20.109(S09)/TRPink

Overall Goal
To grow directional neuron tissue cultures in order to make the possibility of neural regeneration more effective for patients who suffer from neural degeneration and other such neural problems.

Background
Research has been done in just growing neuron tissue cultures in culture. Neurons were shown to be able to form synapses between each other. However, these connections tend to be haphazard and random, unlike neuron pathways in the body which are directed. There has also been minimal research that have shown ways to direct neuron growth using topographically modified/patterned surfaces. We hope to combine these two ideas to generate a scaffold or method of culturing neuron that would create directional neuronal tissue.

Research
1. "Fiber templating of poly(2-hydroxyethyl methacrylate) for neural tissue engineering" - longitudinally oriented channels

- provide guidance to extending axons

- Regulating the size and quantity of the polycaprolactone(PCL) fibers controls the diameter and number of channels

- Useful for guided regeneration of neurons

2. "Building a Bridge: Engineering Spinal Cord Repair" - need to bridge between affected areas

- three components of the bridge: the on-ramp, surface of the bridge itself, and the off-ramp

- can use cellular or cell-free bridges

- purification of large amounts of neurons/schwann cells/glia takes too long, so not very useful

- grafts from other animals lead to immune response

- GOAL: to engineer a biocompatible cell-free bridges with molecular properties needed to promote axon regeneration and control inflammatory and glial reactions

- bridge must provide surfaces on which the axons can grow, and sufficient physical adhesion to permit that growth, yet not be too adhesive, which would prevent growth: look into signaling molecules

- growth cone activations: bridge should incorporate molecules that cause the activation of those signaling pathways that are normally activated by cell adhesion and extracellular matrix molecules

- look into growth factors

- upregulating these growth-associated proteins and increasing regenerative activity in many types of neuron is the application of appropriate trophic factors

- Axons are guided by chemotactic and haptotactic mechanisms

- Peripheral nerve axons regenerate along a structure known as the Band of Bungner which is essentially a long cylinder of Schwann cells surrounded by a sheath of extracellular matrix

- mimic this band of bungner: fiber or a tube of similar or slightly greater size coated with growth-promoting molecules. Axon growth on artificial substrates is straightest when the pathway is restricted, e.g., by either a narrow permissive pathway on a planar surface or on a fiber of small diameter, suggesting that a bridge composed of a large number of small parallel fibers or tubes will facilitate directed growth.

- polymers that release trophic factors and chemoattractants may be advantageous to include within the bridge

3. "Neurite Outgrowth and Growth Cone Morphology on Micropatterned Surfaces" - injured axons demonstrate great ability for regrowth, but repair is inhibited due to lack of direction

- micropatterned surfaces are useful for directing neuron growth

- Clark et al. (1993) showed that microlithography could be used to pattern laminin, a ubiquitous molecule in developmental pathways of the nervous system

- patterned surfaces may be useful where aligned neurite outgrowth is desired

- However, increased interactions between the growth cone and substrate boundaries serve to slow growth cone migration. Therefore narrow pathways while allowing for less wandering, inhibit growth.