Multiscale Modeling in Biomechanics

Discussion

• Multi-scale typically means models that span multiple length and/or time scales. What specifics should be included for biomechanics. For example does the definition need to include concurrent simulation?. i.e. Is developing constitutive equations of tissue and then applying to an organ level FE model constitute multi-scale modeling? Are boundary condition interactions enough?

• About the definition of multiscale modeling, my understanding is that the approach involves coupling of multiple models that reflect features of different length and/or time scales. Coupling does not need to be concurrent, it may also be streamlined, e.g. get boundary conditions from macroscopic model of tissue, apply it to a microscopic model of cell and extracellular matrix.

• Is developing constitutive equations of tissue multiscale modeling? Depends. If you test a sample from the bone for example and fit a function to its data (e.g. get Young's modulus), it is not. If you build a microstructural model of the bone to derive constitutive equations for a macroscopic model, it is.

• Multi-scale can also refer to models with different levels of complexity, e.g. 3D system of equations and a 1D simplified system, or representation of a physical structure that uses different dimensions.

• The following are from a discussion at the January 2008 Pacific Symposium on Biocomputing session (Multiscale Modeling and Simulation: From Molecules to Cells to Organisms)
  • What is multiscale modeling?
    • a buzz word used to get funding
    • something that can be performed with loose coupling between scales
  • A definition of multiscale modeling as it pertains to biomechanics was not reached
  • Other disciplines have a long history of multiscale modeling (i.e. aerospace, material science)
  • The discussion did reveal that a future session in multiscale modeling is needed
  • A multiscale session was proposed (Emerging Challenges in Multiscale Modeling in Biology) and recently accepted by PSB organizers http://psb.stanford.edu/cfp-multiscale.html

• Simbios believes disciplinary boundaries separating different modeling and simulation communities (e.g., structural biology and mechanical engineering) have limited the creation and application of multiscale simulation techniques in biomedicine. The recognition that these boundaries limit our ability to perform useful simulations makes their removal critical for long-term success. Furthermore, multiscale capabilities are not a set of features that can simply be added to existing simulation packages. These packages have fundamental assumptions that make them effective within a certain dynamic range, and ineffective outside. The idea that multiscale capabilities must be built as part of the founding concept of a simulation environment is the basis for the Simulation Toolkit (SimTK).

• Excerpt from the WG's article submitted to IEEE EMB Magazine special issue on mulitscale modeling titled: Multiscale Modeling in Computational Biomechanics: Determining Computational Priorities and Addressing Current Challenges IEEE EMBS Article
  • "Biomechanics is broadly defined as the scientific discipline which investigates the effects of forces acting on and within biological structures. The realm of biomechanics includes the circulatory and respiratory systems, tissue mechanics and mechanotransduction, and the musculoskeletal system and motor control. As in many other biological phenomena, many spatial scales are crossed by biomechanics research: intracellular, multi-cell and extracellular matrix, tissue, organ, and multi-organ systems. It is well established that the effect of forces at higher scales influence behavior at lower scales and that lower scale properties influence higher scale response. However, computational methods that incorporate these interactions in biomechanics are relatively rare. In general, computational models that include representation of multiple spatial or temporal scales are loosely defined as multiscale. The fact that multiscale modeling is not well defined lends the term to a variety of scenarios within the computational physiology community. In biomechanics, multiscale modeling may mean establishing a hierarchical link between spatial and temporal scales while the output of a larger scale system is passed through a finely detailed representation at a lower scale (e.g. body level movement simulations that provide net joint loading for tissue level stress analysis). In reality, multiscale modeling may require more intricate representation of interactions among scales. A concurrent simulation strategy is inevitable to adequately represent nonlinear associations that have been known for decades"

General IMAG/MSM Consortium Discussion on defining multi-scale modeling.

• What exactly is Multiscale Modeling??