Extension of the Voronoi Diagram Algorithm to Orthotropic Space for Material Structural Design.

Nowadays, the interaction of additive technologies and methods for designing or optimizing porous structures has yielded good results. Construction with complex microarchitectures can be created using this approach. Varying the microarchitecture leads to changes in weight and mechanical properties. However, there are problems with geometry reconstruction when dealing with complex microarchitecture. One approach is to use Voronoi cells for geometry reconstruction. In this article, an extension of the Voronoi diagram algorithm to orthotropic space for material structural design is presented. The inputs for the method include porosity, ellipticity, and ellipticity direction fields. As an example, a beam with fixed end faces and center kinematic loading was used. To estimate robust results for different numbers of clusters, 50, 75, and 100 clusters are presented. The porosity for smoothed structures ranged from 21.5% up to 22.8%. The stress-strain state was determined for the resulting structures. The stiffness for the initial and smoothed structures was the same. However, in the case of 75 and 100 clusters, local stress factors appeared in the smoothed structure. The maximum von Mises stress decreased by 20% for all smoothed structures in the area of kinematic loading and increased by 20% for all smoothed structures in the area of end faces.

Consecutive Transcutaneous and Epidural Spinal Cord Neuromodulation to Modify Clinical Complete Paralysis-the Proof of Concept.

Objective: To evaluate the effect of transcutaneous (tSCS) and epidural electrical spinal cord stimulation (EES) in facilitating volitional movements, balance, and nonmotor functions, in this observational study, tSCS and EES were consecutively tested in 2 participants with motor complete spinal cord injury (SCI). Participants and Methods: Two participants (a 48-year-old woman and a 28-year-old man), both classified as motor complete spinal injury, were enrolled in the study. Both participants went through a unified protocol, such as an initial electrophysiological assessment of neural connectivity, consecutive tSCS and EES combined with 8 wks of motor training with electromyography (EMG) and kinematic evaluation. The study was conducted from May 1, 2019, to December 31, 2021. Results: In both participants, tSCS reported a minimal improvement in voluntary movements still essential to start tSCS-enabled rehabilitation. Compared with tSCS, following EES showed immediate improvement in voluntary movements, whereas tSCS was more effective in improving balance and posture. Continuous improvement in nonmotor functions was found during tSCS-enabled and then during EES-enabled motor training. Conclusion: Results report a significant difference in the effect of tSCS and EES on the recovery of neurologic functions and support consecutive tSCS and EES applications as a potential therapy for SCI. The proposed approach may help in selecting patients with SCI responsive to neuromodulation. It would also help initiate neuromodulation and rehabilitation therapy early, particularly for motor complete SCI with minimal effect from conventional rehabilitation.

Method of computational design for additive manufacturing of hip endoprosthesis based on basic-cell concept.

Endoprosthetic hip replacement is the conventional way to treat osteoarthritis or a fracture of a dysfunctional joint. Different manufacturing methods are employed to create reliable patient-specific devices with long-term performance and biocompatibility. Recently, additive manufacturing has become a promising technique for the fabrication of medical devices, because it allows to produce complex samples with various structures of pores. Moreover, the limitations of traditional fabrication methods can be avoided. It is known that a well-designed porous structure provides a better proliferation of cells, leading to improved bone remodeling. Additionally, porosity can be used to adjust the mechanical properties of designed structures. This makes the design and choice of the structure's basic cell a crucial task. This study focuses on a novel computational method, based on the basic-cell concept to design a hip endoprosthesis with an unregularly complex structure. A cube with spheroid pores was utilized as a basic cell, with each cell having its own porosity and mechanical properties. A novelty of the suggested method is in its combination of the topology optimization method and the structural design algorithm. Bending and compression cases were analyzed for a cylinder structure and two hip implants. The ability of basic-cell geometry to influence the structure's stress-strain state was shown. The relative change in the volume of the original structure and the designed cylinder structure was 6.8%. Computational assessments of a stress-strain state using the proposed method and direct modeling were carried out. The volumes of the two types of implants decreased by 9% and 11%, respectively. The maximum von Mises stress was 600 MPa in the initial design. After the algorithm application, it increased to 630 MPa for the first type of implant, while it is not changing in the second type of implant. At the same time, the load-bearing capacity of the hip endoprostheses was retained. The internal structure of the optimized implants was significantly different from the traditional designs, but better structural integrity is likely to be achieved with less material. Additionally, this method leads to time reduction both for the initial design and its variations. Moreover, it enables to produce medical implants with specific functional structures with an additive manufacturing method avoiding the constraints of traditional technologies.

Numerical and Experimental Study of a Lattice Structure for Orthopedic Applications.

Prosthetic reconstructions provide anatomical reconstruction to replace bones and joints. However, these operations have a high number of short- and long-term complications. One of the main problems in surgery is that the implant remains in the body after the operation. The solution to this problem is to use biomaterial for the implant, but biomaterial does not have the required strength characteristics. The implant must also have a mesh-like structure so that the bone can grow into the implant. The additive manufacturing process is ideal for the production of such a structure. The study deals with the correlation between different prosthetic structures, namely, the relationship between geometry, mechanical properties and biological additivity. The main challenge is to design an endoprosthesis that will mimic the geometric structure of bone and also meet the conditions of strength, hardness and stiffness. In order to match the above factors, it is necessary to develop appropriate algorithms. The main objective of this study is to augment the algorithm to ensure minimum structural weight without changing the strength characteristics of the lattice endoprosthesis of long bones. The iterative augmentation process of the algorithm was implemented by removing low-loaded ribs. A low-loaded rib is a rib with a maximum stress that is less than the threshold stress. Values within the range (10, 13, 15, 16, 17, 18, 19 and 20 MPa) were taken as the threshold stress. The supplement to the algorithm was applied to the initial structure and the designed structure at threshold stresses σf = 10, 13, 15, 16, 17, 18, 19 and 20 MPa. A Pareto diagram for maximum stress and the number of ribs is plotted for all cases of the design: original, engineered and lightened structures. The most optimal was the designed "lightweight" structure under the condition σf = 17 MPa. The maximum stress was 147.48 MPa, and the number of ribs was 741. Specimens were manufactured using additive manufacturing and then tested for four-point bending.

The Automatization of the Gait Analysis by the Vicon Video System: A Pilot Study.

The quality of modern measuring instruments has a strong influence on the speed of diagnosing diseases of the human musculoskeletal system. The research is focused on automatization of the method of gait analysis. The study involved six healthy subjects. The subjects walk straight. Each subject made several gait types: casual walking and imitation of a non-standard gait, including shuffling, lameness, clubfoot, walking from the heel, rolling from heel to toe, walking with hands in pockets, and catwalk. Each type of gait was recorded three times. For video fixation, the Vicon Nexus system was used. A total of 27 reflective markers were placed on the special anatomical regions. The goniometry methods were used. The walk data were divided by steps and by step phases. Kinematic parameters for estimation were formulated and calculated. An approach for data clusterization is presented. For this purpose, angle data were interpolated and the interpolation coefficients were used for clustering the data. The data were processed and four cluster groups were found. Typical angulograms for cluster groups were presented. For each group, average angles were calculated. A statistically significant difference was found between received cluster groups.

Structural Design Method for Constructions: Simulation, Manufacturing and Experiment.

The development of additive manufacturing technology leads to new concepts for design implants and prostheses. The necessity of such approaches is fueled by patient-oriented medicine. Such a concept involves a new way of understanding material and includes complex structural geometry, lattice constructions, and metamaterials. This leads to new design concepts. In the article, the structural design method is presented. The general approach is based on the separation of the micro- and macro-mechanical parameters. For this purpose, the investigated region as a complex of the basic cells was considered. Each basic cell can be described by a parameters vector. An initializing vector was introduced to control the changes in the parameters vector. Changing the parameters vector according to the stress-strain state and the initializing vector leads to changes in the basic cells and consequently to changes in the microarchitecture. A medium with a spheroidal pore was considered as a basic cell. Porosity and ellipticity were used for the parameters vector. The initializing vector was initialized and depended on maximum von Mises stress. A sample was designed according to the proposed method. Then, solid and structurally designed samples were produced by additive manufacturing technology. The samples were scanned by computer tomography and then tested by structural loads. The results and analyses were presented.