Background: New techniques are currently being developed to be able to manage hemostasis during surgery. Currently, several methods are employed to prevent bleeding, ranging from metal and polymer clips to sutures that are secured around the vessel(s)[1]. Traditional cable ties became popular in surgery as the self-locking loops enabled a quicker and easier surgical procedure[2]. The use of cable ties in surgery is strongly discouraged as the non-resorbable material may cause pathological responses if left permanently in tissue[3]. In an effort to maintain the surgical advantages of traditional cable ties while improving their in vivo reaction, a novel, resorbable polymer, Glycoprene® 6535, comprised of glycolide and trimethylene carbonate was developed to provide a resorbable ligation device[4]. An innovative design, a flexible band running through a case with a self-locking mechanism, similar to a cable tie, but designed for surgical ligation, was developed and patented by Resorbable Devices AB, and the parts were manufactured via injection molding. Finally, the mechanical performance of the new device and its temporal degradation over time were tested both in vitro and in vivo.
Materials and Methods: Glycoprene® 6535 is a block copolymer prepared from glycolide and trimethylene carbonate, having molecular weight (Mw) suitable for injection molding. Varying molecular weight Glycoprene® 6535 batches were injection molded into the implant design, which has a very high surface area and aspect ratio, making polymer flow a key parameter in producing full length parts (115mm). Differential Scanning Calorimetry (DSC) and Inherent Viscosity (IV) were performed to analyze the polymer.
The injection molded devices were analyzed for tensile strength using an MTS Synergie load frame. Real time in vitro performance was analyzed by incubating specimens in 7.2 pH phosphate buffer at 37°C for 7 and 14 days. Preliminary in vivo studies with canines were also performed to investigate (1) the feasibility of ligating vessels with the device, (2) its biocompatibility, and (3) long-term resorption.
Results: Five of the batches were injection molded into implants. The percentage of the length of the cavity that was filled during injection molding was recorded. The results are presented in Table I. The higher the IV value (which correlates to higher Mw) the lower the polymer flow properties of the batch, resulting in partial mold cavity fill.
Table I: DSC and IV results for Glycoprene® 6535 and their relationship to polymer flow properties represented as approximate percentage of cavity filled.
Injection molded implants were analyzed for initial properties and strength retention. Glycoprene® 6535 parts were degraded after fourteen days in vitro, limiting the amount of tensile data obtained, as seen in Table II. These promising preliminary results reflect the properties required for the specific application of ligation.
Table II: In Vitro strength profile retention for the cable ties placed in 7.2 pH phosphate buffer at 37°C.
Resorbable Devices has initiated in vivo studies. Implants were implanted successfully into canines of different sizes. The implants were used to prevent hemorrhage as ovariohysterectomy was performed in the dogs. Preliminary feedback included that the use was intuitive and the devices had an impressive tightening capacity with the self-lock mechanism. No intra- or postoperative haemorrhage was observed.
Conclusion: Initial development indicates that the custom synthesis of Glycoprene® 6535 successfully produced a resorbable polymer capable of the strength and material properties needed for the ligation of vessels. In addition, Glycoprene® 6535 can be injection molded into high surface area parts, which have been successfully implanted and showed promising results. By creating a novel material, a new resorbable ligation device was manufactured which retains the surgical advantages of the traditional cable ties’ self-locking loop, without the requirement of removal of the part subsequently.
References:
[1] Höglund, Odd Viking. A Resorbable Device for Ligation of Blood Vessels. Upsala : Swedish University of Agricultural Sciences, 2012
[2] Whitney GD. Use of implanted nylon bands in surgical procedures: Canine Practice 1982, 9(1):24, 28-30.
[3] Johnson-Neitman JL, Bahr RJ, Broaddus KD. Fistula formation secondary to a nylon cable band in a dog.: Vet Radiol Ultrasound, 2006, Vol. 47
[4] Shalaby, S. Amorphous polymeric polyaxial initiators and compliant crystalline copolymers therefrom. US Patent 6,462,169 B1, 2002