Biomedical Engineering: Biomaterials - Coursework Example

………………………………………………………………………….xxxxxx …………………………………………………………………….xxxxxx …………………………………………………………………………xxxxx ………………………………………………………………………..xxxxx @2012 Biomaterials Abstract A biomaterial is a synthetic material that is used to replace a rather malfunctioning body part or even to function in intimate contact with living tissues. They are for making devices that are used to replace some part or function of the body such that it is reliable, safe, and economical and physiologically accepted (Pruitt 2011). Examples of biomaterials those devices used in injury and disease treatment such as suture needles, plates and teeth fillings. Before the body part is replaced, compatibility of the biomaterial and the living tissue is of great consideration (Ratner 2004). Biocompatibility is the acceptance of the synthetic biomaterial by the immediate and surrounding tissues and by the body generally (Paul & Kelvin 2009). Appropriate host response is shown by lack of blood clotting, normal heating and resistance to bacterial colonization. It is essential therefore to study the biomaterial composition and also the way in which they react with the environment in which they are put which is the surrounding tissue (Pruitt 2011). Hence, biomaterial selection involves the logical sequence of analysis of the problem, consideration of the requirement and consideration of the biomaterial properties. Biomaterials that match the properties of the bone and teeth These biomaterials have their physical characteristics that are needed to match the properties of the teeth or bone being replaced with (Ratner 2004). The mechanical properties of these biomaterials involve tensile testing that provides data on the characterization of the biomaterial. These properties include; 1. Thermal properties The oral cavity of tooth experiences a wide range of thermal fluctuation following the ingestion of both hot and cold foods and drinks (Paul & Kelvin 2009). It is necessary to measure the rate of heat transfer per unit temperature gradient which is the thermal conductivity of the biomaterial. Good heat conductors hence have high conductivity. Coefficient of thermal expansion or thermal expansion coefficient It is by definition the fractional increase in length of a body for each degree (in centigrade) rise in temperature. α=∆L/Lo oC-1 ∆T Where ∆L is the change in length Lo is the original length of the biomaterial ∆T is the change in temperature The values of α are very small like for amalgam biomaterial, the value of α=0.0000025 oC-1P.P.M Table showing the thermal conductivity coefficient of different biomaterials in parts per million (P.P.M) The original length of the tooth and the length attained when there is temperature change are calculated in order to determine the length of the biomaterial to be used in teeth filling. Expensile structures ensure that the biomaterial conforms to the irregular bony defects (Paul & Kelvin 2009). This also helps prevent the undesired movement of the fibroblast into the graft site and these yields in optimizing the quality of the replaced bones. Coefficient of thermal expansion is widely considered in filling materials such as for the teeth with cavities. The above table shows different thermal conductivity values of different conductors used as biomaterials. Thermal diffusivity (D) Thermal diffusivity is defined by the equation; D=K Cpρ Where, K is the thermal conductivity Cp is the heat capacity ρ is the density A low value of thermal diffusivity is preferred however there are occasions when the high diffusivity level are preferred to the low ones like if the base material to be used is denture. It is necessary since it retains a good response to both cold and hot stimuli in the mouth (Ratner 2004). Physical properties Physical structures and stability of the collagen fibres and matrixes allows for cellular colonization of the biomaterial through out the entire graft volume for example, matribone collagen matrix helps prevent the inadvertent migration of particulates beyond the desired graft site (Misch 2011. In addition to allowing for cellular colonization of the graft site, the stability and physical structure of the matrix serves a support function for adjunctive therapeutic agents such as platelet rich fibrin (Pruitt 2011). Mechanical properties The mechanical properties of the bone ought to be considered in two orthogonal directions; Longitudinal direction Transverse direction Modulus The bone consists of collagen fibers and an inorganic matrix and it is therefore analyses as a fibre composite. Composites refer to those materials that are made of two or more components (Misch 2011). Biomaterials that are made up of composites are used in engineering to create properties that are superior compared to those of the individual component and match the desired property of the biomaterial (Ratner 2004). The rule of mixture and the inverse rule are used to calculate young’s modulus the aligned fibre composites RULE OF MIXTURES Eax = f Ef + (1 - f) Em INVERSE RULE OF MIXTURES Eax=[fE/f+(1−f)/Em]−1 Whereby Ef is the young modulus of fibres Em is the young’s modulus of matrix Eax, Etrans is the young’s modulus of composites in both transverse and axial directions F is the volume of the fibres. This formula is used to show the stiffness of the composite either in the axial direction or the transverse direction (Ratner 2004. Metals are mostly used because they have a high young’s modulus value and are tough and ductile as well as being fatigue resistant. Advantages of metals over polymers as biomaterials Metals are strong and resistant to fatigue degradation while polymers are easily biodegradable Can be sterilized before use unlike polymers They have shape memory Disadvantages of metal and polymer biomaterials Due to chemical reactions in the body they are easily corroded and leached and this leads to wear and tear Metals cause ion toxicity while polymers may absorb important nutrients from the blood The above graph shows values of young’s modulus in both longitudinal and transverse directions over a range of volumes of the fibre. http://www.doitpoms.ac.uk/tlplib/bones/images/cortical_updated.png accessed on 26th November 2012. The stiffness of a biomaterial made of voigt and reuss components is using the young modulus. In the voigt structure the strain is constant for both pure and composite biomaterials but for Reuss the stress is constant (Misch 2011). Using the young’s modulus E of the voigt structure E=EiVi+Em [I-Vi] Whereby Ei is the young’s modulus of inclusions Vi is the volume of fractions of inclusions Em is the young’s modulus of the matrix Tensile and compressive strength of the hard tissue Bones that are subjected to bending during movements such as the femur are subjected to tensile and compressive stress and different bones support different forces and the tensile and compressive nature of the biomaterial need to be accessed before it is replaced into the body (Misch 2011). Most biomaterials used are composites. Source: https://docs.google.com/viewer?pid=bl&srcid=ADGEESjAuAxZqiqTbYQR0LijhsqKxjW3XGumkROmGqAHRYmPo2wyBPz2ACkZpdr4jXUhYmhP4lT2zV2Wb3RirAfIK8U-59qoYUMxE6nC2fUlTlH-onq-p6GCqwZ7_pzam9y8lSrPEFQh&q=cache%3ASG8LQcMuhk8J%3Awww.progressbiomaterials.com%2Fcontent%2Fpdf%2F2194-0517-1-2.pdf%20&docid=a88a4309c3437f27975837709bbb930a&a=bi&pagenumber=13&w=80 0 . Accessed in 26th November 2012. Comparison between the possible biocompatible materials. A biocompatible material allows the body to function without complications such as allergic reaction or even other adverse effects. Biocompatible plastic and fluoropolymers These plastics are used in the manufacture of medical devices. These plastics include polyvinylchloride (PVC), polytetraflouroethylene (PTFE), polyeathersulfone (PES), and polysulfone amongst others. On the other hand fluoropolymers are also used in medical applications such as in single lumen tubing, heat shrink tubing and in special profiles. Many of these two have a wide range of applications and have good compatibility profiles. Their use is increasing because of their cost effectiveness. Steel and metal biocompatibility Stainless steel is used in trauma surgery s its very good material. The implants are of good mechanical strength (ductility, elasticity and stiffness).however their resistance to corrosion is lower and biocompatibility is not optimal and steel poses a potential for allergic reactions and its therefore used for temporary implants as compared to metal biomaterials such as those made of cobalt chrome as they are corrosion resistant and are also fatigue resistant. And no allergic reactions as compared to stainless steel biomaterials. Metal biomaterials are very compatible with the body. Advantages of composite biomaterials These are strong materials and are light in weight hence comfortable to the patient especially for joint replacements They have low density and hence are resistant to corrosion Disadvantage High cost of production And they shape is not easily changeable Advantages of metals and stainless steel biocompatible Resistant to corrosion Highly compatible Disadvantages of steel biocompatible over metals Steel biocompatible easily cause allergy and are therefore used for a short term implants compared to metal implants. Steel biocompatible are more corrosive compared to metal implants. Chemical properties Hydrophilic properties of the bone or tooth allow the biomaterial (sponge like) to expand to several folds of its dry volume when reconstituted (Ratner 2004). The ph of the fluid in the bone or the teeth is also of concern in biomaterial determination. Most biomaterials used are of stainless steel origin because they are resistant to a wide range of corrosive fluids in the body since they have high Cr content which makes the stainless steel materials to be strongly adherent and hence resistant to coating oxide of Cr2O3 (Misch 2011). Conclusion Biomaterials can be made from different materials such as metal plates, ceramics, amorphous carbons, biodegradables among many other materials (Misch 2011). Biomaterials for orthopedics applications are now derived from materials of industrial applications that are able to interact efficiently with the biological environment it is placed in and therefore elicit the required response. The properties of the tissues to be replaced such s the teeth and bone have to match those of the biomaterials for it to be suitable to replace such a tissue without side effects and for durability and for patients’ safety and comfort (Ratner 2004). It is of paramount importance also to determine the biocompatibility of the biomaterial with the tissues surrounding the tissue to be replaced if the biomaterial engineering works is going to be successful. However, more sophisticated biomaterials are yet to be developed for them to match the complexity of the biological systems. For the graph labeling the young’s modulus should be on the y-axis and the bone and teeth properties should be on the x axis. References B D Ratner et al. 2004. Biomaterials science. An introduction to materials in medicine. 2nd edition. Amsterdam Carl Misch. 2005. Dental implant prosthetics. St Louis. Lisa A Pruitt. 2011. Mechanics of biomaterials; fundamental principles for implant design. Cambridge university press. Paul Ducheyne; Kelvin E Healy’ et al. 2009. Comprehensive biomaterial. Biomaterials and clinical use. Volume 6. Amsterdam Roger narayan, Amit Bandyopadhay; Susmita Bose; American ceramic society. 2011. 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