CoatingImplants. ResearchEngineer OrchidOrthopedicSolutions

Transcription

1 2014 CoatingImplants ParimalBapat,Ph.D. ResearchEngineer OrchidOrthopedicSolutions

2 OMTEC 2014 Technical Session: Coating Implants June 11 th :30 PM 2:30 PM Presenter: Dr. Parimal V. Bapat Research Engineer Orchid Orthopedics Solutions

3 Outline Orchid Orthopedic Solutions Coatings on Medical implants Plasma Sprayed HA Coatings: Process and Properties Future of HA coatings FDA regulatory hurdles

4 Orchid Orthopedic Solutions What is Orchid? A world leading Medical Device Contract Design and Manufacturing company that offers a comprehensive portfolio of services for implants and instruments with significant experience in the joint reconstruction, spine, trauma, dental and sports medicine markets

5 Orchid Global Footprint

6 Dr. Parimal V Bapat Research Engineer at Orchid (June 2011 present) Developed a porous rough TPS coating. Developed a jet wash cleaning process. Currently working on ultra thin HA coatings and additive manufactured implants. Work with customer on FDA 510 K submissions. Active ASTM member and a technical contact for ASTM F PhD student at University of Alabama in Birmingham (UAB), USA Thesis: Gas phase laser synthesis and processing of calcium phosphate nanoparticles for biomedical applications Expertise in Nano-bio materials for biomedical applications. Expertise in materials characterization techniques such as XRD, TEM, AFM, Aerosol measurements etc.

7 Why do we need Orthopedic Implants To replace diseased bone & joints Arthritis, Osteoporosis, Cancer etc. Trauma

8 Implants and Implant Evolution Total Knee Replacement Shoulder Replacement Total Hip Replacement Implant materials: Ti and CoCr alloys, SS etc. Properties: Corrosion resistant, strength, rigidity, long fatigue life, biocompatibility etc.

9 Implant Materials and Uses Material Metals Ti and Ti alloys Co-Cr-Mo alloys Stainless steel alloys Polymers Ultrahigh molecular weight polyethylene (UHMWPE) Polymethylmethacrylate (PMMA) Ceramics Alumina Zirconia TJA = total-joint anrthroplasty Primary Uses Plates, screws, nonbearing surfaces of TJA components TJA components, including bearing surfaces Wires, pins, screws, plates, cabling Low-friction inserts for bearing surfaces in TJA Bone cement Bearing-surfaces of TJA components Bearing-surfaces of TJA components

10 Implant-tissue reaction Implant Tissue Reaction Toxic Biologically nearly inert smooth surface Biologically nearly inert porous or threaded surface Bioactive Dissolution of implant Consequence Tissue dies Tissue forms a nonadherent capsule around the implant (no bonding with bone) Tissue grows into pores or threads (forms mechanical bond with bone) Tissue forms interfacial bond with implant (bioactive fixation) Implant resorption and replacement with soft tissues or bone

11 Bone

12 Cells found in Bone

13 Metallic Coatings on Medical Implants 1980s Sintered Bead Coatings Bio-inert Coatings 1990s Plasma Spray Coatings 2000 Foam CP-Ti and CoCr alloy beads CP Titanium alloy Ti alloy Porous Good Mechanical properties Cannot be applied to dissimilar substrate materials Porous Good Mechanical properties Rough surface Can be applied to dissimilar substrate materials Highly Porous Good Mechanical properties Rough surface Standalone products can be made

14 Orchid Implant Coatings Capabilities HA coating on titanium, cobalt-chromium or stainless steel TPS coating on titanium or CoCr substrates RBM surface treatment on titanium substrates Composite coatings including HA on plasma, beads and irregular sintered coatings, as well as TPS on RBM-prepared substrates Porous coatings include spherical bead, Osseomatrix (titanium foam) and Asymmatrix (irregular bead) Passivation per ASTM F86 Custom coating technologies Heat-treating Destructive and non-destructive testing Hydroxyapatite (HA) Osseomatrix Asymmatrix Resorbable Blast Media (RBM) Typical Projects Orthopedic coatings joint and spine Dental coatings Cardiovascular coatings Veterinary coatings Titanium Plasma Spray (TPS) Spherical Bead

15 Bioactive Material: Hydroxyapatite (HA) Major inorganic component of bone ECM Ca 10 (PO 4 ) 6 (OH) 2 High Osteoconductivity /Bioactivity Crystal structure Hexagonal Insulator with band gap 5eV Hardness - 5 on Mohs scale (Diamond is 10 on Mohs scale)

16 History of HA Coatings 1920 The suggestion of use for calcium phosphate materials was first reported as a bone graft material 1973 HA first used as a porous graft material 1980 First plasma sprayed coating on a dental implant 1984 First HA hip implants implanted in the U.S First FDA approval for HA on orthopedic implants Plasma Sprayed Coating

17 Plasma Spray Process High temperature Process ~ 10, C High velocity ~2000 m/s

18 Plasma Spray Coating Coating Properties Mechanical Properties Chemical Properties Morphology Properties Coating Adhesion Strength Static Shear Strength Shear Fatigue Strength Chemical Composition Phase Composition Trace Elements Coating appearance Color of the coating Coating Topography

19 Mechanical Properties Some of the important variables contributing to the mechanical integrity of the coating include: Degree of melting Substrate Surface preparation Coating Thickness Substrate material / mass Plasma sprayed coatings consist of layers of splatted particles

20 Residual Thermal Stress

21 Degree of Melting Over-melting deliberate over melting has the intention of greater adhesion and more efficient deposition this leads to cracking and compromised dissolution / mechanical behavior a b

22 Degree of Melting Under-melting deliberate under melting has the intention of preserving the original characteristics of the powder this leads to porosity and compromised dissolution / mechanical behavior Temperature of the plasma Arc gas Powder flow Gun Configuration

23 Surface Preparation Plasma sprayed HA coatings must ideally be applied to a grit blasted roughened surface which provides more surface area for adhesion Roughened surface Machined surface Grit composition Al 2 O 3 Mesh size Pressure Substrate hardness Nozzle geometry

24 Coating Thickness Optimal Coating thickness < 100 µm a b Powder flow Melting Spray distance

25 Substrate Material Differences in substrate material and mass can lead to varying levels of adhesion and can affect the chemical make-up of the coating. Residual stresses in the coating and how the coating cools is critical for final coating properties. Damage due to the blast procedure Damage due to heating Oxidation, discoloration etc. 15% Reduction in fatigue strength for Titanium substrate. CoCr and Stainless Steel are less affected

26 Chemical Properties Some of the important variables contributing to the Chemical composition of the coating include: Starting powder Phase composition of the coating

27 Powder Purity of the powder Is powder ~ 100% crystalline HA? Starting powder can be 100 % crystalline but resultant product ends up as something else once plasma sprayed Phase composition of the powder what are the predominant phases within the powder? Is powder predominantly HA? Or is made up of some other phases? Particle size distribution What is the average particle size?

28 Phase Composition of the Coating Melting Point of HA ~ 1250 C Pure ~ 100% HA powder Ca 10 (PO 4 ) 6 (OH) 2 α- TCP and β- TCP Ca 3 (PO 4 ) 2 Tetra Calcium Phosphate Ca 4 (PO 4 ) 2 O Calcium Oxide CaO Amorphous phases Dissolution Behavior CaO > amorphous > TTCP > α-tcp > OHA > ß-TCP > HA

29 Some of the Important Variables Contributing to HA Decomposition Powder type/morphology Powder gas pressure Gases used type, purity Gun configuration powder injection, velocity/dwell time Distance a b Spherical Particles Irregular Particles

30 Coating Morphology a b c d e

31 FDA Guidelines for HA Coatings Early HA coatings were not controlled, and had varying degrees of porosity, amorphous phase content and Adhesion. This lead to varying degrees of success with HA in orthopedics. Other factors such as patient selection, implant design, surgical expertise etc. play a role as well.

32 In 1992 the FDA Published Guidelines for HA Coatings Including Mandatory Tests like: Chemical Properties Elemental analysis powder and coating Ca/P ratio powder and coating Density powder and coating XRD powder and coating Infrared Spectroscopy Solubility & Dissolution Mechanical Properties Abrasion resistance Tensile strength Shear strength Fatigue strength Morphology Thickness Roughness

33 FDA Guidance Document Acceptance Criteria: Chemical Tests Powder minimum 95% HA Crystallinity of Coating minimum 62% IR identification of (PO 4 ) 3 and (OH) -1 Trace Elemental analysis Cd, Hg, Pb, As < 50ppm Ca/P ratio, powder Ca/P ratio, coating Density, powder 3.05 g/cm 3, min Density, coating 2.98 g/cm 3, min Mechanical Tests Tensile strength 7400 psi, min Shear strength 3198 psi, min

34 Future of HA Coatings Driving factors for exploring new techniques for HA coatings are: Plasma Sprayed HA Coating Limitations High temperature process Coats only visible area Is osteoconductive but not osteoinductive Cost of coating implants Functionality of the Coatings

35 HA Coating Techniques HA Coating Techniques Sol-gel Electrostatic Spray Deposition Dip Coating Electrophoretic Deposition Physical Vapor deposition Coats 3D porous structures Low processing temperature Relatively cheap Very thin Coatings Uniform Coating on flat surfaces Relatively cheap Inexpensive Quick processing time Coats 3D structures Uniform Coating High deposition rates Coats 3D structures Great Control over coating thickness Great control over chemical composition Processing in controlled atmosphere Limited Coating thickness can be achieved Only coats visible areas Fragile High sintering temperature Fragile High sintering temperature Crack within the coating Coats visible area Expensive and time consuming

36 FDA Regulatory Hurdles for new Coating Techniques OEM Orchid FDA Orchid Master File No set guidelines available for new coatings. Have to compare data with existing plasma spray coating guidelines. FDA relies on ASTM up to certain extent for developing test methods which can take anywhere from 6 18 months to get approved.

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38 2014 View additional OMTEC2014 speakerpresentations.