(600g) Controlled Release of Growth Factors for Bone Regeneration from Two-Phase Hydrogel Systems

Controlled and localized growth factor delivery for bone regeneration remains a major challenge due to the difficulty in achieving sustained release for long-term bone healing and avoiding rapid burst release upon administration. The direct delivery of growth factors is often limited by rapid diffusion and the activity of proteolytic enzymes. Encapsulation of growth factors within micro- or nano-carriers is a promising strategy for growth factor delivery that can provide greater control over their release kinetics by varying parameters such as particle size, crosslinking ratio, and hydrophilicity, as well as protecting the cargo from enzymatic degradation. However, to avoid rapid diffusion from the site of administration, nanoparticles may be combined with hydrogels, which are an attractive choice for use in regenerative medicine due to their ability to provide biocompatible substrates for cell attachment and further control the delivery of therapeutic agents by providing additional barriers to diffusion. Here, we have designed and characterized hydrogels containing polymeric nanoparticles that can deliver multiple agents with different release profiles. We explore strategies in which multiple crosslinked network structures can be used to tune the delivery of therapeutic agents, such as growth factors.

Copolymeric nanoparticles containing methacrylic acid and methyl methacrylate and crosslinked with varying densities of tertraethylene glycol dimethacrylate were synthesized using an aqueous, one-pot UV-initiated emulsion polymerization. Nanoparticle composition was confirmed using Fourier-transform infrared spectroscopy and methacrylic acid incorporation was confirmed using potentiometric titration. Nanoparticle swelling studies was performed using dynamic light scattering and particle zeta potential was analyzed using electrophoretic light scattering. Bioactive agent delivery capacity was studied using a-chymotrypsin as a model protein for bone morphogenetic protein-2, a widely studied growth factor for bone regeneration. Nanoparticles with increased methacrylic acid content were able to achieve higher loading efficiencies up to 90%. After loading the nanoparticles with model proteins by equilibrium partitioning, nanoparticles were covalently attached to 2 wt% chitosan hydrogels via carbodiimide chemistry. Protein loading and release was quantified using microBCA assay. By increasing crosslinking density and methacrylic acid content in the nanoparticles, the burst release of model protein was reduced from 60% to 5% in the first 24 hours. In addition, covalent binding of nanoparticles to chitosan scaffolds improved protein retention within the scaffold over 4 weeks. The results of this work suggest that growth factor delivery can be tuned through nanoparticle properties and that the synthesized dual network system shows promise for sustained growth factor delivery by reducing burst release effects

Acknowledgements: The work was supported in part by National Institutes of Health Grant R01-EB022025 and the Cockrell Family Regents Chair in Engineering. M.S. was supported by an NSF GRFP.