Wrap can be cut to the appropriate size and shape for specific applications. The surgeon may use more than one layer of Wrap to secure the damaged area.

A flexible biodegradable composite for treating damaged areas of the body requiring peripheral nerve repair due to trauma or disease is providing a simpler alternative to sophisticated microsurgical procedures and equipment.

Made of a non-woven, watersoluble glass (CorGlaes®) fiber and bonded with a biodegradable binding solution or polymer, the material known simply as Wrap is a nonshedding flexible sheet. Wrap has a controllable biodegradation rate, is biocompatible, and can be used as an implantable temporary structural support. It is placed around the damaged site and glued using tissue adhesive or an adhesive made from the binder medium or it is sutured.

Wrap and the Cor- Glaes material are by Scotland-based Giltech. Currently undergoing clinical trials, Wrap can be cut to the appropriate size and shape for specific applications; the surgeon may use more than one layer of Wrap to secure the damaged area.

Figure 1. Microsurgical repair requires careful suturing of the damaged nerve ends. This causes further trauma and leads to compression of the joined surfaces.
Select figure to enlarge.

In addition to its use as an implantable temporary structural support, it also can be used for controlled delivery, e.g. of antimicrobials, growth factors or trace elements, or, with the appropriate construction, forms an ideal tissue engineering substrate and a temporary scaffold for the maintenance and delivery of cells. With alternative modifications, Wrap also has shown the ability to prevent post-operative adhesion formation and can be used in sheet form between different tissue layers.

The need

Our initial concept was to simplify the repair of peripheral nerve damage. The normal procedure requires specialist microsurgical intervention, which is costly and time consuming. Microsurgical repair requires careful suturing of the damaged nerve ends (Figure 1). This causes further trauma and leads to compression of the joined surfaces.

The first Wrap prototypes were solid CorGlaes centrifugally cast glass tubules, which were typically 20 to 50mm long and 5 to 10mm in diameter with a wall thickness of 1mm. The ends of the damaged nerve were pushed into each end of the tubule and fastened with sutures fed through small holes drilled near the ends of the tubules (Figure 2). The procedure was simple and fast.

Fixing the nerves away from the damaged endings reduced further nerve trauma and prevented compression of the mating nerve ends. A small gap could also be left if desired. Intubation of nerve ends with a conduit or tube has been used in various guises since the mid 18th century, but biocompatibility and non-degradation created issues leading, potentially, to repair failure. The solid tube format was extensively tested in-vivo looking at repair quality in divisions and gaps under various regimes. These included evaluation of tubes containing growth factors, macerated muscle, and specific cell types believed to improve quality and speed of repair. Tubes were either pre-filled or infused via a side inlet tube. No treatments demonstrated particularly significant improvement in performance, although this is worth re-visiting especially for long gap repair – a ‘holy grail’ for peripheral nerve repair surgery. This device was eventually implanted in a very limited human trial. Indications were that the procedure was at least as good as microsurgery.

Although biocompatible, completely soluble, fast, and easy enough to implant without microsurgical skills or equipment, the problems with a solid glass tube are lack of flexibility, possible breakage as the glass dissolves and a range of sizes to cover different nerve diameters.

To address these issues, Wrap was developed. The starting point was CorGlaes reformulated to produce an equivalent dissolution profile in fiber form. The preferred polymer was PCL (polycaprolactone) selected for its compatibility with the glass and the application. The polymer is present primarily to bond the non-woven fiber web into a coherent sheet. Various Wrap constructions were evaluated. These included permeable/impermeable, aligned fibers/non-aligned, multiply/ single ply, and light weight/heavy.

For this application, where mechanical loading is minimal and a degree of permeability is desirable, light weight, single-ply, random oriented fiber construct was considered most appropriate. Extensive in-vivo evaluation demonstrated that repairs using the wrap were as good as microsurgical repair.