International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 4, April 2012)

A Review on Biomaterials: Scope, Applications & Human Anatomy Significance Nitesh R. Patel1, Piyush P. Gohil2 1,2

Department of Mechanical Engineering, Faculty of Technology & Engineering Charotar University of Science & Technology, Changa (Gujarat) 1

[email protected] [email protected]

2

In the early days all kinds of natural materials such as wood, glue and rubber, and tissues from living forms, and manufactured materials such as iron, gold, zinc and glass were used as biomaterials. The host responses to these materials were extremely varied. Under certain conditions (characteristics of the host tissues and surgical procedure) some materials were tolerated by the body, whereas the same materials were rejected in another situation. Over the last 30 years considerable progress has been made in understanding the interactions between the tissues and the materials. It has been acknowledged that there are profound differences between non-living (avital) and living (vital) materials. A wide range of materials encompassing all the classical materials such as Metals (gold, tantalum, Ti6Al4V, 316L stainless steel, Co-Cr Alloys, titanium alloys), Ceramics (alumina, zirconia, carbon, titania, bioglass, hydroxyapatite(HA)), Composite (Silica/SR, CF/UHMWPE, CF/PTFE, HA/PE, CF/epoxy, CF/PEEK, CF/C, Al2O3/PTFE), Polymers (Ultra high molecular weight polyethylene(UHMWPE), Polyurethane(PE), Polyurethane (PU), Polytetrafuoroethylene (PTFE), Polyacetal (PA), Polymethylmethacrylate (PMMA), Polyethylene Terepthalate (PET), Silicone Rubber (SR), Polyetheretherketone (PEEK), Poly(lactic acid) (PLA), Polysulfone (PS)) have been investigated as biomaterials. Researchers also classified materials into several types such as bioinert and bioactive, biostable and biodegradable, etc. [4]. In broad terms, inert (more strictly, nearly inert) materials prohibited or minimal tissue response. Active materials encourage bonding to surrounding tissue with. Degradable or resorbable materials are incorporated into the surrounding tissue, or may even dissolve completely over a period of time. Metals are typically inert, ceramics may be inert, active or resorbable and polymers may be inert or resorbable [5]. Biomaterials must be nontoxic, noncarcinogenic, chemically inert, stable, and mechanically strong enough to withstand the repeated forces of a lifetime.

Abstract— Biomaterials in the form of implants (sutures, bone plates, joint replacements, etc.) and medical devices (pacemakers, artificial hearts, blood tubes, etc.) are widely used to replace and/or restore the function of traumatized or degenerated tissues or organs, and thus improve the quality of life of the patients. The first and foremost requirement for the choice of the biomaterial is its acceptability by the human body. A biomaterial used for implant should possess some important properties in order to long-term usage in the body without rejection. The most common classes of materials used as biomedical materials are Metals, Polymers, Ceramics, and Composite. These four classes are used singly and in combination to form most of the implantation devices available today. This review should be of value to researchers who are interested in the state of the art of biomaterial evaluation and selection of biomaterials. Keywords—Application, Biomaterials, Human Anatomy

I. INTRODUCTION The National Institutes of Health Consensus Development Conference defined a biomaterial as ‘‘Any substance (other than a drug) 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’’ (Boretos and Eden, 1984). Use of biomaterials dates far back into ancient civilizations. Artificial eyes, ears, teeth, and noses were found on Egyptian mummies [1]. Chinese and Indians used waxes, glues, and tissues in reconstructing missing or defective parts of the body. Over the centuries, advancements in synthetic materials, surgical techniques, and sterilization methods have permitted the use of biomaterials in many ways [2]. Medical practice today utilizes a large number of devices and implants. Biomaterials in the form of implants (ligaments, vascular grafts, heart valves, intraocular lenses, dental implants, etc.) and medical devices (pacemakers, biosensors, artificial hearts, etc.) are widely used to replace and/or restore the function of traumatized or degenerated tissues or organs, and thus improve the quality of life of the patients. 91

International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 4, April 2012) Newer biomaterials even incorporate living cells in order to provide a true biological and mechanical match for the living tissue.

D. Functional Tissue Structure and Pathobiology: Biomaterials incorporated into medical devices are implanted into tissues and organs. Therefore, the key principles governing the structure of normal and abnormal cells, tissues or organs, the technique by which the structure and function of normal and abnormal tissues are studied, and the fundamental mechanisms of disease processes are critical considerations to workers in the field [12]. E. Toxicology: A biomaterial should not be toxic, unless it is specifically engineered for such requirements (for example a "smart" bomb" drug delivery system that targets cancer cells and destroy them). Toxicology for biomaterials deals with the substances that migrate out of the biomaterials. It is reasonable to say that a biomaterial should not give off anything from its mass unless it is specifically designed to do so [12]. F. Appropriate Design and Manufacturability: Biomaterials should be machinable, moldable, extrudable. Finite element analysis is a powerful analytical tool used in the design of any implants. Currently modern manufacturing processes are necessary to guarantee the quality needed in orthopaedic devices. G. Mechanical Properties of Biomaterials: Some of the most important properties of biomaterials that should be carefully studied and analysed in their applications are tensile strength, yield strength, elastic modulus, corrosion and fatigue resistance, surface finish, creep, and hardness. Physical properties are also taking in to account while selecting materials. The dialysis membrane has a specified permeability. The articular cup of the hip joint has high lubricity. The intraocular lens has clarity and refraction requirements. H. High corrosion resistance: Singh & Dahotre [13] did research on corrosion resistance as is an important issue in selection of metallic biomaterials because the corrosion of metallic implants due to the corrosive body fluid is unavoidable. The implants release undesirable metal ions which are nonbiocompatible. Corrosion can reduce the life of implant device and consequently may impose revision surgery. In addition the human life may be decreased by the corrosion phenomenon. Okazaki & Gotoh [14] expressed the fact that dissolved metal ions (corrosion product) either can accumulate in tissues, near the implant or they may be transported to other parts of the body.

II. SELECTION PARAMETERS FOR BIOMATERIALS A Biomaterial used for implant should possess some important properties in order to long-term usage in the body without rejection. The design and selection of biomaterials depend on different properties which are characterized in this section. A. Host Response: Host response is defined as the response of the host organism (local and systemic) to the implanted material or device [6]. B. Biocompatibility: Researchers have coined the words `biomaterial' and `biocompatibility' [7] to indicate the biological performance of materials. Materials that are biocompatible are called biomaterials, and the biocompatibility is a descriptive term which indicates the ability of a material to perform with an appropriate host response, in a specific application [8]. In simple terms it implies compatibility or harmony of the biomaterial with the living systems. Biocompatibility is the ability to exist in contact with tissues of the human body without causing an unacceptable degree of harm to the body. It is not only associated to toxicity, but to all the adverse effects of a material in a biological system [9, 10]. It must not adversely affect the local and systemic host environment of interaction (bone, soft tissues, ionic composition of plasma, as well as intra and extracellular fluids) [11]. It refers to a set of properties that a material must have to be used safely in a biological organism. It should be non-carinogenic, non-pyrogenic, non-toxic, non-allergenic, blood compatible, noninflammatory. The operational definition of biocompatible is "The patient is alive so it must be biocompatible". C. Biofunctionality[11]: Biofunctionality is playing a specific function in physical and mechanical terms. The material must satisfy its design requirements in service:  Load transmission and stress distribution (e.g. bone replacement)  Articulation to allow movement (e.g. artificial knee joint)  Control of blood and fluid flow (e.g. artificial heart)  Space filling (e.g. cosmetic surgery)  Electrical stimuli (e.g. pacemaker)  Light transmission (e.g. implanted lenses)  Sound transmission (e.g. cochlear implant) 92

International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 4, April 2012) I. High wear resistance: The low wear resistance or high coefficient of friction results in implant loosening [15, 16]. Wear debris are found to be biologically active and make a severe inflammatory response that lead to the destruction of the healthy bone which supports the actual implant. Corrosion caused by friction is a big concern since it releases non compatible metallic ions. It should be pointed out that mechanical loading also can result in corrosion fatigue and accelerated wear processes [15]. J. Long fatigue life: The fatigue strength is related to the response of the material to the repeated cyclic loads. Fatigue fracture leads some of major problems associated with implant loosening, stress-shielding and ultimate implant failure and it is frequently reported for hip prostheses [17]. Fatigue characteristics are strongly depends on the microstructures. The microstructures of metallic biomaterials alter according to the processing and heat treatment employed [6]. K. Adequate Strength: Strength of materials from which the implants are fabricated has influence the fracture of artificial organ. In adequate strength can cause to fracture the implant. When the bone implant interface starts to fail, developing a soft fibrous tissue at the interface can make more relative motion between the implant and the bone under loading [9]. This fact causes pain to the patient and after a certain period, the pain becomes unbearable and the implant must be replaced, by a revision procedure [15]. L. Modulus equivalent to that of bone: For major applications such as total joint replacement, higher yield strength is basically coupled with the requirement of a lower modulus close to that of human bones [19, 20]. The magnitude of bone modulus varies from 4 to 30 GPa depending on the type of the bone and the measurement direction [21]. Large difference in the Young’s modulus between implant material and the surrounding bone can contribute to generation of severe stress concentration, namely load shielding from natural

bone that may weaken the bone and deteriorate the implant/bone interface, loosening and consequently failure of implant [9, 22]. The modulus is considered as a main factor for selection of any biomaterials. III. HUMAN ANATOMY The first and foremost requirement for the choice of the biomaterial is its acceptability by the human body (Fig. 1). The success of a biomaterial or an implant is highly dependent on three major factors (i) The properties (mechanical, chemical and tribological) of the biomaterial (ii) biocompatibility of the implant and (iii) the health condition of the recipient and the competency of the surgeon [23]. Generally, tissues are grouped into hard and soft tissues. Bone and tooth are examples of hard tissues, and skin, blood vessels, cartilage and ligaments are a few examples of soft tissues. As the names suggest, in general the hard tissues stiffer (elastic modulus) and stronger (tensile strength) than the soft tissues (Tables 1 and 2). Considering the structural or mechanical compatibility with tissues, metals or ceramics are chosen for hard tissue applications, and polymers for the soft tissue applications. One of the primary reasons that biomaterials are used is to physically replace hard or soft tissues that have become damaged or destroyed through some pathological process [24]. Under these circumstances, it may be possible to remove the diseased tissue and replace it with some suitable synthetic material. TABLE 1 MECHANICAL PROPERTIES OF HARD TISSUE [25]

Hard tissue Cortical bone (longitudinal direction) Cortical bone (transverse direction) Cancellous bone Enamel Dentine

Modulus (GPa)

Tensile Strength (MPa)

17.7

133

12.8

52

0.4 84.3 11.0

7.4 10 39.3

TABLE 2 MECHANICAL PROPERTIES OF SOFT TISSUE [25]

Soft tissue Articular cartilage Fibrocartilage Ligament Tendon Skin Intraocular lens

93

Modulus (MPa) 10.5 159.1 303.0 401.5 0.1-0.2 5.6

Tensile Strength (MPa) 27.5 10.4 29.5 46.5 7.6 2.3

International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 4, April 2012) Dental Implants, Dental Post, Arch Wire & Brackets, Dental Bridges, Dental Restorative Material

Cohlear Implants Intacts Cardiovascular Implants (Vascular Grafts)

Shoulder Prosthesis Pacemaker

Abdominal Wall Prosthesis

Lumbar Disc Replacement, Spine Cage, Plate, Rods and Screws

Prosthetic Arthroplasty

Total Hip Replacement, Acetabular

Intramedullary Nails Knee joint Replacement, Tendon / Ligament, Cartilage Replacement

Bone Cement

Bone Fixation, Bone Plates & Screws

FIGURE 1: IMPLANTS FOR HUMAN ANATOMY SIGNIFICANCE

The main considerations in selecting metals and alloys for biomedical applications are their excellent electrical and thermal conductivity, biocompatibility, appropriate mechanical properties, corrosion resistance, and reasonable cost. It is very important to know the physical and chemical properties of the different metallic materials used in any surgery as well as their interaction with the host tissue of the human body. Stainless Steel: Stainless steel was first used successfully as an important material in the surgical field. Stainless steel is the generic name for a number of different steels used primarily because of their resistance to a wide range of corrosive agents [10, 15]. Stainless steel has been used for wide range of application due to easy availability, lower cost, excellent fabrication properties, accepted biocompatibility and great strength.

IV. IMPLANTABLE MATERIALS The science of biomedical materials involves a study of the composition and properties of materials and the way in which they interact with the environment in which they are placed. The most common classes of materials used as biomedical materials are metals, polymers, ceramics, and composite. These four classes are used singly and in combination to form most of the implantation devices available today. A. Metals and Alloys: Metals have been used almost exclusively for loadbearing implants, such as hip and knee prostheses and fracture fixation wires, pins, screws, and plates. Although pure metals are sometimes used, alloys frequently provide improvement in material properties, such as strength and corrosion resistance. Three material groups dominate biomedical metals: Stainless steel, cobalt-chromiummolybdenum alloy, and titanium and titanium alloys.

94

International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 4, April 2012) TABLE 3 MECHANICAL PROPERTIES OF METALLIC BIOMATERIALS [31]

Cobalt-Chrome: Cobalt chromium alloys can be basically categorized into two types; one is The CoCrMo alloy [ Cr (27-30%), Mo (5-7%), Ni (2.5%)] has been used for many decades in dentistry, and in making artificial joints and the second one The CoNiCrMo alloy [Cr (19-21%), Ni (33-37%), and Mo (9-11%)] has been used for making the stems of prostheses for heavily loaded joints, such as knee and hip [15]. Cobaltbased alloys are highly resistant to corrosion even in chloride environment due to spontaneous formation of passive oxide layer within the human body environment [10, 15, 16, 26, 27]. The thermal treatments used to Co-CrMo alloys modify the microstructure of the alloy and alters the electrochemical and mechanical properties of the biomaterial [26]. The corrosion products of Co-Cr-Mo are more toxic than those of stainless steel 316L. Titanium and its Alloys: There are three structural types of titanium alloys: Alpha (α), Alpha-Beta (α-β) or metastable β and Beta (β).The β phase in Ti alloys tends to exhibit a much lower modulus than α phase, and also it satisfies most of the other necessities or requirements for orthopedic application [28, 29]. Ti alloys due to the combination of its excellent characteristics such as high strength, low density, high specific strength, good resistance to corrosion, complete inertness to body environment, enhanced biocompatibility, moderate elastic modulus of approximately 110 GPa are a suitable choice for implantation. Long-term performance of titanium and its alloys mainly Ti64 has raised some concerns because of releasing aluminum and vanadium [9, 10]. Both Al and V ions are associated with long term health problems, like Alzheimer disease and neuropathy. Furthermore when titanium is rubbed between itself or between other metals, it suffers from severe wear [30]. The mechanical properties of materials are of great importance when designing load-bearing orthopedic and dental implants. Some mechanical properties of metallic biomaterials are listed in Table 3. The mechanical properties of a specific implant depend not only on the type of metal but also on the processes used to fabricate the material and device. The elastic moduli of the metals listed in Table 3 are at least seven times greater than that of natural bone.

Young’s Modulus, E (GPa)

Yield Strength, sy (MPa)

Tensile Strength, sUTS (MPa)

Fatigue Limit, send (MPa)

Stainless steel

190

221–1,213

586–1,351

241–820

Co-Cr alloys

210–253

448–1,606

655–1,896

207–950

Titanium (Ti)

110

485

760

300

Ti-6Al-4V

116

896–1,034

965–1,103

620

15–30

30–70

70–150

Material

Cortical bone

TABLE 4 APPLICATION OF METALS AS IMPLANTS USED IN HUMAN BODY

Types of Materials

Stainless steel

Cobalt-chromium alloy

Titanium and its Alloys

Applications Joint replacements (hip, knee), Bone plate for fracture fixation, Dental implant for tooth fixation, Heart valve, Spinal Instruments, Surgical Instruments, Screws, dental root Implant, pacer, fracture plates, hip nails, Shoulder prosthesis Bone plate for fracture fixation, Screws, dental root implant, pacer, and Suture, dentistry, orthopedic prosthesis, Mini plates, Surgical tools, Bone and Joint replacements (hip, knee), dental implants Cochlear replacement, Bone and Joint Replacements(hip, knee),Dental Implants for tooth fixation, Screws, Suture, parts for orthodontic surgery, bone fixation devices like nails, screws and plates, artificial heart valves and surgical instruments, heart pacemakers, artificial heart valves

B. Ceramics Ceramics are polycrystalline materials. The main characteristics of ceramic materials are hardness and brittleness, great strength and stiffness, resistance to corrosion and wear, and low density. They work mainly on compression forces; on tension forces, their behavior is poor. Ceramics are typically electrical and thermal insulators. Ceramics are used in several different fields such as dentistry, orthopedics, and as medical sensors. [32]. Overall, however, these biomaterials have been used less extensively than either metals or polymers. Ceramics typically fail with little, if any, plastic deformation, and they are sensitive to the presence of cracks or other defects.

95

International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 4, April 2012) Ceramics have become a diverse class of biomaterials presently including three basic types: bioinert, bioactive, bioresorbable ceramics [33]. Alumina (Al2O3), Zirconia (ZrO2) and Pyrolytic carbon are termed bioinert. Bioglass and glass ceramics are bioactive. Calcium phosphate ceramics are categorized as bioresorbable. Bioinert refers to a material that retains its structure in the body after implantation and does not induce any immunologic host reactions. Alumina (Al2O3): High density high purity (>99.5%) alumina (Al2O3) was the first ceramic widely used clinically. It is used in loadbearing hip prostheses and dental implants, because of its combination of excellent corrosion resistance, good biocompatibility, and high wear resistance, and high strength. The reasons for the excellent wear and friction behavior of (Al2O3) are associated with the surface energy and surface smoothness of this ceramic. The biocompatibility of alumina ceramic has been tested by many researchers. Noiri et al. [34] evaluated the biocompatibility of alumina-ceramic material histopathalogically for eight weeks by implanting in the eye sockets of albino rabbits. The results showed no signs of implant rejection or prolapse of the implanted piece. After a period of four weeks of implantation, fibroblast proliferation and vascular invasion were noted and by eighth week, tissue growth was noted in the pores of the implant [34]. Single crystal alumina screws and pins were implanted in the femoral bone of mature rabbits. Changes in the implant-bone interface were observed. Alumina was never in direct contact with the bone and hemidesmosomes were not observed in the interface [35]. The cytotoxicity of single crystal alumina ceramics was studied in L cell line culture. They displayed the same colony formation and survival rates as the controls showed that they have no cytotoxicity and if implanted in bone marrow they would not be toxic to circumferential tissue [36]. Zirconia (ZrO2): Zirconia is a biomaterial that has a bright future because of its high mechanical strength and fracture toughness. Zirconia ceramics have several advantages over other ceramic materials due to the transformation toughening mechanisms operating in their microstructure that can be manifested in components made out of them. The research on the use of zirconia ceramics as biomaterials commenced about twenty years ago and now zirconia is in clinical use in total hip replacement (THR) but developments are in progress for application in other medical devices. Today's main application of zirconia ceramics is in THR ball heads [37].

The osteointegration of zirconia was investigated in normal and osteopenic rats by means of histomorphometry. The data showed that the tested material was biocompatible in vitro and confirmed that bone mineral density is a strong predictor of the osteointegration of an orthopedic implant and that the use of pathological animal models is necessary to completely characterize biomaterials [38]. It is said that very small traces of radioelements, which can be found even in fully refined ceramics, have a negative effect on organs and tissues. Zirconia contains very small traces of radioelements [39]. The cytotoxicity of polycrystalline zirconia was speculated in L cell line culture. The study revealed its noncytotoxicity [36]. Pyrolytic Carbon: Carbon is a versatile element and exists in a variety of forms. Good compatibility of carbonaceous materials with bone and other tissue and the similarity of the mechanical properties of carbon to those of bone indicate that carbon is an exciting candidate for orthopedic implants [40]. Unlike metals, polymers and other ceramics, these carbonaceous materials do not suffer from fatigue. However, their intrinsic brittleness and low tensile strength limits their use in major load bearing applications. The mechanical bonding between the carbon fiber reinforced carbon and host tissue was investigated. The bonding developed three months after intrabone implantation and is accompanied by a decrease of the implant strength [41]. Bioactive refers to materials that form direct chemical bonds with bone or even with soft tissue of a living organism. Bioglass & Glass Ceramic: A common characteristic of such bioactive materials is a modification of the surface that occurs upon implantation. Bonding to bone was first demonstrated for a range of bioactive glasses, which contained specific amounts of SiO2, CaO, and P2O5 [42]. This material has been widely used for filling bone defects. The porosity of bioglass is beneficial for resorption and bioactivity [43]. The interface reaction was interpreted as a chemical process, which includes a slight solubility of the glass ceramic and a solidstate reaction between the stable apatite crystals in the glass ceramic and the bone [44]. Bioresorbable refers to materials that degrade (by hydrolytic breakdown) in the body while they are being replaced by regenerating natural tissue; the chemical byproducts of the degrading materials are absorbed and released via metabolic processes of the body. Calcium phosphate ceramics: Different phases of calcium phosphate ceramics are used depending upon whether a resorbable or bioactive material is desired. 96

International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 4, April 2012) Calcium phosphate (CaP) biomaterials are available in various physical forms. One of their main characteristics is their porosity. The ideal pore size for bioceramic is similar to that of spongy bone [45]. The prime requirement for calcium phosphate materials to be bioactive and bond to living bone is the formation of a bone like apatite layer on their surface [46]. The major drawbacks to the use of ceramics and glasses as implants are their brittleness and poor tensile properties (Table 5). Although they can have outstanding strength when loaded in compression, ceramics and glasses fail at low stress when loaded in tension or bending. Among biomedical ceramics, alumina has the highest mechanical properties, but its tensile properties are still below those of metallic biomaterials.

C. POLYMERIC BIOMATERIALS The development of polymeric biomaterials can be considered as an evolutionary process. Reports on the applications of natural polymers as biomaterials date back thousands of years [48]. Polymers are the most widely used materials in biomedical applications. Polymers are organic materials that form large chains made up of many repeating units. The uses for polymeric materials are more diverse than for metallic implants, but their interchangeability is not as great. In most of applications, polymers have little or no competition from other types of materials. Their unique properties are: Flexibility, Resistance to biochemical attack, Good biocompatibility, Lightweight, Available in a wide variety of compositions with adequate physical and mechanical properties, Can be easily manufactured into products with the desired shape. A few of the major classes of polymer are listed below: Poly (methyl methacrylate), PMMA: It is a hard brittle polymer that appears to be unsuitable for most clinical applications, but it does have several important characteristics. It can be prepared under ambient conditions so that it can be manipulated in the operating theater or dental clinic, explaining its use in dentures and bone cement. The relative success of many joint prostheses is dependent on the performance of the PMMA cement, which is prepared intraoperatively by mixing powdered polymer with monomeric methylmethacrylate, which forms dough that can be placed in the bone, where it then sets. Silicone Rubbers: Both heat-vulcanizing and room temperature vulcanizing silicones are in use today and both exhibit advantages and disadvantages. Room temperature vulcanizing silicones are supplied as single- paste systems. Heat-vulcanizing silicone is supplied as a semi-solid material that requires milling, packing under pressure. Ultra High Molecular Weight Polyethylene (UHMWPE): Much research is progressing in examining the wear properties of UHMWPE. The coefficient of friction between polyethylene and cobalt-chromium alloy has been reported to be between 0.03 and 0.16, with excellent wear rates. UHMWPE is used as the bearing surface in total joint arthroplasty, it has 90% success rates at 15 years with metal on polyethylene. Submicron particles found in periprosthetic tissues when polyethylene wear present. (But no better material has been developed to date) The mechanical properties of polymers depend on several factors, including the composition and structure of the macromolecular chains and their molecular weight. Table 7 lists some mechanical properties of selected polymeric biomaterials.

TABLE 5 MECHANICAL PROPERTIES OF CERAMIC BIOMATERIALS [47]

Alumina Zirconia Pyrolytic carbon Bioglassceramics Calcium phosphates

Young’s Modulus, E (GPa) 380 150-200

Compressive Strength, sUCS (MPa) 4500 2000

Tensile Strength, sUTS (MPa) 350 200-500

18-28

517

280-560

22

500

56-83

40-117

510-896

69-193

TABLE 6 APPLICATION OF CERAMICS AS IMPLANTS USED IN HUMAN BODY

Types of Materials

Alumina

Zirconia

Pyrolytic carbon

Bioglass-ceramics

Calcium phosphates

Applications Artificial total joint replacement, acetabular and femoral components, vertebrae spacers and extensors, orthodontic anchors, dental implant for tooth fixation Replacement for hips, knees, teeth, tendons and ligaments, repair for periodontal disease, bone fillers after tumor surgery Prosthetic heart valves, End osseous tooth replacement implants, permanently implanted artificial limbs Dental implants, middle ear implants, heart valves, artificial total joint replacement, bone plates, screws, wires, intramedullary nails, spinal fusion, tooth replacement implants Skin treatments, dental implants, jawbone reconstruction, orthopedics, facial surgery, ear, nose and throat repair, dental implant

97

International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 4, April 2012) Examples of current applications include vascular grafts, heart valves, artificial hearts, breast implants, contact lenses, intraocular lenses, components of extracorporeal oxygenators, dialyzers and plasmapheresis units, coatings for pharmaceutical tablets and capsules, sutures, adhesives, and blood substitutes, kidney, liver, pancreas, bladder, bone cement, catheters, external and internal ear repairs, cardiac assist devices, implantable pumps, joint replacements, pacemaker, encapsulations, soft-tissue replacement, artificial blood vessels, artificial skin, Dentistry, Drug delivery and targeting into sites of inflammation or tumors, Bags for the transport of blood plasma.

Bone itself achieves most of its mechanical properties as a natural composite material composed of calcium phosphate ceramics in a highly organized collagen matrix. Composite biomaterials are made with a filler (reinforcement) addition to a matrix material in order to obtain properties that improve every one of the components. This means that the composite materials may have several phases. Some matrix materials may be combined with different types of fillers. Polymers containing particulate fillers are known as particulate composites. The first composite to come into general use, initially made by an orthopedic surgeon, was the plaster of Paris bandage. This has been refined to fiberglass with a polymeric matrix in the current synthetic casting materials. A composite for internal prosthetic applications is based on the addition of chopped carbon fiber to improve the mechanical properties of polyethylene components [52]. Only carbon fiber is being studied for orthopedic applications [53]. Composite structures are typically produced from laminates. A laminate is a thin sheet of composite material in which all the fibers run in one direction and are held together by a thin coating of the polymer matrix material. This laminate is combined with other laminates to form a bulk composite; the properties of this composite vary depending on the orientation of each layer of the laminate [54]. None of these materials are currently in clinical use because of the inability to modify the shapes of the implants intraoperatively to fit the bone; because of liberation of carbon fibers into the adjacent tissues; and because the difficulties of predicting the resorption of polymers in larger loadbearing implants, as opposed to screws and pins, has thus far precluded their use for these larger implants. No doubt, implants in this category will be available in the future, perhaps even containing bone inductive proteins.

TABLE 7 MECHANICAL PROPERTIES OF POLYMERS [49]

Polymer Poly(methyl methacrylate) (PMMA) Nylon 6/6 Poly(ethylene terephthalate) Poly(lactic acid) Polypropylene Polytetrafluoroethylene Silicone rubber Ultra-high-molecularweight polyethylene (UHMWPE)

Tensile Strength SUTS(MPa)

Young’s Modulus, E(GPa)

% Elongation

30

2.2

1.4

76

2.8

90

53

2.14

300

28-50 28-36 17-28 2.8

1.2-3 1.1-1.55 0.5 Up to 10

2-6 400-900 120-350 160

>35

4-12

>300

D. BIOCOMPOSITE MATERIALS Biocomposites are composite materials composed of biodegradable matrix and biodegradable natural fibres as reinforcement. The development of biocomposites has attracted great interest due to their environmental benefit and improved performance [50]. Plant-based fibers like flax, jute, sisal and kenaf have been frequently used (Table 8). Most of studies concern biodegradable matrix based on aliphatic polyesters reinforced with various vegetable fillers. With wide-ranging uses from environment-friendly biodegradable composites to biomedical composites for drug/gene delivery, tissue engineering applications and cosmetic orthodontics. They often mimic the structures of the living materials involved in the process in addition to the strengthening properties of the matrix that was used but still providing biocompatibility. Those markets are significantly rising, mainly because of the increase in oil price, and recycling and environment necessities [51].

TABLE 8 CONSTITUENTS OF BIOMEDICAL COMPOSITES

98

Particles Inorganic Glass Alumina

Fibers Polymers Aromatic Polyamides (aramids) UHMWPE Polyesters Polyolefins PTFE

Matrix Thermosets Epoxy Polyacrylates Polymethacrylates Polyesters Silicones

Organic Polyacrylate Polymethacrylate

Resorbable polymers Polylactide, and its copolymers with polyglyocolide

Thermoplastics Polyolefins (PP, PE) UHMWPE Polysulfones

International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 4, April 2012) Silk Collagen Inorganic Carbon Glass Hydroxyapatite Tricalcium phosphate

Poly(ether ketones) Polyesters Inorganic Hydroxyapatite Glass ceramics Calcium carbonate ceramics Calcium phosphate ceramics Carbon Steel Titanium Resorbable polymers Polylactide, polyglycolide and their copolymers Polydioxanone

V. CONCLUDING REMARKS A biomaterial is any substance (other than drugs), natural or synthetic, that treats, augments, or replaces any tissue, organ, and body function. Biomaterial selection is one of the most challenging issues due to crucial requirements and biocompatibility, so it has been of major interest to material designers in recent years. This review of biomaterials has attempted to demonstrate the very significant progress that has been made with the use of advanced materials within the human body. The present study reviewed the currently used biomaterials; metals, ceramics, polymers, and composite. Metals are susceptible to degradation by corrosion, a process that can release by-products that may cause adverse biological responses. Ceramics are attractive as biological implants for their biocompatibility. The studies show that alumina with high mechanical strength show minimal or no tissue reaction, nontoxic to tissues and blood compatibility tests were also satisfactory. Carbon with similar mechanical properties of bone is an exciting candidate, for it elicits blood compatibility, no tissue reaction and nontoxicity to cells. The availability of a wide range of polymers significantly influenced the growth of tissue engineering and controlled drug delivery technologies. Innovations in the composite material design and fabrication processes are raising the possibility of realizing implants with improved performance. However, for successful application, surgeons must be convinced with the long term durability and reliability of composite biomaterials. In the past, success of materials in biomedical applications was not so much the outcome of meticulous selection based on biocompatibility criteria but rather the result of serendipity, continuous refinement in fabrication technology, and advances in material surface treatment. In the present and future, election of a biomaterial for a specific application must be based on several criteria. Biocompatibility is the paramount criterion that must be met by every biomaterial. Medical research continues to explore new scientific frontiers for diagnosing, treating, curing, and preventing diseases at the molecular/genetic level. This review should be of value to researchers who are interested in the state of the art of biomaterial evaluation and selection of biomaterials.

TABLE 9 APPLICATION OF COMPOSITE AS IMPLANTS USED IN HUMAN BODY

Applications

Dentistry

Vascular Grafts

Joint replacements

Bone cement

Bone Replacement Materials Spine Cage, Plate, Rods, Screws, Disc, Finger Joint, Intramedullary Nails, Abdominal wall Prosthesis,

Types of materials CF/C, SiC/C,CF/Epoxy, GF/Polyester, GF/PC, GF/PP, GF/Nylon, GF/PMMA,UHMWPE/PMMA, CF/PMMA, GF/PMMA, KF/PMMA, Silica/BIS-GMA Cells/PTFE, Cells/PET, PET/Collagen, PET/Gelation, PU/PU-PELA PET/PHEMA, KF/PMA, KF/PE, CF/PTFE,CF/PLLA, GF/PU, PET/PU, PTFE/PU, CF/PTFE, CF/C, CF/UHMWPE,UHMWPE/UHMWPE, CF/Epoxy, CF/PS, CF/PEEK, CF/UHMWPE, CF/PE, Bone particles/PMMA, Titanium/PMMA, UHMWPE/PMMA, GF/PMMA, CF/PMMA, Bio-Glass/BisGMA HA/PHB, HA/PEG-PHB, CF/PTFE, PET/PU, HA/HDPE, HA/PE, BioGlass/PE, Bio-Glass/PHB, Bio-Glass/PS, HA/PLA

PET/PU, PET/Collagen, CF/LCP, CF/PEEK, GF/PEEK, CF/Epoxy, CF/PS, Bio-glass/PU, Bio-glass/PS, PET/SR, PET/Hydrogel, CF/UHMWPE

99

International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 4, April 2012) [24] D. Williams, An Introduction to Medical and Dental Materials,

REFERENCES

Concise Encyclopedia of Medical & Dental Materials, D. Williams, Ed., Pergamon Press and The MIT Press, 1990, p xvii–xx.

[1] Williams DF, Cunningham J. Materials in Clinical Dentistry. Oxford, UK; Oxford University Press, 1979.

[25] Black J, Hastings GW. Handbook of Biomaterials Properties.

[2] Park JB. Biomaterials Science and Engineering. New York; Plenum

London, UK: Chapman and Hall, 1998.

Press, 1984.

[3] [4] [5] [6]

[26] Vidal, C.V. and A.I. Muñoz, Effect of thermal treatment and applied

J American Ceramic Society 1991;74:1487-510

potential on the electrochemical behavior of CoCrMo biomedical alloy. Electrochimica Acta, 2008.

Hench LL. Bioceramics: from concept

www.azom.com Biomaterials: An Overview.

[27] Oztürk, O., U. Türkan, and A.E. Eroglu, Metal ion release from nitrogen ion implanted CoCrMo orthopedic implant material. Surface & Coatings Technology, 2006. 200(20-21): p. 5687-5697.

Boretos, J.W., Eden, M. Contemporary Biomaterials, Material and Host Response, Clinical Applications, New Technology and Legal Aspects. Noyes Publications, Park Ridge, NJ (1984), pp. 232–233.]

[28] Nag, S., et al., Characterization of novel borides in Ti–Nb–Zr–Ta+ 2B metal-matrix composites. Materials characterization, 2009. 60(2): p. 106-113.

[7] Williams DF. Consensus and definitions in biomaterials. In; dePutter C, deLange K,de groot K, Lee AJC, editors. Advabces in biomaterials. Elsevier Science: Amaterdam, 1988. p. 11-16.

[29] Eisenbarth, E., et al., Biocompatibility of â-stabilizing elements of titanium alloys. Biomaterials, 2004. 25(26): p. 5705-5713.

[8] Black J, Hastings GW. Handbook of biomaterials Properties.

[30] Miller, P.D. and J.W. Holladay, Friction and wear properties of

London, UK; chapman and Hall, 1988.

titanium. Wear, 1958. 2(2): p. 133-140.

[9] Geetha, M., et al., Ti based biomaterials, the ultimate choice for orthopaedic implants–A review. Progress in Materials Science, 2008,

[31] Adapted from J.B. Brunski. Metals, pp. 37–50 in B.D. Ratner, A.S.

[10] Navarro, M., et al., Biomaterials in orthopaedics. Journal of The

Hoffman, F.J. Shoen, and J.E. Lemons (eds.), Biomaterials Science: An Introduction to Materials in Medicine, Academic Press, San Diego (1996).

Royal Society Interface, 2008. 5(27): p. 1137-1158.

[11] Courtesy R. Zenz, Conference on Biomaterials WS2008,For

[32] http://www.biomed.tamu.edu [33] V .A.Dubok, Powder Metallurgy and Metal Ceramics, 39(7-8), 381-

Genomics and Bioinformatics

[12] A textbook on Biomaterials, ch-1, p;9-10 [13] Singh, R. and N.B. Dahotre, Corrosion degradation and prevention

394 (2000).

by surface modification of biometallic materials. Journal of Materials Science: Materials in Medicine, 2007. 18(5): p. 725-751.

[34] A. Noiri, F.Hoshi, H.Murakami, K.Sato, S.Kawai, K.Kawai, Ganki,

[14] Okazaki, Y. and E. Gotoh, Comparison of metal release from various

[35] S.Kondoh, Seitai Zairyo, 8(2) 56-72 (1990). [36] N.Kanematsu, K.Shibata, A.Yamagami, S.Kotera, Y.Yoshihara,

53(6), 476- 480 (2002).

metallic biomaterials in vitro. Biomaterials, 2005. 26(1): p. 11-21.

Shika Kiso Igakkai Zasshi, 27(1), 382-384 (1985).

[15] Alvarado, J., et al., BIOMECHANICS OF HIP AND KNEE

[37] K. Yamada, S.Nakamura, T. Tsuchiya, K. Yamashita, Key

PROSTHESES. 2003,

Engineering Materials, 216 (Electro Cermacis in Japan IV), 149-152 (2002).

[16] Ramsden, J.J., et al., The Design and Manufacture of Biomedical Surfaces. CIRP Annals-Manufacturing Technology, 2007. 56(2): p. 687-711.

[38] M.Fini,

G.Glavaresi, N.N.Aldini, P.Torricelli, G.Morrone, G.A.Guzzardella, R.Giardino, K.Krajewski, A.Ravaglioli, M.M.Belmonte, A.De Benedittis, G.Biagini, Journal of Materials Science: Materials in Medicine, 11(9),579-585 (2000).

[17] Teoh, S.H., Fatigue of biomaterials: A review. International Journal of Fatigue, 2000. 22(10): p. 825-837.

[18] Niinomi, M., Fatigue characteristics of metallic biomaterials. [19] Long, M. and H.J. Rack, Titanium alloys in total joint replacement—

[39] H.Kawatani, K.Fukumoto, Seitai Zairyo, 12(3) 119-126 (1994). [40] J.C.Bokras, L.D.LaGrange, F.J.Schoen, Chern. Phys. Carbon 9, 104-

a materials science perspective. Biomaterials, 1998. 19(18): p. 16211639.

[41] M.Lewandow Szumiei, J.Komender, A.Gorecki, M.Kowalski,

International Journal of Fatigue, 2007. 29(6): p. 992-1000.

169 (1992). Journal of Materials Science Materials in Medicine, 8(8), 485-488 (1997).

[20] Wang, K., The use of titanium for medical applications in the USA. Materials science & engineering. A, Structural materials: properties, microstructure and processing, 1996. 213(1-2): p. 134-137.

[42] J. Wilson, G.H.Pigott, F.J.Schoen, L.L.Hench, Journal of Biomedical Materials Research, 15(6), 805-817 (1981).

[21] Katz, J.L., Anisotropy of Young’s modulus of bone. Nature, 1980.

[43] H.lrie, Kokai Tokkyo Koho, 7 (1995). [44] W.Hoeland, W.Vogel, K.Waumann, J.Gummel, Journal of

283(5742): p. 106-107.

[22] Au, A.G., et al., Contribution of loading conditions and material properties to stress shielding near the tibial component of total knee replacements. Journal of biomechanics, 2007. 40(6): p. 1410-1416.

Biomedical Materials Research, 19(3). 303-312 (1985).

[45] J.Ruan, M.H.Grant, Journal of Central South University of

[23] Biomedical Implants: Corrosion and its Prevention - A Review

Technology, 8(1), 1-8 (2001).

Geetha Manivasagam, Durgalakshmi Dhinasekaran and Asokamani Rajamanickam, School of Mechanical and Building Sciences, VIT University, Vellore 632 014, Tamil Nadu, India Recent Patents on Corrosion Science, 2010, 2, 40-54 1877-6108.

[46] E.S.Thian, N.H.Loh, K.A.Khor, S.B.Tor, Journal of Biomedical Materials Research 63(2), 79-87 (2002).

100

International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 4, April 2012) [47] Compiled from L.L. Hench. Ceramics, Glasses, and Glass-Ceramics, pp. 73–84 in B.D. Ratner, A.S. Hof-man, F.J. Shoen, and J.E. Lemons (eds), Biomaterials Science: An Introduction to Materials in Medicine, Academic Press, San Diego (1996);

[48] Compiled from J. Kohn and R. Langer. Bioresorbable and Bioerodible Materials, pp. 64–73 in B.D. atner, A.S. Ho¤man, F.J. Shoen, and J.E. Lemons (eds.), Biomaterials Science: An Introduction to Materials in Medicine, Academic Press, San Diego (1996);

[49] M. M. Schwartz, Composite Materials Handbook, 2d ed. New York: McGraw-Hill, 1992

[50] P. K. Mallick, Composites Engineering Handbook. New York: Marcel Dekker, 1997.

[51] H. Alexander, Composites, in Biomaterials Science, B. D. Ratner (ed.). San Diego: Academic Press, 1996, pp. 94-105.

[52] R. Christensen, Mechanics of Composite Materials. New York: Wiley, 1979.

[53] Cogswell FN. Thermoplastic Aromatic Polymer Composites. UK: Butterworth Heinemann, 1992.

[54] M. W. Beatty, M. L. Swartz, B. K. Moore, et al., ìEffect of microfiller fraction and silane treatment on resin composite properties,î Journal of Biomedical Materials Research 40:12ñ23 (1998).

101