Materials

Materials used as replacement parts in the skeletal system include: Silicone Ultra High Weight Polyethylene (UHMWPE) Super Alloy Cement – to hold replacement parts in place.

9.3.3 d Identify the properties of silicone that make it suitable for use in bionics.Identify Vocabulary: Silicone – is a largely inert, man-made compound with a wide variety of forms and uses. Typically heat-resistant, nonstick, and rubber-like, it is commonly used in cookware, medical applications, sealants, adhesives, lubricants, insulation, and breast implants.

PropertyWhy it is useful as a biomaterial High ElongationIt can stretch without breaking High ElasticityWill not deform if stretched Similar chemical structure to collagen It is highly biocompatible Similar density to natural tissue It is highly biocompatible High permeability to oxygenpermeability Does not obstruct the distribution of oxygen around the body Low reactivity/toxicityWill not react with bodily fluids

9.3.3 e Explain why silicone joints would be suitable substitutes for small joints in the fingers and toes that bear little force.Explain

Silicone joints would be suitable substitutes for small joints in the fingers and toes because they can be made as strong and as flexible as natural joints. They are biocompatible, as they allow the flow of oxygen and do not react with living tissue. They would last a long time, as they do not dissolve in water.

9.3.3 f Describe the properties that make ultra-high molecular weight polyethylene (UHMWPE) a suitable alternative to cartilage surrounding a ball and socket joint in terms of its:Describe Biocompatibility with surrounding tissue Low friction Durability Vocabulary: Low Friction – is slippery or smooth. Durability – Lasts along time and is resistant to wear.

Ultra-high molecular weight polyethylene (UHMWPE) is biocompatible with surrounding tissue. It possesses a similar density to living tissue, and therefore tends not to cause problems in the body.

UHMWPE has a low friction coefficient and this, along with other exhibited characteristics, such as high hardness, high tensile strength, high elasticity, add to its suitability of it for use in joints as artificial cartilage. Vocabulary: Tensile Strength – A measurement of the strength required to pull something until it breaks.

UHMWPE is very durable. It has no known effective solvent at mild temperatures. High temperatures and pressures must be used to manipulate the material and gain the desired product. UHMWPE also exhibits a very high creep resistance. Creep resistance is the tendency for polymers to deform when under constant stress.

9.3.3 g Explain why artificial joints have the articulating ends covered in polyethyleneExplain Vocabulary: Articulating Ends – “Jointed Ends” These are the ends of bones that end in synovial joints

The articulating ends of a natural joint are covered by a cartilage which cushions the bones in the joint and provides ease of movement when lubricated with synovial fluid. When constructing artificial joints, it is important to replicate the natural structure of the joint.

Polyethylene is used to coat the articulating ends of artificial joints because: it has a similar density to living tissue it is relatively elastic (especially high-density polyethylene) it has a low coefficient of friction it has low creep properties i.e. it will not deform under stress.

9.3.3 h Describe the properties of the materials, including ‘superalloy’ that make a ball and stem for the bone components of a large joint including:Describe high strength low weight good compatibility with body tissue inertness

A superalloy is an alloy that exhibits excellent mechanical strength and creep resistance at high temperatures, good surface stability, and corrosion and oxidation resistance.

Many alloys are very strong. Co-Ni-Cr-Mo alloy is used for making stems of prostheses for heavily loaded joints like the knee. Super alloys needs to be very strong due to the stress placed on the alloy in load bearing joints such as the knee and hip joints

Many metals are not suitable for implantation because they are heavy, and may lead to damage of surrounding living tissue. Titanium-based alloys are very lightweight (lighter than stainless steel and Co-alloys), as are the polymer components of the artificial joint.

Carbon-based alloys show a high level of biocompatibility. For this reason, carbon or carbon-based alloys are integrated into the development of new materials.

Corrosion is a major concern, as it may lead to the breakage of load-bearing joints like the artificial hip joint. Metal alloys generally have much lower corrosion factors than stainless steel. Co-Cr alloys are inert in the body, remaining literally unchanged under physiological conditions.

9.3.3 I Identify that artificial implants can be either cemented or uncemented into place.Identify j Describe the properties of the cement that is used in implants and discuss how an uncemented implant forms a bond with a bone.Describe Vocabulary: Cement – Cement is used as a biomaterial to fix artificial joints into place.

1.Use the Venn Diagram supplied to organise the information gathered from the PowerPoint presentation. 2.Using the completed Venn Diagram to justify your response, compare the strengths of UHMWPE and Super Alloy (write 1/3 to ½ page).

Bone cement for the fixation of artificial hip joints was introduced in the 1950s. Once the diseased bone is removed, the medullar canal is filled with a doughy bone cement, and the implant is inserted. Alignment of the implant with the other components of the joint is verified before the bone cement sets. The cement used in a cemented implant serves many purposes: It allows the initial fixation of the implant to the bone. It acts as a shock absorber for the joint. It helps to spread the load more evenly over a large area and reduces the stress concentrated on the bone by the prosthesis.

Cement-free implants are coated with a porous layer, which comes into contact with the bone. This places less pressure on the bone. The porous layer of cement-free implants allows the bone to grow into the implant, creating a dynamic interface of bone and implant. Cement-free implants are more vulnerable to loosening than cemented implants, and it is expected that the time required before the patient can walk will be longer than for cemented implants.

Cemented Cement-Free

9.3.3 p Analyse secondary information to compare the strength of UHMWPE and “superalloy” metal.Analyse Analyse: Make and justify generalisations.