Evaluation of Stability of Amylose Inclusion Complexes Depending on Guest Polymers and Their Application to Supramolecular Polymeric Materials
This paper describes the evaluation of the stability of amylose–polymer inclusion complexes under solution state in dimethyl sulfoxide (DMSO) depending on guest polymers. The three complexes were prepared by the vine-twining polymerization method using polytetrahydrofuran (PTHF), poly(ε-caprolactone) (PCL), and poly(l-lactide) (PLLA) as guest polymers. The stability investigation was conducted at desired temperatures (25, 30, 40, 60 °C) in DMSO solutions of the complexes. Consequently, the amylose–PTHF inclusion complex was dissociated at 25 °C, while the other complexes were stable under the same conditions. When the temperatures were elevated, the amylose–PCL and amylose–PLLA complexes were dissociated at 40 and 60 °C, respectively. We also found that amylose inclusion supramolecular polymers which were prepared by the vine-twining polymerization using primer-guest conjugates formed films by the acetylation of amylose segments. The film from acetylated amylose–PLLA supramolecular polymer had higher storage modulus than that from acetylated amylose–PTHF supramolecular polymer, as a function of temperature.
Mechanically cartilage-mimicking poly(PCL-PTHF urethane)/collagen nanofibers induce chondrogenesis by blocking NF-kappa B signaling pathway.
Cartilage cannot self-repair and thus regeneration is a promising approach to its repair. Here we developed new electrospun nanofibers, made of poly (ε-caprolactone)/polytetrahydrofuran (PCL-PTHF urethane) and collagen I from calf skin (termed PC), to trigger the chondrogenic differentiation of mesenchymal stem cells (MSCs) and the cartilage regeneration in vivo. We found that the PC nanofibers had a modulus (4.3 Mpa) lower than the PCL-PTHF urethane nanofibers without collagen I from calf skin (termed P) (6.8 Mpa) although both values are within the range of the modulus of natural cartilage (1-10 MPa). Both P and PC nanofibers did not show obvious difference in the morphology and size. Surprisingly, in the absence of the additional chondrogenesis inducers, the softer PC nanofibers could induce the chondrogenic differentiation in vitro and cartilage regeneration in vivo more efficiently than the stiffer P nanofibers. Using mRNA-sequence analysis, we found that the PC nanofibers outperformed P nanofibers in inducing chondrogenesis by specifically blocking the NF-kappa B signaling pathway to suppress inflammation. Our work shows that the PC nanofibers can serve as building blocks of new scaffolds for cartilage regeneration and provides new insights on the effect of the mechanical properties of the nanofibers on the cartilage regeneration.
A Critical Assessment on Functional Attributes and Degradation Mechanism of Membrane Electrode Assembly Components in Direct Methanol Fuel Cells
Direct methanol fuel cells (DMFC) are typically a subset of polymer electrolyte membrane fuel cells (PEMFC) that possess benefits such as fuel flexibility, reduction in plant balance, and benign operation. Due to their benefits, DMFCs could play a substantial role in the future, specifically in replacing Li-ion batteries for portable and military applications. However, the critical concern with DMFCs is the degradation and inadequate reliability that affect the overall value chain and can potentially impede the commercialization of DMFCs. As a consequence, a reliability assessment can provide more insight into a DMFC component’s attributes. The membrane electrode assembly (MEA) is the integral component of the DMFC stack. A comprehensive understanding of its functional attributes and degradation mechanism plays a significant role in its commercialization. The methanol crossover through the membrane, carbon monoxide poisoning, high anode polarization by methanol oxidation, and operating parameters such as temperature, humidity, and others are significant contributions to MEA degradation. In addition, inadequate reliability of the MEA impacts the failure mechanism of DMFC, resulting in poor efficiency. Consequently, this paper provides a comprehensive assessment of several factors leading to the MEA degradation mechanism in order to develop a holistic understanding.