Researchers here demonstrate the ability to grow neural networks, consisting of neurons linked by long axons, in the laboratory and transplant them into rats, where they integrate with brain tissue. This is a strategy that might in the future be employed to augment the natural plasticity of brain tissue, or repair damage in the central nervous system, as long axons don't to tend to regrow on their own:
Complex brain function derives from the activity of populations of neurons - discrete processing centers - connected by long fibrous projections known as axons. When these connections are damaged, by injury or diseases such as Parkinson's or Alzheimer's disease, they, unlike many other cells in the body, have very limited capacity to regenerate. Researchers have shown that lab-grown neural networks have the ability to replace lost axonal tracks in the brains of patients with severe head injuries, strokes or neurodegenerative diseases and can be safely delivered with minimal disruption to brain tissue.
Researchers have been working to grow replacement connections, referred to as micro-tissue engineered neural networks (micro-TENNS), in the lab and test their ability to "wire-in" to replace broken axon pathways when implanted in the brain. They have advanced the micro-TENNs to consist of discrete populations of mature cerebral cortical neurons spanned by long axonal projections within miniature hair-like structures. Preformed micro-TENNS can be delivered into the brains of rats to form new brain architecture that simultaneously replace neurons as well as long axonal projections. "The micro-TENNS formed synaptic connections to existing neural networks in the cerebral cortex and the thalamus - involved in sensory and motor processing - and maintained their axonal architecture for several weeks to structurally emulate long-distance axon connections."
In the latest paper, the research team report on a new, less invasive delivery method enabled by applying an ultra-thin coating to the micro-TENNs using a gel commonly found in food and biomedical products. This new biomaterial strategy allows the encapsulation of fully formed engineered neural networks for insertion into the brain without the use of a needle. "We searched for materials that could form a hard shell that would soften immediately following insertion to better match the mechanical properties of the native brain tissue." This, the team hypothesized, would minimize the body's reaction and improve the survival and integration of the neural networks. The additional coating was not detrimental to the number of surviving neurons, and the needleless method substantially reduces the implant footprint, suggesting that it would cause less damage and thus provide a more hospitable environment for implanted neurons to integrate with the brain's existing nervous system.