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Biomedical subjects

R T Greer

Publications and source records attributed to R T Greer.

5 recordsLinked to original sources
PubMed1987

Development of ocular inserts for cattle.

Ring shaped ocular inserts have been developed to administer a therapeutic level of tylosin tartrate throughout a five day period to treat pinkeye in cattle. The inserts are based on polyvinyl chloride rings which are dip coated with a copolymer containing the antibiotic (tylosin tartrate). Scanning electron microscope (SEM) characterization of surfaces has been of value to evaluate the presence and extent of surface flaws in the hydrogel coating, and to contribute to improvement in fabrication of the rings to insure the establishment of satisfactory seals at joints, uniformity of microporosity and cross sections, and the absence of significant cracking or flaking. In vitro release rates were determined using thin layer chromatography techniques, and rates were seen to be above a few micrograms of antibiotic per hour for experiments as long as nine days at simulated tear rates as high as 2 milliliters per hour.

Animals↗
PubMed1982

Ex vivo shunt testing of hydrogel-silicone rubber composite materials.

Hydrogel polymers consisting of HEMA (2-hydroxyethyl methacrylate) alone or co-polymerized with NVP N-(vinyl pyrrolidone) were incorporated into silicone rubber tubing to produce hydrophilic composite materials. Polymerization methods of the interpenetrating network (IPN) and radiation-induced type were used to impregnate the silicone rubber substrates. These methods produced materials with varied wettability (contact angle with water ranged from 57 degrees to 95 degrees) but similar texture. The surface morphology as observed in the scanning electron microscope was the same for all the materials. Four types of composite materials and two sizes of silicone rubber control tubing in a total of 19 dogs were used as ex vivo femoral artery-to-vein (A-V) shunts and were sampled at 5, 15, 30, 45, and 60 min. Data obtained by using scanning electron microscopy (SEM) were used to determine the type and amount of adhering blood cells at the time intervals described. Large platelet aggregates and/or a variable initial response were found to be predictors of shunt failure (occlusion). Most samples showed only varied levels of platelet adhesion, but other cell types were seen in some samples. The adhesion was found to peak in all cases by 30 min and to reach lower levels by 60 min, suggesting that an initial phase of reaction was complete. The course of platelet adhesion for a 60-min period is presented.

Animals↗
PubMed1980

Controlled microstructure of two stage polyhydroxyethyl methacrylate coatings on polyethylene terephthalate substrates for potential prosthetic applications.

Two types of polyethylene terephthalate (Dacron) substrates (USCI DeBakey Vasculour-D and USCI Sauvage filamentous) have been selectively coated with Poly-hydroxyethyl methacrylate (P-HEMA) in a two-stage process. Using scanning electon microscopy (SEM) techniques, the microstructural details of the fabrications were identified. The first stage of this process imparted a coating of P-HEMA having a heterogeneous macroporous structure and the second stage yielded an internal surface coating of hydrogel with a homogeneous microporous surface structure. The morphology on a colloidal level was controlled by adjustment of the cosolvent ratios holding other fabrication parameters constant. These microstructural features coupled with the chemical properties of the hydrogel suggest potential medical prosthetic applications. The results of initial canine carotid artery implantations indicate that an endothelial-like cell layer can be established within 21 days on the luminal surface of specific hydrogel impregnated Dacron knitted prosthetic materials. The chemical and morphological properties of a hydrogel impregnated Dacron prosthesis may present a blood flow surface which allows proper conditioning protein and cellular deposition leading to an accelerated endothelial development without the need to preclot the prosthesis wall.

Acrylates↗
PubMedDate not supplied

Evaluation of in vivo adsorption of blood elements onto hydrogel-coated silicone rubber by scanning electron microscopy and fourier transform infrared spectroscopy.

Three hydrogel formulations consisting of 2-hydroxyethyl methacrylate (HEMA) copolymerized with N-vinyl pyrrolidone (NVP) were incorporated into silicone rubber by irradiation-induced polymerization. These coatings were chosen to represent different degrees of hydrophilicity, and they changed the hydrophobic character of the silicone rubber surface to that of hydrophilic. These composite materials and the silicone rubber comparison material were used as femoral artery-to-vein (A-V) shunts and were removed at 15 min, an approximate time representative of an initial buildup stage of blood elements on test surfaces. Data obtained by scanning electron microscopy (SEM) were used to determine the type and amount of adhering blood cells and fibrin at the time interval described. One-half of each specimen was used for Fourier Transform Infrared (FT-IR) analysis to provide a direct comparison of the relative amounts of protein present on the silicone rubber and the three hydrogel composite samples. The combined SEM and FT-IR analyses were performed on A-V samples from three dogs. Differences in the response of blood to the surfaces were found by the combined SEM and FT-IR analyses. The more hydrophilic a hydrogel grafted surface, the less fibrin and cellular elements were seen deposited on it. This is not interpreted as an indication of less reactivity, but is more likely due to thrombus buildup and a degree of subsequent embolization (a tearing of sections of the platelet matting away from a surface, revealing an area that again can be covered.

Acrylates↗