S. Dropcova

The development of in vitro biocompatibility tests for the evaluation of intraocular biomaterials.

Recent developments in ocular implant technology require the in vitro evaluation of ocular compatibility in early stage development programs. This requires an understanding and appreciation of the biological interactions which occur in the ocular environment and their relevance with respect to the clinical complications associated with surgical implantation of devices. This paper describes the development of a series of clinically reflective in vitro assays for assessing the potential ocular compatibility of novel intraocular lens materials. Staphylococcus epidermidis attachment, fibrinogen adsorption, mouse embryo fibroblast 3T3 adhesion and proliferation, primary rabbit lens cell adhesion, human peripheral blood macrophage adhesion and granulocyte activation tests were employed to evaluate two widely used intraocular biomaterials poly(methyl methacrylate) (PMMA) and silicone, and a novel biomimetic phosphorylcholine-based coating (PC). The performance of these materials in the in vitro assays was compared to their ability to reduce postoperative inflammation in vivo in a rabbit model. The results demonstrated that the in vitro assays described here are predictive of in vivo ocular compatibility. These assays offer a more relevant means of assessing the ocular compatibility of biomaterials than those presently required by the authorities for regulatory approval of medical devices and implants.

A standard strain of human ocular keratocytes.

The ability of an injured cornea to regenerate from deep tissue trauma is largely due to wound healing processes mediated by the surviving stromal keratocytes. Despite the importance of the wound healing process, and the ease with which keratocytes can be grown in tissue culture, a standardised strain of the cells has never been made available. Accordingly, this study reports a strain of human embryonic keratocytes, designated EK1.BR as a research tool for the ophthalmic community. EK1.BR has been characterised with respect to life-span, fraction of dividing cells and maintenance of a keratocyte phenotype in culture. It is hoped that these cells will prove useful in the in vitro study of stromal wound healing and the characterisation of keratocyte gene expression.

Glycocalyx adsorption enhances biocompatibility of poly(methyl methacrylate)

A major goal of modern biocompatibility is to identify factors which will inhibit the attachment of various cell types to implanted prosthetic devices. The glycocalyx of mammalian cells is a loosely defined network of lipids, proteoglycans and proteins which forms the outer layer of mammalian cells. Components of the glycocalyx are known to mediate cell adhesion and are an obvious area of interest in the development of biocompatible coatings. This report describes the development of an assay system capable of evaluating the effects of single glycocalyx components on mammalian cell attachment and the correlation of those effects with the changes observed in the dynamic contact angles of the test surfaces. The data suggest that physical-chemical and biological tests have the potential to be used in tandem in the development of more biocompatible implants.

4214 Senescence of corneal endothelial cells

Logistic regression methods were used to analyse the influence of donor and storage factors on the quality of c~meas stored by organ culture in the Bristol eve bank in 1991. Averaae donor a(18 was 57 vears fsd 22. n=2770) -and time from death to en~cleation v& 8 hours (&I 7, n&782): Corneas were placed into organ culture within 27 houra (sd 10, n+2550) of donor death and were stored for 22 days (sd 7, n=2716). Preliminary results ,showed that 126 of 2744 corneas (4.5%) we10 discarded through contamination. The risk of contamination increased with inauasing death to enucleation time (p<O.O37), but corneas from CVA donors were less likely to be contaminated (p<O.O03). Overall, 27% of corneas wwre not suitable for PKP because of endotheliel defects. Corneas storud for more than 4 weeks or corneas from donors over 80 years old were less likely to be suitable for PKP (both pcO.0001). But the likelihood of onneas having high endothelial cell densities (~2500 cells/mm2) was reduced with donors over 20 years old (p<O.OOl), with storage times more than 2 weeks (p<O.O04), or when corneas came from donors that died of cancer (p<O.O4) or respiratory disease (p<O.O20). Corneas from CVA donors, however, were more likely to be suitable for PKP (P<O.O05). Analyses such as this are important for monitoring donor procurement practices and the efficacy of eye banking techniques.