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Biomedical subjects

H G Clark

Publications and source records attributed to H G Clark.

13 recordsLinked to original sources
PubMed1997

Iloprost in alginate decreases the thrombogenicity of expanded polytetrafluoroethylene.

Vascular prostheses of small diameter perform poorly in vivo, in part because of the high thrombogenicity of available biomaterials. This study examined the thrombogenicity of expanded polytetrafluoroethylene (ePTFE) vascular graft segments (10 mm long x 4 mm i.d.) in vitro before and after impregnation with saline, alginate, or alginate containing the stable prostacyclin analog, iloprost. Each segment was immersed in activated whole blood and the weight of the adherent thrombus was measured at specified intervals. At 6 and 7 min the saline-denucleated group accumulated significantly less thrombus than control (p < .05). Alginate alone was not significantly different from controls. The graft segments treated with alginate + iloprost accumulated significantly less thrombus (p < .05) than all other groups after 6 min. These data demonstrate that denucleation of ePTFE with iloprost in alginate dramatically decreases its in vitro thrombogenicity.

Alginates↗
PubMed1992

Evaluation of poly(L-lactic acid) as a material for intravascular polymeric stents.

Poly(L-lactic acid) (PLLA) monofilaments were evaluated for use as intravascular polymeric stents. The PLLA monofilaments were extruded and drawn to different draw ratios. They were then subjected to different thermal treatments and their mechanical properties characterized. Stents constructed with similar monofilaments were tested under hydrostatic pressure, and the results correlated with the properties of the monofilaments. Stent collapse pressure was a decreasing function of stent diameter and filament draw ratio.

Biocompatible Materials↗
PubMed1992

Deformation characteristics of a bioabsorbable intravascular stent.

RATIONALE AND OBJECTIVES: Biodegradable polymeric stents offer an alternative to metallic stents, which have a significant compliance mismatch with blood vessels and have the potential for long-term complications. In the current study, the deformation characteristics of polymeric stents have been investigated. METHODS: Stents were subjected to radial compressive pressure by inserting them in a wrap-around collar, one end of which was loaded in tension using dead-weights. The resulting decrease in stent diameter was measured under an optical microscope. Deformation curves for the stents were plotted, and an effective stiffness, E', was determined for each. RESULTS: The deformation curves exhibited two different regions: an initial linear region, followed by a steep nonlinear region. The transition from the linear region occurred at a fractional decrease in stent diameter of approximately 0.5. CONCLUSION: E' decreases with increasing stent diameter and filament draw-ratio. The relationship between E' and the initial stent diameter is not linear. The deformation curves can be used for choosing the appropriate stents for specific applications.

Biodegradation, Environmental↗
PubMed1992

The effect of interstitial air on the in vitro thrombogenicity of ePTFE vascular grafts.

Gas trapped in the interstices of the biomaterials used for vascular prostheses causes thrombosis, and the process of eliminating this gas is known as denucleation. An apparatus was developed for testing in the in vitro effects of denucleation on 4 mm I.D. expanded polytetrafluoroethylene (ePTFE) Vitagraft (Johnson and Johnson). The apparatus was designed to ensure that neither the blood nor the grafts came in contact with air. Blood from a single donor was incubated with control and denucleated grafts for 5, 10, 15, 20, and 30 minutes. The thrombus volume in the graft lumen was measured with a computer assisted videometric system. Little thrombus formed by 5 or 10 minutes, but there was less thrombus in the denucleated graft than in the control graft at all times. The differences were statistically significant at 15 and 20 minutes (p < 0.05). Denucleation nearly doubled the thrombus formation time. Thrombus was more adherent to denucleated grafts than to control grafts. These results are consistent with in vivo observations in the rat where denucleation decreased thrombus formation and increased patency duration.

Air↗
PubMed1988

Abdominal pain and sicklemia in a patient with sickle cell trait.

We have presented a case of thrombotic thrombocytopenic purpura initially misdiagnosed as sickle cell crisis. Based on the "history" of hemoglobin S disease, anemia, and the presence of apparent sickled cells on the peripheral blood smear, the diagnosis of sickle cell crisis seemed reasonable. The patient is described because of unusual features of the case, to emphasize again a hazard of sickle cell screening and the value of reviewing the peripheral blood smear in cases of anemia.

Abdomen↗
PubMed1975

Bubble growth and mechanical properties of tissue in decompression.

A survey of decompression literature leads to the conclusion that when tissue is subjected to gaseous supersaturation, pre-existing gas micronuclei grow into the gas bubbles which are routinely observed in decompression studies. These micronuclei may originate from mechanically induced tribonucleation or cavitation within joints. A new tissue model for decompression sickness based upon failure theory in rubber is proposed. The model shows theoretically that pre-existing sea-level nuclei can be stabilized at depth by elastic forces in tissue. These same elastic forces restrain the growth of nuclei when supersaturation occurs. Mechanical stress will lower the gaseous supersaturation required for growth of nuclei. Gaseous supersaturation, mechanical stress, and the elastic properties of various tissues interact to produce unbounded bubble growth leading to tissue lesions when combined gaseous and mechanical supersaturation exceeds a threshold value. The recommendation is made that the high levels of supersaturation generally used for the decompression of men be reduced.

Animals↗