Cell type specific microspheres incorporating growth factors as injectable cell carriers for tissue repair

The detection, isolation and sorting of cells holds an important role in cell therapy and regenerative medicine. Also, injectable systems have been explored for tissue regeneration in vivo, because it allows repairing complex shaped tissue defects through minimally invasive procedures. Here, we report the use of polymeric microspheres to simultaneously isolate and enrich specific cell types that can be also used as an injectable cell carrier system to form small tissue constructs in situ. The rationale was to functionalize the particles with antibodies to target specific cell types and release growth factors (GFs), first to increase the number of cells growing over the particle surface and then induce the differentiation of these cells by a sustained release from the particle core. GFs loaded microspheres of photocrosslinkable chitosan were fabricated using a flow focusing microfluidic chip. The droplets produced were crosslinked by UV while flowing inside a Tygon tube before being collected into an eppendorf. Monoclonal antibodies against cell surface antigens specific to endothelial cells and stem cells were immobilized on the surface of the microspheres. Experimental results showed that the microfabricated spheres provide suitable surfaces to capture a target cell type and subsequent expansion of the captured cells. The aggregation of the functionalized microspheres has been also shown to successfully form 3D robust structures upon injection into a mold.