Design of electrohydrodynamic sprayed polyethylene glycol hydrogel microspheres for cell encapsulation

Hydrogel Biomaterials for Stem Cell Microencapsulation

Stem cell transplantation has been recognized as a promising strategy to induce the regeneration of injured and diseased tissues and sustain therapeutic molecules for prolonged periods in vivo. However, stem cell-based therapy is often ineffective due to low survival, poor engraftment, and a lack of site-specificity. Hydrogels can offer several advantages as cell delivery vehicles, including cell stabilization and the provision of tissue-like environments with specific cellular signals; however, the administration of bulk hydrogels is still not appropriate to obtain safe and effective outcomes. Hence, stem cell encapsulation in uniform micro-sized hydrogels and their transplantation in vivo have recently garnered great attention for minimally invasive administration and the enhancement of therapeutic activities of the transplanted stem cells. Several important methods for stem cell microencapsulation are described in this review. In addition, various natural and synthetic polymers, which have been employed for the microencapsulation of stem cells, are reviewed in this article.

Assembly of PEG Microgels into Porous Cell-Instructive 3D Scaffolds via Thiol-Ene Click Chemistry

The assembly of microgel building blocks into 3D scaffolds is an emerging strategy for tissue engineering. A key advantage is that the inherent microporosity of these scaffolds provides cells with a more permissive environment than conventional nanoporous hydrogels. Here, norbornene-bearing poly(ethylene glycol) (PEG) based microgels are assembled into 3D cell-instructive scaffolds using a PEG-dithiol linker and thiol-ene click photopolymerization. The bulk modulus of these materials depends primarily on the crosslink density of the microgel building blocks. However, the linker and initiator concentrations used during assembly have significant effects on cell spreading and proliferation when human mesenchymal stem cells (hMSCs) are incorporated in the scaffolds. The cell response is also affected by the properties of the modular microgel building blocks, as hMSCs growing in scaffolds assembled from stiff but not soft microgels activate Yes-associated protein signaling. These results indicate that PEG microgel scaffolds assembled via thiol-ene click chemistry can be engineered to provide a cell-instructive 3D milieu, making them a promising 3D platform for tissue engineering.

Intra-articular drug delivery systems for joint diseases

Intra-articular (IA) injections directly deliver high concentrations of therapeutics to the joint space and are routinely used in various musculoskeletal conditions such as osteoarthritis (OA) and rheumatoid arthritis (RA). However, current IA-injected drugs are rapidly cleared and do not significantly affect the course of joint disease. In this review, we highlight recent developments in IA therapy, with a special emphasis on current and emerging therapeutic carriers and their potential to deliver disease-modifying treatment modalities for arthritis. Recent IA approaches concentrate on platforms that are safe with efficient tissue penetration, and readily translatable for controlled and sustained delivery of therapeutic agents. Gene therapy delivered by viral or non-viral vectors and cell-based therapy for cartilage preservation and regeneration are being intensively explored.