Disulfide-Mediated Bioconjugation: Disulfide Formation and Restructuring on the Surface of Nanomanufactured (Microfluidics) Nanoparticles.

This study is about (1) nanomanufacturing (focusing on microfluidic-assisted nanoprecipitation), (2) advanced colloid characterization (focusing on field flow fractionation), and (3) the possible restructuring of surface disulfides. Disulfides are dynamic and exchangeable groups, and here we specifically focus, first, on their use to introduce biofunctional groups and, second, on their re-organization, which may lead to variable surface chemistries and uncontrolled cell interactions. The particles were obtained via microfluidic-assisted (flow-focused) nanoprecipitation of poly(ethylene glycol)-b-poly(ε-caprolactone) bearing or not a 2-pyridyl disulfide (PDS) terminal group, which quantitatively exchanges with thiols in solution. In this study, we have paid specific attention to size characterization, thereby also demonstrating the limitations of dynamic light scattering (DLS) as a stand-alone technique. By using asymmetric flow field flow fractionation coupled with DLS, static light scattering (SLS), and refractive index detectors, we show that relatively small amounts of >100 nm aggregates (cryogenic transmission electron microscopy and SLS/DLS comparison suggesting them to be wormlike micelles) dominated the stand-alone DLS results, whereas the "real" size distributions picked <50 nm. Our key result is that the kinetics of the conjugation based on PDS-thiol exchange was controlled by the thiol pKa, and this also determined the rate of the exchange between the resulting disulfides and glutathione (GSH). In particular, more acidic thiols (e.g., peptides, where a cysteine is flanked by cationic residues) react faster with PDS, but their disulfides hardly exchange with GSH; the reverse applies to thiols with a higher pKa. Disulfides that resist against restructuring via thiol-disulfide exchange allow for a stable bioconjugation, although they may be bad news for payload release under reducing conditions. However, experiments of both thiol release and nanoparticles uptake in cells (HCT116) show that also the disulfides formed from less-acidic and, therefore, less-reactive, and more exchangeable thiols were stable for at least a few hours even in a GSH-rich (10 mM) environment; this suggests a sufficiently long stability of surface groups to achieve, for example, a cell-targeting effect.

Polymer degradation and drug delivery in PLGA-based drug-polymer applications: A review of experiments and theories.

Poly (lactic-co-glycolic acid) (PLGA) copolymers have been broadly used in controlled drug release applications. Because these polymers are biodegradable, they provide an attractive option for drug delivery vehicles. There are a variety of material, processing, and physiological factors that impact the degradation rates of PLGA polymers and concurrent drug release kinetics. This work is intended to provide a comprehensive and collective review of the physicochemical and physiological factors that dictate the degradation behavior of PLGA polymers and drug release from contemporary PLGA-based drug-polymer products. In conjunction with the existing experimental results, analytical and numerical theories developed to predict drug release from PLGA-based polymers are summarized and correlated with the experimental observations. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1692-1716, 2017.

Feasibility of laparoendoscopic single-site partial nephrectomy in a porcine model.

PURPOSE: We performed laparoendoscopic single-site (LESS) partial nephrectomy in a porcine model with the objectives of overcoming the technical challenges of this surgery and exploring its feasibility. MATERIALS AND METHODS: Six partial nephrectomies were performed on a pig aged 5 months, three cases on each kidney, by four surgeons: two urologists with much experience in laparoscopic surgery (E1, E2) and two less-experienced urologists (B1, B2). While under general anesthesia, the swine was placed in a lateral flank position. Umbilical placement of an Octoport was done with a 2.5 cm incision. After dissection of the renal hilum and Gerota's fascia, a bulldog clamp was applied on the renal artery and parenchymal resection was done. Renorrhaphy was then performed with interrupted sutures with the use of a sliding knot technique. RESULTS: All six partial nephrectomies were performed successfully after repair of the vascular and collecting system at the resection margin and renorrhaphy without the need to introduce any additional ports. There were no noticeable intra- or postoperative complications. The mean warm ischemic time was 42 minutes (range, 30-60 minutes). The shortest warm ischemic time, 30 minutes, was achieved by using the early unclamping technique during renorrhaphy. The longest warm ischemic time was 60 minutes. The average number of renorrhaphy stitches was 3.2 (range, 2-5). CONCLUSIONS: LESS partial nephrectomy was successfully performed in a porcine model but resulted in a longer ischemic time than that of conventional laparoscopic surgeries. Therefore, further laboratory disciplinary efforts are needed to decrease the warm ischemic time and to improve this surgical technique.