Microfluidics-Assisted Fabrication of Gelatin-Silica Core–Shell Microgels for Injectable Tissue Constructs

Abstract

Microfabrication technology provides a highly versatile platform for engineering hydrogels used in biomedical applications with high-resolution control and injectability. Herein, we present a strategy of microfluidics-assisted fabrication photo-cross-linkable gelatin microgels, coupled with providing protective silica hydrogel layer on the microgel surface to ultimately generate gelatin-silica core–shell microgels for applications as in vitro cell culture platform and injectable tissue constructs. A microfluidic device having flow-focusing channel geometry was utilized to generate droplets containing methacrylated gelatin (GelMA), followed by a photo-cross-linking step to synthesize GelMA microgels. The size of the microgels could easily be controlled by varying the ratio of flow rates of aqueous and oil phases. Then, the GelMA microgels were used as in vitro cell culture platform to grow cardiac side population cells on the microgel surface. The cells readily adhered on the microgel surface and proliferated over time while maintaining high viability (∼90%). The cells on the microgels were also able to migrate to their surrounding area. In addition, the microgels eventually degraded over time. These results demonstrate that cell-seeded GelMA microgels have a great potential as injectable tissue constructs. Furthermore, we demonstrated that coating the cells on GelMA microgels with biocompatible and biodegradable silica hydrogels via sol–gel method provided significant protection against oxidative stress which is often encountered during and after injection into host tissues, and detrimental to the cells. Overall, the microfluidic approach to generate cell-adhesive microgel core, coupled with silica hydrogels as a protective shell, will be highly useful as a cell culture platform to generate a wide range of injectable tissue constructs.

An automated system for high-throughput generation and optimization of microdroplets

“…19 Therefore, 20% surfactant has been widely-used for generating hydrogel droplets. 15,16 The viscosity of PBS and 8% PEGDA solution was measured by a viscometer (Cannon Instrument, State College, PA, USA).…”

“…Electronic mail: keekyoung.kim@ubc.ca and simple device fabrication process. 14 Flow-focusing devices were used to generate hydrogel microdroplets for seeding cells, 15 cell-laden hydrogel microdroplets, 16 and magnetically controllable droplets. 17 Fig.…”

“…The diameter of droplets is a key indicator of the size of droplets and has been widely used to characterize droplet generation mechanism. 8,10,14,15,19 The two most common methods to measure the diameter of droplets are optical sensing and electrical sensing. The electrical sensing is a low-cost, scalable method and uses the electrical property difference between aqueous and oil phase to detect the diameter of droplets.…”

“…15,19 This manual process is ineffective, time-consuming, and labor intensive, since the process includes first manually adjusting the syringe pumps to control the flow rates, waiting until the flows reach equilibrium, and checking whether the diameter of specific droplets meet their requirement or not. Here, for the first time, we present an automated droplet generation and optimization system which is based on the image processing and digital feedback control.…”

Advances in monoliths and related porous materials for microfluidics

“…Additionally, the endothelial layer of cells protected the interstitial cells from shear stress, consistent with macroscale models. Similarly, gelatin-methacrylate hydrogels photopolymerized in a microfluidic flow focusing PDMS device were used as an elastic scaffold by Cha et al 99 Cells proliferating on the hydrogel surface were promising for transplantation into a host. To reduce the oxidative and mechanical stress, as well as decrease the immune response associated with transplantation, a protective biodegradable silica hydrogel shell was formed over the cardiac side population cell seeded microgels.…”