Soft tissues are found in all animals, and their mechanical properties play a central role in development, physiology, and disease. For example, atherosclerosis and aneurysms are cardiovascular diseases, where the arterial wall suffers local changes in stiffness and strength (i.e., the ability to withstand a load without failing). Under the pressure exerted by the pulsatile blood flow, the weakened tissues are vulnerable to ruptures. The dramatic pathological consequences of these events notably contribute to making cardiovascular diseases the second cause of death in the UK, just below cancer. It is clear that underpinning the mechanical basis of the failures is essential for their prevention and timely treatment.
Quantifying the mechanics of soft tissues is thus a necessary assessment for clinicians, but also for engineers, scientists and industry in the healthcare sector. Methods to measure tissue properties are therefore in high demand. Yet, most current in vitro techniques are not standardised, and fall short of some important features. First, they are often unreliable: soft tissues are hard to handle and to mount on an instrument, and end up being misaligned or deteriorated during the measurements. Second, they generally require large specimens, and the many localised changes in properties of inhomogeneous tissues are irremediably averaged throughout and cannot be measured. And third, the methods are rarely fit to measure tissue properties under the dynamic loads met in real physiological conditions.
This research programme develops a new in-vitro technique that addresses these issues. First, we develop a protocol to precisely excise small, millimetre-scale specimens of tissues with well-controlled dimensions. Second, we implement an instrument that can reliably and precisely measure the mechanical properties of these small specimens. The instrument is compact enough to be installed on a microscope and further observe the microstructure of the tissues while the measurements are performed. Our new technique relies on two innovative features: first, a set of press-punch tools are used to simultaneously excise, align and attach the specimen to the apparatus using minimally invasive chemical adhesive; second, the sensors of the instrument use a fast, accurate and computer-controlled electromagnetic technology. Our instrument (diagrams, part numbers or 3D-printing files, etc.), the protocol, and associated software will further be made freely available as open-source. That way, we hope to reach researchers from more disciplines, such as tissue engineering, biophysics, or the emerging field of mechanobiology, but also in subjects outside the biomechanics arena.
The second step of the programme is to measure the mechanical properties of human atherosclerotic and aneurysmal tissues. These measurements will fully exploit the combined benefit of our new technique, to provide, for the first time, a map of stiffness and strength values in the diseased arteries under dynamic loading. This data will then be employed to perform numerical simulations that can explain the mechanical conditions triggering tissue rupture events. These findings will undoubtedly help clinicians, researchers and industry to improve treatments and optimise physical interventions, such as surgery and angioplasty (stents). Our project provides a strong contribution to addressing some of the "Healthcare Technologies Grand Challenges", indeed flagged as an important research priority by the EPSRC.