Microporous poly(L-lactic acid) membranes fabricated by polyethylene glycol solvent-cast/particulate leaching technique.

With the eventual goal of developing a tissue-engineered tear secretory system, we found that primary lacrimal gland acinar cells grown on solid poly(L-lactic acid) (PLLA) supports expressed the best histiotypic morphology. However, to be able to perform vectorial transport functions, epithelia must be supported by a permeable substratum. In the present study, we describe the use of a solvent-cast/particulate leaching technique to fabricate microporous PLLA membranes (mpPLLAm) from PLLA/polyethylene glycol blends. Scanning electron microscopy revealed pores on both the air-cured ( approximately 4 microm) and glass-cured sides (<2 microm) of the mpPLLAm. Diffusion studies were performed with mpPLLAm fabricated from 57.1% PLLA/42.9% polyethylene glycol blends to confirm the presence of channelized pores. The data reveal that glucose, L-tryptophan, and dextran (a high molecular weight glucose polymer) readily permeate mpPLLAm. Diffusion of the immunoglobulin G through the mpPLLAm decreased with time, suggesting the possible adsorption and occlusion of the pores. Cells cultured on the mpPLLAm (57.1/42.9 wt%) grew to subconfluent monolayers but retained histiotypic morphological and physiological characteristics of lacrimal acinar cells in vivo. Our results suggest that mpPLLAm fabricated using this technique may be useful as a scaffold for a bioartificial lacrimal gland device.

Nanopore formation and phosphatidylserine externalization in a phospholipid bilayer at high transmembrane potential.

Atomic-resolution molecular dynamics simulations of lipid bilayers containing 7% phosphatidylserine (PS) on one leaflet are consistent with experimental observations of membrane poration and PS externalization in living cells exposed to nanosecond, megavolt-per-meter electric pulses. Nanometer-diameter aqueous pores develop within nanoseconds after application of an electric field of 450 mV/nm, and electrophoretic transport of the anionic PS headgroup along the newly constructed hydrophilic pore surface commences even while pore formation is still in progress.

Monitoring the degradation process of biopolymers by ultrasonic longitudinal wave pulse-echo technique.

A non-destructive ultrasonic longitudinal wave pulse-echo technique was utilized to monitor the degradation process of three biodegradable polymers: poly(glycolic acid) (PGA), poly(L-lactic acid) (PLLA) and 50:50 poly(D,L-lactide-co-glycolide) (PDLLG). The degradation processes of PGA and PLLA, which have different molecular structure, were also studied by differential scanning calorimetry (DSC). The degradation processes of PDLLG specimens prepared by different methods were characterized by the ultrasonic wave technique and gel permeation chromatography (GPC). The resulting acoustic and thermal properties indicate that PLLA and PGA exhibit distinctly different degradation behavior, whereas the acoustic properties and molecular weight of PDLLG are sensitive with preparation methods. The present study demonstrates that ultrasonic wave technique provides a powerful tool in detecting the property changes of biodegradable polymers prepared with different manufacturing process and that the degradation behavior of biodegradable polymers can be closely monitored by ultrasonic technique.