Photoenhancement of platelet adhesion to biomaterial surfaces observed with epifluorescent video microscopy (EVM).
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Biocompatible Materials↗
Biomedical subjects
B D Ratner
Publications and source records attributed to B D Ratner.
Endothelial cell growth on oxygen-containing films deposited by radio-frequency plasmas: the role of surface carbonyl groups.
Polystyrene substrates were modified by radio-frequency plasma deposition from mixtures of various organic vapors (acetone, methane, methanol, and formic acid) and oxygen. The resulting surfaces exhibited a wide range of surface oxygen concentrations, as measured by electron spectroscopy for chemical analysis (ESCA). The surface hydroxyl, carboxyl, and carbonyl groups were derivatized with trifluoroacetic anhydride, trifluoroethanol, or hydrazine, respectively, and their concentrations subsequently determined by ESCA. The growth of bovine aortic endothelial cells was found to increase with the surface carbonyl concentration but did not appear to correlate with the hydroxyl or carboxyl concentrations.
Acetone↗
TFE-plasma polymerized dermal sheep collagen for the repair of abdominal wall defects.
The aim of this study was to design and evaluate a degradable biomaterial for the repair of abdominal wall defects. Hexamethylenediisocyanate-tanned dermal sheep collagen (HDSC) was plasma-polymerized with tetrafluoroethylene (TFE) which resulted in a hydrophobic surface on the visceral side (TFE-HDSC). Full-thickness abdominal wall defects were made in rats and repaired with HDSC or TFE-HDSC implants. Unmodified HDSC implants showed excellent fixation to the adjacent muscle tissue but intestinal adhesions were observed. These implants showed insufficient strength after four weeks, illustrated by bulging of the peritoneal contents (herniation). Plasma-polymerized implants after four weeks of implantation showed firm incorporation into the surrounding muscle tissue. With one exception there were no bowel adhesions. Fewer herniations were observed, indicating a prolonged degradation period. Further studies on the optimalization of degradation time are in progress.
Abdominal Muscles↗
Poly(dimethylsiloxane)-poly(ethylene oxide)-heparin block copolymers. III: Surface and bulk compositional differences.
Previously observed bioactivity of poly(dimethylsiloxane)-poly(ethylene oxide)-heparin (PDMS-PEO-Hep) triblock copolymers has prompted studies of the surface and bulk character of this copolymer using angular-dependent electron spectroscopy for chemical analysis (ADESCA), static secondary mass spectroscopy (SIMS), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Because the low-energy PDMS phase dominates surfaces of this copolymer when solvent cast under air or vacuum conditions, attempts were made to explain surface restructuring and rearrangements induced in hydrated or aqueous environments that permit surface accessibility and bioactivity of heparin moieties. Based on comparisons with PDMS, PEO, and heparin homopolymers, PEO/heparin blends, and an unheparinized PDMS-PEO diblock copolymer, PDMS-PEO-heparin demonstrates both phase-mixed and phase-separated regions in DSC analysis. During annealing cycles above the Tg values of the copolymer constituents, phase-mixed regions become increasingly phase separated and PEO enriched. TGA analysis confirmed the presence block copolymer constituents and presented evidence of intermolecular segmental interactions, hence phase-mixing in the copolymers. ADESCA analysis indicates that the outer 5 A of both the PDMS-PEO and PDMS-PEO-Hep copolymers is essentially pure PDMS. However, significant amounts of PEO are detected 5 to 20 A below the surface. Static SIMS also detects the presence of PDMS at the surfaces of the PDMS-PEO and PDMS-PEO-Hep copolymers. Compositional models based on ADESCA, SIMS, and DSC data are presented for desiccated and hydrated copolymer surfaces.
Biocompatible Materials↗
Characterization of alkyl grafted polyurethane block copolymers by variable takeoff angle x-ray photoelectron spectroscopy.
Variable takeoff angle x-ray photoelectron spectroscopy was used to determine the surface composition of five polyurethane block copolymers. The high-resolution C1s spectra from all five polyurethane samples had peaks at binding energies of 285.0, 286.5, and 289.5 eV, which are consistent with the presence of hydrocarbon, ether, and urethane carbon species. Both the measured elemental compositions at the low takeoff angles (deepest sampling depths) and the calculated elemental compositions for depths greater than 15 A generally showed good agreement with the expected bulk compositions. The outer 15 A of the surface of all five samples was depleted in the nitrogen-containing hard segment. For the base polyurethane sample in this series, an enrichment of the poly(tetramethylene oxide) soft segment and the presence of an organic silicone impurity were detected. Doubling the chain length of both the hard and soft segments resulted in a further decrease of the hard segment concentration in the outer surface of the sample. The grafting of C2 and C18 alkyl groups onto 10 or 20% of the urethane linkages resulted in an increase in the percentage of aliphatic carbon species present on the surface. In the case of the C18-alkylated material, the presence of alkyl chains at the surface was inferred using contact angle measurements.
Biocompatible Materials↗
Radiofrequency plasma deposition of oxygen-containing films on polystyrene and poly(ethylene terephthalate) substrates improves endothelial cell growth.
Polystyrene and poly(ethylene terephthalate) substrates were modified by radiofrequency plasma deposition with organic vapors comprised of carbon, oxygen, and hydrogen (acetone, methanol, glutaraldehyde, formic acid, allyl alcohol, and ethylene oxide). The treatments resulted in the deposition of a film at least 100 A thick containing up to 26% atomic oxygen at the surface. A high oxygen incorporation was observed for vapors with a large oxygen-to-carbon ratio. Bovine aortic endothelial cell growth measured on acetone, methanol, and glutaraldehyde films was linearly correlated with the oxygen content of the treated surfaces. Nitrogen was incorporated in the surface by blending nitrogen gas into the organic vapor used for plasma deposition. The resulting nitrogen-containing substrates exhibited a high affinity for serum fibronectin but a moderate cell growth.
Adsorption↗
Adhesion and aggregation of thrombin prestimulated human platelets: evaluation of a series of biomaterials characterized by ESCA.
Five materials of interest in blood contact applications (PVC, Silastic, Biomer and siliconized glass) were internally coated on glass tubes and exposed to suspensions of platelets and red cells. Uncoated glass was also examined. Thrombin was added (prestimulation) to some suspensions before exposure to the biomaterial surfaces. The three polymeric surfaces were characterized by electron spectroscopy for chemical analysis (ESCA). Prestimulation with thrombin leads to increased adhesion of single platelets only with Silastic. With a wide range of surface types, thrombin prestimulation consistently leads to higher levels of platelet accumulation in the form of aggregates; the PVC-coated material showed the highest levels. ESCA analysis of PVC, however, suggested our coating was impure or an oxidized material.
Biocompatible Materials↗
Surface characterization of a series of polyurethanes by X-ray photoelectron spectroscopy and contact angle methods.
X-ray photoelectron spectroscopy (XPS) and contact angle methods were used to examine the surfaces of an homologous series of poly(ether urethane) (PEU) samples before and after cleaning treatments. Four PEU films with Shore hardnesses varying from 45 to 75 D were studied as well as two commercially available intravenous catheters of related PEUs. The four as received PEU films have similar surface compositions (approximately 79% C, approximately 17% O, approximately 2% N, and approximately 2% Si) although they differ in bulk composition. Critical surface tension (gamma c) values are all similar and high (45-46 dynes/cm). The similarity in the surfaces of the four PEUs, despite the differences in their mechanical properties, demonstrates that surface properties do not necessarily reflect bulk properties. Soap washing and methanol-acetone extraction of the PEU films resulted in surfaces more representative of the bulk compositions of the PEUs. Analysis of the intravenous catheters confirmed that they are lubricated with PDMS, a common practice in the medical device industry. This study documents the value of detailed surface analysis for an enhanced understanding of the surface zone of PEUs. It also illustrates how cleaning protocols can remove labile surface species.
Biocompatible Materials↗
IR spectral changes of bovine serum albumin upon surface adsorption.
The adsorption of bovine serum albumin from flowing solutions onto germanium and three polyetherurethanes varying in soft segment content was studied by a Fourier transform infrared/attenuated total reflectance technique. Spectral differences observed in the amide I, II, and III regions upon adsorption to all four surfaces were consistent with a loss of helix and gain of beta-structure. There appeared to be a slight difference between BSA adsorbed to germanium and the PEUs, but no distinction could be made between BSA adsorbed to the different PEUs.
Adsorption↗
Relating the surface properties of intraocular lens materials to endothelial cell adhesion damage.
Relationships between corneal endothelial cell adhesion and intraocular lens (IOL) surface properties were studied to develop a lens surface with a lower potential to damage the corneal endothelium. The surfaces examined were poly(methyl methacrylate) (PMMA) and four types of plasma-deposited coatings on PMMA. These four films were prepared from perfluoropropane, ethylene oxide, 2-hydroxyethyl methacrylate (HEMA), and N-vinyl-2-pyrrolidone (NVP). These "monomers" were chosen to produce surfaces with a range in surface chemistry and surface energy. Each type of coating was characterized by electron spectroscopy for chemical analysis (ESCA) and contact angle techniques. In addition, these surfaces were contacted with rabbit corneal endothelium over a force range of 4000-20,000 dynes. The extent of endothelial cell damage was measured. Over the force range investigated, each modified surface was found to induce a significantly different degree of cell adhesion than that caused by PMMA. The perfluoropropane plasma film induced a constant lower degree of adhesion damage than the PMMA for all forces of contact. Although the HEMA and NVP hydrogel surfaces also induced lower adhesion damage than PMMA, the cell loss associated with each did increase as a function of force. The ethylene oxide film caused a significant increase in cell loss compared to the PMMA-induced losses. Based upon the correlation between the surface analysis data and the cell-surface contacting results, we suggest that a "soft" high-energy surface or a "rigid" low-energy surface is favorable for reduced cell adhesion. Also, the results indicate that cell adhesion increases for materials with increased hydrocarbon enrichment and for materials with lower (ether bonding)/(ester and ketone linkages) ratios.
Animals↗
Cell adhesion to a series of hydrophilic-hydrophobic copolymers studied with a spinning disc apparatus.
Adhesion of cells to substrates strongly influences many of their functions and therefore plays an important role in a variety of processes, including growth, phagocytosis, hemostasis, and the response of tissue to implanted materials. In previous studies, the influence of substrate hydrophilicity on cell adhesion has not been separated from effects due to major differences in other properties of the substrate, such as charge, rigidity, and the specific chemical composition of the materials. In addition, very few careful studies of the force required for cell detachment from various substrates have been performed. In this study, 3T3 cell detachment from a chemically homologous series of copolymers based on hydroxyethylmethacrylate (HEMA) and ethylmethacrylate (EMA) was measured with a spinning-disc apparatus. The spinning-disc technique allowed measurements of cell detachment over a wide range of applied shear stress on each sample. Cell detachment did not occur until a critical value of shear stress was exceeded. The critical shear stress of detachment decreased linearly with increasing HEMA content, from 18 dynes/cm2 on poly-EMA to 0 on the polymers containing 83% or more HEMA. "Plating efficiency," calculated as the fraction of cells initially applied which remained after dip rinsing the surfaces, did not vary significantly among most of the copolymers. Dip rinsing, however, exposes the cells to only one, relatively low shear stress (estimated to be somewhat less than 3 dynes/cm2). The existence of a critical shear stress for 3T3 cell detachment suggests that cell adhesion to surfaces cannot be fully understood with single shear stress methods because cells may attach with a wide range of strengths which are either all above or all below the applied shear stress. The influence of surface hydrophilicity on cell adhesion and the variety of forces which may contribute to this phenomenon are discussed.
Animals↗
Analysis of in vitro enzymatic and oxidative degradation of polyurethanes.
In vitro biodegradation studies were performed to assess the long-term stability of poly(ether urethane) (PEU) implants. Three PEU's and one poly(ester urethane) were treated with enzymes characteristic of those released from inflammatory cells during the foreign body reaction. In addition, the effect of hydrogen peroxide was observed to examine oxidative degradation. Polymers were prepared as thin films on glass, gold, silver, and copper substrates to test the possibility of metal-catalyzed degradation. Molecular weights and polydispersities of the polymers were measured by gel permeation chromatography (GPC) before and after treatment. Changes in peak shape and location were also monitored. The results demonstrate that varying degrees of both enzymatic and oxidative degradation occurred.
Chymotrypsin↗
Adsorption of proteins from artificial tear solutions to contact lens materials.
A series of polymers and copolymers of 2-hydroxyethyl methacrylate (HEMA) and methyl methacrylate (MMA) were synthesized in order to find surfaces that would adsorb minimal amounts of protein. The adsorption of albumin, lysozyme and immunoglobulin G from a three-way mixture of these proteins in isotonic buffered saline to the polymers was measured using 125I-labeled proteins. Apparently high protein uptake on copolymers rich in HEMA was found to be due to sorption of unbound 125I by the polymers. 125I sorption by the polymers was minimized by dialysis of the protein solution to remove unbound 125I iodide and inclusion of 0.01 M sodium iodide to block uptake of residual 125I iodide. Using these improved protocols, minimal total protein uptake was observed on copolymers containing 50% or more HEMA. The majority of adsorbed protein on all p(MMA-HEMA) polymers was albumin. Total protein uptake was greatest on pMMA. Commercial contact lenses composed of copolymers of HEMA and N-vinyl pyrrolidone (NVP) or acrylamide (AAm) adsorbed small amounts of all proteins whereas copolymers of methacrylic acid (MAAc) and HEMA adsorbed much larger quantities of lysozyme. These results indicate that protein uptake by contact lens materials varies greatly with polymer composition. Artifactually high "adsorption" can occur if precautions are not taken to prevent uptake of unbound 125I.
Acrylates↗
Biomaterial surfaces.
The nature of a biomaterial surface governs the processes involved in biological response. Surface properties such as surface chemistry, surface energy, and morphology may be measured in order to understand the surface region of a biomaterial. In this article, we describe the surface characteristics of a few common biomaterials, review the techniques used to measure surface properties, and discuss the application of surface information in developing novel and improved biomaterials.
Biocompatible Materials↗
Enzymatically controlled drug release systems.
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Animals↗
Effects of a tetrafluoroethylene glow discharge on patency of small diameter dacron vascular grafts.
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Animals↗
Analysis of surface contaminants on intraocular lenses.
Surface contaminants have been studied on a variety of intraocular lenses by three methods: scanning electron microscopy, energy dispersive x-ray analysis (EDXA), and electron spectroscopy for chemical analysis (ESCA). Many particulate contaminants were observed on both commercially available lenses packaged for implantation and experimental batches of lenses. The nature of these particles could be inferred using the EDXA technique. Thin films of sodium dodecyl sulfate (SDS) that were resistant to removal were found on many of the lenses by ESCA. Cleaning procedures were developed that did not involve SDS and that generated extremely clean lens surfaces.
Animals↗
Surface characterization of biomaterials by electron spectroscopy for chemical analysis.
Electron spectroscopy for chemical analysis (ESCA) is perhaps the most valuable single method available for characterizing the surfaces of biomaterials. The ESCA analytical method is rich in information, observes a relevant surface region, and has been shown to generate results that correlate with biological response. In this article, the analysis of actual ESCA data is illustrated by reviewing a study in which polymer-coated glass surfaces, prepared for use as tissue culture substrates, are examined by ESCA. The application of more advanced ESCA techniques such as angular-dependent analysis to this situation is also considered. Finally, published applications of ESCA to the study of polyurethanes, hydrogels, protein films, cell culture substrates, and dental materials are briefly reviewed.
Biocompatible Materials↗