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1.  In Vivo Biodegradation and Biocompatibility of PEG/Sebacic Acid-Based Hydrogels using a Cage Implant System 
Comprehensive in vivo biodegradability and biocompatibility of unmodified and Arg-Gly-Asp (RGD) peptide-modified PEG/Sebacic acid based hydrogels were evaluated and compared to the control material poly(lactide-co-glycolide) (PLGA) using a cage implantation system, as well as direct subcutaneous implantation for up to 12 weeks. The total weight loss after 12 weeks of implantation for unmodified PEGSDA and RGD-modified PEGSDA in the cage was approximately 42% and 52%, respectively, with no statistical difference (p> 0.05). The exudate analysis showed that PEGSDA hydrogels induced minimal inflammatory response up to 21 days following implantation, similar to the controls (empty cage and the cage containing PLGA discs). Histology analysis from direct subcutaneous implantation of the hydrogels and PLGA scaffold showed statistically similar resolution of the acute and chronic inflammatory responses with development of the fibrous capsule between the PEGSDA hydrogels and the control (PLGA). The cage system, as well as the histology analysis, demonstrated that the degradation products of both hydrogels, with or without RGD peptide modification, are biocompatible without statistically significant differences in the inflammatory responses, as compared to PLGA.
PMCID: PMC2928850  PMID: 20574982
In vivo biocompatibility; In vivo biodegradation; PEG sebacic acid diacrylate; Hydrogel; RGD-modified hydrogel; Cage implantation
2.  Importance of the vasculature in cyst formation after spinal cord injury 
Journal of neurosurgery. Spine  2009;11(4):432-437.
Glial scar and cystic formation greatly contribute to the inhibition of axonal regeneration after spinal cord injury (SCI). Attempts to promote axonal regeneration are extremely challenging in this type of hostile environment. The objective of this study was to examine the surgical methods that may be used to assess the factors that influence the level of scar and cystic formation in SCI.
In the first part of this study, a complete transection was performed at vertebral level T9–10 in adult female Sprague-Dawley rats. The dura mater was either left open (control group) or was closed using sutures or hyaluronic acid. In the second part of the study, complete or subpial transection was performed, with the same dural closure technique applied to both groups. Histological analysis of longitudinal sections of the spinal cord was performed, and the percentage of scar and cyst formation was determined.
Dural closure using sutures resulted in significantly less glial scar formation (p = 0.0248), while incorporation of the subpial transection surgical technique was then shown to significantly decrease cyst formation (p < 0.0001).
In this study, the authors demonstrated the importance of the vasculature in cyst formation after spinal cord trauma and confirmed the importance of dural closure in reducing glial scar formation.
PMCID: PMC2981802  PMID: 19929340
traumatic spinal cord injury; vascular injury; glial cell response to injury
3.  Relationship between Scaffold Channel Diameter and Number of Regenerating Axons in the Transected Rat Spinal Cord 
Acta biomaterialia  2009;5(7):2551-2559.
Regeneration of endogenous axons through a Schwann cell (SC)-seeded scaffold implant has been demonstrated in the transected rat spinal cord. The formation of a cellular lining in the scaffold channel may limit the degree of axonal regeneration. Spinal cords of adult rats were transected and implanted with the SC-loaded polylactic co-glycollic acid (PLGA) scaffold implants containing seven parallel-aligned channels, either 450-μm (n=19) or 660-μm in diameter (n=14). Animals were sacrificed after 1, 2, and 3 months. Immunohistochemistry for neurofilament-expression was performed. The cross-sectional area of fibrous tissue and regenerative core was calculated. We found that the 450-μm scaffolds had significantly greater axon fibers per channel at the one month (186 ± 37) and three month (78 ± 11) endpoints than the 660-μm scaffolds (90 ± 19 and 40 ± 6, respectively) (P=0.0164 & 0.0149, respectively). The difference in the area of fibrous rim between the 450-μm and 660-μm channels was most pronounced at the one month endpoint, at 28,046 μm2 ± 6,551 and 58,633 μm2 ± 7,063, respectively (P=0.0105). Our study suggests that fabricating scaffolds with smaller diameter channels promotes greater regeneration over larger diameter channels. Axonal regeneration was reduced in the larger channels due to the generation of a large fibrous rim. Optimization of this scaffold environment establishes a platform for future studies of the effects of cell types, trophic factors or pharmacological agents on the regenerative capacity of the injured spinal cord.
PMCID: PMC2731813  PMID: 19409869
Biomedical Engineering; Tissue Development and Growth; Central Nervous System; Polymeric Scaffolds
4.  Rigid Fixation of the Spinal Column Improves Scaffold Alignment and Prevents Scoliosis in the Transected Rat Spinal Cord 
Spine  2008;33(24):E914-E919.
Study Design
A controlled study to evaluate a new technique for spinal rod fixation after spinal cord injury in rats. Alignment of implanted tissue-engineered scaffolds was assessed radiographically and by magnetic resonance imaging.
To evaluate the stability of implanted scaffolds and the extent of kyphoscoliotic deformities after spinal fixation.
Summary of Background Data
Biodegradable scaffolds provide an excellent platform for the quantitative assessment of cellular and molecular factors that promote regeneration within the transected cord. Successful delivery of scaffolds to the damaged cord can be hampered by malalignment following transplantation, which in turn, hinders the assessment of neural regeneration.
Radio-opaque barium sulfate-impregnated poly-lactic-co-glycolic acid scaffolds were implanted into spinal transection injuries in adult rats. Spinal fixation was performed in one group of animals using a metal rod fixed to the spinous processes above and below the site of injury, while the control group received no fixation. Radiographic morphometry was performed after 2 and 4 weeks, and 3-dimensional magnetic resonance microscopy analysis 4 weeks after surgery.
Over the course of 4 weeks, progressive scoliosis was evident in the unfixed group, where a Cobb angle of 8.13 ± 2.03° was measured. The fixed group demonstrated significantly less scoliosis, with a Cobb angle measurement of 1.89 ± 0.75° (P = 0.0004). Similarly, a trend for less kyphosis was evident in the fixed group (7.33 ± 1.68°) compared with the unfixed group (10.13 ± 1.46°). Quantitative measurements of the degree of malalignment of the scaffolds were also significantly less in the fixed group (5 ± 1.23°) compared with the unfixed group (11 ± 2.82°) (P = 0.0143).
Radio-opaque barium sulfate allows for visualization of scaffolds in vivo using radiographic analysis. Spinal fixation was shown to prevent scoliosis, reduce kyphosis, and reduce scaffold malalignment within the transected rat spinal cord. Using a highly optimized model will increase the potential for finding a therapy for restoring function to the injured cord.
PMCID: PMC2773001  PMID: 19011531
spine fixation; transection spinal cord injury; scaffold; scoliosis
5.  Synthesis, Material Properties and Biocompatibility of a Novel Self-Crosslinkable Poly(caprolactone fumarate) as an Injectable Tissue Engineering Scaffold 
Biomacromolecules  2005;6(5):2503-2511.
A novel self-crosslinkable and biodegradable macromer poly(caprolactone fumarate) (PCLF) has been developed for guided bone regeneration. This macromer is a copolymer of fumaryl chloride, which contains double bonds for in-situ crosslinking, and poly(ε-caprolactone) that has a flexible chain to facilitate self-crosslinkability. PCLF was characterized with Fourier transform infrared (FTIR) spectroscopy, 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, and gel permeation chromatography (GPC). Porous scaffolds were fabricated with sodium chloride particles as the porogen and a chemical initiation system. The PCLF scaffolds were characterized with scanning electron microscopy (SEM) and micro-computed tomography (micro-CT). The cytotoxicity and in vivo biocompatibility of PCLF were also assessed. Our results suggest that this novel copolymer, PCLF, is an injectable, self-crosslinkable, and biocompatible macromer that may be potentially used as a scaffold for tissue engineering applications.
PMCID: PMC2530909  PMID: 16153086

Results 1-5 (5)