Roberto Meneghello

Powder-based 3D printing for bone tissue engineering

Bone tissue engineered 3-D constructs customized to patient-specific needs are emerging as attractive biomimetic scaffolds to enhance bone cell and tissue growth and differentiation. The article outlines the features of the most common additive manufacturing technologies (3D printing, stereolithography, fused deposition modeling, and selective laser sintering) used to fabricate bone tissue engineering scaffolds. It concentrates, in particular, on the current state of knowledge concerning powder-based 3D printing, including a description of the properties of powders and binder solutions, the critical phases of scaffold manufacturing, and its applications in bone tissue engineering. Clinical aspects and future applications are also discussed.

The precision of fit of cast and milled full-arch implant-supported restorations.

PURPOSE The purpose of this study was to investigate the marginal precision of computer numeric control-milled frameworks fabricated of grade 4 commercially pure titanium or cobalt-chrome alloy through digital technology and to compare them with conventional cast frameworks. MATERIAL AND METHODS A titanium cast of a mandibular arch with six implant analogs was used as a master. The master cast was measured with a coordinate measuring machine. Fifteen rigid anatomic frameworks were created on the master cast in cast gold alloy and milled in titanium or cobalt-chrome material. The fifteen anatomic frameworks were measured in the same manner as the master cast. While the milled frameworks were measured once, at the end of the milling process, the cast anatomic frameworks were measured twice: immediately after the casting and divesting procedures and again after a technical adaptation procedure. Each anatomic framework was weighed. To compare the measurements obtained from each group of frameworks, descriptive statistics were calculated and one-way analysis of variance was performed, with values considered statistically significant at P < .05. RESULTS The mean weight of the cast frameworks was 33.41 g, the cobalt-chrome frameworks weighed 18.12 g on average, and the titanium frameworks averaged 8.7 g. The mean values for three-dimensional deviation of the center point position for each group of frameworks were 261 μm (cast frameworks before adaptation), 49 μm (cast frameworks after adaptation), 26 μm (milled frameworks in cobalt-chrome), and 26 μm (milled frameworks in titanium). CONCLUSIONS Within the limitations of this in vitro study, absolute passive fit cannot be achieved, regardless of material and fabrication technique. Anatomic milled frameworks fabricated in titanium or cobalt-chrome presented reduced center point deviation compared to cast frameworks. Titanium frameworks weighed less than cobalt-chrome and cast gold alloy frameworks.

Unilateral masseter muscle hypertrophy: morphofunctional analysis of the relapse after treatment with botulinum toxin.

Abstract This is a case of unilateral masseter muscle hypertrophy (MMH) treated with botulinum toxin (NHAI - normalised hemi-facial asymmetry index improvement from 5.48 to 3.04). After 19 months, the treatment was repeated because of hypertrophy relapse (NHAI increase up to 6.82). The volume variations in the masseter area were monitored during 25 months using a laser scanner to compute facial volume. In order to relate the cause of hypertrophy and relapse to the presence of parafunctional activities, a nocturnal electromyography (EMG) study was conducted with positive results (nocturnal parafunctions of patients 4074.99 μV to be compared with a control group value of 1644.63 μV). The lack of the left inferior molars and the consequent right occlusal support seemed to justify the hypertrophy of right masseter (MMRight-POC [percent overlapping coefficient] 91.9%). However, the prosthetic rehabilitation did not prevent relapse in the same muscle. The EMG analysis of both the muscular activation (MMRight-POC 66.0% after relapse) and inhibition activity in Maximum Voluntary Clench (MVC) resulted in contradictory conclusions. At present, the available knowledge regarding MMH physiopathology is very limited and does not support a therapeutic rationale for relapse prevention.

Shape analysis of a parametric human lens model based on geometrical constraints

Several simple models, such as conicoid models, are usually adopted to describe the surfaces of the human crystalline lens; unfortunately they do not provide a continuous junction between the anterior and the posterior surface of the lens and then they cannot qualify for biomechanical simulation. Vice versa, more complex mathematical models give a continuous junction between the anterior and the posterior surface, but do not provide a geometrical or optical interpretation of the coefficients of the model. In this work we propose a continuous curvature lens model in which the coefficients are derived by geometrical constraints. In this way, both the continuity in the junction zone and a geometrical-physical interpretation of the coefficient involved in the model are obtained. Shape, volume and curvature of the proposed model were compared with four models presented in the literature: two independent conic equations, two interdependent figuring conicoid equations, conic patches model and modulated hyperbolic cosine.

Optimization of lattice structures for Additive Manufacturing Technologies

Additive manufacturing technologies enable the fabrication of parts characterized by shape complexity and therefore allow the design of optimized components based on minimal material usage and weight. In the literature two approaches are available to reach this goal: adoption of lattice structures and topology optimization. In a recent work a Computer-Aided method for generative design and optimization of regular lattice structures was proposed. The method was investigated in few configurations of a cantilever beam, considering six different cell types and two load conditions. In order to strengthen the method, in this paper a number of test cases have been carried out. Results explain the behavior of the method during the iterations, and the effects of the load and of the cell dimension. Moreover, a visual comparison between the proposed method and the results achieved by topology optimization is shown.

Computation of Femoral Canine Morphometric Parameters in Three‐Dimensional Geometrical Models

OBJECTIVE To define and validate a method for the measurement of 3-dimensional (3D) morphometric parameters in polygonal mesh models of canine femora. STUDY DESIGN Ex vivo/computerized model. SAMPLE POPULATION Sixteen femora from 8 medium to large-breed canine cadavers (mean body weight 28.3 kg, mean age 5.3 years). METHODS Femora were measured with a 3D scanner, obtaining 3D meshes. A computer-aided design-based (CAD) software tool was purposely developed, which allowed automatic calculation of morphometric parameters on a mesh model. Anatomic and mechanical lateral proximal femoral angles (aLPFA and mLPFA), anatomic and mechanical lateral distal femoral angles (aLDFA and mLDFA), femoral neck angle (FNA), femoral torsion angle (FTA), and femoral varus angle (FVA) were measured in 3D space. Angles were also measured onto projected planes and radiographic images. RESULTS Mean (SD) femoral angles (degrees) measured in 3D space were: aLPFA 115.2 (3.9), mLPFA 105.5 (4.2), aLDFA 88.6 (4.5), mLDFA 93.4 (3.9), FNA 129.6 (4.3), FTA 45 (4.5), and FVA -1.4 (4.5). Onto projection planes, aLPFA was 103.7 (5.9), mLPFA 98.4 (5.3), aLDFA 88.3 (5.5), mLDFA 93.6 (4.2), FNA 132.1 (3.5), FTA 19.1 (5.7), and FVA -1.7 (5.5). With radiographic imaging, aLPFA was 109.6 (5.9), mLPFA 105.3 (5.2), aLDFA 92.6 (3.8), mLDFA 96.9 (2.9), FNA 120.2 (8.0), FTA 30.2 (5.7), and FVA 2.6 (3.8). CONCLUSION The proposed method gives reliable and consistent information about 3D bone conformation. Results are obtained automatically and depend only on femur morphology, avoiding any operator-related bias. Angles in 3D space are different from those measured with standard radiographic methods, mainly due to the different definition of femoral axes.

Geometric modeling of lattice structures for additive manufacturing

This paper aims to propose a consistent approach to geometric modeling of optimized lattice structures for additive manufacturing technologies.,The proposed method applies subdivision surfaces schemes to an automatically defined initial mesh model of an arbitrarily complex lattice structure. The approach has been developed for cubic cells. Considering different aspects, five subdivision schemes have been studied: Mid-Edge, an original scheme proposed by the authors, Doo–Sabin, Catmull–Clark and Bi-Quartic. A generalization to other types of cell has also been proposed.,The proposed approach allows to obtain consistent and smooth geometric models of optimized lattice structures, overcoming critical issues on complex models highlighted in literature, such as scalability, robustness and automation. Moreover, no sharp edge is obtained, and consequently, stress concentration is reduced, improving static and fatigue resistance of the whole structure.,An original and robust method for modeling optimized lattice structures was proposed, allowing to obtain mesh models suitable for additive manufacturing technologies. The method opens new perspectives in the development of specific computer-aided design tools for additive manufacturing, based on mesh modeling and surface subdivision. These approaches and slicing tools are suitable for parallel computation, therefore allowing the implementation of algorithms dedicated to graphics cards.

Shape and curvature error estimation in polished surfaces of ground glass molds

Abstract. In the fabrication process of aspheric glass lens and molds, shape characterization is a fundamental task to control geometrical errors. Nevertheless, the more significant geometrical functional aspect related to the optical properties is the curvature, which is rarely investigated in the manufacturing process of lenses. Algorithms for the assessment of shape and curvature errors on aspheric surface profile are presented. The method has been investigated on profiles measured before and at different steps of the membrane polishing process. The results show how surface roughness, shape, and curvature change during the polishing process as a function of the machining time.

Mechanical Properties of Orthopaedic Insoles under Cyclic Loads and Correlation with Daily Use

Aim of the work was the definition of an experimental procedure enabling to evaluate the mechanical properties of orthopaedic insoles used in daily and sport activities. Customers and manufacturers can be interested in knowing which is the durability of the insoles for a correct substitution of an exhausted sole together with for product liability. A cyclic test was developed for the measure of stiffness and damping properties of different types of insoles under pulsated compression loads applied by means of a servo hydraulic test machine. Accelerated fatigue tests were performed by applying repeated blocks of compression overloads and measuring periodically the mechanical properties of the insoles to estimate the insole durability. Finally, a group of subjects wearing insoles during daily life was involved in the study and two pairs of identical insoles were prepared for each subject: one pair underwent the fatigue test and the other pair was used by the subject in his daily activity (normal or sport) during a given period of time. Final comparison between the mechanical properties of used and tested insoles enabled to define the number of equivalent damage cycles per month of each type of customer.

Automated computation of femoral angles in dogs from three-dimensional computed tomography reconstructions: Comparison with manual techniques

The aim of this ex vivo study was to test a novel three-dimensional (3D) automated computer-aided design (CAD) method (aCAD) for the computation of femoral angles in dogs from 3D reconstructions of computed tomography (CT) images. The repeatability and reproducibility of three manual radiography, manual CT reconstructions and the aCAD method for the measurement of three femoral angles were evaluated: (1) anatomical lateral distal femoral angle (aLDFA); (2) femoral neck angle (FNA); and (3) femoral torsion angle (FTA). Femoral angles of 22 femurs obtained from 16 cadavers were measured by three blinded observers. Measurements were repeated three times by each observer for each diagnostic technique. Femoral angle measurements were analysed using a mixed effects linear model for repeated measures to determine the levels of intra-observer agreement (repeatability) and inter-observer agreement (reproducibility). Repeatability and reproducibility of measurements using the aCAD method were excellent (intra-class coefficients, ICCs≥0.98) for all three angles assessed. Manual radiography and CT exhibited excellent agreement for the aLDFA measurement (ICCs≥0.90). However, FNA repeatability and reproducibility were poor (ICCs<0.8), whereas FTA measurement showed slightly higher ICCs values, except for the radiographic reproducibility, which was poor (ICCs<0.8). The computation of the 3D aCAD method provided the highest repeatability and reproducibility among the tested methodologies.