Conference Session A10Paper #5177

USING ALUMINA IN CERAMIC IMPLANTS FOR PROSTHETICS

Kaylene Kowalski (kbk18@pitt.edu, Vidic 2:00), Margot Shore (mas564@pitt.edu, Sanchez 4:00)

Abstract- During the past 50 years, chemical and biomedical engineers have researched and developed uses for alumina in the construction of ceramic prosthetics. Recent studies have indicated that ceramics using alumina (Al2O3) are superior to hard plastics and metal implants in terms of durability, biocompatibility, and sustainability.

Using alumina in ceramic prosthetics is beneficial to replacement joint longevity for patients of various needs and abilities. Joint replacement surgeries are commonly believed to cure discomfort and restricted movement caused by a variety of conditions, ranging from rheumatoid arthritis to sports injuries. Though plastic and metal implants are the most commonly used materials for prosthetics, extended research indicates that plastic and metal implants must be replaced within 20 to 30 years [1]. By comparison, ceramic with alumina composite implants are proven structurally and experimentally to have better durability and longevity, lasting well beyond the expected “lifetime” of metal or plastic implants. Though still a developing, sustainable technology, alumina is far more resilient to stress than metal and plastic implants because the core structure of alumina is able to harden ceramic material more effectively than the aforementioned traditional materials. In addition, ceramic implants with alumina in their chemical makeup possess a carefully balanced set of alloys that will not breakdown in the body like other types of ceramic chemical makeups [2].

This paper will explain the science and engineering of alumina ceramics and, via a focus on the use of alumina ceramics in osteoplastic replacements, this paper will explain the sustainable aspects of alumina in society and for the individual

Key Words- Alumina development, Alumina strength, Alumina zirconia nanocomposite, ceramic prosthetics, chemical properties of Alumina, gamma strengthening, population sustainability

BRIEF HISTORY OF ALUMINA DEVELOPMENT

A Continuing History Comes to Life in Prosthetics

The first in vivo (within the living) ceramic implant with alumina composite was recorded in 1963. Since then, there has been definite advancement in the technology, engineering processes, and biocompatibility of joint replacements. Specifically related to the development of prosthetic joints, chemical engineers and bioengineers have put more effort into understanding porous materials. Porous materials, such as ceramic implants with alumina composite,

are absorbed by the bone and become an integrated piece of the prosthetic joint. Because this technology received little attention in its early development, engineers have conducted research in bonding ions (such as Al2O3) within a porous material. To gain a basis of understanding alumina, many alumina ceramic developers in the early 1970s through the 1980s placed implants in dogs, rabbits, and monkeys, the most closely related mammal to humans in DNA structure. Though various cases of failure were sporadic in results, ultimately, very little failure was found in vivo amongst a variety of mammals.

Research to create structurally sound ceramic materials has been ongoing since the 1980s through present day. The findings have lead to the construction of prosthetic implants with a progressively higher percent composition of alumina composite. Over time, engineers developed coatings of alumina to layer on metal and plastic prosthetics in hopes of strengthening the underlying material.

In this paper, the continuous development and importance of alumina composite will be discussed in order to compare this ion-strengthened material with common materials for implanted prosthetics such as metal alloys and hard plastic. By doing this, ceramic implants with alumina composite will be proven most useful and crucial to biocompatible materials for people of the aging population, arthritic patients, and young athletes who are the target audience for receiving osteoplastic surgery [3].

ALUMINA IN PROSTHETIC TECHNOLOGY

Molecular Structure of Alumina

Osteoplastic surgeries are not a revolutionary new development in the medical field. However, making alumina composite a key ingredient of ceramic prosthetics is a clear indication that engineers and medical professionals are developing new ways to refurbish the human body effectively.

Ceramics are generally made with a powder and often resemble cement before being exposed to extreme heat and pressure to form hard solid substances. To gain a perspective about how intense the environment these substances are made in, an implant preparation is outlined as follows: “Implant material was prepared by mechanically mixing CaO and Al2O3 powders before calcining (a process in which more complex gas–solid reactions take place between the furnace atmosphere and the solids) them at 1200°F for 48 hours,” [4]. Table 1 shows the composition of alumina powder before the mixture is transitioned into a cement [4].

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After this, “The resulting partially sintered compact was reground in a mortar and pestle, mixed with a small amount of distilled water, cold pressure into the required shape, and sintered for 16 hours at 1225°C,” [4]. With these conditions in mind, ceramics with alumina composite exhibit optimal structural arrangement and hardness.

TABLE 1 [5]

Chemical “Recipe” of Alumina Composite

Alumina composite is not completely comprised of aluminum and oxygen. Though the formula Al2O3 is 96.1% of the weight in alumina powder used to create the ceramic, more components are necessary to complete the alumina composite composition [5]. This “recipe” for alumina powder creates a hard structure in which aluminum and oxygen are able to still bond together and exhibit strong forces with neighboring ions.

FIGURE 1 [4]

Crystal Lattice Structure of Al2O3 is simple, yet it is arranged under high temperature and heat to organize

the atoms into a strong lattice structure.

The basic molecular structure of alumina (Al2O3) contains much of the strength that creates such a structurally sound solid. “When alumina undergoes hydrolysis, it forms tiny hexagonal platelets with crystallographic dimensions,” [4]. The picture above is a singular lattice structure of alumina. This compound can stand by itself as a component of the ceramic’s chemical makeup or can be bonded with another metallic oxide, such as CaO. Regardless of the

composed mixture, alumina’s metallic properties and ionic properties create a noteworthy structure. Viewed as a metallic structure, each aluminum ion resembles a metallic bond in which electron clouds form and pass electrons from aluminum to aluminum [4]. This resembles a resonance structure that ultimately hardens in the weakest bonds while undergoing formation by extreme heat and pressure. This makes alumina highly ordered with an arrangement that is compact and thoroughly self-strengthened by physical arrangement. In addition, this “neutralizes” many of the magnetic dipoles containing electronegative ions by having a uniformly de-magnetized material [4].

Discussed in a later section of sustainability, this neutralization removes many problems that metallic prosthesis face when taking an MRI. The magnets of an MRI machine are drawn significantly less to a ceramic material with alumina composite compared to a traditional metallic prosthesis [4]. When carefully reviewing the success of an osteoplastic implant, usually MRI scans are the best way to analyze success of the implant. This makes metal implants less sustainable since MRI scans are integrated into the analysis procedure, so metal implants will be less sought after. Alternatives, such as ceramic implants with alumina will suffice to replace metal implants to solve magnetic attraction in the post-operative analysis stages of recovery for patients.

Aside from avoiding a foreseen problem with magnetism, alumina composite offers other benefits by containing ionic bonds in addition to metallic ones. Alumina contains two alumina ions bonded to three oxygen ions by donated electrons. Though this may seem counter-intuitive to the metallic bonds described previously, this is not the case. Metallic bonds are exhibited between the arranged lattice structures while ionic bonds are comprised of the individual atoms within the lattice. Having both characteristics of ionic bonds and metallic bonds allows the alumina composite to be structurally sound as a stable, organized arrangement of ions.

This pairing of characteristics results in a material that is very durable and able to withstand high pressure. “The high hardness, low friction coefficient and excellent corrosion resistance of alumina offers a very low wear rate at the articulating surfaces in orthopedic applications. Medical grade alumina has a very low concentration of sintering additives (<0.5 wt.%), very small grain size (<7 µm) and a narrow grain size distribution. Such a microstructure is capable of inhibiting static fatigue and slow crack growth while the ceramic is under load,” [6]. Even within the body, implants must be able to withstand constant stress and use.

Osseous Design to Allow Bone Growth

Bioceramic and chemical engineers are challenged by two goals when developing ceramic materials with alumina composite: to investigate the growth of bone into a porous ceramic material, and “to develop an experimental procedure

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capable of identifying specifically the type of tissue ingrowth and the overall compatibility of the ceramic with the musculoskeletal system,” [4]. To be an integrated biocompatible material, the bone must be able to grow into the prosthetic by a standardized depth of 100 micrometers. In addition, the prosthetic must be able to allow blood vessels to grow on, around, and through the material [7]. Increasing the pore size of a sample increases the ingrowth by muscular tissue and bone.

Unfortunately, creating a material that is structurally sound and porous is not the simplest combination to achieve. “The success of porous materials for skeletal attachment will depend on simulating acceptable stress patterns as well as designing a material with a porous structure capable of accepting bone ingrowth,” [4]. To ensure success of a material, prosthetic developers work to create ceramic implants that are encouraging of healing and development by the body in a nontoxic environment, which would lead to a labeled “successful” prosthetic implant. This topic will be briefly compared later on to metal implants that can yield some amount of uncertainty in toxicity post-operation.

In order to make a highly porous material in a ceramic structure, fine grain aluminum oxide is reacted with a granular solid that controls the pore size of the material. A metal oxide and carbon dioxide typically form, creating small bubbles throughout the material. For example, alumina and calcium carbonate reacted to form a porous material with each diameter measuring between 40 and 200 micrometers [7].

To examine the potential ingrowth, electron microbes are most commonly used to scan sections of the material. After dyeing a cross-section of the extracted material, microscopic observations are taken to identify mineralized bone by x-ray absorption. In the late 1960s, samples taken from test groups of monkeys with ceramic implants showed 5 micrometers of ingrowth to the ceramic prosthetic within a year [4]. Though research is still being conducted to improve upon the porousness of ceramic implants with alumina composite, it is noteworthy to state animal testing has become less and less socially acceptable since the late 1960s. For this reason, continuing to document specific cases over lifetimes of humans without harmful extraction will help researchers to decide what is an acceptable balance of durability and bone integration. This makes the research continuously sustainable to further examine better materials for biocompatibility and humane testing.

Applications in Prosthetic Research

Whole joint replacement surgeries have become a commonplace and low-risk surgery around the world. In recent studies, it has been estimated that approximately one million knee and hip replacements are performed every year in the United States. These statistics indicate that almost 2 percent of the American population is living with either a complete knee or hip replacement, and this number is

expected to rise drastically as the population continues to age. As the number of joint replacements continues to climb, the need for corrective surgery is also expected to rise; total joint replacements begin to deteriorate in vivo towards the end of their lifespan, and patients often require additional surgeries to replace the prosthetic. In addition to the natural wearing of the prosthetic, patients who undergo a joint replacement often require multiple joint replacements, as the biomechanics of their bodies often change quite drastically to compensate for the prosthetic [8].

The rapid wearing of prosthetic knee and hip replacements is often due to the material of the prosthetic. The most commonly used prosthetic is generally made of metal or of a combination of metal and polyethylene [9]. These combinations have been in use since hip replacements were first attempted in 1960. Another material, although less popular, is also used to create joint implants. Alumina, a durable ceramic, has been used in artificial hip prosthetics since 1973 in Europe, but was only approved by the FDA in the 1980s [2]. Issues with shattering and squeaking throughout the 1980s and 1990s, as well as a higher cost stunted the use of ceramic in joint replacements [10]. The increased durability of ceramics could improve the lifetime of artificial joint prosthetics and eliminate the need for revision surgery, which would lighten the burden on both the patient and the medical field.

ALUMINA COMPARED TO MAINSTREAM OSTEOPLASTY MATERIALS

Ceramic materials with alumina composite are the most structurally sound material for prosthetic replacement for reasons that include hardness, physical molecular structure, and durability. Though plastic and metal prosthetics are generally the most commonly used in vivo, ceramic implants are unsurpassed in strength and see high rates of success in numerous studies testing qualities such as strength and biocompatibility

Ceramic implants with alumina composite are molecularly bonded in a solidified, nonpolar structure that metal implants cannot compare to simply by basic chemistry. Metals, which are conductors, are able to share electrons throughout a prosthetic structure even post-operation [7]. Unstable, metallic structures with conductive properties are receptacle to decomposition of alloy metals that can be toxic to the body. For example, a certain patient was followed for twenty years post-operation with titanium prosthetic. Traces of titanium ions were found sparingly in his blood stream and accumulated in his intestines [7]. Though there are few extensive cases studying definite titanium effects in the body, the inorganic titanium ions can cause internal problems as proven by this post-operative following.

Compared to alumina, the core structure of Al2O3 is a non-conducting material with lesser likelihood to release

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ions of aluminum or oxygen into the body. This likelihood is based on the intramolecular forces (forces between atoms within a molecule which are commonly mistaken for forces that describe attractions between neighboring molecules called intermolecular forces). Ionic bonds are able to hold electrons between oxygen and aluminum. (The visual representation of these attractive forces can be seen in Figure 2 on the next page.) The metallic and ionic bonding properties described previously showcase the stable structure of alumina as a biomaterial with little decomposition over time. This implies extended longevity is very possible with alumina composite. In a currently on-going, 5-year survival rate study of abutment (arch support) prosthetics in vivo, there was a 99.1% confidence survival for ceramics with alumina composite and 97.4% confidence survival for metal implants. Though small in difference, this calculated performance is an indication that development is putting more confidence in alumina prosthetics compared to metallic prosthetics [11].

FIGURE 2 [4]

Atoms can experience multiple types of attractive forces between bonded atoms and neighboring molecules and compounds. The above figure shows various types of

attractions and demonstrates what each force is physically exhibiting.

To continue comparing durability over a length time, ceramic implants with alumina composite are small and resistant to wear and tear. The common grain size of alumina is <7 µm, which can be used to calculate strength of ceramics according to the equation in the proceeding column [6]. In this equation, sigma is the compressional, tensile, bend, or impact strength, A and n are constants determined by temperature dependence, and d is the grain size. This equation indicates that as particle size decreases, strength increases. By this, grain sizes that are larger, such as slices of metal or hard plastic prosthetics, will have a lesser value of calculated strength [7]. Also below the strength equation is a chart that shows the hardness versus the alumina particle size. Essentially, this chart shows there is an optimal particle size for the hardest possible substance. A harder substance increases the durability over time of the prosthetic.

EQUATION 1 [7]

This equation for strength in ceramics calculates strength of a ceramic material. The equation is

temperature dependent to find A and n. Ultimately, as d (particle size) decreases, strength (sigma) increases.

CHART 1 [5]

Hardness versus Alumina Particle Size: This chart shows the general trend of the relationship between hardness

alumina material based on alumina particle size. (Between zero and ten micrometers, there is an obvious

peak in the graph, which represents the optimal characteristic of hardness with a corresponding particle

size.)

In addition to durability of the material, the ability to track previous experimentation of materials and to diagnose problems in vivo is beneficial to the success of prosthetics. Most simply, x-ray images of metallic prosthetics are clouded by an overwhelming brightness in the image. Usually the next step would be to take an MRI scan to diagnose and look at the surrounding area to observe bone growth and muscle tissue healing. However, metal prosthetics sometimes are magnetically polar, causing issues when being scanned in a highly magnetic machine [12].

Ceramic prosthetics by comparison are magnetically nonpolar, exhibiting little attraction to magnets. This allows research to proceed normally while taking post-operative notes of patients as they are healing. As far as the future of

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prosthetics go, it would be unwise to send someone with a potentially magnetically attractive prosthetic through a machine containing a huge magnet to take a digital image because it increases risk of patient injury and prosthetic dislocation [12]. Ceramic materials with alumina composite have metallic properties, making the chemical bonds stronger, without being attracted to magnets. For this reason, research can be readily conducted on patients with ceramic implants with alumina composite, thus advancing the technology and discovering more easily how to improve alumina ceramic osteoplastic implants.

SOLUTIONS TO PROBLEMATIC PROSTHETICS

Is Failure an Option?

Alumina prosthetics remain an imperfect technology. As the development of ceramic prosthetics continues to evolve, both successes and failures during testing can steer research in the right direction. Failure in vivo and in testing can reveal important structural and design errors that will, in theory, be remedied in order to create a better prosthetic. For example, frequent degradation of metal and plastic implants resulted in the discovery of ceramics as a suitable material for implants. The failure or malfunction of ceramic implants in vivo is indicative of new improvements that can be brought to the technology. Issues that present themselves in clinical trials or in post-operation check-ups, such as squeaking and cracking, are still issues today. Lennox Hill Hospital followed 131 patients who had received a ceramic hip implant, and documented fourteen (10.7%) patients who complained of squeaking, and one patient requested revision surgery to amend the squeaking. The cause of squeaking remains unknown, but can also affect the quality of life of post-operation patients [13]. Failure in vivo remains a more dangerous concern. De Aza wrote “In the pioneer times the fracture rate was quite high, mainly for alumina-alumina pairs. A recent compilation of case studies show that the in vivo fracture ratio (number of fractures/number of implanted heads) of current-day alumina heads-polyethylene combinations can stand below 0.01% for the past ten years,” [13]. The rate has dropped substantially since the introduction of ceramic prosthetics, however the sources of failure (cracking and biocompatibility issues, for example) remain important venues for innovation and improvement.

Improving Current Alumina Designs

The recurring problems that occur in ceramic prosthetics remain pressing issues that affect both the popularity and effectiveness of joint implants. Squeaking and shattering in vivo of alumina ceramic implants has resulted in increased research into improvements and alternate designs for hip prosthetics. The Nanomaterials and Nanotechnology

Research Center, have been actively researching alternative materials. The institute has recently produced an alumina-zirconia nanocomposite that is expected to have a lifespan of over 70 years in vivo. Fracture toughness is defined as the “indication of the amount of stress required to propagate a preexisting flaw,” and is an important criterion when evaluating materials for implants [14]. The proposed combination of alumina and zirconia has a toughness value of more than 9 [MPa.m1/2], versus pure aluminum oxide, which has a fracture toughness of 4.2 [MPa.m1/2] [15]. In “Crack growth resistance of alumina, zirconia and zirconia toughened alumina ceramics for joint prostheses”, De Aza compares several qualities of alumina, zirconia, and alumina-zirconia composites. The fracture threshold and hardness of the materials were tested through a series of trials, which indicated that the alumina-zirconia composite is harder than pure zirconia, with values of 1530±50 Vickers versus 1290±50 Vickers. Pure alumina is harder than the composite, but also considerably less tough. The alumina-zirconia composite had a much higher fracture threshold (4.0±0.2 Mpa m1/2) than zirconia (3.1±0.2 Mpa m1/2) and alumina (2.5±0.2 Mpa m1/2). The increased hardness and crack threshold of alumina-zirconia composites would improve the reliability and lifespan of ceramic prosthetics [16].

The Changzhou Institute of Light Industry Technology (CIT) has developed a method of strengthening traditional materials, in particular ultra-high-molecular-weight polyethylene (UHMWP) and other plastic joints in order to improve the lifespan and durability of the prosthetic. Plastic hip and knee implants are formed by long polymer chains, which spread microscopic fractures throughout the material and cause the failure of the prosthetic [17]. The addition of ceramic particles to UHMWP prosthetics can drastically improve the rate of fatigue wear in vivo, however Xue and the CIT believe that irradiating the prosthetic with gamma radiation will further toughen the joints. The short burst of gamma radiation breaks the long polymer strands inside the plastic into small pieces (radicals). The radicals relink to form a tougher material that does not propagate stress throughout the structure [18].

The use of ceramics to improve traditional prosthetics is not limited to polyethylene implants. In Vivo Bone-Bonding Study of Bioglass®-Coated Titanium Alloy studies the applications of specific glasses (know as Bioglass) as a coating for titanium alloy implants. Glasses such as these are able to chemically bond to bone without a porous surface or cement. Bioglasses tend to be brittle, and are therefore most useful as coating for harder materials, such as titanium alloy or stainless steel. Titanium alloy rods were dipped in Bioglass and then implanted into dogs. The coating process proved to be defective in West’s study, due to bubbles at the glass-metal interface of the prosthetic, which ultimately caused the failure of the prosthetics [19]. The U.S. Department of Energy's Lawrence Berkeley National Laboratory has also been conducting research into the use of

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ceramic coatings to improve the biocompatibility of metallic implants. A bioactive silicate glass would be capable of bonding with both metal and bone, although 2-3 graded layers are required to effectively bind the surfaces. The enamelling procedure, which requires temperatures of 800-900 degrees Celsius, would coat a metal implant with 20-200 microns of glass. Thermal stresses during the enamelling process have compromised the integrity of implants in past studies, however by ensuring that the thermal coefficient of the glass and the metal are the same, the effect of thermal stresses can be substantially reduced [20].

The ongoing research in the field of ceramic prosthetics testifies to the potential of this technology. Sub-standard materials such as aluminum and polyethylene have been widely accepted as the norm for joint implants, although the ideal qualities of ceramic implants could create a more durable and less problematic joint replacement. To do so, however, recurring issues that plague current models of alumina hip implants must be resolved with further research. The recent innovations outlined above make a strong case for the sustainability of alumina hip replacements. This research could immensely improve the quality of life of current and future patients who require total joint replacement, as common malfunctions and causes of failure could be eliminated. The advances in bioceramics represent sustainable research, as the findings promote further innovation and inquiry to encourage more profound investigation.

ETHICS: THE ONGOING DILEMMA

Ethics remain an important concern in engineering and in medicine, and especially within the transplant community. Medical devices must undergo several forms of testing, including testing in animals and eventually a clinical trial with human participants. The safety of the participants must remain a priority, even at the cost of advancement. The Biomedical Engineering Society (BMES) Code of Ethics begins by listing the two obligations of professional bioengineers:

1. “Use their knowledge, skills, and abilities to enhance the safety, health, and welfare of the public.

2. Strive by action, example, and influence to increase the competence, prestige, and honor of the biomedical engineering profession,” [21].

The Code of Ethics reiterates that although one of the primary goals of bioengineers is to advance the profession and strive for innovation, the safety of the public must remain the top priority. In the case of artificial joint replacement, advancing the techniques and materials used in prosthetics must not come at the price of comfort and mobility for trial patients. As an engineer, many potential sources of error can be eliminated in preliminary tests, but

there remains an element of unpredictability in bioengineering. Issues such as squeaking, fracturing, or the rejection of the implant can occur without warning in post-op patients. Chemical engineers specifically must be conscious of the effect of substances on both the patient and the environment. Many substances can be harmful when left in the body, and chemical engineers must be aware of the risks. The repercussions of the fabrication of the material must also be considered. In a society that is increasingly strict and aware of the environment, the fabrication process of the material will be highly scrutinized. Before the technology can be tested in animals and humans, it is the engineer’s professional and ethical responsibility to ensure the safety of the implant in order to ensure the well being of the future patients and the advancement of the technology.

Alumina in Relation to Sustainability

Alumina prosthetics represent a sustainable product in several regards; they contribute to improving the quality of life of thousands of patients who would otherwise suffer from debilitating conditions, but also provide an example of sustainable research. According to the National Institute of Arthritis and Musculoskeletal and Skin Diseases, the most common reasons to undergo hip replacement surgery are osteoarthritis, rheumatoid arthritis, and bone tumors or injuries that damage the joint [22]. These incapacitating conditions can substantially reduce mobility and are extremely painful for suffers. As a result, patients suffering from these ailments are often unable to walk and have a reduced quality of life. Alumina prosthetics provide a reliable and effective treatment for patients with reduced mobility as they have the potential to last longer than traditional implants. Ceramic hip implants are better equipped to sustain a higher quality of life for post-op patients due to their superior lifespan and chemical composition. Ceramic prosthetics have become the ethical and practical choice, as the high durability, toughness, and biocompatibility of the material allow for a higher quality of life for patients who have undergone total joint replacement surgery.

Alumina ceramic hip implants provide a higher of quality of life not only for the individual, but also for the population on a larger scale. Without safe and effective hip prosthetics, 2 percent of the American population alone would be plagued with debilitating pain [8]. This would pose an immense problem for society, as these patients would likely be unable to walk and would require substantial care. They would also be unable to contribute to the workforce, and may be reliant on government aid for disabilities. By performing successful joint replacements, more people would be able to maintain a higher quality of life, as they would not be limited by their lack of mobility.

The research into other models of ceramic hip implants also advocates for the sustainability of the technology. Ceramic implants have an untapped potential, which is

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confirmed by the recent surge of research into the use of ceramics in prosthetics. Recent advances, such as gamma blasted ceramic coatings and improved ceramic nanocomposites, demonstrate the necessity of further research by showing the vast promise of ceramics. Although current hip prosthetics, such as polyethylene and aluminum models, are widely used and accepted, significant issues such as the limited lifespan and poor biocompatibility of these prosthetics could be resolved with improved ceramic implants. Ceramic prosthetics represent a sustainable technology as research has been (slowly) increasing in the field since the conception of the technology in the 1970s. The development of longer-lasting and more dependable hip implants will prove vital to the quality of life of an ageing population; it is therefore essential that researchers continue to investigate biocompatible materials for artificial joints.

A PROSTHETIC FOR THE FUTURE

Since its conception in the 1970s, total joint replacement has become a standard operation in most hospitals around the world. Traditional hip and knee replacements (using metal or plastic prostheses) are not optimally biocompatible in the body. As a result, they wear down in vivo and release particles that can cause inflammation in the patient. This results in a high number of revision surgeries, which place an enormous burden on both patients and the medical industry. Ceramic implants are an alternative to traditional materials, however recurring issues such as squeaking, cracking, and failure in vivo have limited its popularity.

Ceramics (such as alumina) have a number of chemical qualities that make them the ideal material for implants. Alumina contains a unique combination of both metallic and ionic bonds that make it extremely durable and resilient in vivo. Toughness and hardness are key traits for prospective implant materials, as hip and knee prosthetics undergo an incredible amount of stress and wearing in vivo. Ceramics are substantially more durable than traditional materials such as metal and plastic, which break down in the body and release harmful particles into the body until the implant ultimately fails. Alumina is also a porous material, which allows the bone to grow directly into the implant rather than using an intermediate layer such as cement to attach the prosthetic. This increases the biocompatibility of the artificial joint and provides a more stable environment for the implant.

Several improvements have been proposed in order to improve ceramic implants. One solution is the use of an alumina-zirconia nanocomposite instead of pure alumina. The combination of the hardness of zirconia and the toughness of alumina eliminates the materials’ flaws to create an ideal substance for prosthetics. Another proposal would use ceramics as a coating for traditional materials, such as titanium alloy or polyethylene. Plastic implants become dramatically tougher when coated with alumina and

then blasted with gamma radiation. The long polymer chains in the plastic are broken and relink to form a stronger material that does not propagate stress throughout the prosthetic. By coating metal and plastic implants with glass or ceramic, cement and porous materials are not needed to attach the prosthetic to the bone.

Ethics play an important role in both the engineering and the transplant community. Throughout the process of developing a new medical device (or improving an old one), the product undergoes trials on both animals and humans. The engineer must ensure that the product has been sufficiently tested, and that any avoidable sources of error have been addressed.

The sources of error can often be unpredictable. The human body extremely variable, and unforeseen complications are the norm in medicine. The complications that arise in testing are often indicative of new paths to take in research. The degradation of metal and plastic joint in vivo, for example, led to the use of ceramics as a more durable alternative. Other issues, such as a persistent squeaking noise in the joint, draw attention to flaws in current design.

Alumina and alumina-coated prostheses provide a large and sustainable avenue for joint replacement research. The advantages of alumina, such as its hardness, toughness, and biocompatibility, largely outweigh the disadvantages of the material. As the population continues to age, the rate of hip and knee joint replacements is expected to surge as well. The improved resilience of alumina would drastically reduce the number of revision surgeries and would improve the quality of post-op life of the patients. Recent strides in research into ceramic implants ensure that they will surpass traditional materials in coming years. 

REFERENCES

[1] “Hip Replacement Implant Materials.” BoneSmart: Knee Replacement & Hip ReplacementPatient Advocacy & Online Community. (website). http://bonesmart.org/hip/hip-replacement-implant-materials/[2] Kinamed, Inc. (1992). “Role of ceramic implants. Design and clinical success with total hip prosthetic ceramic-to-ceramic bearings.” (online article). http://www.ncbi.nlm.nih.gov/pubmed/1516312# [3] S.F. Hulbert, J.J. Klawitter. (1972). “History of cermic orthopedic implants.” (online article).http://www.sciencedirect.com/science/article/pii/0025540872901031[4] C.W. Hall, S.F. Hulbert, S.N. Levine, et al. (1970). BIOCERAMICS- Engineering in Medicine (Part 1). New York, New York: Interscience Publishers. (print book). [5] N. Parvin, M. Rahimian. (2012). “The Characteristics of Alumina Particle Reinforced Pure Al Matrix Composite.” (online report). http://przyrbwn.icm.edu.pl/APP/PDF/121/a121z1p32.pdf

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[6] R. Cordingley, L. Kohan, B. Ben-Nissan, et al. (2003). “Alumina as an Orthopaedic Biomaterial - Characteristics, Properties, Performance and Applications.” (online article). http://www.azom.com/article.aspx?ArticleID=2160[7] P. Ducheyne, G.W. Hastings. (1984). METAL and CERAMIC BIOMATERIALS. Boca Raton, Florida: CRC Press. (print book). [8] J. Davis. (2014). “Adding Up How Many Americans Are Living With Hip and Knee Implants.” Arthritis Foundation. (online article). http://www.arthritistoday.org/news/americans-with-artificial-joints-337.php [9] J. Cluett. (2014). “Hip Replacement Implant Options.” About Health. (online article). http://orthopedics.about.com/od/hipkneereplacement/a/implants.htm [10] “Hip Replacement Implant Materials.” BoneSmart. (online article).http://bonesmart.org/hip/hip-replacement-implant-materials/[11] A. Keenan, D. Levenson. (2010). “Are ceramic and metal implants abutments performance similar?” (online report). http://www.nature.com/ebd/journal/v11/n3/full/6400731a.html[12] K.M. Koch, B.A. Hargreaves, K. Butts, et all. (2010). “Magnetic resonance imaging neat metal implants.” (online article). http://rt4rf9qn2y.search.serialssolutions.com/?ctx_ver=Z39.88-2004&ctx_enc=info%3Aofi%2Fenc%3AUTF-8&rfr_id=info:sid/summon.serialssolutions.com&rft_val_fmt=info:ofi/fmt:kev:mtx:journal&rft.genre=article&rft.atitle=Magnetic+resonance+imaging+near+metal+implants&rft.jtitle=Journal+of+magnetic+resonance+imaging+%3A+JMRI&rft.au=Koch%2C+K+M&rft.au=Hargreaves%2C+B+A&rft.au=Pauly%2C+K+Butts&rft.au=Chen%2C+W&rft.date=2010-10-01&rft.eissn=1522-2586&rft.volume=32&rft.issue=4&rft.spage=773&rft_id=info:pmid/20882607&rft.externalDocID=20882607&paramdict=en-US). [13] C.A. Jarrett et al. (2009). “The squeaking hip: a phenomenon of ceramic-on-ceramic total hip arthroplasty.” The Journal of Bone and Joint Surgery. (online article). http://www.ncbi.nlm.nih.gov/nlmcatalog?term=%22J+Bone+Joint+Surg+Am%22[Title+Abbreviation] [14] “Fracture Toughness.” NDT Resource Center. (online article).https://www.nde-ed.org/EducationResources/CommunityCollege/Materials/Mechanical/FractureToughness.htm [15] “Aluminum Oxide, Al2O3 Ceramic Properties.” Accuratus. (online article). http://accuratus.com/alumox.html [16] A.H. De Aza et al. (2002). “Crack growth resistance of alumina, zirconia and zirconia toughened alumina ceramics for joint prostheses.” Biomaterials. (online article).

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Society. (online article). DOI: 10.1111/j.1551-2916.2007.01725.x.C.S. Ramesh, C. Shashishekar. (2012). “Contact analysis of prosthetic knee joint using ANSYS.” Biomaterials. (online article). DOI: 10.4028/www.scientific.net/AMR.415-417.1235

ACKNOWLEDGEMENTS

This topic is very near and dear to the authors of this paper. As young people involved with athletics, this topic could be of great use to us and our generation that puts so much wear, tear, and stress on our bodies during games and in every day demands. One author’s father is in consideration for receiving an osteoplastic knee surgery, and many of his friends have gone through the entire replacement surgery process. This paper has provided insight to a useful and sustainable research process.

Margot Shore and Kaylene Kowalski would like to thank multiple people for helping with this paper which would not have been possible to complete so thoroughly without their support. The authors would like to thank Sarah Foran for providing helpful tips during the writing process on style and focus. They would also like to thank Dr. Don Schock who is the chair advisor for the engineering conference for providing an engineer’s perspective on our topic. In addition, the authors of this paper would like to thank Beth Newborg for her careful attention to connecting science and effective informational writing.

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