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Objectives:During recent years, microgels have emerged as an effective type of drug delivery system (DDS), due to their tuneable size, increased surface area and injectability. The current study focuses on the use of microfluidic techniques for the generation of monodisperse type-I collagen (col-I) microgels crosslinked with PEG-4S, encapsulating hollow collagen spheres with glial-derived neurotrophic factor (GDNF) and bone morphogenetic protein 2 (BMP-2) for regenerative therapies in Parkinson’s Disease and bone repair, respectively. Methods:Col-I (Collagen Solutions, UK) was crosslinked with 4S-Star-PEG succinimide glutarate (Jenkem, USA). Crosslinking occurred after merging col-I with PEG-4S crosslinker in the nozzle of a double-chamber capillary within an oil flow, gelification being completed in a coiled tube. Microgel size and mechanical properties were controlled with e.g. nozzle size and pH. Microgels were characterized with TNBS assay and their cytotoxicity with LIVE-DEAD® assay. Hollow spheres were prepared by covalently attaching collagen to silica templates which are later dissolved with hydrofluoric acid. Morphochemical characterization included: scanning electron microscopy, and Fourier-Transform Infrared. Hollow spheres were loaded with GDNF and BMP-2, seeded with different cell-types and encapsulated in the microgels within the microfluidic device. Results:Microgels with different size and stiffness were successfully synthetized in a glass microfluidic device. The microgels are non-cytotoxic to cells and foster cell growth at different crosslinker concentrations. In the synthesis of hollow spheres, no harmful by-products appeared, and their size ranged around 200 nm. Discussion:We demonstrate that microfluidics is an adequate technique for automatically generating monodisperse collagen microgels, and provides a simple tool for the posterior encapsulation of nanospheres and cells. The combination of microgels encapsulating hollow spheres is expected to provide a controlled and sustained delivery system of different therapeutic molecules. |
