Bladder tissue passive response to monotonic and cyclic loading

The fundamental passive mechanical properties of the bladder need to be known in order to design the most appropriate long-term surgical repair procedures and develop materials for bladder reconstruction. This study has focused on the bladder tissue viscoelastic behavior, providing a comprehensive analysis of the effects of fibers orientation, strain rate and loading history. Whole bladders harvested from one year old fat pigs (160 kg approximate weight) were dissected along the apex-to-base direction and samples were isolated from the lateral region of the wall, as well as along apex-to-base and transverse directions. Uniaxial monotonic (stress relaxation) and cyclic tests at different frequencies have been performed with the Bose Electroforce® 3200. Normalized stress relaxation functions have been interpolated using a second-order exponential series and loading and unloading stress-strain curves have been interpolated with a non-linear elastic model. The passive mechanical behavior of bladder tissue was shown to be heavily influenced by frequency and loading history, both in monotonic and cyclic tests. The anisotropy of the tissue was evident in monotonic and in cyclic tests as well, especially in tests performed on an exercised tissue and at high frequencies. In contrast, transverse and apex-to-base samples demonstrated an analogous relaxation behavior

Mechanical Behavior of Elastic Self-Locking Nails for Intramedullary Fracture Fixation: A Numerical Analysis of Innovative Nail Designs

Intramedullary nails constitute a viable alternative to extramedullary fixation devices; their use is growing in recent years, especially with reference to self-locking nails. Different designs are available, and it is not trivial to foresee the respective in vivo performances and to provide clinical indications in relation to the type of bone and fracture. In this work a numerical methodology was set up and validated in order to compare the mechanical behavior of two new nailing device concepts with one already used in clinic. In detail, three different nails were studied: (1) the Marchetti-Vicenzi's nail (MV1), (2) a revised concept of this device (MV2), and (3) a new Terzini-Putame's nail (TP) concept. Firstly, the mechanical behavior of the MV1 device was assessed through experimental loading tests employing a 3D-printed component aimed at reproducing the bone geometry inside which the device is implanted. In the next step, the respective numerical model was created, based on a multibody approach including flexible parts, and this model was validated against the previously obtained experimental results. Finally, numerical models of the MV2 and TP concepts were implemented and compared with the MV1 nail, focusing the attention on the response of all devices to compression, tension, bending, and torsion. A stability index (SI) was defined to quantify the mechanical stability provided to the nail-bone assembly by the elastic self-locking mechanism for the various loading conditions. In addition, results in terms of nail-bone assembly stiffness, computed from force/moment vs. displacement/rotation curves, were presented and discussed. Findings revealed that numerical models were able to provide good estimates of load vs. displacement curves. The TP nail concept proved to be able to generate a significantly higher SI (27 N for MV1 vs. 380 N for TP) and a greater stiffening action (up to a stiffness difference for bending load that ranges from 370 Nmm/° for MV1 to 1,532 Nmm/° for TP) than the other two devices which showed similar performances. On the whole, a demonstration was given of information which can be obtained from numerical simulations of expandable fixation devices

An electro-mechanical bioreactor providing physiological cardiac stimuli

In cardiac tissue engineering it has been widely demonstrated the fundamental role of physical stimuli in improving structural and functional properties of the engineered cardiac constructs. An electro-mechanical bioreactor has been designed and developed to provide physiological uniaxial stretching and electrical stimuli for inducing functional differentiation and promoting morphological and structural maturation of cultured cardiac constructs obtained from stem cell-seeded scaffolds. The bioreactor is composed of: a transparent and sterilizable culture chamber for housing four cell-seeded scaffolds and the culture medium (working volume = 70 ml); a mechanical stimulation system, with a dedicated grasping system, to provide cyclic stretching (strain up to 20%, cycling frequency up to 2 Hz); an electrical stimulation system to provide electrical monophasic square pulses (1-6 V/cm, 0.25-10 ms, 1-5 Hz); a recirculation system for the automated medium change; a control system for data acquisition and mechanical stimulation. Preliminary in-house tests confirmed the suitability and the performances of the bioreactor as regards fittingness of chamber isolation, grasping system, and physical stimulation systems. Cell culture tests are in progress for investigating the influence of stretching and electrical stimuli on development of engineered cardiac constructs. Due to its high versatility, this bioreactor is a multipurpose adaptable system for dynamic culture of cell-seeded scaffolds for tissue engineering research and application

Engineering and manufacturing of a dynamizable fracture fixation device system

The present work illustrates the dynamization of an orthopaedic plate for internal fracture fixation which is thought to shorten healing times and enhance the quality of the new formed bone. The dynamization is performed wirelessly thanks to a magnetic coupling. The paper shows the peculiarities of the design and manufacturing of this system: it involves two components, sliding with respect to each other with an uncertain coefficient of friction, and with a specific compounded geometry; there are stringent limits on component size, and on the required activation energy. Finally, the device belongs to medical devices and, as such, it must comply with the respective regulation (EU 2017/745, ASTM F382). The design of the dynamizable fracture fixation plate has required verifying the dynamic of the unlocking mechanism through the development of a parametric multibody model which has allowed us to fix the main design variables. As a second step, the fatigue strength of the device and the static strength of the whole bone-plate system was evaluated by finite element analysis. Both analyses have contributed to defining the final optimized geometry and the constitutive materials of the plate; finally, the respective working process was set up and its performance was tested experimentally on a reference fractured femur. As a result of these tests, the flexural stiffness of the bone-plate system resulted equal to 370 N/mm, while a maximum bending moment equal to 75.3 kNmm can be withstood without plate failure. On the whole, the performance of this dynamic plate was proved to be equal or superior to those measured for static plates already on the market, with excellent clinical results. At the same time, pre-clinical tests will be an interesting step of the future research, for which more prototypes are now being produced

Design and characterization of a minimally invasive bipolar electrode for electroporation

Objective: To test a new bipolar electrode for electroporation consisting of a single minimally invasive needle. Methods: A theoretical study was performed by using Comsol Multiphysics® software. The prototypes of electrode have been tested on potatoes and pigs, adopting an irreversible electroporation protocol. Different applied voltages and different geometries of bipolar electrode prototype have been evaluated. Results: Simulations and pre-clinical tests have shown that the volume of ablated area is mainly influenced by applied voltage, while the diameter of the electrode had a lesser impact, making the goal of minimal-invasiveness possible. The conductive pole’s length determined an increase of electroporated volume, while the insulated pole length inversely affects the electroporated volume size and shape; when the insulated pole length decreases, a more regular shape of the electric field is obtained. Moreover, the geometry of the electrode determined a different shape of the electroporated volume. A parenchymal damage in the liver of pigs due to irreversible electroporation protocol was observed. Conclusion: The minimally invasive bipolar electrode is able to treat an electroporated volume of about 10 mm in diameter by using a single-needle electrode. Moreover, the geometry and the electric characteristics can be selected to produce ellipsoidal ablation volumes

In vitro simulation of dental implant bridges removal: Influence of luting agent and abutments geometry on retrievability

Implant fixed dental prostheses are widely used for the treatment of edentulism, often preferred over the screw-retained ones. However, one of the main features of an implant-supported prosthesis is retrievability, which could be necessary in the case of implant complications. In this study, the retrievability of implant-fixed dental prostheses was investigated considering two of the main factors dental practitioners have to deal with: the abutments geometry and the luting agent. Impulsive forces were applied to dental bridge models to simulate crowns’ retrievability in clinical conditions. The number of impulses and the impulsive force delivered during each test were recorded and used as retrievability indexes. One-hundred-and-five tests were conducted on 21 combinations of bridges and luting agents, and a Kruskal-Wallis test was performed on the results. The abutment geometry significantly influenced the number of impulses needed for retrieval (p < 0.05), and a cement-dependent trend was observed as well. On the other hand, the forces measured during tests showed no clear correlation with bridge retrievability. The best retrievability was obtained with long, slightly tapered abutments and a temporary luting agent

REHABILITATION OF AMELOGENESIS IMPERFECTA AND VDO REDUCTION WITH DISILICATE VENEERS AND OVER- LAYS: A CASE REPORT.

Amelogenesis imperfecta(AI) is an inherited enamel dysplasia involving both dentitions with no other systemic effects. Here it is presented a case of a hypocalci ed enamel dysplasia(type III according to Wiktop classi cation) in a 21 year old male who was successfully treated with disilicate veneers and overlays

In vitro impact testing to simulate implant-supported prosthesis retrievability in clinical practice: Influence of cement and abutment geometry

Cement-retained implant-supported prosthetics are gaining popularity compared to the alternative screw-retained type, a rise that serves to highlight the importance of retrievability. The aim of the present investigation is to determine the influence of luting agent, abutment height and taper angle on the retrievability of abutment-coping cementations. Abutments with different heights and tapers were screwed onto an implant and their cobalt-chrome copings were cemented on the abutments using three different luting agents. The removals were performed by means of Coronaflex®. The number of impulses and the forces were recorded and analyzed with a Kruskal-Wallis test. Harvard cement needed the highest number of impulses for retrieval, followed by Telio CS and Temp Bond. However, abutment height and taper showed a greater influence on the cap's retrievability (p < 0.05). Long and tapered abutments provided the highest percentage of good retrievability. The influence of the luting agent and the abutment geometry on the cap's retrieval performed by Coronaflex® reflects data from literature about the influence of the same factor on the maximum force reached during uniaxial tensile tests. The impulse force was slightly affected by the same factors

A low-cost scalable 3D-printed sample-holder for agitation-based decellularization of biological tissues

Decellularized extracellular matrix is one of the most promising biological scaffold supporting in vitro tissue growth and in vivo tissue regeneration in both preclinical research and clinical practice. In case of thick tissues or even organs, conventional static decellularization methods based on chemical or enzymatic treatments are not effective in removing the native cellular material without affecting the extracellular matrix. To overcome this limitation, dynamic decellularization methods, mostly based on perfusion and agitation, have been proposed. In this study, we developed a low-cost scalable 3D-printed sample-holder for agitation-based decellularization purposes, designed for treating multiple specimens simultaneously and for improving efficiency, homogeneity and reproducibility of the decellularization treatment with respect to conventional agitation-based approaches. In detail, the proposed sample-holder is able to house up to four specimens and, immersed in the decellularizing solution within a beaker placed on a magnetic stirrer, to expose them to convective flow, enhancing the solution transport through the specimens while protecting them. Computational fluid dynamics analyses were performed to investigate the fluid phenomena establishing within the beaker and to support the sample-holder design. Exploratory biological tests performed on human skin specimens demonstrated that the sample-holder reduces process duration and increases treatment homogeneity and reproducibility