Degradation of five polyurethane gastric bubbles following in vivo use: SEC, ATR-IR and DSC studies.

Five Garren-Edwards Gastric Bubbles were characterized, following up to 4 months use in vivo, using size exclusion chromatography, differential scanning calorimetry and attenuated total reflectance infrared spectroscopy. These techniques show that the material used to construct the bubble is probably an aromatic polyester urethane and revealed a 39-55% decrease in number average molecular weight, a 9 degrees C decrease in glass transition temperature, the disappearance of soft segment crystallinity and a broadening of the hard segment melting region after exposure to highly acidic (approximately pH 1.2) gastric fluid. The results indicate that significant chemical and morphological changes have taken place in the bubble material, including loss in chemical functionality, phase separation and increased hard segment aggregation. A comparison of the decrease in glass transition temperature as a function of molecular weight suggests that glass transition temperature is a sensitive predictor of this material's stability. Additionally, evidence is provided that the broad infrared absorption at 1077-1067 cm-1 normally assigned to C-O-C hard segment may represent two types of C-O-C stretching: (1) C-O-C stretching of the free urethane carbonyl, and (2) C-O-C stretching of the hydrogen bonded urethane carbonyl.

An evaluation of the analgesic efficacy of proquazone and aspirin in postoperative dental pain.

The analgesic efficacy of 75, 150, and 300 mg proquazone, a new nonsteroidal antiinflammatory agents, was compared to that of 650 mg aspirin and a placebo in outpatients who had moderate or severe pain following the surgical removal of impacted third molars. Estimates of the relative potency of proquazone to aspirin ranged from 4.9 to 6.2 for total analgesic effect and from 7.7 to 8.4 for peak analgesic effect. Each dosage level of proquazone and aspirin provided significant analgesia compared to placebo and was well tolerated. Adverse effects were transitory and did not appear to be dose related for proquazone.

Determination of cholesterol and cortisone absorption in polyurethane. I. Methodology using size-exclusion chromatography and dual detection.

A size-exclusion chromatographic method is described for measuring the absorption of the steroid-based lipids cholesterol and cortisone into Pellethane 2363, a polyurethane used in biomedical implants. The method uses refractometry and ultraviolet diode-array detection, with tetrahydrofuran as the mobile phase. Using an injection volume of 150 microliters, the lower limit of accurate measurement for cholesterol (refractive index detection) was 6 micrograms/ml with a lower limit of detection, based on a 2:1 signal-to-noise ratio, of 0.15 micrograms (1 microgram/ml). For cortisone (ultraviolet detection), the lower accurate limit was 0.6 micrograms/ml with a lower limit of 0.015 micrograms (0.1 micrograms/ml). The results show that after 44 h, 2037 micrograms/g cholesterol and 3131 micrograms/g cortisone were absorbed by the polyurethane. The method eliminates extensive sample manipulation and is sensitive to low levels of lipid in the presence of a high-molecular-mass synthetic polymer.

Tissue response and in vivo degradation of selected polyhydroxyacids: polylactides (PLA), poly(3-hydroxybutyrate) (PHB), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB/VA).

The tissue response and in vivo molecular stability of injection-molded polyhydroxyacids--polylactides (PLA), poly(3-hydroxybutyrate) (PHB), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB/VA, 5-22% VA content)--were studied. Polymers were implanted subcutaneously in mice and extirpated at 1, 3, and 6 months in order to study tissue response and polymer degradation. All polymers were well tolerated by the tissue. No acute inflammation, abscess formation, or tissue necrosis was observed in tissues adjacent to the implanted materials. Furthermore, no tissue reactivity or cellular mobilization was evident remote from the implant site. Mononuclear macrophages, proliferating fibroblasts, and mature vascularized fibrous capsules were typical of the tissue response. Degradation of the polymers was accompanied by an increase in collagen deposition. For the polylactide series, the inflammatory response after 1 month of implantation was less for materials containing the D-unit in the polymer chain, whereas in the case of the polyhydroxybutyrate/valerates, the number of inflammatory cells increased with increasing content of the valerate unit in the polymer chain. Between 1-3 months, there was slightly more tissue response to the PHB and PHB/VA polymers than to PLA. This response is attributed to the presence of leachable impurities and a low molecular weight soluble component in the polyhydroxybutyrate/valerates. At 6 months, the extent of tissue reaction was similar for both types of polymers. All polylactides degraded significantly (56-99%) by 6 months. For a poly(L-lactide) series, degradation rate in vivo decreased with increasing initial molecular weight of the injection-molded polymer. Several samples showed pronounced bimodal molecular weight distributions (MWD), which may be due to differences in degradation rate, resulting from variability in distribution of crystalline and amorphous regions within the samples. This may also be the result of two different mechanisms, i.e., nonenzymatic and enzymatic, which are involved in the degradation process, the latter being more extensive at the later stage of partially hydrolyzed polymer. The PHB and PHB/VA polymers degraded less (15-43%) than the polylactides following 6 months of implantation. Generally, the polymer with higher valerate content (19%, 22%) degraded most. The decrease in molecular weight was accompanied by a narrowing of the MWD for PHB and copolymers; there was no evidence of a bimodal MWD, possibly indicating that the critical molecular weight that would permit enzyme/polymer interaction had not been reached. Weight loss during implantation ranged from 0-50% for the polylactides, whereas for the PHB polymers weight loss ranged from 0-1.6%.