Advanced biomaterial strategies to transplant preformed micro-tissue engineered neural networks into the brain

Abstract

Objective Connectome disruption is a hallmark of many neurological diseases and trauma with no current strategies to restore lost long-distance axonal pathways in the brain. We are creating transplantable micro-tissue engineered neural networks (micro-TENNs), which are preformed constructs consisting of embedded neurons and long axonal tracts to integrate with the nervous system to physically reconstitute lost axonal pathways. Approach We advanced micro-tissue engineering techniques to generate micro-TENNs consisting of discrete populations of mature primary cerebral cortical neurons spanned by long axonal fascicles encased in miniature hydrogel micro-columns. Further, we improved the biomaterial encasement scheme by adding a thin layer of low viscosity carboxymethylcellulose (CMC) to enable needle-less insertion and rapid softening for mechanical similarity with brain tissue. Main results The engineered architecture of cortical micro-TENNs facilitated robust neuronal viability and axonal cytoarchitecture to at least 22 days in vitro. Micro-TENNs displayed discrete neuronal populations spanned by long axonal fasciculation throughout the core, thus mimicking the general systems-level anatomy of gray matter—white matter in the brain. Additionally, micro columns with thin CMC-coating upon mild dehydration were able to withstand a force of 893 ± 457 mN before buckling, whereas a solid agarose cylinder of similar dimensions was predicted to withstand less than 150 μN of force. This thin CMC coating increased the stiffness by three orders of magnitude, enabling needle-less insertion into brain while significantly reducing the footprint of previous needle-based delivery methods to minimize insertion trauma. Significance Our novel micro-TENNs are the first strategy designed for minimally invasive implantation to facilitate nervous system repair by simultaneously providing neuronal replacement and physical reconstruction of long-distance axon pathways in the brain. The micro-TENN approach may offer the ability to treat several disorders that disrupt the connectome, including Parkinson’s disease, traumatic brain injury, stroke, and brain tumor excision

Transplantable living scaffolds comprised of micro-tissue engineered aligned astrocyte networks to facilitate central nervous system regeneration

“…Due to the small size and self-contained design of these aligned astrocyte constructs, they have the potential to be directly transplanted into the CNS (Fig. 1C) as we have shown with similar micro-constructs [17,19]. In the current study, we have shown that it is possible to remove the astrocyte constructs from the hydrogel encasement (Figs.…”

Neurothreads: Cryogel carrier-based differentiation and delivery of mature neurons in the treatment of Parkinson’s disease

“…The possibility to transplant neurons with mature morphology and synaptic connectivity in a fully porous scaffold also offers fundamentally novel possibilities in the emerging field of preassembled neural circuitry. Some initial steps in this direction have indeed been made with tubular micro-tissue engineered neural tracts 28,29 or chemical definition of reconstruction pathways. 90 But the difficulty to maintain neural viability, yet enable rapid interaction with the surrounding tissue during transplantation has so far let this field largely unexplored 19 .…”

“…21,25,26 While improving aspects of cell survival, these studies do not address the question of how a fully organized and mature neural network might be transplanted. Nerve-guide inspired cylindrical sheaths have been shown to successfully maintain mature tissue integrity [27][28][29] . While offering the exciting possibility to transplant neural tracts intra-cerebrally in small animal models 28,29 , by construction, these implants physically limit lateral access for vascularization required for larger volumes 30 .…”

Mechanical elongation of astrocyte processes to create living scaffolds for nervous system regeneration

“…They are thus able to modulate signalling based on the state and progression of the regenerative process. On this front, there are a number of promising emerging strategies for the development of regenerative scaffolds consisting of aligned glial cells (East et al ., ) and longitudinal axonal tract (Cullen et al ., ; Harris et al ., ; Pfister et al ., ; Smith, ; Struzyna et al ., ). Living scaffolds have the potential to advance the field of neuroregenerative medicine by guiding the re‐establishment of complex neural structures and axonal connections, potentially ultimately facilitating functional recovery following a range of currently untreatable traumatic and neurodegenerative disorders (Struzyna et al ., ).…”