An organotypic uniaxial strain model using microfluidics

Abstract

Traumatic brain injuries are the leading cause of disability each year in the US. The most common and devastating consequence is the stretching of axons caused by shear deformation that occurs during rotational acceleration of the brain during injury. The injury effects on axonal molecular and functional events are not fully characterized. We have developed a strain injury model that maintains the three dimensional cell architecture and neuronal networks found in vivo with the ability to visualize individual axons and their response to a mechanical injury. The advantage of this model is that it can apply uniaxial strains to axons that make functional connections between two organotypic slices and injury responses can be observed in real-time and over long term. This uniaxial strain model was designed to be capable of applying an array of mechanical strains at various rates of strain, thus replicating a range of modes of axonal injury. Long term culture, preservation of slice and cell orientation, and slice-slice connection on the device was demonstrated. The device has the ability to strain either individual axons or bundles of axons through the control of microchannel dimensions. The fidelity of the model was verified by observing characteristic responses to various strain injuries which included axonal beading, delayed elastic effects and breakdown in microtubules. Microtubule breakdown was shown to be dependent on the degree of the applied strain field, where maximal breakdown was observed at peak strain and minimal breakdown is observed at low strain. This strain injury model could be a powerful tool in assessing strain injury effects on functional axonal connections.

Brain-on-a-chip microsystem for investigating traumatic brain injury: Axon diameter and mitochondrial membrane changes play a significant role in axonal response to strain injuries

“…When axons are subjected to high rates of strain they are known to temporarily form undulations along the length of the axon 20,25 ( Fig. 3a).…”

“…We previously described our brain-on-a-chip technology that can uniquely separate cell soma and individual axon responses. Our initial studies characterized the effect of strain on axonal morphology and cytoskeletal changes 20 . The model we used in our studies incorporates the connection and communication that occurs between two organotypic hippocampal slice cultures.…”

Device-Based In Vitro Techniques for Mechanical Stimulation of Vascular Cells: A Review

“…Cells cultured on the membrane experienced up to 20% stretch when actuated by cyclic pressure applied continuously for up to 7 days [103]. Similar systems have been used in studies of neuronal axons [104] and lung epithelium/endothelium coculture [105]. Researchers can more accurately replicate in vivo conditions by stretching cells cultured in 3D gels in addition to 2D membranes [106,107].…”

Microfluidic culture platform for studying neuronal response to mild to very mild axonal stretch injury

“…This allows axons growing on top of the PDMS membrane to be discretely stretched, providing a new platform to study stretch injuries and, in later stages, has the potential to test the effects of therapeutic agents in isolated axonal or somal compartments following stretch injury. More recently, Dolle and colleagues 28 developed a new device where uniaxial strains were applied to the elastic PDMS substrate on which axons extend between two organotypic hippocampal slices. This device is similar to our device, where upward deflection is applied to the axons growing on PDMS; however, this device applied stretch injury range from 11% to 42%, in a non-fluidically isolated microenvironment over a length of approximately a millimeter, whereas our device applied stretch injury in fluidically isolated microenvironment at a relatively small strain (0.5% or 5%).…”

“…It is important to note this stretch is significantly smaller than strains previously applied in the literature, for example, Doll e et al reported a deflection of up to 1 mm resulting in a 11% strain. 28 We also applied a 25 psi pressure to a 15 lm PDMS membrane and thereby obtained 14.1 lm upward deflection which resulted in a 5% strain to axons [ Fig. 3].…”