What are some examples of polymers used in biomaterials?

Biomaterials are being used since ancient times for healthcare applications because of their high versatility and usefulness, making it possible to treat many complex diseases and conditions like cardiac failure, fractures, deep skin injuries, etc.

Biomaterials are those natural and synthetic materials that can be introduced into living tissue in the form of a medical device or implants. These materials are totally compatible with the body and do not produce any adverse reaction while coming in direct contact with the living tissue.

If any hard or soft tissue of our body has been damaged or destroyed by accident, pathology, etc then it can be replaced physically using biomaterials. There are various applications of biomaterials in the healthcare sector like medical devices, diagnostics, polymeric therapeutics, etc.

Biomaterials are revolutionizing the healthcare sector and are fabricated in such a way that they mimic the biological phenomena of the body.

Properties of Biomaterials

Biocompatibility: The most important property of biomaterials is “biocompatibility.” In short, it means the “acceptance of the body towards the implanted natural or synthetic material.” When a biomaterial is inserted into the body, it should not produce injury, reaction, or rejection and should not interfere with the normal functioning of the body. The main objective of the application of biomaterial is to generate a positive cellular response in the body.

Biocompatibility is dynamic. It varies for different applications. For example, a screw or plate fabricated for bone repair is compatible with the bone and incompatible with skin applications.

Host response: This means when the biomaterial is inserted into the body, how did the body respond to it? Some materials are inert while some are not. Here various factors like length of time, purpose, and site of implantation play an important role.
Non-toxicity and safety: The biomaterial must serve its purpose positively in the body’s environment.
Mechanical properties: Along with biocompatibility, the mechanical properties of the biomaterial are very important because the outcome is dependent on it. The biomaterial is subjected to stress, strain, and shear in the body. The hardness, corrosion resistance, tensile strength, creep, and yield strength are some of the important properties of the biomaterials which are studied and evaluated before placing them in the body. If a biomaterial is placed in the bone, it should have high mechanical strength.
Corrosion
Wear resistance
Fatigue
Easy to use
Minimal cost
Accessible
Sterilization

Types of Biomaterials

Inorganic materials including metals and ceramics.
Organic materials include polymers, natural and synthetic.

Metals are used in load-bearing areas like orthopedic and dental implants. These impart properties to biomaterials like strength, toughness, and rigidity. The stents used in cardiovascular surgeries are made up of metals. Some of the useful metals in the application of biomaterials are titanium, stainless steel, and alloys (cobalt, magnesium, etc).

Ceramics have excellent biocompatibility and important properties like high resistance to corrosion, high strength, stiffness, and hardness. They are commonly used in orthopedics and dentistry. Some examples are alumina and zirconia.

Polymers are macromolecules with low toxicity in biological fluids. Their physical and chemical properties are remarkable.

Natural Biomaterials

Knowledge about the properties of natural biomaterials is very important for their scope in applications of biomaterial. One of the biggest concerns with the use of natural biomaterials is “exploitation”. Their use should not endanger the various species of the ecosystem.

They are obtained from plants, animals, and microorganisms.
Biomaterials derived from animals are collagen (Type I, II, III, X), gelatin, ovomucin, fibrin, silk, fibrillin-1, tropoelastin, lactoferrin, sericin, elastin, adhesive protein, keratin, suckerin, hemocyanin, resilin, chitin, chitosan, chondroitin sulfate, hyaluronic acid, natural coral, calcium carbonate, B-tricalcium phosphate, hydroxyapatite, eggshell matrix, demineralized bone powder, etc.
Biomaterials derived from plants are starch, cellulose, natural rubber, polyurethane, etc.
Biomaterials derived from micro-organisms are alginate, cellulose, polylysine, dextran, polyphosphates, dextran, etc.
Natural bioceramics are obtained from shells, corals, bones, eggshells, etc.

Important Properties of Natural Biomaterials

Non-immunogenic. This means the biomaterial does not invoke the immune response.
Thermal stability
Structural stability
Antimicrobial
Antithrombotic (inhibit platelet aggregation)
Enhanced collagen expression
Bioadhesive
Angiogenic (formation of new blood vessels)
Porous
Induce cell proliferation
Good strength

Application of Natural Biomaterials in the Healthcare Industry

Application of Natural Biomaterials in Healthcare Industry

Fabrication and manufacturing of biomedical implants
Tissue grafts
Cardiovascular applications
Tissue engineering
Wound healing
Suture materials
Cosmetic applications

General Applications of Biomaterials

Pacemaker, valves, and the artificial heart
Lens for eyes (ocular and contact)
Artificial ears and cochlear implants
Nasal implants
Dialysis machines
Burn dressing, artificial skin, and substitutes
Screws, implants, plates, and pins to repair bone defects
Dental materials, dental implants, and dental prostheses
Pacemaker
Ankle implants
Graft materials
Hip implants
Breast prosthesis
Shoulder prosthesis
Maxillofacial prosthesis
Glucose biosensor

Medical Biomaterials

Application of biomaterials in musculoskeletal injuries: Repairing and regenerating musculoskeletal tissue is challenging in healthcare and it depends on the site and type of injury, healing, biomaterial type, etc.
Glucose monitoring via biosensors: A breakthrough in diabetes management. These sensors are placed under the skin and they constantly provide blood glucose readings. The sensors give warning signals in hypoglycemia and hyperglycemia.
Spider silk sutures are superior to synthetic sutures(Prolene polypropylene, Vicryl polyglactin, etc). besides this, spider silk is a great biomaterial that can be used for designing scaffolds. Spider silk has excellent mechanical properties and has a higher Youngs modulus and excellent fatigue behavior. It has a low index of crystallinity. There are studies that have shown that the nanoparticles of spider mite silk when entering the cytoplasm, are responsible for the growth of cells (in vitro). Silk derived from B. Mori has positive effects on cell behavior including cell attachment, proliferation, and differentiation.
Cellulose derived from plants has excellent biocompatibility, causes cell adhesion, and is pro-angiogenic.

Biomaterial Examples

Total hip replacement:

Arthroplasty is the creation of a new joint. The main aim is to improve the quality of a patient’s life and provide pain relief. The prosthesis has a femoral stem, femoral ball, metal acetabular shell, UHMWPE liner (Ultra High Molecular Weight Polyethylene), and a porous coating. The femoral-acetabular component types are Metal-on-polyethylene, Metal-on-metal, Ceramic-on-polyethylene, and Ceramic-on-ceramic.

Knee implants:

Knee act as a hinge joint as it bends and straightens. The geometry and the material are important in determining the knee prosthesis. The two types of knee joint replacement are total and unicondylar. There are 3 types of total knee replacements are:

Nonconstrained knee replacements
Semiconstrained knee replacements
Constrained knee replacements

The unicondylar knee replacement is also known as the half replacement and is indicated when half of the joint is damaged.

The biomaterials used are:

Titanium Alloys
Cobalt-Chromium Alloys
Ceramics
Cross-Linked Ultrahigh Molecular Weight Polyethylene.
Cardiac pacemaker:

Biocompatibility is the most important consideration in cardiac pacemakers. The biomaterial goals are anti-thrombogenic surface, blood-compatible materials, better construction and fixation, porosity, corrosion resistance, non-toxic and inert. The biomaterials used in pacemakers are alloplastic which means they are not biological in origin and include metals, ceramics, glasses, and polymers.

Application of Biomaterials in Breast Reconstruction

These are divided into two categories: Natural and synthetic biomaterials.
Natural biomaterials used in the regeneration of breast tissue are collagen, alginate, hyaluronic acid, chitosan, and decellularized extracellular matrix (DECM).
The synthetic biomaterials are poly e-caprolactone.
Alginate and chitosan provide a suitable microenvironment for adipocytes. DECM plays an important role in promoting cell adhesion, proliferation, and differentiation. These biomaterials play an important role in the formation of adipose tissue. Synthetic biomaterials play an important role in providing mechanical strength.
The fillers are also used in breast reconstruction like hydrophilic gel and hyaluronic acid.

Application of Biomaterials as Medical Patches

Some of the important applications of biomaterials are:

Collagen-based scaffolds are used in cardiac patches. Natural collagen shares similarities regarding structural, biochemical, and physical properties with the extracellular matrix of the heart.
Fibrin is a natural biomaterial and induces the formation of blood vessels. This is used in ischemic myocardium.
Chitosan is the most versatile biomaterial and has wide applications in tissue engineering and wound dressings. It is safe and has been used as a drug carrier. Chitosan-based medical patches are used in the regeneration of bone, cartilage, and skin.
Hyaluronic acid is a nonsulfated glycosaminoglycan and it has been approved by FDA for soft tissue defect filling.
Polyurethane (PU) is used in tissue scaffolds and it has potential in wound dressing and skin tissue engineering. Filler can be placed into PU scaffolds for peripheral nerve regeneration.
Polydimethylsiloxane is excellent in biocompatibility and thermal stability. It is widely used in wearable devices and sensors. This material is the most promising for skin patches.

Applications of Biomaterials in Growth Factor Delivery

Growth factors play an important role in tissue repair and regeneration. These are the main basis for bone tissue engineering and are best delivered by suitable biomaterials. Like, for example, alginate hydrogels deliver Vascular Endothelial Growth Factor and Insulin Derived Growth Factor.

Growth factors play an important role in angiogenesis which is critical for the success of bone tissue engineering and many other aspects of tissue engineering.

Applications of Biomaterials in Cancer

Immunotherapy means boosting the immune system to recognize and fight cancer cells. According to the American Cancer Society, immunotherapy means using a person's own immune system to fight cancer. In cancer immunotherapy, biomaterials play an important role.

Liposomes, polymers, and silica are some of the biomaterials used in cancer immunotherapy. Liposome-wrapped drugs have increased circulation time and the side effects are also less. They have also been used as vectors of immunotherapy including vaccines for influenza, hepatitis, and malaria.
Gold nanoparticles are used in cancer immunotherapy and antitumor immune response.
Microneedles are used to deliver small molecules, protein drugs, and vaccines.
Iron oxide nanoparticles are used for imaging.
Siliceous nanoparticles are used in vaccines like Japanese encephalitis, oral hepatitis B vaccine, etc.
Hydrogels of hyaluronic acid-tyramine-based hydrogels deliver interferon α to the site of injection.
Indocyanine green and imiquimob coloaded by PLGA aid in the eradication of the preexisting tumors.
PLGA-based microspheres are used in prostate carcinomas.
PLGA copolymers are used in the production of surgical sutures.
PLGA delivers drugs like paclitaxel, 9-nitrocamptothecin, and estradiol. It is also used to deliver cancer vaccines.

Take-Home Points

Natural biomaterials have useful properties for the application of biomaterials.
The processing of natural biomaterial has challenges and limitations including scaling up, purity, sustainability, and reproducibility.
Biomaterial advancement in breast reconstruction has been revolutionary and has enhanced the durability, safety, and life quality of the patient.
Three-dimensional biomaterials recover 3D structures and cellular function.

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