Controlling the mechanical properties of poly(<SC>L</SC>-lactide– ɛ-caprolactone) monofilament sutures by an acetone/water treatment

For monofilament biodegradable sutures fabricated from the <SC>L</SC>-lactide–ɛ-caprolactone (75/25) copolymer [P(LLA/CL)], there have been some concerns regarding their mechanical properties, such as the knot-pull strength and stiffness. This article demonstrates the further potentiality of these sutures through improvements in those properties. With the aim of diminishing the molecular orientation, particularly in the suture surface region, we adopted an expedient method to treat P(LLA/CL) sutures with an acetone/water mixture, using different times and time patterns. The changes in the molecular orientation distributions across the suture cross sections were characterized by the specific index of birefringence measured with an interference microscope. The crystal orientations, knot-pull strengths, tensile strengths, and bending rigidity were measured. The conformational changes in suture breaking during knot-pull tests were analyzed with high-speed-video observations. Morphological analyses of the fractural surfaces were performed with scanning electron microscopy. The knot-pull strength tended to rise, in comparison with that of untreated samples, up to a certain treatment time and was accompanied by a minimal decrement of the tensile strength. The knot-pull strength did not show an increasing trend with further treatment, whereas the tensile strength declined remarkably. The birefringence, crystal orientation, bending rigidity, fractured surface analysis, and high-speed-video observations revealed molecular disorientation mainly in the filament outer layers for that particular treatment causing the sutures to be considerably softer. The suture softness played a role in changing the deformation behavior of the knot when a load was applied and caused the knot-pull strength to rise. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2449–2462, 2002