Tomaso Villa - Academia.edu (original) (raw)
Papers by Tomaso Villa
Journal of applied biomaterials & biomechanics (JABB)
Contracture of the fibrous connective capsules that form around breast implants is the most frequ... more Contracture of the fibrous connective capsules that form around breast implants is the most frequent complication for silicone mammary prostheses. Capsule contraction is thought to be associated with the alteration in the mechanical properties of the tissue, but to date such a correlation has not been quantified. This study aimed to develop an experimental protocol to investigate the mechanical properties of the periprosthetic tissue and their dependence on the severity of capsular ontracture. Capsule samples were harvested from donors undergoing surgical correction or re-implantation of breast prostheses; strip spec-imens were cut along both the meridian and circumferential directions of the capsular dome. The experimental protocol consisted of mechanical preconditioning, stress relaxation tests and tensile tests to rupture. The capsular tissue exhibited non-linear stress-strain relationships and stress relaxation behavior; nevertheless, both the elastic and the relaxation properti...
Journal of applied biomaterials & biomechanics (JABB)
Surgical interventions on the arterial wall can produce modifications to its tissue characteristi... more Surgical interventions on the arterial wall can produce modifications to its tissue characteristics, and the addition of synthetic materials of different types can have implications on hemodynamics and blood vessel wall behavior. This work studies the midterm effects of end-to-end anastomosis (E/E), Gore-tex graft interposition (GGI) and Gore-tex patch graft aortoplasty (GPGA) in aortic arch reconstruction. The study comprised of two groups of healthy Danish sows. The sows in the first group (short term (ST)) weighed about 40 kg, underwent a surgical operation and were sacrificed on the same day. The sows in the second group (midterm (MT)) weighed 5-10 kg, underwent a surgical operation and were then allowed to grow to a weight of about 30-40 kg, before being sacrificed. One sow in each group was scheduled for E/E and one sow for GGI. One sow in ST and two sows in MT received GPGA. The overall average wall thickness was 1.93 mm. Relaxation constant values were significantly higher f...
The International journal of oral & maxillofacial implants
The aim of this in vitro study was to evaluate the stress pattern on the abutments in two differe... more The aim of this in vitro study was to evaluate the stress pattern on the abutments in two different full-arch implant-supported clinically equivalent prosthetic rehabilitations. Two steel master casts were created and titanium implants were inserted in two different configurations. One configuration used four implants, with the distal implants tilted 30 degrees (4IMP configuration), and the other used five axially inclined implants (5IMP configuration). A straight multiunit abutment (MUA) was connected to every axial implant and a 30-degree angulated MUA was connected to each tilted implant. One titanium framework was fabricated for each configuration, with a 5-mm (4IMP configuration) or a 15-mm (5IMP configuration) distal cantilever length. Six cycles of vertical loading between 20 and 200 N were applied unilaterally at the most distal point of the frameworks on both sides. Readings of the deformations at the abutment level were obtained with the use of linear strain gauges. A simi...
Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine, 2014
Preclinical evaluation of spinal implants is a necessary step to ensure their reliability and saf... more Preclinical evaluation of spinal implants is a necessary step to ensure their reliability and safety before implantation. The American Society for Testing and Materials reapproved F1717 standard for the assessment of mechanical properties of posterior spinal fixators, which simulates a vertebrectomy model and recommends mimicking vertebral bodies using polyethylene blocks. This set-up should represent the clinical use, but available data in the literature are few. Anatomical parameters depending on the spinal level were compared to published data or measurements on biplanar stereoradiography on 13 patients. Other mechanical variables, describing implant design were considered, and all parameters were investigated using a numerical parametric finite element model. Stress values were calculated by considering either the combination of the average values for each parameter or their worst-case combination depending on the spinal level. The standard set-up represents quite well the anato...
ABSTRACT Three experimental tasks are of primary interest in biomechanics: determination of the m... more ABSTRACT Three experimental tasks are of primary interest in biomechanics: determination of the mechanical properties of biomaterials, including tissues and artificial materials; validation of the mechanical reliability of implantable devices; assessment of the compatibility of the mechanical properties of such devices with the surrounding biological environment. Due to the complexity of the in vivo conditions, most of these studies are performed on in vitro models. This contribution presents a review of some methods that are currently utilised at the Laboratory of Biological Structure Mechanics at the Politecnico of Milan.
The Journal of Prosthetic Dentistry, 2014
Metal ceramic systems are used for the majority of dental crowns and fixed dental prostheses. How... more Metal ceramic systems are used for the majority of dental crowns and fixed dental prostheses. However, problems with porcelain bonding are encountered when titanium is used as the substrate. The purpose of this study was to evaluate the effect of intermediate calcium oxide-stabilized zirconia (ZrO2-CaO) coatings deposited by cold thermal spraying on the titanium-porcelain bonding in dental restorations. Two different types of ZrO2-CaO coatings obtained by oxyacetylene cold thermal spraying deposition were applied on commercially pure titanium bars before adding the porcelain layer. Type 1 was obtained by directly spraying the ZrO2-CaO powder on the titanium substrate. Type 2 was obtained by spraying a bond coat of nickel-aluminum-molybdenum alloy before spraying the ZrO2-CaO powder. Three-point bend tests according to International Organization of Standardization 9693-1:2012 were carried out to evaluate the debonding strength for the ZrO2-CaO-coated specimens (types 1 and 2) in comparison with a noncoated group (control), which received a traditional bonder-based adhesive technique. The results were compared with ANOVA, followed by the Student-Newman-Keuls test for pairwise comparisons. Scanning electron microscopy and energy dispersion spectroscopy were used to examine the interfacial properties and the failure mode of each group. Mean (±standard deviation) debonding strength values for type 1 coating (25.97 ±2.53 MPa) and control (23.51 ±2.94 MPa) were near the acceptable lower limit of 25 MPa indicated by the International Organization of Standardization 9693-1:2012 and were not significantly different (Student-Newman-Keuls test, P>.05). Type 2 coating produced an improved titanium-porcelain bonding (debonding strength=39.47 ±4.12 MPa), significantly higher than both type 1 (Student-Newman-Keuls test, P<.05) and control (Student-Newman-Keuls test, P<.05). Scanning electron microscopy-energy dispersion spectroscopy analysis confirmed these findings, which revealed a predominant cohesive failure mode for type 2. An intermediate coating layer of ZrO2-CaO plus a substrate of bonding nickel-aluminum-molybdenum alloy applied by oxyacetylene cold thermal spraying deposition provided an improved titanium-porcelain bond.
The spine journal : official journal of the North American Spine Society, 2014
Journal of Applied Biomaterials & Biomechanics, 2011
Experimental tests have played a major role in the assessment of fatigue endurance of orthopedic ... more Experimental tests have played a major role in the assessment of fatigue endurance of orthopedic prostheses; however, cyclic tests on devices entail high costs. Here, a multiaxial fatigue criterion coupled with computational simulations and material properties measurements has been employed to predict fatigue life of the tibial component of a polymeric PMMA spacer. The ultimate aim is to obtain valid information on fatigue behavior avoiding fatigue tests on the device. First, an accurate measurement of the static and fatigue properties of PMMA samples is performed. Then, numeric simulations of the fatigue behavior of the PMMA spacer reproducing the experimental test conditions according to ISO 14879-1 were carried out in order to calculate the stress field throughout the device. Finally, a Risk Index was calculated by using a proper multiaxial fatigue criterion for brittle materials (Kakuno-Kawada) for the assessment of the device fatigue behavior by predicting the F-N curves. The numeric results were validated by comparing the predictions against experimental data already published by our group. The multiaxial fatigue criterion was able to predict the most critical point on the spacer upper surface and the fatigue behavior of the device that nicely matched the experimental curves. This approach represents a valuable tool to investigate the mechanical reliability of implantable devices; nevertheless, the use of advanced and specific failure criteria coupled with accurate data of the device’s material is mandatory to represent a real alternative to the experimental approach in fatigue life prediction.??Key words: Acrylic bone cement, Fatigue endurance, Finite element analyses, Knee spacer.
The Foot, 2014
Objective: Sports people always strive to avoid injury. Sports shoe designs in many sports have b... more Objective: Sports people always strive to avoid injury. Sports shoe designs in many sports have been shown to affect traction and injury rates. The aim of this study is to demonstrate the differing stiffness and torque in rugby boots that are designed for the same effect. Methods: Five different types of rugby shoes commonly worn by scrum forwards were laboratory tested for rotational stiffness and peak torque on a natural playing surface generating force patterns that would be consistent with a rugby scrum. Results: The overall internal rotation peak torque was 57.75 ± 6.26 N m while that of external rotation was 56.55 ± 4.36 N m. The Peak internal and external rotational stiffness were 0.696 ± 0.1 and 0.708 ± 0.06 N m/deg respectively. Our results, when compared to rotational stiffness and peak torques of football shoes published in the literature, show that shoes worn by rugby players exert higher rotational and peak torque stiffness compared to football shoes when tested on the same natural surfaces. There was significant difference between the tested rugby shoes brands. Conclusion: In our opinion, to maximize potential performance and lower the potential of non-contact injury, care should be taken in choosing boots with stiffness appropriate to the players main playing role.
Frontiers in Bioengineering and Biotechnology, 2014
Knee ligaments are elastic bands of soft tissue with a complex microstructure and biomechanics, w... more Knee ligaments are elastic bands of soft tissue with a complex microstructure and biomechanics, which are critical to determine the kinematics as well as the stress bearing behavior of the knee joint. Their correct implementation in terms of material models and properties is therefore necessary in the development of finite element models of the knee, which has been performed for decades for the investigation of both its basic biomechanics and the development of replacement implants and repair strategies for degenerative and traumatic pathologies. Indeed, a wide range of element types and material models has been used to represent knee ligaments, ranging from elastic unidimensional elements to complex hyperelastic three-dimensional structures with anatomically realistic shapes. This paper systematically reviews literature studies, which described finite element models of the knee, and summarizes the approaches, which have been used to model the ligaments highlighting their strengths and weaknesses.
The Spine Journal, 2014
Preclinical evaluation of the long-term reliability of devices for lumbar fixation is a mandatory... more Preclinical evaluation of the long-term reliability of devices for lumbar fixation is a mandatory activity before they are put into market. The experimental setups are described in two different standards edited by the International Organization for Standardization (ISO) and the American Society for Testing Materials (ASTM), but the evaluation of the suitability of such tests to simulate the actual loading with in vivo situations has never been performed. To calculate through finite element (FE) simulations the stress in the rods of the fixator when subjected to ASTM and ISO standards. To compare the calculated stresses arising in the same fixator once it has been virtually mounted in a physiological environment and loaded with physiological forces and moments. FE simulations and validation experimental tests. FE models of the ISO and ASTM setups were created to conduct simulations of the tests prescribed by standards and calculate stresses in the rods. Validation of the simulations were performed through experimental tests; the same fixator was virtually mounted in an L2-L4 FE model of the lumbar spine and stresses in the rods were calculated when the spine was subjected to physiological forces and moments. The comparison between FE simulations and experimental tests showed good agreement between results obtained using the two methodologies, thus confirming the suitability of the FE method to evaluate stresses in the device in different loading situations. The usage of a physiological load with ASTM standard is impossible due to the extreme severity of the ASTM configuration; in this circumstance, the presence of an anterior support is suggested. Also, ISO prescriptions, although the choice of the setup correctly simulates the mechanical contribution of the discs, seem to overstress the device as compared with a physiological loading condition. Some daily activities, other than walking, can induce a further state of stress in the device that should be taken into account in setting up new experimental procedures. ISO standard loading prescriptions seems to be more severe than the expected physiological ones. The ASTM standard should be completed by including some anterior supporting device and declaring the value of the load to be imposed. Moreover, a further enhancement of standards would be simulating other movements representative of daily activities different from walking.
The Spine Journal, 2013
BACKGROUND CONTEXT: There is no universal consensus regarding the biomechanical aspects and relev... more BACKGROUND CONTEXT: There is no universal consensus regarding the biomechanical aspects and relevance on the primary stability of misplaced pedicle screws. PURPOSE: The study is aimed to the determination of the correlation between axial pullout forces of pedicle screws with the possible screw misplacement, including mild and severe cortical violations. METHODS: Eighty-eight monoaxial pedicle screws were implanted into 44 porcine lumbar vertebral bodies, paying attention on trying to obtain a wide range of placement accuracy. After screw implantation, all specimens underwent a spiral computed tomography scan, and the screw placements were graded following the scales of Laine et al. and Abul Kasim et al. Axial pullout tests were then performed on a servohydraulic material testing system. RESULTS: Decreasing pullout forces were determined for screws implanted with increasing cortical violation. A smaller influence of cortical violations in the medial direction with respect to the lateral direction was observed. Screws implanted with a large cortical violation and misplacement in the craniocaudal direction were found to be significantly less stable than screws having comparable cortical violation but in a centered sagittal position. CONCLUSIONS: These results provide adjunctive criteria to evaluate more accurately the fate of a spine instrumentation. Particular care should be placed in the screw evaluation regarding the craniocaudal positioning and alignment. Ó
Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine, 2011
Abstract: The long-term success of surgical applications requiring bone cement is strongly influe... more Abstract: The long-term success of surgical applications requiring bone cement is strongly influenced by the cement's rheological properties. Previous studies showed a clear non-Newtonian, pseudoplastic, time-dependent rheological behaviour of acrylic bone cement during the ...
Materials Science and Engineering: C, 2013
A novel hierarchical textile structure made of silk fibroin from Bombyx mori capable of matching ... more A novel hierarchical textile structure made of silk fibroin from Bombyx mori capable of matching the mechanical performance requirements of anterior cruciate ligament (ACL) and in vitro cell ingrowth is described. This sericin-free, Silk Fibroin Knitted Sheath with Braided Core (SF-KSBC) structure was fabricated using available textile technologies. Micro-CT analysis confirmed that the core was highly porous and had a higher degree of interconnectivity than that observed for the sheath. The in vivo cell colonization of the scaffolds is thus expected to penetrate even the internal parts of the structure. Tensile mechanical tests demonstrated a maximum load of 1212.4±56.4 N (under hydrated conditions), confirming the scaffold's suitability for ACL reconstruction. The absence of cytotoxic substances in the extracts of the SF-KSBC structure in culture medium was verified by in vitro tests with L929 fibroblasts. In terms of extracellular matrix production, Human Periodontal Ligament Fibroblasts (HPdLFs) cultured in direct contact with SF-KSBC, compared to control samples, demonstrated an increased secretion of aggrecan (PG) and fibronectin (FBN) at 3 and 7 days of culture, and no change in IL-6 and TNF-α secretion. Altogether, the outcomes of this investigation confirm the significant utility of this novel scaffold for ACL tissue regeneration.
The Knee, 2007
Infection of knee prostheses is still one of the major concerns of the reliability over time of t... more Infection of knee prostheses is still one of the major concerns of the reliability over time of these implantable devices. The preferred treatment of this condition has turned out to be the use of a knee spacer in a two-stage reimplantation technique. The advantages of this technique associated with the use of a mobile spacer lies both in the possibility for the patient to move during the interim period, thus decreasing the risk of muscle contracture due to immobilisation, as well as in the ability to release antibiotics directly to the site of infection. The evaluation of the biomechanical properties of new mobile spacers preformed in three different sizes has been carried out subjecting the spacers to i) cyclic tests on a knee simulator for 500,000 walking cycles, ii) constraint tests in medio-lateral, antero-posterior and internal-external directions, iii) fatigue tests on the tibial tray. Particular attention was addressed to the evaluation of the mechanical resistance of the devices, to the quantity of wear debris produced during the tests and to the extent that such debris was influenced by the test parameters and geometrical dimensions of the spacers themselves. Results showed no sign of failure for any of the tested spacers, the constraint and fatigue behaviours were similar to those shown by a total knee prosthesis and the amount of debris turned out to be directly correlated to the size of the devices: in conclusion, the devices showed a good level of mechanical performance and, consequently, a sufficiently high degree of suitability for clinical use.
Journal of Mechanics in Medicine and Biology, 2010
ABSTRACT Glenoid failure is one of the major indications for revision in total shoulder arthropla... more ABSTRACT Glenoid failure is one of the major indications for revision in total shoulder arthroplasty. Glenoid components should be carefully designed to improve the reliability of the prostheses, and mechanical testing can be a key tool to compare the performances of different designs. The most relevant guidelines for mechanical testing of glenoid prostheses are included in the ASTM F2028-05 Standard. The Standard refers to glenoid subluxation tests, designed to evaluate the intrinsic stability of the prosthesis system, and to glenoid edge displacement tests, which estimate the risk of micro-motions at the bone-glenoid interface. However, some indications given by the Standard are not mandatory, leaving the possibility to choose some parameters of the testing set-up and procedure. The main goal of this study was to investigate how different testing parameters (i.e. loads, velocities and bone-glenoid conformity) may affect the test results. In order to reach this target an experimental apparatus was developed and mechanical tests were performed on a keeled glenoid. The study showed that the applied load and the bone-glenoid conformity have a significant effect on the tests results, because of bone and glenoid deformation. Contrarily, the testing velocity was not found to be an influencing testing parameter.
Journal of Biomedical Materials Research Part A, 2012
Crosslinked vitamin-E-stabilized polyethylene acetabular cups were compared with both commerciall... more Crosslinked vitamin-E-stabilized polyethylene acetabular cups were compared with both commercially available conventional and custom-crosslinked polyethylene acetabular cups in terms of wear behavior, in a hip joint simulator for five millions cycles, using bovine calf serum as lubricant. We correlated the wear experiments results with the chemical characterization of the investigated materials: Fourier transformed infrared (FTIR) spectroscopic analyses, differential scanning calorimetry, and crosslink density measurements were used to assess the chemical characteristics of the pristine materials. In addition, further FTIR analyses and cyclohexane extraction were carried out after the simulator experiments. Lipids absorption was observed in all tested specimens and it has been shown to strongly affect the results of the wear test. Corrected gravimetric wear measurements showed that vitamin-E blended, crosslinked polyethylene wore more than the traditional crosslinked polyethylene but exhibited a much lower wear than conventional ultrahigh-molecular weight polyethylene. The chemical analyses showed that the addition of vitamin E reduced the crosslinking efficiency. Given the correlation between crosslink density and wear resistance, this gave an explanation for the observed wear performances. V C 2011 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 00A: 000-000, 2011.
Journal of Biomechanics, 2006
Journal of Biomechanics, 2012
Journal of Biomechanics, 2004
The evaluation of contact areas and pressures in total knee prosthesis is a key issue to prevent ... more The evaluation of contact areas and pressures in total knee prosthesis is a key issue to prevent early failure. The first part of this study is based on the hypothesis that the patterns of contact stresses on the tibial insert of a knee prosthesis at different stages of the gait cycle could be an indicator of the wear performances of a knee prosthesis. Contact stresses were calculated for a mobile bearing knee prosthesis by means of finite element method (FEM). Contact areas and stresses were also measured through in vitro tests using Fuji Prescale film in order to support the FEM findings.
Journal of applied biomaterials & biomechanics (JABB)
Contracture of the fibrous connective capsules that form around breast implants is the most frequ... more Contracture of the fibrous connective capsules that form around breast implants is the most frequent complication for silicone mammary prostheses. Capsule contraction is thought to be associated with the alteration in the mechanical properties of the tissue, but to date such a correlation has not been quantified. This study aimed to develop an experimental protocol to investigate the mechanical properties of the periprosthetic tissue and their dependence on the severity of capsular ontracture. Capsule samples were harvested from donors undergoing surgical correction or re-implantation of breast prostheses; strip spec-imens were cut along both the meridian and circumferential directions of the capsular dome. The experimental protocol consisted of mechanical preconditioning, stress relaxation tests and tensile tests to rupture. The capsular tissue exhibited non-linear stress-strain relationships and stress relaxation behavior; nevertheless, both the elastic and the relaxation properti...
Journal of applied biomaterials & biomechanics (JABB)
Surgical interventions on the arterial wall can produce modifications to its tissue characteristi... more Surgical interventions on the arterial wall can produce modifications to its tissue characteristics, and the addition of synthetic materials of different types can have implications on hemodynamics and blood vessel wall behavior. This work studies the midterm effects of end-to-end anastomosis (E/E), Gore-tex graft interposition (GGI) and Gore-tex patch graft aortoplasty (GPGA) in aortic arch reconstruction. The study comprised of two groups of healthy Danish sows. The sows in the first group (short term (ST)) weighed about 40 kg, underwent a surgical operation and were sacrificed on the same day. The sows in the second group (midterm (MT)) weighed 5-10 kg, underwent a surgical operation and were then allowed to grow to a weight of about 30-40 kg, before being sacrificed. One sow in each group was scheduled for E/E and one sow for GGI. One sow in ST and two sows in MT received GPGA. The overall average wall thickness was 1.93 mm. Relaxation constant values were significantly higher f...
The International journal of oral & maxillofacial implants
The aim of this in vitro study was to evaluate the stress pattern on the abutments in two differe... more The aim of this in vitro study was to evaluate the stress pattern on the abutments in two different full-arch implant-supported clinically equivalent prosthetic rehabilitations. Two steel master casts were created and titanium implants were inserted in two different configurations. One configuration used four implants, with the distal implants tilted 30 degrees (4IMP configuration), and the other used five axially inclined implants (5IMP configuration). A straight multiunit abutment (MUA) was connected to every axial implant and a 30-degree angulated MUA was connected to each tilted implant. One titanium framework was fabricated for each configuration, with a 5-mm (4IMP configuration) or a 15-mm (5IMP configuration) distal cantilever length. Six cycles of vertical loading between 20 and 200 N were applied unilaterally at the most distal point of the frameworks on both sides. Readings of the deformations at the abutment level were obtained with the use of linear strain gauges. A simi...
Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine, 2014
Preclinical evaluation of spinal implants is a necessary step to ensure their reliability and saf... more Preclinical evaluation of spinal implants is a necessary step to ensure their reliability and safety before implantation. The American Society for Testing and Materials reapproved F1717 standard for the assessment of mechanical properties of posterior spinal fixators, which simulates a vertebrectomy model and recommends mimicking vertebral bodies using polyethylene blocks. This set-up should represent the clinical use, but available data in the literature are few. Anatomical parameters depending on the spinal level were compared to published data or measurements on biplanar stereoradiography on 13 patients. Other mechanical variables, describing implant design were considered, and all parameters were investigated using a numerical parametric finite element model. Stress values were calculated by considering either the combination of the average values for each parameter or their worst-case combination depending on the spinal level. The standard set-up represents quite well the anato...
ABSTRACT Three experimental tasks are of primary interest in biomechanics: determination of the m... more ABSTRACT Three experimental tasks are of primary interest in biomechanics: determination of the mechanical properties of biomaterials, including tissues and artificial materials; validation of the mechanical reliability of implantable devices; assessment of the compatibility of the mechanical properties of such devices with the surrounding biological environment. Due to the complexity of the in vivo conditions, most of these studies are performed on in vitro models. This contribution presents a review of some methods that are currently utilised at the Laboratory of Biological Structure Mechanics at the Politecnico of Milan.
The Journal of Prosthetic Dentistry, 2014
Metal ceramic systems are used for the majority of dental crowns and fixed dental prostheses. How... more Metal ceramic systems are used for the majority of dental crowns and fixed dental prostheses. However, problems with porcelain bonding are encountered when titanium is used as the substrate. The purpose of this study was to evaluate the effect of intermediate calcium oxide-stabilized zirconia (ZrO2-CaO) coatings deposited by cold thermal spraying on the titanium-porcelain bonding in dental restorations. Two different types of ZrO2-CaO coatings obtained by oxyacetylene cold thermal spraying deposition were applied on commercially pure titanium bars before adding the porcelain layer. Type 1 was obtained by directly spraying the ZrO2-CaO powder on the titanium substrate. Type 2 was obtained by spraying a bond coat of nickel-aluminum-molybdenum alloy before spraying the ZrO2-CaO powder. Three-point bend tests according to International Organization of Standardization 9693-1:2012 were carried out to evaluate the debonding strength for the ZrO2-CaO-coated specimens (types 1 and 2) in comparison with a noncoated group (control), which received a traditional bonder-based adhesive technique. The results were compared with ANOVA, followed by the Student-Newman-Keuls test for pairwise comparisons. Scanning electron microscopy and energy dispersion spectroscopy were used to examine the interfacial properties and the failure mode of each group. Mean (±standard deviation) debonding strength values for type 1 coating (25.97 ±2.53 MPa) and control (23.51 ±2.94 MPa) were near the acceptable lower limit of 25 MPa indicated by the International Organization of Standardization 9693-1:2012 and were not significantly different (Student-Newman-Keuls test, P>.05). Type 2 coating produced an improved titanium-porcelain bonding (debonding strength=39.47 ±4.12 MPa), significantly higher than both type 1 (Student-Newman-Keuls test, P<.05) and control (Student-Newman-Keuls test, P<.05). Scanning electron microscopy-energy dispersion spectroscopy analysis confirmed these findings, which revealed a predominant cohesive failure mode for type 2. An intermediate coating layer of ZrO2-CaO plus a substrate of bonding nickel-aluminum-molybdenum alloy applied by oxyacetylene cold thermal spraying deposition provided an improved titanium-porcelain bond.
The spine journal : official journal of the North American Spine Society, 2014
Journal of Applied Biomaterials & Biomechanics, 2011
Experimental tests have played a major role in the assessment of fatigue endurance of orthopedic ... more Experimental tests have played a major role in the assessment of fatigue endurance of orthopedic prostheses; however, cyclic tests on devices entail high costs. Here, a multiaxial fatigue criterion coupled with computational simulations and material properties measurements has been employed to predict fatigue life of the tibial component of a polymeric PMMA spacer. The ultimate aim is to obtain valid information on fatigue behavior avoiding fatigue tests on the device. First, an accurate measurement of the static and fatigue properties of PMMA samples is performed. Then, numeric simulations of the fatigue behavior of the PMMA spacer reproducing the experimental test conditions according to ISO 14879-1 were carried out in order to calculate the stress field throughout the device. Finally, a Risk Index was calculated by using a proper multiaxial fatigue criterion for brittle materials (Kakuno-Kawada) for the assessment of the device fatigue behavior by predicting the F-N curves. The numeric results were validated by comparing the predictions against experimental data already published by our group. The multiaxial fatigue criterion was able to predict the most critical point on the spacer upper surface and the fatigue behavior of the device that nicely matched the experimental curves. This approach represents a valuable tool to investigate the mechanical reliability of implantable devices; nevertheless, the use of advanced and specific failure criteria coupled with accurate data of the device’s material is mandatory to represent a real alternative to the experimental approach in fatigue life prediction.??Key words: Acrylic bone cement, Fatigue endurance, Finite element analyses, Knee spacer.
The Foot, 2014
Objective: Sports people always strive to avoid injury. Sports shoe designs in many sports have b... more Objective: Sports people always strive to avoid injury. Sports shoe designs in many sports have been shown to affect traction and injury rates. The aim of this study is to demonstrate the differing stiffness and torque in rugby boots that are designed for the same effect. Methods: Five different types of rugby shoes commonly worn by scrum forwards were laboratory tested for rotational stiffness and peak torque on a natural playing surface generating force patterns that would be consistent with a rugby scrum. Results: The overall internal rotation peak torque was 57.75 ± 6.26 N m while that of external rotation was 56.55 ± 4.36 N m. The Peak internal and external rotational stiffness were 0.696 ± 0.1 and 0.708 ± 0.06 N m/deg respectively. Our results, when compared to rotational stiffness and peak torques of football shoes published in the literature, show that shoes worn by rugby players exert higher rotational and peak torque stiffness compared to football shoes when tested on the same natural surfaces. There was significant difference between the tested rugby shoes brands. Conclusion: In our opinion, to maximize potential performance and lower the potential of non-contact injury, care should be taken in choosing boots with stiffness appropriate to the players main playing role.
Frontiers in Bioengineering and Biotechnology, 2014
Knee ligaments are elastic bands of soft tissue with a complex microstructure and biomechanics, w... more Knee ligaments are elastic bands of soft tissue with a complex microstructure and biomechanics, which are critical to determine the kinematics as well as the stress bearing behavior of the knee joint. Their correct implementation in terms of material models and properties is therefore necessary in the development of finite element models of the knee, which has been performed for decades for the investigation of both its basic biomechanics and the development of replacement implants and repair strategies for degenerative and traumatic pathologies. Indeed, a wide range of element types and material models has been used to represent knee ligaments, ranging from elastic unidimensional elements to complex hyperelastic three-dimensional structures with anatomically realistic shapes. This paper systematically reviews literature studies, which described finite element models of the knee, and summarizes the approaches, which have been used to model the ligaments highlighting their strengths and weaknesses.
The Spine Journal, 2014
Preclinical evaluation of the long-term reliability of devices for lumbar fixation is a mandatory... more Preclinical evaluation of the long-term reliability of devices for lumbar fixation is a mandatory activity before they are put into market. The experimental setups are described in two different standards edited by the International Organization for Standardization (ISO) and the American Society for Testing Materials (ASTM), but the evaluation of the suitability of such tests to simulate the actual loading with in vivo situations has never been performed. To calculate through finite element (FE) simulations the stress in the rods of the fixator when subjected to ASTM and ISO standards. To compare the calculated stresses arising in the same fixator once it has been virtually mounted in a physiological environment and loaded with physiological forces and moments. FE simulations and validation experimental tests. FE models of the ISO and ASTM setups were created to conduct simulations of the tests prescribed by standards and calculate stresses in the rods. Validation of the simulations were performed through experimental tests; the same fixator was virtually mounted in an L2-L4 FE model of the lumbar spine and stresses in the rods were calculated when the spine was subjected to physiological forces and moments. The comparison between FE simulations and experimental tests showed good agreement between results obtained using the two methodologies, thus confirming the suitability of the FE method to evaluate stresses in the device in different loading situations. The usage of a physiological load with ASTM standard is impossible due to the extreme severity of the ASTM configuration; in this circumstance, the presence of an anterior support is suggested. Also, ISO prescriptions, although the choice of the setup correctly simulates the mechanical contribution of the discs, seem to overstress the device as compared with a physiological loading condition. Some daily activities, other than walking, can induce a further state of stress in the device that should be taken into account in setting up new experimental procedures. ISO standard loading prescriptions seems to be more severe than the expected physiological ones. The ASTM standard should be completed by including some anterior supporting device and declaring the value of the load to be imposed. Moreover, a further enhancement of standards would be simulating other movements representative of daily activities different from walking.
The Spine Journal, 2013
BACKGROUND CONTEXT: There is no universal consensus regarding the biomechanical aspects and relev... more BACKGROUND CONTEXT: There is no universal consensus regarding the biomechanical aspects and relevance on the primary stability of misplaced pedicle screws. PURPOSE: The study is aimed to the determination of the correlation between axial pullout forces of pedicle screws with the possible screw misplacement, including mild and severe cortical violations. METHODS: Eighty-eight monoaxial pedicle screws were implanted into 44 porcine lumbar vertebral bodies, paying attention on trying to obtain a wide range of placement accuracy. After screw implantation, all specimens underwent a spiral computed tomography scan, and the screw placements were graded following the scales of Laine et al. and Abul Kasim et al. Axial pullout tests were then performed on a servohydraulic material testing system. RESULTS: Decreasing pullout forces were determined for screws implanted with increasing cortical violation. A smaller influence of cortical violations in the medial direction with respect to the lateral direction was observed. Screws implanted with a large cortical violation and misplacement in the craniocaudal direction were found to be significantly less stable than screws having comparable cortical violation but in a centered sagittal position. CONCLUSIONS: These results provide adjunctive criteria to evaluate more accurately the fate of a spine instrumentation. Particular care should be placed in the screw evaluation regarding the craniocaudal positioning and alignment. Ó
Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine, 2011
Abstract: The long-term success of surgical applications requiring bone cement is strongly influe... more Abstract: The long-term success of surgical applications requiring bone cement is strongly influenced by the cement's rheological properties. Previous studies showed a clear non-Newtonian, pseudoplastic, time-dependent rheological behaviour of acrylic bone cement during the ...
Materials Science and Engineering: C, 2013
A novel hierarchical textile structure made of silk fibroin from Bombyx mori capable of matching ... more A novel hierarchical textile structure made of silk fibroin from Bombyx mori capable of matching the mechanical performance requirements of anterior cruciate ligament (ACL) and in vitro cell ingrowth is described. This sericin-free, Silk Fibroin Knitted Sheath with Braided Core (SF-KSBC) structure was fabricated using available textile technologies. Micro-CT analysis confirmed that the core was highly porous and had a higher degree of interconnectivity than that observed for the sheath. The in vivo cell colonization of the scaffolds is thus expected to penetrate even the internal parts of the structure. Tensile mechanical tests demonstrated a maximum load of 1212.4±56.4 N (under hydrated conditions), confirming the scaffold's suitability for ACL reconstruction. The absence of cytotoxic substances in the extracts of the SF-KSBC structure in culture medium was verified by in vitro tests with L929 fibroblasts. In terms of extracellular matrix production, Human Periodontal Ligament Fibroblasts (HPdLFs) cultured in direct contact with SF-KSBC, compared to control samples, demonstrated an increased secretion of aggrecan (PG) and fibronectin (FBN) at 3 and 7 days of culture, and no change in IL-6 and TNF-α secretion. Altogether, the outcomes of this investigation confirm the significant utility of this novel scaffold for ACL tissue regeneration.
The Knee, 2007
Infection of knee prostheses is still one of the major concerns of the reliability over time of t... more Infection of knee prostheses is still one of the major concerns of the reliability over time of these implantable devices. The preferred treatment of this condition has turned out to be the use of a knee spacer in a two-stage reimplantation technique. The advantages of this technique associated with the use of a mobile spacer lies both in the possibility for the patient to move during the interim period, thus decreasing the risk of muscle contracture due to immobilisation, as well as in the ability to release antibiotics directly to the site of infection. The evaluation of the biomechanical properties of new mobile spacers preformed in three different sizes has been carried out subjecting the spacers to i) cyclic tests on a knee simulator for 500,000 walking cycles, ii) constraint tests in medio-lateral, antero-posterior and internal-external directions, iii) fatigue tests on the tibial tray. Particular attention was addressed to the evaluation of the mechanical resistance of the devices, to the quantity of wear debris produced during the tests and to the extent that such debris was influenced by the test parameters and geometrical dimensions of the spacers themselves. Results showed no sign of failure for any of the tested spacers, the constraint and fatigue behaviours were similar to those shown by a total knee prosthesis and the amount of debris turned out to be directly correlated to the size of the devices: in conclusion, the devices showed a good level of mechanical performance and, consequently, a sufficiently high degree of suitability for clinical use.
Journal of Mechanics in Medicine and Biology, 2010
ABSTRACT Glenoid failure is one of the major indications for revision in total shoulder arthropla... more ABSTRACT Glenoid failure is one of the major indications for revision in total shoulder arthroplasty. Glenoid components should be carefully designed to improve the reliability of the prostheses, and mechanical testing can be a key tool to compare the performances of different designs. The most relevant guidelines for mechanical testing of glenoid prostheses are included in the ASTM F2028-05 Standard. The Standard refers to glenoid subluxation tests, designed to evaluate the intrinsic stability of the prosthesis system, and to glenoid edge displacement tests, which estimate the risk of micro-motions at the bone-glenoid interface. However, some indications given by the Standard are not mandatory, leaving the possibility to choose some parameters of the testing set-up and procedure. The main goal of this study was to investigate how different testing parameters (i.e. loads, velocities and bone-glenoid conformity) may affect the test results. In order to reach this target an experimental apparatus was developed and mechanical tests were performed on a keeled glenoid. The study showed that the applied load and the bone-glenoid conformity have a significant effect on the tests results, because of bone and glenoid deformation. Contrarily, the testing velocity was not found to be an influencing testing parameter.
Journal of Biomedical Materials Research Part A, 2012
Crosslinked vitamin-E-stabilized polyethylene acetabular cups were compared with both commerciall... more Crosslinked vitamin-E-stabilized polyethylene acetabular cups were compared with both commercially available conventional and custom-crosslinked polyethylene acetabular cups in terms of wear behavior, in a hip joint simulator for five millions cycles, using bovine calf serum as lubricant. We correlated the wear experiments results with the chemical characterization of the investigated materials: Fourier transformed infrared (FTIR) spectroscopic analyses, differential scanning calorimetry, and crosslink density measurements were used to assess the chemical characteristics of the pristine materials. In addition, further FTIR analyses and cyclohexane extraction were carried out after the simulator experiments. Lipids absorption was observed in all tested specimens and it has been shown to strongly affect the results of the wear test. Corrected gravimetric wear measurements showed that vitamin-E blended, crosslinked polyethylene wore more than the traditional crosslinked polyethylene but exhibited a much lower wear than conventional ultrahigh-molecular weight polyethylene. The chemical analyses showed that the addition of vitamin E reduced the crosslinking efficiency. Given the correlation between crosslink density and wear resistance, this gave an explanation for the observed wear performances. V C 2011 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 00A: 000-000, 2011.
Journal of Biomechanics, 2006
Journal of Biomechanics, 2012
Journal of Biomechanics, 2004
The evaluation of contact areas and pressures in total knee prosthesis is a key issue to prevent ... more The evaluation of contact areas and pressures in total knee prosthesis is a key issue to prevent early failure. The first part of this study is based on the hypothesis that the patterns of contact stresses on the tibial insert of a knee prosthesis at different stages of the gait cycle could be an indicator of the wear performances of a knee prosthesis. Contact stresses were calculated for a mobile bearing knee prosthesis by means of finite element method (FEM). Contact areas and stresses were also measured through in vitro tests using Fuji Prescale film in order to support the FEM findings.