Surface-modified Polymethylmethacrylate Research Articles

Gold-implanted shallow conducting layers in polymethylmethacrylate

PMMA (polymethylmethacrylate) was ion implanted with gold at very low energy and over a range of different doses using a filtered cathodic arc metal plasma system. A nanometer scale conducting layer was formed, fully buried below the polymer surface at low implantation dose, and evolving to include a gold surface layer as the dose was increased. Depth profiles of the implanted material were calculated using the Dynamic TRIM computer simulation program. The electrical conductivity of the gold-implanted PMMA was measured in situ as a function of dose. Samples formed at a number of different doses were subsequently characterized by Rutherford backscattering spectrometry, and test patterns were formed on the polymer by electron beam lithography. Lithographic patterns were imaged by atomic force microscopy and demonstrated that the contrast properties of the lithography were well maintained in the surface-modified PMMA.

Influence of optic and haptic materials on the adherence of Staphylococcus epidermidis to intraocular lenses: a pilot study.

To evaluate in vitro the adherence of Staphylococcus epidermidis to intraocular lenses (IOL) of different optic and haptic materials and design, we used a quantitative cultural method. Polymethylmethacrylate (PMMA), PMMA-prolene, polyHEMA, silicone and surface-modified PMMA (wet and dry) implants were tested. Adherence differed significantly in the various groups, with the best performance by all-PMMA IOL.

In vivo documentation of cellular reactions on lens surfaces for assessing the biocompatibility of different intraocular implants.

This prospective study was undertaken to assess the biocompatibility of different intraocular implants and to determine factors influencing cellular reactions on intraocular lenses (IOLs). Cellular reactions seen on the surface of 653 IOLs have been documented by specular microscopy. Various types of IOLs were used with different surgical procedures in humans. The 11 lens types used fall into five groups of materials: polymethylmethacrylate (PMMA), heparin surface-modified PMMA, surface-modified PMMA, poly Hema and silicone. Factors influencing the cellular reaction on intraocular implants were elaborated on in this study. Besides the foreign-body reaction itself, cellular reactions were influenced by an increased inflammatory disposition, surgical trauma, peri-operative treatment, implant positioning and lens style. A significant correlation was found between the development of posterior synechiae and the existence of giant cells on the anterior lens surface. The incidence of cellular reactions on IOLs revealed significant differences specific to lens and material. Hydrophilic surfaces show cellular reactions in a lower percentage of cases compared with hydrophobic surfaces. An accurate and individual selection of lens material and style is mandatory to guarantee optimal after surgery.

Immobilization of proteins on poly(methyl methacrylate) films

Polymethyl methacrylate (PMMA) films were treated by oxygen plasma discharge followed by acrylic acid (AA) grafting. The amount of carboxyl groups introduced by the grafting of AA on to the film surfaces was in the range 0.47–9.48 μmol/cm 2, depending on the pressure of the plasma chamber during the discharge treatment. The carboxyl groups of the PMMA film surface previously activated with water soluble carbodiimide were coupled with bovine serum albumin, collagen and gelatin. The protein immobilization on the surface was confirmed by attenuated total reflection Fourier transform infra-red spectroscopy (ATR-FTIR) and electron spectroscopy for chemical analysis (ESCA). The amount of albumin, collagen and gelatin immobilized on the PMMA surface was 6.25, 7.25 and 13.75 μg/cm 2, respectively, as determined by the coomassie brilliant blue-protein interaction. The water contact angle of the PMMA film was markedly decreased by oxygen plasma treatment, AA grafting or protein immobilization, indicating the increase of hydrophilicity of the surface-modified PMMA films. The protein-immobilized PMMA films may be widely used as a biocompatible material.

Intraocular lens material evaluation by iris abrasion in vitro: A scanning electron microscope study

Prosthetic posterior chamber intraocular lenses can abrade the iris pigmented epithelium, resulting in pigment dispersion, callus formation, and iris adhesions. To evaluate iris abrasion from intraocular lens materials, we developed an in vitro test and studied three materials: polymethylmethacrylate (PMMA), silicone, and PMMA surface-modified by covalent binding of a hydrophilic polymer (surface-modified PMMA). Each lens was rubbed 1,000 times on the posterior iris of pigmented rabbits using a total force of 0.5 gram. Scanning electron micrographs of the abraded irides were scored using a subjective, nonparametric numerical scale. Polymethylmethacrylate lenses removed iris epithelium completely, exposing underlying connective tissue. Silicone lenses damaged an area longer and narrower than the PMMA lens and also exposed connective tissue. Surface-modified PMMA lenses caused only slight surface damage, including flattening or breaking of protruding suspensory ligaments. The test conditions used cannot precisely mimic prolonged lens implantation in living subjects. Nevertheless, the results indicate that iris-lens interaction may be reduced in viva by using a surface-modified PMMA lens. This hypothesis should be further verified by animal implantation studies.

In vitro evaluation of iris chafe protection afforded by hydrophilic surface modification of polymethylmethacrylate intraocular lenses

An in vitro iris chafe test was developed to evaluate possible differences in abrasive interaction of various intraocular lens (IOL) materials with the posterior surface of the iris. The materials that were compared in initial tests with rabbit irides were high molecular weight polymethylmethacrylate (PMMA), the primary IOL material in current use, and surface-modified PMMA, which had a permanent, chemically bound, hydrophilic, polymer surface. Scanning electron microscopy, light microscopy, and examination of histological sections were used to assess tissue damage. A “window defect” type of abrasive damage was observed by light microscopy for PMMA lenses and is very similar in appearance to that seen for iris abrasion by human implants when viewed in vivo in slitlamp examinations. Results for both pigmented and albino rabbit irides indicate a reduction in abrasive insult to the external iris basement membrane and underlying pigment epithelium by the hydrophilic surface modification of PMMA. These results are consistent with our observation of a major reduction in corneal endothelium damage on contact with the hydrophilic surface-modified PMMA as compared with PMMA itself. This in vitro iris abrasion test, therefore, appears to be a useful technique for future evaluation of IOL surface properties.