Injectable PolyHIPEs as High-Porosity Bone Grafts

Abstract

Polymerization of high internal phase emulsions (polyHIPEs) is a relatively new method for the production of high porosity scaffolds. The tunable architecture of these polyHIPE foams make them attractive candidates for tissue engineered bone grafts. Previously studied polyHIPE systems require either toxic diluents or high cure temperatures which prohibit their use as an injectable bone graft. In contrast, we have developed an injectable polyHIPE that cures at physiological temperatures to a rigid, high-porosity foam. First, a biodegradable macromer, propylene fumarate dimethacrylate (PFDMA), was synthesized that has appropriate viscosity and hydrophobicity for emulsification. The process of surfactant selection is detailed with particular focus on the key structural features of both polymer (log P values, hydrogen bond acceptor sites) and surfactant (HLB values, hydrogen bond donor sites) that enable stable HIPE formation. Incubation of HIPEs at 37°C was used to initiate radical crosslinking of the unsaturated double bond of the methacrylate groups to polymerize the continuous phase and lock in the emulsion geometry. The resulting polyHIPEs exhibited ~75% porosity, pore sizes ranging from 4 to 29 μm, and an average compressive modulus and strength of 33 and 5 MPa, respectively. These findings highlight the great potential of these scaffolds as injectable, tissue engineered bone grafts.

Osteoinductive PolyHIPE Foams as Injectable Bone Grafts

“…Altering compositional and processing parameters results in monoliths with a range of pore sizes, porosities, pore morphologies (open vs. closed), compressive properties, and cure times. [1][2][3][4][5][6][7][8][9][10][11] However, a major challenge in designing functional bone grafts is determining a material composition that promotes ingrowth of surrounding bone and proliferation of cells (osteoconduction), the differentiation of progenitor cells down an osteoblastic lineage (osteoinduction), and osseointegration with the native bone. Various scaffold chemistries and bioactive agents are currently being studied to determine a matrix that presents cues to stimulate osteoblastic differentiation of human mesenchymal stem cells (hMSCs) and promote integration and healing.…”

Degradable emulsion-templated scaffolds for tissue engineering from thiol–ene photopolymerisation

“…This imparts (bio)degradability to these materials and opens up the prospect of their use as scaffolds for tissue engineering. Emulsion-templated scaffolds have previously been explored as scaffolds for tissue engineering [26][27][28][33][34][35][36][37][38][39][40][41] , however in almost all cases the materials used contain significant amounts of non-degradable carbon backbone polymer chains, potentially limiting their clinical applicability (the exception are enzymatically crosslinked gelatin scaffolds developed by Barbetta et al 28 ). In addition, non-degradable styrene-based polyHIPEs have been used extensively for in vitro 3D cell culture [42][43][44][45] …”

Protein Immobilization onto Poly(acrylic acid) Functional Macroporous PolyHIPE Obtained by Surface-Initiated ARGET ATRP

“…11 A material that has received increasing attention in that respect is prepared from concentred high internal phase emulsions (HIPE) containing more than 74% internal phase volume. 12,13,14,15 If the continuous phase contains one or more monomeric species and polymerization is initiated, highly porous materials referred to as polyHIPEs are produced once the dispersed phase droplets are removed. Initially developed by Unilever 16 , polyHIPE preparation traditionally involves the formation of a stable concentred water-in-oil emulsion using hydrophopic monomers as part of the continuous phase and an aqueous phase as the dispersed phase.…”