Bioengineered glial strands for nerve regeneration.

Nerve guide implants approved for human application in the peripheral nervous system generally fail to bridge lesion gaps longer than 2 cm and cannot match the clinical performance of autologous nerve transplants. Since current synthetic implants are simply hollow tubes, we aim to recreate the native microarchitecture of nerves inside the tubular implants. Most importantly, in the regenerating nerve, dedifferentiated Schwann cells align to form thousands of long glial strands, which act as guiding structures for the regrowing axons. In order to artificially induce the formation of Schwann cell strands, 28 µm thick, endless poly-p-dioxanone filaments (PDO) were synthesized with longitudinal grooves. A polycationic coating on the PDO filaments rendered the polymer surface cell-permissive and induced the growth of highly oriented Schwann cells with polarized expression of N-cadherin at cell-cell contact sites. In vitro cell proliferation on three-dimensional PDO filaments was significantly increased in comparison to planar PDO substrates. Time lapse video recordings revealed high Schwann cell motility, which is advantageous for the repopulation of cell-free implants after implantation. In a pilot study we employed a novel microsurgical technique in vivo. All axon fascicles were selectively dissected from sciatic rat nerves, and the remaining epineural tube was filled with hundreds of PDO filaments. Histological analysis 6 weeks postoperatively showed no fibrosis or encapsulation but instead longitudinal cell alignment and axonal regrowth. The data suggest that the addition of microstructured PDO filaments to the lumen of synthetic tubular implants might significantly improve performance.

A novel gelatin sponge for accelerated hemostasis.

To more effectively manage the substantial bleeding encountered during surgical procedures in oto-rhino-laryngology, we developed a novel hemostatic sponge made of pharmaceutical grade, chemically cross-linked gelatin. The sponge is characterized by a high pore density, reduced ligaments, and a high nanoscale roughness of lamella surfaces in the matrix. In vitro blood uptake assays revealed a very rapid absorption of human blood, which was two to three times faster than that measured with comparative hemostyptic devices. In an in vitro hemorrhage model using human veins, the novel gelatin sponge matrix induced hemostasis less than a minute after bleeding was induced. The sponge was shown to bring about rapid hemostasis when it was administered in a young patient suffering from acute bleeding of a pharyngeal angiofibroma, even though the patient had been treated with an anticoagulant because of a transient ischemic attack. As the gelatin matrix of the sponge is biocompatible and resorbable, the hemostyptic device could be left in place and was shown to be resorbed within 2 weeks. We hypothesize that the excellent hemostatic performance of the sponge might be linked to enhanced capillary effects in conjunction with optimized anchoring of fibrinogen on the nano-rough material surface, as suggested by scanning electron microscopy. The novel gelatin sponge appears to be a promising hemostatic matrix, which could be of great benefit for patients suffering from epistaxis and other acute injuries resulting in severe bleeding.

A novel microsurgical nerve implantation technique preserving outer nerve layers.

A novel epineural tube implantation paradigm in the adult rat was designed for the analysis of regulatory cell interactions in peripheral nerves and for the development of therapeutic implants. The aim was to allow the integration of synthetic regenerative structures and cells into the nerve interior while preserving an outer nerve tissue layer with a supportive vasculature. The microsurgical technique allowed us to remove the interfascicular epineurium, leaving behind an epineural tube with an intact tissue wall of about 0.1-0.2mm. The resulting tube was filled with hundreds of bioengineered bands of Büngner which were composed of resorbable polymer filaments seeded with Schwann cells. Alternatively, purified cells to be analyzed or different types of growth matrices were injected into the epineural tube. Such manipulations will allow to generate and investigate concentration gradients of biological factors or to analyse cell-matrix interactions under defined conditions in a supportive in vivo environment. Our current aim is to evaluate bioengineered neural implants. In summary, a microsurgical in vivo paradigm has been developed to address multiple aspects of peripheral nerve regeneration.