Porous PolyHIPE microspheres for protein delivery from an injectable bone graft

Abstract

Delivery of osteoinductive factors such as bone morphogenetic protein 2 (BMP-2) has emerged as a prominent strategy to improve regeneration in bone grafting procedures. However, it remains challenging to identify a carrier that provides the requisite loading efficiency and release kinetics without compromising the mechanical properties of the bone graft. Previously, we reported on porous, polymerized high internal phase emulsion (polyHIPE) microspheres fabricated using controlled fluidics. Uniquely, this solvent-free method provides advantages over current microsphere fabrication strategies including in-line loading of growth factors to improve loading efficiency. In the current study, we utilized this platform to fabricate protein-loaded microspheres and investigated the effect of particle size (~400 vs ~800 μm) and pore size (~15 vs 30 μm) on release profiles. Although there was no significant effect of these variables on the substantial burst release profile of the microspheres, the incorporation of the protein-loaded microspheres within the injectable polyHIPE resulted in a sustained release of protein from the bulk scaffold over a two-week period with minimal burst release. Bioactivity retention of encapsulated BMP-2 was confirmed first using a genetically-modified osteoblast reporter cell line. A functional assay with human mesenchymal stem cells established that the BMP-2 release from microspheres induced osteogenic differentiation. Finally, microsphere incorporation had minimal effect on the cure and compressive properties of an injectable polyHIPE bone graft. Overall, this work demonstrates that these microsphere-polyHIPE composites have strong potential to enhance bone regeneration through controlled release of BMP-2 and other growth factors.

Basic Principles of Emulsion Templating and Its Use as an Emerging Manufacturing Method of Tissue Engineering Scaffolds

“…They reported that while the encapsulation efficiency of their system was up to 73%, but this efficiency reduced to as low as 15% in the processes which require purification. In the follow-up study from the same group, they have shown the sustained release of BMP-2 in at least 14 days, and the retention of bioactivity was confirmed by osteogenic differentiation of osteoblasts cultured on these microspheres (Whitely et al, 2019).…”

“…Microporous PolyHIPE particles can be applied to the defect site by injecting and used as substrates for controlled drug delivery ( Moglia et al, 2014a ; Whitely et al, 2019 ). They can be created using multiphasic emulsion systems that are mostly water-in-oil-in-water (w/o/w) emulsions.…”

Porous Polymers from High Internal Phase Emulsions as Scaffolds for Biological Applications

“…Unlike styrene-based polyHIPEs, acrylate-based ones are degradable to a certain extent and have a larger selection of monomers that can be used in the polymerisation procedures. Examples of such monomers are ethylene glycol dimethacrylate (EGDMA), propylene fumarate dimethacrylate (PFDMA), trimethylolpropane triacrylate (TMPTA), EHA, butanediol dimethacrylate (BDMA), glycerol monomethacrylate (GMMA) and hydroxyethylmethacrylate (HEMA), to name a few [ 56 , 57 , 58 ]. For example, EGDMA and PFDMA have been used for the culture of human mesenchymal stem cells (hMSCs).…”

“…For example, EGDMA and PFDMA have been used for the culture of human mesenchymal stem cells (hMSCs). Both have been shown to have high cell viabilities of the seeded hMSCs (90% in the case of PFDMA) [ 56 ]. A copolymer made up of EGDMA, PFDMA and BDMA was also shown to have high cell viability for hMSCs [ 57 ].…”

Self-Encapsulation of Biomacromolecule Drugs in Porous Microscaffolds with Aqueous Two-Phase Systems

“…Whitely M. et al found that high protein loading efficiencies were achieved in porous microspheres. Although there is a short period of explosive release, the protein sustained released with minimal burst release [ 6 ]. Protein is encapsulated into porous microparticles/microscaffolds to avoid the problems caused by traditional preparation methods.…”