Lecture Outline. History. Purpose? Func:on of Bioscaffolds. Extracellular Matrix (ECM) 12/08/15

Transcription

1 Associate Professor Rod Dilley Dr Rob Marano Ear Sciences Centre School of Surgery Harry Perkins Research Building 4 th Floor Lecture Outline History Purpose Functions Properties Approaches to bioscaffold design Clinical Example Video History Use of implants dates back over 2000 years Modern devices began in late 1940 s British Ophthalmologist treating fighter pilots Eye injuries containing shards of canopy plastic healed with no apparent side effects or reactions. Concluded that canopy material may be used as artificial lens (first implanted in 1949) Late 60 s collaborations between engineers, chemists, biologists, and physicians, led to formalizing design principles and synthesis strategies for biomaterials Purpose? Used in tissue engineering. Overall aim of developing a substitute to restore, replace or regenerate defective tissues. Bioscaffolds + cells + growth stimulating signals (bioactive molecules) are known as the Tissue Engineering Triad. Func:on of Bioscaffolds Extracellular Matrix (ECM) Mimic the form and function of the extracellular matrix (ECM). Almost all cells are anchorage dependent i.e need to be attached to something.ecm ECM has multiple components and is tissue specific. 1

2 ECM Five broad functions 1. Structural support and physical environment for cells to grow. 2. Provides structural/mechanical properties 3. Provision of bioactive cues (cellular alignment). 4. Acts as a reservoir of growth factors. 5. Provides a changeable environment to allow for events such as remodeling and neovascularisation (wound healing) ECM Han, D. & Gouma, P. I. Electrospun bioscaffolds that mimic the topology of extracellular matrix. Nanomedicine 2, (2006). 1. Architecture 2. Tissue compatibility 3. Bioactivity 4. Mechanical Properties 1. Architecture: Void volume (vascularisation, new tissue formation) Porous (metabolite and nutrient transport) Biodegradable (degradation rate matching that of neo- tissue formation). 2. Tissue compatibility: Cells must be able to grow upon it and differentiate. Scaffold and its breakdown products must be non toxic. 3. Bioactivity: Able to interact with cells to regulate activities. Bioscaffold may include certain biological cues either through topography or through the presentation of bioactive molecules. 2

3 Topography 4. Mechanical Properties: Provide shape and stability to tissue defect. Could be similar to that of the host tissue. Important for cell differentiation. Approaches to Scaffold Design Four Main Approaches 1. Pre- made porous scaffolds for cell seeding 2. Decellularised extracellular matrix 3. Cell sheets with secreted ECM 4. Cells encapsulated in self assembled hydrogel 1. Porous Scaffolds a. Natural Derived from biological material Silk, collagen, alginates etc b. Synthetic Non- biological Glass, ceramics etc. a. Natural Scaffolds Autogenic/Autologous Derived from the patient Allogenic/Homogenic Derived from different individual same species Xenogenic From a different species a. Natural Scaffolds Advantages Excellent biocompatibility, good cell attachment etc. Disadvantages Limited physical and mechanical stability (not suitable for load bearing situations). 3

4 b. Synthe:c Greater control over physical and mechanical properties. Inorganic Glass, ceramics (Hydroxyapatite) Organic Polypropylene, nylon, teflon, polystyrene, polymethylmethacrylate (plexiglas) b. Synthe:c Inorganic myweb/photo.htm Organic Glass Hydroxyapatite Teflon arterial stent Manufacture Process of manufacture will determine the final properties of the bioscaffold. Electrospinning Casting Nanoweaving 3D printing Electrospinning Cas:ng Kumbar, S. G., James, R., Nukavarapu, S. P. & Laurencin, C. T. Electrospun nanofiber scaffolds: engineering soft tissues. Biomed Mater 3, (2008). Wang, Y. et al. The synergistic effects of 3-D porous silk fibroin matrix scaffold properties and hydrodynamic environment in cartilage tissue regeneration. Biomaterials 31, (2010). 4

5 Nanoweaving 3D Prin:ng 2. Decellularised ECM Generally derived from an allograft or xenograft. All cellular components are removed. Left with the ECM ECM components are well conserved between species. Decellularised ECM Advantages: Properties are perfect for homologous functions Also useful for non- homologous functions if properties are similar. Excellent biocompatibility Disadvantages: Poor distribution of cells when seeding. Possible immune reactions if not properly decellularised. 2. Decellularised ECM 3. Cell Sheets Cells are grown on a specialised surface until confluent. Secrete their own ECM. Cells + ECM are removed from the culture surface as a single sheet. Can be stacked into multiple layers. 5

6 3. Cell Sheets 3. Cell Sheets Advantages: Secretes own ECM Rapid neovascularisaton No sutures to keep in place Disadvantages: Limited thickness Not good for load bearing tissue 3. Cell Sheets A. Lorenti, "Wound Healing: From Epidermis Culture to Tissue Engineering," CellBio, Vol. 1 No. 2, 2012, pp Cell Encapsula:on Entrapment of living cells within a homogenous solid mass. Most recent is use of self assembling polymer scaffold from liquid monomers. Can suspend cells in liquid and inject into defect. 4. Cell Encapsula:on Advantages: Good for irregularly shaped defects Disadvantages: Not good for load bearing tissues. 4. Cell Encapsula:on Injectable hydrogel scaffold starts as a soluble liquid at room temperature, left, and forms a stable, nonshrinking gel, right, at body temperature after one minute. Tiffany N. Vo, Adam K. Ekenseair, Fred Kurtis Kasper, Antonios G. Mikos, Synthesis, Physicochemical Characterization, and Cytocompatibility of Bioresorbable, Dual-Gelling Injectable Hydrogels, Biomacromolecules, 2013, 6

7 5. Combina:on Scaffolds Utilise the best qualities from two or more devices Custom to suit purpose E.g. Combination of high strength of synthetic material coupled with cell growth properties of natural compounds for bone regeneration. 5. Combina:on Scaffolds SEM of the hybrid scaffold with composition of 50% bioactive glass and 50% PVA for comboscaffold. In vitro and in vivo osteogenic potential of bioactive glass PVA hybrid scaffolds colonized by mesenchymal stem cells Viviane S Gomide et al 2012 Biomed. Mater Clinical Example Tissue Engineering a Tympanic Membrane Cells Scaffold Bioactive Molecules Silk Fibroin Fibroin studied with biomedical applications Biocompatibility Biodegradability Mechanical properties Ability to form diverse morphologies Silk scaffolds Overall Goal Safety and compatibility Growth factors Optimising silk designs Silkworm (Bombyx mori) Normal Perforation Culture of TM Cells Repair Hole Grow on bioscaffold Optimise Scaffold- Cell Interaction Bioactive Molecules 7

8 Silk Fibroin Silk from silkworms or spiders 1. Fibroin (structural) 2. Seracin (glue- like) Immunogenic (e.g. sutures) Silk Fibroin htm cells seeded onto SF membranes at cells/well Degummed Solublised and Cast Silk from Bombyx mori cocoon Fibroin Remains Fibroin Membrane Cells incubated 15 days at 37 o C Tissue Engineering A TM SEM of htm cells on SF membrane Biocompa:bility/Degrada:on Middle Ear Cavity Subcutaneous Effect on Perfora:on Healing Short Video anthony_atala_growing_organs_engineering_tissue.ht ml Reproduced from Shen, Y. et al. Laryngoscope (2013). 8