Modeling Materials Coextrusion in Polymers Additive Manufacturing.

Material extrusion additive manufacturing enables us to combine more materials in the same nozzle during the deposition process. This technology, called material coextrusion, generates an expanded range of material properties, which can gradually change in the design domain, ensuring blending or higher bonding/interlocking among the different materials. To exploit the opportunities offered by these technologies, it is necessary to know the behavior of the combined materials according to the materials fractions. In this work, two compatible pairs of materials, namely Polylactic Acid (PLA)-Thermoplastic Polyurethane (TPU) and Acrylonitrile Styrene Acrylate (ASA)-TPU, were investigated by changing the material fractions in the coextrusion process. An original model describing the distribution of the materials is proposed. Based on this, the mechanical properties were investigated by analytical and numerical approaches. The analytical model was developed on the simplified assumption that the coextruded materials are a set of rods, whereas the more realistic numerical model is based on homogenization theory, adopting the finite element analysis of a representative volume element. To verify the deposition model, a specific experimental test was developed, and the modeled material deposition was superimposed and qualitatively compared with the actual microscope images regarding the different deposition directions and material fractions. The analytical and numerical models show similar trends, and it can be assumed that the finite element model has a more realistic behavior due to the higher accuracy of the model description. The elastic moduli obtained by the models was verified in experimental tensile tests. The tensile tests show Young's moduli of 3425 MPa for PLA, 1812 MPa for ASA, and 162 MPa for TPU. At the intermediate material fraction, the Young's modulus shows an almost linear trend between PLA and TPU and between ASA and TPU. The ultimate tensile strength values are 63.9 MPa for PLA, 35.7 MPa for ASA, and 63.5 MPa for TPU, whereas at the intermediate material fraction, they assume lower values. In this initial work, the results show a good agreement between models and experiments, providing useful tools for designers and contributing to a new branch in additive manufacturing research.

Implantoplasty: Carbide burs vs diamond sonic tips. An in vitro study.

OBJECTIVES: Implantoplasty (IP) is a treatment option for peri-implantitis. Mechanical concerns were raised on fracture resistance of implants subjected to this procedure. This study aimed to compare two methods of IP in terms of implant wear and fracture resistance, and of surface topography. MATERIAL AND METHODS: Eighteen cylindrical screw-shaped dental implants (4 mm diameter, 13 mm length) with an external hexagonal connection were used. IP was performed on the first 6-mm implant surface with a sequence of burs or diamond sonic tips, both followed by an Arkansas finishing. IP duration and implant weight variation were recorded. Micro-computed tomography (micro-CT) was used to evaluate material loss. Implant fracture resistance was assessed by static compression test. Surface topography analysis was performed with a stylus profilometer. Scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) was applied for implant surface morphology and elemental characterization. RESULTS: Micro-CT showed less material loss in sonic compared to burs. No statistically significant difference was found between the mean fracture resistance values reached in bur and sonic, both followed by Arkansas, and with respect to control. IP performed with burs led to a smoother surface compared to sonic. Equivalent final surface roughness was found after Arkansas in both IP procedures. SEM-EDS showed a deburring effect associated to sonic and revealed carbon and aluminum peaks attributable to contamination with sonic diamond tips and Arkansas bur, respectively. CONCLUSIONS: IP with sonic diamond tips was found to be more conservative in terms of structure loss. This could have a clinical relevance in case of narrow-diameter implants.

Numerical modelling of abdominal wall mechanics: The role of muscular contraction and intra-abdominal pressure.

The biomechanics of the abdominal wall depends on muscular activation, tissue mechanical behavior and Intra-Abdominal Pressure (IAP). In this work, a numerical model of a human abdomen is presented, based on abdominal wall geometry from medical images. Specific constitutive formulations describe tissues mechanical behavior. Connective tissues are modelled as hyperelastic fiber-reinforced materials, while muscular tissues are described by means of a three-element Hill's model. The abdominal cavity is represented by a volume region interacting with the abdominal wall. Numerical analyses are developed by applying a muscular contraction, inducing a volume reduction of the abdominal cavity and a simultaneous IAP increase. Numerical results of abdomen displacement at IAP corresponding to an abdominal crunch are compared with experimental results acquired via 3D laser scanning on a healthy subject. Numerical and experimental results are mutually consistent and show that muscular activation induces a raising in the region adjacent to linea alba along the posterior-anterior direction and a lowering along lateral-medial direction of the abdominal wall sides. The numerical model developed in this work allows a coherent representation of the abdominal wall mechanics.

Accuracy of an automated three-dimensional technique for the computation of femoral angles in dogs.

AIMS: The purpose of the study was to evaluate the accuracy of a three-dimensional (3D) automated technique (computer-aided design (aCAD)) for the measurement of three canine femoral angles: anatomical lateral distal femoral angle (aLDFA), femoral neck angle (FNA) and femoral torsion angle. METHODS: Twenty-eight femurs equally divided intotwo groups (normal and abnormal) were obtained from 14 dogs of different conformations (dolicomorphic and chondrodystrophicCT scans and 3D scanner acquisitions were used to create stereolithographic (STL) files , which were run in a CAD platform. Two blinded observers separately performed the measurements using the STL obtained from CT scans (CT aCAD) and 3D scanner (3D aCAD), which was considered the gold standard method. C orrelation coefficients were used to investigate the strength of the relationship between the two measurements. RESULTS: A ccuracy of the aCAD computation was good, being always above the threshold of R2 of greater than 80 per cent for all three angles assessed in both groups. a LDFA and FNA were the most accurate angles (accuracy >90 per cent). CONCLUSIONS: The proposed 3D aCAD protocol can be considered a reliable technique to assess femoral angle measurements in canine femur. The developed algorithm automatically calculates the femoral angles in 3D, thus considering the subjective intrinsic femur morphology. The main benefit relies on a fast user-independent computation, which avoids user-related measurement variability. The accuracy of 3D details may be helpful for patellar luxation and femoral bone deformity correction, as well as for the design of patient- specific, custom-made hip prosthesis implants.

3D surface imaging of abdominal wall muscular contraction.

BACKGROUND AND OBJECTIVE: The biomechanical analysis of the abdominal wall should take into account muscle activation and related phenomena, such as intra-abdominal pressure variation and abdomen surface deformation. The geometry of abdominal surface and its deformation during contraction have not been extensively characterized, while represent a key issue to be investigated. METHODS: In this work, the antero-lateral abdominal wall surface of ten healthy volunteers in supine position is acquired via laser scanning in relaxed conditions and during abdominal muscles contraction, repeating each acquisition six times. The average relaxed and contracted abdominal surfaces are compared for each subject and displacements measured. RESULTS: Muscular activation induces raising in the region adjacent to linea alba along the posterior-anterior direction and a simultaneous lowering along lateral-medial direction of the abdominal wall sides. Displacements reach a maximum value of 12.5 mm for the involved subjects. The coefficient of variation associated to the abdomen surface measurements in the same configuration (relaxed or contracted) is below 0.75%. Non-parametric Mann-Whitney U test highlights that the differences between relaxed and contracted abdominal wall surfaces are significant (p < 0.01). CONCLUSIONS: Laser scanning is an accurate and reliable method to evaluate surface changes on the abdominal wall during muscular contraction. The results of this experimental activity can be useful to validate numerical models aimed at describing abdominal wall biomechanics.

Geometric Modeling of Cellular Materials for Additive Manufacturing in Biomedical Field: A Review.

Advances in additive manufacturing technologies facilitate the fabrication of cellular materials that have tailored functional characteristics. The application of solid freeform fabrication techniques is especially exploited in designing scaffolds for tissue engineering. In this review, firstly, a classification of cellular materials from a geometric point of view is proposed; then, the main approaches on geometric modeling of cellular materials are discussed. Finally, an investigation on porous scaffolds fabricated by additive manufacturing technologies is pointed out. Perspectives in geometric modeling of scaffolds for tissue engineering are also proposed.

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.

Spring-bite: a new device for jaw motion rehabilitation. A case report.

The present paper describes the design features, potential indications and a clinical application of a newly designed device for jaw motion rehabilitation, the Spring-Bite. This device is characterized by a first class lever mechanism, which allows performing passive jaw motion rehabilitation at constant load without an active participation by the patient. Spring-Bite was developed for the management of temporomandibular joint (TMJ) hypomobility and its application may be much useful in the post-operatory phases of TMJ or orthognathic surgeries as well as in patients with reduced muscular force.

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

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 microV to be compared with a control group value of 1644.63 microV). 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.

A 3-Dimensional Facial Morpho-Dynamic Database in the development of a prediction model in orthognathic surgery.

BACKGROUND: Current methodologies in the prevision of post-surgical features of the face in orthognathic surgery are mainly 2-D. An improvement is certainly given by the introduction of CT, but its acceptance is controversial due to its high biological cost. As an alternative, in this study an effective procedure for the construction of a 3-D textured digital model of the face and dental arches of patients with dentofacial malformations using a 3-D laser scanner at no biological cost is presented. METHODS: A 3-D Laser scanner Konica-Minolta VIVID 910 is used to obtain multiple scans from different perspectives of the face of patients with dentofacial malocclusions requiring orthognathic surgery. These multiple views are then recombined, integrating also the maxillary and mandibular arch plaster casts, to obtain the 3-D textured model of the face and occlusion with minimal error. RESULTS: A viable methodology was identified for the face and occlusal modeling of orthognathic patients and validated in a test case, confirming its effectiveness: the 3-D model created accurately describes the actual features of the patient's face; the proposed methodology can be easily applied in the clinical routine to accurately record the steps of the surgical treatment and to perform accurate anthropometric analyses of the facial morphology, and thus constitute the necessary database for the development of previsional tools in orthognathic surgery. CONCLUSIONS: The proposed method is effective in recording all the morphological facial features of patients with dentofacial malformations, to develop a facial modification database and tools for virtual surgery.