Methods for medical applications

In this paper various architectures of electromagnetic harvesting devices, realized in the Department of Information Engineering of the University of Brescia, is reported, estimating their usability for biomedical applications. Furthermore, this paper shows a first attempt of a new electromagnetic generator architecture. The proposed system is modelled and simulated showing promising results.

Keywords: Biomedical devices , Eletromechanical generator , Human energy harvesting

The Zona Pellucida (ZP) is the extracellular coat surrounding mammalian oocytes. The so called "zona hardening" has a key role in the fertilization process as it produces a block of polyspermy also through an increase of the stiffness of the membrane. The full comprehension of the mechanisms involved in the structural reorganization of the ZP leading to mechanical hardening as well as a correct estimation of its elastic properties is still lacking. In this study, mechanical properties of the ZP membranes extracted from mature and fertilized bovine oocytes were investigated with Atomic Force Microscopy nanoindentation measurements. Both inner and outer sides of the fertilized oocyte's ZP were characterized in order to investigate the propagation of the zona hardening through the thickness of the membrane. This work proposes the application of a hybrid procedure combining experimental measurements, Finite Element analysis and optimization algorithms to analyze the indentation curves.

Keywords: Atomic Force Microscopy , Hyperelasticity , Nanoindentation , Non linear optimization , Zona Pellucida

The aim of this study was to investigate the performance of different orthodontic devices for mandibular symphyseal distraction osteogenesis (MSDO). Two performance parameters were analysed, the first of which concerned the stability guaranteed by a distractor in the fracture gap under mastication loads and the second the level of reliability with which a distractor transfers a given expansion to the mandibular bone, inasmuch as the more reliable the device the smaller the difference between the degree of expansion provided to the device and the displacement achieved on the mandibular arch. Hence, a non-linear finite element (FE) model of a human mandible with different devices (tooth-borne, bone-borne, and hybrid) was constructed and then utilized to assess the structural behaviour of the mandibular bone under distraction and mastication loads. An ad hoc algorithm was developed to simulate progressive expansion of the devices; a distraction protocol comprising a 10 day latency period and a 6 day distraction period was hypothesized. The first hypothetical expansion given to the device was 2 mm, and the five subsequent expansions were 1 mm. The results showed that the hybrid device was the most stable appliance under mastication loads, followed by the tooth- and bone-borne devices. However, parasitic rotations of the mandibular arms caused by mastication might counteract the benefits of distraction. The tooth-borne device was found to have the highest reliability in transferring expansion to the mandibular bone. For this device, mandibular expansion was less than the nominal aperture of the distractor by no more than 15 per cent. Lower values of reliability were achieved with the bone-borne device. As the values of the aperture of the appliances increased, the stability guaranteed in the fracture gap increased while the reliability in transferring expansion to the mandibular arch decreased. © The Author 2010.

In this study a multi-scale mechano-regulation model was developed in order to investigate the mechanobiology of trabecular fracture healing in vertebral bodies. A macro-scale finite element model of the spinal segment L3-L4-L5, including a mild wedge fracture in the body of the L4 vertebra, was used to determine the boundary conditions acting on a micro-scale finite element model simulating a portion of fractured trabecular bone. The micro-scale model, in turn, was utilized to predict the local patterns of tissue differentiation within the fracture gap and then how the equivalent mechanical properties of the macro-scale model change with time. The patterns of tissue differentiation predicted by the model appeared consistent with those observed in vivo. Bone formation occurred primarily through endochondral ossification. New woven bone was predicted to occupy the majority of the space within the fracture site approximately 7-8 weeks after the fracture event. Remodeling of cancellous bone architecture was then predicted, with complete new trabeculae forming due to bridging of the microcallus between the remnant trabeculae. Copyright © 2010 Orthopaedic Research Society.

Keywords: finite element analysis , fracture repair , mechanobiology , tissue differentiation , vertebral body

This study discusses the application of a hybrid experimental-numerical approach to analyze nano-indentation curves of a biological membrane acquired with an Atomic Force Microscope. The proposed procedure combines experimental measurements, FEM analysis and numerical optimization and is completely general. Variations of estimated Young modulus of the membrane are determined when attributing different constitutive laws to the sample and in the case of progressive blunting of the AFM tip during the measurement. Since traditional analysis of Atomic Force Microscope indentation curves relies on an inappropriate application of the classical Hertz theory, a comparison between the hybrid approach and the Hertzian model in the determination of the elastic properties of the sample is presented. In particular, it is found that large errors occur in the derivation of the Young modulus when the Hertzian model is used for the analyis of experimental data.

The most severe limitation of the Left Ventricular Assist Devices (LVADs) currently utilized is their invasivity; they work as a bypass between the left ventricular apex and the aorta. A possible strategy that can be adopted to overcome such a limitation consists in utilizing systems that assist the heart in its contraction from the outside without directly transporting the blood and that do not require highly invasive surgical treatments. In this study we conduct the feasibility analysis of a novel LVAD design that allows the principal limitations of traditional circulatory support systems to be overcome. © 2011 IEEE.

Keywords: Cardiac Failure , Circulatory Assist Devices , Ventricular Assist Device

Techniques of bone reconstructive surgery are largely based on conventional, non-cell-based therapies that rely on the use of durable materials from outside the patient's body. In contrast to conventional materials, bone tissue engineering is an interdisciplinary field that applies the principles of engineering and life sciences towards the development of biological substitutes that restore, maintain, or improve bone tissue function. Bone tissue engineering has led to great expectations for clinical surgery or various diseases that cannot be solved with traditional devices. For example, critical-sized defects in bone, whether induced by primary tumor resection, trauma, or selective surgery have in many cases presented insurmountable challenges to the current gold standard treatment for bone repair. The primary purpose of bone tissue engineering is to apply engineering principles to incite and promote the natural healing process of bone which does not occur in critical-sized defects. The total market for bone tissue regeneration and repair was valued at $1.1 billion in 2007 and is projected to increase to nearly $1.6 billion by 2014. Usually, temporary biomimetic scaffolds are utilized for accommodating cell growth and bone tissue genesis. The scaffold has to promote biological processes such as the production of extra-cellular matrix and vascularisation, furthermore the scaffold has to withstand the mechanical loads acting on it and to transfer them to the natural tissues located in the vicinity. The design of a scaffold for the guided regeneration of a bony tissue requires a multidisciplinary approach. Finite element method and mechanobiology can be used in an integrated approach to find the optimal parameters governing bone scaffold performance. In this paper, a review of the studies that through a combined use of finite element method and mechano-regulation algorithms described the possible patterns of tissue differentiation in biomimetic scaffolds for bone tissue engineering is given. Firstly, the generalities of the finite element method of structural analysis are outlined; second, the issues related to the generation of a finite element model of a given anatomical site or of a bone scaffold are discussed; thirdly, the principles on which mechanobiology is based, the principal theories as well as the main applications of mechano-regulation models in bone tissue engineering are described; finally, the limitations of the mechanobiological models and the future perspectives are indicated. © Ivyspring International Publisher.

Keywords: Bone tissue engineering , Finite element analysis , Mechano-regulation algorithms , Mechanobiology , Scaffold

Interacting with computers by using the bodily motion is one of the challenging topics in the Virtual Reality field, especially as regards the interaction with large scale virtual environments. This paper presents a device for interacting with a Virtual Reality environment that is based on the detection of the muscular activity and movements of the user by the fusion of two different signals. The idea is that through muscular activities a user is capable of moving a cursor in the virtual space, and making some actions through gestures. The device is based on an accelerometer and on electromyography, a technique that derives from the medical field and that is able to recognize the electrical activity produced by skeletal muscles during their contraction. The device consists of cheap and easy to replicate components: seven electrodes pads and a small and wearable board for the acquisition of the sEMG signals from the user's forearm, a 3 DOF accelerometer that is positioned on the user's wrist (used for moving the cursor in the space) and a glove worn on the forearm in which these components are inserted. The device can be easily used without tedious settings and training. In order to test the functionality, performances and usability issues of the device we have implemented an application that has been tested by a group of users. Specifically, the device has been used as natural interaction technique in an application for drawing in a large scale virtual environment. The muscular activity is acquired by the device and used by the application for controlling the dimension and color of the brush. Copyright © 2011 by ASME.

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. © 2011 Copyright Taylor and Francis Group, LLC.

Keywords: curvature , geometrical constraint , human crystalline lens , shape , volume

The main objective of this works is to develop a wearable device to improve sport training in lower limb. The system consists of a pair of spandex shorts which embed a processor unit, 2 accelerometers, 2 vibro motors, a SD card reader\writer module and a real time clock. The accelerometers are located in proximity to the knees and are used to measure in real time the tri-axial accelerations for each leg. We present a novel algorithm to compute asymmetry from the 3 axial sensor data. We propose two applications of the system: for real time active correction and for data logging. In the correction mode, adjustment signal are sent to the user during the training by vibrations. The vibration signal is sent to the specific leg and its intensity is related to the entity of required correction. The second application of the system is as datalogger. The device stores all the training data in a SD card. Those log files can be processed using a dedicated application on a PC. This information can be very useful for long term analysis. This novel approach to sport training is very useful to athletes and sport medicine doctor in order to improve posture, efficiency and performance, but it can be also useful in other medical appliances such as rehabilitation. © 2011 IEEE.

Keywords: posture correction , sport training , vibro feedback , wearable

We present a novel framework for computer aided measurements which supports physicians during 3D virtual colonoscopy. We propose a four steps methodology: (i) segment colon regions, (ii) search for colorectal polyps by means of a supervised neural network architecture, (iii) 3D reconstruction of polyp geometry using a synthetic model and (iv) qualitative and quantitative geometrical analysis. Doctor can graphically visualize and inspect the surface and search for irregularities. This qualitative visual support is extended with mathematical tools which computes diagnostic indicators. The proposed tool was tested with two different data sets of polyps. The proposed approach can be an effective diagnostic tool to evaluate the degree of malignancy of the cancer. Due to its generality, the presented framework can be easily extended to search for other types of cancers. © 2011 IEEE.

Keywords: 2D segmentation , 3D rendering and 2D and 3D measurements , neural networks , polyps , Virtual Conolonoscopy

Magnetic scaffolds for bone tissue engineering based on a poly(ω-caprolactone) (PCL) matrix and iron oxide (Fe3O 4) magnetic nanoparticles were designed and developed through a three-dimensional (3D) fiber-deposition technique. PCL/Fe3O 4 scaffolds were characterized by a 90/10 w/w composition. Tensile and magnetic measurements were carried out, and nondestructive 3D imaging was performed through microcomputed tomography (Micro-CT). Furthermore, confocal analysis was undertaken to investigate human mesenchymal stem cell adhesion and spreading on the PCL/Fe3O4 nanocomposite fibers. The results suggest that nanoparticles mechanically reinforced the PCL matrix; the elastic modulus and the maximum stress increased about 10 and 30%, respectively. However, the maximum strain decreased about 50%; this suggested an enhanced brittleness. Magnetic results evidenced a superparamagnetic behavior for these nanocomposite scaffolds. Micro-CT suggested an almost uniform distribution of nanoparticles. Confocal analysis highlighted interesting results in terms of cell adhesion and spreading. All of these results show that a magnetic feature could be incorporated into a polymeric matrix that could be processed to manufacture scaffolds for advanced bone tissue engineering and, thus, provide new opportunity in terms of scaffold fixation and functionalization. © 2011 Wiley Periodicals, Inc.

Keywords: biocompatibility , nanocomposites , nanoparticles , polyesters

Chitosan (Ch) is a nontoxic and biocompatible polysaccharide extensively used in biomedical applications. Ch, as a polycation, can be combined with anionic polymers by layer-bylayer (LbL) self-assembly, giving rise to multilayered complexed architectures. These structures can be used in tissue engineering strategies, as drug delivery systems, or artificial matrices mimicking the extracellular microenvironment. In this work, Ch was combined with poly(γ-glutamic acid) (γ-PGA). γ-PGA is a polyanion, which was microbially produced, and is known for its low immunogenic reaction and low cytotoxicity. Multilayered ultrathin films were assembled by LbL, with a maximum of six layers. The interaction between both polymers was analyzed by: ellipsometry, quartz crystal microbalance with dissipation, Fourier transform infrared spectroscopy, atomic force microscopy, and zeta potential measurements. Ch/γ-PGA polyelectrolyte multilayers (PEMs) revealed no cytotoxicity according to ISO 10993-5. Overall, this study demonstrates that Ch can interact electrostatically with γ-PGA forming multilayered films. Furthermore, this study provides a comprehensive characterization of Ch/γ-PGA PEM structures, elucidating the contribution of each layer for the nanostructured films. These model surfaces can be useful substrates to study cell-biomaterial interactions in tissue regeneration. © 2011 American Chemical Society.

In order to mimic the behaviors of natural tissue, the optimal approach for designing novel biomaterials has to be inspired to nature guidelines. One of the major challenge consists in the development of well-organized structures or scaffolds with controlled porosity in terms of pore size, pore shape and interconnection degree able to guide new tissue formation during the in vivo degradation following the scaffold implantation. Scaffolds endowed with molecular cues together to a controlled degradation profile should contribute to cell proliferation and differentiation, controlled vascularization, promoting the remodeling of neo tissue through a gradual transmission of biochemicals and biophysical signals as performed by the extracellular matrix (ECM). Here, different polymers and composites have been investigated to design scaffolds with peculiar micro and/or nanometric morphological features in order to satisfy all these requirements: a) bioactive scaffolds, with tailored porosity and high pores interconnectivity were developed by integrating PLA fibres, Calcium Phosphates particles or Hyaff11 phases into a Poly(ε-caprolactone) (PCL) matrix by the combination of filament winding technology and phase inversion/salt leaching technique as mineralised ECM analogue for bone regeneration; b) custom made PCL/hydroxyapatite scaffolds were designed by imaging and rapid prototyping technologies for the osteochondral defect. c) Ester of Hyaluronic Acid reinforced with degradable fibres were processed by composite technology, phase inversion and salt leaching technique, to obtain scaffolds for meniscus regeneration. d) PCL and gelatin nanofibres were obtained by highly customized fibre deposition via electrospinning to guide the nerve outgrowth in nerve regeneration. All the proposed approaches offer the chance of realizing tailor-made platforms with micro/nanoscale architecture and chemical composition suitable for the regeneration of the extracellular matrix of a large variety of natural tissues (i.e, bone, menisci, osteochondral and peripheral nervous tissues). © (2011) Trans Tech Publications, Switzerland.

Keywords: Composite , Polycaprolactone , Scaffold , Tissue engineering

The goal of this study was to produce and characterize the scaffolds by combining the advantages of both natural and synthetic polymers for engineering fibro-cartilaginous tissues. Porous three-dimensional composite scaffolds were produced based on glycosaminoglycans and hyaluronic acid (HYAFF11) reinforced with polycaprolactone. The mechanical properties of scaffolds were evaluated as a function of time and compared with those of scaffolds seeded with human chondrocytes (constructs) and cultured in vitro up to 6 weeks. The composite scaffolds had a porosity of 68% with interconnected macropores with average pore sizes of 200 μm, an equilibrium swelling of 350%, and a predominant elastic behavior, typical of a macromolecular gel. The composite constructs maintained chondrocyte phenotype and degraded with the deposition of macromolecules synthesized by the cells. The scaffold presented mechanical properties and the ability to dissipate energy similar to the fibro-cartilaginous tissue. © The Author(s) 2011.

Keywords: cartilage tissue engineering , hyaluronic acid derivatives , mechanical properties , PCL , scaffolds

Polymer-based composite materials are ideal for applications where high stiffness-to-weight and strength-to-weight ratios are required. From aerospace and aeronautical field to biomedical applications, fiber-reinforced polymers have replaced metals, thus emerging as an interesting alternative. As widely reported, the mechanical behavior of the composite materials involves investigation on micro- and macro-scale, taking into consideration micromechanics, macromechanics and lamination theory. Clinical situations often require repairing connective tissues and the use of composite materials may be suitable for these applications because of the possibility to design tissue substitutes or implants with the required mechanical properties. Accordingly, this review aims at stressing the importance of fiber-reinforced composite materials to make advanced and biomimetic prostheses with tailored mechanical properties, starting from the basic principle design, technologies, and a brief overview of composites applications in several fields. Fiber-reinforced composite materials for artificial tendons, ligaments, and intervertebral discs, as well as for hip stems and mandible models will be reviewed, highlighting the possibility to mimic the mechanical properties of the soft and hard tissues that they replace. © 2011 Società Italiana Biomateriali.

Keywords: Applications , Basic principles , Fiber-reinforced composite materials , Prosthetic implants and models , Tailored properties , Technologies

Spinal disease due to intervertebral disc degeneration represents a serious medical problem which affects many people worldwide. Disc arthroplasty may be considered the future "gold standard" of back pain treatment, even if problems related to available disc prostheses are considered. Hence, the aim of the present study was to improve the artificial disc technology by proposing the engineering of a pilot-scale device production process for a total multi-component intervertebral disc prosthesis. The device is made up of a poly(2-hydroxyethyl methacrylate)/poly(methyl methacrylate) (PHEMA/PMMA) (80/20 w/w) semi-interpenetrating polymer network (s-IPN) composite hydrogel reinforced with poly(ethylene terephthalate) (PET) fibers as annulus/nucleus substitute, and two hydroxyapatite-reinforced polyethylene composite (HAPEXTM) endplates in order to anchor the multi-component device to the vertebral bodies. Static and dynamic-mechanical characterization show appropriate mechanical behavior. An example of engineering of a suitable pilot-scale device production process is also proposed in order to manufacture custom made implants. © 2010 The Author(s).

Keywords: customized prosthesis , fiber-reinforced hydrogel , intervertebral disc , mechanical testing. , multi-component model , reverse engineering , technologies