Flashcards in Tissue engineering in the peripheral nervous system Deck (49):
what is the structure of a nerve generally?
epinerium around the pernuerium which contain neurons and a perineum with its nerves is called a fasicle
what supports the surrounding of the nerves?
what is the role of the ECM around the nerves?
aligns the axons
what does the perineurium do ?
has tight junctions between the cell and control fluid movement into and out of the endonuerium
what is the collagen like in the epinerium
like a woven sheath
what is biomechanical anatomy?
looking at the materials and the interactions between these materials of the nerve and tissue
why is nerve biomechanisms important?
critical to repair choices and normal function- tension causes fibrosis, adhesion restricts movement
- is repair different depending on anatomical location?
- artificial replacement tissues need to match and restore mechanical integrity
- it is poorly understood
what happens generally when damage in inflicted on the nerves of the peripheral nervous system?
- the distal tip generates
- the schwann cells change their phenotype and recruit the macrophages d start to digest the myelin and also become a repair schwann cell
- the form bands of bunger and pump out lots of neurotrophic factors
- the axon sprouts and then one will make it back to the muscle and you get a restored function
- but also a neuroma can form
what generally causes here damage?
- bone breaks
- accidents- road
- compression syndromes
what is the current procedure for nerve repair?
- if it is small, tweezers can be used to pull the epinerial together and then sowing up.
- if there is a gap then you will get tension when you do this and yo dont want tension so instead you can use an autograft where a surgion finds a spare bit of nerve and then this gets used to bridge the gap
what is wrong with using an autograft approach?
there is limited availability of autograft material- if there is a big damage then you urn out of nerves that you can use. It provides schwann cells, tissue architecture, biomechanicsl properites and guidance cues. But it doesn't provide neurons
what does an autograft provide?
schwann cells, tissue architecture, biomechanicsl properites and guidance cues. But it doesn't provide neurons
what can be used to circumvent the problems with using autografts?
using a conduit that has been enriched
?when are conduits good
for a shorter gap
when are plain conduits bad?
when there is larger gap and the neurons need support
what is a decellularised allograft?
- empty nerves that ave been deculluarisd and just have the ECM
what is important to be involved in the autograft?
what are the 5 things that need to be in an autograft?
•Biocompatible & bioresorbable
•Cell guidance substrate (core)
•Schwann cells (or alternatives)
•Doesn’t adhere to surrounding tissue (sheath) •Mechanical support/protection (sheath)
how can you use a collagen hydrogel to create an alignment of the cells and the collagen?
put cells into a collagen hydrogel- they stat to attach to it and pull on it. This causes it to shrink.
- you can take advantage of this and anchor opposite ends so that it can only shrink in one direction and causes the cells to be aligned. cells and collagen becomes highly aligned.
- then take the water out- compression and results in a flat sheet
how can you use the aligned sheet idea to produce a supportive construct for enrols?
- yo put cells into the collagen hydrogel and hey become aligned and then these can be rolled up and put into a tube and implant this . You create a 15 mm gap which is where a tube wouldn't work. Use GFp to distinguish between cells pt in and cells already there. you can then look at the regeneration rate and cat promote nerve growth in a rat
what cells can be put into engineered neural tubes and why?
- can put rat adipose tissue derived stem cells because these will upregulate lots of trophic factors when put in the collagen gel and they aligned nicely. The guide neuronal growth in vitro and in vivo when compared to the neural tube
- pulp derived stem cells can also be used- they are neural crest derived which means that these are geared towards making neurons and schwann cells and you can differentiate them into something that behaves like a schwann cell
how can engineered NT be made using 'off the shelf' allogeneic stem cells?
- with the stem cell idea from adipose and death pulp, this would have to be autologous but you can get clinicl grade human neural stem cels that have been developed which do not promote an immune response
what is the importance of stiffness and how are human neural stem cells engineered tube good for this?
- the stiffness of a cells environment can influence how it differentiates and there are methods for controlling the the stiffness of the neural stem cell tubes
what are the remaining problems in nerve repair?
• Neuroma formation
• Muscle atrophy
• Damage due to sensory loss
• Cortical remodelling
• Poor functional outcome
what is the micro-channel electrode array method?
- ant silicie fitting is sutured to the proximal and distal endings of the injured nerve. The implant length from 0.5 to 5mm.
what is the biological relay approach
build a structure which has living neuron sin and try to connect at each end- put a bridge in to get function back immediately
what factors have been shown to promotee survival of axons after injury?
- ALCAR and phosphoisesterase inhiitor- sildenafil
what different types of topography have been used in order to promote scaffold success?
- electrospun fibres
what scaffold promotes SC elongation?
polycaprolactone (PCL) films
why should ECM molecules be futon scaffolds?
whilst ECM molecules support SC attachment and stimulate excretion of neurite promoting factors
what growth factors have been suggested to promote regeneration of axons?
- NGF, BDNF and CTNF improves te refeneration distance
- regeneration speed can be improved by IGF-1, FGF and GDNF
- NRG1 signalling is a key player for axonal myelination during development
what is difficult about applying growth factors?
- different levels or different factors have actually been linked to inhibited growth so getting the levels right is paramount
as well as SCs, which other cell can be used to support regrowth potentially?
- olfactory ensheathing cells
what is the problem with using schwann cells or OECs?
the sourcing of these requires the sacrifice of a functional nerve and both OECs and SC have limited expansion capailites.
give an example of an experiment using stem cells to promote neural regrowth (3)
- Mouse ESC-derived neural progenitor cells promoted nerve repair in a rat sciatic nerve 10 mm gap as shown by histological, molecular and electrophysiological studies
-SC-like precursors can be generated from human ESC and have been shown to express myelin protein in models of peripheral nerve regeneration in vitro
- NSC showed results comparable to au- tografts when seeded in chitosan nerve guides to repair a 10 mm nerve gap , and they can be genetically engineered to overexpress GDNF or NT-3, which can potentially improve their regenerative potential
- iPSC can efficiently generate functional neural crest cells and have been used, in combination with FGF-incorporated gelatin micro- spheres, to repair 10 mm nerve gaps with 50% poly l-lactide (PLA) and 50% poly ε-caprolactone porous nerve conduits
rather than ESC or iPSC, what stem cell can be used? why arteries maybe preferable?
MSCs-Compared to ESC and iPSC, the use of MSC in regenerative medicine comes with less ethical implications regarding the sourcing of the cells, and the risk of teratoma formation or undesired cell differentiation.
why are ASCs preferable to MSCs?
some of the problems related to the use of BM-MSC include the painful procedure for the har- vest of marrow aspirates and the low yield of mononucleated colony forming units (CFU). By contrast, ASC obtained from the stromal vascu- lar fraction (SVF) following digestion of adipose tissue contain 600× more CFU, and these cells proliferate faster and for longer durations.
- Like BM-MSC they are multipotent and they can generate functional SC-like cells
name a degradable conduit that degrades after 48 months?
- neuragen - collagen type -1 conduit
what a synthetic conduit
eurolac - PDLLA conduit - 16 months to degrade
what type of conduits are bad and why?
nonresorbable- chronic inflammation
why are naturally derived materials sometimes good but risky?
Naturally-derived materials have advantageous properties such as cell binding domains encouraging neuronal and glial attachment and migration.20 However, these are usually from animal sources and carry a minor risk of disease transmission
as well as collagen, what other material can be used and why?
Silk fibroin has been recently investigated, and is attrac- tive due to favorable degradation properties and low in- flammatory response.
what are 2 synthetic materials used for nerve conduit?
what key ECM molecule can be added to a nerve conduit? what has it been shown to do
laminin - promote SC proliferation
how can gradients be used in conduit construction?
Dodla et al.75 reported that gradients of laminin and NGF contained within anisotropic agarose hydrogels stimulate nerve regeneration in a 20 mm rat sciatic model comparable to syngeneic grafts.
how can topology be used in conduit construction?
Britland et al.81 found that grooved surfaces 12mm wide and 6 mm deep were optimal for DRG neuronal alignment.
how can intralumincal guidance be used? give one example.
- he presence of internal scaffolds either as synthetic polymers or as matrix proteins contained within the lumen of nerve guides for improved physical or chemical guidance.
- Cai et al. reported on improved distal regeneration when PLA or silicone con- duits contained 16 aligned PLLA microfilaments using a rat sciatic model.
describe the principle behind micro-channel electrode arrays:
Peripheral nerve electrode interfaces are designed to capture and/or stimulate the APs via implanted electrodes in order to re-establish lost functional connectivity . Ideally, they should reliably and efficiently interface with a large number of nerve fi- bres. It is hoped that high-resolution interfaces will eventually provide a means to restore function to nerve-injured patients by, for example, extracting signals from motor fibres proximal to an injury and using them to drive distal muscle stimulators to im- prove strength and precision. Interfaces might also provide an amputee with control and sensation over an artificial limb.
- the idea is that the micro channel electrode impact can promote the regeneration of axons while also detecting impasse fired and using these to stimulate the distal axons while the injured ones regenerate. The strategy we are using is to make the axons grow down microchannels, in which the electrical signal from action potentials is greatly amplified, making recording possible. This can circumvent the issues of axons growing randomly and connecting to the wrong muscles and skin regions.