Francesco Montagna

Hepatic vessel segmentation for 3D planning of liver surgery experimental evaluation of a new fully automatic algorithm.

RATIONALE AND OBJECTIVES The aim of this study was to identify the optimal parameter configuration of a new algorithm for fully automatic segmentation of hepatic vessels, evaluating its accuracy in view of its use in a computer system for three-dimensional (3D) planning of liver surgery. MATERIALS AND METHODS A phantom reproduction of a human liver with vessels up to the fourth subsegment order, corresponding to a minimum diameter of 0.2 mm, was realized through stereolithography, exploiting a 3D model derived from a real human computed tomographic data set. Algorithm parameter configuration was experimentally optimized, and the maximum achievable segmentation accuracy was quantified for both single two-dimensional slices and 3D reconstruction of the vessel network, through an analytic comparison of the automatic segmentation performed on contrast-enhanced computed tomographic phantom images with actual model features. RESULTS The optimal algorithm configuration resulted in a vessel detection sensitivity of 100% for vessels > 1 mm in diameter, 50% in the range 0.5 to 1 mm, and 14% in the range 0.2 to 0.5 mm. An average area overlap of 94.9% was obtained between automatically and manually segmented vessel sections, with an average difference of 0.06 mm(2). The average values of corresponding false-positive and false-negative ratios were 7.7% and 2.3%, respectively. CONCLUSIONS A robust and accurate algorithm for automatic extraction of the hepatic vessel tree from contrast-enhanced computed tomographic volume images was proposed and experimentally assessed on a liver model, showing unprecedented sensitivity in vessel delineation. This automatic segmentation algorithm is promising for supporting liver surgery planning and for guiding intraoperative resections.

Free form fabrication of silica moulds for aluminium casting by stereolithography

Purpose – In this work, the production of ceramic moulds for aluminium casting using a stereolithographic apparatus (SLA) is presented.Design/methodology/approach – Suspensions of silica powders in a photoreactive resin were used in a standard SLA equipment in order to build green parts. SLA, SLA‐250 (3D System, Valencia, CA) was modified in order to fabricate a ceramic green parts.Findings – A characterization of mechanical properties of the material samples was performed. Finally, moulds for aluminium casting were obtained either using the stereolithographic part as a green mould, either by pyrolisis of the organic binder and subsequent sintering at high temperature.Research limitations/implications – Future investigations will be devoted to optimise the process and the mechanical performances of the sintered parts, improving the rheological properties of suspensions and reducing the building time.Originality/value – This is a novel work on the production of ceramic moulds for aluminium casting using a SLA.

Ultrasonic assisted consolidation of commingled thermoplastic/glass fiber rovings

Thermoplastic matrix composites are finding new applications in different industrial area thanks to their intrinsic advantages related to environmental compatibility and processability. The approach presented in this work consists in the development of a technology for the simultaneous deposition and consolidation of commingled thermoplastic rovings through to the application of high energy ultrasound. An experimental equipment, integrating both fiber impregnation and ply consolidation in a single process, has been designed and tested. It is made of an ultrasonic welder, whose titanium sonotrode is integrated on a filament winding machine. During winding, the commingled roving is at the same time in contact with the mandrel and the horn. The intermolecular friction generated by ultrasound is able to melt the thermoplastic matrix and impregnate the reinforcement fibers. The heat transfer phenomena occurring during the in situ consolidation were simulated solving by finite element (FE) analysis an energy balance accounting for the heat generated by ultrasonic waves and the melting characteristics of the matrix. To this aim, a calorimetric characterization of the thermoplastic matrix has been carried out to obtain the input parameters for the model. The FE analysis has enabled to predict the temperature distribution in the composite during heating and cooling The simulation results have been validated by the measurement of the temperature evolution during ultrasonic consolidation. The reliability of the developed consolidation equipment was proved by producing hoop wound cylinder prototypes using commingled continuous E-glass rovings and Polypropylene (PP) filaments. The consolidated composite cylinders are characterized by high mechanical properties, with values comparable with the theoretical ones predicted by the micromechanical analysis.

Ultrasonic transducers for cure monitoring: design, modelling and validation

The finite element method (FEM) has been applied to simulate the ultrasonic wave propagation in a multilayered transducer, expressly designed for high-frequency dynamic mechanical analysis of polymers. The FEM model includes an electro-acoustic (active element) and some acoustic (passive elements) transmission lines. The simulation of the acoustic propagation accounts for the interaction between the piezoceramic and the materials in the buffer rod and backing, and the coupling between the electric and mechanical properties of the piezoelectric material. As a result of the simulations, the geometry and size of the modelled ultrasonic transducer has been optimized and used for the realization of a prototype transducer for cure monitoring. The transducer performance has been validated by measuring the velocity changes during the polymerization of a thermosetting matrix of composite materials.

Development of semi- and grafted interpenetrating polymer networks based on poly(ethylene glycol) diacrylate and collagen

Purpose The objective of this work was to develop composite hydrogels based on poly(ethylene glycol) diacrylate (PEGDA) and collagen (Coll), potentially useful for biomedical applications. Methods Semi-interpenetrating polymer networks (semi-IPNs) were obtained by photo-stabilizing aqueous solutions of PEGDA and acrylic acid (AA), in the presence of collagen. Further grafting of the collagen macromolecules to the PEGDA/poly(AA) network was achieved by means of a carbodiimide-mediated crosslinking reaction. The resulting hydrogels were characterized in terms of swelling capability, collagen content and mechanical properties. Results and Conclusions The grafting procedure was found to significantly improve the mechanical stability of the IPN hydrogels, due to the establishment of covalent bonding between the PEGDA/poly(AA) and the collagen networks. The suitability of the composite hydrogels to be processed by means of stereolithography (SLA) was also investigated, toward creating biomimetic constructs with complex shapes, which might be useful either as platforms for tissue engineering applications or as tissue mimicking phantoms.

On-line Consolidation of Commingled Polypropylene/Glass Roving During Filament Winding

In this study, the in situ consolidation of polypropylene matrix/glass reinforced rovings was performed combining two heating systems, an infrared oven and a hot air gun, and a roll pressing the commingled roving during hoop winding on a cylindrical mandrel. Process parameters were set up on the basis of a preliminary simulation of the heat transfer along the roving and then comparison of the results with experimental temperature profiles obtained by a noncontact thermometer. Composite samples were cut along the cylinder axis for mechanical characterization. Physical properties, such as density and void content, obtained using different processing conditions, were compared. Electron microscopy was performed in order to assess how processing conditions affect fiber–matrix impregnation.

Lay-Up and Consolidation of a Composite Pipe by In Situ Ultrasonic Welding of a Thermoplastic Matrix Composite Tape

In this work, the potential of preformed thermoplastic matrix composite tapes for the manufacturing of composite pipes by filament winding assisted by in situ ultrasonic welding was evaluated. Unidirectional tapes of E-glass-reinforcedamorphous poly (ethylene terephthalate) were laid up and consolidated in a filament winding machine that was modified with a set-up enabling ultrasonic welding. The obtained composite specimens were characterized by means of morphological and dynamic mechanical analysis as well as void content evaluation, in order to correlate welding parameters to composite properties.

3D printing of hydroxyapatite polymer-based composites for bone tissue engineering

Abstract Skeletal defects reconstruction, using custom-made substitutes, represents a valid solution to replacing lost and damaged anatomical bone structures, renew their original function, and at the same time, restore the original aesthetic aspect. Rapid prototyping (RP) techniques allow the construction of complex physical models based on 3D clinical images. However, RP machines usually work with synthetic polymers; therefore, producing custom-made scaffolds using a biocompatible material directly by RP is an exciting challenge. The aim of the present work is to investigate the potentiality of 3D printing as a manufacturing method to produce an osteogenic hydroxyapatite-polylactic acid bone graft substitute.

Acrylic-based hydrogel phantom for in vitro ultrasound contrast agent characterization

Phantoms are commonly used to perform several tasks within the field of medical imaging and radiation therapy. A novel approach to the manufacture of polymeric phantom for tissue mimicking applications by means of stereolithography (SL) is presented. A water solution of polyethylene glycol diacrylate (PEGDA) and a blend of proprietary photoinitiators were used. An SL device was modified with a custom designed elevator-driven build table with the aim of reducing the material volume during the building process. The second step of this work was addressed to the manufacture of a prototype mimicking a simplified vascular system. The prototype was drawn using a computer-aided-design package and the resulting geometric data were used to drive the SL process leading finally to the fabrication a PEGDA phantom. A preliminary echographic study was also carried out to verify the phantom suitability for in in vitro ultrasound contrast agent characterization.

Relaxation of residual stresses during curing of polymer matrix composites

Stress relaxation behavior of unidirectional AS4/8852 carbon/epoxy composites at high temperatures has been investigated. Specimens with an off axis angle of 90° and ±45° have been exposed to constant strain and high temperature. The mechanical results have been modeled by Standard Linear Solid model. The obtained parameters have been implemented in a finite element (FEM) model able to predict the residual stresses in carbon fiber reinforced composites, both in the elastic and in the viscoelastic field.Stress relaxation behavior of unidirectional AS4/8852 carbon/epoxy composites at high temperatures has been investigated. Specimens with an off axis angle of 90° and ±45° have been exposed to constant strain and high temperature. The mechanical results have been modeled by Standard Linear Solid model. The obtained parameters have been implemented in a finite element (FEM) model able to predict the residual stresses in carbon fiber reinforced composites, both in the elastic and in the viscoelastic field.