Experimental studies on bone induction using low-molecular-weight poly (DL-lactide-co-glycolide) as a carrier for recombinant human bone morphogenetic protein-2

Periodontal Tissue as a Biomaterial for Hard-Tissue Regeneration following bmp-2 Gene Transfer

The application of periodontal tissue in regenerative medicine has gained increasing interest since it has a high potential to induce hard-tissue regeneration, and is easy to handle and graft to other areas of the oral cavity or tissues. Additionally, bone morphogenetic protein-2 (BMP-2) has a high potential to induce the differentiation of mesenchymal stem cells into osteogenic cells. We previously developed a system for a gene transfer to the periodontal tissues in animal models. In this study, we aimed to reveal the potential and efficiency of periodontal tissue as a biomaterial for hard-tissue regeneration following a bmp-2 gene transfer. A non-viral expression vector carrying bmp-2 was injected into the palate of the periodontal tissues of Wistar rats, followed by electroporation. The periodontal tissues were analyzed through bone morphometric analyses, including mineral apposition rate (MAR) determination and collagen micro-arrangement, which is a bone quality parameter, before and after a gene transfer. The MAR was significantly higher 3-6 d after the gene transfer than that before the gene transfer. Collagen orientation was normally maintained even after the bmp-2 gene transfer, suggesting that the bmp-2 gene transfer has no adverse effects on bone quality. Our results suggest that periodontal tissue electroporated with bmp-2 could be a novel biomaterial candidate for hard-tissue regeneration therapy.

Comparative analysis of bone regeneration behavior using recombinant human BMP-2 versus plasmid DNA of BMP-2

Bone regeneration and the osteoinductive capacity of implants are challenging issues in clinical medicine. Currently, recombinant growth factors and nonviral gene transfer are the most frequently investigated methods for bone growth enhancement, although the more favorable method remains unclear. There is a lack of knowledge in literature about the in vivo comparison of these methods for bone regeneration. BMP-2, which is the most commonly used growth factor for osteogenesis, was applied at its most efficient dose as a recombinant growth factor (rhBMP-2) and as a growth-factor-encoding copolymer protected gene vector (pBMP-2) in a critical size bone defect (CSD) model to determine the most suitable method for bone regeneration. CSDs were induced bilaterally in 32 Sprague-Dawley rats. RhBMP-2 (62.5 μg) or pBMP-2 (2.5 μg) was embedded in poly(d,l-)lactide-coated titanium discs. Survival times were set at 14, 28, 56, and 112 days. After euthanasia, samples were analyzed via micro-computed tomography, polychrome sequential fluorescent labeling, and immunohistochemistry. Whereas defects in both groups were bridged with new bone after 56 days, rhBMP-2 initially induced ectopic new bone formation that was later remodeled in an unorganized hypodense manner. In contrast, pBMP-2 led to slower but steady bone regeneration with physiological tissue morphology, as confirmed by high osteoblast activity shown by osteocalcin staining. CD68 and TRAP staining verified high osteoclast activity for the rhBMP-2 group. pBMP-2 successfully induced locally controlled physiological bone regeneration, whereas rhBMP-2 triggered rapid and ectopic but insufficient bone formation. Thus, nonviral gene transfer appears to be more favorable for clinical applications. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 163-173, 2019.

Analysis of mineral apposition rates during alveolar bone regeneration over three weeks following transfer of BMP-2/7 gene via in vivo electroporation

Alveolar bone is not spontaneously regenerated following trauma or periodontitis. We previously proposed an animal model for new alveolar bone regeneration therapy based on the non-viral BMP-2/7 gene expression vector and in vivo electroporation, which induced the formation of new alveolar bone over the course of a week. Here, we analysed alveolar bone during a period of three weeks following gene transfer to periodontal tissue. Non-viral plasmid vector pCAGGS-BMP-2/7 or pCAGGS control was injected into palatal periodontal tissue of the first molar of the rat maxilla and immediately electroporated with 32 pulses of 50 V for 50 msec. Over the following three weeks, rats were double bone-stained by calcein and tetracycline every three days and mineral apposition rates (MAR) were measured. Double bonestaining revealed that MAR of alveolar bone was at similar level three days before BMP-2/7 gene transfer as three days after gene transfer. However, from 3 to 6 days, 6 to 9 days, 9 to 12 days, 12 to 15 days, 15 to 18 days, and 18 to 20 days after, MARs were significantly higher than prior to gene transfer. Our proposed gene therapy for alveolar bone regeneration combining nonviral BMP-2/7 gene expression vector and in vivo electroporation could increase alveolar bone regeneration potential in the targeted area for up to three weeks.

Mechanical properties and state of miscibility in poly(racD,L-lactide-co-glycolide)/(L-lactide-co-ε-caprolactone) blends

Polymers based on lactic acid (PLA) are a very promising category of biopolymers. As they are multi-stimuli responsive, can, in many ways, positively interact with the host, stimulating the innate reparative machinery of the human body. Since biopolymers for medical applications are subject to restrictive regulations, blending stands out as an effective method for obtaining tailored properties within a reduced time to market if compared to synthesis. Hence, in this study a set of PDLGA/PLCL blends was obtained by means of thermoplastic techniques and then further characterized. Evaluation techniques include GPC, NMR, DSC, tensile testing and SEM. Although mixtures proved to be immiscible, a full range of tensile properties was achieved. Observation of the surfaces of fracture provided visual evidence of the deformation mechanisms that occurred during the tensile tests which in the end led to failure. Interpretation of the thermal events based on molecular characterization parameters revealed phase separation, crystallization and plasticisation mechanisms that are relevant to any potential applications based on mechanical performance and shape memory behaviour.

Release Behavior and Biological Activity of Recombinant Human Bone Morphogenetic Protein-2 from Porous PLGA Scaffold

The feasibility of using the poly-(DL-lactic-co-glycolic acid) (PLGA) scaffold as a carrier for controlled recombinant human bone morphogenetic protein-2 (rhBMP-2) delivery was assessed. PLGA rhBMP-2-loaded scaffolds were fabricated by emulsion polymerization and freeze-dried; a porous morphology was observed by scanning electron microscopy. The in vitro release of rhBMP-2 from the polymer was assessed using high performance liquid chromatography. An initial burst release of the incorporated rhBMP-2 was observed over the first 24h followed by an 80.6% sustained release for one month. The rhBMP-2-loaded scaffolds were implanted bilaterally into rat ectopic muscle pouches. The rhBMP-2 implanted animals showed bone formation submuscle space and osteoblasts located in the new bone region while none was seen in the control groups.

Non-mulberry silk fibroin grafted poly (Є-caprolactone)/nano hydroxyapatite nanofibrous scaffold for dual growth factor delivery to promote bone regeneration

HYPOTHESIS

This study aims at developing biodegradable, mineralized, nanofibrous scaffolds for use in bone regeneration. Scaffolds are loaded with combinations of bone morphogenic protein-2 (rhBMP-2) and transforming growth factor beta (TGF-β) and evaluated in vitro for enhancement in osteoinductivity.

EXPERIMENTS

Poly(Є-caprolactone) (PCL) doped with different portions of nano-hydroxyapatite is electrospun into nanofibrous scaffolds. Non-mulberry silk fibroin (NSF) obtained from Antheraea mylitta is grafted by aminolysis onto them. Scaffolds prepared have three concentrations of nano-hydroxyapatite: 0% (NSF-PCL), 25% (NSF-PCL/n25), and 50% (NSF-PCL/n50). Growth factor loading is carried out in three different combinations, solely rhBMP-2 (BN25), solely TGF-β (TN25) and rhBMP-2+TGF-β (T/B N25) via carbodiimide coupling.

FINDINGS

NSF-PCL/n25 showed the best results in examination of mechanical properties, bioactivity, and cell viability. Hence only NSF-PCL/n25 is selected for loading growth factors and subsequent detailed in vitro experiments using MG-63 cell-line. Both growth factors show sustain release kinetics from the matrix. The T/B N25 scaffolds support cellular activity, proliferation, and triggering of bone-associated genes' expression better and promote earlier cell differentiation. Dual growth factor loaded NSF grafted electrospun PCL/nHAp scaffolds show promise for further development into a suitable scaffold for bone tissue engineering.

A glass polyalkenoate cement carrier for bone morphogenetic proteins

This work considers a glass polyalkenoate cement (GPC)-based carrier for the effective delivery of bone morphogenetic proteins (BMPs) at an implantation site. A 0.12 CaO-0.04 SrO-0.36 ZnO-0.48 SiO2 based glass and poly(acrylic acid) (PAA, Mw 213,000) were employed for the fabrication of the GPC. The media used for the water source in the GPC reaction was altered to produce a series of GPCs. The GPC liquid media was either 100 % distilled water with additions of albumin at 0, 2, 5 and 8 wt% of the glass content, 100 % formulation buffer (IFB), and 100 % BMP (150 µg rhBMP-2/ml IFB). Rheological properties, compressive strength, ion release profiles and BMP release were evaluated. Working times (Tw) of the formulated GPCs significantly increased with the addition of 2 % albumin and remained constant with further increases in albumin content or IFB solutions. Setting time (Ts) experienced an increase with 2 and 5 % albumin content, but a decrease with 8 % albumin. Changing the liquid source to IFB containing 5 % albumin had no significant effect on Ts compared to the 8 % albumin-containing BT101. Replacing the albumin with IFB/BMP-2 did not significantly affect Tw. However, Ts increased for the BT101_BMP-2 containing GPCs, compared to all other samples. The compressive strength evaluated 1 day post cement mixing was not affected significantly by the incorporation of BMPs, but the ion release did increase from the cements, particularly for Zn and Sr. The GPCs released BMP after the first day, which decreased in content during the following 6 days. This study has proven that BMPs can be immobilized into GPCs and may result in novel materials for clinical applications.

Bone morphogenetic protein-2-impregnated biomimetic scaffolds successfully induce bone healing in a marginal mandibular defect

OBJECTIVES/HYPOTHESIS

To test the osteoregenerative potential and dosing of bone morphogenetic protein-2 (BMP-2)-impregnated biomimetic scaffolds in a rat model of a mandibular defect.

STUDY DESIGN

Prospective study using an animal model.

METHODS

Varied doses of BMP-2 (0.5, 1, 0.5, 0.5 in microspheres, 5, and 15 μg) were absorbed onto a biomimetic scaffold. Scaffolds were then implanted into marginal mandibular defects in rats. Blank scaffolds and unfilled defects were used as negative controls. Two months postoperatively, bone healing was analyzed with microcomputerized tomography (microCT).

RESULTS

MicroCT analysis demonstrated that all doses of BMP-2 induced successful healing of marginal mandibular defects in a rat mandible. Increasing doses of BMP-2 on the scaffolds produced increased tissue healing, with 15 μg demonstrating significantly more healing than all other dosing (P < .01).

CONCLUSIONS

BMP-2-impregnated biomimetic scaffolds successfully induce bone healing in a marginal mandibular defect in the rat. Percentage healing of defect, percentage of bone within healed tissue, and total bone volume are all a function of BMP-2 dosing. There appears to be an optimal dose of 5 μg beyond which there is no increase in bone volume.

LEVEL OF EVIDENCE

NA.

Drug delivery from hydroxyapatite-coated titanium surfaces using biodegradable particle carriers

The goal of this study was to develop a functional titanium (Ti) implant loaded with bioactive molecules using biodegradable polymeric particles as drug delivery carrier for dental applications. In this study, dexamethasone (DEX)-loaded poly(lactic-co-glycolic acid) (PLGA) particles were electrostatically immobilized on a Ti disc surface coated with hydroxyapatite (HA) nanocrystals using a low temperature high speed collision (LTHSC) method. Resorbable blasting media (RBM) Ti discs (S1), HA-Ti discs (S2), and HA-Ti discs treated with DEX-loaded PLGA particles (S3) were fabricated in this study as sample discs. To facilitate surface immobilization, PLGA particles were coated with polyethyleneimine (PEI) to produce a positive surface charge. This modification of PLGA particle surfaces, allowed DEX-loaded PLGA particles to be immobilized on negatively charged S2 disc surface. It was found that DEX-loaded PLGA particles were well dispersed and immobilized onto the S3 disc surfaces. Release profile studies of DEX from S3 discs in a 4-week immersion study indicated an initial burst release followed by sustained release. In vitro evaluation of bone marrow derived mesenchymal stem cells (BMSCs) cultured for 1 and 2 weeks on S3 discs showed greater BMSC differentiation than on S1 or S2 discs, demonstrating that this innovative delivery platform potently induced BMSC differentiation in vitro, and suggesting that it could be exploited for stem cell therapy purposes or to enhance in vivo osteogenesis. In addition, the results of the present study shows that various bioactive molecules that promote bone regeneration can be efficiently incorporated onto HA-Ti surfaces using biodegradable polymeric particles.

Biomaterial delivery of morphogens to mimic the natural healing cascade in bone

Complications in treatment of large bone defects using bone grafting still remain. Our understanding of the endogenous bone regeneration cascade has inspired the exploration of a wide variety of growth factors (GFs) in an effort to mimic the natural signaling that controls bone healing. Biomaterial-based delivery of single exogenous GFs has shown therapeutic efficacy, and this likely relates to its ability to recruit and promote replication of cells involved in tissue development and the healing process. However, as the natural bone healing cascade involves the action of multiple factors, each acting in a specific spatiotemporal pattern, strategies aiming to mimic the critical aspects of this process will likely benefit from the usage of multiple therapeutic agents. This article reviews the current status of approaches to deliver single GFs, as well as ongoing efforts to develop sophisticated delivery platforms to deliver multiple lineage-directing morphogens (multiple GFs) during bone healing.

Studies of bone morphogenetic protein-based surgical repair

Over the past several decades, recombinant human bone morphogenetic proteins (rhBMPs) have been the most extensively studied and widely used osteoinductive agents for clinical bone repair. Since rhBMP-2 and rhBMP-7 were cleared by the U.S. Food and Drug Administration for certain clinical uses, millions of patients worldwide have been treated with rhBMPs for various musculoskeletal disorders. Current clinical applications include treatment of long bone fracture non-unions, spinal surgeries, and oral maxillofacial surgeries. Considering the growing number of recent publications related to clincal research of rhBMPs, there exists enormous promise for these proteins to be used in bone regenerative medicine. The authors take this opportunity to review the rhBMP literature paying specific attention to the current applications of rhBMPs in bone repair and spine surgery. The prospective future of rhBMPs delivered in combination with tissue engineered scaffolds is also reviewed.

Heterotopic ossification associated with recombinant human bone morphogenetic protein-2 (infuse) in posterolateral lumbar spine fusion: a case report

STUDY DESIGN

A case of heterotopic ossification in the lumbar spine associated with the off-label use of recombinant human bone morphogenetic protein-2 (rhBMP-2) is reported.

OBJECTIVE

To highlight a previously unreported complication of rhBMP-2 use and to review the literature pertinent to the topic.

SUMMARY OF BACKGROUND DATA

There is no report in the literature regarding a large mass of rhBMP-2-associated heterotopic ossification surrounding the paraspinal musculature.

METHODS

The clinical and radiographical features of this complication and treatment course are presented.

RESULTS

The surgical excision of heterotopic ossification and removal of symptomatic instrumentation have resulted in the patient remaining asymptomatic at 1 year of follow-up examination.

CONCLUSION

The reported case adds to the literature of off-label use of rhBMP-2 and the potential for the formation of heterotopic ossification with its use.

Combined Mesenchymal Stem Cell Sheets and rhBMP-2-Releasing Calcium Sulfate–rhBMP-2 Scaffolds for Segmental Bone Tissue Engineering

Repair of segmental bone defects remains a major challenge for orthopedic surgeons. This study aimed to investigate whether recombinant human bone morphogenetic protein-2 (rhBMP-2)-loaded calcium sulfate (CS) combined with mesenchymal stem cell (MSC) sheets could accelerate bone regeneration in ulnar segmental defects of rabbits. In vitro, the osteogenic differentiation of MSCs cultured on rhBMP-2-loaded CS was investigated. Forty complete 1.2-cm bone defects were treated with CS (group A), rhBMP-2-loaded CS (group B), MSC sheet-wrapped CS (group C), and MSC sheet-wrapped rhBMP-2-loaded CS (group D). At 4 and 8 weeks after implantation, the samples were treated by X-ray, microcomputed tomography, and histological observation. The rhBMP-2 could be released from the rhBMP-2-loaded CS scaffolds and maintain its bioactivity. The alkaline phosphatase (ALP) of MSCs cultured on rhBMP-2-loaded CS was significantly higher than that of CS at both 7 and 14 days ( p < 0.05). The defects treated with MSC sheet-wrapped rhBMP-2-loaded CS showed significantly higher scores by X-ray analysis and more bone formation determined by both histology and microcomputed tomography than the other three groups at both 4 and 8 weeks after implantation ( p < 0.05). No significant difference in X-ray score and bone formation was found between groups B and C, both significantly higher than group A ( p < 0.05). The results suggested that MSC sheet-wrapped rhBMP-2-loaded CS may be an effective approach to promote the repair of segmental bone defects and has great potential for repairing large segmental bone defects in clinic.

Osteoinduction by repeat plasmid injection of human bone morphogenetic protein-2

BACKGROUND

Bone morphogenetic protein-2 (BMP-2) is an osteoinductive protein and is considered useful for the treatment of skeletal disorders. Previous studies using BMP-2 in clinical applications have encountered difficulties, including the lack of an efficient, safe, inexpensive and simple delivery system. The gene transfer approach is a promising option for utilizing BMP-2. Although viral vector-mediated gene transfer is efficient, safety concerns prevent its clinical application for common diseases. On the other hand, plasmid-based gene transfer is a safe method and can be harnessed for practical applications.

METHODS

A plasmid encoding human BMP-2 (pCAGGS-BMP-2) was used and injected repeatedly (one to eight times) into the skeletal muscle of mice at a divided dose. We compared the capability of osteoinduction in the skeletal muscle of mice after gene transfer by repeat injection. BMP-2 production was assessed via immunohistochemistry, and osteoinduction was evaluated using radiography, histology and biochemical assays.

RESULTS

The BMP-2 gene was transferred into the skeletal muscle of mice by repeat injection using pCAGGS-BMP-2. Mature bone was frequently observed in mice injected repeatedly with pCAGGS-BMP-2 at a divided dose. This confirms that, if the total dose is fixed, repeat injection with pCAGGS-BMP-2 at a divided dose causes osteoinduction more frequently in the skeletal muscle of mice.

CONCLUSIONS

These results suggest the possibility of the effective clinical use of human BMP-2 gene therapy by direct DNA injection, and facilitate the clinical application of BMP-2 gene therapy.

Biocompatibility and safety of a hybrid core-shell nanoparticulate OP-1 delivery system intramuscularly administered in rats

A hybrid, localized and release-controlled delivery system for bone growth factors consisting of a liposomal core incorporated into a shell of alternating layer-by-layer self-assembled natural polyelectrolytes has been formulated. Hydrophilic, monodisperse, spherical and stable cationic nanoparticles (< or =350 nm) with an extended shelf-life resulted. Cytocompatibility was previously assayed with MC3T3-E1.4 mouse preosteoblasts showing no adverse effects on cell viability. In this study, the in vivo biocompatibility of unloaded and loaded nanoparticles with osteogenic protein-1 or OP-1 was investigated. Young male Wistar rats were injected intramuscularly and monitored over a period of 10 weeks for signs of inflammation and/or adverse reactions. Blood samples (600 microL/collection) were withdrawn followed by hematological and biochemical analysis. Body weight changes over the treatment period were noted. Major organs were harvested, weighed and examined histologically for any pathological changes. Finally, the injection site was identified and examined immunohistochemically. Overall, all animals showed no obvious toxic health effects, immune responses and/or change in organ functions. This hybrid core-shell nanoparticulate delivery system localizes the effect of the released bioactive load within the site of injection in muscle with no significant tissue distress. Hence, a safe and promising carrier for therapeutic growth factors and possibly other biomolecules is presented.

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

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 microg 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 microg/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.

Biocompatibility of different biopolymers after being implanted into the rat cochlea

OBJECTIVE

To assess the biocompatibility of different biopolymers with cochlea implant.

MATERIALS AND METHODS

Six bioabsorbable polymers and biostable silicone were used for testing histologic reactions in the cochlea of the rat. The samples were prepared from three 50/50 poly(DL-lactide-co-glycolide) PDLLGA having different inherent viscosity (IV) values and 75/25 poly(DL-lactide-co-epsilon-caprolactone) P(DLLA/CL), poly-epsilon-caprolactone PCL, silicone, and chitosan by extruding the biomaterial as a rod using melt molding (for 50/50 PDLLGAs and 75/25 P(DLLA/CL) and PCL), blending (for silicone), and solving (for chitosan). The rods were cut into samples of diameter of 0.5 mm and length of 2 mm. All the samples were packed and sterilized by gamma irradiation (18 kGy, less than 42 degrees C). Twenty-two male and female Sprague-Dawley rats were used in the study. Four months after the implantation, the animals were killed for histologic observation.

RESULTS

Chitosan does not degrade in the cochlea 4 months after implantation and, therefore, stimulates very weak inflammatory reaction. The 50/50 PDLLGA (IV, 0.83 dL/g) degrades in the cochlea 4 months after implantation and does not stimulate inflammatory reaction. The 50/50 PDLLGA (IV, 0.41 dL/g; IV, 0.37 dL/g), 75/25 P(DLLA/CL), PCL, and silicone might induce strong inflammatory reaction in the cochlea.

CONCLUSION

Different degradation property of biomaterials in the cochlea indicates diverse drug releasing time in a controlled way. Chitosan is suitable for long-lasting drug delivery, whereas 50/50 PDLLGA (IV, 0.83 dL/g) favors quicker releasing. Both chitosan and 50/50 PDLLGA (IV, 0.83 dL/g) are ideal materials for cochlear drug delivery.

A porcine collagen-derived matrix as a carrier for recombinant human bone morphogenetic protein-2 enhances spinal fusion in rats

BACKGROUND CONTEXT

Recombinant bone morphogenetic proteins (rhBMPs) have been used successfully in clinical trials. However, large doses of rhBMPs were required to induce adequate bone repair. Collagen sponges (CSs) have failed to allow a more sustained release of rhBMPs. Ongoing research aims to design carriers that allow a more controlled and sustained release of the protein. E-Matrix is a injectable scaffold matrix that may enhance rhBMP activity and stimulate bone regeneration.

PURPOSE

The purpose of this study was to test E-Matrix as a carrier for rhBMPs in a CS and examine its feasibility in clinical applications by using a rat spinal fusion model.

PATIENT SAMPLE

A total of 80 Lewis rats aged 8-16 weeks were divided into nine groups.

STUDY DESIGN/SETTING

Rat spinal fusion model.

OUTCOME MEASURES

Radiographs were obtained at 4, 6, and 8 weeks. The rats were sacrificed and their spines were explanted and assessed by manual palpation, high-resolution microcomputed tomography (micro-CT), and histologic analysis.

METHODS

Group I animals were implanted with CS alone (negative control); Group II animals with CS containing 10microg rhBMP-2 (positive control); Group III animals with CS containing 3microg rhBMP-2; Group IV animals with CS containing 3microg rhBMP-2 and E-Matrix; Group V animals with CS containing 1microg rhBMP-2; Group VI animals with CS containing 1microg rhBMP-2 and E-Matrix; Group VII animals with CS containing 0.5microg rhBMP-2; Group VIII animals with CS containing 0.5microg rhBMP-2 and E-Matrix; and Group IX animals with CS and E-Matrix without rhBMP-2.

RESULTS

Radiographic evaluation, micro-CT, and manual palpation revealed spinal fusion in all rats in the BMP-2 and E-Matrix groups (IV, VI, and VIII) and high-dose BMP-2 groups (II and III). Four spines in the 3microg rhBMP-2 group (V) fused, and one spine in the 0.5microg rhBMP-2 group (VII) exhibited fusion. No spines were fused in Groups I (CS alone) and IX (E-Matrix alone). The volume of new bone in the area between the tip of the L4 transverse process and the base of the L5 transverse process in Group IV was equivalent to the volumes observed in Group II.

CONCLUSION

E-matrix enhances spinal fusion as a carrier for rhBMP-2 in a rat spinal fusion model. The results of this study suggest that E-Matrix as a growth factor carrier may be applicable to spinal fusion and may improve rhBMP-2's activity at the fusion site.

Retention of in vitro and in vivo BMP-2 bioactivities in sustained delivery vehicles for bone tissue engineering

In this study, we investigated the in vitro and in vivo biological activities of bone morphogenetic protein 2 (BMP-2) released from four sustained delivery vehicles for bone regeneration. BMP-2 was incorporated into (1) a gelatin hydrogel, (2) poly(lactic-co-glycolic acid) (PLGA) microspheres embedded in a gelatin hydrogel, (3) microspheres embedded in a poly(propylene fumarate) (PPF) scaffold and (4) microspheres embedded in a PPF scaffold surrounded by a gelatin hydrogel. A fraction of the incorporated BMP-2 was radiolabeled with (125)I to determine its in vitro and in vivo release profiles. The release and bioactivity of BMP-2 were tested weekly over a period of 12 weeks in preosteoblast W20-17 cell line culture and in a rat subcutaneous implantation model. Outcome parameters for in vitro and in vivo bioactivities of the released BMP-2 were alkaline phosphatase (AP) induction and bone formation, respectively. The four implant types showed different in vitro release profiles over the 12-week period, which changed significantly upon implantation. The AP induction by BMP-2 released from gelatin implants showed a loss in bioactivity after 6 weeks in culture, while the BMP-2 released from the other implants continued to show bioactivity over the full 12-week period. Micro-CT and histological analysis of the delivery vehicles after 6 weeks of implantation showed significantly more bone in the microsphere/PPF scaffold composites (Implant 3, p<0.02). After 12 weeks, the amount of newly formed bone in the microsphere/PPF scaffolds remained significantly higher than that in the gelatin and microsphere/gelatin hydrogels (p<0.001), however, there was no statistical difference compared to the microsphere/PPF/gelatin composite. Overall, the results from this study show that BMP-2 could be incorporated into various bone tissue engineering composites for sustained release over a prolonged period of time with retention of bioactivity.

Nell-1-induced bone regeneration in calvarial defects

Many craniofacial birth defects contain skeletal components requiring bone grafting. We previously identified the novel secreted osteogenic molecule NELL-1, first noted to be overexpressed during premature bone formation in calvarial sutures of craniosynostosis patients. Nell-1 overexpression significantly increases differentiation and mineralization selectively in osteoblasts, while newborn Nell-1 transgenic mice significantly increase premature bone formation in calvarial sutures. In the current study, cultured calvarial explants isolated from Nell-1 transgenic newborn mice (with mild sagittal synostosis) demonstrated continuous bone growth and overlapping sagittal sutures. Further investigation into gene expression cascades revealed that fibroblast growth factor-2 and transforming growth factor-beta1 stimulated Nell-1 expression, whereas bone morphogenetic protein (BMP)-2 had no direct effect. Additionally, Nell-1-induced osteogenesis in MC3T3-E1 osteoblasts through reduction in the expression of early up-regulated osteogenic regulators (OSX and ALP) but induction of later markers (OPN and OCN). Grafting Nell-1 protein-coated PLGA scaffolds into rat calvarial defects revealed the osteogenic potential of Nell-1 to induce bone regeneration equivalent to BMP-2, whereas immunohistochemistry indicated that Nell-1 reduced osterix-producing cells and increased bone sialoprotein, osteocalcin, and BMP-7 expression. Insights into Nell-1-regulated osteogenesis coupled with its ability to stimulate bone regeneration revealed a potential therapeutic role and an alternative to the currently accepted techniques for bone regeneration.

Novel solvent-free fabrication of biodegradable poly-lactic-glycolic acid (PLGA) capsules for antibiotics and rhBMP-2 delivery

Osteomyelitis has been one of the most common causes of post-operative problems and complications despite the advances in surgical techniques and the availability of newly developed antibiotics. Local antibiotic and growth factor delivery devices for treatment of various surgical infections have been studied recently, especially in the case of orthopedic infections. The report was to develop novel solvent-free biodegradable capsules for antibiotics and growth factors delivery. To fabricate a biodegradable capsule, polylactide-polyglycolide copolymers were pre-mixed with vancomycin. The mixture was then compression molded and sintered to form a cylinder with a cover of 8 mm in diameter. After the addition of 1 and 10 microg recombinant bone morphogenetic protein (rhBMP-2) into the core, an ultrasonic welder was used to seal the capsules. An elution method was employed to characterize the in vitro release characteristics of the antibiotics and the rhBMP-2 over a 30-day period. The HPLC analysis and the bacterial inhibition test showed that biodegradable capsules released high concentrations and activity of vancomycin (well above the minimum inhibition concentration) in vitro for the period of time needed to treat bone infection; i.e. 4-6 weeks. In addition, the results of ELISA and ALP tests also suggested that the capsules released active rhBMP-2 for up to 30 days. By adopting this novel technique, we will be able to fabricate biodegradable capsules of various medicines for long-term drug deliveries.

Comparing ectopic bone growth induced by rhBMP-2 on an absorbable collagen sponge in rat and rabbit models

Recombinant human Bone Morphogenetic Protein-2 (rhBMP-2) is currently employed as an autograft replacement for spinal fusion. The morphogen is incorporated onto its carrier, an absorbable collagen sponge (ACS), in the operating room. Although the effectiveness of the rhBMP-2/ACS implant in stimulating bone formation in human subjects has now been well established, further investigations of its use are necessary to deepen our understanding of its performance. The objective of the present study was to determine whether fluid released from the rhBMP-2/ACS implant could induce bone growth in tissue sites away from the implant site. We first measured the amount of protein in the fluid released from the rhBMP-2-soaked ACS during intraoperative handling. Variables included soak time and degree of compression. In the compression group that most closely approximated intraoperative conditions, more than 95% of the rhBMP-2 protein was retained by the ACS following a 15-min. soak time. This in vitro study was followed by an in vivo ectopic implant experiment using rat and rabbit models. The animal investigation compared the amount of bone induced by rhBMP-2 solution alone versus the de novo bone formation induced by rhBMP-2/ACS implants with varying concentrations of rhBMP-2. No ossicles were found at the sites where rhBMP-2 solution was injected in either animal species. Twenty-two of the 24 subcutaneous sites in the rats implanted with the rhBMP-2/ACS constructs displayed the presence of the typical 4- and 12-week ossicle. There were no noticeable differences in the size and shape of the ossicles after 4 and 12 weeks. There was a greater percentage of implant sites without ossicles in the rabbits, compared to the rats.

A novel hydroxyapatite fiber mesh as a carrier for recombinant human bone morphogenetic protein-2 enhances bone union in rat posterolateral fusion model

STUDY DESIGN

An experimental study, in which spinal fusion in rats was conducted using a hydroxyapatite fiber mesh (HAM) as a carrier for recombinant human bone morphogenetic protein (rhBMP)-2.

OBJECTIVES

To study the usefulness of the HAM as a carrier and seek the possibility of clinical application in spinal fusion.

SUMMARY OF BACKGROUND DATA

Several biomaterials have been used as a carrier for BMP to achieve spine fusion, however, to our knowledge, the most effective carrier has not been established.

METHODS

In experiment No. 1, HAMs and the controls (commercially available hydroxyapatite ceramic body), loaded with rhBMP-2, were immersed in phosphate-buffered saline to evaluate the time course of the release of rhBMP-2. In experiment No. 2, posterolateral fusion was conducted in rats using HAM and the control loaded with rhBMP-2. The fusion status was evaluated radiologically and histologically after surgery.

RESULTS

In experiment No. 1, HAMs released a larger amount of rhBMP-2 for up to 28 days than the controls (49.5% vs 7.8%). In experiment No. 2, the fusion rate was significantly higher in the HAM group (>80%) than in the control group (20%). Dense new bone formed close to the spine, and the HAMs were markedly absorbed compared with the controls.

CONCLUSION

HAM provided more solid fusion mass than the control, suggesting that HAM is an efficient carrier for BMP.

Intramuscular delivery of DNA releasing microspheres: microsphere properties and transgene expression

Plasmid-loaded microspheres can provide localized and sustained release into the target tissue, and thus have the potential to enhance the efficiency of naked DNA at promoting transgene expression. In this report, microsphere design parameters are investigated by correlating the extent and duration of transgene expression intramuscularly to the polymer molecular weight and the mass of DNA delivered. Plasmid DNA was incorporated into poly (lactide-co-glycolide) microspheres using a cryogenic double emulsion process, and microspheres were injected intramuscularly. Bolus injection of naked plasmid was used for control, which exhibited transfection of muscle cells with transgene expression that gradually decreased over time. Microspheres fabricated from low molecular weight polymer had expression levels that increased from day 1 to day 92, which subsequently decreased through day 174. Decreasing the microsphere mass delivered resulted in steady expression during the same time. However, microspheres fabricated with high molecular weight polymer had expression for only 14 days. Intramuscular injection resulted in a foreign body response to the microspheres, and these infiltrating cells adjacent were primarily transfected. This understanding of microsphere properties that determine transgene expression and the distribution of transfected cells may facilitate their application to fields such as tissue engineering or DNA vaccines.

Carrier materials for spinal fusion

BACKGROUND CONTEXT

The rise in spinal fusion procedures has led to an increase in the available number and variety of bone graft substitutes. As our understanding of the biologic processes that influence bony fusion has improved, appreciation for the role of the carrier material involved in bone grafts has also increased.

PURPOSE

The abundance of products available leaves a surgeon with many choices. Knowledge of the current advances will allow for more critical review of the literature and improved decision making when choosing bone graft materials.

STUDY DESIGN/SETTING

Review of the English-language literature.

METHODS

A critical review of basic science, animal and human studies that investigate the types and role of carrier materials used in spine surgery.

RESULTS

The myriad of carrier material available to the spine surgeon is related to the many options in bone graft material. Allograft is an important osteoconductive agent but has its disadvantages especially in regard to disease transmission and immunogenicity. Collagen in various forms is an effective carrier for bone morphogenic protein and autogenous stem cells and can be easily combined with other bone graft materials. Synthetic options include hydroxyapatite and calcium phosphate ceramic materials with different formulations; all are osteoconductive only but can be combined with osteoinductive and/or osteogenic components. Bioabsorbable carriers are effective for use with bone morphogenic protein and can also be used in multiple forms and settings.

CONCLUSIONS

Many bone graft carriers exist, and multiple studies have shown their efficacy. It appears that no one carrier is ideal but each situation might influence the choice of one carrier over another.

Ectopic osteoinduction and early degradation of recombinant human bone morphogenetic protein-2-loaded porous β-tricalcium phosphate in mice

The present study investigated the ectopic osteoinduction and early degradation of recombinant human bone morphogenetic protein-2 (rhBMP-2)-loaded porous beta-tricalcium phosphate (beta-TCP) in mice. The porous beta-TCP with 50 microg of rhBMP-2 (n = 25) and porous beta-TCP (control group, n = 25) were implanted into muscle pouches in the right and left thigh of 28-day-old mice (n = 25), respectively. At every time point (3, 7, 14, 21 and 28 days after implantation), five mice were euthanized and the histological examinations of implantation sites were performed. In addition, the alkaline phosphatase (ALP) activity was also quantitatively analyzed. For the rhBMP-2-loaded group, blood vessel formation and immature cartilage was observed within the porous beta-TCP 3 days after implantation. Mature cartilage was observed 7 days after implantation of rhBMP-2-loaded porous beta-TCP. Newly formed woven bone, lamellar bone as well as marrow were observed 14 and 21 days after implantation of the rhBMP-2-loaded porous beta-TCP. Lamellar bone and marrow were observed 28 days after implantation of the rhBMP-2-loaded porous beta-TCP. For the control group, no bone or cartilage was observed at all time points. However, multinucleated giant cells and fibrous tissues were observed in the control group at 7 and 28 days after implantation, respectively. At 21 and 28 days after implantation, porous beta-TCP was observed to fragment indicating early degradation of the porous beta-TCP in both groups. In addition, ALP was observed to be significantly higher in the rhBMP-2-loaded beta-TCP as compared to the control beta-TCP. It was concluded from this study that the rhBMP-2-loaded porous beta-TCP induced blood vessel and ectopic bone formation.

Delivery of bone morphogenetic proteins for orthopedic tissue regeneration

Carriers for bone morphogenetic proteins (BMPs) are used to increase retention of these factors at orthopedic treatment sites for a sufficient period of time to allow regenerative tissue forming cells to migrate to the area of injury and to proliferate and differentiate. Carriers can also serve as a matrix for cell infiltration while maintaining the volume in which repair tissue can form. Carriers have to be biocompatible and are often required to be bioresorbable. Carriers also have to be easily, and cost-effectively, manufactured for large-scale production, conveniently sterilized and have appropriate storage requirements and stability. All of these processes have to be approvable by regulatory agencies. The four major categories of BMP carrier materials include natural polymers, inorganic materials, synthetic polymers, composites of these materials. Autograft or allograft carriers have also used. Carrier configurations range from simple depot delivery systems to more complex systems mimicking the extracellular matrix structure and function. Bone regenerative carriers include depot delivery systems for fracture repair, three-dimensional polymer or ceramic composites for segmental repairs and spine fusion and metal or metal/ceramic composites for augmenting implant integration. Tendon/ligament regenerative carriers range from depot delivery systems to three-dimensional carriers that are either randomly oriented or linearly oriented to improve regenerative tissue alignment. Cartilage regenerative systems generally require three-dimensional matrices and often incorporate cells in addition to factors to augment the repair. Alternative BMP delivery systems include viral vectors, genetically altered cells, conjugated factors and small molecules.

Novel PCL-based honeycomb scaffolds as drug delivery systems for rhBMP-2

This study investigated a novel drug delivery system (DDS), consisting of polycaprolactone (PCL) or polycaprolactone 20% tricalcium phosphate (PCL-TCP) biodegradable scaffolds, fibrin Tisseel sealant and recombinant bone morphogenetic protein-2 (rhBMP-2) for bone regeneration. PCL and PCL-TCP-fibrin composites displayed a loading efficiency of 70% and 43%, respectively. Fluorescence and scanning electron microscopy revealed sparse clumps of rhBMP-2 particles, non-uniformly distributed on the rods' surface of PCL-fibrin composites. In contrast, individual rhBMP-2 particles were evident and uniformly distributed on the rods' surface of the PCL-TCP-fibrin composites. PCL-fibrin composites loaded with 10 and 20 microg/ml rhBMP-2 demonstrated a triphasic release profile as quantified by an enzyme-linked immunosorbent assay (ELISA). This consisted of burst releases at 2 h, and days 7 and 16. A biphasic release profile was observed for PCL-TCP-fibrin composites loaded with 10 microg/ml rhBMP-2, consisting of burst releases at 2 h and day 14. PCL-TCP-fibrin composites loaded with 20 microg/ml rhBMP-2 showed a tri-phasic release profile, consisting of burst releases at 2 h, and days 10 and 21. We conclude that the addition of TCP caused a delay in rhBMP-2 release. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and alkaline phosphatase assay verified the stability and bioactivity of eluted rhBMP-2 at all time points.

Collagen–chondroitin sulfate-based PLLA–SAIB-coated rhBMP-2 delivery system for bone repair

Bone morphogenetic proteins (BMPs) are osteoinductive proteins used intensively in clinical investigations involving various bone-related treatments. Owing to their high potential in new bone formation they require local application at the treatment site. For this purpose various controlled delivery systems with BMPs as the excipients have been prepared in recent years. Focusing on this clinical need a disc-shaped BMP carrier was designed as a local delivery system using soluble collagen and chondroitin sulfate. In situ release studies carried out with a model protein (FITC-labeled Protein A) presented a very high rate of release; with most of the protein content being released within 24 h. This rate could be decreased by providing a poly(L-lactide) (PLLA) and sucrose acetate isobutyrate-based (SAIB-based) coat around the release system, applied after BMP loading. In this way, it was possible to extend the release period from 24 h to about 12 days. In situ release of BMP from the same carriers, as quantitated using an ELISA kit, was even slower, with 50% of the protein being released in 15 days. In order to be able to secure the BMP delivery system at the bone defect site and to provide support a mesh knitted using Vicryl sutures and bonded with poly(L-lactide-co-glycolide) (PLGA) was tested in in vivo. Two time periods, 1 and 3 weeks, were used to evaluate the healing process. Osteoinduction by the BMP carrier system was assessed by histology-based bone scoring and X-ray examinations. PLLA-SAIB-coated collagen discs containing BMP presented good biocompatibility and optimum osteogenic stimulation. Structural changes in histological micrographs at week 1 indicated dose-dependent periosteal ossification. At the end of week 3 histological findings with both BMP (1 and 2 microg) doses were almost the same.

Regeneration of rat auditory ossicles using recombinant human BMP-2/collagen composites

Tympanoplasty operations to improve hearing impairment require a wide middle ear cavity and reconstruction of columellar formations. There is no specific material for use in the reconstruction of columellar formations. Tissue response to BMP has been employed as regenerative material. To our knowledge, however, there are no reports of the reconstruction of columellar formations using recombinant human bone morphogenetic protein-2/bovine collagen composites in the middle ear. The purpose of this study is to investigate whether recombinant human bone morphogenetic protein-2/bovine collagen composites (rhBMP-2 composites) are appropriate for use as regenerative material for tympanoplasty. In the form of pellets, rhBMP-2 composites were implanted as columellae into the tympanic cavity. At 2, 4, 6, 8, and 12 weeks after surgery, the middle ear of the animals (n = 4 at each week) was stained with hematoxylin-eosin for light microscopic observation. All composites were in the process of ossification or had ossified according to their developmental stages and were covered with a single layer of squamous or cuboidal epithelium. The new bone formed in these composites was persistently stable and displayed some columellar conditions assessed by histological examination. This study led to the conclusion that rhBMP-2 composites make excellent regenerative material for auditory ossicles.

A novel osteotropic biomaterial OG-PLG: Synthesis andin vitro release

Statins (e.g., simvastatin) have shown to induce expression of the bone morphogenic protein-2 gene in bone cells, but they are not used clinically because of a lack of a suitable delivery device. The overall objective is to develop optimized statin delivery devices for bone regeneration. The specific objective was to determine the effect of grafting statins to biodegradable poly[lactide-co-glycolide] (PLG) on release kinetics. Simvastatin was grafted to PLG (OG-PLG) and characterized using contact-angle measurements, attenuated total reflectance-Fourier transform infrared, and ultraviolet-visible spectroscopy to determine success of the synthesis. An ultraviolet-visible assay for measuring release of statins and degraded OG-PLG in media was also developed. In vitro release studies using films and scaffolds made with PLG, PLG blended with simvastatin (PLG + Sim), and OG-PLG (simvastatin grafted to PLG) blended into PLG at different concentrations showed that release rate of OG-PLG from films was significantly greater than that of PLG + Sim. However, release rate from scaffolds showed PLG + Sim to be significantly higher than that of OG-PLG. The diffusion-controlled release kinetics of simvastatin from PLG + Sim seems to be more heavily affected by device morphology, whereas the degradation-controlled release kinetics seem to be less affected. In short, release kinetics can be modulated by grafting statins to PLG.

Dual growth factor delivery and controlled scaffold degradation enhance in vivo bone formation by transplanted bone marrow stromal cells

Supraphysiological concentrations of exogenous growth factors are typically required to obtain bone regeneration, and it is unclear why lower levels are not effective. We hypothesized that delivery of bone progenitor cells along with appropriate combinations of growth factors and scaffold characteristics would allow physiological doses of proteins to be used for therapeutic bone regeneration. We tested this hypothesis by measuring bone formation by rat bone marrow stromal cells (BMSCs) transplanted ectopically in SCID mice using alginate hydrogels. The alginate was gamma-irradiated to vary the degradation rate and then covalently modified with RGD-containing peptides to control cell behavior. In the same delivery vehicle, we incorporated bone morphogenetic protein-2 (BMP2) and transforming growth factor-beta3 (TGF-beta3), either individually or in combination. Individual delivery of BMP2 or TGF-beta3 resulted in negligible bone tissue formation up to 22 weeks, regardless of the implant degradation rate. In contrast, when growth factors were delivered together from readily degradable hydrogels, there was significant bone formation by the transplanted BMSCs as early as 6 weeks after implantation. Furthermore, bone formation, which appeared to occur by endochondral ossification, was achieved with the dual growth factor condition at protein concentrations that were more than an order of magnitude less than those reported previously to be necessary for bone formation. These data demonstrate that appropriate combinations of soluble and biomaterial-mediated regulatory signals in cell-based tissue engineering systems can result in both more efficient and more effective tissue regeneration.

Ectopic bone formation by human bone morphogenetic protein-2 gene transfer to skeletal muscle using transcutaneous electroporation

Therapy using recombinant human bone morphogenetic protein-2 (rhBMP-2) is expected to promote bone healing and regeneration. Previous studies using protein or virus vectors for direct clinical application had problems, including a lack of efficiency, safety, and simplicity of the delivery system, and required an expensive protein, carrier matrix, or antigenic viral vector. In vivo gene transfer by electroporation is a simple and inexpensive method that only requires a plasmid and an electroporation device. Here, we created a plasmid-based human BMP-2 construct (pCAGGS-BMP-2) and examined the induction of bone in the skeletal muscle of rats after transferring different doses of this plasmid (25 microg, 100 microg, and 400 microg) by transcutaneous electroporation (8 electrical pulses of 100 V and 50 msec, in 1 to 5 sessions). First, we verified the gene transfer by transcutaneous electroporation using pCAGGS-lacZ. Next, the BMP-2 gene transfer and the production and localization of BMP-2 were identified by reverse transcription-polymerase chain reaction (RT-PCR), Western blots, and immunohistochemistry. Ectopic bone formation was verified by radiography, histologic and immunohistochemical analyses, and quantitative examination. Ectopic bone formation, consisting of active osteoblasts and osteoclasts, was observed in all rats treated with electroporation. Thus, transcutaneous electroporation with pCAGGS-BMP-2 induced ectopic bone formation in the skeletal muscle of rats. This supports the possibility of applying human BMP-2 gene transfer using transcutaneous electroporation clinically.

Protein-based signaling systems in tissue engineering

Tissue engineering aims to replace damaged tissues or organs using either transplanted cells or host cells recruited to the target site. Protein signaling is crucial to regulate cell phenotype and thus engineered tissue structure and function. Biomaterial vehicles are being designed to incorporate and locally deliver various molecules involved in this signaling, including both growth factors and peptides that mimick whole proteins. Controlling the concentration, local duration and spatial distribution of these factors is key to their utility and efficacy. Recent advances have been made in the development of polymeric delivery systems intended to achieve this control.

Polymeric growth factor delivery strategies for tissue engineering

PURPOSE

Tissue engineering seeks to replace and regrow damaged or diseased tissues and organs from either cells resident in the surrounding tissue or cells transplanted to the tissue site. The purpose of this review is to present the application of polymeric delivery systems for growth factor delivery in tissue engineering.

METHODS

Growth factors direct the phenotype of both differentiated and stem cells, and methods used to deliver these molecules include the development of systems to deliver the protein itself, genes encoding the factor, or cells secreting the factor.

RESULTS

Results in animal models and clinical trials indicate that these approaches may be successfully used to promote the regeneration of numerous tissue types.

CONCLUSIONS

Controlling the dose, location, and duration of these factors through polymeric delivery strategies will dictate their utility in tissue regeneration.

Controllable delivery of non-viral DNA from porous scaffolds

The inductive approach to tissue engineering combines three-dimensional porous scaffolds with drug delivery to direct the action of progenitor cells into a functional tissue. We present an approach to fabricate scaffolds capable of controlled, sustained delivery by the assembly and subsequent fusion of drug-loaded microspheres using a gas foaming/particulate leaching process. DNA-loaded microspheres were fabricated from the copolymers of lactide and glycolide (PLG) using a cryogenic double emulsion process. Microspheres were fabricated in four populations with mean diameters ranging from 12.3 microm to 92.5 microm. Scaffolds fabricated by fusion of these microspheres had an interconnected open pore structure, maintained DNA integrity, and exhibited sustained release for 21 days. Control over the release was obtained through manipulating the properties of the polymer, microspheres, and the foaming process. Decreasing the microsphere diameter or the molecular weight of the polymer used for microsphere fabrication led to increased rates of release from the porous scaffold. Additionally, increasing the pressure of CO(2) increased the DNA release rate. The ability to create porous polymer scaffolds capable of controlled release rates may provide a means to enhance and regulate gene transfer within a developing tissue, which will increase their utility in tissue engineering.