Hydrolytic Degradation of Polylactic Acid Fibers as a Function of pH and Exposure Time

Polylactic acid (PLA) is a widely used bioresorbable polymer in medical devices owing to its biocompatibility, bioresorbability, and biodegradability. It is also considered a sustainable solution for a wide variety of other applications, including packaging. Because of its widespread use, there have been many studies evaluating this polymer. However, gaps still exist in our understanding of the hydrolytic degradation in extreme pH environments and its impact on physical and mechanical properties, especially in fibrous materials. The goal of this work is to explore the hydrolytic degradation of PLA fibers as a function of a wide range of pH values and exposure times. To complement the experimental measurements, molecular-level details were obtained using both molecular dynamics (MD) simulations with ReaxFF and density functional theory (DFT) calculations. The hydrolytic degradation of PLA fibers from both experiments and simulations was observed to have a faster rate of degradation in alkaline conditions, with 40% of strength loss of the fibers in just 25 days together with an increase in the percent crystallinity of the degraded samples. Additionally, surface erosion was observed in these PLA fibers, especially in extreme alkaline environments, in contrast to bulk erosion observed in molded PLA grafts and other materials, which is attributed to the increased crystallinity induced during the fiber spinning process. These results indicate that spun PLA fibers function in a predictable manner as a bioresorbable medical device when totally degraded at end-of-life in more alkaline conditions.     

Uranyl ion uptake capacity of poly (N-isopropylacrylamide/maleic acid) copolymeric hydrogels prepared by gamma rays

The effect of gel composition, absorbed dose and pH of the solution on the uranyl ion uptake capacity of N-isopropylacrylamide/maleic acid copolymeric hydrogels containing 0–3 mol% of maleic acid at 48 kGy have been investigated. Uranyl uptake capacity of hydrogels are found to increase from 18.5 to 94.8 mg [UO₂²⁺]/g dry gel as the mole % of maleic acid content in the gel structure increased from 0 to 3. The percent swelling, equilibrium swelling and diffusion coefficient values have been evaluated for poly(N-isopropylacrylamide/maleic acid) hydrogels at 500 ppm of uranyl nitrate solution.     

A comprehensive electric field analysis of a multifunctional electrospinning platform

The electric field is one of the most critical parameters in electrospinning process. This study provides a comprehensive electric field analysis of a multifunctional electrospinning platform performed by FEMM 4.2. In this paper firstly information about the electrospinning method is mentioned. Electric field distribution of the multifunctional electrospinning platform is analyzed in different voltage levels. The effect of the applied voltage between the needles and the collector on nanofibers is investigated which are collected on the chassis. Furthermore the analysis results clearly demonstrated the effect of electrostatic force on the multiple jets which are at the needle tips.     

Synthesis,characterization, and biological activity of N‐(4‐acetylphenyl)maleimide and its oxime,carbazone, thiosemicarbazone derivatives and their polymers

A new type of maleimide monomer, N‐(4‐acetylphenyl)maleimide (NAPMI), was synthesized. The oxime, carbazone, and thiosemicarbazone derivatives of NAPMI were prepared with hydroxylamine hydrochloride, semicarbazide hydrochloride, and thiosemicarbazide hydrochloride, respectively. Radical homopolymerization of NAPMI and its derivatives were prepared at 60 °C in dimethyl sulfoxide solution with azobisisobutyronitrile as an initiator. The monomers and theirs homopolymers were characterized with Fourier transform infrared and NMR techniques. The glass‐transition temperatures, thermal stability, and ultraviolet stability of the polymers are compared. The activation energies of the thermal degradation of polymers were calculated by the Kissinger method. The antibacterial and antifungal effects of the monomers and polymers were also investigated on various bacteria and fungi. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1942–1951, 2003     

NEW POLY(METHACRYLATE)S CONTAINING OXIME ESTERS MOIETIES BASED ON CYCLOHEXANON AND CYCLOPENTANON

The synthesis of two new methacrylates such as 2-[(cyclohexylideneamino)oxy]-2-oxoethyl methylacrylate (CHOEMA)and 2-[(cyclopentylideneamino)oxy]-2-oxoethyl methylacrylate(CPOEMA)are described.The monomers produced from the reaction of corresponding cyclohexanone O-(2-chloroacetyl)oxime and cyclopentanone O-(2- chloroacetyl)oxime with sodium methacrylate was polymerized in 1,4-dioxane solution at 65℃using AIBN as an initiator. The monomers and their polymers were characterized by IR,~1H- and ~(13)C-NMR s...