Lecture 5 Flashcards
(13 cards)
What are biomaterials?
Biocompatible materials that are delivered to and implanted in the body to augment repair and/or replace damaged tissues.
They can act as supporting scaffolds for cell growth, provide mechanical, chemical and genetic cues, act as void-fillers and initiate repair response in host cells.
What is bioengineering?
The techniques used to engineer 3D scaffold structures to support and/or direct cell function to aid or replace defective, damaged or missing body parts.
What are the desired characteristics of biomaterials?
Biocompatibile, with minimal inflammation and immune-rejection.
Resorbable, with an appropriate degradation rate and non-toxic degradation products.
Porous to allow cell infiltration.
Interconnected pores to allow a continuous route for nutrient transfer and waste removal.
Describe decellularisation
Donor tissue stored in distilled water for 72h.
Cells removed by detergent-enzymatic treatment:
4% sodium deoxycholate and deoxyribonuclease I in 1mM NaCl
25 cycles over 6 weeks
Determined the presence of cellular elements and MHC-positive cells after each cycle.
Compare the advantages and disadvantages of natural intact ECM to single ECM components
Natural intact ECMs: Advantages
Retain natural ECM structure and composition
Relatively easy extraction and manufacturing
Natural intact ECMs: Disadvantages
Potentially immunogenic
Disease transfer
Variability
Single ECM components:
For example, collagens, hyaluronic acid, fibrin.
Can be processed individually or combined and assembled to produce ECM-like structures.
Less variability and immunogenicity.
Can be generated to meet ECM organisation requirements.
describe how type 1 collagen is used as a biomaterial
Collagen fibres self-assemble at neutral pH to produce a hydrated gel-like structure in a water-based solvent
Collagen type I hydrogel seeded with MSCs can integrate well at site of cartilage defect
What is alginate?
Biodegradable polysaccharide with mannuronic and guluronic acid repeating units.
Extracted from seaweed.
Polyanionic structures.
Gelation achieved in a solution rich in divalent cations, usually Ca2+
Alginate used for cell encapsulation
eg Pancreatic islet cells, encapsulated in alginate capsules for delivery and restoration of pancreatic function in diabetes.
Immuno-isolation, avoid immune detection.
natural polymer used as biomaterial
Give examples of synthetic polymers used as biomaterials
Poly (lactic acid) (PLA)
Poly (glycolic acid) (PGA)
Synthetic biodegradable polymers derived from glycolic acid and lactic acid monomers
PLA, PGA copolymer = Poly (lactic acid-co-glycolic acid) (PLGA)
Another common polymer = Polycaprolactone (PCL)
Adjustments in material properties of these polymers can alter rates of hydration and degradation to meet tissue requirements.
Describe how these polymers can be converted into 3D structures
Thermally-induced phase separation (TIPS) causes polymers in solution to separate into two phases:
Polymer rich phase
Polymer lean phase
Produces hydrated gel structures; hydrogels
Porous, allows cells to infiltrate
Synthetic Hydrogels e.g. poly-N-isopropyl acrylamide (PNIPAM)
Thermoresponsive: Polymer switches from hydrophilic into hydrophobic state at the lower critical solution temperature (LCST).
Transition from liquid to gel (e.g. at body temperature), to fill voids, encapsulate cells, deliver biomolecules etc
Liquid at room temp, gel at body temperature
Injectable, polymerises at body temp to dimensions of defect
With or without growth factors for example
What is electrospinning?
Method of producing nano- and micro-scale fibrous networks, equivalent to ECM dimensions using natural and synthetic polymers.
Electrical field applied to draw out a viscoelastic solution into a fine fibre.
Polymers (natural and synthetic) subjected to high voltage (several 1000 volts relative to grounded collecting plate).
Viscosity, polymer type and concentration, voltage, distance to collecting plate can all affect fibre size and quality and can be modified to fit purpose.
What is bioplotting?
using heat-based system to extrude out the polymer from the nozzle in different patterns – can make bespoke materials
Shows how different bioplotted structures affects mechanical strength and therefore can be adapted for different applications/tissue types
What does bioactive mean?
A material that elicits a specific biological response at the interface of the material which results in the formation of a bond between the tissues and the material
Describe how Three-dimensional Hard Tissues are created
Selective laser sintering, a form of 3D printing
3D objects with complex geometries and internal architectures are produced in a layer-by-layer manner using data directly from a computer-generated model (e.g. CT, MRI).
Achieved by sintering and fusing material (e.g. glass particles) using a laser to produce a 3D structure.
