Bioactive dextran-based scaffolds from emulsion templates co-stabilized by poly(lactic-co-glycolic acid) nanocarriers

Porous polymer scaffolds are widely investigated as temporary implants in regenerative medicine to repair damaged tissues. While biocompatibility, degradability, mechanical properties comparable to the native tissues and controlled porosity are prerequisite for these scaffolds, their loading with pharmaceutical or biological active ingredients such as growth factors, in particular proteins, opens up new perspective for tissue engineering applications. This implies the development of scaffold loading strategies that minimize the risk of protein denaturation and allow to control their release profile. This work reports on a straightforward method for preparing bioactive dextran-based scaffolds from high internal phase emulsion (HIPE) templates containing poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) serving both as co-stabilizers for the emulsion and nanocarriers for drug or therapeutic protein models. Scaffold synthesis are achieved by photocuring of methacrylated dextran located in the external phase of a HIPE stabilized by the NPs in combination or not with a non-ionic surfactant. Fluorescent labelling of the NPs highlights their integration in the scaffold. The introduction of NPs, and even more so when combined with a surfactant, increases the stability and mechanical properties of the scaffolds. Cell viability tests demonstrate the non-toxic nature of these NPs-loaded scaffolds. The study of the release of a model protein from the scaffold, namely lysozyme, shows that its encapsulation in nanoparticles decreases the release rate and provides additional control over the release profile.

Hydroxyapatite nanoparticle-modified porous bone grafts with improved cell attachment

Emulsion-templated foams have displayed promise as injectable bone grafts; however, the use of a surfactant as an emulsifier resulted in relatively small pores and impedes cell attachment. Hydroxyapatite nanoparticles were explored as an alternative stabilizer to address these limitations. To this end, hydroxyapatite nanoparticles were first modified with myristic acid to generate the appropriate balance of hydrophobicity to stabilize a water-in-oil emulsion of neopentyl glycol diacrylate and 1,4-butanedithiol. In situ surface modification of the resulting foam with hydroxyapatite was confirmed with elemental mapping and transmission electron microscopy. Nanoparticle-stabilized foams displayed improved human mesenchymal stem cell viability (91 ± 5%) over surfactant-stabilized foams (23 ± 11%). Although the pore size was appropriate for bone grafting applications (115 ± 71 μm), the foams lacked the interconnected architecture necessary for cell infiltration. We hypothesized that a co-stabilization approach with both surfactant and nanoparticles could be used to achieve interconnected pores while maintaining improved cell attachment and larger pore sizes. A range of hydroxyapatite nanoparticle and surfactant concentrations were investigated to determine the effects on microarchitecture and cell behavior. By balancing these interactions, a co-stabilized foam was identified that possessed large, interconnected pores (108 ± 67 μm) and improved cell viability and attachment. The co-stabilized foam was then evaluated as an injectable bone graft including network formation, microscale integration with bone, push out strength, and compressive properties. Overall, this work demonstrated that in situ surface modification with nHA improved cell attachment while retaining desirable bone grafting features and injectability.

Synthesis and Applications of Elastomeric Polymerized High Internal Phase Emulsions (PolyHIPEs)

Polymer foams (PFs) are among the most industrially produced polymeric materials, and they are found in applications including aerospace, packaging, textiles, and biomaterials. PFs are predominantly prepared using gas-blowing techniques, but PFs can also be prepared from templating techniques such as polymerized high internal phase emulsions (polyHIPEs). PolyHIPEs have many experimental design variables which control the physical, mechanical, and chemical properties of the resulting PFs. Both rigid and elastic polyHIPEs can be prepared, but while elastomeric polyHIPEs are less commonly reported than hard polyHIPEs, elastomeric polyHIPEs are instrumental in the realization of new materials in applications including flexible separation membranes, energy storage in soft robotics, and 3D-printed soft tissue engineering scaffolds. Furthermore, there are few limitations to the types of polymers and polymerization methods that have been used to prepare elastic polyHIPEs due to the wide range of polymerization conditions that are compatible with the polyHIPE method. In this review, an overview of the chemistry used to prepare elastic polyHIPEs from early reports to modern polymerization methods is provided, focusing on the applications that flexible polyHIPEs are used in. The review consists of four sections organized around polymer classes used in the preparation of polyHIPEs: (meth)acrylics and (meth)acrylamides, silicones, polyesters and polyurethanes, and naturally occurring polymers. Within each section, the common properties, current challenges, and an outlook is suggested on where elastomeric polyHIPEs can be expected to continue to make broad, positive impacts on materials and technology for the future.