Synthetic hydrogel polymers were prepared by free radical photopolymerization in aqueous solution of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid (Na-AMPS). Poly(ethylene glycol) diacrylate (PEGDA) and 4,4'-azo-bis(4-cyanopentanoic acid) were used as the crosslinker and UV-photoinitiator, respectively. The effects of varying the Na-AMPS monomer concentration within the range of 30-50% w/v and the crosslinker concentration within the range of 0.1-1.0% mol (relative to monomer) were studied in terms of their influence on water absorption properties. The hydrogel sheets exhibited extremely high swelling capacities in aqueous media which were dependent on monomer concentration, crosslink density, and the ionic strength and composition of the immersion medium. The effects of varying the number-average molecular weight of the PEGDA crosslinker from [Formula: see text] = 250 to 700 were also investigated. Interestingly, it was found that increasing the molecular weight and therefore the crosslink length at constant crosslink density decreased both the rate of water absorption and the equilibrium water content. Cytotoxicity testing by the direct contact method with mouse fibroblast L929 cells indicated that the synthesized hydrogels were nontoxic. On the basis of these results, it is considered that photopolymerized Na-AMPS hydrogels crosslinked with PEGDA show considerable potential for biomedical use as dressings for partial thickness burns. This paper describes some structural effects which are relevant to their design as biomaterials for this particular application.
Co/terpolymers of L-lactide (LL), e -caprolactone (CL)and glycolide (G)arebiodegradable in the humanbodyand,assuch, haveconsiderable potentialforuseinbiomedicalapplications suchasabsorbable surgicalsutures,nerveg uides,b one fixation devicesand drugd elivery systems.Thiss tudyfocusesits attention on theirpotentialasmonofilamentfibers forabsorbable sutureapplications.Random co/terpolymers withd ifferentcompositionsof LL, CL and Gweresynthesized viab ulk ring-opening polymerization. The polymers obtained weremelt spunats lows peedsintoi ce-cooled watert op roduceas-spun monofilamentfibers withaslittle molecularorientation and crystallinity aspossible. Combinationsof off-line hot-drawing and annealing stepsundercontrolled conditionsof drawrate, drawratio,temperatureand time werethen employed in order tod evelop the fiber'soriented semi-crystalline morphology. The mechanicalpropertiesof the fibers weretested aftereach processing step and compared. The tensile test results showed thatt he tensile strengthwass tronglydependenton the draw ratio. Ahigh drawratio wasobtained bymultiple off-line hotdrawingsw ithi ntermediateannealing. The first hot-drawing step dramaticallyenhanced the mechanicalpropertiesrelative tothoseo fthe weak,highlyextensible as-spunf iber.Subsequentannealing atasuitable temperatureand foranappropriatelengthoftime increased fiberflexibility asaresultof molecularr elaxation. Additionalh ot-drawing steps,a gain under precisetemperature-time conditions,increased the totald raw ratio and furtherenhanced the fiber's mechanicalstrength. 1IntroductionCo/terpolymers of L-lactide (LL), e -caprolactone (CL)and glycolide (G)arek nowntobebothbiocompatible and biodegradable in the humanbodyand soarewidelyused in biomedicalapplicationss uchasabsorbable surgicalsutures(Baimark etal.). Biodegradation proceedsviasimple hydrolysis(random chain scission) leading top rogressivelylowermolecular weightfragments whicharethen removed from the implantsite bythe body'sownbiologicalmechanisms.The added valueof thesem aterialsliesin theirv ersatility.Byv arying the co/terpolymercomposition,monomers equencing and molecular weight,the polymerpropertiescanbespecificallyt ailored to meetthe requirements of eachparticularapplication. Inthisr esearchwork,a ttention isfocused on absorbable monofilaments urgicalsutures.Absorbable surgicalsutures canbeclassified intotwomain groups,namely:monofilaments and multifilaments.Monofilaments utureshaveasmoothsurfaceand thereforeshowless tendencytoharborbacteria-majoradvantagesin minimizing tissuedragand tissuereaction respectively.However,c ompared withm ultifilaments,theyare relativelys tiff and nots oe asy toh andle. Anappropriatebalanceo fm echanicalp ropertiesist hereforee ssentialf ort heir useinthistype of application. Forexample,the tensile strength of the fibermust besufficientlyhigh while still maintaining sufficientflexibility forhandling purposes.Att he same time, the rateo fbiodegradation (hydrolysis)m ust beappropriateto the time required forabsorption. The rationale fort he choic...
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