New implant materials in offing

In a recent article (Key innovations in joint replacements, DH Panorama, May 9), a medical expert showcased the revolutions in orthopaedic bioimplants providing solutions to a multitude of people requiring joint repair and replacements. Also highlighted were improvised technology and surgical methods using advanced devices. Medical requirements have paved the way for medical engineering, which is contributing several possibilities to surgical implant devices to assist the functioning of weakened or damaged body parts. From cosmetic to complex neural surgeries, bioimplants are providing solutions to critical medical conditions.

Behind the cutting-edge technology lies a crucial factor. Bioimplants rely heavily on the exhaustive study of material science and extensive research in the exploration of suitable materials that are compatible with residing inside the human body. The last few decades have seen tremendous advances in synthesis of such materials called biomaterials, used widely in medical devices such as screws to hold parts together or wires, connectors, fine meshes, tubes and plates or entire joints. As with technology, biomaterials too, are continually evolving.

Various options

The selection of biomaterials is a critical factor for a long-lasting implant. Based on the requirement and function, metals, alloys, ceramics, and composites are widely called for in the making of the device.

Metals such as Titanium and derived alloys have been a primary and popular choice, due to their machinability, high mechanical strength, ductility, malleability and surface finish. However, their intrinsic nature yields them to wear and tear, and gradually corrode when exposed to bodily fluids. Eventually, they may need replacement by surgical procedures. Such limitations make metallic implants impermanent.

The introduction of a ceramic — Zirconia, in 1969 brought a new dimension to the making of implants. Ceramics are better than their metallic counterparts as they are porous, lighter, chemically inert with negligible wear and tear. However, though widely used, ceramics are brittle in nature, and hence their use in load-bearing parts is avoided.

Further experiments resulted in the making of composites —the combination of a base element (matrix) with a reinforced element. The result is an enhanced material which incorporates the advantages of both the materials.

Despite various investigations with alloys, polymers, and composites, no known material has the acquired mechanical strength, enough porosity, biocompatibility and physiological stability of the bone. Bone and teeth are made up of a composite called Hydroxyapatite (HAp) — a form of the mineral calcium.The natural source of Hydroxyapatite is bovine bone marrow tissue, and synthetic HAp is fabricated from high-temperature processes and sintering.

Synthetic HAp has a porous structure which offers the right scaffold for the regrowth of bone tissue. Moreover, it is bioactive and quickly bonds with the surrounding cells, making it an increasingly popular choice. Intrinsically ceramic in nature, HAp is brittle, throwing a challenge to overcome the limitation.

Nanotechnology has permeated every aspect of science, and its presence in biomaterials is fast gaining ground. Nanotechnology modifies the structural and in turn mechanical properties of a material by making modifications at the molecular and atomic level.

In a recent study, C Gautam et al., from the Advanced Glass and Glass Ceramics Research Laboratory, induced nanoparticles of the wonder material graphene into HAp matrix. Their experiments yielded the highest available mechanical property of the composite.

The process did not alter the basic porous structure of HAp thereby retaining its bioactive property. Along with mechanical properties, the study also established the biocompatibility of the composite in living cells, projecting the potential of the new material in bone engineering. Moreover, the chromatography trials indicate that the enhanced HAp exhibits fluorescence which shows its use in bioimaging applications as well.

With these preliminary results, newer challenges will arise, resulting in further research to improvise the biomaterials. The years to come are promising; science will witness the making of futuristic biomedical devices, at the heart of which lay futuristic materials.

(The writer is a science communicator and evaluator- AWSAR, DST)