Collagen Microgels for Regenerative Medicine
Creators: name: Rey, Jose
name: Pandit, Abhay
name: Busby, Grahame
name: Salmeron-Sanchez, Manuel
name: Gonzalez-Garcia, Cristina
Publisher: name: Zenodo
Year: 2018
Subjects: Collagen
Microfluidics

description: INTRODUCTION<br> During recent years, microgels have emerged as an effective type of drug delivery system (DDS), showing advantages such as tuneable size, increased surface area and injectability1. Collagen has been extensively studied as a scaffold for regenerative medicine and drug delivery due to its biocompatibility, non-immunogenicity and degradability2,3. The current study focuses on the use of microfluidic techniques for the automated 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. <br> MATERIALS AND METHODS<br> Col-1 (Collagen Solutions, UK) stock was characterized in a rotational viscometer and UV-Vis spectrophotometer to determine the fibrillogenesis conditions. Collagen was crosslinked with 4S-Star-PEG succinimide glutarate (Jenkem, USA) to form hydrogels. Crosslinking occurred after merging col-I with PEG-4S crosslinker in the nozzle of a double-chamber capillary within an oil flow. A coiled tube was placed at the outlet for microgels to gelify inside the device. Microgel size was controlled varying the nozzle diameter and flow speeds, and the mechanical properties modulated through pH and concentration of collagen/crosslinker. Microgels were characterized with TNBS assay and their cytotoxicity with LIVE-DEAD® assay (Neu-7 astrocytes, n=3). Hollow spheres were prepared by covalently attaching collagen to silica templates that are later dissolved with hydrofluoric acid. They were characterized morphologically and chemically, namely: scanning electron microscopy, dynamic light scattering and Fourier-Transform Infrared (FTIR). Hollow spheres were loaded with GDNF and BMP-2 by diffusion, seeded with different cell-types and encapsulated in the microgels within the microfluidic device. <br> RESULTS AND DISCUSSION<br> Microgels with different size and stiffness were successfully synthetized in a glass microfluidic device. The microgels are non-cytotoxic to cells (fig.1C) and foster cell growth at different crosslinker concentrations. In the synthesis of hollow spheres, no harmful by-products appeared (fig.1D), and their size ranged around 200 nm (fig.1E). Microfluidic-generated hydrogels encapsulating hollow spheres can therefore be used for sustained delivery of GDNF and BMP-2.<br> CONCLUSIONS<br> We demonstrate that microfluidics is an adequate technique for automatically generating monodisperse collagen microgels and provides a simple and useful 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 factors.<br> <br> AKNOWLEDGEMENTS<br> The authors would like to thank European Union H2020 Programme (H2020-MSCA-ITN-2015) and Grant No. 676408 for providing financial support to this project. <br>
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