Topology optimization is a design method for maximizing desired performance based on mathematics and physics. While this method can generate innovative designs due to its high degree of freedom, it often produces structures that are too complex to manufacture. In the design of compliant mechanisms using topology optimization, the hinge problem is a well-known manufacturability issue. To address this, Zhu et al. proposed a topology optimization method using moving wide spline curves with constrained ends [1]. This method utilizes a set of wide spline curves to explicitly represent configurations, with control points and thickness defined as design variables. By constraining the ends of the spline curves based on boundary conditions and setting a lower bound for thickness, hinge problem can be avoided. We have developed novel topology optimization methods based on structural representation with spline curves. First, we propose a multi-material topology optimization method for compliant mechanism design to improve performance. This method combines the multi-material level set (MM-LS) method [2] with the topology optimization method using moving wide spline curves with constrained ends. Second, we apply this topology optimization method to fluid-pipe design problems. While the original method [1] represents structures using spline curves, our proposed method uses spline curves to represent fluid domains. Thanks to the constrained ends, this optimization method ensures connectivity from the inlet to the outlet. This connectivity achieves the stability of optimization calculations and faster convergence. The validities of our proposed methods are demonstrated through several numerical examples. REFERENCES [1] B. Zhu, R. Wang, J. Liang, J. Lai, H. Zhang, H. Li, H. Li, S. Nishiwaki, and X. Zhang,“Design of compliant mechanisms: An explicit topology optimization method using end-constrained spline curves with variable width,” Mechanism and Machine Theory, vol. 171, p. 104713, 2022. [2] Y. Wang, Z. Luo, Z. Kang, and N. Zhang, “A multi-material level set-based topology and shape optimization method,” International Journal for Numerical Methods in Engineering, vol. 283, pp. 1570 1586, 2015.