PDMS Curing Inhibition on 3D-Printed Molds: Why? Also, How to Avoid It?

Three-dimensional (3D)-printing techniques such as stereolithography (SLA) are currently gaining momentum for the production of miniaturized analytical devices and molds for soft lithography. However, most commercially available SLA resins inhibit polydimethylsiloxane (PDMS) curing, impeding reliable replication of the 3D-printed structures in this elastomeric material. Here, we report a systematic study, using 16 commercial resins, to identify a fast and straightforward treatment of 3D-printed structures and to support accurate PDMS replication using UV and/or thermal post-curing. In-depth analysis using Raman spectroscopy, nuclear magnetic resonance, and high-resolution mass spectrometry revealed that phosphine oxide-based photo-initiators, leaching out of the 3D-printed structures, are poisoning the Pt-based PDMS catalyst. Yet, upon UV and/or thermal treatments, photo-initiators were both eliminated and recombined into high molecular weight species that were sequestered in the molds.

Regio- and Stereo-Specific Chemical Depolymerization of High Molecular Weight Polybutadiene and Polyisoprene for Their Analysis by High-Resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry: Comparison with Pyrolysis-Comprehensive Two-Dimensional Gas Chromatography/Mass Spectrometry, Atmospheric Solid Analysis Probe, Direct Inlet Probe-Atmospheric Pressure Chemical Ionization Mass Spectrometry, and Ion Mobility Spectrometry-Mass Spectrometry.

Polybutadiene (PB) and polyisoprene (PI), the two most common polydienes (PD), are involved in a large number of materials and used in a wide variety of applications. The characterization of these polymers by mass spectrometry (MS) continues to be very challenging due to their high insolubility and the difficulty to ionize them. In this work, a cross-metathesis reaction was used to generate end-functionalized acetoxy ionizable oligomers for the structural deciphering of different commercial PB and PI samples. A cross-metathesis reaction was carried out between polymers and the Z-1,4-diacetoxy-2-butene as a chain transfer agent in dichloromethane using a Hoveyda-Grubbs second-generation catalyst. Well-defined acetoxy telechelic structures were obtained and analyzed by Fourier transform ion cyclotron resonance (FTICR) high-resolution MS. However, after depolymerization, low molar mass polyolefins contained some units with different configurations, suggesting an olefin isomerization reaction due to the decomposition of the catalyst. The addition of an electron-deficient reagent such as 2,6-dichloro-1,4-benzoquinone suppressed this isomerization in the case of both Z- and E-PB and PI. Ion mobility spectrometry-mass spectrometry (IMS-MS) and energy-resolved tandem mass spectrometry (ERMS) analyses confirmed a successful isomerization suppression. For comparing the results obtained by depolymerization with classical methods for polymer analysis, pyrolysis-comprehensive two-dimensional gas chromatography/mass spectrometry (Py-GC × GC-MS), atmospheric solid analysis probe (ASAP), and direct inlet probe-atmospheric pressure chemical ionization (DIP-APCI) analyses were performed on the same polymers. This strategy can be applied on a variety of synthetic and natural not yet characterized polymers.

Flapless Piezotome Crest Split Achieves Comparable Outcomes to Autologous Onlay Grafts With Significant Less Patient Morbidity and Complications-A Randomized Clinical Study.

PURPOSE: In the management of the narrow alveolar ridge, the flapless piezotome crest split (FPCS) technique with horizontal distraction was introduced as an alternative to lateral alveolar ridge augmentation using autologous bone block grafting (ABBG). The study purpose was to measure and compare the alveolar crest width and complications between FPCS and ABBG. MATERIALS AND METHODS: We implemented a nonblinded, randomized clinical trial. The sample included patients requiring lateral alveolar ridge augmentation before implant insertion. The predictor variable was lateral alveolar ridge augmentation performed using ABBG (control group) or FPCS using an ultrasonic surgical device (Piezotome II or Piezotome CUBE; Acteon, Norwich, UK) and specific crest split working tips (test group). The primary outcome variable was the overall coronal crest width achieved after completed healing measured at 6 months using 3-dimensional imaging studies. Other study variables included the postoperative morbidity, staged using the Universal Pain Assessment Scale, complications, and surgery duration. Descriptive and bivariate statistics were computed using SPSS, version 22.0 (IBM Corp, Armonk, NY), and P ≤ .05 was considered to indicate statistical significance. RESULTS: The sample included 567 patients treated with ABBG (56.1% female; age, 64.1 ± 20.2 years) and 562 treated with FPCS (57.2% female; age, 62.3 ± 18.2 years). The baseline crest width in the control and test groups was 2.1 ± 0.5 mm and 1.9 ± 0.4 mm, respectively. The final crest width achieved with ABBG and FPCS was 5.8 ± 0.8 mm and 6.5 ± 0.7 mm, respectively (P > .05). Statistically significant differences (P < .05) were found between the ABBG and FPCS groups in the postoperative complication rate, morbidity, and operative time, all in favor of FPCS. CONCLUSIONS: FPCS seems to be a significantly less traumatic alternative to buccal onlay grafting with autologous bone blocks, providing a comparable or better net gain in the alveolar crest width with a significantly shorter operative time and less postoperative morbidity.