Other aspects also include factors such as biocompatibility, practicality and cost. Finally, according to the principles set out in ‘Wolff’s Law’ about bone remodelling: ”Bone is deposited and reinforced at areas of greatest stress” 15.Theoretically, the three classes of biomaterials are: • Bio-inert materials or Biologically inert materials (first generation).
• Bio-active materials or Biologically active materials (second generation).• Bioresorbable materials (third generation).First generation materials are still in heavy use, specifically in hard-tissue applications, and that field research is growing. Second and third generation materials are meant to create novel methods for the treatment.
Composites are found to be beneficial in this regard of development of the complex. In third generation the materials are specific to cellular responses 16,17. They form biodegradable scaffolds and organized structures 12,17,18. Furthermore, it is important to state that these materials first go through rigorous test and trails before being accepted in commercial and surgical practices 5,19,20.
Future objectives for next generation biomaterial is also briefly outlined coupled with the study of recent key discoveries.2//Tissue Engineering applicationsSoft tissue engineering prospects deals with scafflods structures in the bone which specifically relates to bone tissue engineering. Methods like allogrfting and autografting are used to traet the defective bone21,22. These days researches are more inclined towards osteoconductiveness, osteoinductiveness and more importantly towards biocompatability.Biomaterials also used in conjuntion with drugs and antibiotics to improve healing and prevent infections22-26. Modern bone tissue gives us many advantages27:1.
Time required for skeletal cells from donor tissue will be reduced.2. The defective bone can be replaced with appropriate biomaterial.3. Treatment with stems cells can reduce risk of patient’s life.3//Orthopedic ApplicationsThe use of biomaterials is highly demanded in the field of orthopedics. This is certainly beneficial for both commericializatiopn and research purposese and composites used are studied and experiments to enhance the performance of the previous defective bones.3.
1// Bone graftBasically if we observe the bone at the microscopic level we will find the cellular composition of osteocytes and matrix. Matrix composed of collagen fibres,helps in giving the strength and flexibility to the bone and associated HA microcrystals and minerals salts for hardness. The bone tissue is constantly replaced and remodelled giving the name Bone Remodelling. The stimulus from the osteocytes helps initiate ostoeblast and osteoclast to remodel which also depends upon the stress loading. In the defective bone performing autografts has its limitations and same as the case with allografts and it is in continious research.Studies for composites in which graft consist demineralised bone powder between two collagen layers have been developed32. The test are conducted in Vitro and in vivo showing cell migration.
Bioactive ceramics which function as a HA layer on the fractured bone helps in increase in osteoblast quickly thus healing the bone. Also studies suggest combination of HA layer with high-density polyethylene(HDPE) as a replacement material for bone 33,34-39. This has been tested and commercially named as HAPEXTM. The range of HA is usually taken between 20 to 40 % by volume.
Empirical results has been convincing of osteoblast over bioactive ceramic layer of HA particles40.Composites from the bioactive ceramics combined with HA particles and collagen fibres have the potential to be the artificial subtitute of the bone41. Also the graft has been proven of good mechanical properties42.
HA/alumina has been proposed as bone substitute43. One reserach also concludes on mixing P2O5 glass with HA particles gets near to natural bone characteristics44. 33 not foundAn investigation also claims on improving by incomplete resorbable composites produced from polymeric matrix for example PEG,PBT,PLLA,PHB,alginate and gelatin. The HA particles in conjunction with polymeric matrix with covalent bonding helps in achieving bone replacement45.Elastomeric D, L-lactide and ?-caprolactone copolymers (ratio 60/40) strengthen HA powder were observed to describe the impact of the HA content 46. A bioactive ceramic TCP along with HA also provide us necessary requirement for the artificial bone48.
High modification can be achieved with the help of coupling agents. In order to decrease the cytotoxity of the cytoblasts cells to avoid inhibition of cellular growth the cross linking of glutaraldehyde cross linked with composite should be lower than 8% 49,50.TCP also combined with biodegradable PP as a temporary replacement for trabecular bone51. In the in vivo examination it was found that composites maintain the compressive stregth and modulus greater than minimum vlaue of trabecular bone replacement.Furthermore, with the technology of bioglass came, it revolutionazied the biomaterial replacements.
Composites have been prepared using 37% by wt. bioactive glass powder, 27% by wt. PLA, 27% by wt.
PMMA and 9% by wt. antibiotic 52.In vitro results have shown desirable results by growth of apatite-like layer over the composite, but long term effects are still being studied. Bioglass have also been combined with PE matrix 53. The matrix adhesion is weak however the mechanical properties are desirable and the osteoconductive properties are high, with this also this composite requires lesser time to incorporate with the bone tissues. Carbon fibre have also been tested in vivo and gave results that adhesion between the tissue and impant is by the porosity of the material 54.
Another composite of mainly CaCO3 and collagen has been tested and used for treatment of defective bone with no infections 55.3.2// Bone Fracture repairDifferent methods are being adopted for bone fracture repair, this usually done by . Extrnal fixation. Internal fixationExternal fixation keeps bone aligned with the use of splints,braces and casts or any other fixation system can be utilized. Previously materials are made from plaster of salt with cotten33. Breath free cast were further developed to stop shedding of pateint’s skin56.
Recent technologies hass now developed carbon fibre casts which are very light weight and also easily avaliable at doctor’s disposal56. Carbon fibre is used to strengthed the plastic thereby improving the nimbleness, gait and walking speed57. Internal fixation uses implants like plates, screws, wires and pins for holding bone fragments in place.
Compound composites are divided into 2 classes . avital/avital. vital/vitalAvital/aital composites consist of ‘non-living’ matrix whereas vital/avital composites have ‘living’ matrix.In the area of avital/avital composites, it can be further categorized as. Resorbable. Partially resorbable .
Fully-resorbable compositions 33,58.In resorbable bone plates, their is gradual increase in stress on the bone which progresses through healing therefore stress shielding perhaps is reduced can thus prevent osteopenia. Many resorbable polymers have been accepted and used, like PLLA, PGA and PGLA, by the doctors. Although it has slow rate of degredation apart from having good mechanical properties and also to boost properties polymers have been reinforced with fibre58.Attention is also given to the thermoplastic composites and carbon fibre/poly ether ether organic compound(CF/PEEK) 33,60. This has high mechanical stregth and high fatigue resistance61. The problem arises in manufacturing CF/PEEK which were taken into account by Fujihara et.
al. 61,62 in which fabricating of unwoven and adorned CF/PEEK compression plates idea was given and also touches ideas of pre-loading stress and screw holes were mentioned. Hung et. al. 63 worked the idea of unwoven fabric and carried out analysis in his paper. Intramedullary nails could be helpful for fractures like in leg bone, neck bone5. Further, carbon fibre with liquid crystalline compound (LCP/CF) along with GF/PEEK material mixtures are also been studied 33,64,65.
3.3// Joint prosthesesThe biomaterial used in artificial joints is an emerging field. Prostheses with good stress and strain distribution on the equipment coupled with the physological response helps the user in the long run with promising effects and clinical success. The clinica experiments usually takes time and also high concerns are with the biocompatibility of the material.3.3.1// Total knee replacementMuch effort is required in knee replacement and are often most troublesome. The wear resistance is the main issue of concern which was previously done with synthetic UHMWPE by reinforcing carbon fibres which resulted in poor bonding between them 33.
Same was the case with UHMPWE with UHMPWE fibres but we got improved improved strength and stiffness in this case 33. In recent study by Utzschneider et. al.66 tested wear resistance of cross linked resin in a very large variety of knee joints and found statistically lower wear rates as compared to UHMWPE.
Many characteristics for materials used in knee replacement were summarised by Rahaman et. al.68 and were–. High strength, elastic modulus, fracture toughness, and fatigue resistance while under loading; loads in body ranges from 3kN (normal walking) to 8kN (while jogging or stumbling).
High corrosion resistance for bio-inertness and biocompatibilty in vivo.. High hardness and good surface finish in support of wear resistance for long term life.
Good wetting at bearing surface.3.3.2// Total hip replacementAcross America there are almost 150,000 operations per year and which makes it common type of replacement33. At clinical level it is a success with 93% success upto 10 years and 85% upto 15 years69.
Yet, the replacement gives physiological stesses with the bone. Fashionable prostheses(Fig.1) made of chemical compounds also give the strength and stiffness along with the style. The protheses should have optimal level of stress shielding and minimum stress stiffness so that it doesnt cause pain because of low amplitude oscillatory motion70. Futhermore, the prostheses with supported quality metal hip alloy hip style might not strructurally adequate71. The Finite part analysis is been used to check and optimize hip implants and a large scale analysis for future development of implants is done by Srinivasan et.
al.72. Use of computational methods to analyze stresses and performances helps in designing of optimal implants for example carbon fibre/polyamide12 (CF/PA12) and carbon fibre/Polyamide (CF/PA) and CF/HAP 69,73-75.Apart from the style and properties fixation is very crucial in total hip replacements, the spheroidea fixation concentrates on approaches of cementing bone growth 76-79.
3.4// Artificial tendonsIn combination of properties like structure, resistance and biocompatability much attention also given to look and fabrication of composite nerve sinew prostheses. Mostly tendon substitute are polyesters and hydrogels.
The properties of PHEMA matrix with PET fibres are been studied in 80,81. Also composite with from ethylene-butene polymer with UMHWPE has been tested in 82 to conclude the fatigue resistance. Polyester with polyose, which can used as a wound healing catalyst, has been analysed to guage polyose effects83.3.5// Artificial ligamentsMost ligament injuries are associated with anterior symmetric ligament or simply ACL.
The composites for ligaments made are usually of polymer-composites whose success rate is not very high. Mechnical failures of these polymers are covered in 84 and is mainly due to weak fatigue resistance,abrasion and along with torsional fatigue are reasons of failure in long run. For this fact composites of PLLA and hyaluronic acid ester, which decay gradually and natural tissue growth occurs, were studied. Some experiments shows that PET could induce rubor thus terephtalate polyester plain-woven fibres are combined with living matrix albuminioid85.
The composite is tested in vivo shows no sign of fracture or inflammations or reaction. 3.6// Artificial cartilageCartilage replacement biomaterials are repair inherent. The fibre content and matrix composition in the material can be changed to get the desired properties like those of natural discs.
A biocomposite made from UHMWPE with 3 dimensional structure coated with u-HA particles has been developed and has the potential to used in articular animal tissue and disc bones 86,87. The implant becomes the natural part of the tissue and by this integrates the mechanical properties in it. This composite is tested in in vivo showing no wear or infection however methods to repair gaint defects has not been found yet.