Today, tremendous medical advances allow people to live longer, but this also means that we are more susceptible to suffering an assortment of 'diseases of old age'.
Of the many diseases that afflict the elderly, cardiovascular disease has arguably been at the fore – leading to more sickness and death than any other disease.
Our sedentary lifestyle, fatty foods and ill-habits contribute to higher circulating fats and cholesterols, which in turn accumulate on the inner surfaces of blood vessels over the course of decades.
The result can be a heart attack if the heart muscle doesn’t get enough blood flow.
Depending on blood vessel location and the patient's health, intervention options can generally be grouped into:
(i) stenting and angioplasty,
(ii) endarterectomy, or
(iii) bypass grafting.
Angioplasty is a technique where a small deflated balloon is threaded into an artery and guided using X-ray scanning to the blockage.
The balloon is then inflated, breaking up the fatty plaque (which may have hardened due to calcium deposit or scar formation, like a scab).
Commonly a stent (a tubular wire mesh) is used to prop open the vessel.
Angioplasty and stenting is a common procedure for a variety of blood vessels and is typically performed with stainless steel or shape memory alloys.
Endarterectomy is a procedure where the diseased portion of the vessel is surgically opened along its length and the fatty deposit tweezed out.
Endartarectomies are more common in the carotid vasculature, which is a major vessel that supplies the brain and face with blood.
The third common procedure is bypass grafting. Here, blood vessels are rerouted or harvested from the same patient (a chest artery, internal thoracic artery or a vein in the leg) and used to bypass a blocked vessel.
This is similar to creating a detour road when the main road is blocked.
For people who require multiple bypass, have vascular disease, or cannot withstand multiple surgeries, alternative plastic-based materials are used.
Synthetic grafts are typically made from expanded polytetrafluroethylene or polyethylene terephathalate.
These materials are highly stable and were once thought to be the optimal graft materials, since Teflon is, afterall, non-stick.
However, grafts made out of Teflon, same as the coating of some frying pans, or Dacron, the material many mineral water bottles are made of, have a lifespan of 10 to 15 years before revision surgeries or alternative interventions may be required.
For smaller blood vessels of less that 6 millimeters, which are common in the heart or below the knee, there exist no synthetic graft material.
This is as these grafts rapidly form blood clots on the inner surface, form thick new tissue that blocks blood flow, or are prone to infection.
Tissue engineering is thus a burgeoning field that hopes to address this problem. By taking cues from native blood vessels and by understanding the building blocks of blood vessels, physicians and engineers are creating bio-mimicking constructs that supplant diseased tissue, potentially improving function and ultimately mimicking structure and function.
There are several challenges that designers face when attempting to develop vascular grafts.
One challenge is how to ensure elasticity in tissue engineered blood vessels for them to avoid bursting due to blood pressure. Another is how to ensure the body does not reject implants.
It will take a concerted effort from medical professionals to develop novel treatments that involve the next generation of tissue mimetic or tissue based constructs that may ultimately replace the plastic tubes used today.
This article was contributed by Vivek A. Kumar, PhD American Heart Association Fellow Wyss Institute, Harvard University BIDMC, Harvard Medical School.