Miloš Stojković

Reverse modeling and solid free-form fabrication of sternum implant

The paper presents a case where an implant for a part of the sternum (with costal cartilages) affected by cancer was created and implanted by using the specific reverse modeling method and solid free-form fabrication. The method provides surgeons with a fast and reliable tool for tissue engineering and implantation and therefore improves the quality of life for patients. Digital images of healthy sternum samples were used to develop a reverse modeling algorithm that semi-automatically generates a necessary and sufficient simplification of the tissue geometry to be fabricated in an inexpensive and applicable manner. In this particular case, the redesign of the missing part of the sternum in CAD software took three designer-hours. At the same time, the suitable simplification of the geometry affects the fabrication of simpler and less expensive casting molds. Furthermore, the core of the developed algorithm for the reverse modeling of sternum can be applied in the reverse modeling improvement of other tile (or plate-like) bones.

A case of using the Semantic Interoperability Framework for custom orthopedic implants manufacturing

Abstract The efficiency and effectiveness of the daily practice in orthopedic surgery depend on the availability, interoperability and unique access to a wide set of information, related to the patient’s medical record and diagnosis, domain knowledge and available resources and staff. The most important of the tangible resources, needed for the therapeutic or preventive actions are orthopedic implants. In some cases, the implants may be highly complex and customized products, which need to be manufactured (assembled) on basis of the above information in a shortest possible timeframe. In this paper, the case of the custom orthopedic implants manufacturing is described from the perspective of the collaborative enterprising, with special consideration of the interoperability issues of the involved enterprise collaboration. It is shown how the previously developed Semantic Interoperability Framework can be used to improve the efficiency of the manufacturing and other relevant processes.

Metal Laser Sintering for Rapid Tooling in Application to Tyre Tread Pattern Mould

SLS1, DMLS2 and SLM3 belong to the family of additive manufacturing technologies (we will use term Metal Laser Sintering technologies or MLS abbreviation further in text due to simplicity) that build the geometry of the part by solidification of metal powders using laser power (Kruth et al., 2005; Khaing, 2001).What particularly distinguishes them from other additive technologies is the possibility to produce fully functional metal parts. This feature as well as the ability to create highly complex geometrical shapes, which are often not possible, or at least very difficult to make by conventional manufacturing processes, promote these technologies as perfect candidates for moulding and rapid tooling (RT) (Simchi et al., 2003; Pessard et al. 2008). This is why MLS technologies attract a great attention of mouldmakers for more than a decade. On the other side, the whole range of features of the parts that are manufactured by MLS technologies such as high price of metal powder, porosity, chemical reactivity, then the limitations regard to geometric accuracy, available materials, size of building chambers and necessity for additional post‐processing create a barrier for the application of these technologies in manufacturing of moulds.

DESIGN STUDY OF ANATOMICALLY SHAPED LATTICED SCAFFOLDS FOR THE BONE TISSUE RECOVERY

The current major scaffold design concepts for bone tissue recovery are characterized by labyrinthine design. Their main shortcomings are low level of permeability for new growing tissue, poor design adaptability in regard to particular anatomy and required biomechanical conditions during recovery, as well as very demanding post processing after free form fabrication. In contrast to the most of the existing solutions, latticed scaffold design does not try to imitate the trabecular structure and rejects the labyrinthine concept. It is characterized by simple 3D latticed support structure, which provides a high level of permeability for the new growing tissue cells, and in the same time a proper level of bio-adhesiveness. In addition, its design is easy to manage in order to make it follow the particular anatomical shape and at the same time provide the required elastic properties and structural strength. The paper presents a part of design concept proving process, which is related to stress analysis of the anatomically shaped lattice scaffold design. The aim of the analysis was to identify functional relation between design parameters and elastic properties of the scaffold. The established relations are crucial for getting optimal values of elastic properties of scaffold that are required in a specific trauma-fixation case. The design study shown in the paper was done for the case of lattice scaffold anatomically shaped to the upper part of proximal diaphyseal trauma of rabbit tibia. Design parameters which were altered within the design study were lattice’s struts cross-sectional area, density of the struts and angle of the struts intersection. The analysis showed that structural flexibility of latticelike scaffold may easily be changed through modification of three selected design parameters. In this way, it is confirmed that the proposed type of scaffold has an important capability to adapt its elastic properties to the required values, while being able to keep its great permeability and geometrical consistency to the particular anatomy of trauma region.

Analysis of semantic features in free-form objects reconstruction

Abstract One of the biggest challenges associated with design and digital reconstruction of free forms comes from uniqueness and unrepeatability of these shapes. During digital reconstruction of these forms, the designer has to choose the right set of geometric features and then compose them in a way that will enable the most accurate reconstruction of the geometry. While doing this, the designer primarily relies on personal experience gained through work with free-form objects of similar geometry. In our opinion, the analysis of free-form objects geometry should rely upon semantic interpretation of their geometric and other features, and the greatest challenge of automation of digital reconstruction and free-form object design in general is closely related to automation of semantic interpretation of geometric and other free-form object features. In this paper, a case of chest bone implant digital reconstruction is presented, where a new semantic model called the active semantic model was used for modeling the meaning of geometric elements, that is, the semantic features of a free-form object. The active semantic model and its analogy-based reasoning algorithms have shown themselves as applicable for the automation of semantic interpretation of the unique, unrepeatable, and unpredictable forms of chest bone. Moreover, this semantic model showed the potential to help automate selecting and composing of geometric features for efficient digital reconstruction of the geometry of free forms.

Recognizing Topological Analogy in Semantic Network

Recognizing topological analogy between the parts of semantic network seems to be very important step in the process of semantic categorization and interpretation of data that are embedded into the semantic network. Considering the semantic network as a set of graphs, recognition of topological analogy between the parts of semantic network can be treated as maximum common subgraph problem which falls in the group of exact graph matching problems. In this paper authors propose a new algorithm for maximum common subgraph detection aimed to a specific semantic network called Active Semantic Model (ASM). This semantic network can be represented as the set of labeled directed multigraphs with unique node labels. The structure of these graphs is specific because associations or edges are labeled with several attributes and some of them are related to nodes connected by edge. That kind of association-oriented structure enables associations or edges to play key role in the process of semantic categorization and interpretation of data. Furthermore, this kind of structure enables modeling semantic contexts in a form of semantically designated graphs (of associations). Proposed algorithm is capable of recognizing simultaneously maximum common subgraph of input graph and each of the graphs representing different contexts in ASM semantic network.

MATERIAL CHARACTERIZATION ISSUES IN FEA OF LONG BONES

One of the main issues that arise during preparation of models for subject specific finite element analysis (FEA) of long bones is the accuracy of material characterization. This paper tends to identify the most common sources of material characterization errors, which are sometimes also interconnected with bone geometry reconstruction errors, in order to help in creation of more accurate finite element models of long bones. Reconstruction of patients bone geometry is usually based on medical images obtained by means of computational tomography (CT). Material characterization is performed either by segmentation of the model to characteristic zones that are assigned typical averaged material properties, or by local material mapping, based on bone density values estimated from CT numbers. Some of the main factors that influence material characterization accuracy are the choice of material model, the approach to material properties averaging, x-ray tube parameters, scanner calibration, relations between CT image gray values and bone density and relations between bone density and elastic properties of the bone. The paper brings a comparison of numerical results obtained from a number of subject-specific analyses of human femur, in which the approaches to material modeling were varied. Material modeling was performed using either geometry segmentation with material properties averaging or local material mapping. The results of the analyses were examined and mutually compared, and the influence of material characterization errors to analyses results was identified and explained.

Customized anatomically adjusted plate for fixation of mandible internal fractures

Mandible internal fractures are a common injury because of the mandibles lack of structural support. For the treatment of such injuries various fixation elements are used. In order to improve quality of the orthodontists interventions anatomically correct and geometrically accurate customized implants are necessary. In this paper an example of accurate geometrical model of the customized plate implant for the fixation of mandible fracture is presented. For the creation of such model new method has been developed. This method is based on reverse engineering techniques applied on the CT scan of the specific patient mandible. With the application of this method it is possible to create geometrical model of the customized plate implant which geometry and topology conforms to the shape of the mandible of the specific patient. The side of the implant, which is in contact with a periosteum outer layer of the mandible, is fully aligned with the shape of the mandible outer surface near the fracture. The obtained model(s) can be used for production of plate implants, and/or for simulation of orthodontist interventions.