Jennifer Vernengo

A pilot study of poly(N-isopropylacrylamide)-g-polyethylene glycol and poly(N-isopropylacrylamide)-g-methylcellulose branched copolymers as injectable scaffolds for local delivery of neurotrophins and cellular transplants into the injured spinal cord.

OBJECT The authors investigated the feasibility of using injectable hydrogels, based on poly(N-isopropylacrylamide) (PNIPAAm), lightly cross-linked with polyethylene glycol (PEG) or methylcellulose (MC), to serve as injectable scaffolds for local delivery of neurotrophins and cellular transplants into the injured spinal cord. The primary aims of this work were to assess the biocompatibility of the scaffolds by evaluating graft cell survival and the host tissue immune response. The scaffolds were also evaluated for their ability to promote axonal growth through the action of released brain-derived neurotrophic factor (BDNF). METHODS The in vivo performance of PNIPAAm-g-PEG and PNIPAAm-g-MC was evaluated using a rodent model of spinal cord injury (SCI). The hydrogels were injected as viscous liquids into the injury site and formed space-filling hydrogels. The host immune response and biocompatibility of the scaffolds were evaluated at 2 weeks by histological and fluorescent immunohistochemical analysis. Commercially available matrices were used as a control and examined for comparison. RESULTS Experiments showed that the scaffolds did not contribute to an injury-related inflammatory response. PNIPAAm-g-PEG was also shown to be an effective vehicle for delivery of cellular transplants and supported graft survival. Additionally, PNIPAAm-g-PEG and PNIPAAm-g-MC are permissive to axonal growth and can serve as injectable scaffolds for local delivery of BDNF. CONCLUSIONS Based on the results, the authors suggest that these copolymers are feasible injectable scaffolds for cell grafting into the injured spinal cord and for delivery of therapeutic factors.

Implications of poly(N-isopropylacrylamide)-g-poly(ethylene glycol) with codissolved brain-derived neurotrophic factor injectable scaffold on motor function recovery rate following cervical dorsolateral funiculotomy in the rat.

OBJECT In a follow-up study to their prior work, the authors evaluated a novel delivery system for a previously established treatment for spinal cord injury (SCI), based on a poly(N-isopropylacrylamide) (PNIPAAm), lightly cross-linked with a polyethylene glycol (PEG) injectable scaffold. The primary aim of this work was to assess the recovery of both spontaneous and skilled forelimb function following a cervical dorsolateral funiculotomy in the rat. This injury ablates the rubrospinal tract (RST) but spares the dorsal and ventral corticospinal tract and can severely impair reaching and grasping abilities. METHODS Animals received an implant of either PNIPAAm-g-PEG or PNIPAAm-g-PEG + brain-derived neurotrophic factor (BDNF). The single-pellet reach-to-grasp task and the staircase-reaching task were used to assess skilled motor function associated with reaching and grasping abilities, and the cylinder task was used to assess spontaneous motor function, both before and after injury. RESULTS Because BDNF can stimulate regenerating RST axons, the authors showed that animals receiving an implant of PNIPAAm-g-PEG with codissolved BDNF had an increased recovery rate of fine motor function when compared with a control group (PNIPAAm-g-PEG only) on both a staircase-reaching task at 4 and 8 weeks post-SCI and on a single-pellet reach-to-grasp task at 5 weeks post-SCI. In addition, spontaneous motor function, as measured in the cylinder test, recovered to preinjury values in animals receiving PNIPAAm-g-PEG + BDNF. Fluorescence immunochemistry indicated the presence of both regenerating axons and BDA-labeled fibers growing up to or within the host-graft interface in animals receiving PNIPAAm-g-PEG + BDNF. CONCLUSIONS Based on their results, the authors suggest that BDNF delivered by the scaffold promoted the growth of RST axons into the lesion, which may have contributed in part to the increased recovery rate.

Injectable multifunctional scaffold for spinal cord repair

Spinal cord injury (SCI) affects thousands of Americans each year. The injury results in local cell loss in the spinal cord, interrupting the connections between brain and periphery. Current treatment options for SCI are limited due to the inability of adult neurons to regenerate in the inhibitory environment of the injured central nervous system (CNS). The primary goal of this work is to design a multifunctional, injectable hydrogel that supports neural repair following SCI. This project proposes the use of a branched copolymer based on poly(N-isopropylacryalmide) (PNIPAAm) and poly(ethylene glycol) (PEG). The thermosensitive nature of the hydrogel allows for easy implantation together with cellular grafts, and the controlled delivery of therapeutic factors. In this study, we investigated the cytocompatibility of the scaffold in vitro and also report its performance in vivo, with and without brain derived neurotrophic factor (BDNF) in a rodent model of SCI. Our results show that the injectable PNIPAAm-PEG scaffold completely fills the injury site, and does not elicit a larger host inflammatory response than a commercially available gelatin sponge. In addition, we have shown that the scaffold loaded with BDNF is permissive to host axon growth. With these promising results, we suggest that an injectable PNIPAAm-PEG hydrogel can serve as a multifunctional device that will result in an effective platform technology for the treatment of SCI.

Tissue Engineering of the Intervertebral Disc

Tissue engineering is a rapidly growing field of research that aims to repair damaged tissues within the body. Among tissue engineering approaches is the use of scaffolds to help regenerate lost tissues. Scaffolds provide structural support for specific areas within the body, namely load bearing regions, and allow for cells to be seeded within the scaffold for tissue regeneration. Scaffolds that specifically replicate the properties and/or composition of native tissues are referred to as biomimetic scaffolds.Copyright

Design of a Bioreactor for Mechanical Stimulation of Adipose Derived Stem Cells for Intervertebral Disc Tissue Engineering

Lower back pain is one of the most common medical problems in the world [1], affecting between 70% and 85% of the US population at some point during their lives [2]. Disc degeneration is caused by biological changes in the disc, which result in dehydration of the nucleus pulposus (NP). The long term goal of this project is to treat disc degeneration with a tissue engineering strategy for the regeneration of the nucleus pulposus using messechymal stem cells derived from adipose tissue. It has been established in cartilage regeneration studies that cyclic compressive loading of stem cells is beneficial for tissue formation compared to static culture [3–7]. In this work, a bioreactor is being developed that can subject cell-seeded polymeric tissue engineering scaffolds to dynamic compressive forces. Ultimately, the bioreactor will be used to study the effects of different loading parameters on the production of new nucleus pulposus tissue from adipose-derived stem cells.Copyright