What is Biocompatibility?
Biocompatibility can be defined as the ability of a material to adapt itself, interact and function in coherence within living cells and tissues. When a material is biocompatible, it will not interfere with the normal functioning of any organ.
If a foreign particle is placed or inserted within living cells, the body might provoke an immune response to fight against the foreign particle. When a severe response is initiated from the body, such a foreign particle is non-biocompatible as it is not suitable for functioning within living cells.
What are Biomaterials?
Biomaterials can be defined as substances which are safe and suitable to be placed and function within living cells and tissues. Commonly used biomaterials are metals, ceramics etc. Biomaterials are widely used in bone and dental implants, cochlear implants, contact lenses, suture materials, prosthetic heart valves, drug delivery systems etc.
One of the main requirements of a biomaterial is its non-toxic nature. Any chemical composition of a biomaterial should not cause harm to the cells or tissues at any point of time. In certain specific cases, a biomaterial is expected to degrade on its own and disappear completely when its designated function is over and its support is no longer needed. Any specific biomaterial which is biocompatible for a specific organ/function may not be suitable for another organ/function.
History of Biomaterials
Surprisingly, the history of usage of biomaterials dates back to the third century and beyond. Though the term ‘Biomaterial’ was introduced very recently, a number of archaeological findings of human remains with metal implants signify its wide range of applications in prehistoric times.
Earliest applications of biomaterials are dental implants and sutures. Gold was widely used as a dental implant which also served the purpose of fashion and beauty. Later metal sutures were used to close open wounds which were well tolerated by the human body. At some instances, when any metal weapon accidentally penetrated inside the body, it remained as such, without initiating any adverse immune reaction.
Such findings from archaeological remains shed light upon the usage of biomaterials during the prehistoric era. These discoveries also pushed the scientists forward towards the finding of new materials that are highly biocompatible.
Types of Biomaterials
Biomaterials can be classified based on origin as Natural biomaterials and Synthetic biomaterials. Natural biomaterials are those obtained from living things such as plants, animals and sometimes even from humans. Synthetic biomaterials are those obtained from polymers, ceramics etc. Most commonly used biomaterials are metals such as Titanium and stainless steel.
Applications of biomaterials
Intraocular lens is used as a replacement for natural lens surgically removed as a treatment for cataract. This procedure was introduced only in 1950 when a type of plastic material called PMMA (polymethylmethacrylate) was used to manufacture artificial lenses. As this material is highly biocompatible, it was successfully designed and implanted as an Intraocular lens. Future developments in the design of Intraocular lens include the usage of Silicone which is highly flexible.
Usage of biomaterials in dentistry is common since ancient times as metals were commonly used for beauty and alignment. Recent advancements in dentistry propose biomaterials such as polymers (PMMA), ceramics, titanium alloys, composites etc as ideal substances that could withstand and exhibit biocompatibility within the oral atmosphere. Future advancements in this area might witness the advent of nanoparticles.
Heart valves and stent
One of the important applications of biomaterials is artificial heart valves. Malfunctioning natural heart valves lead to heart failure and hence prosthetic heart valves are used to enable normal functioning of the heart. Two types of mechanical heart valves are commonly used – tilting disc and bileaflet valves.
Tilting disc valves are made up of pyrolytic carbon placed inside a metal ring in the form of a swing. It allows the flow of blood by functioning like a swing. Bileaflet valves are designed with two semi-circular flat plates positioned inside struts. Both these mechanical heart valves carry the risk of blood clot formation and hence anticoagulants are prescribed for patients with artificial heart valves. However, the biomaterials used in the design of heart valves are highly durable and function ideally for years.
Other important applications of biomaterials include sutures and surgical mesh, skin grafts, cochlear implants, hip joints and knee replacements.
Future trends of Biomaterials
Small diameter vascular grafts
Small diameter vascular grafts are designed to bypass amputations and they also form a reliable alternative for current therapeutic procedures in cardiology. For a variety of reasons, these small diameter vascular grafts are not yet widely accepted and they are still on their way towards wide commercial use. Scientists believe that these tiny products may replace a variety of painful procedures in the near future.
Microneedle arrays in drug delivery
The application of microneedles in drug delivery is a recently evolved technique which replaces conventional drug delivery methods such as a syringe. This model consists of a patch with microneedles that could inject drugs into the body through skin.
Very recent innovation in the field of microneedle drug delivery is the application of a polymer called Fibroin. The polymer is designed as a microneedle which contains drugs within. The polymer itself is non-toxic and dissolvable inside the body. Fibroin is a silk based protein employed in microneedle arrays.
In certain cases of brain tumours, chemotherapy wafers containing drugs are placed (implanted) which delivers drugs. This type of wafers are made from biodegradable biomaterials which dissolve by itself after delivering the drugs.
Most commonly used chemotherapy wafer is Gliadel wafer which contains the drug carmustine. Chemotherapy drugs are formulated to affect cell division and hence they inhibit the multiplication and spread of cancer cells. Some types of chemotherapy drugs act upon cells when they divide while others can affect cells when they are at rest.
Carmustine is a cell cycle nonspecific drug that could kill tumour cells while at rest. Chemotherapy wafers placed inside the site of brain tumour (after removal of tumour) dissolve by themselves after releasing the drug at the site. The drug proceeds further to kill any tumour cells remaining at the site by any chance.
There are a few other areas where applications of biomaterials have a promising future. Smart hydrogel biomaterials, bio-sensors in Brain Computer interface, 3D biomaterials and tissue engineering.