ANALYTICAL AND EXPERIMENTAL STUDY ON PDC DRILL BITS QUALITY
Under geological extreme conditions, polycrystalline diamond compact bits (PDC) are a relevant choice because of their interesting drilling performances. In this way, the quality of innovating PDC bits materials has to be determined with accuracy by measuring cutting efficiency and wear rate, both related to the overall mechanical properties. A lathe-type test device was used to proceed to the first experiments. During these tests, cutters have been worn over an abrasion length greater than 15 km, with a mean normal load range from 3000 to 5000 N, a cutting speed about 1:8 m/ s and a penetration depth close to 2 mm. Analyses are based on models establishing coupled relations between cutting and friction stresses related to the drag bits excavation mechanism. In this work, models are implemented in order to evaluate cutting efficiency and to estimate the life time of the diamond insert. A variety of cutters was characterized by wear rates ranged from 9.4•10^(-15) to 1.1•10^(-13) mm^3/(Nm) (Archard’s model) and cutting efficiencies at 10 km evaluated between 31 and 55%. From here, an original approach is developed to describe the overall cutter quality by defining a ratio between efficiency and wear. The reference samples during preliminary tests clearly revealed various mechanical behaviors due to changes in the material composition and distinct manufacturing production methods. These changes are detected at several levels: coatings, grain sizes, surface roughness, etc.
Mathematical Modeling of PDC Bit Drilling Process Based on a Single-Cutter Mechanics
An analytical development of a new mechanistic drilling model for polycrystalline diamond compact (PDC) bits is presented. The derivation accounts for static balance of forces acting on a single PDC cutter and is based on assumed similarity between bit and cutter. The model is fully explicit with physical meanings given to all constants and functions. Three equations constitute the mathematical model: torque, drilling rate, and bit life. The equations comprise cutter’s geometry, rock properties drilling parameters, and four empirical constants. The constants are used to match the model to a PDC drilling process. Also presented are qualitative and predictive verifications of the model. Qualitative verification shows that the model’s response to drilling process variables is similar to the behavior of full-size PDC bits. However, accuracy of the model’s predictions of PDC bit performance is limited primarily by imprecision of bit-dull evaluation. The verification study is based upon the reported laboratory drilling and field drilling tests as well as field data collected by the authors.
Two-Year COMPASS Trial Results: Supraciliary Microstenting with Phacoemulsification in Patients with Open-Angle Glaucoma and Cataracts.
PURPOSE
We evaluated 2-year safety and efficacy of supraciliary microstenting (CyPass Micro-Stent; Transcend Medical, Inc., Menlo Park, CA) for treating mild-to-moderate primary open-angle glaucoma (POAG) in patients undergoing cataract surgery.


DESIGN
Multicenter (24 US sites), interventional randomized clinical trial (RCT) (ClinicalTrials.gov identifier, NCT01085357).


PARTICIPANTS
Subjects were enrolled beginning July 2011, with study completion in March 2015. Subjects had POAG with mean diurnal unmedicated intraocular pressure (IOP) 21-33 mmHg and were undergoing phacoemulsification cataract surgery.


METHODS
After completing cataract surgery, subjects were intraoperatively randomized to phacoemulsification only (control) or supraciliary microstenting with phacoemulsification (microstent) groups (1:3 ratio). Microstent implantation via an ab interno approach to the supraciliary space allowed concomitant cataract and glaucoma surgery.


MAIN OUTCOME MEASURES
Outcome measures included percentage of subjects achieving ≥20% unmedicated diurnal IOP lowering versus baseline, mean IOP change and glaucoma medication use, and ocular adverse event (AE) incidence through 24 months.


RESULTS
Of 505 subjects, 131 were randomized to the control group and 374 were randomized to the microstent group. Baseline mean IOPs in the control and microstent groups were similar: 24.5±3.0 and 24.4±2.8 mmHg, respectively (P > 0.05); mean medications were 1.3±1.0 and 1.4±0.9, respectively (P > 0.05). There was early and sustained IOP reduction, with 60% of controls versus 77% of microstent subjects achieving ≥20% unmedicated IOP lowering versus baseline at 24 months (P = 0.001; per-protocol analysis). Mean IOP reduction was ↓7.4 mmHg for the microstent group versus ↓5.4 mmHg in controls (P < 0.001), with 85% of microstent subjects not requiring IOP medications at 24 months. Mean 24-month medication use was 67% lower in microstent subjects (P < 0.001); 59% of control versus 85% of microstent subjects were medication free. Mean medication use in controls decreased from 1.3±1.0 drugs at baseline to 0.7±0.9 and 0.6±0.8 drugs at 12 and 24 months, respectively, and in the microstent group from 1.4±0.9 to 0.2±0.6 drugs at both 12 and 24 months (P < 0.001 for reductions in both groups at both follow-ups vs. baseline). No vision-threatening microstent-related AEs occurred. Visual acuity was high in both groups through 24 months; >98% of all subjects achieved 20/40 best-corrected visual acuity or better.


CONCLUSIONS
This RCT demonstrated safe and sustained 2-year reduction in IOP and glaucoma medication use after microinterventional surgical treatment for mild-to-moderate POAG.