# Design and Optimization of Lattice Structures: A Review
## 5 Summary and Overview  
This paper reviews the lattice structures by retrieving a lot of appropriate literature. First, the lattice structures are distinguished and compared with foams and honeycombs, and the definition and classification of lattice structures are explained. Second, the properties of lattice structures are analyzed in detail, and the wide applications of lattice structures are introduced. The primary work of this paper is to review methods of designing and optimizing of uniform lattice structures and non-uniform lattice structures. It is clear in the article that the outstanding properties of lattice structures are closely related to the topology structures of unit cells. As for the design of lattice structures, it is mainly based on the design of unit cells. Through the review of lattice structure literature, some problems in the design of lattice structures are found. If these problems are not solved in time, the development of lattice structures will be limited as following:  
1. In the current researches of lattice structures, the design of cell topological shape is insufficient, and most of the literature are still studying the existing cell structures. The performance of cell structure is directly related to lattice structure, so it is necessary to design cell topology with special performance. [PERSON] et al. [PERSON] et al. (2016) made a preliminary exploration of the potentialities of H-C and H-C+D lattice structures. 2. In the topology optimization of lattice structures, most researcher are still focused on the strut's sizes. The single optimization is not conducive to the design of lattice structures. Only from the point of view of optimizing struts, the lattice structures cannot meet the specific requirements. [PERSON] et al. [PERSON] et al. (2017) proposed the geometry projection method, to optimizing the multi-material lattice structures. This is a new method to optimize lattice structure, which enriches the method of lattice topology optimization. However, as the applications of lattice structures are more and more extensive, the design methods are more and more diverse. At present, the investigations of lattice structures are not limited to regular, and irregular structures. The application of materials with uniform Poisson's ratio and non-uniform  
Figure 22: Non-uniform lattice structure based on HOC method [PERSON] et al. (2016). Poisson's ratio enriches the lattice structures. Moreover, the performance requirements of lattice structures are different in various fields. In addition to lightweight, high strength, and other perfect properties, lattice structures with multiple properties are the most popular material in the future. It has become the basic requirements of the application field to develop lattice structures to meet specific requirements. Additionally, the materials used in lattice structures are more and more diverse. Metal materials, ceramic materials, rubber materials, composite materials and other materials are widely used to design lattice structure. In a word, lattice structures are hot materials in the future development of various industries. Because of the outstanding performance and different characteristics, lattice structures will be widely used in biological tissue engineering, aerospace, automation manufacturing, and other fields that need lightweight and high-strength structure in the future. With the development of processing technology, such as additive manufacturing technology, the processing methods of lattice structures have also made a breakthrough. Additive manufacturing technology not only provides good opportunities for researchers to design lattice structure, but also brings great challenges. Therefore, with the development of multi-disciplinary interaction and based on the advantages of additive manufacturing technology, the development trend of lattice structure is predicted in the following directions:  
1. Multi-material lattice structures.