CHAPTER 6

1. BiomaterialProcessing CHAPTER 6 6.1 Introduction: Importance of Biomaterials Processing Processing --- bulk or surface properties, shape alteration, sterilization 6.2 Processing to Improve Bulk Properties Mechanical strength increase with reduced dislocation motion 6.2.1. Metals Defects in crystal structure --- decreased dislocation motion

2. (1) Alloying alloys vs. pure metals solid solution with substitutional point defects localized lattice strain [tensile vs. compressive strain] Dislocation --- crystal distortion larger atoms on tensile side of an edge dislocation stabilization Moving dislocation away from impurity overall lattice strain 증가 increase the shear stress to cause dislocation movement (strength) (2) Strain hardening line defects (dislocation 수 증가) dislocation --- lattice strain more energy to move the stress field of a dislocation through the combined localized strains plastic deformation --- # of dislocation 증가 --- higher energy Cold working at T < Tm : strength 증가, ductility 감소

3. (3) Grain size refinement polycrystalline metals Plastic deformation: 1) dislocations must cross between grains 2) mismatch: discontinuity of slip planes between grains Metals with small grains ---- stronger 1) addition of grain boundaries 2) grain size via thermal processing 3) relative orientations of the grains (4) Annealing ductility and toughness 증가, internal stress 감소, specific grain structure Heat treatment 1) grain size 증가 2) # of grain boundaries 감소 (decrease in area of the grain boundaries) Three stages 1) heating; 2) maintaining/soaking; 3) quenching Parameters affecting products 1) material composition 2) quenching rate Heat extraction water > oil > air high surface area to volume ratio

4. (5) Precipitation hardening addition of volume defects local lattice strains --- barrier to dislocation motion 6.2.2. Ceramics difficult dislocation motion improve ductility by increasing number of slip systems 6.2.3. Polymers semicrystalline polymers --- % crystallinity 1) thermal processing method 2) pre-drawing procedure 3) crosslinking chain mobility 감소 6.3. Processing to Form Desired Shapes plastic deformation ---- strength & fabrication of complex shapes 6.4. Processing of Metals 6.4.1. Forming Metals 1) Forming operation at T>about 0.3 Tm (recrystallization temp) hot working 2) cold-worked materials

5. Forging metals • blacksmith / closed-die forging • (2) Rolling metals • (3) Extrusion of metals • (4) Drawing metals • Metal fibers --- 3-D meshes • --- tissue engineering application • 6.4.2. Casting Metals • Sand casting of metals • Investment casting of metals

6. 6.4.3. Powder Processing of Metals Powder metallurgy (P/M) green compact hot isotactic pressing (HIP) 100 M Pa & 1100 oC sintered metal powder [densified by removing small voids] amalgamation at high temp 6.4.4. Rapid Manufacturing of Metals solid freeform fabrication (SFF) selective laser sintering (SLS) metal powder --- laser scanning --- localized energy --- small solid layer --- layer-by-layer prep.

7. 6.4.5. Welding Metals joining two materials together --- solid bridge 6.4.6. Machining of Metals cutting implement (metals and polymers) 6.5. Processing of Ceramics glasses, crystalline ceramics, glass-ceramics 6.5.1. Glass forming techniques glasses --- amorphous softening point [viscosity 4x107 P] working point [viscosity 104 P] glass shaping between SP and WP 1) pressing (metal forging) 2) blowing 3) drawing

8. 6.5.2. Casting and Firing of Ceramics • Casting ceramics • small ceramic particles + water/organic binder • green ware • shrinkage and cracking • (2) Firing ceramics • fire the cast pieces at 900 – 1400 oC • density and mechanical property 증가 • cf) porous ceramic prep • temp and length of firing • 1) polycrystalline ceramics • 2) vitrified materials [soft glass formation --- filling the void areas] • 3) glass-ceramics • Glass becomes polycrystalline ceramics. • 6.5.3. Powder Processing of Ceramics • powdered ceramic + water/binding agent • hot pressing procedure • sufficient atomic diffusion to reduce overall surface area • reduced porosity

9. 6.5.4. Rapid Manufacturing of Ceramics 1) three-dim printing (3DP) binder-based method 2) SFF ---- mold prep 6.6. Processing of Polymers 6.6.1. Thermoplasts vs. thermosets 1) thermoplast heat --- soften cool --- harden forming and casting 2) thermostet heat --- permanent hardening no softening covalent crosslinking casting 6.6.2. Forming Polymers (1) Extrusion of polymers (2) Fiber spinning of polymers

10. Mesh formation [carriers for cells or bioactive agents] weaving, knitting, braiding porosity: diameter and packing density of fibers For fibers < 10 mm electrospinning strong electric field (5-30 kV) fine looping fibers three-dimensional non-weaven mesh 6.6.3. Casting Polymers molding for polymers (1) Compression molding of polymers

11. (2) Injection molding of polymers • speed fabrication • (3) Blow molding of polymers • 6.6.4. Rapid Manufacturing of Polymers • 1) 3DP (SFF techniques) • binder: organic solvent • 2) stereolithography • liquid stock • 6.7. Processing to Improve Biocompatibility • materials with no infection • no immune responses • 6.7.1. Sterilization • sterility assurance level (SAL) • time and dose of sterilization • methods of sterilization • compatibility • Steam sterilization (autoclave) • Ethylene oxide sterilization • Radiation sterilization • g-ray (60Co) and electron beam 6.7.2. Fixation of Natural Materials immune response X-linking of collagen-derived materials