Injectable Stem Cell‐Laden Photocrosslinkable Microspheres Fabricated Using Microfluidics for Rapid Generation of Osteogenic Tissue Constructs

Abstract

Direct injection is a minimally invasive method of stem cell transplantation for numerous injuries and diseases. However, despite its promising potential, its clinical translation is diffi cult due to the low cell retention and engraftment after injection. With high versatility, high-resolution control and injectability, microfabrication of stem-cell laden biomedical hydrogels holds great potential as minimally invasive technology. Herein, a strategy of microfl uidicsassisted technology entrapping bone marrow-derived mesenchymal stem cells (BMSCs) and growth factors in photocrosslinkable gelatin (GelMA) microspheres to ultimately generate injectable osteogenic tissue constructs is presented. Additionally, it is demonstrated that the GelMA microspheres can sustain stem cell viability, support cell spreading inside the microspheres and migration from the interior to the surface as well as enhance cell proliferation. This fi nding shows that encapsulated cells have the potential to directly and actively participate in the regeneration process. Furthermore, it is found that BMSCs encapsulated in GelMA microspheres show enhanced osteogenesis in vitro and in vivo, associated with a signifi cant increase in mineralization. In short, the proposed strategy can be utilized to facilitate bone regeneration with minimum invasiveness, and can potentially be applied along with other matrices for extended applications. One potential attractive strategy for stem cell delivery that overcomes these limitations is to suspend the stem cells in hydrogels which can be injected and solidifi ed in situ . Hydrogels have a high water content, similar to tissues, which not only enables homogeneous encapsulation of cells and growth factors, but also allows for facile delivery via injection. Their readily tunable degradation properties provide further control over the release behavior of incorporated cargo material. [ 5 ] Hydrogels of synthetic origin, poly (ethylene glycol) diacrylate (PEGDA), [ 6 ] and of natural origin, such as hyaluronic acid (HA), [ 7 ] alginate, [ 8 ] collagen, [ 9 ] and gelatin [ 10 ] have been tested. However, their clinical success has frequently been impeded by insuffi cient oxygen and nutrient supply due to the large size of the bone defects, which compromises cell survival and performance, resulting in poor bone regeneration. [ 11 ] Furthermore, the bulk environment and the limited interfacial interactions between the cells and the hydrogel material restrict tissue regeneration. Therefore, development of alternate hydrogel geometries for stem cell delivery is required to further drive clinical translation of BMSC-based bone repair strategies. DOIOne such geometry is hydrogel microspheres which can encapsulate both stem cells and their growth factors; they facilitate nutrient and waste transfer and thereby maintain the viability of preseeded cells, while also preserving the scaffold's injectability. [ 12,13 ] In addition, such 3D scaffolds have large surface area which improves cell-matrix interactions. Thus the us...

Cell-laden microfluidic microgels for tissue regeneration

“…18 Bioactive and cell-adhesive motifs in gelatin promote cell attachment and proliferation, while matrix metalloprotease (MMP)-sensitive degradation sites enable gelatin-containing microgels to be easily degraded to release the encapsulated cells. 7,83 Furthermore, gelatin is cytocompatible and shows lower antigenicity compared to collagen. 84 At room temperature, gelatin solidifies due to its extensive physical bonds.…”

“…6,7 Cell-laden microgels have been used in tissue engineering applications as building blocks for complex tissue mimics, 8 co-culture systems for developing three-dimensional organ models, 9 and controlled microenvironments for directing stem cell differentiation. 10 In all of these applications, control over the size and size distribution of the microgels is important as they can influence the phenotypes of the encapsulated cells.…”

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