Bio-functionalized silk hydrogel microfluidic systems

Abstract

Bio-functionalized microfluidic systems were developed based on a silk protein hydrogel elastomeric materials. A facile multilayer fabrication method using gelatin sacrificial molding and layer-by-layer assembly was implemented to construct interconnected, three dimensional (3D) microchannel networks in silk hydrogels at 100 μm minimum feature resolution. Mechanically activated valves were implemented to demonstrate pneumatic control of microflow. The silk hydrogel microfluidics exhibit controllable mechanical properties, long-term stability in various environmental conditions, tunable in vitro and in vivo degradability in addition to optical transparency, providing unique features for cell/tissue-related applications than conventional polydimethylsiloxane (PDMS) and existing hydrogel-based microfluidic options. As demonstrated in the work here, the all aqueous-based fabrication process at ambient conditions enabled the incorporation of active biological substances in the bulk phase of these new silk microfluidic systems during device fabrication, including enzymes and living cells, which are able to interact with the fluid flow in the microchannels. These silk hydrogel-based microfluidic systems offer new opportunities in engineering active diagnostic devices, tissues and organs that could be integrated in vivo, and for on-chip cell sensing systems.

Enzymatically crosslinked silk-hyaluronic acid hydrogels

“…These other degradable polymers often require the addition of functional groups to facilitate crosslinking, have mechanical properties limited to a few kPa and rapidly degrade in vivo . As observed in silk-based enzymatically crosslinked hydrogels, depending on the degree of crosslinking and external environmental stimuli, the tendency of silk to self-assemble into ß-sheet secondary structures results in stiffening of the initial crosslinked gels over time [13, 47, 48]. Therefore, silk-HA composite hydrogels were formed in hopes to develop a hybrid scaffold with unique properties that cannot be achieved with single polymer materials.…”

“…Additionally, other silk-based hydrogels using a similar method of preparation, showed mechanical properties and extent of stiffening controllable by altering silk molecular weight and concentration [13, 59], as well as the ratios of the cross-linking components [48], which if applied to the silk-HA hybrid system, can further the versatility and tunability of the hydrogels.…”

Spatially and temporally controlled hydrogels for tissue engineering

“…For example, the use of multiple positive and negative replica molds expands the possibilities of the technique and allows the replication of the superficial features and volumetric shapes of practically any object. Gelatin has been widely used as a sacrificial molding material [41, 42]. After crosslinking of the prepolymer solution, the gelatin molding can be sacrificed by heating the mold to above 37 °C.…”

“…After crosslinking of the prepolymer solution, the gelatin molding can be sacrificed by heating the mold to above 37 °C. For example, Zhao et al used gelatin as the sacrificial material to cast channels within microfluidic devices made from silk fibroin-based hydrogels [42]. Other sacrificial materials including sugars and proteins have been demonstrated [38].…”

Microfluidic On-Chip Biomimicry for 3D Cell Culture: a Fit-For-Purpose Investigation From the End User Standpoint

“…Also of critical importance, the optical transparency of PDMS enables real-time imaging, which is desirable for almost all branches of biomedical research. Over the past decade, a myriad of microfluidic designs with complex microarchitecture, significant bioelectrical and biochemical functionality have been realized through the addition of pneumatic valves [88], pillars [89], droplets [90], electrodes [91], hydrogel matrices [92] and electrospun fiber scaffolds [63,93]. Such delicate microfluidics platforms have the potential to be developed for 3D biomimetic tissues and organotypic cultures, for a range of biomedical purposes.…”