MODELING FOR STRUCTURAL STUDIES OF ARTIFICIAL MUSCLES

The three-dimensional volume data are convert the iso-surface polygon mesh model by ImageJ software. Then, the cylinder objects are fitted into the volume using Blender. Two areas, a dense area and a surface area that represents the overall volume, were created and saved in STL format file.

Using ImageJ the volume data are converted to a 8 bit/pixel ZStack, then on "Plugins / 3D Viewer" window, "Display Surface" command generates the isosurface data at a threshold value. Surfaces at two different threshold were exported and imported into Blender.

Cylinders are assigned to fit the 3D volue density. Radius of the cylinder was 500nm that was about 3 pixels width on the isosurface map at 120 nm mesh. This resolution would be a limit of the light microscopy. The actual microtubule radius 25 nm would becomes a thin line on this figure.

　

Isosurface and cylinder models are superimposed in Blender.

Using the layer function in Blender, or collection function in Blender version 2.8, isosurface maps and cylinder models can be superimporsed interactively, so the fitness of the model was examined. The transparency rendering for cylinder as shown in this figure takes several seconds on a standard PC, but interactive rendering without transparency would be useful in a modeling study.

　 　

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In Blender, the model represented by a cylinder or polygon can be used as a rigid body to simulate the movement when a force is applied by the physical calculation function. The action of kinesin molecule was introduced to the model of microtubules represented by the arrangement of cylinders, and the force to pull the microtubules was applied.

Research and development of protein-based actuators is still underway, and in the solution of various problems such as control of contraction and relaxation and stabilization of materials, it will be used as a tool to promote discussion of molecular structure improvement based on structure.

CONSTRUCTION OF SKELETAL MUSCLE FILAMENT MODEL

The muscle filaments that make up skeletal muscle are arranged in a hexagonal lattice. It is known that vertebrate muscle has a unique layout of thick and thin filaments compared to the other spices. On muscle contraction, the lattice spacing becomes wider according to the shorting of the muscle cell. This model was made to investigate the intermolecular interaction between actin and myosin of each filaments in the sarcomere model by reconstructing the structure of the filament lattice that accompanies lattice spacing change. The particle system facility in Blender was applied using low resolution polygon models of actin and myosin molecules. Basically the particle system in blender provide multiple child objects grow on a parent object, and we nested additional particle system objects nested to the children object, i.e, one is a particle model with leaves on the branches of the tree, and the other is a particle model of the trunk with multiple branches.

There are ways to layout duplicated objects in Blender. For example, Group function allows us to register and reuse the parts that consist of multiple objects, we can build a similar model with the Gorup function. In addition, a python script can be used to copy or place multiple objects, or the objects created with particles can be converted into ordinary objects. Using script is also useful to change the attributes of multiple objects at once and animate them. We also tried to construct a much detailed sarcomere model using python script that is avalable upon request before release.

PREDICTION OF SMOOTH MUSCLE FILAMENT MODEL

Since smooth muscle does not have a sarcomere structure, its detailed structure would be experimentally explored in near future. In order to discuss various force generation mechanisms of biomolecules, we tried to predict a filament model of smooth muscle based on literature. A unit structure of contraction is composed of actin filaments from the textbook explanation. This unit structures will be linked together to form the filament network and the portion connecting filaments would becomes a dens body in the smooth muscle. The contraction of the whole network were possible by shortening of the unit structure.

Structural studies of smooth muscles are explained in various textbooks, mainly by pioneering reports by electron microscopes, but with the recent development of fluorescence microscopy, the visualization of muscle filaments in smooth muscle cells provides new insights. It is being obtained, and it is expected that the detailed structure will be revealed.