Contact Mechanics of Soft and Complex Biological Tissues

Project Information

BIOCONTACT

Grant agreement ID: 845756

DOI

10.3030/845756

Project closed

EC signature date 18 March 2019

Start date 1 April 2019

End date 30 September 2021

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 212 933,76

EU contribution

€ 212 933,76

Coordinated by

IMPERIAL COLLEGE OF SCIENCE TECHNOLOGY AND MEDICINE
United Kingdom

Periodic Reporting for period 1 - BIOCONTACT (Contact Mechanics of Soft and Complex Biological Tissues)

Reporting period: 2019-04-01 to 2021-03-31

Summary of the context and overall objectives of the project

This project focused on the investigation of the contact mechanics of biological materials, such as skin and internal tissues, which present inhomogeneous, anisotropic, and swollen behavior. Since biological tissues are usually arranged in multi-layer strata, the assumption of homogeneous half-space behavior (common in classical contact mechanics studies) falls short in describing their continuum mechanics response, and the geometry of the contacting bodies has to be taken into account. For these reasons, in order to model the contact behavior of biological thin tissues at the level of accuracy required for scientific purposes and industrial R&D applications, a specific contact mechanics model is needed, able to deal with thin viscoelastic layers opportunely assembled to mimic the composition of real tissues.
Several real-life applications will benefit from this study as it provides, for instance, the chance to model the contact between the eyelid, the contact lens and the cornea epithelium, thus allowing for the optimization of the contact lens mechanical and biological compatibility against the surrounding tissues. By exploiting BIOCONTACT results, advanced contact mechanics studies could be led to specifically take into account for the thickness and viscoelasticity of the eyelid tissue, eventually allowing for the optimization of the lens in terms of surface roughness, thickness and adhesion energy, aiming at enhancing the final user comfort. Similarly, also the mechanical compatibility of prosthetic bones with surrounding tissues (e.g. muscles or connective tissues) will be enhanced by means of BIOCONTACT results, as the accurate prediction of the contacting normal and tangential stresses acting on the soft biological tissues provides an efficient tool to reduce bedsores in long-term bedridden patients.
For these reasons, the main objective of BIOCONTACT was to develop an advanced contact mechanics model able to accurately describe the contact behavior of elastic/viscoelastic thin layers in the presence of repulsive and adhesive interfacial interactions, which could therefore be employed in investigating the mechanical behavior of biological contacts involving thin tissues with specific interfacial interactions. Moreover, aiming at allowing the broadest possible field of applications to benefit from the project output, we sought for a parametric model which can be also adopted in studying the general-purpose contact mechanics of rubber-like materials.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Most of the work has been spent in implement the biological tissue constitutive models in a modular contact mechanics solver to simulate different kind of interfacial interactions, allowing further extensions to incorporate chemo-mechanical effects. The path to achieve this general-purpose formulation necessarily passed through the development of a specific contact analysis methodology, which took inspiration from scientific areas far from classical contact mechanics. Indeed, in order to model the repulsive and adhesive interactions between the soft tissues and the rigid contacting counterpart (e.g. prosthetic bones, surgical tools, etc.), we borrowed from Molecular Dynamics (MD) the concept of gap-dependent force potentials. However, since modelling the mechanical response of the thin soft viscoelastic layers involved in the contact by relying on complete MD simulations would have required a huge computational effort, we developed a different approach which, building on Boundary Element Method (BEM), exploits viscoelastic Green’s functions. These have been specifically calculated in the framework of elastic continuum mechanics, which has then been extended to also encompass viscoelastic materials. The resulting model merges MD methods to advanced BEM formulations, thus exploiting the benefits of both. Specifically, the BEM numerical solution technique has been developed in the Fourier domain adopting uniform successive mesh refinement to strongly reduce computation time. Nonetheless, it also allow for maintaining a very high resolution even at the smallest scales, which is of utmost importance to accurately model rough elastic/viscoelastic contacts in the presence of adhesion.
Moreover, due to the generic nature of the BEM-like formulation developed in BIOCONTACT, the solver can be exploited in investigating different physical problems related real-like applications ranging from adhesive peeling behavior of Band Aids and wound dressing against skin to the nonlinear damping provided by thin rubber layers in seismic isolators.
These results have led to five publications on prestigious scientific journals; nonetheless, calculations are still ongoing, and two manuscripts are in preparation to further disseminate the project results in the scientific community. Similarly, scientific talks have been provided in specialized conferences to guarantee the highest possible outreach to the methodology developed during the project.
Peculiar applications of this tool will likely spread, among the others, to the investigation of dry viscoelastic contacts in the presence of adhesive interfacial interactions, such as those involved in biomedical devices design (e.g. band-aids and wound dressing peeling) and industrial packaging issues (e.g. thin film removal from soft goods).

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

BIOCONTACT results significantly contribute to push ahead the state of the art in terms of knowledge of the mechanical behavior of thin elastic and viscoelastic layers, with specific reference to biological tissues contact mechanics. A comprehensive and innovative mathematical formulation of the continuum mechanics has been developed for thin deformable layers, which helped in shedding light on the interplay between the normal and tangential elastic fields in contacts involving viscoelastic layered materials, such as biological tissues and skin.
In the long long-term, we may predict a significant beneficial effects of the theoretical and methodological advances delivered by the project on different real-life applications. Among the others, the opportunity to increase the mechanical compatibility of bio-medical tools in direct contact with the skin, by considering both the interfacial normal pressure and tangential shear stress, is probably one of the most effective. Indeed, recent studies have shown that in preventing pressure ulcers and bed sores, which cost about £2 billion per annum in the sole UK, the effect of the shear stress acting on the skin surface cannot be neglected; therefore, BIOCONTACT mechanical model represents a key opportunity to optimize the fabric properties to control contact interfacial stresses. Interestingly, also the face masks market (which has recently experienced a rapid rise due to Covid-19 pandemic) could benefit of similar developments. In this case, the increased wearing comfort might also lead to a wider use of the masks, with corresponding long-term societal benefit in contrasting not only the Covid-19 pandemic, but any further diffusion of diseases by aerosol.
Moreover, thanks to the specific formalism adopted, the BIOCONTACT model can be easily generalized for applications very different from biological tissues. For instance, the contact mechanics behavior of rubber-like thin viscoelastic layers can be investigated.

Graphical abstract