Konstantinos Tsioris

Bio-microfluidics: biomaterials and biomimetic designs.

Bio-microfluidics applies biomaterials and biologically inspired structural designs (biomimetics) to microfluidic devices. Microfluidics, the techniques for constraining fluids on the micrometer and sub-micrometer scale, offer applications ranging from lab-on-a-chip to optofluidics. Despite this wealth of applications, the design of typical microfluidic devices imparts relatively simple, laminar behavior on fluids and is realized using materials and techniques from silicon planar fabrication. On the other hand, highly complex microfluidic behavior is commonplace in nature, where fluids with nonlinear rheology flow through chaotic vasculature composed from a range of biopolymers. In this Review, the current state of bio-microfluidic materials, designs and applications are examined. Biopolymers enable bio-microfluidic devices with versatile functionalization chemistries, flexibility in fabrication, and biocompatibility in vitro and in vivo. Polymeric materials such as alginate, collagen, chitosan, and silk are being explored as bulk and film materials for bio-microfluidics. Hydrogels offer options for mechanically functional devices for microfluidic systems such as self-regulating valves, microlens arrays and drug release systems, vital for integrated bio-microfluidic devices. These devices including growth factor gradients to study cell responses, blood analysis, biomimetic capillary designs, and blood vessel tissue culture systems, as some recent examples of inroads in the field that should lead the way in a new generation of microfluidic devices for bio-related needs and applications. Perhaps one of the most intriguing directions for the future will be fully implantable microfluidic devices that will also integrate with existing vasculature and slowly degrade to fully recapitulate native tissue structure and function, yet serve critical interim functions, such as tissue maintenance, drug release, mechanical support, and cell delivery.

Rapid Transfer-Based Micropatterning and Dry Etching of Silk Microstructures

Over the last two decades silk produced by the silkworm Bombyx mori has found new utility as a sustainable material platform for high-technology applications encompassing photonics, electronics and optoelectronics [1-4]. Silk fibers have been used as an FDA approved medical suture material for decades [5] due to their biocompatibility and mechanical properties [6]. These properties, along with the inherent biodegradability of silk, has driven the use of this protein for biological studies [6]. Native silk fibers can be solubilized and reprocessed into an aqueous silk fibroin protein solution [7], which can then be used to generate a multitude of new material formats [5] such as hydrogels [8], foams [9], electrospun mats [10] and sponges [11]. These new forms of silk are finding utility in drug delivery, cell culture and tissue engineering applications. Silk films with excellent optical properties (> 90% transmission in the visible spectrum) [12] are currently being explored for applications in optics and biophotonics [3, 4]. Additionally, the environmentally benign, all-aqueous processing conditions and the chemistry of silk allow bioactive components, such as enzymes to be stabilized in the protein matrix [13].

The Effect of Hydrophobic Patterning on Micromolding of Aqueous-Derived Silk Structures

A novel micromolding approach was developed to process liquid biopolymers with high aqueous solvent contents (>90% water). Specifically silk fibroin was cast into a well-defined scaffold-like structure for potential tissue engineering applications. A method was developed to pattern the hydrophilicity and hydrophobicity of the polydimethylsiloxane (PDMS) mold surfaces. The water based biopolymer solution could then be directly applied to the desired regions on the cast surface. The variations in degree of hydrophilicity and hydrophobicity on the PDMS surfaces were quantified through contact angle measurements and compared to the outcome of the molded silk structures. Through this method free-standing structures (vs. relief surface-patterning) could be fabricated.