**1. Introduction**

The modern approach for design implants and prostheses implies patient-oriented solutions. Such an approach involves not only new manufacturing methods but also a new vision of the product. Additive manufacturing allows production constructions with complex geometry. However, the solution for the automation of the design of such products is still open. So, nowadays lattice constructions have become popular for this purpose. Yet, the dependence between the different geometries of the lattice, the mechanical properties, and the biological adaptive is being researched [1–3]. Additionally, a manifestation of the brittle properties and the geometry deviations after manufacturing is still an issue of the day [4–7]. By changing the materials and melting modes [8–10], the mechanical parameters can be improved or vice versa. Despite the aforementioned difficulties, it is obvious that additive manufacturing and patient-oriented design can notably increase the quality of the medical treatments.

This article is focused on an approach for the structural design method. Previously, a method for designing a lattice endoprosthesis for long bones was developed [11]. The endoprosthesis was manufactured and passed clinical experiments. The developed approach was generalized. The main idea is based on the bone adaptation analogy. It is known that adaptation can be formulated by Wolff's law [12]. To describe bone tissue orthotropy, a fabric tensor is used. The fabric tensor is also used to calculate the stiffness tensor [12,13]. The foundation of the adaptation model is an alignment of the stress and stiffness tensors.

**Citation:** Bolshakov, P.; Kharin, N.; Kashapov, R.; Sachenkov, O. Structural Design Method for Constructions: Simulation, Manufacturing and Experiment. *Materials* **2021**, *14*, 6064. https:// doi.org/10.3390/ma14206064

Academic Editor: Aleksander Muc

Received: 25 August 2021 Accepted: 12 October 2021 Published: 14 October 2021

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In terms of the fabric tensor, it means that the orthotropic directions are equal to the stress principal directions [13,14]. The widespread approach is to use representative volumes to determine the fabric tensor and the effective mechanical properties [15,16].

It has been shown [17–19] that implants interact with bone tissue and that the structure and the microstructure of the implant influence the quality of this interaction. Additive manufacturing allows the generation of solid irregular or lattice geometry [20,21], but on the other hand, local microporosity decreases fatigue resistance. Classical post-processing, such as tempering, allows the counteraction of the negative sides of the technology [22,23]. Despite the aforementioned technological barriers, the opening opportunities are promising. The ability to design material within a product opens up new possibilities in patientspecific prostheses [24,25]. The complexity of such an approach appears in defining the external loads and the formulation criteria of the design [26,27]. A novel approach is the use of additive manufacturing technology for liquid crystal elastomers, the exceptional properties of which show good usage in a range of applications in the fields of biology and medicine [28–30].

In this article, a method of structural design is presented. An example of structurally designed construction is presented. The designed and regular constructions were manufactured and compared in natural experiments.
