Since their first approval by the US Food and Drug Administration, and their introduction into plastic surgery practice, barbed surgical sutures have successfully achieved superior cosmesis, and have been widely used in a variety of experimental surgical procedures, including urology, arthroplasty, orthopedics, obstetrics and gynecology (Lin et al. 2016). The presence of directional barbs fabricated on the surface of monofilament sutures allows free movement of the suture in one direction, while generating resistance in the reverse direction, because the barbs engage with the surrounding tissue. The advantages of using barbed sutures include, but are not limit to, the elimination of knot tying, a uniform distribution of stress along the suture and more efficient wound apposition.

Polydioxanone (PDO) is one of the most popular and commonly used absorbable barbed sutures on the US commercial market. More recently, a new generation of absorbable aliphatic polyesters, poly-4-hydroxybutyrate (P4HB), has received clearance from the US FDA as a novel suture material (Williams et al. 2013). P4HB has good potential for being used as a barbed suture device on account of its higher mechanical strength, prolonged degradation profile and great biocompatibility in living tissue. The primary goal of this study was to discover the feasibility of using P4HB as a potential long-term absorbable material for barbed suture applications. In particular, the approach focused on three different aspects of this question by studying its hydrolytic degradation, in vitro anchoring performance, and in vivo inflammatory response using an animal model.

PDO and P4HB barbed sutures were fabricated in the laboratory using a prototype mechanical barbing machine. Various material characteristics such as the mechanical, thermal and structural properties of both suture materials were tested using different analytical techniques. A 10-week hydrolytic degradation study was conducted to discover the effect of hydrolytic degradation on the changes in mechanical properties and barb morphology of PDO and P4HB barbed and non-barbed sutures. The anchoring performance of a barbed suture, which is the essence of its functionality, was measured in vitro mainly by a suture/tissue pullout test and a wound closure test. The in vivo anchoring performance and the inflammatory response of both types of barbed sutures were studied in a rat model. After the barbing process, P4HB barbed sutures had equivalent tensile properties and anchoring performance to the two commercial barbed suture devices but an inferior anchoring performance compared to PDO. The P4HB monofilaments maintained superior tensile properties compared to the PDO monofilaments over a 10-week hydrolysis period. The in vitro anchoring performance measured as the maximum pullout force was significantly influenced by suture material, suture size, barb geometry, needle type, and tissue type. However, the anchoring performance measured by the wound closure test was related more closely to the suture material rather than the suture size. Due to different suture failure modes, no correlation was found for the anchoring performance measured by these two test methods. The in vivo anchoring performance of PDO barbed sutures decreased continuously over the 28-day implantation period, while the performance of the P4HB barbed sutures increased between Day 14 and Day 28. In general, P4HB barbed sutures generated a less severe inflammatory response than PDO in rat skin tissue. By including images of both the cross-sections and longitudinal-sections, it was possible to directly view the histological interactions between the barbs and the surrounding tissue. Histological barb-tissue interactions were visualized by combining cross-sectional views and longitudinal tissue sections. In summary, although not typically used as a knotless wound closure device, P4HB shows promise as a barbed suture material, especially for long-term use.