Cellular processes are linked to the alignment (anisotropy) and orientation (directionality) of collagen fibers (i.e., landscape) in the native extracellular matrix (ECM). Given the vital role that cell‐matrix interactions play in regulating biological functions, several microfluidic methods have successfully established anisotropic 3D collagen gels to develop quantitative relationships between structural cues and cellular responses. However, independently tailoring the fiber anisotropy and fiber directionality within a landscape remains a challenge. Here, a user‐friendly microfluidic platform with a non‐uniform channel geometry is used to control the degree of fiber anisotropy and directionality as a function of extensional strain rate and a defined flow path, respectively. New experimental capabilities, including independent control over the degree of fiber anisotropy and directionality, spatial gradients in anisotropy, and multi‐material interfaces, are demonstrated. A channel peel‐off technique provides direct access to the microengineered collagen landscapes, and the alignment of single MD‐MB‐231 cancer cells and monolayers of human umbilical vein endothelial cells (HUVEC) is shown. Finally, the platform's modular capability is highlighted by integrating an ultrathin porous Parylene (UPP) membrane onto the microengineered collagen landscape as a method to control the degree of cell‐matrix interaction.
Randomly oriented type I collagen (COL1) fibers in the extracellular matrix are reorganized by biophysical forces into aligned domains extending several millimeters and with varying degrees of fiber alignment. These aligned fibers can transmit traction forces, guide tumor cell migration, facilitate angiogenesis, and influence tissue morphogenesis. To create aligned COL1 domains in microfluidic cell culture models, shear flows have been used to align thin COL1 matrices (<50 µm in height) in a microchannel. However, there has been limited investigation into the role of shear flows in aligning 3D hydrogels (>130 µm). Here, we show that pure shear flows do not induce fiber alignment in 3D atelo COL1 hydrogels, but the simple addition of local extensional flow promotes alignment that is maintained across several millimeters, with a degree of alignment directly related to the extensional strain rate. We further advance experimental capabilities by addressing the practical challenge of accessing a 3D hydrogel formed within a microchannel by introducing a magnetically coupled modular platform that can be released to expose the microengineered hydrogel. We demonstrate the platform’s capability to pattern cells and fabricate multi-layered COL1 matrices using layer-by-layer fabrication and specialized modules. Our approach provides an easy-to-use fabrication method to achieve advanced hydrogel microengineering capabilities that combine fiber alignment with biofabrication capabilities.
It is well-known that biophysical properties of the extracellular matrix (ECM) in- including, stiffness, porosity, composition, and fiber alignment (anisotropy) play a crucial role in controlling cell behavior in vivo. Type I collagen (collagen I) is a ubiquitous structural component in the ECM and has become a popular hydrogel material that can be tuned to replicate the mechanical properties found in vivo. In this review article, we describe popular methods to create 2D and 3D collagen I hydrogels with anisotropic fiber architectures. We focus on methods that can be readily translated from engineering and materials science laboratories to the life science community with the overall goal of helping to increase the physiological relevance of cell culture assays.
Advanced in vitro tissue chip models can reduce and replace animal experimentation and may eventually support “on‐chip” clinical trials. To realize this potential, however, tissue chip platforms must be both mass‐produced and reconfigurable to allow for customized design. To address these unmet needs, an extension of the µSiM (microdevice featuring a silicon‐nitride membrane) platform is introduced. The modular µSiM (m‐µSiM) uses mass‐produced components to enable rapid assembly and reconfiguration by laboratories without knowledge of microfabrication. The utility of the m‐µSiM is demonstrated by establishing an hiPSC‐derived blood–brain barrier (BBB) in bioengineering and nonengineering, brain barriers focused laboratories. In situ and sampling‐based assays of small molecule diffusion are developed and validated as a measure of barrier function. BBB properties show excellent interlaboratory agreement and match expectations from literature, validating the m‐µSiM as a platform for barrier models and demonstrating successful dissemination of components and protocols. The ability to quickly reconfigure the m‐µSiM for coculture and immune cell transmigration studies through addition of accessories and/or quick exchange of components is then demonstrated. Because the development of modified components and accessories is easily achieved, custom designs of the m‐µSiM shall be accessible to any laboratory desiring a barrier‐style tissue chip platform.
Advanced in vitro tissue chip models can reduce and replace animal experimentation and may eventually support 'on-chip' clinical trials. To realize this potential, however, tissue chip platforms must be both mass-produced and reconfigurable to allow for customized design. To address these unmet needs, we introduce an extension of our μSiM (microdevice featuring a silicon-nitride membrane) platform. The modular μSiM (m-μSiM) uses mass-produced components to enable rapid assembly and reconfiguration by laboratories without knowledge of microfabrication. We demonstrate the utility of the m-μSiM by establishing an hiPSC-derived blood-brain barrier (BBB) in bioengineering and non-engineering, brain barriers focused laboratories. We develop and validate in situ and sampling-based assays of small molecule diffusion as a measure of barrier function. BBB properties show excellent interlaboratory agreement and match expectations from literature, validating the m-μSiM as a platform for barrier models and demonstrating successful dissemination of components and protocols. We then demonstrate the ability to quickly reconfigure the m-μSiM for co-culture and immune cell transmigration studies through addition of accessories and/or quick exchange of components. Because the development of modified components and accessories is easily achieved, custom designs of the m-μSiM should be accessible to any laboratory desiring a barrier-style tissue chip platform.
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