Methods for medical applications

The mechanical behaviour of skin is very important as regards dermatology, surgery and impact trauma. Engineered skin substitutes can bring significant medical benefit, in particular to patients with extensive burn wounds, even if current skin substitutes do not restore normal skin anatomy and its natural mechanical properties. This work considers the mechanical characterization of a particular layer of skin: dermis. Dermis can be used as a filling material and as support in different areas of reconstructive plastic surgery such as post mastectomy reconstructive surgery and abdominal surgery. The aim was to verify the influence of the decellularization treatment on its properties. The specimens were subjected to uniaxial static tests performed with Bose Electroforce® 3200 and experimental data were represented with engineering and real time stress-strain curves. To begin, descriptive parameters were identified for stress vs. strain curves, such as ultimate tensile strength and maximum Young's modulus, and they were subsequently compared through multivariate analysis of variance to determine the influence of specimen cut orientation and decellularization treatment duration. Dermis, that had been decellularized over 5 or 6 weeks, exhibited mechanical properties comparable with natural ones and ultimate tensile strength and maximum Young's modulus were shown to be considerably higher in real time curves than in engineering ones. © 2013 WIT Press.

Keywords: Decellularization treatment , Human dermis , Static characterization

Objective: To evaluate the reliability and accuracy of computer-designed surgical guides in osseointegrated oral implant rehabilitation. Materials and methods: Six implant rehabilitations, with a total of 17 implants, were completed with computer-designed surgical guides, performed with the master model developed by muco-compressive and muco-static impressions. In the first case, the surgical guide had exclusively mucosal support, in the second case exclusively dental support. For all six cases computer-aided surgical planning was performed by virtual analyses with 3D models obtained by dental scan DICOM data. The accuracy and stability of implant osseointegration over two years post surgery was then evaluated with clinical and radiographic examinations. Radiographic examination, performed with digital acquisitions (RVG - Radio Video graph) and parallel techniques, allowed two-dimensional feedback with a margin of linear error of 10%. Results: Implant osseointegration was recorded for all the examined rehabilitations. During the clinical and radiographic post-surgical assessments, over the following two years, the peri-implant bone level was found to be stable and without appearance of any complications. The margin of error recorded between pre-operative positions assigned by virtual analysis and the post-surgical digital radiographic observations was as low as 0.2 mm. Significance: Computer-guided implant surgery can be very effective in oral rehabilitations, providing an opportunity for the surgeon: (a) to avoid the necessity of muco-periosteal detachments and then (b) to perform minimally invasive interventions, whenever appropriate, with a flapless approach. © 2012 Academy of Dental Materials.

Keywords: Minimally invasive approach , Muco-compressive impression , Muco-static impression , Osseointegration , Surgical guides , Virtual modeling

Objective: In the paper laser scanning was used to evaluate, by indirect methods, the accuracy of computer-designed surgical guides in the oral implant supported rehabilitation of partially or completely edentulous patients. Materials and methods: Five implant supported rehabilitations for a total of twenty-three implants were carried out by computer-designed surgical guides, performed with the master model developed by muco-compressive and muco-static impressions. For all cases the surgical virtual planning, starting from 3D models obtained by dental scan DICOM data, was performed. The implants were inserted on the pre-surgical casts in the position defined in the virtual planning. These positions were acquired by three-dimensional optical laser scanning and compared with the laser scans of the intraoral impressions taken post-operatively. Results: The comparison between the post-surgical implant replica positions and the positions in the pre-operative cast, for the five patients, shows a maximum distance in the range 1.02-1.25 mm, an average distance in the range 0.21-0.41 mm and a standard deviation in the range 0.21-0.29 mm. Significance: The results of this research demonstrate accurate transfer of implant replica position by virtual implant insertion into a pre-operative cast and a post-operative cast obtained from impressioning. In previous studies the evaluation of the implant positions have required a post-surgical CT scan. With the indirect methods by laser scanning technique, proposed in the paper, this extra radiation exposure of the patient can be eliminated. © 2012 Academy of Dental Materials.

Keywords: Dental implants , Guided implant surgery , Impressions , Laser scan , Virtual modeling

Objective: To investigate the influence of implant design factors in terms of bone integrity and implant stability. Materials and methods: A 3D parametric CAD model was developed. Then, once domain settings and boundary conditions were defined, a 3D FEM model was created. To simulate the physical interaction at the bone-implant interface, identity pairs were introduced. After generating different design scenarios with a DOE approach, the most significant design factors were obtained. Results: This study showed that the geometry of the screw thread highly influenced the implant stability. In particular the degree of bone damage became minimal when adopting 0.40 mm for the thread width and 0.05 mm for the thickness. Significance: Thread width and thickness play a crucial role to reduce induced stresses and damage in bone. Considering these preliminary results, future improvements should focus on investigating also two-factor and higher interactions to better understand the implant loading mechanism. © 2012 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Keywords: Bone-stress distribution , Dental implants , DOE design , FEM modeling , Osseo-integration , Thread parameterization , Titanium implants

In this work, a new technique for symmetry line detection for asymmetric postures, which can not be investigated with the other methods presented in the literature, is proposed. It evaluates the symmetry line by means an adaptive process in which a first attempt is modified step by step until the solution converges to the best estimation. The method here proposed is validated by analysing four different asymmetric postures in which the spine lies far outside the sagittal plane, having as reference the cutaneous marking. Results are analysed and critically discussed. © 2012 Springer-Verlag.

Keywords: Anatomical landmarks , Back shape analysis , Posture prediction , Raster stereography , Symmetry line

The aim of this work is the analysis of the contact area in a knee prosthesis using two different approaches. In particular, the interface between the femoral component and the polyethylene insert has been studied both numerically and experimentally. The interest in studying the contact area is related to the fact that the wear of the polyethylene insert, due to the high contact pressures, represents one of the major causes of failure of the total knee prosthesis. The possibility to evaluate the contact area at different loads and mutual position between femur and tibia is, therefore, of fundamental importance to study the service life of a prosthesis and to improve its performance. The finite element numerical approach has required the acquisition, through reverse engineering, and CAD modelling of the prosthetic components. Then the FEM simulations have been developed considering two different load conditions. In order to compare the calculated data, the same load configurations have been used for experimental tests based on ultrasonic method. In this case, some preliminary tests were required to calibrate the system depending on the particular characteristics of materials, geometries and surface finish of the prosthesis. The results show a good correlation between the data obtained with the two different approaches and, consequently, a good level of reliability of the procedures developed for the numerical and experimental evaluation of the contact area. The numerical procedure can be used to determine the area for different angles and loads, but especially in the design phase. The ultrasonic technique can be used to validate the numerical data.

Computer-aided tools can help to realize custom-fit products characterized by a strict interaction with human body and definitely improve quality of life, in particular of people with disabilities. The paper refers to this context and to a specific custom-fit product, the lower limb prosthesis. It presents an innovative framework centred on virtual models of the patient's body, to design and configure lower limb prosthesis, both transfemoral and transtibial. The framework integrates virtual prototyping and knowledge-based tools to support the orthopaedic technician during all the steps of the lower limb prosthesis design, suggesting rules and procedures for each task. First, the considered product is introduced, and then, the new design framework is described as well as main steps and related tools, from socket modelling to standards component selection and final prosthesis assembly. Results of preliminary experimentation and final remarks conclude the paper. © 2012 Springer-Verlag.

Keywords: Custom-fit products , Knowledge-based systems , Lower limb prosthesis , Socket , Virtual prototyping

An algorithm for both human-like motion generation and joint torques computation for digital humans is addressed in this paper. This goal has been achieved using techniques derived from robotics. In particular, the so-called augmented Jacobian has been used to solve the inverse kinematics problem with a single closed loop inverse kinematics algorithm. Furthermore, a position control for the center of mass of the kinematic chain, and for its projection on the support plane (center of pressure), has been implemented to achieve easy posture control. Thus, the inverse kinematics can be solved taking into account the static balance of the digital human. Moreover, the proposed algorithm allows simulating quite complex tasks, which involve the motion of the whole body, by means of only few task-related control points arbitrary located on the whole kinematic chain. The resulting movements are quite natural even for complex tasks as can be seen on the simulation experiments reported which show the effectiveness of the proposed approach. Finally, the joint torques can be computed thanks to the kinetostatics duality: the results are in accordance with biomechanical analyses. © 2011 Springer-Verlag.

Keywords: Digital humans , Human-like motion generation , Kinetostatic duality , Low-back biomechanical analysis , Multiple-point kinematic control , Posture control

Background: A fundamental pre-requisite for the clinical success in dental implant surgery is the fast and stable implant osseointegration. The press-fit phenomenon occurring at implant insertion induces biomechanical effects in the bone tissues, which ensure implant primary stability. In the field of dental surgery, the understanding of the key factors governing the osseointegration process still remains of utmost importance. A thorough analysis of the biomechanics of dental implantology requires a detailed knowledge of bone mechanical properties as well as an accurate definition of the jaw bone geometry.Methods: In this work, a CT image-based approach, combined with the Finite Element Method (FEM), has been used to investigate the effect of the drill size on the biomechanics of the dental implant technique. A very accurate model of the human mandible bone segment has been created by processing high resolution micro-CT image data. The press-fit phenomenon has been simulated by FE analyses for different common drill diameters (D A = 2.8 mm, D B = 3.3 mm, and D C = 3.8 mm) with depth L = 12 mm. A virtual implant model has been assumed with a cylindrical geometry having height L = 11 mm and diameter D = 4 mm.Results: The maximum stresses calculated for drill diameters D A, D B and D C have been 12.31 GPa, 7.74 GPa and 4.52 GPa, respectively. High strain values have been measured in the cortical area for the models of diameters D A and D B, while a uniform distribution has been observed for the model of diameter D C . The maximum logarithmic strains, calculated in nonlinear analyses, have been ε{lunate} = 2.46, 0.51 and 0.49 for the three models, respectively.Conclusions: This study introduces a very powerful, accurate and non-destructive methodology for investigating the effect of the drill size on the biomechanics of the dental implant technique.Further studies could aim at understanding how different drill shapes can determine the optimal press-fit condition with an equally distributed preload on both the cortical and trabecular structure around the implant. © 2012 Frisardi et al.; licensee BioMed Central Ltd.

This paper describes a miniaturized electromechanical generator, integrable in a human total knee prosthesis, in which the mechanical energy, related to the knee joint movement, is converted into electrical energy. This device has been conceived in order to power an autonomous sensor system, integrated into the prosthesis, able to monitor the loads on the articular surfaces and to transmit those outside the body. © 2012 IEEE.

Keywords: biomechatronics , biomedical devices , electromechanical generator , human energy harvesting , knee prosthesis , system health

Left ventricular assist devices (LVADs) work as a bypass between the left ventricular apex and the ascending aorta. The surgical procedure for their insertion requires the opening of the cardiac cavities and the dissection of the great vessels, the blood is constrained to flow through the device components and the risk can be run of thrombogenesis, haemolysis and infections. A possible strategy to overcome this limitation consists in utilizing external systems that assist the heart in its contraction from the outside without directly transporting the blood. In this study we conduct the feasibility analysis of a novel external LVAD design that does not require the opening of the cardiac cavities and the dissection of the great vessels and that allows the removal procedure to be easily achieved. The device, including a stepper motor, three metallic wires and three elastic elements, works alternatively between a contraction condition where it induces an elastic compulsion on the heart and a release condition where it elastically releases the organ. The values of force acting on the wires and the values of current supplied to the motor were measured and utilized for a preliminary study design. The experimental measurements demonstrated the feasibility of the system. © 2012 Informa Healthcare.

Keywords: Cardiac failure , Circulatory assist devices , Feasibility study , Ventricular assist device

In spite of the consolidated clinical use of minimally invasive percutaneous fixation techniques, little is reported in the literature providing a mechanobiological explanation for how the design of fixation devices can affect the healing process within fractured vertebrae. The aim of this study was to develop a multi-scale mechano-regulation model capable of predicting how the patterns of tissue differentiation within a vertebral fracture change in the presence or in the absence of fixation devices and how the dimensions of the device, and the materials it is made from (Ti-6Al-4V alloy and cobalt chrome alloy) can affect the outcome of the healing process. The macro-scale model simulates the spinal segment L3-L4-L5, including the fractured body of the L4 vertebra, while the micro-scale model represents a fractured portion of cancellous bone. The macro-scale model also includes a minimally invasive percutaneous fixation device. The model predicts that fixation devices significantly shorten healing times. Increasing values of the rod diameter D and decreasing values of its radius of curvature R lead to shorter durations of the healing period. Manufacturing the rods in cobalt chrome alloy is also predicted to reduce slightly the healing period by providing greater mechanical stability within the fracture callus. © International Federation for Medical and Biological Engineering 2012.

Keywords: Mechanobiology , Minimally invasive percutaneous fixation , Spine , Tissue differentiation , Vertebral fracture

This study represents a preliminary activity for the biomechanical numerical modeling aimed at the prediction of the human foot behavior and the deformation under different load conditions. It also represents the starting point to develop a scientific approach for the functional mass customization aimed at the optimization of comfort in footwear. Reverse Engineering (RE) methodologies developed for building up the external shape of the human foot are presented and discussed. Aim of this work is to study the problem of the digitalization of human feet under different conditions using three technologies: shape from stereo, from silhouette and from shading. The foot is one of the most difficult human parts to reconstruct taking into account the complex surface and the high curvature. In this article the disadvantage and advantage of each technique are analyzed. In particular tests about reliability and precision of the measure are considered. ©2010 Society for Experimental Mechanics Inc.

We present a novel approach to the early diagnosis of lung tumors that considers new malignancy indexes by using a metaball-based representation of this neoplasia. Starting from CT data we extract the suspected tumors represented as approximating metaballs and calculate malignancy indexes based on precise volume and surface irregularity evaluation. The mentioned approximation is performed resolving a constraint problem using a genetic algorithm whose objective function is a mathematical representation of the metaball. Compared to existing art, the metaball approximation provides a consistent reference surface for the evaluation of novel diagnosis parameters borrowed from engineering surface analysis. We have implemented the method in a demonstrator software and analyzed three different test cases. Copyright 2012 ACM.

Keywords: Biomedical computation , Genetic algorithm constrained optimization problem , GENOCOP III , Lung Tumor diagnosis , Surface analysis

Background: It is common practice to prescribe customised footwear to people with diabetes to reduce the risk of foot ulceration. Although shoe customising systems have been proposed, effective tools for designing shoe lasts for diabetic patients are lacking. The shape of the lasts must meet certain biomechanical objectives, while maintaining the style of the shoe.Method: The main contributions of this work are as follows: the creation of an artificial-neural-network-based framework to correlate foot measurements and medical data to required footwear features; the definition of repeatable geometrical procedures to measure foot and last scans; and the definition of geometrical operators to modify the last shape according to its original aesthetic and specific footwear parameters. These parameters are computed by a knowledge-based system on the basis of the patient's pathology and best practices of experienced technicians.Results: Dedicated software systems integrated in a common platform are implemented to support the last design process. Test case studies and a survey show the advantages provided by the proposed approach in terms of achieved quality and shoe developing time (72% time savings).Conclusions: A design framework with dedicated tools is proposed for the customisation of shoe lasts for diabetic patients. Further research should be focused on tools to design the insole, outsole and other shoe components. © 2012 Copyright Taylor and Francis Group, LLC.

Keywords: diabetic foot , foot-last fitting , last design , last measurement

Hydrogels currently represent a powerful solution to promote the regeneration of soft and hard tissues. Primarily, they assure efficient bio-molecular interactions with cells, also regulating their basic functions, guiding the spatially and temporally complex multi-cellular processes of tissue formation, and ultimately facilitating the restoration of structure and function of damaged or dysfunctional tissues. In order to overcome basic drawbacks of traditional synthesized hydrogels, many recent strategies have been implemented to realize multi-component hydrogels based on natural and/or synthetic materials with tailored chemistries and different degradation kinetics. Here, a critical review of main strategies has been proposed based on the use of hydrogels-based devices for the regeneration of complex tissues, i.e., osteo-chondral tissues and intervertebral disc. © 2012 by the authors.

Keywords: Disc nucleus , Hydrogels , Osteochondral tissue , Scaffolds , Tissue regeneration

An Additive Manufacturing technique for the fabrication of three-dimensional polymeric scaffolds, based on wet-spinning of poly(ε-caprolactone) (PCL) or PCL/hydroxyapatite (HA) solutions, was developed. The processing conditions to fabricate scaffolds with a layer-by-layer approach were optimized by studying their influence on fibres morphology and alignment. Two different scaffold architectures were designed and fabricated by tuning inter-fibre distance and fibres staggering. The developed scaffolds showed good reproducibility of the internal architecture characterized by highly porous, aligned fibres with an average diameter in the range 200-250 μm. Mechanical characterization showed that the architecture and HA loading influenced the scaffold compressive modulus and strength. Cell culture experiments employing MC3T3-E1 preosteoblast cell line showed good cell adhesion, proliferation, alkaline phosphatase activity and bone mineralization on the developed scaffolds. © 2012 Springer Science+Business Media, LLC.

Keywords: Additive manufacturing , Polycaprolactone , Scaffolds , Tissue engineering , Wet-spinning

As reported in the literature, scaffolds for soft and hard tissue regeneration should satisfy several requirements. In the present work, the potential of 3D fiber deposition technique to design morphologically controlled scaffolds consisting of poly(ε-caprolactone) reinforced with sol-gel synthesized organic-inorganic hybrid fillers was demonstrated, also benefiting from a basic study carried out on 2D composite substrates. Finite element analysis, biological and mechanical tests were properly performed to assess the effects of the inclusion of the hybrid fillers on the performances of 2D substrates and 3D structures. © 2012 American Institute of Physics.

Keywords: Alamar Blueâ„¢ assay , Composite scaffolds , Finite element analysis , Mechanical properties , Organic-inorganic hybrid , Poly(e-caprolactone) , Tissue engineering