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MECH 500: Bionic Implants and Devices

Lecture 2 : Functional Biomaterials. . Lecture 2: Functional Biomaterials. How does the human body respond to a biomaterial ? What materials are currently used as biomaterials?How are these biomaterials characterised? What happens to the biomaterial once implanted?What kind of surface modificatio

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MECH 500: Bionic Implants and Devices

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    1. MECH 500: Bionic Implants and Devices Sumitra Rajagopalan sumitra.rajagopalan@polymtl.ca Office Hours: 5pm – 5:30 pm Mondays 4 pm- 5pm Fridays Office : B- 364

    2. Lecture 2 : Functional Biomaterials

    3. Lecture 2: Functional Biomaterials How does the human body respond to a biomaterial ? What materials are currently used as biomaterials? How are these biomaterials characterised? What happens to the biomaterial once implanted? What kind of surface modification can improve the biocompatibility of the biomaterial? What changes in the bulk can improve the performance of the biomaterial? How does nature "design" biological materials? Mimicking Nature: Biomimetic (Bionic) Material Design Where do we go from here ? Lecture 3: Combining materials with living tissues – tissue engineering.

    4. Human Blood: A Hostile Environment Blood: Red Blood Cells + White Blood Cells ONLY White Blood Cells (LEUKOCYTES) are involved in the body’s response Neutrophiles (poly) engulf and destroy foreign material : PHAGOCYSTOSIS Monocytes turn into giant MACROPHAGES to gulp foreign body particles Biomaterial debris often targetted by macrophages Scavenger Cells!

    5. Site becomes red Site becomes swollen The site becomes warm The site becomes painful Blood clots, Polys appear at the site of injury: ACUTE INFLAMMATION If splinter is removed, then tissue returns to normal If splinter is not removed, polys recruit monocytes, then macrophages Inflammation turns into CHRONIC INFLAMMATION Inflammation Reaction:Splinter in Finger

    6. After the clean-up: Wound Healing Blood vessels begin to grow at site Tissue called fibroblasts synthesize collagen *************** Normal Tissue Repair cannot happen if biomaterial persists in body First Reaction ? Fibroblasts then lay down a layers of fibrous tissue to wall-off the implant The thinner the capsule the more it is biocompatible Serious complications if the inflammation persists: CHRONIC INFLAMMATION

    7. In what instances would this fibrous capsule impede the preformance of the implant? Porous or textured surfaces do not provoke capsule formation. Why?

    8. Lecture 2: Functional Biomaterials How does the human body respond to a biomaterial ? What materials are currently used as biomaterials? How are these biomaterials characterised? What happens to the biomaterial once implanted? What kind of surface modification can improve the biocompatibility of the biomaterial? What changes in the bulk can improve the performance of the biomaterial? How does nature "design" biological materials? Mimicking Nature: Biomimetic (Bionic) Material Design Where do we go from here ? Lecture 3: Combining materials with living tissues – tissue engineering.

    9. BIO-MATERIALS POLYMERS METALS/ALLOYS CERAMICS COMPOSITES " Smart Materials" will be dealt with along with Bioactive Implants

    10. Polymers Long-chained molecule Repeating units called monomers Highly versatile: gels, foams, rubbers, cements, glass Most biological materials are polymers : DNA, proteins, peptides, ALL soft tissue What is the difference between a synthetic polymer and a biological polymer?

    11. Metals, Ceramics and Glasses Metals: Platinum, Nickel, Stainless Steel, Titanium, commonly used Metals can corrode in the human body? How ? How can this be averted ? Ceramics are oxides of metals :alumina, sappire, silica Carbon, graphite, Mineral phase of bone(hydroxyapatite) What are the mechanical properties of metal vs. Ceramics? What are the advantages of ceramic vs. Metals?

    12. Lecture 2: Functional Biomaterials How does the human body respond to a biomaterial ? What materials are currently used as biomaterials? How are these biomaterials characterised? What happens to the biomaterial once implanted? What kind of surface modification can improve the biocompatibility of the biomaterial? What changes in the bulk can improve the performance of the biomaterial? How does nature "design" biological materials? Mimicking Nature: Biomimetic (Bionic) Material Design Where do we go from here ? Lecture 3: Combining materials with living tissues – tissue engineering.

    13. Characterisation of Biomaterials Bulk: FTIR, DMA, DSC, TGA Surface: X-Ray Photoelectron spectroscopy, TOF-SIMS, In-vitro: Simulated Body Fluid In-vivo: Biocompatibility, Cytotoxicity

    14. Lecture 2: Functional Biomaterials How does the human body respond to a biomaterial ? What materials are currently used as biomaterials? How are these biomaterials characterised? What happens to the biomaterial once implanted? What kind of surface modification can improve the biocompatibility of the biomaterial? What changes in the bulk can improve the performance of the biomaterial? How does nature "design" biological materials? Mimicking Nature: Biomimetic (Bionic) Material Design Where do we go from here ? Lecture 3: Combining materials with living tissues – tissue engineering.

    15. Architecture of Soft Tissue vs. Synthetic Gel Ordered microstructure and nanostructure Anisotropic Self-assembly of small molecules High Charge density Tough Amorphous Isotropic Crosslinking of long chains Low charge density Fragile

    16. Hard Tissue Architecture: Some numbers

    17. Hard Tissue Architecture: Nature, The Original Nanotechnologist? Biological Materials exhibit many levels of heirarchical structures from macroscopic to microscopic length scales. Bone has 7 orders of heirarchy Hard Tissue: Mineral crystals embedded in soft organic matrix The protein matrix behaves like a soft wrap around the mineral plateltes and HOMOGENIZES the stress distribution within the composite

    18. Architecture of Hard Tissue Staggered mineral platelets (hydroxyapataite) embedded in a collagen matrix Arrangement of platelets in preferred orientations makes biocomposites intrinsically anisotropic Under an applied tensile stress, the mineral platelets carry most of the tensile load Protein matrix transfers the load between mineral crystals via shear Biocomposites can be describes through tension-shear model described by Ji et. al.

    19. Lecture 2: Functional Biomaterials How does the human body respond to a biomaterial ? What materials are currently used as biomaterials? How are these biomaterials characterised? What happens to the biomaterial once implanted? What kind of surface modification can improve the biocompatibility of the biomaterial? What changes in the bulk can improve the performance of the biomaterial? How does nature "design" biological materials? Mimicking Nature: Biomimetic (Bionic) Material Design Where do we go from here ? Lecture 3: Combining materials with living tissues – tissue engineering.

    20. Example 1: Biomimetic Deposition of Apatite Coating on Surface-Modified NiTi Alloy High content of Ni is of concern with regards to biocompatibility TiO2 is method of choice to modify NiTi The heat-treated alloy was immersed in SBF to allow for biomimetic deposition of the apatite layer on the surface of the coating Heat-treated NiTi induced a layer of microcrystalline carbonate containing hydroxyapatite How so?

    21. Example 2: Synthesis of bone-like apatite/collagen nanocomposite Bone-like nanoapatite was prepared by addition of calcium nitrate aqueous solution into the neutral collgen sol containing ammonium phosphate Composite showed features of natural bone

    22. Cartilage : Active Material?

    23. Lecture 2: Functional Biomaterials How does the human body respond to a biomaterial ? What materials are currently used as biomaterials? How are these biomaterials characterised? What happens to the biomaterial once implanted? What kind of surface modification can improve the biocompatibility of the biomaterial? What changes in the bulk can improve the performance of the biomaterial? How does nature "design" biological materials? Mimicking Nature: Biomimetic (Bionic) Material Design Where do we go from here ? Lecture 3: Combining materials with living tissues – tissue engineering.

    24. Bionic Implant & Device Implant that mimics – as far as possible – the structure AND function of the body part it replaces. Interacts with the human body in a bidirectional fashion Examples of Bionic Devices: Artificial Heart, Artificial Muscle, Cochlear Implant, Bioelectrodes, Mechanoactive Cartilage Towards seamless integration of implant with physiological environment Describe the evolution of a conventional bone implant towards a bionic bone implant,

    25. What surface modifications would you suggest to mitigate debris formation in existing metallic implants ? What fundamental changes would you bring about? What material combination would you use to replicate the spongy interior and the tough exterior of the bone?

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