Biomimetic_Design_of - Biomimetic Design of a Ceramic/Polymer Bioactive Composite J J Mecholsky Jr Materials Science and Engineering University of

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Unformatted text preview: Biomimetic Design of a Ceramic/Polymer Bioactive Composite J. J. Mecholsky, Jr. Materials Science and Engineering University of Florida Gainesville FL Imperial College July 19, 2010 Outline • Objective • Background Properties – Strength & Toughness Materials -Manatee Rib Bones, Menippe mercanaria chelae, Strombus gigas shell • Mechanical (Structural) Properties Properties - Toughness, stress-strain, hardness Material-ceramic-polymer composites Structure - multilayer, laminated • Potential Application • Conclusions & Design Principles Objective To use our observations of the mechanical properties and fracture path in selected biological structures to suggest improved designs for synthesized structures. Hierarchical Structure of Bone Does It Best Human Bone Rho J., Kuhn-Spearing L., Zioupos P., Mechanical properties and the hierarchical structure of bone. Med. Eng. & Phy. 20 (1998) 92-102 Names Can Lead To Confusion Biological Structures - Fabricated naturally with naturally occurring materials. Bio-inspired Structures - Developing synthetic or a combination of synthetic and natural materials based on principles of biological structures. Biomimetic Structures - Structures which mimic nature either by imitating structure or function ( or both). There Are Several Properties That Are Important For Composites: Elastic Modulus – Governs Deflection S e Strength – Governs Load Bearing Capacity Toughness – Governs Crack Propagation Elastic Modulus = Stress / Strain P Work Of Fracture = A = Area = π r 2 A = Brittle Area Under Stress – Strain Curve S or σ r P Strain = e or ε S =Stress = P / A e = Strain = ∆ L / L B = Ductile Crack Size Governs Strength P A = Area = π r 2 c1 Kc =Toughness = Y S1 c1 1/2 Kc = Toughness = Y S2 c2 1/2 Strength = Stress at fracture r P If c1 < c2 then S1 > S2 NOTE: Toughness Is Equal ! c2 Lamination Induces Toughness Increase P A = Area = π r 2 Kc1 =Toughness = Y S1 c1 1/2 c1 c2 Kc2 = Toughness = Y S2 c2 1/2 r P c1 < c2 & Kc2 > Kc1 Composite structures increase mechanical properties by orders of magnitude M Sarikaya and IA Aksay, Biomimetics: Design and Processing of Materials, AIP Press, New York. (1995) p.49. Observations of Many Biological Structures Show That Ceramic-Polymer Composites Improve Properties Manatee Rib Bone - HA-polymer (protein) composite Crab Chelae - multi-layered (calcite)CaCO3 - fibrous (chitin)/(protein) polymer composite Conch Shell - hierarchical multi-layered (aragonite) CaCO3 (protein) polymer composite Manatees Are Friendly And Lovable 17 to 19 pairs of ribs cover most of the body and protect the organs inside the ribs K. Clifton Ph.D. UF Thesis 2005 Manatee Bones Fracture Similar to Ceramics Porosity Affects Toughness KC=2.6 MPam1/2 MSTM0102 #9 Dist B1 J. H Yan, MSE UF 2002 KC=2.0 MPam1/2 MSTM0102 #9 Dist A3 Smaller manatees have greater porosity Manatees keep filling in spaces and laying down plexiform bone on periosteal surface as they grow. J. H Yan, MSE UF 2002 Strength (σ ) & Toughness (KC) Show Similar Trends Strength Toughness 3.0 2.8 1/2 ) Females Males 160 140 Toughness (MPam Flexural strength (MPa) 180 120 100 R2=.79 80 2.6 Females Males 2.4 2.2 2.0 1.8 R2=.73 1.6 1.4 60 50 100 150 200 250 300 Total body length (cm) 350 400 1.2 100 200 300 Total body length (cm) N.B. : Age is considered directly related to body length 400 Kc, WOF & J –Integral Provide Different Views of Fracture 100 2.7 Kc 80 Load (N) 60 40 Calf Subadult Subadult Adult 81 N 14 E 6.1 W 75 N 17 E 2.4 W 2.6 Kc 59 N 13 E 10.3 W 49 N 11 E 2.2 W 20 1.8Kc 0 0.0 0.5 1.0 1.5 2.0 Displacement (mm) K. Clifton, Ph.D. UF Thesis 2005 2.5 3.0 3.5 Conclusions For Manatee Bones ­ Fractography Can Be Used To Measure Toughness in Manatee Rib Bone. ­ Fracture toughness varies in different areas of rib bone due to the compactness of the bone. ­ Microstructure Affects Properties - Multiple Tests Are Needed To Describe Behavior Observations of Many Biological Structures Show Ceramic-Polymer Composites Manatee Rib Bone - HA-polymer composite Crab Chelae - multi-layered CaCO3 fibrous composite Conch Shell - Hierarchical Multi-layered Composite The Florida Stone Crab Is Difficult To Obtain Menippe mercenaria requirements are relatively simple : • Florida stone crabs are bellicose and must have hard shells. • Exoskeleton must protect against impact and also must be porous for filtering nutrients from sea water. • Stone crabs break clam shells for meat. Crab Chelae Are Tanned (Blackened) Indentation shows damage greater in untanned exoskeleton Tanned (black) exoskeleton Untanned (yellow) exoskeleton Tanned Region Is Harder, Stronger & Tougher Than Untanned Property/ Region Light (Yellow) Dark (Black) Elastic Modulus, GPa Hardness, GPa Strength, MPa 1/2 Toughness, MPam 15 0.48 ± 0.04 32 ± 24 1.0 ± 0.4 26 1.33 ± 0.06 109± 23 2.3 ± 0.4 Vertical Pores Are Filled­in for Tanned (Black) Exoskeleton exterior Interior of exoskeleton Conclusions For Florida Stone Crab Results • Porosity is necessary for survival. • Increased toughness and hardness of tanned regions result from (polymeric) proteins filling in pores when and where needed. • Lamination & microstructure help deflect cracks. Observations of Many Biological Structures Show Ceramic-Polymer Composites Manatee Rib Bone - HA-polymer composite Crab Chelae - multi-layered CaCO3 fibrous composite Conch Shell - Hierarchical Multi-layered Composite The Strombus gigas (Queen Conch) Is Beautiful And Tough Conch shell has a highly organized hierarchical structure 1st order lamella 2nd order lamella 3rd order lamella First order lamellae show different fracture surfaces Inner Layer (A) Middle Layer (B) Brittle behavior after removal of protein Stress [MPa] 40.00 30.00 20.00 10.00 0.00 0.0004 0.0008 0.0012 0.0015 Strain Heat Treatment (200°C; 24h); tested in air, room temp. 0.1mm/min. Strength (m)= 34.6 ± 19.5 MPa WOF =0.6± 0.4 kJ/m2 Stress-strain diagram shows composite behavior 150.00 100.00 50.00 0.006 0.005 0.004 0.003 0.002 0.001 0.00 strain Stress [MPa] 200.00 Strain Strength (m)= 176.9 ± 65.2 Air, Room Temperature, 0.1 mm/min MPa WOF = 4.8± 2.9 kJ/m2 0.009 0.007 0.006 0.005 0.004 0.003 0.002 300.00 250.00 200.00 150.00 100.00 50.00 0.00 0.001 Stress [Mpa] WOF increases for wet conditions Strain Tested Wet, Room Temperature, 0.1mm/ min Strength (m)= 249.2 ± 86.8 MPa Fracture surface changes with amount of water Burn out Air Wet Work of Fracture (kJ/m^2) Water results are consistent with VE behavior 14.00 12.00 10.00 8.00 WOF dry 6.00 WOF wet 4.00 2.00 0.00 0.02 0.5 20 500 Stressing Rate (MPa/s) Presence of protein evident in DI group Also between first order lamina Delocalized damage leads to increased WOF • Multiple Channel Cracks • Crack bridging • Crack branching • Delamination Kuhn-Spearing et al., J. Mater. Sci. 31,6583-6594(1996). Conclusions For Conch • The absence of protein leads to fracture in a brittle manner. • Evidence of ductile bridging present for specimens stored in aqueous solutions. • The presence of water improves mechanical properties. • Lamination aids toughness. • Hierarchical structure helps in crack arrest. Observations of Many Biological Structures Show Natural Design Principles • Non-linear Stress-Strain Behavior • Multi-layered (hierarchical ) Design • Structure & Materials Serve Need - Form Follows Function Human dentin is part of a FG multilayered composite structure He and Swain, Journal of Dentistry 37 ( 2009 ) 596 – 603 Human dentin has a complicated structure that can produce many toughening mechanisms. Peritubular dentin Intertubular dentin Human dentin has a structure that shows many toughening mechanisms: - crack bridging1 - microcracking and crack deflection1 - fiber (dentin tubules) pullout2 1) Nalla RK, Kinney JH, Ritchie RO (2003). Biomaterials 24(22):3955-3968. 2) Imbeni V, Nalla RK, Bosi C, Kinney JH, Ritchie RO (2003). J Biomed Mat Res 66A(1):1-9. Lamination Provides Crack Bridging & Multiple Cracking Interfacial bonding produces different stress strain curves D. Mitchell, Ph.D. Dissertation, UF (2001) Hierarchical Structures Provide Guidance Arthropod Cuticle Conch Shell 1st order lamella 2nd order lamella 3rd order lamella Vincent J., Structural Biomaterials (Princeton Univerasity Press, Princeton N.J., 1990) pg.133 Hill T., Ph.D. Dissertation, Univ. of. Fla. 2001 Materials Selected For Composite Fabrication Are Reported to be Biocompatible Polysulfone (PSu) Hydroxyapatite (HA) – Thermoplastic – Good Thermal Stability – Used for blood filtration membranes – Bioglass/PSu composites tested In vivo1 – Ca10(PO4)6(OH)2 – Primary mineral phase found in bone – Biocompatible – Porous versions can be bioactive O CH3 H3C O C O CH3 1 Marcolongo M., et. al. J. Biomed. Mater. Res. 39: 161-170 (1998) S O CH3 n Different geometries are named according to the scheme Outer HA Layer-PSu Layer-Middle-HA Layer Outer HA Layer PSu Layer Middle HA Layer PSu Layer Outer HA Layer For example, laminates with five layers of thicknesses 400μm-200μm-800μm-200μm-400μm are identified as 400-200-800 400 μm HA 200 μm PSu 800 μm HA 200 μm PSu 400 μm HA Laminate Behavior Is Superior To Monolithic HA Comparison of Monolithic HA and Laminate Load­Displacement Curves Laminates Show Better Mechanical Properties in All Measured Areas 700 Laminates 600 Monoliths 500 400 300 200 100 0 Failure Load (N) Failure Stress (MPa) WoF (J/m2) Toughness (kJ/m3) Percent Increases Failure Load = 140% Failure Stress = 154% Work of Fracture = 5500% Toughness = 1100% T = ∫ σdε Determination of Failure Mechanisms • Laminate failure mechanisms determined through a combination of fractography and laminate theory calculations. • Different failure mechanisms exist for laminates with different outer HA layer thicknesses. Fracture Origins Identified Using Fractography 200 μm Fracture Mechanics Equation K c = Yσ f c Failure Stress = σ a 2b K = 0.6 MPa-m for Monolithic HA c = 300 - 350 μm Middle Layer Failure Results From Crack Reinitiation Outer HA Layer PSu Layer Middle HA Layer Outer HA and PSu Layers 500 μm Optical Micrograph SEM Middle Layer Failure Stress Calculated From Flaw Size and Laminate Theory Failure Stress of Middle HA Layer from Flaw Size Measurement: Kc σf = Yc Failure Stress of Middle HA Layer from Laminate Theory Calculations: σ f = P × σ LT − M Results Calculation Method Failure Stress Flaw Size 30 ± 2 Laminate Theory 28 ± 6 n = 13, 400-200-800 laminates Agreement of these numbers indicates failure of the laminates is controlled by the flaw size of the middle layer!!! Different Failure Mechanism for Laminates with Outer Layer Thickness < 400 μm • • • • 200 μm Flaws are larger than outer layer thickness Initial Flaw spans the two outer layers and penetrates the middle layer The entire area acts as the initial flaw Presence of PSu increases the fracture toughness of the initial flaw region PSu Penetrates the Entire Thickness of the HA Layers … and bridges cracks in the HA Layers HA/PSu Laminates Show Tremendous Potential For Bone Replacements HA/PSu Laminates Points indicate the average composite modulus for each laminate geometry calculated through rule of mixtures Box indicates the range of the upper and lower bounds for the composite modulus After:Suchanek W., Yashimura M., J. of Materials Research, 13 [1]: 94-117 (1998) Designed Multi-layerTape Cast Bridge Offers Potential Improvement • Many Failure Sources Are Near Interfaces • Design Strategy Will Be To Create Multilayer, Reinforced Laminates • 3 unit Bridges Can Be Tape Cast! The hierarchical composite structure will have three organizational levels: 1. Laminate structure 2. Fiber orientation within lamina 3. Compositional gradient within each lamina. Fibers Align Through Tape Casting • Doctor Blade Method Double Casting Method Tape Casting Can Align Fibers Kragness E.D., Amateau M.F. Messing G.L. Processing and Characterization of Lamianted SiC Whisker Reinforced Al2O3 J. Comp. Mater. 25 416-432 (1991) First Hierarchical Level: Laminate Structure Ceramic Lamina With Oriented Glass Fibers Polymer Second Hierarchical Level: Fiber Orientation Ceramic Laminae Third Hierarchical Level: Compositional Gradient Multifunctional Ceramics Research Center Tapecasting Can Be Used For All-Ceramic Crown Bridge (I) (a) prepared teeth (b) duplicated stone (c) alumina tapes (d) laminated tapes to form pontic (e) alumina tape pressed (f) stone model sectioned before sintering on stone mold Korea Institute of Science and Technology Multifunctional Ceramics Research Center Multilayer Structures Are Possible For All-Ceramic Crown Bridge (II) Korea Institute of Science and Technology Designing tough, strong structures means: • Producing a multi-layer composite; • Attempting to use low modulus materials; • Producing a hierarchical structure with at least three length scales; • Controlling the bonding of the interface with specific end groups; and • Maintaining the viscoelastic nature of the polymer. The End or Just The Beginning? University of Florida, Gainesville FL Present & former students deserve much credit: Dr. Jia - Hau Yan - Manatee research Dr. Kari Clifton - Manatee research Dr. Tom Hill - Strombus gigas research Jim Mellman – Protein identification research Cindy Melnick Sloop - Menippe mercanaria research Dr. Burak Taskonak – Bridge Work Failure Analysis Dr. Clifford Wilson – Lamination of CeramicPolymer Composites We thank NIDR/NIH for partial support of this work. Hard Tissues In The Body Can Be Modeled As Ceramic-Polymer Composites Main Structural Hard Tissues : Ca(OH)2 • 3Ca3 (PO4)2 [HA] {Really = [Ca5(PO4CO3)3] Carbonated Apatite} Main Model Materials : Ca3(PO4)2 – PE Ca3(PO4)2 – PLA-PGA Ca CO3 - PLA Ca CO3 - Protein Cracks Can Occur Near Connector Region Proposed toughening mechanisms • Viscoplastic deformation of organic layers. • Crack deflection by organic layers. • Delocalization of damage. Menig et al., Mater. Sci & Engr.A297 (2001) 203-211. Manatee Bone Is Highly Mineralized • Trabecular (Cancellous) bone: porous • Compact bone: dense Plexiform bone: type of primary lamellar bone •Manatee rib bones are dense (compact bone), plexiform bone and lack marrow cavities. These dense bones have been considered to be a result of the manatee’s low metabolic rate. Toughness Decreases From Cranial To Caudal in Younger Manatees MSTM0102(60,96,89) 2.8 265cm 2.6 K c (MPa*m1/2) 2.4 MSW0134(10,13,20) 2.2 205 cm 2.0 1.8 MSW0057(17,9,9 ) 1.6 1.4 1.2 1.0 #4 Head #10 or #9 Middle #14 Tail 201 cm Applying Fracture Mechanics to the Failure Analysis (FA) of Dental Materials • FA can help dentists produce improved materials for restorations. • FA of failed bridges and crowns from patients have identified needed improvements for commercial products. Thompson et al. J Dent Res 1994 73(12) 1824 Majority of the fractures originated from the connector area. 9 connector fractures 3 veneer fractures 1 core fracture The majority of the connector fractures originated within occlusal surface. Occlusal surface The failure stress of the veneered glass-ceramic FPDs is controlled by the veneer layer. Interface Interface Origin Ductile Layer Reinforcement Increases Strength & Toughness Alumina / Nickel Chen and Mecholsky, 1993 Laminate Strength is Insensitive to Flaw Size Mechanisms of Toughening * Ductile layer bridging * Plastic deformation Strengthening Mechanism * Residual compressive stress field Chen and Mecholsky, 1993 Ductile Layer Reinforcement Increases Bioglass Toughness SEM 326A 12x Bioglass Forms Bond with Ductile Metallic Layer SEM 326A 250X Crack Travels Along Interface Then Arrests Interface Toughness Can Be Determined Using CNDCB D a0 GIc = A2 P2 / (E1 D13) KIcSR = A P / D3/2 E1d13=E2d23 θ P Material 1 d1 Material 2 d2 P A = Calibration Constant ~ 23 Mecholsky & Barker ASTM STP 855, 324 Fractal Dimension Characterizes Interface Ductile Layer Reinforcement Increases Strength & Toughness Increases σ, KIC controlled by interfacial bonding Chen and Mecholsky, 1993 Each layer demonstrates unique fracture surfaces A B Majority of the fractures originated from the connector area. 9 connector fractures 3 veneer fractures 1 core fracture Crack Propagation Can Result in Partial Fracture Ductile Layer Increases Strength Ductile and Toughness 4.50 4.00 3.50 Load (kg) 3.00 2.50 2.00 1.50 1.00 0.50 0.00 0 100 200 300 400 500 Displacement (microns) 600 700 Larger manatees have higher apparent fracture toughness in sub­adults Kc [MPa(m)1/2] Sub-Adult Calf ...
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This note was uploaded on 06/10/2011 for the course EMA 6715 taught by Professor Mecholsky during the Fall '08 term at University of Florida.

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