PubMed · 2634777
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L I Linkow. 1989. Titanium subperiosteal implants.. https://pubmed.ncbi.nlm.nih.gov/2634777/
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Leukocyte activation is one test for the evaluation of blood-materials interaction. The expression of adhesion molecules analyzed by flow cytometry provides a simple method to evaluate leukocyte activation by biomaterials: any change in these molecules can be predictive of the inflammatory activity of the materials. In this study the contact between leukocytes and uncoated polyethylene terephthalate or pyrolytic carbon-coated polyethylene terephthalate (PET and PET-PC, respectively) was inspected by analyzing whether the expression of some adhesion molecules involved in leukocyte activation, namely LFA-1 (CD11a/ CD18), Mac-1/CR3 (CD11b/CD18), and LECAM-1 (CD62L) can be modified. By flow cytometry expression of the adhesion molecules can be studied separately on lymphocytes and myeloid cells. The materials tested reduced the total numbers of both leukocytes and neutrophils, although not significantly. Neither PET nor PET-PC changed the expression of the adhesion molecules in lymphocytes: this suggests that no specific immune response is stimulated. On the contrary, statistically significant changes were observed for monocytes and granulocytes: the percentage of cells expressing Mac-1 and the density of such antigens on cell membranes increased while the percentage of LECAM-1 positive cells decreased. Similar changes were observed when the cells underwent the inflammatory stimulus provided by an in vitro challenge with bacterial endotoxin. Our results demonstrated that polyethylene terephthalate activates leukocytes by modifying the expression in neutrophils of the molecules involved in the early phase of the inflammatory response. Even after coating PET with pyrolytic carbon, the ability of this material to activate circulating leukocytes was maintained.
Thermally processed hydroxyapatite coatings used on dental implants and hip prostheses for enhanced fixation may typically consist of a number of chemical and structural phases. These phases affect coating performance and tissue attachment. Hydroxyapatite was plasma sprayed to examine the phase evolution during processing. Coatings were examined with X-ray diffraction and elemental analysis. Results indicate that phase transformations are produced by (a) preferential removal of hydroxyl and phosphate leading to a change in melt composition, and (b) the high cooling rate due to the thermal spray process. Hydroxyl group removal promotes the amorphous phase and oxyapatite. Further heating produces a less viscous melt facilitating decomposition of hydroxyapatite to tricalcium and tetracalcium phosphate. Phosphate removal during flight produces a more calcium-rich melt preferring tetracalcium phosphate and calcium oxide formation. A proposed model shows the phase location within the lamellae of these coatings. Coating processes must thus prevent removal of hydroxide and phosphate during processing to maximize the hydroxyapatite content.
The effective long-term use of indwelling ureteral stents is often hindered by the formation of encrusting deposits which may cause obstruction and blockage of the stent. Development of improved ureteral stent biomaterials capable of preventing or reducing encrustation is therefore particularly desirable. In this study, the suitability as a ureteral stent biomaterial of Aquavene, a novel poly(ethylene oxide)/polyurethane composite hydrogel was compared with that of silicone and polyurethane, two materials widely employed in ureteral stent manufacture. Examination of Aquavene in dry and hydrated states by confocal laser scanning microscopy, scanning electron microscopy, and atomic force microscopy showed the presence of numerous channels within a cellular matrix structure. The channel size increased considerably to as much as 10 microm in diameter in the hydrated state. Aquavene provided superior resistance to encrustation and intraluminal blockage over a 24-week period in a simulated urine flow model. Unobstructed urine flow continued with Aquavene at 24 weeks, whereas silicone and polyurethane stents became blocked with encrustation at 8 and 10 weeks, respectively. Weight loss within Aquavene on the order of 9% (w/w) over the 24-week flow period indicates that extraction of the noncrosslinked poly(ethylene oxide) hydrogel may be responsible for the prevention of encrustation blockage of this biomaterial. In the dry state, Aquavene was significantly harder than either silicone or polyurethane, as shown by Young's modulus, and rapidly became soft on hydration. These additional properties of Aquavene would facilitate ease of stent insertion in the dry state past obstructions in the ureter and provide improved patient comfort on subsequent biomaterial hydration in situ. Aquavene is a promising candidate for use in the urinary tract, as it is probable that effective long-term urine drainage would be maintained in vivo. Further evaluation of this novel biomaterial is therefore warranted.