Enhancement of mechanical strength of poly(2-hydroxyethyl methacrylate) sponges

2-Methacryloyloxyethyl N-butylcarbamate: a new co-monomer for synthesis of polyurethane hydrogels with improved mechanical properties for biomedical applications

Hydrogels with tunable hydrophilic and mechanical properties were synthesized by the free radical polymerization of 2-hydroxyethyl methacrylate (HEMA) and 2-methacryloyloxyethyl N-butylcarbamate. The resulting hydrogels were investigated for their equilibrium water content, sessile drop water contact angles, gel fraction, mechanical properties and protein adsorption. Results indicated that co-polymer hydrogels have good hydrophilicity and that, with the incorporation of the 2-methacryloyloxyethyl N-butylcarbamate, mechanical properties could be improved significantly. without affecting other important properties. Lysozyme and albumin adsorption experiments demonstrated that, similar to most hydrogel materials, the co-polymer hydrogels adsorb more lysozyme than albumin and that the adsorption was dependent on hydrophilicity. The control poly(HEMA) hydrogels were found to adsorb more protein than the co-polymer hydrogels; this is thought to be primarily a consequence of protein absorption rather than protein adsorption.

An overview of the development of artificial corneas with porous skirts and the use of PHEMA for such an application

An overview of the efforts to develop functional polymeric artificial corneas (keratoprostheses) by incorporating a porous skirt is presented. The development of such a device by the author's group using poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogels, as a combination of their homogeneous and heterogeneous states, and the rationale of this choice are also discussed. The latest results of the clinical trials with the PHEMA keratoprosthesis in human patients indicate a lower risk of the complications traditionally associated with the implantation of artificial corneas.

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) (PHEMA) sponges as implantable devices is their inherently poor mechanical strength. 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 homointerpenetrating polymer network (homo-IPN) sponges were made by using HEMA as the precursor for generating both the first network and the successive interpenetrated networks. Following the formation of network I, the sponge was squeezed to remove the interstitial water, soaked in the second monomer (also HEMA), and squeezed again to remove the excess monomer from the pores before being subjected to the second polymerization leading to the formation of network II. Two two-component IPN sponges (K2 and K4) with increasing HEMA content in the network II and a three-component IPN sponge (K3) were produced, and their properties were compared to those of a homopolymer PHEMA sponge (control). Apart from elongation, the tensile properties were all significantly enhanced in the IPN sponges; the water content was the same as in the control sponge, except for sponge K4, which was lower. Light microscopy revealed similar pore morphologies of the control and IPN sponges K2 and K3, and the majority of the pores were around 25 microm. Sponge K4 displayed smaller pores of around 10 microm. Cellular invasion into the sponges was examined in vitro (incubation with 3T3 fibroblasts) and in vivo (implantation 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 to 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 with the corneal stroma, but much less cellular invasion and no neovascularization in sponge K4. We concluded that IPN formation is a valid method to enhance the strength of PHEMA sponges, provided that the content of HEMA in the successive networks is not too high.