Biomedical subjects

Monica Soncini

Publications and source records attributed to Monica Soncini.

9 recordsLinked to original sources

PubMed2006

Mechanical response and conformational changes of alpha-actinin domains during unfolding: a molecular dynamics study.

Alpha-actinin is a cytoskeleton-binding protein involved in the assembly and regulation of the actin filaments. In this work molecular dynamics method was applied to investigate the mechanical behaviour of the human skeletal muscle alpha-actinin. Five configurations were unfolded at an elongation speed of 0.1 nm/ps in order to investigate the conformational changes occurring during the extension process. Moreover, a sensitivity analysis at different velocities was performed for one of the R2-R3 spectrin-like repeat configuration extracted in order to evaluate the effect of the pulling speed on the mechanical behaviour of the molecule. Two different behaviours were recognized with respect to the pulling speed. In particular, at speed higher than 0.025 nm/ps a continuous rearrangement without evident force peaks was obtained, on the contrary at lower speed evident peaks in the range 500-750 pN were detected. R3 repeat resulted more stable than R2 during mechanical unfolding, due to the lower hydrophobic surface available to the solvent. The characterization of the R2-R3 units can be useful for the development of cytoskeleton network models based on stiffness values obtained by analyses performed at the molecular level.

Actinin↗

PubMed2005

An annular prosthesis for the treatment of functional mitral regurgitation: finite element model analysis of a dog bone-shaped ring prosthesis.

BACKGROUND: Undersized annuloplasty is commonly used in the treatment of functional mitral regurgitation. However, in the case of severely dilated ventricles, annuloplasty may be inadequate to counteract leaflet tethering. My colleagues and I hypothesized that modifying the shape of the annular prosthesis to account for the specific anatomy of functional mitral regurgitation could challenge extreme leaflet tethering. METHODS: Using finite element model simulations, we tested valve competence after the implantation of conventional D-shaped versus dog bone-shaped annuloplasty rings, the latter of which was designed to selectively reduce the septolateral dimension of the annulus. Three models were compared: model A, simulating the native mitral valve; model B, simulating the same valve after annuloplasty with a conventional D-shaped annuloplasty; and model C, simulating a dog-bone annuloplasty ring implantation. Each model was then challenged by progressively pulling the tip of the papillary muscles away from the annulus plane to simulate ventricular remodeling and leaflet tethering. Valve competence was compared in each model for each degree of leaflet tethering. RESULTS: After maximal leaflet tethering simulation (4-mm apical displacement of the papillary tips), the regurgitant area increase was 70.4 mm2 for model A and 52.9 mm2 for model B. In model C, the regurgitant area was only negligibly affected by papillary displacement, increasing to 3.9 mm2. CONCLUSIONS: An annular prosthesis with selective reduction in the septolateral dimension is more effective than a conventional prosthesis for treating leaflet tethering in functional mitral regurgitation. Use of disease-specific annular prostheses is needed to improve the results of valve reconstruction.

Animals↗

PubMed2004

Haemodynamics and mechanics following partial left ventriculectomy: a computer modeling analysis.

Mechanics following partial left ventriculectomy is still poorly understood. A computational cylindrical model of the left ventricle was developed, based on the myocardial fibre behaviour for the evaluation of the mechanical and haemodynamical effects of the operation. A healthy left ventricle with physiological geometry and function and a dilated hypokinetic heart were investigated. Haemodynamic and mechanical data were obtained at baseline and compared with those obtained at different degrees of volume reduction. Data included: ejection fraction (EF); stroke volume (SV); end-systolic and end-diastolic pressure-volume relationships (ESPVR and EDPVR), and efficiency. EF increases following volume reduction in both simulation but, concurrently, SV shows modest improvement (dilated ventricle) or reduction (healthy ventricle) at progressive degrees of resection. The ESPVR and EDPVR slope increases and shifts leftward with the resection extent, but the increase of the ESPVR slope is more pronounced in dilated ventricle. Efficiency is improved in the dilated heart after resections, while does not improve when the healthy-heart volume is reduced. The simulation of partial left ventriculectomy suggests an improvement of systolic performance, counterbalanced by increased diastolic stiffness following inverse remodelling. Efficiency of simulated dilated ventricles is enhanced by volume reduction, suggesting a favourable effect of reduction of the metabolic demand of the failing heart.

Animals↗

PubMed2004

3-D simulation of the St. Jude Medical bileaflet valve opening process: fluid-structure interaction study and experimental validation.

BACKGROUND AND AIM OF THE STUDY: Simulation of the opening and closure dynamics of a mechanical valve through a moving deforming mesh algorithm presents a challenge because of the large rotations of the leaflet and of the small gaps between the housing and the leaflets, which make remeshing a critical issue. The present study offers a computational approach to the simulation of valve leaflet motion during the opening process, together with an experimental set-up for validation of the model. METHODS: A fully 3-D simulation of the 27 mm St. Jude Medical Hemodynamic Plus mechanical valve was performed using the computational code, Fluent. Interaction between the leaflet and fluid was simulated through customized user subroutines which, according to a weakly coupled approach, update the leaflet velocities through subsequent time steps by means of an under-relaxation procedure. A parallel, experimental test was defined to collect data for the set-up of simulations and for validation purposes. RESULTS: The computed leaflet velocity and angular displacement compared well with experimental data. The model captured the main features of the opening process, and did so also from a quantitative viewpoint. Nonetheless, some discrepancies were observed, including a delay of approximately 7 ms in the computed leaflet displacement and an underestimation by approximately 7% of the maximum computed leaflet velocity. CONCLUSION: The weakly coupled approach adopted here limited computational costs, thus allowing the simulation of a fully 3-D realistic mechanical valve within 154 CPU hours at minimal computational costs. No significant drawbacks were raised in comparison with the fully coupled approach. The opening process delay was similar to that reported previously, and cannot be ascribed to the weakly coupled approach adopted here.

Biomechanical Phenomena↗

PubMed2003

Behavior of the bone-titanium interface after push-in testing: a morphological study.

Fourteen titanium dental implants (Tioblast) were implanted singly in the proximal tibia of New Zealand rabbits for 120 days. A bone defect was surgically produced and filled with Bio-Oss around six of these implants. After the animals were sacrificed and their organs harvested, bone segments were fixed and methacrylate embedded after the push-in test had been performed. Microradiography was performed on longitudinal sections of the implants, whereas scanning electron microscope analysis was performed on the remaining embedded half-implants using secondary electrons only. The results showed that the implants were apically and coronally surrounded by bone, whether Bio-Oss was used or not. Fractures were evident through the newly formed bone and between the pre-existing and newly formed bone. Some fracture lines propagated through the bone and stopped at the implant surface without continuing along the bone-titanium interface. Detachment between the implant and the bone occurred at the coronal extremity of the implants and along its cervical region. These results highlight the fact that the bone-titanium interface has a high resistance to loading. It exhibited greater resistance than the newly formed bone and seems to behave in a manner similar to the cement lines of osteons.

Animals↗

PubMed2002

Experimental procedure for the evaluation of the mechanical properties of the bone surrounding dental implants.

The mechanical stability of the fixture in bone is one of the most important factors for the long-term reliability of dental implants. This paper focuses on an experimental procedure to evaluate the mechanical properties of the bone surrounding dental implants. The procedure is based on a surgical animal model followed by mechanical tests. The experimental mechanical testing has been used for preliminary investigations on the role played by different parameters such as the healing time and the surgical technique (standard or with regenerative material). The procedure has been evaluated in some preliminary tests on a few specimens. Microradiographic analyses have been performed on the bone surrounding the implants in order to give an interpretation of the bone properties on the basis of the bone morphology and to distinguish the newly formed bone from the pre-existing bone. The preliminary results relevant to 10 threaded titanium implants are presented and discussed. Our findings show that the mechanical properties of the bone surrounding the implant improve with the increase in the healing time from 24 to 45 days. The ultimate loads recorded during mechanical tests arise from 395 N to 2665 N in case of coronal defects filled with bone regenerative and from 2200 N to 5700 N in case of standard technique.

Animals↗

PubMed2002

A computerized method to measure systolic pressure variation (SPV) in mechanically ventilated patients.

INTRODUCTION: Intrathoracic pressure variation during mechanical ventilation has different effects on cardiac preload and stroke volume in both ventricles. Changes in left ventricle stroke volume are reflected by fluctuations of the arterial pressure waveform or Systolic Pressure Variation (SPV). SPV has been proposed as a way to evaluate vascular volume status in mechanically ventilated patients as well as responsiveness of the left ventricle stroke volume to volume loading. OBJECTIVE: In this paper an automated system is presented which is designed in order to provide physicians with information on SPV in mechanically ventilated patients. Methods. The developed system acquires the pressure transducer signal and analyses the pressure waveform in order to detect and identify the hemodynamic changes. Five patients underwent the clinical protocol in order to evaluate the software reliability. Each patient underwent measurements with positive end-expiratory pressure (PEEP) equal to 0 cm H2O, at an increase of 30% tidal volume, and at 15 cm H2O of PEEP, before and after infusion of 7 ml/kg of colloid solution. RESULTS: The reliability of the automated procedure has been verified by comparing the obtained results with data collected manually in order to test on whether the new method data are correlated with the conventional procedure. Our results show that in the worst case when the widest range for the limits of agreement is considered, the error is within 15%. CONCLUSIONS: The automated SPV measurement requires less time as well as human errors compared to the manual method; this makes SPV calculation a competitive alternative to methods for the measurements of stroke volume variations as arterial thermodilution technique and transesophageal echocardiography, which require sophisticated equipment and specific experience.

Blood Pressure Determination↗

PubMed2002

Quantitative approach for the prediction of tooth movement during orthodontic treatment.

The orthodontic treatment is aimed to displace and/or rotate the teeth to obtain the functionally correct occlusion and the best aesthetics and consists in applying forces and/or couples to tooth crowns. The applied loads are generated by the elastic recovery of metallic wires linked to the tooth crowns by brackets. These loads generate a stress state into the periodontal ligament and hence, in the alveolar bone, causing the bone remodeling responsible for the tooth movement. The orthodontic appliance is usually designed on the basis of the clinical experience of the orthodontist. In this work, a quantitative approach for the prediction of the tooth movement is presented that has been developed as a first step to build up a computer tool to aid the orthodontist in designing the orthodontic appliance. The model calculates the tooth movement through time with respect to a fixed Cartesian frame located in the middle of the dental arch. The user interface panel has been designed to allow the orthodontist to manage the standard geometrical references and parameters usually adopted to design the treatment. Simulations of specific cases are reported for which the parameters of the model are selected in order to reproduce forecasts of tooth movement matching data published in experimental works.

Animals↗

PubMed2002

3-D computational analysis of the stress distribution on the leaflets after edge-to-edge repair of mitral regurgitation.

BACKGROUND AND AIM OF THE STUDY: Edge-to-edge repair is an effective, recently introduced method to correct mitral insufficiency by suturing the leaflets at the site of regurgitation, though durability of the method has not been proven. To overcome the limitations of the clinical approach, simulations may be used to predict clinical outcome. In this study, the mechanical stress acting on leaflets imposed by the edge-to-edge suture was evaluated as a means of assessing the clinical risk of late fibrosis or tissue degeneration. METHODS: A 3-D finite element simulated the stress pattern following edge-to-edge repair. Valve behavior was evaluated both in systole and in diastole. Both 4-mm and 8-mm edge-to-edge sutures were simulated, as well as annular dilation. RESULTS: Systolic simulations validated the model by comparison with previous models of the mitral valve. Diastolic stresses were negligible in the native mitral valve; after edge-to-edge repair (8-mm suture), circumferential and longitudinal stress values were 308 kPa and 489 kPa, respectively, and comparable with those observed at systolic peak (449 kPa and 617 kPa, respectively). With a 4-mm suture, longitudinal stresses decreased both close to the suture (-41.5%) and in the annular region (-68%), while circumferential stresses increased (+37%) close to the suture and decreased (-27%) in the annular region. A 20% dilation of the annulus was followed by increased stresses in the annular region and close to the suture. CONCLUSION: Leaflet distortion and altered stress distribution occur on the leaflets after edge-to-edge repair. Diastolic peak stress values were comparable with those calculated in systole. The clinical implication is a doubled exposure of valve components to systolic stresses, as if the heart rate were doubled. The use of a prosthetic annuloplasty ring is favorable in the presence of annular dilation to reduce stresses acting on the leaflets after edge-to-edge repair.

Chordae Tendineae↗