Absorbable coating composition and suture coated therewith

#This invention relates to an absorbable coating composition for surgical sutures and to a coated surgical suture exhibiting improved knot tie-down and/or knot security characteristics.

#Since monofilament synthetic absorbable suture materials are generally stiffer than their catgut or collagen counterparts, multifilament, e.g., braided or twisted, constructions have been employed in many instances for greater softness and flexibility. Multifilament sutures, however, exhibit a certain degree of undesirable roughness in what is generally referred to as knot tie-down performance, i.e., the ease or difficulty of sliding a knot into place down the suture. It has therefore become a common practice to coat sutures, particularly those of the multifilament variety, with compositions which improve their knot tie-down performance and perhaps one or more other properties of the sutures as well. Known suture coating compositions include those described in U.S. Pat. Nos. 3,867,190; 3,942,532; 4,027,676; 4,043,344; 4,047,533; 4,080,969, 4,105,034; 4,185,637, 4,201,216; 4,470,416; 4,624,256; 4,649,020; 4,716,203, 4,788,979; and, 4,857,602.

#U.S. patent application Ser. No. 07/707,437, filed May 28, 1991 describes an absorbable composition for improving the knot tie-down properties of a suture, the composition being either a copolymer derived from the copolymerization of a low molecular weight poly(oxyethylene) glycol, glycolide monomer and a lactide monomer or a copolymer derived from the copolymerization of a low molecular weight polyalkylene glycol and a preformed copolymer of lactide and glycolide.

#This example illustrates the preparation of an absorbable suture coating composition in accordance with the invention.

#A poly(oxypropylene) glycol of 4,000 average molecular weight (nominal) and a viscosity of from 900-1200 cp, 677.+-.1 g, was introduced into a reactor equipped with a stirrer. Following a minimum 6 hour period of drying the poly(oxypropylene) glycol in a stream of anhydrous nitrogen gas, a previously dried lactide/glycolide copolymer containing 82 mole percent lactide and 18 mole percent glycolide and an inherent viscosity of at least 0.9 when measured in chloroform at a concentration of 0.25 g/dl (prepared as disclosed in U.S. Pat. No. 4,523,591 referred to above), 1,323.+-.1 g, was introduced into the reactor. The reactor, which was maintained under a blanket of nitrogen gas, was heated to a temperature of 155.degree.-170.degree. C. Thereafter, 0.4.+-.0.05 g stannous octoate catalyst and 0.4.+-.0.05 g diethylene glycol initiator were added to the reactor, the latter being stirred at a rate of 55-60 rpm. Following a reaction period of 20-25 hours, the reaction product was recovered and residual reactant(s) removed therefrom at elevated temperature and under a pressure not exceeding 10 Torr, the temperature profile being as follows:

#1. Ramped to 80.degree. C. at 5.degree. C./hr.