By Will Soutter
Introduction to Nanocomposites
A nanocomposite is a multiphase solid material in which one of the phases has one, two or three dimensions of less than 100 nm. Nanocomposites are not always artificial structures - they can also be found in nature, for example in the structure of the abalone shell and bone.
Bioactive materials are used to interact with or have an effect on tissue in the human body. Nanocomposites are a natural choice when designing bioactive materials, as many biological structures and interfaces also have nanoscale features, making interactionmuch more effective. Bioactive nanocomposites can be used in the form of a thin biocatalytic coating or as bulk product.
Many bioactive nanocomposites have been developed by embedding various types of biomolecules into a sol-gel matrix. The embedded biomolecules retain their conformation and chemical and physical properties. External reagents can be transported to the embedded biomolecules so that chemical reactions and interactions are possible.
Natural nanocomposites are found in a surprisingly large number of places. Now artificial nanomaterials are being designed to interact with biological systems. Image credit: University of Connecticut
The following are the various bioactive nanocomposite innovations:
Collagen/Hydroxyapatite (HA) Nanocomposite Thin Films
In 2008, researchers were able to create collagen/hydroxyapatite (HA) nanocomposite thin films that contained 10, 20, and 30 wt.% HA. This was prepared on commercially pure titanium substrates by spin coating their homogeneous sols. The nanocomposite thin films possessed a thickness of ~7.5 µm with uniform and solid surface but without any grouping of the HA particles. At 20 wt.% HA, a minimum contact angle of 36.5° was obtained, which indicated that these thin films were likely to display the best hydrophilicity.
It was noted during in vitro cellular assays that the nanocomposite thin film coating on titanium substrates supported the adhesion of osteoblast-like cells and extensively enhanced the cell proliferation rate. The cells on the nanocomposite thin film coating displayed much higher alkaline phosphatase (ALP) levels than those on the uncoated titanium substrates. Also when the quantity of HA was increased, a gradual progress in the ALP activity was recorded. With all these features the nanocomposite thin film coating can be adapted as implant materials for hard tissue engineering.
Bone Cement Nanocomposites
Calcium phosphate cements (CPCs) are widely used in orthopedic surgery as bone fillers due to its excellent biocompatibility; however its insufficient mechanical properties have greatly hampered its clinical applications. In 2009, researchers began work on calcium phosphate cements to make it strong and tough, it could over take the present polymethyl methacrylate (PMMA) bone cement’s market, which is about $200 million.
Nanova Inc., a company using cutting edge technology, including nanotechnology, to develop devices and sensors for medical and non-medical applications, has been involved in developing new bone cement nanocomposites consisting super-strong and ultra-long hydroxyapatite (HA) fibers. The new cement nanocomposites will hopefully have better mechanical properties and can be used for numerous orthopedic applications such as plateau fracture fixation, prosthesis fixation, general bone grafts, vertebroplasty and kyphoplasty. According to a market report, the demand for these newly developed cements is estimated to reach $1 billion.
Bioactive Gelatin–Graphene Oxide (GO) Nanocomposites
In 2011, researchers created bioactive gelatin–graphene oxide (GO) nanocomposites with varying GO contents by a solution-casting method. For example, when 1 wt% GO was added, the tensile strength, energy at break, and Young's modulus of gelatin were found to increase by 84%, 158%, and 65%, respectively.
The GO nanosheets enhanced the bioactivity of gelatin by producing more calcium phosphate nanocrystals on the composites. Researchers also noted that GO acts as both an effective reinforcement filler and a biological activator in hydrophilic biopolymers such as gelatin, thereby providing the biopolymer–GO nanocomposites immense possibilities to be further developed in biomedical fields.
Nanocomposites in Bone Grafts
In 2012, researchers were involved in creating nanocomposites that could be applied in bone grafts especially hydroxyapatite/collagen system as the existing options in bone and tissue transplantation with controlled drug delivery were complicated with the use of ancient methods of bone grafting such as allogenic and autogenous grafts.
These methods posed high infection risks and donors were scarce. The upgraded synthetic bone grafting materials also had some flaws including differing from natural bone either in structure or composition. Researchers are studying the effects of nanocomposites in drug delivery using injectable cell scaffolds and the use of silica-based bioactive ceramics for bone tissues.
Nanocomposites have the potential to play a crucial role in a number of huge growth areas within life science, particularly tissue engineering and regenerative medicine. The various research studies highlighted here reinforce the fact that nanocomposites are invaluable for the future growth and development of bone grafting and drug delivery carriers.