Fabrication And Properties Of Braided Biodegradable Nerve Regeneration Conduits

Peripheral nerve defects continue to be one of the most challenging problems to surgeons. The ability to regeneration of peripheral nerve is very poor because of its unique structure and function, thus most of the peripheral nerve defects are not permit to repair by direct tensionless suture. In such situation, grafting with a segment of autologous nerve is a usual and effective clinical practice, but has drawbacks such as donor site morbidity, and incomplete recovery of function. In addition, grafting with allograft nerves has strong immunological rejection in spite of their abundant source. With the development of tissue engineering, recent approaches have been developed in which a nerve regeneration conduit may be used to replace the need for nerve grafting. Thanks to the use of artificial nerve regeneration conduits, much progress has been made in the repairs of peripheral nerve defects.After selection and evaluation of the constituent biological materials, a tubular braid was fabricated from biodegradable poly (glycolide-co-L-lactide) (PGLA) on a conventional 2-D tubular braiding machine. The braided composite nerve regeneration conduits with adequate mechanical strength and elasticity were made by coating and heat setting methods. This biodegradable braided nerve regeneration conduit possesses excellent biocompatibility and bioactive properties.Before braiding the nerve conduits, the author investigated the braiding process of tubular braids by experimental work and theoretical analysis. In order to prevent the tubular braids from being flattened due to taking-up operation and to get desired inner diameter, a cylindrical metal mandrel was adopted during braiding. Three kinds of braided structures, diamond, regular and triaixal were used by adjusting the arrangement of carriers and introducing the axial yarns through stationary guide eyes. Besides the braided structure, the braiding angle is another important geometric parameter of tubular braids. In the case of braiding with a cylindrical mandrel, the braiding process angle is considered approximately as the braiding angle of tubular braids. The braiding process angle is controlled by changing the teeth number of gear which accomplishes the matching of the velocities of both the traction wheel and the carriers. However, the maximum and minimum values of the braiding process angles were determined respectively by the effective yarn reserve of carriers and the dimension of braiding machine.The radial compressive tests of lateral compression of braided conduits were carried out on custom-built compression device to examine their radial compressive behaviors. The effects of braided structure and braiding angle on the compressive properties and the change of cross-sectional area of braided conduits caused by radial compression are analyzed. The axial tensile tests of braided conduits were carried out by clamping the samples with modified clamping device to examine their axial tensile behaviors. The effects of braided structure and braiding angle on the tensile properties and the changes of length, cross-sectional area and yarn cover factor of braided conduits caused by primary small axial tension are analyzed. The author finds that changing braiding structure and optimizing structure parameters can raise the radial compressive and axial tensional resistances to meet the requirements for the repair of peripheral nerve defects.Basic information about the changes of radial compressive property, mass loss and appearance of braided conduits were obtained through simulation in vitro degradation tests. The effects of the composition of polymeric materials, braided structure and coating on the changes of the properties of braided conduits during the degradation were analyzed. The animal tests were made by repairing rat sciatic nerve defects and dog tibial nerve defects with triaixal braided nerve conduit coated with chitosan and filled with a guide-fiber. The testing results have show that triaixal braided PGLA conduits coated with chitosan and filled with a guide-fiber offer a possible substitute for the repair of peripheral nerve defects.Achievements obtained from this research work could be used as a valuable reference which provides a certain foundation for the investigation of braided biodegradable nerve regeneration conduits and promote the development of textile products used in medical field.