Geometric modeling and processing

This study presents an alternative process for designing and manufacturing customized trays for dental-whitening treatments. The process is based on a digitized approach consisting of three main stages: design of a reference model, its manufacturing by AM, and thermoforming of the tray. The aim of the study was to develop a high-performance tray, able to guarantee comfort, safety, and efficacy for whitening treatments. To evaluate the patient's experience, some tests under real operating conditions were performed. Twenty people carried out a nighttime treatment of 14 days. Each patient was asked to assess the overall level of satisfaction and the comfort of the tray and its ability to retain the gel. Tooth whitening was also determined according to the VITAPAN scale. All patients involved in the study were satisfied and provided positive feedback about comfort and tightness of the tray. At the end of the treatment, 15 out of 20 patients achieved shade A1 on the VITAPAN scale. The mean improvement in color shades was about 7. These results confirmed the great potential of the proposed dental tray. Its use was proven to guarantee a high level of quality, flexibility, and customization of dental-whitening treatments, improving comfort, safety, and efficacy.

Keywords: additive technologies , bespoke dental trays , custom design , dental engineering , digital manufacturing , esthetic dentistry , tooth whitening

Background: Orthopaedic and Trauma surgery is expected to undergo profound trans-formation as a result of the adoption of 3D technology. Among the various applications, patient specific manufacturing of splints and casts would appear to be, particularly in children, an interesting implementation. This study aims to assess the safety of patient specific 3D casts obtained with a newly developed 3D-scanning devise in a small case series. We therefore conducted a clinical outcome and pre-marketing study in 10 consecutive patients with distal radius fractures treated at an Academic Level I Pediatric Trauma Center. After the application of the 3D cast, patients underwent three consecutive evaluations in the following 21 days. The main outcome measurements were: pain, skin lesions and general comfort, and acceptance of the cast. The three domains were measured with the Visual Analogue Scale (VAS), the NPUAP/EPUAP classification and the Positive affect-Negative affect Scale for Children (PANAS-C), the Self-Assessment Manikin (SAM) clinical psychology tests and a Likert-type five item questionnaire, respectively. A final mechanical analysis of the cast was carried out to confirm product integrity. Results: The results obtained were consistently positive in the investigated domains of general comfort, efficacy of contention and mechanical integrity of the 3D-printed cast as well as in the practicability of the supply chain. Conclusions: This study provides Level IV evidence that patient specific 3D printed casts obtained with a specifically designed software were safe in the management of “buckle” fractures of the distal radius in children. These results encourage to extend the technology to the treatment of more demanding fractures.

Keywords: 3D printing , customized implants , orthopedic device , orthosis modeling , pediatrics , personalized medicine , reverse engineering

In radiotherapy, the treatment of skin tumors requires the application of tissue-equivalent devices in order to avoid the skin-sparing effect, and thus maximize and equalize the dose on the target. In the common clinical practice these devices, called bolus, are standard pads that do not perfectly adapt to the geometry of the patient generating empty spaces at the skin-bolus interface. This phenomenon hinders an efficient planning of the dose to be administered due to the non-adherence and the unpredictability of the position of the air gaps. In this work a workflow for the production of patient-specific bolus in Ecoflex® 00–10 silicone rubber (soft, biocompatible and sterilizable material) is proposed. The process exploits modern Reverse Engineering and Additive Manufacturing technologies to guarantee an accurate compliance with the involved geometries. Significant improvement, with respect to flat boluses, in the adhesion of the medical device to the anatomical region were found through in-vitro testing using replicas of the involved anatomy. Repeatability tests of the positioning performed on the customized bolus led to satisfying results demonstrating the possibility of accurate and predictable treatment planning.

Keywords: CAD modeling , Custom bolus , Molding , Radiotherapy

Home-based rehabilitation is becoming a gold standard for patient who have undergone knee arthroplasty or full knee replacement, as it helps healthcare costs to be minimized. Nevertheless, there is a chance of increasing adverse health effects in case of home care, primarily due to the patients' lack of motivation and the doctors' difficulty in carrying out rigorous supervision. The development of devices to assess the efficient recovery of the operated joint is highly valued both for the patient, who feels encouraged to perform the proper number of activities, and for the doctor, who can track him/her remotely. Accordingly, this paper introduces an interactive approach to angular range calculation of hip and knee joints based on the use of low-cost devices which can be operated at home. First, the patient's body posture is estimated using a 2D acquisition method. Subsequently, the 3D posture is evaluated by using the depth information coming from an RGB-D sensor. Preliminary results show that the proposed method effectively overcomes many limitations by fusing the results obtained by the state-of-the-art robust 2D pose estimation algorithms with the 3D data of depth cameras by allowing the patient to be correctly tracked during rehabilitation exercises.

Keywords: 3D model , Body tracking , Data fusion , Joints estimation , RGB-D camera

In this paper an interactive computational methodology was developed assuming that shape and size optimization of flexible components can significantly improve energy absorption or storage ability in assembled systems with flexible components (AS-FC). A radial basis functions mesh morphing formulation in non-linear numerical finite element analysis, including contact problems and flow interaction, was adopted as optimal design method to optimize shape and size design parameters in AS-FC. Flexible components were assembled in finite element environment according to functional ISO-ASME tolerances specification; non-linear structural analysis with flow interaction analysis was performed. The results of the study showed that the proposed method allows to optimize the shape and size of the flexible components in AS-FC maximizing the system's ability to absorb or store energy. The potentiality of the method and its forecasting capability were discussed for the case study of an automotive crash shock in which the specific energy absorption was increased by over 40%. The case studied refers to a simple flexible component geometry, but the method could be extended to systems with more complex geometries.

Keywords: Crash shock absorber , ISO-ASME tolerances specification , Radial basis functions , Shape and size optimization , Specific energy absorption

In the Cultural Heritage field, the choice of materials and exhibit structures is essential to properly house and support artifacts without causing damage or deterioration. This problem is even more evident in the case of finds made of stone for which, due to their weight, a proper selection and dimensioning of the relative supports is required. In fact, without adequate support, this can result in stress concentrations that could compromise the artifact's state of conservation. As a consequence, more often such exhibition supports are customized items, that are designed and manufactured to meet specific functional and artistic setup needs. In this context, the paper presents a design approach that combines topology optimization and additive manufacturing techniques to develop customized support structures which undertake the twofold purpose of preserving the artifact and making it available for the exhibition in the museum. The proposed approach has been assessed through the case study of a sandstone Ionic capital hosted in the Brettii & Enotri Museum in Cosenza (Italy). The proposed approach is therefore meant as a guideline for the design of customized exhibit supports especially in the case of sandstone artifacts with a complex shape or a conservation condition that requires specific attention.

Keywords: Additive manufacturing , Cultural heritage , Design methods , Exhibit supports , Photogrammetry , Topology optimization

Using the EEG features extracted from the EEG signals, the presented study investigates differences in the cognitive load posed on engineers while 3D CAD modelling in two different conditions, depending on the visual representations used as stimulus - a 2D and a 3D technical drawing of parts. The results indicate a higher cognitive load during the 2D drawing task. In addition, common indicators of the ongoing spatial information processing were recognised - a suppression of parietal and occipital alpha power, a higher frontal theta, and differences in theta power between the hemispheres.

Keywords: brain activity , computer-aided design (CAD) , design cognition , electroencephalography , visualisation

This paper presents an approach to identify and validate indicators for the use of virtual prototypes (VPs) during distributed design activities. Identification of indicators is based on various data collection methods (interview, observational methods, literature review), whereas their validation and usage are based on the protocol analysis method. Using the approach, four indicators are proposed for a design review activity context. These indicators describe both the individual and collaborative use of the VP. To further delineate collaborative use, indicators distinguish personal and shared viewpoints, providing insights into synchronous collaboration. The implementation of the proposed approach and the four identified indicators were demonstrated on a design review session. The preliminary results show that, in a distributed design review activity, team members spend a small fraction of the time viewing the VP. On a team level, about half of that time was spent viewing the VP individually, while another half of time was spent working simultaneously (either synchronously or asynchronously) in pairs, triplets or four-members. However, this distribution varies among team members. Furthermore, team members utilised both personal and shared viewpoints, again varying among team members. Finally, instances of using the VP were usually brief but occurred throughout the whole session. Based on the conducted study, it can be argued that the design review involves continuous use of the VP throughout the session, either individually or with others (sharing the view or not). The proposed approach, indicators and preliminary results provide new insights for practitioners who develop tools for VP use, design teams that want to improve their efficiency in using VPs, and scholars that study the collaboration within distributed design activities.

Keywords: Collaboration indicators , Collaborative CAD , Distributed design activities , Distributed team , Virtual prototype (VP)

In this work, a Coarse-Grained Lattice Spring Model to characterize the mechanical behavior of human mesenchymal stem cells subjected to nanoindentation measurements is presented. The model simulated the action of adhesive structures acting on cells, necessary for attaching them to a substrate, and a nanoindentation process, performed by means of an atomic force microscope with a spherical tip. Cells were hypothesized to behave as elastic materials and the model included several subcellular components such as cell cortex and cytoskeleton. The lattice spring model was integrated within an optimization algorithm that iteratively compared the force-indentation curve numerically predicted to the data experimentally obtained, until a best fit condition was reached. The computed mechanical properties of the cell were compared to those obtained via the Hertz contact theory and finite element modelling, showing a good agreement. The proposed lattice spring model appears as a promising tool that can be used, with a very low computational cost, to characterize cell materials and other biological materials.

Keywords: Cell mechanical properties , Lattice spring models , Nanoindentation , Stem cells

The diffusion of Fab Labs and the continuous development of Additive Manufacturing technologies are undoubtedly two relevant phenomena nowadays. The former fuels the latter and vice versa, but their mutual relationship has not been systematically explored so far. This paper presents an exploratory study based on a survey, in which various aspects of the use of 3D printers in Fab Labs are investigated. The results show how different scales of Fab Labs are present in terms of investments made in 3D printing, as well as work purposes are not negligible for many attendees. In addition, the outcomes of the survey show that 3D printers are considered easy to use, as well as manufactured parts are deemed satisfactory. Despite this, there are still some barriers to boosting the market of domestic 3D printers for Fab Lab visitors.

Keywords: 3D printers , CAD , Design for Additive Manufacturing , Fab Labs , Skills

There is a large body of research devoted to identifying the complexity of structures in networks. In the context of network theory, a complex network is a graph with nontrivial topological features—features that do not occur in simple networks, such as lattices or random graphs, but often occur in graphs modeling real systems. The study of complex networks is a young and active area of scientific research inspired largely by the empirical study of real-world networks, such as computer networks and logistic transport networks. Transport is of great importance for the economic and cultural cooperation of any country with other countries, the strengthening and development of the economic management system, and in solving social and economic problems. Provision of the territory with a well-developed transport system is one of the factors for attracting population and production, serving as an important advantage for locating productive forces and providing an integration effect. In this paper, we introduce a new method for quantifying the complexity of a network based on presenting the nodes of the network in Cartesian coordinates, converting to polar coordinates, and calculating the fractal dimension using the ReScaled ranged (R/S) method. Our results suggest that this approach can be used to determine complexity for any type of network that has fixed nodes, and it presents an application of this method in the public transport system.

Keywords: complexity , fractal , Hurst exponent H , network , public transport

The compression behaviour in quasi-static and dynamic conditions of cellular materials is crucial for their applications both for ensuring structural strength and high energy absorption capability. Despite the recent progress made in understanding the experimental observations, analytical and numerical modelling still requires improvements in the Representative Volume Element (RVE) identification that can be uncertain due to the limited dimensions of the investigated specimens and to the cell inhomogeneity. The objective of this paper is to implement a material model able to consider the statistical distribution so that its effect can be quantitatively highlighted, mitigating uncertainty of the RVE identification. The applied methodology started with morphological and topological analyses on samples extracted from an ingot of AA7075T6 foam, which was manufactured by compact powder technology. Quasi-static and dynamic experimental compression tests have been carried out and compared with 3D mesoscale numerical simulations in order to correlate the mechanical behaviour of the foam to the cell characteristics. Finally, an equivalent material model, which is a function of the statistical distributions of cells morphology and topology, has been proposed and analytically verified.

Keywords: Aluminium foam , Cellular material , High strain rate , Homogeneous formulation , RVE , SHPB

Within the literature concerning modern machine learning techniques applied to the medical field, there is a growing interest in the application of these technologies to the nephrological area, espe-cially regarding the study of renal pathologies, because they are very common and widespread in our society, afflicting a high percentage of the population and leading to various complications, up to death in some cases. For these reasons, the authors have considered it appropriate to collect, using one of the major bibliographic databases available, and analyze the studies carried out until February 2022 on the use of machine learning techniques in the nephrological field, grouping them according to the addressed pathologies: renal masses, acute kidney injury, chronic kidney disease, kidney stone, glomerular disease, kidney transplant, and others less widespread. Of a total of 224 studies, 59 were analyzed according to inclusion and exclusion criteria in this review, considering the method used and the type of data availa-ble. Based on the study conducted, it is possible to see a growing trend and interest in the use of machine learning applications in nephrology, becoming an additional tool for physicians, which can enable them to make more accurate and faster diagnoses, although there remains a major limitation given the diffi-culty in creating public databases that can be used by the scientific community to corroborate and even-tually make a positive contribution in this area.

Keywords: artificial intelligence , deep learning , machine learning , renal pathology

The present paper presents the development of a novel procedure for the modeling of Surgical Cutting Guides (SCGs) exploiting an implicit modeling approach. As discussed in the text, this approach allows for a streamlined and efficient design of this type of medical device. A procedural approach based on the application of a series of a priori-known implicit modeling function allows the generation of personalized surgical guides starting from the i) patient's anatomy and ii) clinical decisions made by the medical staff. The CAD procedure is detailed in the text; achieved results are discussed and compared with a traditional CAD modeling approach on three case studies.

Keywords: CAD , Implicit Modelling , Patient-Specific Instrument , Personalized Medical Device

Dealing with the design of personalized medical devices, mass production is not an option that can be hypothesized. Indeed, a cumbersome production process must be considered in such cases, mainly to account for a delicate design phase that needs to take into consideration, as input, an anatomy that vary each time. This article discusses the development of a statistical tool able to support the design of patient-specific devices. By expanding the classical formulation of the Statistical Shape Model (SSM) with the introduction of multiple levels of information within the same model, the authors have experimented with the concept of an “enhanced SSM”. While the traditional SSM only provides information on the variations that a class of shapes can manifest, the eSSM may include more levels of information. The article discusses two possible mathematical formulations of such statistical tool. Its application to the design of custom-made pelvic implants is discussed. Such application scenario is described starting from the generation of the eSSM for the pelvis. The features of interest considered in this paper are the centers of the acetabular regions of the pelvis, the segmentation of the anatomy in a series of semantical regions that must be considered when developing a load-bearing implant. Finally, the conclusions of this research are drawn and discussed together with possible future development of eSSMs.

Keywords: Biomedical engineering , Custom implant design , Human modelling , Pelvis , SSM , Statistical shape analysis

Well-established advantages as design freedom, acceleration of design-to-manufacturing cycle, decreased internal logistics reflect on the wider application of Additive Manufacturing as the main manufacturing process. However, its application to large-scale components manufacturing is still an open challenge, because of the limited printing volume available in off-the-shelf machines, slow manufacturing process, and low production volume. After a review of the available contributions, this paper proposes a methodology to handle large-scale 3D models, to be applied before the slicing process. The methodology is based upon the large-scale component subdivision into subparts within CAD environments, using an innovative approach tailored to the problem, and exploits the multi-head capability of collaborative large-scale AM machines. A UAV fixed-wing shows the positive effects in terms of speeding up the manufacturing process. The approach can significantly reduce the printing time of large parts, but a new generation of Additive Manufacturing machines is required to exploit the methodology.

Keywords: Additive Manufacturing , Aerospace , Automotive , Collaborative Manufacturing , Large-Scale Part , Multi-head Extruder

The panel method is a potential-flow numerical approach that shows valuable performances to solve aerodynamic problems in the preliminary design stages. It shows a lower computational effort compared with Computational Fluid Dynamics, wind tunnel tests or ‘on the field' experiments. However, the 3D surface discretization in rectangular panels is tedious and must be often carried out manually from scratch. Moreover, the panel method can't be used to compute the overall drag force due to strong assumptions. To solve these two challenging aspects, the authors propose a voxel-based fluid dynamic approach integrating its programmed functions within a panel method. Voxelization is used to automatically distribute coherently the panels along the external surface of a 3D model in an automated way. A parametric study is included to demonstrate how the voxel resolution affects the aerodynamic results and provide guidelines for future research. Overall drag is estimated using corrections for both the skin friction and the form drag sources. The Ahmed body case study is included and demonstrates a good agreement between the voxel-based fluid dynamics approach and the literature benchmarking values, but with lower computational efforts. Further studies involving more complex shapes should be performed to better understand the performances and limitations of the approach.

Keywords: Ahmed body , Automotive , CAD , Conceptual Design , Panel method , Voxelization

The Panel method is an approach for the estimation of the lift of 3D models which is faster than CFD. This can be useful especially in the conceptual design stage where several configurations should be evaluated in a reduced time with a limited computational cost. However, the meshing of the 3D body surface with rectangular panels can be a time-consuming activity because the designer should define from scratch a cloud of points that matches the external surfaces of the tested object to obtain consistent panelling. Therefore, a voxelization-based methodology has been developed to obtain the panels' position, speeding up and automating the model preparation process. The obtained discretization has been integrated into a panel method available in the literature. Four case studies, of increasing complexity, have been analyzed to investigate the capability of the innovative voxel-based panel methodology. A parametric study has been carried out to study the effect of the voxel grid dimension on the accuracy of the results. Benchmarking values of lift coefficient obtained from literature or xFoil software have been used to evaluate the precision that can be achieved with this approach. The results show a good agreement between the voxel-based panel method and the literature when the overall pressure distributions and aerodynamic coefficient values are considered. Higher errors are noticed with drag.

Keywords: Fluid dynamics , Panel method , Potential flow , Voxelization

The interest of industrial companies for the Additive Manufacturing (AM) technology is growing year after year due to its capability of producing components with complex shapes that fit industrial engineering necessities better than traditionally manufactured parts. However, conventional Computer-Aided Design (CAD) software are often limited for the design and representation of complex geometries, especially when dealing with lattice structures: these are bio-inspired structures composed of repeated small elements, called struts, which are combined to shape a unit cell that is repeated across a domain. This design method generates a lightweight but stiff component. The scope of this work is to analyse the problem of the lattice structures representation in 2 D technical drawings and propose some contributions to support the development of Standards for their 2 D representation. This work is focused on the proposal of rules useful to represent such hierarchic structures. Python language and the open-source software FreeCadâ„¢ are used as a software platform to evaluate the suitability and usability of the proposed representation standard. This is based on simplified symbols to describe complex lattice structures instead of representing all the elements which constitute the lattice. The standard is thought to be used in technical 2 D drawings where assemblies are represented and lattice components are used (e.g. parts assembly, maintenance, parts catalogues). A case study is included to describe how the proposed standard could be integrated into a 2 D assembly drawing, following technical product documentation production typical workflow.

Keywords: Additive manufacturing , design , drawing standards , ISO standards , lattice structures

In this work a new approach for the creation of Articulated Total Body (ATB) models for person-specific multi-body simulations is presented, with the main aim of overcoming limitations related to classical multi-ellipsoids ATB models, based on regression equations having only the weight and the height of the subject as input. The new methodology is based on a Statistical Shape Model (SSM), morphable according to up to 24 input parameters: the SSM was obtained from Principal Component Analysis (PCA), applied on a wide database of 3D human scans (CAESAR). The so obtained geometry can be segmented automatically to generate body segments with the respective inertial properties (mass, principal moments of inertia, and centres of mass location). The routine has been tested on a random set of 20 male subjects and the classical multi-ellipsoids models were compared to these in terms of inertial properties and 3D external geometry: the highest differences were registered at the abdomen and the thighs for what concerns the mass (60%), principal moments (75%) and centres of mass (50 mm) properties; the trunk, the shoulder and the calves are the most critical areas for the external geometry (average distance between the anthropomorphic and ellipsoids models equal to 50 mm). A contribution has been made to build person-specific multibody models. This is a valuable method since approximations made by multi-ellipsoidal models have resulted to be relevant at specific body areas, and personalised models can be a support to design and to forensic analyses.

Keywords: 3D parametric human model , Articulated total body , Forensic biomechanics , Multibody analysis , Principal component analysis (PCA)