Quantitation of rabbit corneal epithelial cell outgrowth on polymeric substrates in vitro.
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The outgrowth of corneal epithelial cells onto a polymeric substrate is expected to be the primary event in the epithelialization of a synthetic corneal graft. To study the effects of polymer surface properties on corneal epithelial cell outgrowth, a quantitative in vitro cell outgrowth assay was done. Polymers with systematic variations in hydroxyl content were used as outgrowth substrates. These polymers were characterized by electron spectroscopy for chemical analysis for elemental surface composition and by captive air-bubble contact angle for surface wettability. Circular corneal buttons were punched from excised rabbit corneas, placed onto these substrates, and incubated in a hormonally enriched culture medium. Outgrowth of the epithelial cells was allowed to proceed onto the substrates for 4 days. The outgrowth areas were measured, and an outgrowth index was calculated for each substrate by comparing it with tissue culture polystyrene substrate. The highest outgrowth generally occurred on substrates with intermediate wettabilities (captive air-bubble contact angles of approximately 45-75 degree); it was less on substrates of lower or higher wettabilities. Protein coatings of albumin, immunoglobulin G (IgG), fibronectin, and culture medium were found to lower the wettabilities of native substrates. Albumin and IgG precoating were shown to reduce epithelial cell outgrowth; fibronectin precoating was shown to improve outgrowth on most substrates. These results suggest that epithelial cell outgrowth is influenced by both substrate and protein interactions. (+info)
Preparation of surfactant-free nanoparticles of methacrylic acid copolymers used for film coating.
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The aim of the present study was to prepare surfactant-free pseudolatexes of various methacrylic acid copolymers. These aqueous colloidal dispersions of polymeric materials for oral administration are intended for film coating of solid dosage forms or for direct manufacturing of nanoparticles. Nanoparticulate dispersions were produced by an emulsification-diffusion method involving the use of partially water-miscible solvents and the mutual saturation of the aqueous and organic phases prior to the emulsification in order to reduce the initial thermodynamic instability of the emulsion. Because of the self-emulsifying properties of the methacrylic acid copolymers, it was possible to prepare aqueous dispersions of colloidal size containing up to 30% wt/vol of Eudragit RL, RS, and E using 2-butanone or methyl acetate as partially water-miscible solvents, but without any surfactant. However, in the case of the cationic Eudragit E, protonation of the tertiary amine groups by acidification of the aqueous phase was necessary to improve the emulsion stability in the absence of surfactant and subsequently to prevent droplet coalescence during evaporation. In addition, a pseudolatex of Eudragit E was used to validate the coating properties of the formulation for solid dosage forms. Film-coated tablets of quinidine sulfate showed a transparent glossy continuous film that was firmly attached to the tablet. The dissolution profile of quinidine sulfate from the tablets coated with the Eudragit E pseudolatex was comparable to that of tablets coated with an acetonic solution of Eudragit E. Furthermore, both types of coating ensured similar taste masking. The emulsification-evaporation method used was shown to be appropriate for the preparation of surfactant-free colloidal dispersions of the 3 types of preformed methacrylic acid copolymers; the dispersions can subsequently be used for film coating of solid dosage forms. (+info)
Modification of 4-META/MMA-TBB resin for safe debonding of orthodontic brackets--influence of the addition of degradable additives or fluoride compound.
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The purpose of this study was to evaluate the performance of modified 4-META/MMA-TBB resin cements (Superbond C&B) in terms of debonding orthodontic brackets easily and safely from enamel without the loss of proper bracket bond strength. Poly (DL-lactide-co-glycolide) (PLGA), calcium fluoride (CaF2), or alpha-tricalcium phosphate (alpha-TCP) was added to the polymer powder of 4-META/MMA-TBB resin, and the shear bond strength of orthodontic brackets to human enamel using modified resins was measured before and after 10,000-cycle thermal cycling test between 5 degrees C and 55 degrees C. The modified resins tended to provide lower bond strength compared with the original 4-META/MMA-TBB resin. However, alpha-TCP- or CaF2-modified resin showed no significant differences in bond strength before and after thermal cycling. Moreover, there was a tendency of more residual resin remaining on the tooth surface after debonding, thereby suggesting a lower risk of enamel fracture. In conclusion, alpha-TCP- or CaF2-modified 4-META/MMA-TBB resin seemed to allow easy and safe debonding of orthodontic brackets without loss of proper bracket bond strength. (+info)
A comparison of 141 polymacon (Iogel) and 140 poly(methyl methacrylate) intraocular lens implants.
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In a prospective controlled trial 290 consecutive patients were randomly allocated a polymacon or a poly(methyl methacrylate) (PMMA) intraocular lens. Early Treatment of Diabetic Retinopathy Study (ETDRS) acuity charts gave similar results with both lenses. However Pelli-Robson contrast sensitivity charts gave a better result with PMMA lenses. Polymacon lenses appeared to remain free of any adhesions after implantation raising the question of long term stability. Four patients experienced problems related to this, three involved total lens dislocation. Seven patients developed early 'fibrin' membranes coating the polymacon lens, of which three were florid. (+info)
Induction of corneal epithelial cytochrome P-450 arachidonate metabolism by contact lens wear.
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Two biologically active cytochrome P-450 arachidonate metabolites previously were characterized: 12(R)-hydroxy-5,8,10,14-eicosatetraenoic acid (12(R)-HETE) and 12(R)-hydroxy-5,8,14-eicosatrienoic acid (12(R)-DH-HETE), which are endogenously formed in the corneal epithelium. The functional activity of these novel metabolites mimics changes observed in hypoxic corneas. Therefore, the effect of hypoxic stress was examined on metabolite formation in rabbits fitted with polymethylmethacrylate contact lenses. Although applied lenses fit tightly to the rabbit cornea, mechanical irritation also may contribute to the ocular response. Contact lens-induced hypoxic stress stimulated endogenous formation of both 12(R)-HETE (a sodium, potassium adenosine triphosphatase inhibitor) and 12(R)-DH-HETE (a vasodilatory, chemotactic, and angiogenic factor) in a time-dependent manner. After 4 hr of contact lens wear, a 21-fold increase in endogenous 12(R)-HETE formation concomitant with an increase in corneal thickness was observed. After prolonged contact lens wear (144 hr), a 23-fold increase in endogenous 12(R)-DH-HETE formation was found, corresponding with the appearance of a marked conjunctival inflammation characterized by corneal neovascularization. The increased formation of these compounds was associated with time-dependent changes in corneal endothelial morphology. The ability of 12(R)-HETE and 12(R)-DH-HETE to mediate the clinical signs of corneal hypoxia suggest these metabolites may be potential mediators of contact lens complications that followed conditions of hypoxic stress and possibly mechanical irritation in this model. (+info)
Development of an affinity silica monolith containing human serum albumin for chiral separations.
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An affinity monolith based on silica and containing immobilized human serum albumin (HSA) was developed and evaluated in terms of its binding, efficiency and selectivity in chiral separations. The results were compared with data obtained for the same protein when used as a chiral stationary phase with HPLC-grade silica particles or a monolith based on a copolymer of glycidyl methacrylate (GMA) and ethylene dimethacrylate (EDMA). The surface coverage of HSA in the silica monolith was similar to values obtained with silica particles and a GMA/EDMA monolith. However, the higher surface area of the silica monolith gave a material that contained 1.3-2.2-times more immobilized HSA per unit volume when compared to silica particles or a GMA/EDMA monolith. The retention, efficiency and resolving power of the HSA silica monolith were evaluated using two chiral analytes: d/l-tryptophan and R/S-warfarin. The separation of R- and S-ibuprofen was also considered. The HSA silica monolith gave higher retention and higher or comparable resolution and efficiency when compared with HSA columns that contained silica particles or a GMA/EDMA monolith. The silica monolith also gave lower back pressures and separation impedances than these other materials. It was concluded that silica monoliths can be valuable alternatives to silica particles or GMA/EDMA monoliths when used with immobilized HSA as a chiral stationary phase. (+info)
New symptomatic compression fracture after percutaneous vertebroplasty at the thoracolumbar junction.
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BACKGROUND AND PURPOSE: The purpose of this study was to investigate the risk factors for new symptomatic vertebral compression fractures after vertebroplasty at the thoracolumbar junction. MATERIALS AND METHODS: We conducted a retrospective analysis of 53 patients treated with percutaneous vertebroplasty at the thoracolumbar junction (T12, L1). The follow-up period was 15-27 months. The occurrence of new symptomatic vertebral compression fractures was recorded after vertebroplasty. We evaluated patient age and sex, amount of injected cement, vacuum clefts in the collapsed bodies, initial wedge angle of the compression fracture, change of the wedge angle after vertebroplasty, intradiskal cement leak, and percentage of height restoration of the vertebral body. In this report, we surveyed the possible risk factors for new symptomatic vertebral compression fractures. RESULTS: Thirty-nine (74%) of the 53 patients had fluid and/or air in the compression fracture at the thoracolumbar junction (T12, L1). Eight (20.5%) of the 39 patients with vacuum clefts had new symptomatic compression fracture after vertebroplasty between 1 month and 4 days after surgery to 23 months and 4 days after surgery. The patients with new symptomatic compression fracture had higher initial wedge angle and wedge angle change (more than 7 degrees ) after vertebroplasty than those without fractures; these data were considered statistically significant. CONCLUSIONS: The incidence of vacuum clefts in the compression fracture at the thoracolumbar junction is high (74%). The severity of initial wedge angle and wedge angle change affects the incidence of new symptomatic compression fracture. (+info)
Cardiovascular changes after pulmonary cement embolism: an experimental study in sheep.
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BACKGROUND AND PURPOSE: Most cement leaks during vertebroplasty are asymptomatic, but pulmonary cement embolism has been reported to cause cardiovascular disturbances and even death. Adding hydroxyapatite (HA) to polymethylmethacrylate (PMMA) cement to reduce the quantity of barium may aggravate cardiovascular deterioration in the event of cement embolism by activating coagulation. Thus, we investigated the cardiovascular changes after pulmonary cement embolism of PMMA with and without HA. MATERIALS AND METHODS: In 13 sheep, cement (2.0 mL) was injected into the pulmonary trunk. Two different cements were used: 1) standard PMMA and 2) PMMA with 10% HA (PMMA & HA). Arterial, central venous and pulmonary arterial pressures, heart rate, and cardiac output were monitored continuously until 60 minutes after the injection. Blood gases and coagulation parameters (antithrombin, D-dimer) were measured before and after injection. RESULTS: Mean pulmonary arterial pressure had increased by approximately 9% (PMMA) and 14% (PMMA & HA) 1 minute after injection and stayed elevated. There were no significant differences between the groups. No evidence of thromboembolism was detected. CONCLUSION: Cement embolism did not result in clinically significant pulmonary arterial hypertension. Adding HA to PMMA cement did not cause more severe cardiovascular changes. (+info)