Biocompatible surfaces prepared by immobilized heparin or hyaluronate

Biomolecular modification of implant surfaces

In this review, surface modification of implant devices by immobilization of biological molecules is discussed. A brief introduction to the development of biomolecular surface science is presented, followed by a review of current activities in selected fields. Bone-contacting devices and some cardiovascular implant devices are reviewed as paradigmatic examples of research that is currently taking place. Advances in the basic fields of cell and tissue biology, in addition to concurrent developments in surface science tools, suggest that 'peri-implant biologics', or the control and direction of the host response at the implant-tissue interface by implant-surface-linked biomolecules, could be a major area of growth in the medical devices field in the next few years.

Enhanced in-vitro blood compatibility of 316L stainless steel surfaces by reactive landing of hyaluronan ions

A novel dry process for immobilization of hyaluronan on stainless steel surfaces is presented. This process that we call reactive landing is based on an interaction of hyperthermal gas-phase hyaluronan ions with plasma-cleaned and activated stainless steel surfaces. Reactive landing is performed on a unique instrument that combines an in-situ plasma reactor with an electrospray ion source and ion transfer optics. Gas-phase hyaluronan anions are obtained by electrospray ionization of sodium hyaluronan solutions and immobilized by reactive landing on large-area stainless steel surfaces. The immobilized hyaluronan withstands extensive washing with polar solvents and solutions, and the washed surfaces maintain the protective properties against blood platelet activation. The mechanism of hyaluronan discharge and immobilization is discussed.

Nonfouling surfaces: a review of principles and applications for microarray capture assay designs

Microarray technology, like many other surface-capture diagnostic methods, relies on fidelity of affinity interactions between a surface-bound probe (e.g., nucleic acid or antibody) and its target in the sample milieu to produce an assay signal specific to analyte. These interfacial interactions produce the assay result with the associated assay requirements for sensitivity, specificity, reproducibility, and ease-of-use. For surface-capture assays, surface properties play a critical role in this performance. Microarray surfaces are routinely immersed into aqueous target solutions of varying complexity, from simple saline or buffer solutions to serum, tissue, food, or microbiological lysates involving thousands of different solutes. The surface chemistry must not only be capable of immobilizing probes at high density in microscale patterned spots, retaining probe affinity for target within these spots, reducing target capture outside of these spots, but also be efficient at eliminating nontarget capture anywhere else on the surface. Historically, the development of surface chemistry with these specific "nonfouling" properties has been an intense interest for bioassays, with many types of architectures, molecular compositions, and performance capabilities across many different surface-capture assays. The unique environment of the bioassay, including the long-standing problems associated with high concentrations of "nontarget" proteins and other surface-active biomolecules in the assay milieu, has proven to be quite challenging to surface chemistry performance. Microarray technology designs with microspotted patterns must address these problems in these challenging dimensions in order to improve signal:noise ratios for captured target signals on surfaces. This chapter reviews principles of protein-surface interfacial physical chemistry, protein adsorption as a source of assay noise, and various approaches to control this interface in the context of surface-capture assay fabrication and improving assay performance from complex milieu. Practical methods to modify surfaces for biological assay are presented. Polymer substrate coating methods, including "grafting from" and "grafting to" strategies, polymer brushes, and alternative surface modification methods are reviewed. Methods to assess biological "fouling" in the bioassay format are also discussed.

Adherence of human lens epithelial cells to conventional poly(methyl methacrylate), heparin-surface-modified, and polyHema lenses

We developed an in vitro model to assess the adherence of human lens epithelial cells to three types of intraocular lenses: poly(methyl methacrylate) (PMMA), heparin-surface-modified PMMA (HSM-PMMA), and polyHema. Lenses were incubated with a fixed number of human lens epithelial cells. Adherent cells were counted after 72 hours in culture. Scanning electron microscopy showed significantly fewer cells adhering to the HSM-PMMA and polyHema lenses than to the PMMA lenses (P < .01). Repeat experiments on cell lines established from different donors confirmed these findings.

Cellular reaction following cataract surgery with implantation of the heparin-surface-modified intraocular lens in rabbits with experimental uveitis

The inflammatory response after cataract surgery and intraocular lens (IOL) implantation was studied in rabbits with endotoxin-induced uveitis. On days 1, 3, 7, 14, and 30 postoperatively the rabbits were sacrificed and the number of white blood cells in the aqueous humor and cellular deposits on the IOLs were estimated. On days 14 and 30 the rabbits also had slitlamp examination to study the clinical outcome of the surgery. At day 1 after lens extraction and IOL implantation, the number of white blood cells in the aqueous humor was significantly lower (P < .05) in eyes with heparin-surface-modified (HSM) IOLs (795.2 +/- 262.9; mean +/- SEM) than in eyes with poly(methyl methacrylate) (PMMA) lenses (1386.5 +/- 247.9). No differences were seen at day 3, 7, 14, or 30 postoperatively. The choice of IOL material had no effect on the amount of cell deposits on the IOL surface or on clinical parameters such as anterior synechias, posterior synechias, fibrosis, and posterior capsular opacification. There was a trend toward a greater number of cellular deposits on the PMMA lenses, but this was not statistically significant. This study provides further evidence of improved biocompatibility of the HSM PMMA lens, as demonstrated by a decreased acute inflammatory response.

Cellular reactions on heparin surface-modified versus regular PMMA lenses during the first postoperative month. A double-masked and randomized study using specular microphotography

Specular microscopy was used for investigation of cellular reactions on the intraocular lens (IOL) anterior surface of Heparin surface-modified (HSM) versus regular polymethylmethacrylate (PMMA) lenses (Pharmacia types 700C versus 700B, respectively). The double-masked randomized study included 53 patients investigated at 1 and 4 weeks postoperatively. Giant cells were only found on control lenses and more frequently at 4 weeks. Small cells were found on both lens types, but in a higher frequency on the control lenses. The number of small cells decreased during the first 4 weeks on both the control and HSM lenses. However, those control lenses that had giant cells on their surface showed an increase in the number of small cells during the same time. The results of the current study show that HSM lenses give rise to less postoperative inflammatory cellular reactions than regular PMMA lenses.

Improved biocompatibility of intraocular lenses by heparin surface modification: a 12-month implantation study in monkeys

To evaluate the long-term biocompatibility and potential side effects of heparin surface modification of a poly(methyl methacrylate) intraocular lens (IOL), a heparin surface modified IOL was implanted in the left posterior chamber of 24 cynomolgus monkeys and a reference IOL (without surface modification) was implanted in the right eye in 12 of these animals. Twelve eyes were not operated on. Eleven eyes in seven monkeys were lens extracted as a control of the surgical method. Slitlamp examinations and intraocular pressure recordings were made one day, one and two weeks, and 1, 2, 2 1/2, 3 1/2, 6, 8, 10, and 12 months after the operation. Eleven monkeys were sacrificed after 3 1/2 months and the remaining animals after 12 months for morphological examination of the eyes. Slitlamp and morphological examinations showed that cell deposits, pigmentation, and posterior synechias were significantly less in eyes with heparin surface modified IOLs than in eyes with reference IOLs throughout the 12-month observation period. The intraocular pressure was equally reduced in eyes with heparin surface modified IOLs and reference IOLs for about one month, after which it returned to normal. No side effects following the implantation of heparin surface modified IOLs were observed. We concluded that heparin surface modification of IOLs is efficient for long-term reduction of cell deposits and posterior synechias after implantation in monkey eyes and may also be effective in lowering the degree of side effects to IOL implantation in humans.

Heparin surface modified intraocular lenses implanted in the monkey eye

The biocompatibility of heparin surface modified poly(methyl methacrylate) intraocular lenses (IOLs) was evaluated in two experiments following implantation in the anterior and posterior eye chambers of adult cynomolgus monkeys. Throughout the study, large inflammatory cells and prominent pigment deposits were seen on the unmodified lenses, whereas the heparin surface modified IOLs remained almost free of precipitates. Similarly, fewer posterior synechias were observed in eyes implanted with surface modified IOLs in the posterior chamber than in eyes implanted with control lenses. Histopathological examination of enucleated eyes confirmed the clinical findings. These experiments strongly support the idea that surface modification with heparin is a useful way to reduce clinical complications following cataract surgery with IOL implantation.