## 5 Lattice Structures in Medical Devices and Applications
### Design Criteria for Cellular Scaffolds in Spinal Implants
At the same time, a porous design can reduce implant stiffness, helping to alleviate stress shielding and reduce the degree of bone resorption around the implant site [106]. To achieve these goals, open cellular structures are increasingly used in orthopedic implants due to their increased surface area and capacity to support bone ingrowth. These structures are designed to reduce the implant's stiffness, promote better load sharing between the implant and the bone, and enhance the biological integration of the implant into the body [129,130]. By carefully designing the topological characteristics of the scaffold,such as porosity, pore size, strut thickness, shape, and overall mechanical properties, implant developers can create devices that not only support bone regeneration, but also reduce the risk of long-term complications, such as bone resorption and implant loosening [89,129]. The pore size plays a particularly important role, as it must be large enough to allow cells and blood vessels to infiltrate the scaffold, while still providing sufficient mechanical stability [87]. Strut thickness and pore shape are also important design considerations, as these factors influence both the implant's structural integrity and its ability to interact with surrounding bone tissue [104,106]. Together, these variables affect the mechanical performance of the implant and its capacity to support the regeneration of healthy bone tissue. Scaffold designs for orthopedic applications must effectively perform under prolonged physiological loading, while accommodating variations in bone healing rates, which differ significantly with age [131,132]. In younger individuals, bone fractures may take up to six weeks to support weight-bearing and approximately one year for full integration, while elderly individuals often experience much slower repair rates [132]. This variation necessitates the careful consideration of scaffold properties tailored to different patient profiles. A critical challenge lies in managing the balance between mechanical properties and structural functionality. Scaffolds that demonstrate promising mechanical performance in vitro often fail in vivo due to poor vascularization and insufficient cell infiltration [132]. Achieving efficient vascularization and cellular integration requires an optimal porous architecture that supports both mechanical stability and biological activity. Advanced testing protocols are essential to evaluate scaffold designs under conditions that replicate real-world physiological loading. These protocols should simulate cyclic loading, nutrient perfusion, and in vivo biochemical conditions to predict scaffold behavior accurately [133, 134, 135]. By addressing these challenges and integrating innovative materials, lattice designs can better support vascularization, cell infiltration, and prolonged physiological loading, ultimately improving outcomes in tissue engineering applications [131,133]. The success of spinal implants relies on a carefully balanced combination of functional, morphological, and structural design elements. Using advanced materials and open cellular structures in orthopedic implants allows for an improved biomechanical performance, enhanced osseointegration, and better patient outcomes [135]. Continued research into scaffold design, including the optimization of porosity and mechanical properties, will further advance the development of next-generation implants that better replicate the natural ECM and improve the success rates of orthopedic surgeries.