SOY PROTEIN ISOLATE (SPI) “GREEN” SCAFFOLDS WITH ORIENTED MICROCHANNELS FOR APPLICATIONS IN SPINAL CORD INJURY

Abstract

Every year, accidents, falls, sport injuries and other incidents cause thousands of people to suffer spinal cord injury (SCI). In the United States alone, it is estimated that the number of Americans that live with SCI is around 259,000, with 12,000 new cases that happen annually (1). These injuries lead to spinal cord damages expressed by massive nerve tract degeneration followed by neurological loss, paralysis and disabilities. Therapy of SCI patients with non-steroidal anti-inflammatory drugs (NSAIDs) help in diminishing secondary injury and lessen pain and swelling. However these drugs do not promote tissue repair. Therefore there is an unmet clinical need to develop technologies and therapeutic strategies that compensate loss of neuronal tissue, support and facilitate reestablishment of nerve tracks connectivity in the injured spinal cord. Recent progress in nerve regeneration indicates that a tissue engineering approach using soft tissue scaffolds, stem cells and neurotrophins, can lead to a partial therapy in animal models of SCI. Bioengineered scaffolds prepared by freeze casting technology provide an experimental tool for guidance of regenerating neuronal tracts and/or axons and therefore are useful for regeneration of injured spinal cord. In this engineering approach for scaffold preparation, temperature controlled directional solidification of an aqueous polymer(s) solution creates channels of different diameters that can direct axonal outgrowth of neurons populating the scaffold. In a previous study from our laboratory, such scaffolds promoted differentiation of neurons, a process facilitated by co-population of the scaffold’s channels with endothelial cells. “Green” plant proteins, such as soybean proteins, are becoming an attractive alternative source of natural polymers for a variety of biomedical applications including scaffold fabrication for neuronal tissue regeneration. In the present study, we developed a second generation of improved, microchanneled composite scaffolds from gelatin and soy protein isolate cross-linked with genipin (2 w/v %, 0.5 w/v %, 1 w/v %, respectively). The fabrication of these scaffolds by a controlled freeze drying technique, their mechanical properties (stiffness, ~3-4 kPa) as well as their uniform longitudinal channels of a diameter of ~30-55 µm is described. Preliminary biocompatibility experiments in 2D and 3D using the above mentioned scaffolds populated with either undifferentiated PC12 cells or nerve growth factor differentiated PC12 cells indicated partial biocompatibility of the scaffolds for neuronal growth. Improving the biocompatibility of these composite scaffolds is under investigation in our laboratory.