Correspondence of high-frequency ultrasound and histomorphometry of healing rabbit achilles tendon tissue

Abstract Objectives: Static and dynamic high-frequency ultrasound of healing rabbit Achilles tendons were set in relationship to histomorphometric analyses at three and six weeks post-surgery. Materials and Methods: Twelve New Zealand White rabbits received a clean-cut Achilles tendon laceration (the medial and lateral M. gastrocnemius) and were repaired with a 4-strand Becker suture. Six rabbits got additionally a tight polyester urethane tube at the repair site in order to vary the adhesion extent. Tendons were analyzed by static and dynamic ultrasound (control: healthy contralateral legs). The ultrasound outcome was corresponded to the tendon shape, tenocyte and tenoblast density, tenocyte and tenoblast nuclei width, collagen fibre orientation and adhesion extent. Results: The spindle-like morphology of healing tendons (ultrasound) was confirmed by the swollen epitenon (histology). Prediction of adhesion formation by dynamic ultrasound assessment was confirmed by histology (contact region to surrounding tissue). Hyperechogenic areas corresponded to acellular zones with aligned fibres and hypoechogenic zones to not yet oriented fibres and to cell rich areas. Conclusions: These findings add new in-depth structural knowledge to the established non-invasive analytical tool, ultrasound

Synthesis, characterization and histomorphometric analysis of cellular response to a new elastic DegraPol® polymer for rabbit Achilles tendon rupture repair

Tendon rupture repair is a surgical field where improvements are still required due to problems such as repeat ruptures, adhesion formation and joint stiffness. In the current study, a reversibly expandable and contractible electrospun tube based on a biocompatible and biodegradable polymer was implanted around a transected and conventionally sutured rabbit Achilles tendon. The material used was DegraPol® (DP), a polyester urethane. To make DP softer, more elastic and surgeon-friendly, the synthesis protocol was slightly modified. Material properties of conventional and new DP film electrospun meshes are presented. At 12 weeks post-surgery, tenocyte and tenoblast density, nuclei and width, collagen fibre structure and inflammation levels were analyzed histomorphometrically. Additionally, a comprehensive histological scoring system by Stoll et al. (2011) was used to compare healing outcomes. Results showed that there were no adverse reactions of the tendon tissue following the implant. No differences were found whether the DP tube was applied or not for both traditional and new DP materials. As a result, the new DP material was shown to be an excellent carrier for delivery of growth factors, stem cells and other agents responsible for tendon healing

Bioactive, elastic, and biodegradable emulsion electrospun degrapol tube delivering PDGF-BB for tendon rupture repair

Healing of tendon ruptures represents a major challenge in musculoskeletal injuries and combinations of biomaterials with biological factors are suggested as viable option for improved healing. The standard approach of repair by conventional suture leads to incomplete healing or rerupture. Here, a new elastic type of DegraPol® (DP), a polyester urethane, is explored as a delivery device for platelet-derived growth factor-BB (PDGF-BB) to promote tendon healing. Using emulsion electrospinning as an easy method for incorporation of biomolecules within polymers, DegraPol® supports loading and release of PDGF-BB. Morphological, mechanical and delivery device properties of the bioactive DP scaffolds, as well as differences arising due to different electrospinning parameters are studied. Emulsion electrospun DP scaffolds result in thinner fibers than pure DP scaffolds and experience decreased strain at break [%], but high enough for successful surgeon handling. PDGF-BB is released in a sustained manner from emulsion electrospun DP, but not completely, with still large amount of it being inside the polymeric fibers after 30 d. In vitro studies show that the bioactive scaffolds promote tenocyte proliferation in serum free and serum(+) conditions, demonstrating the potential of this surgeon-friendly bioactive delivery device to be used for tendon repair

Prevention of Peritendinous Adhesions Using an Electrospun DegraPol Polymer Tube: A Histological, Ultrasonographic, and Biomechanical Study in Rabbits

PURPOSE: One of the great challenges in surgical tendon rupture repair is to minimize peritendinous adhesions. In order to reduce adhesion formation, a physical barrier was applied to a sutured rabbit Achilles tendon, with two different immobilization protocols used postoperatively. METHODS: Thirty New Zealand white rabbits received a laceration on the Achilles tendon, sutured with a 4-strand Becker suture, and half of the rabbits got a DegraPol tube at the repair site. While fifteen rabbits had their treated hind leg in a 180° stretched position during 6 weeks (adhesion provoking immobilization), the other fifteen rabbits were recasted with a 150° position after 3 weeks (adhesion inhibiting immobilization). Adhesion extent was analysed macroscopically, via ultrasound and histology. Inflammation was determined histologically. Biomechanical properties were analysed. RESULTS: Application of a DegraPol tube reduced adhesion formation by approximately 20%--independently of the immobilization protocol. Biomechanical properties of extracted specimen were not affected by the tube application. There was no serious inflammatory reaction towards the implant material. CONCLUSIONS: Implantation of a DegraPol tube tightly set around a sutured tendon acts as a beneficial physical barrier and prevents adhesion formation significantly--without affecting the tendon healing process