Water vapour transmission and degradation properties of biaxially stretched PCL films and cell-permeable membranes

Abstract

Introduction of minimal amount of foreign material may invoke lesser unwelcome host response. The design and fabrication of thin films have been the focus of a number of current researchers. So in a continuous effort to improve the properties of existing Microthin (10i??3i?-m) poly (i?Y-caprolactone) (PCL) films, the fabrication of thinner PCL film, Ultrathin (4i??1i?-m), with improved moisture permeability is reported. As an alternative means to improve permeability, the feasibility of perforating existing biaxially stretched Microthin films by Robotic Puncturing was explored. Perforated (Perf1 and Perf2) films with hole diameters 180i??5i?-m and 275i??10 i?-m, respectively, were successfully fabricated.Moisture permeability of both unperforated and perforated films was evaluated and compared by determining water vapour transmission rate (WVTR) across the films. Moisture permeability of Perf1 and Perf2 and Ultrathin films were 50%, 80% and 30%, respectively more than Microthin films. Despite the perforations Perf1 and Perf2 films have only slightly lower tensile strength and elongation at break and than Microthin films. In the same way, Ultrathin films have enhanced mechanical properties, and in addition they are more flexible and pliable than Microthin films. The hydrolytic degradation of PCL is very slow compared to other aliphatic polyesters. Results of degradation of PCL films in vitro in phosphate buffer saline (PBS, pH = 7.4) carried out for 12 months verified this. Slow rate of hydrolysis of PCL was attributed mainly to the high initial molecular weight (Mn = 80,000).Therefore this prompted the accelerated degradation of PCL by base promotion. The effect on degradation rate with three concentrations (1M, 3M and 5M) of NaOH solution was examined, in order to understand the degradation kinetics and to model the rate of hydrolysis process. Hydrolytic degradation in a high basic pH (>13) medium occurred mostly by random chain scission of backbone ester bonds on the film surface followed by loss of material due to surface erosion.Accelerated degradation of films suggested a pseudo first-order hydrolysis process, which consisted of an initial stage involving slow rate of mass loss due to preferential degradation of amorphous regions and a second stage that showed rapid mass loss due to film fragmentation. Results indicated that all three films followed a similar degradation profile. In general the Ultrathin films were the fastest to degrade, followed by the Perf1 films and then Microthin films. Rate of degradation increased with increasing NaOH concentration. The presence of flap-like structures in Perf1 films was assigned as the main reason why the degradation rate was faster than that of Microthin films. Faster degradation of Ultrathin films was attributed to their lower surface area to volume ratio and presence of more inherent defects and microvoids in comparison to Microthin films. SEM images showed that surface erosion led to extensive formation of micropores and surface roughness, which increased the surface area and this in turn enhanced the hydrolysis process. In conclusion, results suggest that the rate of loss of film mass was a function of degradation time, film thickness, total surface area of films and concentration of the basic pH medium used.