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9.3 Medical technology — Bionics 1. Options for maintaining humans

Syllabus reference (October 2002 version)
1. Increases in scientific understanding and technological advances have broadened options for maintaining humans as functioning organisms	Students learn to: identify parts of the body and the biomaterials and biomedical devices that can be used to replace damaged or diseased body parts including: pins, screws and plates artificial joints pacemakers artificial valves crowns, dentures lenses prosthetic limbs cochlear implants	Students: gather and process information from secondary sources to trace the historical development of one of the following implants: cochlear implants artificial valves

Extract from Senior Science Stage 6 Syllabus (Amended October 2002). © Board of Studies, NSW.

[Edit: 10 Sept 08]

Prior learning: Preliminary modules 8.4 (subsections 1, 2, 3, 4, 5 and 6)

Science Stages 4-5 syllabus: Outcomes 4.8 (content 4.8.1 a, b, c, d; 4.8.4 b, c, d and 4.8.5 a, b), Outcome 5.8 (content 5.8.1 a), Outcome 5.12 (content 5.12 d, f, g)

Background: Scientific understanding about the workings of the human body, along with technological advances in the development of materials to replace body parts, has led to the development of specialised structures designed to take the place of real-life joints, organs and limbs.

identify parts of the body and the biomaterials and biomedical devices that can be used to replace damaged or diseased body parts including:

• pins, screws and plates
• artificial joints
• pacemakers
• artificial valves
• crowns, dentures
• lenses
• prosthetic limbs
• cochlear implants

Pins, screws and plates

• These are used to repair bone fractures. They are almost all made from metallic alloys.
  
  
• The pin is a versatile implant used for the fixation of bone fragments and is used when the fracture is in a place where it is difficult to use a plate.
  
  
• Pins are also used when it is difficult to obtain adequate stability of the bone fracture by any other means.
  
  
• Screws are some of the most widely used devices for repairing fractures. They are used to fix bone plates to bones.
  
  
• Bone plates are also used to repair bone fractures. They are designed to be very strong and absorb the large stress forces generated when the bone moves.
  
  
• It is also important that the bone plate be fixed to the bone with the use of screws.

Artificial joints

• These replace joints that have been largely destroyed by degenerative diseases such as arthritis or damaged badly in an accident.
  
  
• Common examples are knee, hip and shoulder joints; the latter two are ball and socket type joints [more information on ball and socket joints is provided in 9.3 Medical Technology - Bionics, subsection 3].
  
  
• Artificial hip joints are often made from a stainless steel-polyethylene or cobalt-chromium alloy-polyethylene combination. Other materials that can be used are:
  • titanium
  • titanium-aluminium-vanadium alloy
  • ultra high molecular weight polyethylene
  • metal-pyrolytic carbon coating
  • metal-bioglass coating
  • composites made from poly-methyl methacrylate (PMMA) and carbon fibre
  • porous stainless steel.
    
    
• Artificial knee joints are known to sink into the lower bone of the leg, causing crushing of the trabecular bone. To combat this problem, knee joints are now made from a layer of ultra-high molecular weight polyethylene (UHMW polyethylene) on a metal base.
  
  
• Other joint replacements, such as fingers and ankles, have not been as successful, because of the complexity of movement of these joints.

Pacemakers

• Pacemakers are used to correct arrhythmias, that is, when the heart beats too fast, too slowly or irregularly. A pacemaker is a battery-operated device designed to stimulate contraction of the heart at a certain rate. Some are internal (surgically implanted) and others are external. Pacemakers are connected to a small electrode, which is placed near the wall of the heart. Small electrical charges travel through a wire to the electrode, stimulating the heart to contract.
  
  
• The casing of a pacemaker can be made of stainless steel or titanium. The electrodes are made from platinum or platinum-iridium alloy. Silicon rubber, polypropylene or epoxy can be used to seal parts of the pacemaker.

Artificial valves

• Artificial valves can be used to replace damaged valves in the body that are no longer functioning to keep blood flowing in one direction only.
  
  
• Early artificial valves in the 1960s were made from flexible leaflets, but could not withstand the fatigue for periods longer than about three years.
  
  
• Most artificial valves have a fabric ring surrounding them, which allows a surgeon to sew the device into place during implantation.
  
  
• Where appropriate, artificial valves are constructed from collagen-rich materials, such as pericardial tissues which have been obtained from pigs or cows and treated (to denature any animal proteins), to minimise the risk of rejection by the human body. Other materials used are cobalt-chromium alloys, low-temperature carbon and titanium alloy with pyrolytic carbon discs or balls.

Crowns and dentures

• A crown is a tooth cap that is placed over an artificial or natural root system.
  
  
• Crowns have traditionally been constructed from ceramic materials, which have relatively low strength. The development of metal-ceramic crowns has led to an increase in strength.
  
  Dental crowns / dental "caps" Web Medical and Dental Science (WMDS, Inc. USA)
  
  
• Dentures (false teeth) are generally made from acrylic for ease of fabrication.
  
  
• Dentures present problems because:
  • they are not particularly stable
  • they do not always look natural
  • they allow the jawbone to absorb substances.

Lenses

Artificial lenses restore function in the eye where a cataract has caused the previous lens to go cloudy.

• Artificial lens are commonly made from PMMA, silicone rubber, copolymer blends; nylon; Dacron; or polypropylene. Tiny platinum, titanium or gold loops are sometimes used to hold lenses in place.

• There are two types of implants available: nonfoldable and foldable.
  Nonfoldable lenses are made of PMMA, a hard plastic material. Foldable lenses are made of either silicone or acrylic.

New advances in cataract surgery - Philip J Penrose MD , Momterey County Eye Associates, californian prepress.com, USA

Prosthetic limbs

• These are artificial limbs that are commonly used to replace entire limbs, or part limbs on amputees.
  
  This website has an activity for students to do. You may not want to do the activity but it has some good information. Prosthetic Limbs Newtons Apple, USA
  
  
• Materials that are sometimes used include silicone or silicone matrix (for liners), and titanium, aluminium, stainless steel or carbon fibre composites.
  
  
• Modern prosthetic limbs often incorporate electronics and pneumatic mechanisms of considerable complexity.
  
  
• Some current technologies to replace missing limbs are described here .Wikipedia, USA

Cochlear implants

• A cochlear implant is an artificial hearing device that can replace a damaged cochlea. It is designed to stimulate nerves inside the inner ear, thus produce a hearing sensation. The cochlear implant works by converting sound into electrical impulses, which can be used to stimulate the auditory nerves, sending a signal to the brain, which creates a hearing sensation.
  
  
• Cochlear implants generally consist of two main components:
  • a headset with a 22-channel stimulator in a titanium capsule, with platinum electrodes which are implanted inside the skull behind the ear close to nerves.
  • a pocket speech processor, which breaks down speech into its various components before transmitting it back to the stimulator.

gather and process information from secondary sources to trace the historical development of one of the following implants:

• cochlear implants
• artificial valves

• Look in encyclopaedias, CD-ROMS and on the Internet to gather information on the historical development of biomaterials and implants.
  
  Some useful websites for cochlear implants National Institute on Deafness and other Communication Disorders, Maryland, USA, or to learn about the Australian connection to cochlear implants read about Professor Graeme Clark and the work his team did in the 1970s, Cochlear , Australia
  
  Also see The History of Cochlear Implants Brown University, Rhode Island, USA
  
  A comprehensive site for this whole module, including cochlear implants and artificial valves is:
  SENIOR SCIENCE MODULE 9.3 Medical Technology- Bionics , Port Macquarie Science Network, NSW Department of Education and Training

• An efficient way to process the information to produce a timeline would be to construct a data base for computer-assisted analysis. This would allow you to sort on time to illustrate trends and patterns.