Question 2: Ceramics: Please name three ceramics commonly used as biomaterials; for each briefly describe their main use in the human body

The yttrium stabilized zirconia known as Y-TZP fabricates the femoral heads as well as the acetabular cup in the replacement of the total hip joint. It is also commonly used in dentistry, for instance in crowns, to be formed in the office with CAD / CAM method. When a metal post or dyschromic tooth is to be covered, the zirconia is used as its core conceals and hides the discoloration. Some manufacturers also provide zirconia-colored cores to improve the aesthetic results. Zirconia cores for fixed partial dentures (FPD) are now available on posterior and anterior teeth.

It is more advantages than alumina as it has fine grain size and microstructure that is well controlled and lacks Y-TZP residual porosity. It is used as a prosthetic restorative material. Due to the phase transformation toughening process, it is tougher, rigid and has more fracture toughness than alumina. Radiopacity can help the evaluation through radiographic controls. Zirconia has less friction in contact with articular cartilage. It is known as a Bioinert ceramic as it does not react with the body’s environment. It is less wear resistance than alumina.

Calcium phosphate

It is mainly used for the restoration of damaged bones and periodontics because of its chemical similarity to human teeth and bones. It is also in implants and manufacturing artificial bones. Its application includes the synthetic replacements for hips, teeth, ligaments, and tendons. It is also used for maxillofacial reconstruction. Calcium phosphate is also used as bone fillers. The most important form is Calcium phosphate is Hydroxyapatite(crystallized form) as it is naturally found in hard tissue such as bones and teeth.

Aluminum oxide Al2O3 -Alumina

Alumina has high strength and is wear resistance. It has outstanding corrosion resistance less friction coefficient which makes it a helpful in orthopedic applications. It is also used for dental implants. Alumina is used for the femoral stems coating and for knee prosthesis in crystalline form. Alumina is effective for Total Hip Replacements and hip arthroplasty. It is also important for the creation of electrical insulation in the pacemakers, cardiac pumps, and catheter orifices.  It is also used to treat some diseases and health conditions such as fatigue and Dementia.

Question 3: Polymers sterilization: a) Briefly describe three sterilization methods b) For each of these methods describe the problems encountered, giving an example of the polymers where it should NOT be applied to.

Dry heat sterilization

This method uses the dry heat that is free from the water where the bacteria are killed or oxidized. The temperature is set to 160̊ to 190̊ for about 1.5 to 3 hours for effective sterilization. The principle is to heat materials surface temperature to kill any identified microorganisms. It does not cause metal corrosion so it is suitable for sterilization of materials made of metals. It is also used for sterilizing lab glassware and in small clinics. It is ideal for moisture sensitive items. This method is not suitable for substances like plastics fabrics or rubber-ware.

Steam sterilization

In this method, material sterilization occurs in a device called autoclave.  High saturated steam is pressurized into a compartment with relatively low temperatures around 120 and 135 °C. It is used in dental, medical sterile processing and in laboratories and pharmaceuticals. This is not a suitable method for polymers like polyethylene and polyamides (nylons).  Hydrolysis can occur when exposed to water that can deform and degrade the biodegradable polymers. It is also not suited for materials due to the involvement of high temperatures.

Radiation sterilization

The materials are sterilized by using high energy electrons or gamma rays as they have high penetration power. It is suitable for almost all types of material. When the isotope cobalt-60, there is a potential for deterioration where the polymers with exposure to high radiation can break up and recombine their chains. This method leaves no chemical residue and also suitable for thermally stable and heat sensitive materials. It is used for the sterilization of biomedical devices. This sterilization requires highly specialized equipment. This method is not suitable for some polymers for example polyethylene as radiation causes the breakdown of polymer chains.

Question 4: Polymers degradation in the body: For three different types of polymers, once they are inserted in the human body, briefly describe the corresponding (most common) degradation scenarios

The process and rate of polymer biodegradation within the body are related to polymer characteristics and the place of exposure inside the body. Chemical degradation causes the deterioration of the major polymer chains by the random cleavage of covalent bonds. It also causes the crosslinking and depolymerization of linear polymers and the rate of degradation can be controlled by the structure of the polymer.  The three polymers are:

Polyethylene: A tissue reaction is most likely to occur by the by the deterioration of polymer. The hydrolysis reaction will take place if acid or basic water medium or any catalyst is present. It will be broken down when it is in contact with strong acids like HCl in the stomach. It is also degraded by the presence of free radicals inside the body. 

Polymethylmethacrylate: Its degradation depends on the pH and salinity of aqueous medium inside the body. The chains are chains degraded by radiolysis and high-temperature depolymerization but the side esters groups also undergo hydrolysis. If degradation of PMMA occurs, methanol is released into the body which is harmful.

Polyethylene terephthalate: The hydrolysis by water causes scission of an ester linkage in the main chain. If it kept in contact with more acidic or basic medium, degradation will be more. It causes molecular weight to decrease by scission.

Question 5: X-ray micro-computed tomography (micro-CT) imaging: does it allow non-destructive or destructive imaging, of the examined specimen? Discuss

X-ray micro-computed tomography (micro-CT) imaging provides the 3-dimensional and high- resolution imaging of the specimen which cannot be damaged. The specimen's radiographs are recorded at discrete intervals before it is finally reduced to tomograms using the software. The working principle of (micro-CT) imaging is similar to that of standard CT scanner. However, the (micro-CT) image scale is comparatively small and therefore provides higher resolution.  The main components are x-ray source and detector. The specimen image rotates at 180 or 360 degrees in the x-ray beam at different angles so that the images represent the specimen as sliced views on the rotation axis. These images are then combined with the computational process like different software to create 3D images to screen the internal structure of the specimen.

Question 6: Is the measure of bone mineral density (BMD) measured by Dual X-ray energy absorptiometry (DXA) sufficient for assessing fracture risk of an individual? Answer the question, including a justification for your answer.

It is also known as bone density scanning which uses small ionization doses to generate pictures of the inside of the body to estimate the loss of bone. This technique is mainly used for Osteoporosis diagnosis or the risk to develop osteoporosis. It is an easy and quick method to detect bone fractures by using X-ray technology. This machine has a special type of software for calculating and displaying bone density measurements on a monitor. It is less time consuming as the bone density test by DXA is completed in 10-13 minutes. At present, the DXA is the standardized method of diagnosing osteoporosis and is also considered a fine fracture risk estimate but the DXA does not provide information about the bone microarchitecture, trabecular and cortical bone which are an essential determinant of the strength of the bone. A new and most accurate method is the measurement of bone density by the high-resolution peripheral quantitative CT.

Question 7: Analysis and assessment of implants: What are the objectives of pre-clinical testing and post-operative testing? Discuss

Preclinical testing for the implant is an important and serious process to ensure that the implant is safe and biocompatible. The first objective is to ensure the functionality of the implant that deals with the efficiency of the new implant. The implant should function properly in the patient’s bio environment and preclinical biocompatibility tests are required as the new implants can cause genotoxicity or mutagenicity. This is mainly tested in vivo to avoid any harmful or inflammatory effects. The period of the projected patient contact will determine whether single or multiple termination intervals are necessary. A preclinical study reports must be made including the clinical data.

 There are diagnostic trials which plan to identify the improvements in methods used to diagnose diseases. The post-operative testing plays an important role in the process of innovating and improving the implant to avoid any harmful effects in the future.  During this time, the implant can be corrected and maintained based on its functioning level.

Question 8: Analysis and assessment of implants, pre-clinical testing: What are the advantages of using Finite Element analysis over experimental testing? Discuss

Finite element analysis is a type of computer modeling known to have several advantages. Virtual Testing is the main advantage of FEA. It is faster and has less classy design cycle. The variables used in the analysis can also be fully controlled and the simulation time is shorter than experimental. The concurrent calculation and visual representation of an extensive range of physical parameters like stress and temperature, allowing the designer to quickly analyze the performance and potential. It provides designers the opportunity to quickly relate the effects of implant geometry and or material, for example, acetabular cup interface. In addition, complex bone geometries can be accurately shown with the CT scan combination and the FE model can be created automatically using CT image voxels. Another benefit of FE analysis is the use of several implants such as hip components, knee arthroplasty, structured implant interfaces and more. The tissue reactions can be predicted when used with bone remodeling algorithm. It also calculates the structures of dynamic properties.