1. Prepared by Dr Diane Aston, IOM3

2. MODULE TWO
Materials around us
Prepared by Dr Diane Aston, IOM3

3. Materials around us
The aim of this module is to introduce you to three areas in which discoveries and developments in materials have helped to improve our technology in three key areas:
Turbofan engines for civil aircraft
Biomedical materials
Sports equipment
Prepared by Dr Diane Aston, IOM3

4. Session 2 Materials in medicine
Prepared by Dr Diane Aston, IOM3

5. Aims and objectives
The session aims to introduce the field of biomaterials and demonstrate how materials experts and clinicians are working together to repair and replace parts of the body
At the end of this session you should be able to:
Identify the key requirements of a material for it to be biocompatible;
List a range of materials that can be used to replace body parts and give examples of where they are used.
Describe the key properties of a full hip replacement, vascular graft and intraocular lens;
Suggest ways in which biomaterials may help to improve our quality of life in the future.
Prepared by Dr Diane Aston, IOM3

6. Why do we need biomaterials
Biomaterials is a field which is continuing to expand. Scientists, engineers, surgeons and clinicians work together to develop ways of repairing and replacing broken or worn out body parts.
As people live to older ages and want to retain the same quality of life worn bits need replacing.
We sometimes need to repair damaged or broken body parts following disease or accident.
Prepared by Dr Diane Aston, IOM3

7. What are biomaterials?
Biomaterials are a small and special group of metals, polymers, ceramics and composites that are safe to use alongside and inside the human body.
Biomaterials must fulfil a range of criteria:
Similar mechanical properties to the tissue it is replacing in terms of strength, stiffness and fatigue resistance.
Similar values of electrical and thermal conductivity to the tissue it is replacing.
Not allow unwanted diffusion between the implant and surrounding tissue.
Not absorb water from the surrounding tissue.
Stable within the environment of the human body so it does not react chemically with surrounding tissues or fluids.
Compatible with the surrounding tissue, that is it should not be toxic or rejected by human tissues.
The most important consideration when designing any implant is the choice of material. Out of the hundreds of thousands of wonderful materials in everyday use a surprisingly small number are suitable for implantation. The materials used must fulfil a range of criteria:
Mechanical. The material must have the right mechanical properties. Ideally these should be about the same as the tissue that the implant is replacing, and the implant should be able to cope with the large number of cycles (i.e. loading and unloading) required. In the case of a hip replacement this is a huge number as one cycle is effectively one step. In the case of joints or bone plates the implant must not carry more load than the surrounding tissue; if this is the case bone tissue can degrade and eventually be lost (this is a phenomenon known as weight shielding). This can be achieved by choosing a material with a similar stiffness to bone.
Thermal and electrical conductivity. These values must mimic those of the natural tissues the implant is being used around.
Diffusion. Unwanted diffusion must not take place between the implant material and natural tissues.
Water absorption. The implant must not absorb water from the surrounding tissues as this can lead to an imbalance in the natural systems.
Biostability. The material must be stable within the environment of the human body; that is, it should not corrode, dissolve or react chemically in any other way.
Biocompatibility. The material must not be toxic and must not be rejected by the human tissues. Biocompatibility is essentially a surface phenomenon, where there is interaction between the implant and surrounding tissue. Generally a layer of water, proteins and ions will be adsorbed on to the surface of the implant between the bulk material and tissue.
Prepared by Dr Diane Aston, IOM3

8. Which materials can we use? METALS
Uses
Gold
Dental devices (fillings, on-lays, crown bases)
Surgical steel (steel containing, 12-20%Cr, 8- 12%Ni and 0.2-3%Mo
Surgical tools, orthopaedic devices (including joint replacements, bone plates and fixation screws), stents, surgical sutures and staples
Titanium and Ti-6Al-4V alloy
Orthopaedic and dental devices, surgical staples
Cobalt chromium alloy (Co / % Cr / 5-7%Mo
Orthopaedic devices (particularly useful in patients with nickel sensitivity)
Nitinol
Stents, bone plates and dental devices
Prepared by Dr Diane Aston, IOM3

9. Which materials can we use? POLYMERS
Uses
Silicone
Catheters, tubing, reconstruction implants
Dacron
Vascular grafts (artificial arteries), sutures
PMMA
Intraocular lenses and bone cement
Polyurethane
Catheters, pacemaker leads
Nylon
Total joint replacement bearing surfaces (artificial cartilage), sutures
UHMWPE
Total joint replacement bearing surfaces (artificial cartilage),
Hydrogels
Drug delivery, ophthalmic devices
Cyanoacrylate adhesives
Liquid sutures used to glue edges of a wound together
Silk
Absorbable sutures
Dacron – this is the trade name for polyethylene teraphthalate or PET which is a type of polyester.
PMMA – Polymethyl methacrylate commonly known as acrylic or Perspex.
UHMWPE – Ultra high molecular weight polyethylene. This is another variant of LDPE or HDPE used in milk bottles but UHMWPE has much longer polymer molecules. It is much tougher and more wear resistant than HDPE.
Cyanoacrylate adhesives are basically superglue.
Prepared by Dr Diane Aston, IOM3

10. Which materials can we use? CERAMICS
Uses
Alumina
Orthopaedic and dental devices
Porcelain
Dental devices
Hydroxyapatite
Coatings for orthopaedic devices
Prepared by Dr Diane Aston, IOM3

11. Materials in hip replacements
Artificial hips have changed since their introduction.
Surgical steel and nylon have been replaced by UHMWPE and other alloys, including titanium.
Ceramic coatings can be used instead of bone cement.
Full hip replacements now have a predicted design life of over 20 years.
We have been consistently, successfully performing full hip replacement surgery since around 1969 and since then the designs and materials have evolved to accommodate new technology and improvements in our understanding.
In the early days the joints consisted of two parts: a white plastic socket made from nylon which was screwed in place in the patient’s pelvis using screws made from surgical steel, and a metallic part, also made from surgical steel which was made up of a shiny, highly polished ball which sat in the socket and allowed movement and a long thin part called the stem which held the implant in place in the patient’s femur.
The procedure to implant a full hip replacement is quite brutal and should you wish to view how it is done this is a pretty good video but be warned it is VERY GRAPHIC!! Here is a brief description...
Once the surgeon has cut through the skin, fat and muscle to expose the bone they dislocate the hip joint so that both the femoral head (top of your thigh bone) and acetabulum (socket in your pelvis) are accessible. The first job is to clean up the surface of the acetabulum. One of the main reasons for a full hip replacement is degenerative bone disease such as osteoarthritis or osteoporosis where the bone starts to crumble. This damaged tissue is removed to leave a good, sound, solid surface on to which the implant can be attached. The surgeon then implants the socket part of the replacement. In some modern full hip replacements the metallic ball is already in the plastic socket (which is now made from UHMWPE ) and this assembly is glued in place in the pelvis using biocompatible bone cement made from PMMA. Once this is firmly attached the surgeon can work on implanting the stem which could be made from surgical steel, cobalt-chromium or titanium. To do this the femoral head is removed, a hole drilled down into the femur and then the stem is hammered into place. The surgeon forces the top of the stem into to the hole in the socket and these stick with an interference fit. It is important to get the patient up and moving as soon as possible after the surgery to get the joint moving and exercise the bone to aid the healing process.
Modern stems are coated in hydroxyapatite (a naturally occurring calcium phosphate mineral from which the hard part of our bones is made) which encourages new bone tissue to grow on to the implant to grip and hold it in place for longer.
Prepared by Dr Diane Aston, IOM3

12. Materials for vascular grafts
Vascaular grafts can be sewn in or inserted into a blood vessel to provide reinforcement or repair.
Made from woven or knitted polyester fabric.
Can be up to 2cm in diameter and 20cm long
It is possible to replace blocked or damaged blood vessels using vascular grafts.
These are essentially tubes which mimic natural blood vessels.
Artificial arteries are typically made from polyester (often referred to by the trade name DACRON) which has been knitted in a specific way so that it is slightly stretchy along its length but not stretchy at all around its circumference. This allows blood to pulse and flow along the tube rather than sitting in one place and pooling.
In some instances the damaged piece of blood vessel is cut out and the replacement sewn in and sometimes the artificial vessel is placed on the inside of the natural one.
Vascular grafts can be reinforced with other materials such as PTFE to improve their structural integrity.
Prepared by Dr Diane Aston, IOM3

13. Materials for lenses
Used to replace the lens at the front of the eye of cataract patients.
The procedure is carried out as an outpatients and takes around an hour.
The new lens is inserted into eye through a small incision after the natural lens and cataract tissue have been removed.
Replacement intraocular lenses are made from PMMA.
Cataracts are a clouding of the lens in the front of your eye. Cataracts are generally related to ageing but conditions such as high blood pressure and diabetes can affect their development.
Surgery to correct cataracts has come on along way over the last years and corrective surgery is now performed as an outpatient.
The surgeon numbs the area with a local anaesthetic, makes a tiny incision in the front of the eye and uses ultrasound to break up the natural lens and cataract tissue. This is then removed from the eye and a new man-made lens inserted into the capsule in which the lens sits The incisions are filled with saline solution to clean and close them.
After the procedure the eye must remain covered for about 24 hours to reduce the risk of infection and once the patch is removed the patient can see!
Vision can be restored to 20/40 or better.
The lenses are made from PMMA (or acrylic) which is a relatively cheap material. The implant consists of the central lens which is 5-6mm in diameter off which there are two spring arms. The lens is held in place in the ocular cavity purely by the mechanical force of these arms trying to open; it is not stitched or glued.
Prepared by Dr Diane Aston, IOM3

14. Biomaterials in the future
Prosthetic limbs
Tissue engineering
Carbon fibre composites, lightweight alloys and polymer foams are used to create prostheses that look and behave like the limbs they are replacing.
Modern prosthetic limbs incorporate electronics and are designed with increased functionality.
Eventually artificial limbs may use the impulses from severed nerve endings to function.
Use of man-made materials as a scaffold on which to grown natural tissues.
Man-made scaffold, such as PLA, PCL PGA, dissolves over time.
Possible to grow simply structure such as skin, vascular grafts and bladders.
More complex organs may be possible in the future.
Prepared by Dr Diane Aston, IOM3

15. Session 2 Summary
There is no doubt that as we continue to strive to live longer, healthier lives materials will play in increasingly important role.
We will continue to improve the technology, techniques and materials used for existing body part surgery.
We will continue to develop increasingly functional prosthetic limbs.
We will use tissue engineering to be able to grow new body parts from natural tissues.
Materials Scientists will working hand in hand with specialists from other disciplines to develop these life changing solutions.
Prepared by Dr Diane Aston, IOM3

16. Activity time! Investigating implants!
Discussion on biomaterials and where they might go.
Prepared by Dr Diane Aston, IOM3

17. Prepared by Dr Diane Aston, IOM3

18. Session 2 activities Investigating implants
Discussion on biomaterials and where they might go.
Prepared by Dr Diane Aston, IOM3

19. Investigating implants
Ask the students to use the internet to investigate a particular area in which biomaterials are used. They should then write a short article (around 1000 words) on their chosen topic at a level suitable for the general public to read. Topics could include:
Knee replacements
The use of silicone in facial reconstruction
Carbon fibre tendons
Shape memory alloys for artificial muscles
Stents for heart surgery
Materials in dentistry
Materials for drug delivery
The articles should be included in the students’ portfolios and the top 6 articles will be published in the IOM3 Schools Affiliate Scheme newsletter.
Prepared by Dr Diane Aston, IOM3

20. Biomaterials debate
The idea of this activity is to get the students thinking and discussing the pros and cons, advantages and disadvantages of using materials to improve quality of life and potentially prolong life
Split the group in to two teams and get them to do some research on your chosen topic. This could be any of the areas outlined in this session or mentioned for activity one.
Conduct a debate between the two groups and get them to come to a group consensus on their chosen issue.
Each individual should write up their research, their own argument and a summary of the debate for their portfolio.
Prepared by Dr Diane Aston, IOM3

21. Session 2 useful links
There are many excellent website around that describe various types of surgery in great detail for patients. These include:
For details of how the surgery is performed: replacement/Pages/Introduction.aspx
For the anatomy of the hip joint: pain/hip-anatomy.php
For full details of hip replacement surgery
For details on vascular grafts: home.htm?tutorials/graft.htm~right, and
For details of intraocular lenses: and
For details on prosthetic limbs: and
For details on tissue engineering: and
Prepared by Dr Diane Aston, IOM3