Collagen-PEG composite microspheres for bone regeneration

Abstract

Event Abstract Back to Event Collagen-PEG composite microspheres for bone regeneration Candice Sears1, Sarah Dang2, Colin Dodson1, Allison Rice-Ficht3, Carl Gregory3 and Roland Kaunas1 1 Texas A&M University, Biomedical Engineering, United States 2 Texas A&M University, Chemical Engineering, United States 3 Texas A&M Health Science Center, Molecular and Cellular Medicine, United States Introduction: Of the 5.6 million bone fractures that occur annually in the United States, about 10% fail to repair[1]. The canonical Wingless (cWnt) signaling pathway is critical for healing of bone fractures[2]. We have demonstrated that inhibiting peroxisome proliferator-activating receptor gamma with GW9662 (GW) reduces negative cross-talk on the cWnt pathway, resulting in a pro-osteogenic hMSC phenotype (OEhMSCs)[3]. OEhMSCs secrete an extracellular matrix (hMatrix) that mimics the composition of anabolic bone tissue and strongly enhances hMSC retention and subsequent bone repair in vivo[3]. We designed composite microspheres for co-administration of GW and hMatrix to facilitate cell retention and bone repair in vivo. Materials and Methods: GW was co-dissolved with poly(lactic-co-glycolic acid) (PLGA, 10%, w/v) in dichloromethane and PLGA solution was added to poly(vinyl alcohol) solution (8%, w/v). The solution was added to distilled water, and stirring was continued to obtain spheres that were then sieved to obtain a size of 20-32 µm. Poly(ethylene glycol) diacrylate (PEGDA) spheres containing the PLG microspheres were produced using a continuous-flow emulsion and photocrosslinking technique. The continuous phase consisted of mineral oil with 0.5% Span 80, while the dispersed phase was a solution of PLGA spheres, 30% PEGDA and 8% Lithium phenyl-2,4,6-trimethylbenzoylphosphinate in a functionalized collagen (Acrylate-PEG-Collagen) solution. ELISA and qRT-PCR for osteogenic markers were used to assess osteogenesis. Results and Discussion: An osteogenic microsphere was developed to coadminister hMatrix and GW to enhance hMSC retainment and promote osteorepair in vivo. Initial feasibility was demonstrated using collagen type I since this is the major component of hMatrix. We have functionalized collagen type I with photo-cross-linkable groups[4] to enable their incorporation into PEGDA microspheres. We also loaded GW into PLGA nanoparticles which were encapsulated in the PEGDA spheres and quantified the drug release profile. Specific gene and protein detection by qRT-PCR and osteoprotegerin assay of the adhered hMSCs revealed that GW induced osteogenesis. Conclusions: Conventional hMSC therapies have had limited success in bone regeneration. Autologous bone grafting is the gold standard to regenerate critical sized bone defects. Conversely, this procedure is associated with donor site morbidity and a limited volume of material available. The use of bone morphogenetic proteins have also been used, however, their use is associated with ectopic bone growth, paralysis, and inflammation[5]-[9]. Our composite microspheres incorporate biopolymers such as hMatrix to provide a favorable microenvironment and signal to cells to enhance their performance in vivo. We have developed a method to create microspheres for bone regeneration that provides both chemical and bioactive cues to promote new bone growth for critical sized bone defects.