Synthesis, physical characterization, and biological performance of sequential homointerpenetrating polymer network sponges based on poly(2-hydroxyethyl methacrylate)

A Limitation in the use of hydrophilic poly(2-hydroxyethyl methacrylate) (P HEMA) sponges as implantable devices is their inherently poor mechanical st rength. This precludes proper surgical manipulation, especially in the eye where the size of the implant is usually small. In this study a new method was developed to produce mechanically stronger PHEMA sponges. Sequential ho mointerpenetrating polymer network (homo-IPN) sponges were made by using HE MA as the precursor for generating both the first network and the successiv e interpenetrated networks. Following the formation of network I, the spong e was squeezed to remove the interstitial water, soaked in the second monom er (also HEMA), and squeezed again to remove the excess monomer from the po res before being subjected to the second polymerization leading to the form ation of network II. Two two-component IPN sponges (K2 and K4) with increas ing HEMA content in the network II and a three-component IPN sponge (K3) we re produced, and their properties were compared to those of a homopolymer P HEMA sponge (control). Apart from elongation, the tensile properties were a ll significantly enhanced in the IPN sponges; the water content was the sam e as in the control sponge, except for sponge K4, which was lower. Light: m icroscopy revealed similar pore morphologies of the control and IPN sponges K2 and K3, and the majority of the pores were around 25 mu m Sponge K4 dis played smaller pores of around 10 mu m. Cellular invasion into the sponges was examined in vitro (incubation with 3T3 fibroblasts) and in vivo (implan tation in rabbit corneas). Although the in vitro assay detected a change in the cell behavior in the early stage of invasion, which was probably due t o the formation of IPNs, such changes were not reflected in the longer term in vivo experiment. There was a proper integration of sponges K2 and K3 wi th the corneal stroma, but much less cellular invasion and no neovasculariz ation in sponge K4. We concluded that IPN formation is a valid method to en hance the strength of PHEMA sponges, provided that the content of HEMA in t he successive networks is not too high. (C) 1999 John Wiley & Sons, Inc.