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1.  Biomechanical Evaluation of an Injectable and Biodegradable Copolymer P(PF-co-CL) in a Cadaveric Vertebral Body Defect Model 
Tissue Engineering. Part A  2014;20(5-6):1096-1102.
A novel biodegradable copolymer, poly(propylene fumarate-co-caprolactone) [P(PF-co-CL)], has been developed in our laboratory as an injectable scaffold for bone defect repair. In the current study, we evaluated the ability of P(PF-co-CL) to reconstitute the load-bearing capacity of vertebral bodies with lytic lesions. Forty vertebral bodies from four fresh-frozen cadaveric thoracolumbar spines were used for this study. They were randomly divided into four groups: intact vertebral body (intact control), simulated defect without treatment (negative control), defect treated with P(PF-co-CL) (copolymer group), and defect treated with poly(methyl methacrylate) (PMMA group). Simulated metastatic lytic defects were made by removing a central core of the trabecular bone in each vertebral body with an approximate volume of 25% through an access hole in the side of the vertebrae. Defects were then filled by injecting either P(PF-co-CL) or PMMA in situ crosslinkable formulations. After the spines were imaged with quantitative computerized tomography, single vertebral body segments were harvested for mechanical testing. Specimens were compressed until failure or to 25% reduction in body height and ultimate strength and elastic modulus of each specimen were then calculated from the force–displacement data. The average failure strength of the copolymer group was 1.83 times stronger than the untreated negative group and it closely matched the intact vertebral bodies (intact control). The PMMA-treated vertebrae, however, had a failure strength 1.64 times larger compared with the intact control. The elastic modulus followed the same trend. This modulus mismatch between PMMA-treated vertebrae and the host vertebrae could potentially induce a fracture cascade and degenerative changes in adjacent intervertebral discs. In contrast, P(PF-co-CL) restored the mechanical properties of the treated segments similar to the normal, intact, vertebrae. Therefore, P(PF-co-CL) may be a suitable alternative to PMMA for vertebroplasty treatment of vertebral bodies with lytic defects.
PMCID: PMC3938939  PMID: 24256208
2.  Evaluation of Osteoconductive Scaffolds in the Canine Femoral Multi-Defect Model 
Tissue Engineering. Part A  2013;19(5-6):634-648.
Treatment of large segmental bone defects remains an unsolved clinical challenge, despite a wide array of existing bone graft materials. This project was designed to rapidly assess and compare promising biodegradable osteoconductive scaffolds for use in the systematic development of new bone regeneration methodologies that combine scaffolds, sources of osteogenic cells, and bioactive scaffold modifications. Promising biomaterials and scaffold fabrication methods were identified in laboratories at Rutgers, MIT, Integra Life Sciences, and Mayo Clinic. Scaffolds were fabricated from various materials, including poly(L-lactide-co-glycolide) (PLGA), poly(L-lactide-co-ɛ-caprolactone) (PLCL), tyrosine-derived polycarbonate (TyrPC), and poly(propylene fumarate) (PPF). Highly porous three-dimensional (3D) scaffolds were fabricated by 3D printing, laser stereolithography, or solvent casting followed by porogen leaching. The canine femoral multi-defect model was used to systematically compare scaffold performance and enable selection of the most promising substrate(s) on which to add cell sourcing options and bioactive surface modifications. Mineralized cancellous allograft (MCA) was used to provide a comparative reference to the current clinical standard for osteoconductive scaffolds. Percent bone volume within the defect was assessed 4 weeks after implantation using both MicroCT and limited histomorphometry. Bone formed at the periphery of all scaffolds with varying levels of radial ingrowth. MCA produced a rapid and advanced stage of bone formation and remodeling throughout the defect in 4 weeks, greatly exceeding the performance of all polymer scaffolds. Two scaffold constructs, TyrPCPL/TCP and PPF4SLA/HAPLGA Dip, proved to be significantly better than alternative PLGA and PLCL scaffolds, justifying further development. MCA remains the current standard for osteoconductive scaffolds.
PMCID: PMC3568967  PMID: 23215980
3.  In Vivo Transplantation of Autogenous Marrow-Derived Cells Following Rapid Intraoperative Magnetic Separation Based on Hyaluronan to Augment Bone Regeneration 
Tissue Engineering. Part A  2012;19(1-2):125-134.
This project was designed to test the hypothesis that rapid intraoperative processing of bone marrow based on hyaluronan (HA) could be used to improve the outcome of local bone regeneration if the concentration and prevalence of marrow-derived connective tissue progenitors (CTPs) could be increased and nonprogenitors depleted before implantation.
HA was used as a marker for positive selection of marrow-derived CTPs using magnetic separation (MS) to obtain a population of HA-positive cells with an increased CTP prevalence. Mineralized cancellous allograft (MCA) was used as an osteoconductive carrier scaffold for loading of HA-positive cells. The canine femoral multidefect model was used and four cylindrical defects measuring 10 mm in diameter and 15 mm in length were grafted with MCA combined with unprocessed marrow or with MS processed marrow that was enriched in HA+ CTPs and depleted in red blood cells and nonprogenitors. Outcome was assessed at 4 weeks using quantitative 3D microcomputed tomography (micro-CT) analysis of bone formation and histomorphological assessment.
Histomorphological assessment showed a significant increase in new bone formation and in the vascular sinus area in the MS-processed defects. Robust bone formation was found throughout the defect area in both groups (defects grafted with unprocessed marrow or with MS processed marrow.) Percent bone volume in the defects, as assessed by micro-CT, was greater in defects engrafted with MS processed cells, but the difference was not statistically significant.
Rapid intraoperative MS processing to enrich CTPs based on HA as a surface marker can be used to increase the concentration and prevalence of CTPs. MCA grafts supplemented with heparinized bone marrow or MS processed cells resulted in a robust and advanced stage of bone regeneration at 4 weeks. A greater new bone formation and vascular sinus area was found in defects grafted with MS processed cells. These data suggest that MS processing may be used to enhance the performance of marrow-derived CTPs in clinical bone regeneration procedures. Further assessment in a more stringent bone defect model is proposed.
PMCID: PMC3593694  PMID: 23082937
4.  Sustained Delivery of Dibutyryl Cyclic Adenosine Monophosphate to the Transected Spinal Cord Via Oligo [(Polyethylene Glycol) Fumarate] Hydrogels 
Tissue Engineering. Part A  2011;17(9-10):1287-1302.
This study describes the use of oligo [(polyethylene glycol) fumarate] (OPF) hydrogel scaffolds as vehicles for sustained delivery of dibutyryl cyclic adenosine monophosphate (dbcAMP) to the transected spinal cord. dbcAMP was encapsulated in poly(lactic-co-glycolic acid) (PLGA) microspheres, which were embedded within the scaffolds architecture. Functionality of the released dbcAMP was assessed using neurite outgrowth assays in PC12 cells and by delivery to the transected spinal cord within OPF seven channel scaffolds, which had been loaded with Schwann cells or mesenchymal stem cells (MSCs). Our results showed that encapsulation of dbcAMP in microspheres lead to prolonged release and continued functionality in vitro. These microspheres were then successfully incorporated into OPF scaffolds and implanted in the transected thoracic spinal cord. Sustained delivery of dbcAMP inhibited axonal regeneration in the presence of Schwann cells but rescued MSC-induced inhibition of axonal regeneration. dbcAMP was also shown to reduce capillary formation in the presence of MSCs, which was coupled with significant functional improvements. Our findings demonstrate the feasibility of incorporating PLGA microsphere technology for spinal cord transection studies. It represents a novel sustained delivery mechanism within the transected spinal cord and provides a platform for potential delivery of other therapeutic agents.
PMCID: PMC3079174  PMID: 21198413
5.  Enhanced Bone Morphogenetic Protein-2-Induced Ectopic and Orthotopic Bone Formation by Intermittent Parathyroid Hormone (1–34) Administration 
Tissue Engineering. Part A  2010;16(12):3769-3777.
Bone morphogenetic proteins (BMPs) play a central role in local bone regeneration strategies, whereas the anabolic features of parathyroid hormone (PTH) are particularly appealing for the systemic treatment of generalized bone loss. The aim of the current study was to investigate whether local BMP-2-induced bone regeneration could be enhanced by systemic administration of PTH (1–34). Empty or BMP-2-loaded poly(lactic-co glycolic acid)/poly(propylene fumarate)/gelatin composites were implanted subcutaneously and in femoral defects in rats (n = 9). For the orthotopic site, empty defects were also tested. Each of the conditions was investigated in combination with daily administered subcutaneous PTH (1–34) injections in the neck. After 8 weeks of implantation, bone mineral density (BMD) and bone volume were analyzed using microcomputed tomography and histology. Ectopic bone formation and almost complete healing of the femoral defect were only seen in rats that received BMP-2-loaded composites. Additional treatment of the rats with PTH (1–34) resulted in significantly (p < 0.05) enhanced BMD and bone volume in the BMP-2 composites at both implantation sites. Despite its effect on BMD in the humerus and vertebra, PTH (1–34) treatment had no significant effect on BMD and bone volume in the empty femoral defects and the ectopically or orthotopically implanted empty composites. Histological analysis showed that the newly formed bone had a normal woven and trabecular appearance. Overall, this study suggests that intermittent administration of a low PTH dose alone has limited potential to enhance local bone regeneration in a critical-sized defect in rats. However, when combined with local BMP-2-releasing scaffolds, PTH administration significantly enhanced osteogenesis in both ectopic and orthotopic sites.
PMCID: PMC2991197  PMID: 20666615
6.  Potential of Hydrogels Based on Poly(Ethylene Glycol) and Sebacic Acid as Orthopedic Tissue Engineering Scaffolds 
Tissue Engineering. Part A  2009;15(8):2299-2307.
In this study, the bioactive effects of poly(ethylene glycol) (PEG) sebacic acid diacrylate (PEGSDA) hydrogels with or without RGD peptide modification on osteogenic differentiation and mineralization of marrow stromal cells (MSCs) were examined. In a separate experiment, the ability of PEGSDA hydrogel to serve as a delivery vehicle for bone morphogenetic protein 2 (BMP-2) was also investigated. As a scaffold, the attachment and proliferation of MSCs on PEGSDA hydrogel scaffolds with and without RGD peptide modification was similar to the control, tissue culture polystyrene. In contrast, cells were barely seen on unmodified PEG diacrylate (PEGDA) hydrogel throughout the culture period for up to 21 days. Osteogenic phenotypic expression such as alkaline phosphatase (ALP) of MSCs as well as mineralized calcium content were significantly higher on PEGSDA-based hydrogels than those on the control or PEGDA hydrogels. Potential use of PEGSDA scaffold as a delivery vehicle of osteogenic molecules such as BMP-2 was also evaluated. Initial burst release of BMP-2 from PEGSDA hydrogel scaffold (14.7%) was significantly reduced compared to PEGDA hydrogel scaffold (84.2%) during the first 3 days of a 21-day release period. ALP activity of an osteoblast was significantly higher in the presence of BMP-2 released from PEGSDA hydrogel scaffolds compared to that in the presence of BMP-2 released from PEGDA scaffolds, especially after 6 days of release. Overall, PEGSDA hydrogel scaffolds without further modification may be useful as orthopedic tissue engineering scaffolds as well as local drug carriers for prolonged sustained release of osteoinductive molecules.
PMCID: PMC2792107  PMID: 19292677
7.  Solute Transport in Cyclically Deformed Porous Tissue Scaffolds with Controlled Pore Cross-Sectional Geometries 
Tissue Engineering. Part A  2009;15(8):1989-1999.
The objective of this study was to investigate the influence of pore geometry on the transport rate and depth after repetitive mechanical deformation of porous scaffolds for tissue engineering applications. Flexible cubic imaging phantoms with pores in the shape of a circular cylinder, elliptic cylinder, and spheroid were fabricated from a biodegradable polymer blend using a combined 3D printing and injection molding technique. The specimens were immersed in fluid and loaded with a solution of a radiopaque solute. The solute distribution was quantified by recording 20 μm pixel-resolution images in an X-ray microimaging scanner at selected time points after intervals of dynamic straining with a mean strain of 8.6 ± 1.6% at 1.0 Hz. The results show that application of cyclic strain significantly increases the rate and depth of solute transport, as compared to diffusive transport alone, for all pore shapes. In addition, pore shape, pore size, and the orientation of the pore cross-sectional asymmetry with respect to the direction of strain greatly influence solute transport. Thus, pore geometry can be tailored to increase transport rates and depths in cyclically deformed scaffolds, which is of utmost importance when thick, metabolically functional tissues are to be engineered.
PMCID: PMC2792109  PMID: 19196145
8.  Neural Stem Cell– and Schwann Cell–Loaded Biodegradable Polymer Scaffolds Support Axonal Regeneration in the Transected Spinal Cord 
Tissue Engineering. Part A  2009;15(7):1797-1805.
Biodegradable polymer scaffolds provide an excellent approach to quantifying critical factors necessary for restoration of function after a transection spinal cord injury. Neural stem cells (NSCs) and Schwann cells (SCs) support axonal regeneration. This study examines the compatibility of NSCs and SCs with the poly-lactic-co-glycolic acid polymer scaffold and quantitatively assesses their potential to promote regeneration after a spinal cord transection injury in rats. NSCs were cultured as neurospheres and characterized by immunostaining for nestin (NSCs), glial fibrillary acidic protein (GFAP) (astrocytes), βIII-tubulin (immature neurons), oligodendrocyte-4 (immature oligodendrocytes), and myelin oligodendrocyte (mature oligodendrocytes), while SCs were characterized by immunostaining for S-100. Rats with transection injuries received scaffold implants containing NSCs (n = 17), SCs (n = 17), and no cells (control) (n = 8). The degree of axonal regeneration was determined by counting neurofilament-stained axons through the scaffold channels 1 month after transplantation. Serial sectioning through the scaffold channels in NSC- and SC-treated groups revealed the presence of nestin, neurofilament, S-100, and βIII tubulin–positive cells. GFAP-positive cells were only seen at the spinal cord–scaffold border. There were significantly more axons in the NSC- and SC- treated groups compared to the control group. In conclusion, biodegradable scaffolds with aligned columns seeded with NSCs or SCs facilitate regeneration across the transected spinal cord. Further, these multichannel biodegradable polymer scaffolds effectively serve as platforms for quantitative analysis of axonal regeneration.
PMCID: PMC2792101  PMID: 19191513
9.  Effect of Autologous Bone Marrow Stromal Cell Seeding and Bone Morphogenetic Protein-2 Delivery on Ectopic Bone Formation in a Microsphere/Poly(Propylene Fumarate) Composite 
Tissue Engineering. Part A  2008;15(3):587-594.
A biodegradable microsphere/scaffold composite based on the synthetic polymer poly(propylene fumarate) (PPF) holds promise as a scaffold for cell growth and sustained delivery vehicle for growth factors for bone regeneration. The objective of the current work was to investigate the in vitro release and in vivo bone forming capacity of this microsphere/scaffold composite containing bone morphogenetic protein-2 (BMP-2) in combination with autologous bone marrow stromal cells (BMSCs) in a goat ectopic implantation model. Three composites consisting of 0, 0.08, or 8 μg BMP-2 per mg of poly(lactic-co-glycolic acid) microspheres, embedded in a porous PPF scaffold, were combined with either plasma (no cells) or culture-expanded BMSCs. PPF scaffolds impregnated with a BMP-2 solution and combined with BMSCs as well as empty PPF scaffolds were also tested. The eight different composites were implanted subcutaneously in the dorsal thoracolumbar area of goats. Incorporation of BMP-2–loaded microspheres in the PPF scaffold resulted in a more sustained in vitro release with a lower burst phase, as compared to BMP-2–impregnated scaffolds. Histological analysis after 9 weeks of implantation showed bone formation in the pores of 11/16 composites containing 8 μg/mg BMP-2–loaded microspheres with no significant difference between composites with or without BMSCs (6/8 and 5/8, respectively). Bone formation was also observed in 1/8 of the BMP-2–impregnated scaffolds. No bone formation was observed in the other conditions. Overall, this study shows the feasibility of bone induction by BMP-2 release from microspheres/scaffold composites.
PMCID: PMC2810278  PMID: 18925831

Results 1-9 (9)