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March 13, 2012

The evolution of biomaterials

by Roshan Yoganathan

Prosthetic_footI’ve been working in the field of biomaterials for over five years now. A short period of time, but nevertheless I’ve noticed that the field has evolved considerably. Since the inception of “biologically compatible materials,” their capabilities, functionalities and uses have undergone multiple stages of change.

There are distinct turning points when biomaterial research is thought to have evolved. I believe we are currently in the third generation and slowly shifting to the fourth (more on this later).

So here is how I see it, starting from the beginning.

One of the earliest uses of non-biological materials in the body was the wooden toe prosthetic in 1065-740BC in early Egypt. However, research in the field and the first generation of biomaterials was recognized more prominently between 1960 to 1970. During this time period biomaterial research encompassed all materials designed for use in the body. These materials were designed to “achieve a suitable combination of physical properties to match those of the replaced tissue with a minimal toxic response in the host.” Eventually the field started focusing more on classes of materials such as metals, ceramics and polymers. The goal of the first generation was to achieve matching mechanical properties, such as mimicking the compression/tension characteristics of bone/tissue/cartilage.

A second goal was biocompatibility. Needless to say, back then if an immediate inflammatory response was not observed, the material was deemed biologically compatible. To be compatible meant to be inert and it soon became apparent that just being inert within the body might not be enough to help illicit full bone/tissue/cartilage growth and regeneration.

With this in mind in the 1980s there was a progression towards the second generation of biomaterials that were more biologically-active or “bioactive”. By being bioactive the materials could “elicit a controlled action and reaction in the physiological environment.

One of the simplest methods of enhancing bioactivity is to change the surface structure of the material, i.e. increase surface roughness and porosity. For applications such as bone engineering, by increasing the surface roughness and porosity of the biomaterial you are able to increase the osteoconductivity, thereby increasing the surface area exposed to osteoblasts (cells responsible for bone formation). The bone then grows into and around the bioactive surface, creating a stronger and more durable hybrid bone-biomaterial structure.

The most recent paradigm shift has been toward cell and gene activating biomaterials: the third generation of biomaterials. It is believed that the advent of tissue engineering truly began in this phase. This shift occurred at the beginning of this century before I entered the field.

The third generation of biomaterials improves on the initial physiological cues bioactivity created in the second generation, to allow the biomaterial and surrounding environment to adapt and stimulate the regeneration of living tissues within the body. With all the cutting-edge research being done in the world of stem cells, and the realization that differentiation and stability is environment-dependent, I believe the realm of biomaterials is again gearing up for another revolutionary shift.

Along this new wave of thinking, the “smartness” of biomaterials will also grow and evolve. With research now growing in the fields of nanomedicine, BioMEMS, 3D tissue scaffolds, biosensors, and smart polymers, the functionality of biomaterials is no longer just mimicking biological material, but also controlling, regenerating and monitoring the performance of human cells. It’s an interesting time to be working in this field.

I have not said much about the capabilities of biomaterials to monitor and sense changes in various physiological environments. I will save that discussion for another day.

 

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