HEMA hydrogels

Table VII. The Effect of initiator and initiator concentration on properties of HEMA hydrogels HEMA/Glycerine/EGDMA/Initiator at 85/15/0.34/X...

Table VIII. HEMA hydrogel lenses fabricated from monomer mixes containing different initiators.

Gulsen, D., and A. Chauhan. 2005. Dispersion of microemulsion drops in HEMA hydrogel A potential ophthalmic drug delivery vehicle. Int J Pharm 292 95. 

FIGURE 26.9 Representative scanning electron microscopy of HEMA hydrogel cross-linked with 2% EGDMA (xl420). 

Fortunately, highly purified HEMA became available (from Hydro Med Sciences) about this time, and other monomers were readily purified by vacuum distillation. The poly (HEMA) hydrogels made with the purified HEMA showed far lower protein adsorption from either water or buffered saline than hydrogels made with the commercially available HEMA as experiment C, Table I shows. These results emphasize the biological importance of hydrogel composition in particular and biomaterial composition and purity in general. 

Yu L, Urban G, Moser I, Jobst G, Gmber H (1995) Photolithographically pattemable modified poly(HEMA) hydrogel membrane. Polymer Bull 35(6) 759-765... 

Jeyanthi, R. and K. Rao, Controlled release of anticancer drugs from collagen-poly(hema) hydrogel matrices. Journal of Controlled Release, 1990, 13, 91-98. 

YNTHETIC HYDROGEL POLYMERS, first introduced in the early 1960s, made a major impact, initially in the soft contact lens field, and more recently in other biomedical or specialty applications. The first synthetic poly(2-hy-droxyethyl methacrylate) [poly(HEMA)] hydrogel developed by Wichterle (i) remains very important, as do its copolymers with monomers such as N-vinyl-2-pyrrolidinone, acrylic and methacrylic acids, glycerol methacrylate, various acrylamides, and alkoxyalkyl methacrylates. 

Figure 2 Schematic representation of the formation and degrad-tion for dex(lactate)HEMA hydrogels. Gels are formed by radical polymerization of the methacrylate groups using KPS and TEMED as initiator system. Degradation occurs by hydrolysis of the carbonate and lactate ester.

Figure 3 Cumulative release of IgG in time from dex-lactate-HEMA hydrogels (DS 10) with initial water content 90% (A), 80% (B), and 70 % (C). (From Ref 30.).

FIGURE 51.25 Schematic illustration of the particle-laden lens inserted in the eye. (Reprinted from Int. J. Pharm., 292(1-2), Gulsen, D. and Chauhan, A., Dispersion of microemulsion drops in HEMA hydrogel A potential ophthalmic drug delivery vehicle, 95-117. Copyright 2005, with permission from Elsevier.)... 

Kapoor, Y Chauhan, A. Drug and surfactant transport in Cyclosporine A and Brij 98 laden p-HEMA hydrogels. J. Colloid Interface Sci. 2008,322 (2), 624-633. 

Karlsson JO, Gatenhohn P (1997) Preparatirai and characterization of cellulose-supported HEMA hydrogels. Polymer 38 4727-4731... 

Figure 7 showed that neither NaCl nor CaCl2 affected the swellability of poly (PVA-MA) at pH 5 and below. However, NaCl suppressed the expansion significantly between pH 5 and 7. It has been reported that urea enhanced the pH-induced swelling of poly-HEMA hydrogel doped with methacrylic acid. However, we have found fhat urea suppressed the expansion of poly(PVA-MA). 

Soft contact lenses (SCLs) are one of the major products constructed from poly(HEMA) hydrogels. Since their introduction, a variety of such poly-(HEMA)-based hydrogels have been developed to improve lens properties. Both excellent protein adsorption resistance and wettability are required for SCLs, making MFC a good candidate as a suitable monomer. Biocompatible Co. has produced MFC polymer-based SCLs that contain 20% MFC, 80% HEMA, and a small amount of crosslinker (Froclear , omafilcon A), with such lenses now commercially available from CooperVision Co. The Froclear is the only contact lens for reduction of dry-eye syndrome that has been approved by the FDA in the USA. 

S. Eu, K.S. Anseth, Photopolymerization of multilaminated poly(HEMA) hydrogels for controlled release. Journal of Controlled Release, 57, 291-300, 1999. 

---