Bimodal buckling governs human fingers' luxation.

Equilibrium bifurcation in natural systems can sometimes be explained as a route to stress shielding for preventing failure. Although compressive buckling has been known for a long time, its less-intuitive tensile counterpart was only recently discovered and yet never identified in living structures or organisms. Through the analysis of an unprecedented all-in-one paradigm of elastic instability, it is theoretically and experimentally shown that coexistence of two curvatures in human finger joints is the result of an optimal design by nature that exploits both compressive and tensile buckling for inducing luxation in case of traumas, so realizing a unique mechanism for protecting tissues and preventing more severe damage under extreme loads. Our findings might pave the way to conceive complex architectured and bio-inspired materials, as well as next generation artificial joint prostheses and robotic arms for bio-engineering and healthcare applications.

Growth of a flexible fibre in a deformable ring.

We study the equilibrium configurations related to the growth of an elastic fibre in a confining flexible ring. This system represents a paradigm for a variety of biological, medical, and engineering problems. We consider a simplified geometry in which initially the container is a circular ring of radius R. Quasi-static growth is then studied by solving the equilibrium equations as the fibre length l increases, starting from l = 2R. Considering both the fibre and the ring as inextensible and unshearable, we find that beyond a critical length, which depends on the relative bending stiffness, the fibre buckles. Furthermore, as the fibre grows further it folds, distorting the ring until it induces a break in mirror symmetry at l > 2πR. We get that the equilibrium shapes depend only on two dimensionless parameters: the length ratio µ = l/R and the bending stiffnesses ratio κ. These findings are also supported by finite element simulation. Finally we experimentally validate the theoretical results showing a very good quantitative prediction of the observed buckling and folding regimes at variable geometrical parameters.

Flexible sutures reduce bending moments in shells: from the echinoid test to tessellated shell structures.

In the field of structural engineering, lightweight and resistant shell structures can be designed by efficiently integrating and optimizing form, structure and function to achieve the capability to sustain a variety of loading conditions with a reduced use of resources. Interestingly, a limitless variety of high-performance shell structures can be found in nature. Their study can lead to the acquisition of new functional solutions that can be employed to design innovative bioinspired constructions. In this framework, the present study aimed to illustrate the main results obtained in the mechanical analysis of the echinoid test in the common sea urchin Paracentrotus lividus (Lamarck, 1816) and to employ its principles to design lightweight shell structures. For this purpose, visual survey, photogrammetry, three-dimensional modelling, three-point bending tests and finite-element modelling were used to interpret the mechanical behaviour of the tessellated structure that characterize the echinoid test. The results achieved demonstrated that this structural topology, consisting of rigid plates joined by flexible sutures, allows for a significant reduction of bending moments. This strategy was generalized and applied to design both free-form and form-found shell structures for architecture exhibiting improved structural efficiency.

Ultrasound waves in tumors via needle irradiation for precise medicine.

Grounded in the interdisciplinary crosstalk among physics and biological sciences, precision medicine-based diagnosis and treatment strategies have recently gained great attention for the actual applicability of new engineered approaches in many medical fields, particularly in oncology. Within this framework, the use of ultrasounds employed to attack cancer cells in tumors to induce possible mechanical damage at different scales has received growing attention from scholars and scientists worldwide. With these considerations in mind, on the basis of ad hoc elastodynamic solutions and numerical simulations, we propose a pilot study for in silico modeling of the propagation of ultrasound waves inside tissues, with the aim of selecting proper frequencies and powers to be irradiated locally through a new teragnostic platform based on Lab-on-Fiber technology, baptized as a hospital in the needle and already the object of a patent. It is felt that the outcomes and the related biophysical insights gained from the analyses could pave the way for envisaging new integrated diagnostic and therapeutic approaches that might play a central role in future applications of precise medicine, starting from the growing synergy among physics, engineering and biology.

A lesson from earthquake engineering for selectively damaging cancer cell structures.

The progressive falling of barriers among disciplines is opening unforeseen scenarios in diagnosis and treatment of cancer diseases. By sharing models and mature knowledge in physics, engineering, computer sciences and molecular biology, synergistic efforts have in fact contributed in the last years to re-think still unsolved problems, shedding light on key roles of mechanobiology in tumors and envisaging new effective strategies for a precise medicine. The use of ultrasounds for altering cancer cells' program is one of the most attracting grounds to be explored in oncophysics, although how to administer mechanical energy to impair selected cell structures and functions simultaneously overcoming the critical trade-off between the impact of the cure and the patient risk still remains an open issue. Within this framework, by starting from the theoretical possibility of selectively attacking malignant cells by exploiting the stiffness discrepancies between tumor and healthy single cells, first proposed by Fraldi et al. (2015), we here investigate the in-frequency response of an overall spherical close-packing of geometrically equal polyhedral cells to gain insights into how mechanical resonance and vibration-induced failure phenomena can be oriented to destroy specific target units when both the cell populations coexist, as it happens for in vivo cases. Inspired by the dynamic action of earthquakes - which fracture only selected elements among adjacent ones in the same structure or damage individual constructions in contiguous buildings - we study the harmonic response of hierarchically architectured cell agglomerates, inhabited by both tumor and healthy cells that interact mutually throughout the extra-cellular matrix and whose cytoskeleton is modeled as a nonlinear soft-tensegrity structure. Numerical Finite Element results show that, at frequencies compatible with low intensity therapeutic ultrasounds, mechanical resonance and possible fatigue cycles of the pre-stressed actin filaments and microtubules can be selectively induced in cancer cells as a function of the global volume fraction of the cell species, paving the way for future engineered treatment protocols.

Stealthy role of size-driven stresses in biomechanics of breast implants capsular contracture.

Breast Capsular Contracture (BCC) is one of the adverse complications occurring with greater incidence in breast augmentation surgical procedures. Its formation can be interpreted as the conclusive result of the physiological process known as response to a foreign body. From a biochemical standpoint, the formation of the peri-prosthetic capsule is certainly a multifactorial process: many hypotheses concerning its etiology have been suggested in the literature and a number of related pharmacological protocols have been consequently proposed to clinically treat this pathology with the aim to prevent further complications and avoid future re-interventions. However, the vast majority of these theories seems to be only partially supported by clinical outcomes and thus a shared opinion on this matter is still absent among specialists. Within this framework, by starting from clinical observations which highlighted an unexpected correlation between histo-morphological features of fibrotic capsules and overall size of breast implants, the present study investigates the hypothesis that the biomechanical interaction between prosthesis and host tissue may play a crucial role in the biological processes governing the pathological phenomenon at hand. Therefore, to shed light on the underlying mechanisms which could trigger the breast capsular contracture, both simple analytical solutions, in which elasticity and growth are simultaneously taken into account, and more accurate geometrically faithful Finite Element-based numerical simulations have been exploited. The theoretical findings demonstrate that somehow counter-intuitive radial and hoop stress fields occur at the capsula-implant interface in a way such that their combined action, independently from other possible concurrent factors, results significantly amplified for small-size breast prostheses, localized stress peaks in these cases promoting detaching and rippling phenomena actually observed in BCC clinical complications.

Compliance mismatch and compressive wall stresses drive anomalous remodelling of pulmonary trunks reinforced with Dacron grafts.

Synthetic grafts are often satisfactory employed in cardiac and vascular surgery, including expanded poly(ethylene terephthalate) or expanded poly(tetrafluoroethylene). However, accumulating evidences suggest the emergence of worrisome issues concerning the long-term fate of prosthetic grafts as large vessel replacement. Disadvantages related to the use of synthetic grafts can be traced in their inability of mimicking the elasto-mechanical characteristics of the native vascular tissue, local suture overstress leading to several prosthesis-related complications and retrograde deleterious effects on valve competence, cardiac function and perfusion. Motivated by this, in the present work it is analyzed - by means of both elemental biomechanical paradigms and more accurate in silico Finite Element simulations - the physical interaction among aorta, autograft and widely adopted synthetic (Dacron) prostheses utilized in transposition of pulmonary artery, highlighting the crucial role played by somehow unexpected stress fields kindled in the vessel walls and around suture regions, which could be traced as prodromal to the triggering of anomalous remodelling processes and alterations of needed surgical outcomes. Theoretical results are finally compared with histological and surgical data related to a significant experimental animal campaign conducted by performing pulmonary artery transpositions in 30 two-month old growing lambs, followed up during growth for six months. The in vivo observations demonstrate the effectiveness of the proposed biomechanical hypothesis and open the way for possible engineering-guided strategies to support and optimize surgical procedures.