Regular black holes from Kiselev anisotropic fluid

In this paper, we investigate a generalization of Kiselev black holes by introducing a varying equation of state parameter for the anisotropic fluid surrounding the black hole. We extend this model by allowing $w$ in the expression $p_t(r)/\rho(r) = (3w + 1)/2$ to vary as a function of the radial coordinate, and derive new solutions to the Einstein field equations for this configuration. In particular, we study solutions that describe regular black holes. By choosing specific forms of $w(r)$, we obtain regular black hole solutions, and show that the matter surrounding the black hole can satisfy the weak and strong energy conditions under certain values of parameters analyzed. Due to the generality of this treatment, other categories of black holes can be obtained with particular choices of the parameter of equation of state. Our analysis confirms that the curvature invariants associated with the regular black holes remain finite at the origin, indicating the absence of singularities. We also explore the physical properties of the matter associated with these solutions. Due to the versatility, we suggest the possibility of using this approach as a tool to construct new physical solutions associated with regular black holes or other geometries of interest.