The bulk ring-opening copolymerisation of L-lactide (LL) and ε-caprolactone (CL) with an initial comonomer feed ratio of LL:CL = 75:25 mol % was carried out using stannous acetate as the initiator at 120 oC for 48 hrs. The copolymer was characterised by GPC, DSC and TGA. Due to its ability to biodegrade in the human body, this type of copolymer has potential for use as an absorbable surgical suture. The copolymer obtained was melt spun at 153 oC using a small-scale melt-spinning apparatus and extruded into ice-cooled water to produce an as-spun monofilament fibre which was largely if not completely amorphous. Alternate off-line hot-drawing and annealing (3 cycles) was carried out in order to develop the fibre’s oriented semi-crystalline morphology. To complete the processing operation, thermal treatment was necessary to stabilize the fibre morphology. It was found that fixed annealing at 60 oC followed by free annealing at 60 oC stabilized the fibre morphology as a result of molecular relaxation. In vitro hydrolytic degradation studied in a phosphate buffer saline (PBS) solution of pH 7.4 at 37.0 ± 0.1 oC indicated that, after 6 weeks immersion in the buffer, the fibre’s tensile strength decreased by approximately 50% whereas a commercial ‘PDS’ suture of similar size lost its strength completely after only 4 weeks.
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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