Processing methods of ultrathin poly(ε-caprolactone) films for tissue engineering applications

Ultrathin poly(epsilon-caprolactone) (PCL) films were fabricated through biaxially drawn films made from three different methods, namely, spin casting, 2-roll milling, and solution casting. Biaxial drawn spin cast films yield thickness of 1.2 mu m which is 9 and 12 times thinner that 2-roll mill and solvent cast films, respectively. The films fabricated were found to exhibit different drawing ratios. 2-roll mill film exhibits the highest drawing ratio of 4 x 4 while spin cast films can only draw up to a ratio of 2 x 2. The morphology of the films, studied using a polarized microscope and atomic force microscope, showed fine fibrillar networks of different thicknesses. Biaxially drawn 2-roll mill and solvent cast films showed thicker fibrils as compared to those for the spin cast films. Such a difference can be attributed to larger spherulites caused by slower cooling rates during melt pressing for both 2-roll mill and solvent cast films and smaller spherulites because of fast cooling during evaporation for spin cast films. Thermal analysis through differential scanning calorimetry revealed a slight increase in the peak-melting temperature after biaxial drawing. A drop in percentage crystallinity was also noted. The result of the water vapor transmission rate (WVTR) was found to be dependent on fabrication techniques that determine the spherulites formation. It was also found that the WVTR was inversely proportional to the thickness of the films. Tensile strength and modulus of the films showed significant improvements after biaxial stretching. By identifying the unique strengths of each individual PCL film produced via different techniques, it is possible to apply to different areas of membrane tissue engineering such as dermatology, ophthalmology, vascular graft engineering, and soft tissue regeneration.