Introduction
Orthopedics refers to the branch of surgery devoted to the diagnosis and treatment of illness, injuries malformations and deformities of the musculoskeletal system (Goriainov et al. 2014). The system includes the muscles, ligaments, tendons, joints and bones. Orthopedic engineering leverages biomaterials in the form of implants such as sutures, joint replacements, bone plates and so forth. It also deals medical devices to replace damaged and defective parts of the body (Goriainov et al. 2014,"Material, Technology and Profit” 1988).
Biomaterial is termed as "Any substance (other than 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. "(Patel & Gohil, 2012, P. 91). Biomaterials and their usage in orthopedics date back to ancient times and civilization. Numerous kinds of materials were used by the ancient Indians, Chinese, Egyptians and so forth. Few of these materials are not compatible with the body and emphasizes the importance for improvement in technology. With the advancement in technology, biomaterials have passed through many phases including peek and bioglasses but today we have a lot of emerging biomaterials and structures worth putting into consideration owing to their relevance in orthopedic engineering. Needless to say, the application of these biomaterials will go a long way to revolutionize orthopedic engineering and ultimately help in improving the quality of life. Figure 1 is illustrating anatomy of human in regarding implant of different body parts (Goriainov et al. 2014; Navarro et al..2008).The aim of this treatise is to evaluate and look into top emerging biomaterials and structures in medical devices after peek and bioglass.
Figure 1 Anatomy View of the human body for Implant
Source adopted: Patel & Gohil, 2012
Characteristic Features of Biomaterials
Biomaterials must possess some unique characteristic features in order to be suitable for use in vivo. Of course, in vitro experiments, studies must be conducted on a given biomaterial before using its implantation in the human body. There are some essential parameters to be considered that include biocompatibility, toxicology, bio-functionality, corrosion resistance, mechanical properties, and manufacturability. In addition, it has the appropriate design, strength, wear resistance, long fatigue life, and modulus equivalence to that of bone (Patel & Gohil, 2012; Farraro et al. 2014).
Biocompatibility is one of the most important features that a biomaterial should possess. It simply implies that the biomaterial performs well in the host body, in a specific application. Biocompatible materials are known as biomaterials, and it is largely associated with toxicity. Biomaterial is designed in such a way that biocompatibility should be non-toxic such as biomaterials should be non-carcinogenic, blood compatible, non-pyrogenic, non-allergic, non-inflammatory and so forth.
Bioresorbability is another feature that is worth mentioning. Bioresorbable materials are gaining prominence today with the introduction of functional tissue engineering. These materials are unique because they can perfectly replace the patient's tissue. It also is used for delivery of bioactive molecules so as to improve tissue healing (Farraro et al. 2014; Niinomi, 2007). Variety of emerging biomaterials fall under this category and hold promises to the future of orthopedic engineering. Their applications and usages would greatly improve the lives of people who need implant for any unavoidable reason. (Goriainov et al. 2014; Rolfe, B. et al., 2011; Scholz et al. 2011).
Emerging Materials and Structures and Their Applications
The future holds many fortunes for orthopedic engineering as a lot of emerging biomaterials and structures are recently being produced which have the versatility in applications. The list of emerging biomaterials is endless, and many more are popping up as a result of the recent advancement in technology. It is imperative to know that most of these materials are bioresorbable or perhaps possess some characteristics that make them unique.
Bioresorbable Mg and Mg Alloys
The breakthrough in the use of Mg and its alloy as biomaterials is a resounding one. Even though, magnesium has some exceptional qualities such as the stimulation of soft tissue production and promotion of new bone growth. But it was abandoned due to its rapid degradation as well as the formation of hydrogen gas due to the crude technology that could not be controlled in vivo ( Farraro et al. 2014). However, the recent advancement in technology took care of these issues and therefore makes magnesium and its alloy one of the best biomaterials for orthopedic implant. The technological advancements included a new method of alloying, coating, surface treatment and processing. This often involves allowing magnesium with metals like yttrium, zinc, silver, neodymium, manganese and others. The resultant alloy has improved mechanical properties and still maintains degradation. However, to control the degradation of magnesium and its alloy, novel coatings and surface treatments are employed (Cao et al,2012; Farraro et al. 2014)
Magnesium is unique for orthopedic application owing to its lower moduli when compared to titanium based materials (Han et al.2013). As a result, they have similar mechanical properties to cortical bones and with such materials the level of stress shielding could be reduced. They are also stronger than polymers and also very ductile. Magnesium alloy can be employed in anterior cruciate ligament (ACL) reconstruction as an interference screw for fixation of tissue auto-grafts. In this recent study, “the choice of Mg-based interference screw was made because it would allow the effect of Mg on healing and remodelling of the hard and soft tissue interference to be tested. Mg has been shown to promote bone regeneration; the use of Mg-based interference screw may have potential benefit in healing of the graft in the tunnel" (Farraro et al. 2014, P: 1982). In another study, Magnesium’s mechanical properties, controllable degradation and so forth come to play for augmentation of ACL healing (Singh & Dahotre, 2007). The success of magnesium based interference screw has encouraged the development of other biomedical devices such as suture anchors for rotator cuff and acetabular labrum repair. Magnesium is excellent for these applications because of its biocompatibility and osteoinductivity. New magnesium based devices that would withstand corrosion and also give room for better bone healing are recently being developed (Celarek et al., 2012; Farraro et al. 2014; Tschegg, 2011)
Cryogels
Much of the future’s healthcare and biomedical application would rely on cryogels. These are supermacroporous gel matrices which are synthesized below 0o Celsius, specifically at -12 degree Celsius. This biomaterial aids in the formation of interconnected porous network that give the room for rapid increase and migration of cells. Many studies and experiments are being carried out in order to fabricate the cryogel matrices for effective application in different biomedical fields. It includes as tissue engineering, cell separation and so forth (Reichelt et al. 2014; Sumrita & Ashok, 2013). The matrices are quite suitable for a lot of applications and purposes owing to their excellent mechanical properties and many other features. They have the flexibility in terms of design, and hence, they are quite appropriate in different biomedical applications. Some of the features that make cryogel unique are shortly listed (Koshy et al.,2014; Temeno & Mikos,2000):
- They have flexible designs,
- They have excellent mechanical properties,
- The matrices have excellent swelling capacity and hence can take up large volume of solvents,
- Their biodiversity can be enhanced by modifying the gel matrices.
For cartilage tissue engineering, cryogel matrices fabricated using a combination of different natural polymers such as chitosan, agarose, gelatin, alginate and so forth are adequate. The matrices are unique because of their obvious healing effects on cartilage defects as demonstrated in a test on New Zealand white rabbits. “Results with these matrices indicates that synthesized cryogel matrices hold great promise for the patients suffering from accidental injuries of cartilage or other cartilage degenerative diseases” (Sumrita & Ashok, 2013). Cryogel matrices can also be applied in bone engineering as indicated in recent studies. Cryogel holds great promises to biomaterial and structures and of course orthopedic engineering in general ( Koshy et al. 2014).
Hydroxyapatite (HA)
Hydroxyapatite (HA) also has many applications in biomedical engineering. It is chemically similar to bone and also can blend uniquely with the bone in the body. This makes it an exceptional material as a bioactive coating on a metal implant as well as its use as a porous scaffold for bone tissue. However, this material has a major drawback like its brittleness that makes it unsuitable for use as a load-bearing implant. Despite the fact that it holds lots of promises as a bioceramic material, but its potential is still difficult to recognize.
However, recent research on Hydroxyapatite has proven to be very effective. The research conducted Ruys et al. (2013) has resulted in the production of the first ever HA having fracture toughness comparable to bone and pioneering silicone-doping of HA for enhanced bioactivity (Ruys, 2013). Hydroxyapatite is a synthetic material unique for its exceptional and seamless blend with the human body and bone. The body responds to this synthetic material behaving like bone. This material finds application in different fields of orthopedics and biomaterials including as use in bone implant and other forms of orthopedic engineering (“Injectable Silicone Biomaterial” 2005; Mehboob & Chang, 2014).
Titanium material coated with Carbon Nanotube (Ti-CNTs-H2O)
There are mainly two kinds of implantable orthopedic devices. These include devices that are designed to stay within the species’ body as long as possible and those that are implanted to be removed after some time. The second class of materials is worth giving some considerations. Such materials are simply implanted for osteosynthesis to take place. For such material, room for facile removal during surgery should be made.
Carbon Nanotubes (CNTs) hold all the features required for such materials owing to its excellent characteristics. It includes electrical conductivity, electrocatalytic properties, the relative ease of introducing various chemical species on the sidewalls of the tube and many others (Agata et al., 2014). These properties explain why CNTs are applied in usages involving cell adhesion, division and rapid growth.
A study carried out by Agata et al. (2014) that involved the coating of titanium with functionalized and water-dispersible CNTs. That would possess properties such as non-toxicity, inhibition of cell growth, protection against cell proliferation and conductivity. The designed material is to be implanted as a temporal electronic device in order to monitor the regeneration and growth of bones as it occurs and also stimulate bones electrically. The study was designed to evaluate bio-compatibility of the materials in an artificial environment by measuring its electrochemical impedance through electrochemical impedance spectroscopy method.
Differentiated Alveolar Bone Cells in Collagen Scaffolds
Bone defects can be regenerated by a tissue engineering approach, and this is a method of treating bone osseous defects by utilizing cell biology, microbiology and materials science. The concept of tissue engineering was tested in a study conducted by Xiao, Young & Bartold, (2003) that involved collagen I matrices seeded with cells that have bone development ability. This was implanted at place of the bone defect. After a duration of 28 days, it was found that new bone formation occurred at the sites that were treated with osteoblast-derived matrix. This was clearly different from the control group as no bone formation was found at the same location in the control group. The study simply shows that bioengineered scaffolds can incorporate cells obtained from human alveolar bone, and this can be synthesized into a matrix. On implantation of this matrix, bone formation can be effected or induced (Xiao, Young & Bartold, 2003).
UHMwPE Fiber
UHMwPE fiber is a novel biomedical material having characteristics that make it a compatible material for biomedical implant. Traditional orthopedic fibres such as polyesters, polypropylene, nylon and sutures have limitations, but these limitations are clearly addressed in UHMwPE fibre. One of the pluses of UHMwPE fibre is its strength; the fibre is several times stronger than steel. UHMwPE has been widely applied, and its relevance is still evolving. In fact, it is considered a breakthrough in hip arthroplasty. After it had been used in curing hip arthroplasty in 1960, it was discovered that bone cement disease (osteolysis) was caused by the response of the human body to small UHMwPE particles. This sparked researches that were aimed at improving the wear resistance of the fibre. However, with technological advancement of the recent time, a completely new class of UHMwPE is now emerging. Most top biomedical organizations are focused on this new technology. The new UHMwPE fiber has a great advantage over traditional fibre because of its easy crosslinkable feature (Leo. 2009).
Conclusion
Many recent advancement has been made in the field of biomedical engineering. Countless numbers of biomedical materials have been developed, and these materials are put into various applications. Much of the future of orthopedic engineering depends on these emerging materials. The use of biomedical materials can be traced the origin of man as man looks for ways to solve the problems in his environment. This has guided to the evolution of different materials and engineering for the treatment of various conditions.
The 21st century technology advancement has spurred a great revolution as different kinds of material are being developed on a daily basis and these materials have lots of orthopedic applications and benefits. Peek and bioglass were considered as only excellent technology. Today top emerging materials like UHMwPE, collagen scaffolds, and titanium materials coated with functionalized carbon nanotube (Ti-CNTs-H2O), hydroxyapatite, cryogel, hydrogel, bioresorbable magnesium and magnesium alloys and many others have been developed (Mittal , 2011).
These biomaterials share one major property, and that is biocompatibility. Of course, every biomaterial must be compatible in order to be accepted by the host body. This has developed a long way towards improving man's life and ultimately gave way towards greater advancement in technology. One feature of emerging technology is that they have a lot of possibility and risks that have not yet been discovered. Of course, these devices studied in this paper are not an exception to this.
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