Biocomposites used in the field of biomaterials 

Biocomposites are made of biomaterials with a filler element dispersed into a matrix material or a construct with alternating sections of different materials. They are nonviable materials used in biomedical devices intended to interact with biological host systems. The main purpose of these biocomposites is human repair, reconstruction, and reinforcement.

In nature, there exist biocomposites such as wood and bone. Wood is composed of collagen and lignin and bone is composed of hyaluronic acid and collagen.

Synthetic biocomposites play an important role in tissue engineering and these composites are made up of two or more scaffold materials such as synthetic polymers and inorganic materials.

Synthetic biomaterials such as titanium, alumina, glass, carbon fibers PMMA, PLA, PGA, PEEK, bis-GMA, HA, alginite, and other petroleum-based polymers are mostly employed to form the biocomposites.

THE PHASES

The biocomposites have two constitutional phases,(1) the reinforcement phase and (2) the continuous phase. The reinforcement phase mainly consists of fibers or particles while the continuous phase is called a, matrix.  There are three kinds of reinforcement,

• Short fiber reinforcement – for screws and hip joints
• Continuous fiber reinforcement – for bone plate
• Particulate (particles) reinforcement – dental composites

These reinforcements are good for making composites for biomedical applications.

Fiber reinforcement polymers-FRP

Fiber reinforcement polymers(FRP) are used in composites in which the fibers are embedded in a polymeric matrix. The polymer binds the fiber together by giving the shape, distributive stress between the fibers, resists small amounts of stress, and typically protects the fibers from exposure and the environment.

The fiber stiffens the polymer matrix and enhances its mechanical behavior and the matrix enhances the performance durability.

Filler particles are added to the polymers to overcome their inherent weakness, for example, lack of stiffness.

The polymer composite materials used to prepare biocomposites are separated based on their biodegradable properties such as.

• Non-resorbable composites
• Partially resorbable composites
• Fully resorbable composites

Nowadays, polymer-based composites are becoming more popular, for example, Polymethacrylate(PMMA) in restoring lost dentine and enamel.

Here are some of the combinations of polymer composite biomaterials, which are used as the filling and the matrix composites.

Synthetic polymers such as bisphenol A-glycidyl methacrylate (Bis-GMA) or urethane dimethacrylate (UDMA), ( commonly used matrix composites) are mixed with particles or fibers to achieve the biocomposite with the required characteristics. 

Some of the synthetic materials, which have been used as biodegradable polymers are,

•  polyesters such as polylactides
• polycyanoacrylates: isobutyl cyanoacrylate polymer
•  polypeptides: poly(L-glutamic acid), poly(L-lysine)
• polyanhydrides, polyphosphazenes, poly(ortho ester)s

PROPERTIES

The major properties that a biocomposite should possess are,

• Mechanical strength
• Biocompatibility
• antibacterial properties
• Carry inhibiting and regenerating activity
• Elasticity

These properties differ based on the fibers and matrix materials used in the biocomposites and also the production techniques.

Here are some decisive factors that should be considered.

• processing temperature of the material
•  desirable rate of control over the distribution of the different materials, both proportional and geometrical (when designing multi-material parts)
•  required overall porosity and if applicable – fiber size of the construct – 
• required geometrical randomness or periodicity

NEED FOR BIOCOMPOSITES

The most commonly used biomaterials which are homogenous, to form biocomposites are metals, ceramics, and polymers. In the early 2000s, most biomedical devices in clinical use were made of these biomaterials. But, they had their drawbacks like,

• They are too stiff and while healing stress protection on the fractured bone develops
• Produces artifacts under X-ray irradiation, makes it difficult to examine 
• Metal sensitization can occur and the implant may cause mutagenicity

To overcome these drawbacks, the implants are made of polymer matrix composites.

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