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G:\Biomaterial Fabrication

Jun 13, 2015

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fabrication of biomaterials with emphasis on rapid prototyping techniques

  • 1. ARJUN G NAMBOODIRI Polymer processing Laboratory 4/6/10 BIOMATERIAL FABRICATION TECHNIQUES

2. OVERVIEW

  • INTRODUCTION
  • USE OF BIOMATERIALS
  • MATERIALS USED AS BIOMATERIALS
  • EVOLUTION OF BIOMATERIALS
  • SCAFFOLD FABRICATION TECHNIQUES
  • LIMITATIONS
  • RAPID PROTOTYPING
  • TOWARDS NANOTECHNOLOGY
  • CONCLUSION

3. INTRODUCTION Non viable material used in medical devices intended to interact with biological systems (Williams 1987)A biomaterial is "any substance (other than drugs) or combination of substances synthetic or natural in origin, which can be used for any period of time, as a whole or as a part of a system which treats, augments, or replaces any tissue, organ, or function of the body". BIOMATERIAL ONE MUST HAVE EITHER VAST KNOWLEDGE OR DIFFERENT COLLABORATORS WITH DIFFERENT SPECIALITIES INORDER TO DEVELOP BIOMATERIALS IN MEDICINE AND DENTISTRY 4. USE OF BIOMATERIALS REPLACEMENT OF DISEASEDOR DAMAGEDPARTS ASSIST IN HEALING IMPROVE FUNCTION CORRECT FUNCTIONALABNORMALITIES AID TO DIAGONISE AID TO TREATMENT CORRECT COSMETIC PROBLEMS 5. MATERIALS FOR USE AS BIOMATERIALS

  • Polymer: Nylon, Polytetrafluoroethylene,Polyurethane, Silicone rubber,polycaprolactone
  • Metals: Ti, Co-Cr alloy, Stainless Steel, Pt, Au etc
  • Ceramics: Aluminum oxide, Calcium phosphate,Hydroxyapitite, Carbon etc
  • Composites: Fiber reinforced bone cements etc

6. Evolution of Biomaterials StructuralFunctional Tissue Engineering Constructs (Scaffolds) Soft Tissue Replacements First generation Second Generation Third Generation 7. SCAFFOLD FABRICATION TECHNIQUES

  • Solvent Casting and Particulate Leaching
  • Melt molding
  • Gas Foaming
  • Fiber bonding
  • Freeze drying

8. SOLVENT CASTING/ PARTICULATE LEACHING

  • Incorporation of Salt particles
  • Polymer/solvent solution e.g. PLLA/chloroform
  • Casting
  • Vacuum dry
  • Immerse in water
  • salt particlesof a specific diameter to produce a uniform suspension (Mikoset al. , 1994,1996).

9. Advantage -Highly porous scaffold with porosity up to93% and an average pore diameters up to 500u m can beprepared using this technique. Disadvantage- A disadvantage of thismethod is that it can only be used to produce thin wafers or membranes up to 3mm thick. 10. MELT MOLDING

  • This process involves filling a mould with polymer powder/melt and obtaining the shape of the mould.

MELTMOULDING COMPRESSIONMOULDING INJECTIONMOULDING 11. In the work done by Thompson et al in 1995 they used theCOMPRESSION MOULDING PRINCIPLEwhere aTEFLON MOULDwas used with PLGA and gelatin micro spheres of specific diameter, and then heating the mould above the glass-transition temperature of PLGA while applying pressure to the mixture (This treatment causes the PLGA particles to bond together. Once the mould is removed, the gelatin component is leached out by immersing in water and the scaffold is then dried. 12. GAS FOAMING

  • Another approach to using gas as porogen was developed by Nam et al. (Park, 1999; Nam et al. 2000).
  • This technique includes both melt moulding and particulate leaching aspects.
  • Porosities as high as 90% with pore sizes from 200-500 um are attained using this technique.

13.

  • Fabrication process
  • Ammonium bicarbonate is added to a solution of polymer in methylene chloride or chloroform.
  • The resultant mixture ishighly viscous and canbe shaped with a mold .
  • The solvent is thenevaporatedand the composite is eithervacuum driedor immersed in hot water.

14. FREEZE DRYING The pore size can be controlled by the freezing rate and pH; a fast freezing rate produces smaller pores.Freeze-drying works by freezing the material and then reducing the surrounding pressure and adding enough heat to allow the frozen water in the material to sublime directly from the solid phase to the gas phase.Yannaset al., 1980 Collagen scaffolds have been made by freezing a dispersion or solution of collagen and then freeze drying . Dagalakiset al., 1980; Doillon et al., 1986 15. 16. FIBER BONDING PGA fibers are immersed in PLLA solution. 17. LIMITATIONS

  • Poor mechanical integrity
  • Residual organic solvents
  • Lack of structural stability
  • Some techniques can only be used to make very small membranes.
  • All the materials cannot be used for all the processes.
  • Difficult to control membrane porosity and morphology.

18. RAPID PROTOTYPING TECHNIQUE 3D Solidmodeling Datapreparation Part Building Redesign Pass Reject A family of fabrication processes developed to make engineering prototypes in minimum lead time based on a CAD model of the item 19. BENEFITS: 1)Reduced lead times to produce prototype components. 2)Improved ability to visualize the part geometry due to its physical existence. 3)Earlier detection and reduction of design errors. 4)Increased capability to compute manufacturing properties of components and assemblies. 20. RAPID PROTOTYPING PROCESSES

  • Three Dimensional Printing (3DP)
  • Stereolithography (SLA)
  • Selective Laser Sintering (SLS)
  • Fused Deposition Modeling (FDM)
  • Organ printing
  • Membrane lamination

21. Technology invented at MIT byBredt et al (1998) 1. Layer of powder spread on platform 2. Ink-jet printer head deposits drops of binder* on part cross-section 3. Binder dissolves and joins adjacent powder particles 4. Table lowered by layer thickness 5. New layer of powder deposited above previous layer 6. Repeat steps 2-4 till part is built 7. Shake powder to get part *Materials used: starch, plaster-ceramic powder Three Dimensional Printing (3DP) 22.

  • Advantages
  • Easy process
  • Achievable pore size=45500 um
  • High porosity
  • High surface area to volume ratio
  • Independent control of porosity and pore size
  • Wide range of materials
  • Disadvantages
  • Use of toxic organic solvents
  • Lack of mechanical strength

23. 3D printed testpart with interconnecting channels. (a) Whole structure. (b) Detail view of the interconnecting channel structure with diameter of about 500 m. HA scaffolds seeded with MC3T3-E1 cells Binder(Schelofix) 24. STEREOLITHOGRAPHY 1. Raw material:photocurable monomer by a laser beam 2. Part constructed in layers of thickness3. Supporting platformincontainer at depth . UV lasersolidifies part cross- section 4. Platform lowered by5. Part cross-section computed atcurrent height6. Repeat Steps 4, 5 7. Removed completed part, 8. Break off supporting structures 9. Cure the part in oven. Polymerization occurs by theexposure of liquid resin to laser. He-Cd Laser UV beam Rotating mirror High-speed stepper motors Focusing system Liquid resin Part Platform Elevation control Support structures He-Ne Laser Sensor system for resin depth 25.

  • Advantages Relative easy to remove support materials. Relative easy to achieve small feature. Disadvantage Limited by the development ofphoto polymerisable liquid monomer material

26. Porous polylactide constructs Light microscopy images showing the spreading of mouse pre-osteoblasts after 1 d of culturing on PDLLA network 27. SELECTIVE LASER SINTERING

  • Moving laser beam sinters heatfusible powders in areas corresponding to the CAD geometry model one layer at a time to build the solid part
  • After each layer is completed, a new layer of loose powders is spread across the surface
  • Layer by layer, the powders are gradually bonded by the laser beam into a solid mass that forms the 3-D part geometry
  • In areas not sintered, the powders are loose and can be poured out of completed part

28.

  • Advantages
  • High porosity
  • Achievable pore size=45200 um
  • High surface area to volume ratio
  • Complete pore interconnectivity
  • Good compressive strengths
  • Wide range of materials
  • Solvent free
  • Disadvantages
  • High processing temperatures

29. (a) STL design file of porous scaffold. (b) PCL scaffold fabricated by SLS. cortical shell and areas of trabeculated structures within the marrow space 30. FUSED DEPOSITION MODELING

  • FDM uses a moving nozzle to extrude a fibre of polymeric material (x- and y-axis control) from which the physical model is built layer-by-layer.
  • The model is lowered (z-axis control) and the procedure repeated.
  • Although the fibre must also produce external structures to support overhanging or unconnected features that need to be manually removed

31.

  • Advantages
  • High porosity
  • Achievable pore size=2501000 um
  • Complete pore interconnectivity
  • Macro shape control
  • Independent control of porosity and pore size
  • Good compressive strengths