# Multilayered Artificial Dura-Mater Models for a Minimally Invasive Brain Surgery Simulator
## 3 Fabrication Procedure of Dura-Mater Models  
The dura-mater is made of a combination of biological cells and intercellular materials, for example, collagen, elastin, and an interstitial material indicated in Figure 2a,b [20; 21; 22]. Generally, the dura-mater contains approximately 70% water, 20% collagen, 10% elastin, and a small number of other molecules. The tissue exhibits nonlinearity both in terms of the material and geometry. It has various characters, such as incompressibility, inhomogeneity, viscoelasticity, and anisotropy. A new dura-mater model should be better to have similar mechanical properties for use as a surgical simulator model.  
Figure 2: Dura-mater: (**a**) Cross-sectional structure of dura-mater; (**b**) Cross-sectional photograph of porcine dura-mater after hematoxylin-eosin (HE) staining.  
To emulate elastic fibers presented in an actual dura-mater, such as collagen and elastin fibers, non-woven polypropylene fabrics were employed to develop the dura-mater models in our previous paper [23]. In this study, two different non-woven fabrics were chosen for new dura-mater models, as indicated in Table 1. The dura-mater has collagen fibers, which have an anisotropic structure with different sizes of bundles [24]. To mimic the structure of collagen fibers in dura-mater, two different PP non-woven fabrics were employed. An acrylic rubber (BE-1, [PERSON], Osaka, Japan) was used for the elastic part of the dura-mater model. The acrylic rubber is an aqueous rubber, which contains 40% to 50% acrylic resin, 40% to 50% water, 3% defoamer, and 5% surfactant. The fabrication procedure of a dura-mater model is shown in Figure 3[23; 25]. At first, the non-woven fabric was cut to a size of \(100\times 100\) mm\({}^{2}\). The acrylic rubber was diluted with pure water at a weight ratio of 10:7. Two or three non-woven fabrics were stacked in a layer-by-layer manner, and the acrylic rubber aqueous solution was dip-coated. The coated acrylic rubber was dried at about 25 \({}^{\circ}\)C. The acrylic rubber aqueous solution was then spin-coated on one side of the non-woven fabrics. After drying the coated acrylic rubber, the aqueous solution of the acrylic rubber was spin-coated on the other side. In this study, five dura-mater models were prepared as a combination of two different fabrics and acrylic rubber (Figure 4). The dura-mater models shown in Figure 4a-c had two sheets of non-woven fabrics, and the dura-mater models shown in Figure 4d,e had three sheets of the non-woven fabrics. The surface of all dura-mater models was coated by the acrylic rubber. All dura-mater models were prepared at the same thickness that ranged between 0.02 mm and 0.03 mm. The thickness was determined to be the same range of porcine dura-mater thickness to compare the mechanical properties of dura-mater models with the porcine dura-mater in the same condition. The human dura-mater has about twice a larger thickness than the porcine dura-mater [24]. The thickness of dura-mater models can be controlled by changing the thickness of the acrylic rubber layer, or a number of layers of non-woven fabrics. Figure 5a shows the fabricated dura-mater model made of acrylic rubber and non-woven fabrics (soft and soft).  
Figure 4: A cross-sectional structure of developed dura-mater models: (**a**) Acrylic rubber and non-woven fabric (hard and hard); (**b**) Acrylic rubber and non-woven fabric (hard and soft); (**c**) Acrylic rubber and non-woven fabric (soft and soft); (**d**) Acrylic rubber and non-woven fabric (soft and soft and soft); (**e**) Acrylic rubber and non-woven fabric (soft and hard and soft).  
Figure 3: Schematic of the fabrication procedure of dura-mater models.