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Injectable Alginate Hydrogel Cross-Linked by Calcium Gluconate-Loaded Porous Microspheres for Cartilage Tissue Engineering.

ABSTRACT: A great interest has been shown in the injectable scaffolds for cartilage tissue regeneration because it can fill irregularly shaped defects easily through minimally invasive surgical treatments. Herein, we developed a new injectable three-dimensional (3D) alginate hydrogel loaded with biodegradable porous poly(?-caprolactone)-b-poly(ethylene glycol)-b-poly(?-caprolactone) microspheres (MPs/Alg) as the calcium gluconate container to cross-link alginate. Suspensions of chondrocytes/alginate and porous microspheres turned into a gel because of the release of calcium gluconate; thus, the injectable composite hydrogels give a 3D scaffold to fit the defects perfectly and integrate the extracellular-matrix-mimicking architecture to efficiently accommodate cartilage cells in situ. Tissue repair in a full-thickness cartilage defect model was controlled at 6, 12, and 18 weeks after the implant by micro-CT and immunohistochemistry to evaluate the healing status. The defect in the MPs/Alg+ cells group achieved an almost complete repair at 18 weeks, and the repaired chondrocytes regained a normal tissue structure. Moreover, the MPs/Alg+ cells-treated group increased the quality of tissue formed, including the accumulated glycosaminoglycan and the uniformly deposited type II collagen. The results point out the promising application of the injectable MPs/Alg-chondrocytes system for cartilage tissue engineering.

SUBMITTER: Liao J

PROVIDER: S-EPMC6044773 | biostudies-literature | 2017 Feb

REPOSITORIES: biostudies-literature

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Project description: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??m) and pore size (?15 vs 30??m) 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. STATEMENT OF SIGNIFICANCE: This manuscript describes a method for solvent-free fabrication of porous microspheres from high internal phase emulsions using a controlled fluids setup. The principles of emulsion templating and fluid dynamics provide exceptional control of particle size and pore architecture. In addition to the advantage of solvent-free fabrication, this method provides in-line loading of protein directly into the pores of the microspheres with high loading efficiencies. The incorporation of the protein-loaded microspheres within an injectable polyHIPE scaffold resulted in a sustained release of protein over a two-week period with minimal burst release. Retention of BMP-2 bioactivity and incorporation of microspheres with minimal effect on scaffold compressive properties highlights the potential of these new bone grafts.

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Injectable Alginate Hydrogel Cross-Linked by Calcium Gluconate-Loaded Porous Microspheres for Cartilage Tissue Engineering.

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