is available to authorized users. Major surgery presents an important threat to internal homeostasis of fluid and electrolytes, partly due to the volume depleting effects of haemorrhage, evaporative loss and pre-operative dehydration, or by excessive fluid administration causing oedema and organ dysfunction. Intravenous fluid solutions used for resuscitation and maintenance purposes should support the circulation adequately to replace missing plasma, whilst avoiding metabolic disturbance or other adverse effects. Modern perioperative fluid management is based on the principle that, as an intervention with risks and benefits, fluids should only be provided to affect a meaningful clinical variable. This principle influences decisions made for monitoring requirements, timing of administration, volume dosing of fluids and the type of fluids provided to patients.Intravenous fluids, whether crystalloid or colloid, can be categorised as buffered or non-buffered. Hartmann’s fluid formulation more closely matches the constituents of human plasma than 0.9% saline, containing a physiological buffer that helps to maintain acid-base balance. The composition of Hartmann’s fluid also includes additional electrolytes found in plasma, including potassium, magnesium and calcium. Provision of buffered crystalloid fluids may have benefits over 0.9% saline, in which the electrolyte composition is significantly different to the plasma that it is intended to replace.The primary objective of this systematic review is to investigate the clinical effects of perioperative administration of buffered fluids, such as Hartmann’s solution, when compared with non-buffered fluids administered during all types of surgery.This paper is an abridged version of a previously published Cochrane systematic review , MEDLINE (1966 to May 2017), Embase (1980 to May 2017) and the Cumulative Index to Nursing and Allied Health Literature . No language restrictions were applied to the search criteria. Relevant conference abstract proceedings were also searched. Forward and backward citation tracking of all identified studies was performed. The full search strategy used can be found in the review protocol  in which patients received intravenous fluids with and without a buffer  for the purpose of plasma volume expansion or maintenance during the perioperative period. To minimise confounding factors, we considered only RCTs in which the sole difference between experimental and control arms involved the presence or absence of an electrolyte buffer in the fluid. We excluded studies that compared crystalloids with colloids and those that compared fluids with different colloid components. However, we included trials with three or more arms that satisfied the other inclusion criteria. The perioperative period was defined as extending from 2 h before the start of surgery up to 6 h after surgery or until arrival to a post-anaesthetic care unit. We included only studies that used isotonic fluids (osmolarity 250 to 350 mmol/L) and a broadly physiological concentration of sodium (120 to 160 mmol/L).Five review authors  independently screened titles and abstracts of search results to remove irrelevant studies. Two review authors (SB and PO) then reviewed full texts of potentially relevant titles and identified studies that matched inclusion criteria. Data on study characteristics and outcomes were independently extracted from eligible studies by two authors (SB and PO) with disagreements resolved by consensus or by consultation with a third review author (EB). We contacted the authors of included trials to request required data missing from published manuscripts.Mortality Clinically significant organ system dysfunction 2), nausea, and vomitingSurrogate measures of organ system dysfunction including urine output, serum creatinine, partial pressure of arterial carbon dioxide , gastrointestinal, hepatobiliary, gynaecological and urological surgery. One study of patients undergoing coronary artery bypass grafting was included and two studies included patients with minor surgical procedures, which did not involve an invasion of body cavities. No studies of patients undergoing emergency surgery were identified.The exact fluid type used and protocol for fluid delivery to participants varied between studies. Of 18 included trials, 13 used crystalloids in both their experimental and control arms. Of these studies, nine compared lactated Ringer’s solution with 0.9% saline and four compared Plasmalyte 148 with 0.9% saline. The remaining six publications of five trials used colloid solutions in their experimental and control arms, comparing a buffered hydroxyethyl starch (HES) solution versus a non-buffered HES solution. High molecular weight (MW) HES was used in four RCTs . The quality of evidence was downgraded from high to low owing to the imprecision of trial results due to small sample sizes, wide confidence intervals and methodological variability between studies. Studies reporting mortality presented few events, and all three studies were considered to be at unclear risk of bias for this outcome assessment. Overall confidence in the effect estimate is low. A forest plot for the primary outcome is provided in Fig. Three clinical trials with a total of 267 participants reported mortality . A single study reported respiratory failure, enrolling 81 participants with a 9.3% (4/43) incidence of post-operative respiratory failure in the buffered group and 2.6% (1/38) in the non-buffered group. No reports of cardiac, hepatic, gastrointestinal or neurological failure were recorded as outcomes measures.We found low-quality and insufficient evidence to support any effects of fluid therapies on postoperative organ failure. Renal failure leading to the requirement for renal replacement therapy was reported in four trials . Sensitivity analysis was performed to exclude the four studies that included renal transplant patients  in the immediate post-operative measurement and 4.94 μmol/L lower in the non-buffered group  on post-operative day one.Two trials of 113 participants reported relative post-operative serum creatinine change at two time points: immediately post-operatively and on post-operative day one .Absolute creatinine was reported at time points from post-operative day one to day seven. Three trials with a total of 235 participants reported absolute immediate post-operative creatinine values ; there were no significant differences between subgroups of renal transplant and non-transplant patients.Three trials with a total of 211 participants reported postoperative day one creatinine . Two trials with a total of 91 participants reported postoperative day one PaCO2 of 41 mmHg in the buffered fluid group and 37.7 mmHg in the non-buffered fluid group .Seven trials with a total of 446 participants reported postoperative PaCOI2 = 20%).Three trials reported 21/84 (25%) episodes of postoperative vomiting in the buffered fluid group and 28/84 (33%) episodes of postoperative vomiting in the non-buffered fluid group  in the non-buffered group. A forest plot of this outcome is found in Fig. Twelve studies with a total of 720 participants reported postoperative pH . Two trials with a total of 91 participants reported postoperative day one serum sodium of 140.6 mmol/L in the buffered fluid group and 141.8 mmol/L in the non-buffered fluid group .Eight trials with a total of 447 participants reported a postoperative serum sodium concentration of 137.3 mmol/L in the buffered fluid group and 139.4 mmol/L in the non-buffered fluid group .Seven trials with a total of 459 participants reported postoperative serum potassium. Potassium was 4.13 mmol/L in the buffered group and 4.22 mmol/L in the non-buffered group  .I2 = 0%). The clinical significance of this finding is unclear. One trial reported prothrombin time (PT)    reported no important differences between groups and showed mean difference in intraoperative blood loss that was 5.90 ml higher in the buffered group .Five trials with a total of 348 participants reported hospital length of stay  (secondary to respiratory compensation for metabolic acidosis) when non-buffered fluids were used. We rated GRADE evidence for these secondary outcomes as low-moderate quality.The analysis of secondary outcome measures from 18 different RCTs of 1096 participants suggests that intravenous fluids containing a physiological buffer are a safe alternative to saline-based fluids for adult patients undergoing surgery. We found limited evidence on the effects of fluid therapies on postoperative organ dysfunction, particularly on renal failure. For patients not undergoing renal transplantation, there were no differences in terms of renal insufficiency or surrogate markers of renal dysfunction (urine output and serum creatinine). However, there were differences in metabolic variables in post-operative pH, chloride concentration, base-deficits and serum bicarbonate, without significant changes in other electrolytes such as serum potassium and sodium concentrations. High serum chloride is a cause of metabolic acidosis and may explain our findings of both lower pH and lower partial pressure of arterial carbon dioxide  , many of our secondary outcomes displayed substantially greater statistical heterogeneity.Whilst we used an inclusive search strategy and eligibility criteria to maximise identification of relevant studies, this meant that there was considerable clinical heterogeneity in participant characteristics, types of surgery and protocols for administering fluids in the trials. Some RCTs involved minor surgery in otherwise healthy patients  and quality of life measures such as postoperative pain.Additional file 1:Search strategies for CENTRAL, MEDLINE, Embase and CINHAL. (DOCX 16 kb)Additional file 2:Table S1. Characteristics of included studies. (DOCX 49 kb)Additional file 3:Table S2. Summary of findings for the main comparison. (DOCX 16 kb)


The objective of this study was to determine the influence low shear microbore extrusion exerts on the properties of high molecular weight PLLA for medical tubing applications. Results showed that even at low shear rates there was a considerable reduction in molecular weight (Mn = 7–18%) during processing, with a further loss (Mn 11%) associated with resin drying. An increase in melt residence time from ~4 mins to ~6 mins, translated into a 12% greater reduction in molecular weight. The degradation mechanism was determined to be thermal and resulted in a ~22-fold increase in residual monomer. The differences in molecular weight between both batches had no effect on the materials thermal or morphological properties. However, it did affect its mechanical properties, with a significant impact on tensile strength and modulus. Interestingly there was no effect on the elongational proprieties of the tubing. There was also an observed temperature-dependence of mechanical properties below the glass transition temperature.Biodegradable polymers play a crucial role in the medical device field, with a broad range of applications such as suturing, drug delivery, tissue engineering, scaffolding, orthopaedics, and fixation devices. Poly- PLA is a chiral molecule, which can be found in two stereoisomer forms l and d, giving poly-l-lactic acid (PLLA) and poly-d-lactic acid (PDLA) [Bioabsorbable polymers have a broad range of applications in the medical device field; this is due to their biocompatibility, biodegradability, and bioresorbability. Applications include but are not limited to suturing, drug delivery, tissue engineering, scaffolding, orthopaedics, and fixation devices. A significant proportion of the biodegradable polymers used and studied today, come from the family of aliphatic polyesters, such as poly(lactic acid) (PLA), poly(glycolic acid) (PGA), poly(ε-caprolactone) (PCL) and their copolymers. This is due to the presence of an ester covalent bond with a reactive polar nature, which can be easily broken down through hydrolysis . Poly (ld (PDLA) ,3.PLLA is the most widely used form of PLA in biomedical applications since it is the naturally occurring form of lactic acid found in the body. It is described as being a brittle material with a strain of <5% and having a moderate tensile strength of 60–70 MPa, with an elastic modulus of 2–4 GPa [g [w = 300,000–600,0000 g/mol) to withstand the molecular weight loss witnessed during melt processing and sterilisation, which can range from 5 to 88% [PLLA can be processed using traditional thermoplastic melt processing techniques such as extrusion, injection moulding, solvent spinning, and casting. As with any viscoelastic material, the properties of PLLA are dependent on time, temperature and strain rate. It behaves like a glassy polymer at room temperature, given it is below Tg  and is pg . The theg . Crystalg ,9. The cg  and slowg . PLLA’s g . PLLA isg ,13,14. Dg ,16. The 5 to 88% .w < 200,000 g/mol) resin. Twin screw extruders typically generate higher shear rates and viscous heat than microbore extruders. Microbore extruders are typically classified as having a barrel diameter of 1/2” to 1”. Also, the vast majority of post-processing mechanical analysis has been performed on compression or injection moulded samples. Thus, not fully assessing the impact that molecular orientation imparted during tube extrusion plays on the materials mechanical properties. One exception to this was a study on the effect of processing of PLLA [Whilst the effect of melt processing on the properties of PLLA has been extensively researched, this work has pre-dominantly involved the use of twin-screw extruders and lower molecular weight  GMP grade bioabsorbable PLLA. A series of analytical techniques were used to assess the effect melt processing had on the materials thermal, chemical, morphological and mechanical properties and its suitability for load bearing medical applications.The aim of this study was to investigate the influence low shear microbore single screw extrusion exerts on the properties of a high molecular weight (Ml-lactic acid (PLLA), which was obtained from Corbian . It was medical grade homopolymer of L-lactide with the chemical formula (C6H8O4). It has a molecular weight of Mn 325,000 and Mw 650,000, an inherent viscosity specification of 3.8 dl/g, max residual monomer content of 0.1 wt.% and was supplied in the form of white granules.The material used was a poly-l/d ratio and used a conventional straight flight metering screw design with a 3.1:1 compression ratio. It also incorporated a melt pump, which helped to regulate output, but led to a small increase in residence time of the melt. The second batch (identified as Batch B) was processed on a 0.75” extruder barrel with a 24:1 l/d ratio. It also used a metering screw design with a 3:1 compression ratio, but did not incorporate a melt pump. For the purpose of this study, two batches of extruded tubing were manufactured. Both batches were processed using different extrusion tooling configurations, to assess if differences in residence time in the extruder  had an impact on the properties of the tubing. The first batch (identified as Batch A) was processed on a 1” extruder barrel with a 24:1 −1 was calculated for the 1” screw used in Batch A, and a 24 s−1 shear rate for the 0.75” screw used in Batch B. Therefore, any differences noted between the material characteristics of Batch A versus B, could most likely be attributed to differences in their melt residence times.Given the low shear rates generated in a microbore extrusion process, it is unlikely that differences in the two screw designs or the addition of a melt pump for Batch A would have a significant impact on the rheological properties of the material. Using the formula below, the shear rate of the flight depth in the metering section of both screws was calculated. A shear rate of 28 s−1), D = Screw diameter (mm), N = Screw Speed (rev/min) and h = Screw channel depth in metering section (mm) [g) for 16 hours to a moisture content of <100 ppm. Extruder output was less than 0.5 lbs/hr for both batches. The extruded tubing had an outside diameter of 1.9 mm and 0.6 mm wall thickness. ion (mm) . An extr−1 on 12, 22, 41, 76, 141, 260, 481, 889, 1642 and 3033 s−1. The analysis was performed to evaluate the effect of shear rate on melt viscosity. The PLLA pellets were pre-dried as described in Capillary rheology was performed using a Dynisco LCR7001 . The die (Z349-15) used had a 1mm diameter and 15 mm length. The melt flow behaviour in the capillary rheometer was investigated at 219 °C, with shear rate measurements taken between 12 and 3033 sw 162–6,000,000) which were procured from Agilent Technologies . The molecular weight averages calculated by the system were the number average molecular weight (Mn), the weight average molecular weight (Mw) and the polydispersity index (PDI), which is calculated from the simple formulae of Mw/Mn.Gel permeation chromatography (GPC) was used to determine the molecular weight of the extruded tubing. The analysis was carried out using a Polymer Laboratories PL GPC-120 system  equipped with an auto-sampler and in-built differential refractometer detector. The samples were prepared by dissolving 50 mg of sample in 5 mL of tetrahydrofuran (THF) to provide a final concentration of 1 mg/mL. The system was fitted with a PL-gel 5 μm Mixed D column . The GPC system was calibrated using a mixture of linear polystyrene standards  was used to provide spectra analysis of the dried PLLA resin and extruded tubing from Batch A. FTIR spectra were recorded using a Thermo Electron Corporation Nicolet 5700 FTIR spectrometer  equipped with a universal attenuated total reflectance. The spectra were recorded between 4000 and 500 cmGas chromatography-flame ionization detection (GC-FID) was performed on the dried PLLA resin and extruded tubing from Batch A and B, using Agilent 6890 GC with the HP7673A autosampler attached . The system used a DB-17MS, 20 m × 0.18 mm × 0.18 μm column, with split/splitless, injector at 200°C. The injector volume was 1μL, with Helium, 1.3 mL/min, 10:1 split carrier gas. The column temperature program comprised of 50 °C for 1 min, 25 °C/minute ramp to 320 °C and held for 5 min. The detector temperature was set at 335 °C. GC-FID was used to determine the percentage of residual lactide monomer in the samples.p), glass transition temperature (Tg), melt recrystallisation temperature (Tmc), melting temperature (Tm), cold crystallization temperature (Tcc), enthalpy of melting (ΔHm) and enthalpy of cold crystallisation (ΔHc) were determined during the first heating cycle to establish the influence of thermal history during processing. All indicated temperatures are peak temperatures. The degree of crystallinity (Xc) was calculated using the enthalpy (heat) of melting ΔHm and the enthalpy of cold crystallization ΔHc (where present), through the following equation;Thermal and morphological properties were determined by a DSC instrument . The samples (8–12 mg) were heated from 30 to 250 °C at a rate of 10 °C/min under a constant nitrogen flow rate of 30 mL/min. The specific heat change . The gauge length for each specimen was set to 65 mm, with parts subjected to an extension rate of 50 mm/min up to the point of failure. This allowed for the evaluation of Young’s (elastic) modulus, maximum tensile stress, strain at maximum load and strain at break. An average value of 6 samples in each group was presented with their standard deviation. Statistical analysis was performed using a 2-sample T-Test. Tests were conducted using Minitab 17 software. P values of less than 0.05 were deemed statistically significant. The sample size selected was based off an 80% power and capable of detecting a practically significant difference in the means. Practical significance was determined for each attribute by applying engineering knowledge of the process output requirements.Dynamic mechanical analysis (DMA) was performed using TA Instruments DMA Q800 . The test was performed in tension mode using a frequency of 1Hz and an amplitude of 15μm. The temperature range between 0 and 140 °C with a 5 °C/min ramp rate was utilised to determine the storage modulus (E’). A representative DMA plot from 3 samples tested in each group was presented.The rheology of PLLA melts has been extensively studied ,21,22,23−1; Batch B = 24 s−1) fall within the materials zero shear region and would therefore not effect melt viscosity. Like most thermoplastic polymers, PLLA exhibits Newtonian behaviour at low shear rates (<10 s–1) and non-Newtonian behaviour (shear thinning) at the high shear rates (>10 s–1), as well a reduction in viscosity with increasing processing temperatures [Capillary rheology was performed on the dried resin prior to processing. eratures .The heat required to plasticise a polymer during extrusion comes from a combination of conductive heat from the barrel wall and viscous dissipation through the shearing action of screw rotation. Whilst viscous dissipation typically accounts for 80–90% of polymer melting in a conventional extruder under normal operating conditions , its plaGel permeation chromatography (GPC) analysis was carried out on both batches of extruded tubing to determine the effect that different processing conditions had on the molecular weight and molecular weight distribution of the polymer. For comparison, samples from the as received (undried) and dried PLLA resin pellets were also analysed. n and to a lesser degree in Mw observed during the resin drying and extrusion processes, as well as a corresponding increase in PDI. The as received (undried) resin saw a reduction in Mn of 11.2% and 2.5% in Mw during the drying process. This trend continued during the processing of extrusion Batch A, with a further 17.7% reduction in Mn and 12.4% in Mw. However, the same degree of molecular weight loss was not witnessed for Batch B, whereby there was only a 6.9% Mn and 1.5% Mw reduction from the extruded material compared to the dried material. The increase in PDI from 2.16 in the undried resin up to 2.5 in the extruded resin, can be attributed to random chain scission resulting in an increase in lower molecular weight chains and an overall broader distribution [There was a notable reduction in Mribution .Degradation during melt processing is typically through hydrolytic or thermal degradation mechanisms, resulting in chain scission. The presence of moisture in the raw resin prior to processing leads to hydrolysis of the ester bonds. Thermal degradation in PLLA has been attributed to a combination of the following; zipper like depolymerization, oxidative chain scission, intermolecular transesterification to monomer and oligomeric esters and intramolecular transesterification resulting in the formation of monomer and oligomer lactides of low molecular weight . In compGiven the fact that the processing conditions for both extrusion batches were almost identical, then the most likely cause for the greater reduction in molecular weight (~12%) witnessed in extrusion Batch A compared to Batch B, relates to its longer residence time in the extruder. As reported in −1, is related to the stretching of the OH (hydroxyl) group. The bands at 2997 and 2947 cm cm−1 correspond to CH3 symmetric and asymmetric stretching respectively. A strong absorption band at 1755 cm−1 is owed to the stretching of the C=O (carbonyl) bond. The two middle peaks at 1458 and 1362 cm−1 relate to the CH3 asymmetric and symmetric bending vibration, respectively. The doublet peak at 1215/1184 cm−11 and a triplet peak 1132/1083/1041 cm−1 (C–O stretching vibration) indicates the nature of ester end-capped PLLA [FTIR spectra analysis of the dried resin and extruded Batch A tubing are represented in ped PLLA ,32,33. W1H NMR and FTIR [A study on the effect of melt processed (injection moulded/extruded) PLLA samples, found the degradation mechanism was non-hydrolytic. This was attributed to the absence of new hydroxyl groups from carboxylic acids and alcohols (which are the products of ester hydrolysis) by using and FTIR . The lac−1 wavelengths. It has been reported that the absorption bands at 1207 cm−1  and 920 cm−1  are representative of the crystalline structure of PLA [−1 and noticeable disappearance of the peak at 921 cm−1, which indicates a reduction in crystallinity. The peak at 955 cm−1 relates to the materials amorphous phase [FTIR has also been used to study the crystallisation behaviour of PLLA. e of PLA . When cous phase , howeverGas-chromatography-flame ionization detector (GC-FID) analysis was carried out on both batches of extruded tubing to determine the effect that different processing conditions had on the percentage of residual lactide monomer present in the material. As a baseline, a sample from the dried PLLA resin pellets was also analysed. The residual monomer found in polymers can be a result of the polymerization process or thermally generated from processing techniques such as melt extrusion . ThermalThermal analysis using differential scanning calorimetry (DSC) was carried out on both batches of extruded tubing to determine the effect different processing conditions had on the thermal and morphological properties of the material. For comparison, the dried PLLA resin was also analysed. The 1st heating cycle from the DSC analysis was used to identify any differences in thermal history between extruded Batches A and B. The thermal history of the resin is removed during the extrusion processing and therefore the 2nd heating cycle was used to look at the intrinsic thermal properties of the dried resin. g) is characterized by a jump in the heat capacity (ΔCp) at Tg, evident in p is dependent on the crystallinity and rigid amorphous fractions of a semi-crystalline polymer [g is a second order transition, where the material starts to transition from a glassy, rigid material to a soft, rubbery material [m). The melting peak is a first order transition, characteristic of a semi-crystalline material and is related to the melting of the crystalline structure. The area under this peak is the enthalpy of heating (ΔHm) and from which the degree of crystallinity (Xc) is calculated. These thermal properties are in-line with those reported previously for PLLA [From the DSC curve for the PLLA resin, the glass transition temperature , which is often found in polymers with slow crystallization kinetics. During rapid cooling from the molten state, the polymer does not have enough time to crystallize. However, upon re-heating above Tg, the thermal energy provides enough molecular mobility to allow the polymer to crystallize [c. The Tcc double exothermic peak has been attributed to the co-existence of two kinds of amorphous regions; interlamellar amorphous regions with some order and complete amorphous regions between spherulites [m relates to melt recrystallisation (Tmc). It may be caused by the presence of more than one crystallographic form; the presence of melting, re-crystallization, and re-melting; or to changes in morphology, such as lamellar thickening and crystal perfecting [Firstly, there is the presence of a broad double exothermic peak after Tstallize . The areerulites . Alternaerulites . The smarfecting . It has rfecting .cc peaks, the thermal and morphological properties of both extruded batches were similar, indicating that the differences in molecular weight reported in The influence of melting conditions on thermal properties is dependent on prior melting conditions (temperature and time), heating and cooling rates and initial molecular weight. It’s important to highlight that the formation of double cold crystallisation and melt re-crystallisation peaks are significantly affected by the different heating and cooling rates applied during DSC analysis . Table 4For medical device applications such as the use of implantable devices, the first stage of hydrolytic degradation is through hydrolysis of the polymers amorphous regions, resulting in molecular weight loss . TherefoTensile testing was performed on tubing from both extrusion batches to assess the impact melt processing had on their mechanical properties. The tensile properties of polymers can be altered through molecular alignment. This is achieved through the orientation of the polymer molecules in the machine direction, resulting in tubes that display anisotropic behaviour. The orientation of polymer molecules results from the stress applied to the melt during processing, where the polymer melt is subjected to both shear and elongational stresses. The molecular chains are distorted from their randomly coiled state and are orientated as they pass through the die. As the extrudate exits the die, the unconstrained polymer molecules will look to revert to their natural disordered state. However, rapid cooling of the extrudate as it exits the die results in frozen-in molecular orientation and stresses. The level of drawdown, cooling and relaxation, all affect the amount of orientation in the tubing and its final properties. The extrudate will also be subjected to differential cooling rates upon exiting the die and entering the water bath. This leads to localised stresses in the tube, which can also impact its final mechanical properties.There are numerous material characteristics that impact the mechanical properties of polymers, such as, chemical structure, molecular weight, crystallinity, and molecular orientation. As shown through DSC analysis, there were only minimal differences in crystallinity between both extruded batches. It is also unlikely that there would be a significant variation in the chemical structure or amount of orientation in both extrusion batches given the tight controls employed during the extrusion process. Therefore, the most likely contributor to the slight differences in tensile strength and stiffness is due to the higher molecular weight of Batch B over Batch A. The mechanical strength of a polymer improves with increasing molecular weight and their relationship is well understood . The preDMA testing was performed on a sample of tubing from both extrusion batches to assess the impact processing had on their mechanical properties. The analysis compared the storage modulus (E’) as a function of temperature between both batches. Storage modulus is a measure of the stored energy in a sample and represents the elastic portion of a viscoelastic material. n values reduced by a range of 17–23% during processing, with resin drying contributing to approximately half of the molecular weight loss. Given the low level of moisture present in the resin (<100 ppm) post-drying, the reduction in molecular weight observed during the extrusion process can most likely be attributed to thermal degradation. This was supported by results from FTIR spectra analysis, which showed no evidence of an increase in hydroxyl groups, which are typically associated with hydrolytic degradation. It was also observed that Batch A, which was processed on the 1” extruder and had the longer melt residence time, resulted in a 12% greater molecular weight loss compared to Batch B. The loss of molecular weight and the effect of residence time in PLLA during melt processing have been widely reported. However, given the similarity in processing conditions between both batches, it was a little surprising the sensitivity to molecular weight loss at such low shear rates and melt residence times. Another important finding in this study, was the notable increase (>22 fold) in residual monomer during melt processing, as determined by GC-FID. Given the significant effect residual monomer can have on the degradation properties of PLLA, it’s clear that this must be closely monitored during melt processing.The tube-extrusion of high molecular weight PLLA using a microbore single screw extruder, resulted in a reduction in molecular weight as determined by GPC. The MThermal and morphological properties of the tubing were analysed using DSC, which highlighted a reduction in crystallinity from the virgin resin (~37%) to the extruded tubes (~14%). This reduction was due to the quench cooling associated with the tube-extrusion process. In addition to these findings, the presence of cold crystallisation and melt-recrystallisation was detected in both batches of extruded tubing, which was attributed to the slow crystallisation kinetics of PLLA. This low level of crystallinity in the extruded tubing, means secondary processing such as annealing, or strain induced crystallisation are most likely required. The differences in molecular weight from Batch A and B did not impact the thermal or morphological properties of the tubing.The mechanical properties of both batches were examined using uniaxial tensile testing and dynamic mechanical analysis. As reported by many other authors, both analytical techniques highlighted the material to be brittle with moderate stiffness and strength when compared to other biodegradable polymers. Tensile testing reported Young’s modulus values in the range of 2400–2500 MPa, the maximum tensile stress in the range of 66–70 MPa and strain at break in the region of <5.5%. The lack of any strain hardening or softening on the extruded tubing is an important consideration for downstream processing such as biaxial expansion.g was also confirmed through the use of DMA.Batch B exhibited slightly higher stiffness and tensile strength than Batch A, which can be attributed to its higher molecular weight. Interestingly the difference in molecular weight had no notable impact on elongational properties. This in part could be owed to the molecular orientation having a stronger influence on elongation, than slight differences in molecular weight. The temperature dependence of mechanical properties below TFrom the findings in this study, the role that low shear microbore extrusion plays in determining the thermal, chemical, morphological and mechanical properties of PLLA tubing is better understood. Whilst many of the results are in agreement with the findings of other researchers, there were some key learnings. Careful consideration of process parameters and tooling configuration must be considered, given the susceptibility of PLLA to thermal degradation during melt processing, at low shear rates. Even at these low shear rates, the residence time in the extruder plays a crucial role in determining the final molecular weight of the material and must be controlled, whilst the level of residual monomer in the finished tubing must be carefully monitored. Small differences in molecular weight (12%) were shown to impact tensile strength and modulus, with no notable effect on elongation, further highlighting the importance of controlling molecular orientation during the extrusion process. There was also an observed temperature-dependence of mechanical properties below the glass transition temperature.


Tissue preparation—brains were quickly extracted and the striatum was isolated and homogenized in either RIPA buffer with protease inhibitors  or in 0.1 N HClO4 (for HPLC processing). The homogenates were processed through fractional centrifugation to remove cellular debris. Lysate samples were frozen at −80°C until ready for analysis. Protein expression quantification—expression of proteins were measured using intensity of bands from Western blots. Lysates were denatured prior to loading with LB with 10% β-mercaptoethanol and 30-minute incubation at 37°C. All immunoblots were normalized to immunoreactivity to α-tubulin. Immunoblot intensity was determined using the ImageJ software. Dopamine/dopamine metabolite quantification HPLC analysis was used to determine dopamine and dopamine metabolite concentration. Aliquots of the lysate were injected onto a C18 column using a mobile phase consisting of 50 mM H2NaO4P·H2O, 0.72 mM sodium octyl sulfate, 75 µM Na2 EDTA, and 10% acetonitrile (pH 3.0). The mobile phase was pumped through the system at 0.3 mL/minute. RESULTS/ANTICIPATED RESULTS: Measured total dopamine concentration through HPLC analysis in the striatum showed no significant differences in the bacteria-treated group relative to the control group. The metabolites DOPAC and HVA had an elevated measured concentration in the bacteria-treated group relative to the control group. Western blot analysis showed decreased immunoreactivity for DAT and TH in the bacteria-treated group compared with the control group. There was no significance difference in the immunoreactivity for VMAT2. DISCUSSION/SIGNIFICANCE OF IMPACT: This study demonstrates that dopamine signaling dynamics in the midbrain can be altered by changes in the gut flora in mice. These results further substantiate the impact of the gut-brain axis and may even point to a potential avenue of bolstering the resilience of dopaminergic neurons in preventing the onset of PD. Further experiments must be performed to understand the mechanism of the observed changes and to determine if these changes have any salutary effect.OBJECTIVES/SPECIFIC AIMS: Several clinical studies have established a correlation between changes in relative bacterial populations in the gut and Parkinson disease. However, few published experiments have been able to parse out whether these associations are causative or correlative. Our aim is to determine how bacteria in the gut may impact the health and resilience of dopaminergic signaling. Our experiment is designed to serve as a proof-of-principle that controlled alterations to the gut microbiome alters mechanisms in dopamine homeostasis in the midbrain. METHODS/STUDY POPULATION: Bacterial inoculation 8–10-week-old germ-free male mice (C57BL/6) were exclusively used in this experiment. Mice were orally gavaged every 3 days  with 100 µL novel bacterial suspension (~108 CFU resuspended in PBS with 1.5% NaHCO