director of the Institute for Bioengineering of Catalonia (IBEC)
Opinion
There has always been a need to substitute or repair human tissue or body parts. However, it was not until the last third of the 20th century that this could be done with any acceptable rate of success.
Transplants have extended and improved the lives of thousands of people across the world, and implants have done the same for millions. Prosthetic hips and knees, intraocular lenses, cardiac valves and myriad other surgically implanted devices have a proven track record of improving the wellbeing of patients. All of these devices must be manufactured from materials that are biologically functional and safe to implant.
Medical care and surgery have evolved in parallel to science and technology. The 20th century witnessed major advances in the development of metallic, ceramic and polymeric materials, all of which have been considered for use in implants. Maintaining homeostasis in the human body demands that implantable materials exhibit a combination of specific qualities; however, only a select few materials meet these requirements. The interaction between the material and the biological medium must be assessed in terms of degradation of the material, as well as in terms of any possible biological responses that may be provoked by the material or its degradation products. Thus, the materials considered for fabricating implants have been chosen for their balance between mechanical resistance and corrosion, and for being lightweight, machinable, processable, and sterilizable.
Therefore, biomaterials have historically been considered inert, and as least toxic as possible for the organism. These materials have traditionally been chosen from pre-existing materials designed for applications in other sectors, including the chemistry, mechanical, food, energy, or aerospace industries. There are currently rules and regulations that dictate which materials can be used for implanted devices.
Scientific progress, especially the recent strides made in nanotechnology and stem cell research, have offered us a glimpse into the future of regenerative medicine and tissue engineering. The premise is that malfunctioning or damaged tissue or organs could simply be regenerated by growing stem cells on a specific scaffold, onto which the cells would anchor and subsequently, proliferate and differentiate as needed. The material for the scaffold must resemble the extracellular matrix of the cells in question, such that it can generate the right signals to orchestrate cellular behavior. These biomaterials-ideally, analogs of the extracellular matrix-must be designed with a high degree of specificity. Therefore, the success of regenerative medicine will ultimately stem from the accuracy achieved in the de novo design of the specific biomaterials used, rather than from simply making the right choice among pre-existing materials designed for other applications.