Metallic scaffolds for bone tissue engineering
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The document discusses metallic scaffolds in bone tissue engineering, highlighting their importance in providing a 3D framework for tissue repair. It covers the types of metallic scaffolds, including titanium alloys, nickel titanium, tantalum, stainless steel, and cobalt chromium, along with their advantages, disadvantages, and fabrication techniques. The text emphasizes various requirements for the scaffolds, such as porosity and mechanical properties needed for effective biological interaction and bone integration.
Metallic scaffolds for bone tissue engineering
- 1. Metallic scaffolds for bone tissue engineering Mohamed Mahmoud Abdul-Monem 09-708 Spring 2019 1
- 2. Content • Introduction • Requirements of metallic scaffolds for bone tissue engineering • Types of metallic scaffolds for bone tissue engineering . • Fabrication techniques of metallic scaffolds for bone tissue engineering • References 2
- 3. Introduction • Bone tissue engineering is an emerging interdisciplinary field in science, combining expertise in medicine, material science and biomechanics. • Porous scaffolds are essential to hard tissue engineering strategies because they provide a 3D framework for delivering cells or regenerative factors in an organized manner to repair or regenerate damaged tissues. 3
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- 5. 5 Scaffolds for bone tissue engineering Polymeric Ceramic Metallic Composites
- 7. Requirements of metallic scaffolds for bone tissue engineering • Total porosity Parameter • Percentage of total void space Definition • Affects mechanical strength of the scaffold Biological response 7
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- 9. Requirements of metallic scaffolds for bone tissue engineering 9 • Open porosity Parameter • Percentage of pores that are interconnected Definition • Affects cell permeability and vascularization, as well as growth factor diffusion Biological response
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- 11. Requirements of metallic scaffolds for bone tissue engineering 11 • Surface area to volume ratio Parameter • Ratio of total scaffold surface area to total scaffold volume Definition • Cell seeding density and concentration of growth factors Biological response
- 12. Requirements of metallic scaffolds for bone tissue engineering 12 • Pore Diameter Parameter • Diameter of largest sphere that fits within pore channel Definition • Cell infiltration and bone ingrowth Biological response
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- 14. Requirements of metallic scaffolds for bone tissue engineering 14 • Stiffness Parameter • Mechanical property Definition • Affects cell attachment Biological response
- 15. Metallic scaffolds Disadvantage How to overcome ? 1. Lack of biological recognition on the material surface (Bioninert) •Surface coating or surface modification •Integrate cell-recognizable ligands and signaling growth factors on the surface of the scaffolds 2.Release of toxic metallic ions and/or particles through corrosion Surface modification 3.High elastic modulus which leads to stress shielding Use of composite scaffolds 4. Difficult in processing and porosity control Rapid prototyping 15
- 16. 16 Non –Biodegredable Metallic scaffolds for bone tissue engineering Titanium alloys Nickel Titanium Tantalum Stainless steel Cobalt Chromium
- 17. I.Titanium alloys scaffolds Advantages Disadvantages •Osseointegration •Toxicity from Aluminum and vanadium •High Mechanical properties •Susceptible to crack propagation •Biocompatible (Passive oxide layer) •Low wear resistance compared to Co-Cr •Low Density •Not ferromagnetic (MRI Compatible) 17
- 18. Surface modification of Titanium scaffolds • Ti alloys are classified as biocompatible materials; however, being bioinert materials, they do not possess the required bioactivity to bond to bone directly, resulting in a longer recovery time for bone regeneration. • Without surface modification ,Ti alloys are generally encapsulated by soft-fibrous connective tissue. 18
- 19. Surface modification of Ti scaffolds 19 Mechanical Machining Grinding Sandblasting Physical Thermal sprayed coatings e.g Plasma arc spray of Hydroxyapatite or Titanium oxide Chemical Acidic treatment Alkaline treatment Hydrogen peroxide Sol-Gel Anodic oxidation
- 20. Mechanical modification of titanium scaffolds 20
- 21. Physical modification of titanium scaffolds 21
- 22. Chemical modification of titanium scaffolds 22
- 23. II.Nickel Titanium alloys scaffolds Advantages Disadvantages •Shape memory •Allergy and Toxicity from Ni In order to overcome this problem: 1. surface modifications such as oxidation treatment of NiTi to obtain a Ni-free surface 2. Ni-free shape memory alloys, mainly niobium based, are currently under development. •Superelasticity •Elastic modulus close to bone 23
- 24. III.Tantalum scaffolds Advantages Disadvantages •High volume porosity (80%) •Higher coefficient of friction than bone •Interconnected pores •High production cost •Modulus of elasticity similar to bone •Difficult processing due to high melting point (3017˚C) compared to Ti (1668˚C) and high oxygen affinity •Biocompatible due to self- passivating oxide layer •High density (16.65 g/cm3 ) compared to Ti(4.5 g/cm3 ) •Corrosion resistant •Osseointegration •Excellent cell attachment 24
- 25. IV.Stainless steel scaffolds Advantages Disadvantages •Corrosion resistance due to high chromium content (12%) •Lower Biocompatibility than Ti alloys due to chromium and Nickel content in some alloys . •Low cost •No osseointegration 25
- 26. V.Cobalt Chromium scaffolds Advantages Disadvantages •Higher wear resistance compared to Ti alloys •Higher modulus of elasticity than bone which leads to great stress shielding •High strength •Low biocompatibility •High ductility •No osseointegration 26
- 27. Comparison between different metallic scaffolds 27
- 28. Elastic modulus of different metallic scaffolds compared to bone 28 UHMW PE : ultra high molecular weight polyethylene
- 29. Fabrication techniques of metallic scaffolds I.Conventional techniques II.Rapid prototyping 29
- 30. I.Conventional techniques 1. Sintered metal powder 2. Sintered metal fibers 3. Space-holder method 4. Gas injection into the metal melt 30
- 31. However, there are inherent limitations in these processing methods, which offer little capability to control precisely pore size, pore geometry, pore interconnectivity and spatial distribution of pores. 31
- 32. 1.Sintered metal powder 32 Sintering Metal powder Porous metallic scaffold
- 33. 2.Sintered metal fiber 33 Sintereing Metal fibers Porous metallic scaffold
- 36. 4.Gas injection into metal melt 36
- 37. II.Rapid prototyping Rapid prototyping allows fully interconnected porous network and highly controllable porosity and pore size. 37
- 38. Rapid prototyping includes: 1. Selective laser sintering (SLS) 2. 3D fiber deposition 38
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- 43. Defect Ta scaffold in place 43
- 44. Push-out test 44
- 45. 45 a Ta+BMP b Ta c Blank
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- 48. References 1. Matassi et al.Porous metal for orthopedics implants Clinical Cases in Mineral and Bone Metabolism 2013; 10(2): 111-115 2. Nouri et al.Biomimetic Porous Titanium Scaffolds for Orthopedic and Dental Applications.Biomemtics learning from nature .2010 :416-450 3. Alvarez et al.Metallic scaffolds for bone regeneration. Materials 2009, 2, 790-832 4. Glenske et al.Applications of Metals for Bone Regeneration. Int. J. Mol. Sci. 2018:1-32 5. Ahmadi Set al. Mechanical behavior of regular open-cell porous biomaterials made of diamond lattice unit cells. Journal of the mechanical behavior of biomedical materials 2014; 34:106-15. 48
- 49. References 6. Hazlehurst Ket al.An investigation into the flexural characteristics of functionally graded cobalt chrome femoral stems manufactured using selective laser melting. Materials & Design 2014; 60:177-83. 7. Wang et al.Application of combined porous tantalum scaffolds loaded with bone morphogenetic protein 7 to repair of osteochondral defect in rabbits.Int Orthoped.2018 :1-12 8. Cheng et al.Advances in Porous Scaffold Design for Bone and Cartilage TissueEngineering and Regeneration. 9. Prasad et al.Metallic Biomaterials: Current Challenges and Opportunities. Materials 2017:1-33 10. Chen et al.Biocompatible porous titanium scaffolds produced using a novel spaceholder technique.Society for biomaterials.2017:2796-2807 11. Wally et al.Porous Titanium for Dental Implant Applications. Metals 2015;5:1902–1920. 12. Pacifici et al. Metals used in maxillofacial surgery. Oral Implantol. 2016, 9,107–111. 49
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