Highest Mean Force Research Articles

Effect of attachment flash on clear aligner force delivery: an in vitro study

BackgroundThe introduction of auxiliaries such as composite attachment has improved the force delivery of clear aligner (CA) therapy. However, the placement of the attachment may give rise to a flash, defined as excess resin around the attachment which may affect CA force delivery. This in vitro study aims to determine the differences in the force generated by the attachment in the presence or absence of flash in CA.Materials and methodsTristar Trubalance aligner sheets were used to fabricate the CAs. Thirty-four resin models were 3D printed and 17 each, were bonded with ellipsoidal or rectangular attachments on maxillary right central incisors. Fuji Prescale pressure film was used to measure the force generated by the attachment of CA. The images of colour density produced on the films were processed using a calibrated pressure mapping system utilising image processing techniques and topographical force mapping to quantify the force. The force measurement process was repeated after the flash was removed from the attachment using tungsten-carbide bur on a slow-speed handpiece.ResultsThe intraclass correlation coefficient showed excellent reliability (ICC = 0.96, 95% CI = 0.92–0.98). The average mean force exerted by ellipsoidal attachments with flash was 8.05 ± 0.16 N, while 8.11 ± 0.18 N was without flash. As for rectangular attachments, the average mean force with flash was 8.48 ± 0.27 N, while 8.53 ± 0.13 N was without flash. Paired t-test revealed no statistically significant difference in the mean force exerted by CA in the presence or absence of flash for both ellipsoidal (p = 0.07) and rectangular attachments (p = 0.41). Rectangular attachments generated statistically significantly (p < 0.001) higher mean force than ellipsoidal attachments for flash and without flash.ConclusionAlthough rectangular attachment generated a significantly higher force than ellipsoidal attachment, the force generated by both attachments in the presence or absence of flash is similar (p > 0.05).

Incidence and predictors of thermal oesophageal and vagus nerve injuries in Ablation Index-guided high-power-short-duration ablation of atrial fibrillation: a prospective study.

High-power-short-duration (HPSD) ablation is an effective treatment for atrial fibrillation but poses risks of thermal injuries to the oesophagus and vagus nerve. This study aims to investigate incidence and predictors of thermal injuries, employing machine learning. A prospective observational study was conducted at Leipzig Heart Centre, Germany, excluding patients with multiple prior ablations. All patients received Ablation Index-guided HPSD ablation and subsequent oesophagogastroduodenoscopy. A machine learning algorithm categorized ablation points by atrial location and analysed ablation data, including Ablation Index, focusing on the posterior wall. The study is registered in clinicaltrials.gov (NCT05709756). Between February 2021 and August 2023, 238 patients were enrolled, of whom 18 (7.6%; nine oesophagus, eight vagus nerve, one both) developed thermal injuries, including eight oesophageal erythemata, two ulcers, and no fistula. Higher mean force (15.8 ± 3.9 g vs. 13.6 ± 3.9 g, P = 0.022), ablation point quantity (61.50 ± 20.45 vs. 48.16 ± 19.60, P = 0.007), and total and maximum Ablation Index (24 114 ± 8765 vs. 18 894 ± 7863, P = 0.008; 499 ± 95 vs. 473 ± 44, P = 0.04, respectively) at the posterior wall, but not oesophagus location, correlated significantly with thermal injury occurrence. Patients with thermal injuries had significantly lower distances between left atrium and oesophagus (3.0 ± 1.5 mm vs. 4.4 ± 2.1 mm, P = 0.012) and smaller atrial surface areas (24.9 ± 6.5 cm2 vs. 29.5 ± 7.5 cm2, P = 0.032). The low thermal lesion's rate (7.6%) during Ablation Index-guided HPSD ablation for atrial fibrillation is noteworthy. Machine learning based ablation data analysis identified several potential predictors of thermal injuries. The correlation between machine learning output and injury development suggests the potential for a clinical tool to enhance procedural safety.

Comparison of Force During the Endotracheal Intubation of Commercial Simulation Manikins.

Background Medical simulation allows clinicians to safely practice the procedural skill of endotracheal intubation. Applied force to oropharyngeal structures increases the risk of patient harm, and video laryngoscopy (VL) requires less force to obtain a glottic view. It is unknown how much force is required to obtain a glottic view using commercially available simulation manikins and if variability exists. This study compares laryngoscopy force for a modified Cormack-Lehane (CL) grade I view in both normal and difficult airway scenarios between three commercially available simulation manikins. Methods Experienced clinicians (≥2 years experience) were recruited to participate from critical care, emergency medicine, and anesthesia specialties. A C-MAC size 3 VL blade was equipped with five force resistor reading (FSR) sensors (four concave surfaces, one convex), measuring resistance (Ohms) in response to applied pressure (1-100 Newtons). The study occurred in a university simulation lab.Using a randomized sequence, 49 physicians performed intubations on three manikins (Laerdal SimMan 3GPlus, Gaumard Hal S3201, CAE Apollo) in normal and difficult airway scenarios. The outcomes were sensor mean pressure, peak force, and CL grade. Summary statistics were calculated. Generalized estimating equations (GEEs) conducted for both scenarios assessed changes in pressure measured in three manikins while accounting for correlated responses of individuals assigned in random order. Paired t-test assessed for the in-manikin difference between scenarios. STATA/BE v17 (R) was used for analysis; results interpreted at type I error alpha is 0.05. Results Participants included 49 experienced clinicians. Mean years' experience was 4(±6.6); median prior intubations were 80 (IQR 50-400).Mean individual sensor pressure varied within scenarios depending on manikin (p<0.001). Higher mean forces were used in difficult scenarios (603.4±128.9, 611.1±101.4, 467.5±72.4 FSR) than normal (462.5±121.9, 596.0±90.5, 290.6±63.2 FSR) for each manikin (p<0.001). All manikins required more peak force in the difficult scenario (p<0.03). The highest mean forces (Laerdal, CAE, difficult scenario) were associated with the higher frequency of grade 2A views (p<0.001). The Gaumard manikin was rated most realistic in terms of force required to intubate. Conclusion Commercially available high-fidelity manikins had significant variability in laryngoscopy force in both normal and difficult airway scenarios. In difficult airway scenarios, significant variability existed in CL grade between manikin brands. Experienced clinicians rated Gaumard Hal as the most realistic force applied during endotracheal intubation.

Study influence of honeycomb structural parameters on impact force responses using reduced order modelling

An electric vehicle is heavier than an internal combustion engine vehicle due to batteries and its enclosure. Weight reduction is one of electric vehicle design target. Honeycomb material can be used in the battery enclosure design as it has light weight and good energy absorption capability. However, it is necessary to understand the mechanical behaviour of honeycomb under impact load. This paper aims to study the effects of honeycomb cell size and wall thickness under impact loading on energy absorption and weight using a reduced order model. The reduced order model was established from a set of finite element simulation data. The prediction capability of the reduced order model was accurate with less than 5 % error. It was employed to predict the initial peak force, the mean force and mass of honeycomb with various sets of the cell size and wall thickness. The study observed that the initial peak force increased linearly with both cell size and wall thickness. For a very thin wall thickness the cell size had little effect. However, with a very small cell size, the effect of wall thickness on the initial peak force was little when comparing with honeycomb with a large cell size. The mean force also increased with increasing cell size at a decreasing rate for the same thickness. Once the maximum mean force was reached, the mean force decreased with increasing cell size for all thickness. However, for all cell size, the mean force increased parabolically with the wall thickness. The mass linearly increased with increasing cell size and the wall thickness. Then, the optimum parameter was suggested 5 mm cell size and 0.1 mm thickness which gave the lowest initial peak force with highest mean force and lightest mass.

Fracture Resistance of CAD/CAM Implant-Supported 3Y-TZP-Zirconia Cantilevers: An In Vitro Study.

(1) Introduction: Implant-supported fixed complete dentures are mostly composed of cantilevers. The purpose of this work was to evaluate the fracture resistance of zirconia (Prettau®, second generation, or Ice Zirkon Translucent, first generation) with cantilever lengths of 6 and 10 mm, and zirconia’s fracture resistance in relation to an average bite force of 250 N. (2) Materials and methods: Forty structures were created in CAD/CAM and divided into four groups: group A (6 mm cantilever in IZT), group B (10 mm cantilever in IZT), group C (6 mm cantilever in Pz), and group D (10 mm cantilever in pz). The study consisted of a traditional “load-to-failure” test. (3) Results: A statistically significant result was found for the effect of cantilever length, t(38) = 16.23 (p < 0.001), with this having a large effect size, d = 4.68. The 6 mm cantilever length (M = 442.30, sd = 47.49) was associated with a higher mean force at break than the 10 mm length (M = 215.18, sd = 40.74). No significant effect was found for the type of zirconia: t(38) = 0.31 (p = 0.757), and d = 0.10. (4) Conclusions: All the components with cantilever lengths of 6 mm broke under forces higher than 250 N. Cantilevers larger than 10 mm should be avoided.

Why are tapes better than wires in knotless rotator cuff repairs? An evaluation of force, pressure and contact area in a tendon bone unit mechanical model

PurposeKnotless repairs have demonstrated encouraging performance regarding retear rate reduction, but literature aiming at identifying the specific variables responsible for these results is scarce and conflictive.The purpose of this paper was to evaluate the effect of the material (tape or wire suture) and medial tendon passage (single or double passage) on the contact force, pressure and area at the tendon bone interface in order to identify the key factors responsible for this repairs´ success.MethodsA specific knotless transosseous equivalent cuff repair was simulated using 2 tape or suture wire loaded medial anchors and 2 lateral anchors, with controlled lateral suture limb tension. The repair was performed in a previously validated sawbones® mechanical model. Testing analyzed force, pressure and area in a predetermined and constant size “repair box” using a Tekscan® sensor, as well as peak force and pressure, force applied by specific sutures and force variation along the repair box.ResultsTapes generate lower contact force and pressure and double medial passage at the medial tendon is associated with higher contact area. Suture wires generate higher peak force and pressure on the repair and higher mean force in their tendon path and at the medial bearing row. Force values decrease from medial to lateral and from posterior to anterior independently of the material or medial passage.ConclusionContrary to most biomechanical literature, suture tape use lowers the pressure and force applied at the tendon bone junction, while higher number of suture passage points medially increases the area of contact. These findings may explain the superior clinical results obtained with the use uf suture tapes because its smaller compressive effect over the tendon may create a better perfusion environment healing while maintaining adequate biomechanical stability.

AVALIAÇÃO DAS PROPRIEDADES MECÂNICAS DE FIOS E BRAQUETES ORTODÔNTICOS ESTÉTICOS

Objetivo: comparar as forças de deflexão nos fios ortodônticos estéticos em braquetes autoligáveis cerâmicos passivos e interativos. Métodos: Quatro corpos de prova foram montados em um modelo de simulação clínica e avaliados em uma Máquina de Ensaio Universal (Emic). Em uma placa de resina acrílica foram fixados 10 dispositivos, onde foram colados os braquetes, simulando o arco dentário superior em forma de parábola. O dispositivo de acrílico representante do incisivo central direito foi movimentado em ativações de 0 a 3 mm, com velocidade constante de 0,5 mm/min. Testes de Análise de Variância e de Tukey, com significância de 5% (P

Mechanical Comparison of 3D-Printed Plates and Screws for Open Reduction and Internal Fixation of Fractures

Objectives:Three-dimensional (3D) printing has emerged as a promising technology in the field of orthopaedic surgery. The purpose of this study was to evaluate the mechanical properties of 3D printed 1/3 tubular plates and cortical screws compared to standard-of-care stainless steel 1/3 tubular plates and cortical screws.Methods:Replication and modification designs were developed for both plates and screws using open-source computer-assisted design (CAD) software. Models were printed in four materials: acrylonitrile butadiene styrene (ABS), carbon fiber reinforced polylactic acid (PLA), polycarbonate (PC), and polyether ether ketone (PEEK). The implants (Figure 1) were tested and compared to surgical steel plates and screws. Plates were tested with three-point bend and torsional loading using an Instron® material testing machine. Screws were analyzed on pull-out strength in a Sawbones® bone model, shear strength, and torsional loading. Each combination of design and material was placed in its own test group with a sample size (n = 5) and compared to a steel control group (n = 5) for each mechanical test.Results:Significant interaction effects between material type and design type were observed for screw shear (p = 0.003), screw torque (p = 0.023), plate 3-point bend (p = 0.002), and plate torque (p = 0.001). A significant interaction effect was not observed for screw pull-out (p = 0.407), however, a statistically significant difference in mean force between material types (p <0.0005) was observed.Screw Shear: The highest mean force when both material and design were considered was for the CFPLA modified flat design with a mean force of 105.83 N (95% CI 88.51 to 123.14).Screw Torque: The highest mean force when both material and design were considered was for the PEEK modified tilt design with a mean force of 49.51 Ncm (95% CI 43.40 to 55.63).Plate 3-Point Bend: The highest mean force when both material and design were considered was for the PEEK modification design with a mean force of 31.93 N (95% CI 30.53 to 33.33).Plate Torque: The highest mean force when both material and design were considered was for the CFPLA modified flat design with a mean force of 46.88 Ncm (95% CI 42.95 to 50.80).Screw Pull-Out: Mean force produced was highest for PC across all test groups (Figure 2) with a total mean force of 211.86 N (95% CI 186.81 to 236.90).Conclusion:This study demonstrates that desktop 3D printers are capable of printing biocompatible materials that can replicate surgical implants. Although the current materials have significant mechanical variability, they do not approximate the properties of stainless steel. The utility of 3D printed surgical implants for internal fracture fixation provides a potential clinical application in locations where equipment is not as readily available, such as developing countries, forward operating military units, or long duration space flight missions. Furthermore, the cost for 3D printers and 3D printable materials has significantly decreased over recent years. This increase in technology and associated decrease in costs, along with numerous open-source 3D modeling software programs, could provide a low-cost alternative to more expensive and less accessible standard-of-care stainless-steel implants.Figure 1.

How Porosity Controls Macroscopic Failure via Propagating Fractures and Percolating Force Chains in Porous Granular Rocks

AbstractThis contribution aims to illuminate the micromechanisms that control the macroscopic failure of porous, granular, and cohesive rocks. With discrete element method simulations, we triaxially compress cohesive granular models composed of interlocking breakable grains, similar to sandstone and oolitic limestone. We track the morphology of the force network and the resulting spatiotemporal fracture distribution. To shed light on the varying applicability of the pore‐emanated and Hertzian fracture models, we focus on differences in the micromechanics that develop between and within grains. For 5–20% porosity rocks, the cement between grains develops 10–50% higher mean forces than material within grains. Force chains that support the highest system‐spanning forces are more localized prior to failure in 20% porosity rocks and are more diffusely spread in 5% porosity rocks. Confining stress reduces this localization, similar to the impact of confining stress on the macroscopic expression of brittle failure. The magnitude and rate of fracture development relative to the axial strain or axial stress increase toward failure, consistent with experimental observations. In contrast, the rate of fracture development relative to the amount of external work done on the system, Wext, is approximately constant. Higher porosity rocks require lower inputs of Wext to produce the same degree of fracturing. Decreasing the cement strength promotes fracture development within the cement, revealing the dominance of intergranular, pore‐emanated fractures. These simulations provide predictions about how porosity controls the persistence of the stress field, with implications on the sequential development of deformation bands, and other deformational processes that modify porosity.

Force Decay Characteristics of commonly used Elastomeric Chains on Exposure to various Mouth Rinses with different Alcohol Concentration: An in vitro Study

The aim of this study was to test the effect of varying alcohol concentrations of various commercially available mouth-washes on force decay of elastomeric chains in prestretched and unstretched condition. A total of five specimen groups were tested with a total sample size of 180 specimens. A specimen is described as a three-link, short module, clear elastomeric chain (3M Unitek, Ortho Plus, Ortho Organizer). The control and test groups were independently submerged in separate 37°C artificial saliva to simulate the oral conditions. Effects of different solution groups and time (initial, 1, 7, 14, 21, and 28 days) on three different elastomeric chains and force (cN) are analyzed with two-way analysis of variance; pair-wise comparisons are done by t-test. Higher mean force was recorded initially followed by 24 hours >7 days >14 days >21 days and 28 days respectively. The difference in mean force decay among the different time intervals was found to be statistically significant (p < 0.001). Among the different solutions, higher mean force was recorded in 21.6% alcohol mixture > Listerine 8.38% > Wokadine > alcohol mixture 8.38% > artificial saliva. In conclusion, alcohol-containing mouth rinses cause an increase in force decay of elastomeric chain over time. These mouth rinses are commonly recommended during orthodontic treatment. The orthodontist can know better that the alcohol content of the mouth rinses and the structural and molecular modification results in the decay of elastomeric chain.

In vivo quantification of the apical fixation forces of different mitral valved stent designs in the beating heart.

The aim of this study was the quantification of the apical fixation forces of mitral valved stents for the first time. A test set-up was developed to measure the forces acting on the apical fixation of mitral valved stents. Twenty pigs received a self-expanding valved stent in the mitral position via a transapical approach in an off-pump procedure. Following stent deployment in the beating heart, the apical fixation forces were recorded following a standardized protocol and normalized. The apical fixation force of two different valved stent designs (AP: sole apical fixation, n=10; SA: additional sub-annular fixation, n=10) was compared to quantify the impact of the design change. Force measurement was successfully conducted in 18 of 20 animals (design AP: n=10; design SA: n=8). Evaluation showed higher mean forces and amplitude in the group with sole apical fixation (p=0.046; Table1). The impact of the additional sub-annular fixation was shown by a significant reduction of the force acting upon the apex of the heart. Quantification of these in vivo forces provides important information about the impact of different stent designs and might provide an objective parameter for stent performance evaluation in clinical application.

Joint mobilization forces and therapist reliability in subjects with knee osteoarthritis

Objectives:This study determined biomechanical force parameters and reliability among clinicians performing knee joint mobilizations.Methods:Sixteen subjects with knee osteoarthritis and six therapists participated in the study. Forces were recorded using a capacitive-based pressure mat for three techniques at two grades of mobilization, each with two trials of 15 seconds. Dosage (force–time integral), amplitude, and frequency were also calculated. Analysis of variance was used to analyze grade differences, intraclass correlation coefficients determined reliability, and correlations assessed force associations with subject and rater variables.Results:Grade IV mobilizations produced higher mean forces (P<0·001) and higher dosage (P<0·001), while grade III produced higher maximum forces (P = 0·001). Grade III forces (Newtons) by technique (mean, maximum) were: extension 48, 81; flexion 41, 68; and medial glide 21, 34. Grade IV forces (Newtons) by technique (mean, maximum) were: extension 58, 78; flexion 44, 60; and medial glide 22, 30. Frequency (Hertz) ranged between 0·9–1·1 (grade III) and 1·4–1·6 (grade IV). Intra-clinician reliability was excellent (>0·90). Inter-clinician reliability was moderate for force and dosage, and poor for amplitude and frequency.Discussion:Force measurements were consistent with previously reported ranges and clinical constructs. Grade III and grade IV mobilizations can be distinguished from each other with differences for force and frequency being small, and dosage and amplitude being large. Intra-clinician reliability was excellent for all biomechanical parameters and inter-clinician reliability for dosage, the main variable of clinical interest, was moderate. This study quantified the applied forces among multiple clinicians, which may help determine optimal dosage and standardize care.

Effect of plasma treatment of acrylic denture teeth and thermocycling on the bonding strength to heat cured acrylic denture base material

Acrylic resin polymer s used in prosthodontic treatment as a denture base material for several decades. Separation and debonding of artificial teeth from denture bases present a laboratory and clinical problem affect patient and dentist. The aim of this study is to evaluate the effect of oxygen plasma and argon plasma treatment of acrylic teeth and thermocycling on bonding strength to hot cured acrylic resin denture base material. Materials and Methods: Sixty denture teeth (right maxillary central incisor) are selected. The denture teeth are waxed onto the beveled surface of rectangular wax block according to Japanese standard for artificial teeth. The control group consisted of 20 denture teeth specimen without any treatment. The oxygen plasma group consisted of 20 denture teeth specimen treated with oxygen plasma for two minutes exposure time at plasma apparatus. The argon plasma group consisted of 20 denture teeth treated with argon plasma for two minuets exposure time. All the specimens are undergone flasking and wax elimination procedure in the conventional way. All specimens stored in distilled water for 7 days at 37°C, then half of the specimens of all groups undergoes thermocycling between 5°C - 55°C in 60 seconds cycles for three days and tested for shear bond strength using universal testing machine the data was collected and analyzed statistically using analysis of variance and independent sample t-test. Results: The plasma treated groups showed the higher mean force required to fracture the acrylic teeth from their heat cured acrylic resin denture bases, as compared to control group, and the oxygen plasma treatment group showed higher shear bond value than the argon plasma treatment. The thermocycling had a deleterious effect on bonding strength for control group while the plasma treated group showed an increase in bond strength following thermocycling. Conclusion: Plasma treatment method was an effective approach for increasing the shear bond strength as a result of surface oxidation and chemical etching effect of oxygen plasma and micromechanical interlocking effect of argon plasma.

Tensile bond strength of silicone-based soft denture liner to two chemically different denture base resins after various surface treatments

This study evaluated the effect of various surface treatments on the tensile bond strength of a silicone-based soft denture liner to two chemically different denture base resins, heat-cured polymethyl methacrylate (PMMA), and light-activated urethane dimethacrylate or Eclipse denture base resin. PMMA test specimens were fabricated and relined with a silicone-based soft denture liner (group AC). Eclipse test specimens were prepared according to the manufacturer's recommendation. Before they were relined with a silicone-based soft denture liner, each received one of three surface treatments: untreated (control, group EC), Eclipse bonding agent applied (group EB), and laser-irradiated (group EL). Tensile bond strength tests (crosshead speed = 5 mm/min) were performed for all specimens, and the results were analyzed using the analysis of variance followed by Tukey's test (p = 0.05). Eclipse denture base and PMMA resins presented similar bond strengths to the silicone-based soft denture liner. The highest mean force was observed in group EL specimens, and the tensile bond strengths in group EL were significantly different (p < 0.05) from those in the other groups.

Measurement of Microscale Shear Forces during Chemical Mechanical Planarization

Polydimethylsiloxane (PDMS) posts with a diameter of 80 μm were used to measure the shearing forces at the wafer-pad interface during chemical mechanical planarization (CMP). Measurements are made at 10 kHz with measurable forces between 40 and 400 μN. The structures were polished using a stiff, ungrooved pad and 3 wt % fumed silica slurry at velocities of 0.3 and 0.6 m/s and average wafer-pad normal load of 5.0 and 9.1 kPa. Due to the small fraction of the pad that contacts the wafer, the local microscale forces can be much larger than the global average force might suggest. Observed lateral forces on the structures averaged, in time, between 230 and 310 μN with RMS deviations of the force about the mean between 47 and 64 μN. The faster polishing case shows a 30% higher mean force, and a 20% reduction in the RMS variation of force. Little change is seen in the force characteristics when increasing from 5.0 to 9.1 kPa downforce. A mathematical model is developed to interpret these forces, allowing estimation of the local pad properties. The model suggests that 5000 asperity contacts are present per square millimeter, asperity lateral stiffness is 0.3 N/m, and asperity slip-off force is 19 μN.

Vertical fracture resistance of roots after ultrasonic removal of fractured instruments

To investigate ex vivo root resistance to vertical fracture after fractured instruments were ultrasonically removed from different locations in the root canal. Fifty-three canine roots were weighed and divided into four groups. Eight roots served as a control group in which canals were instrumented to a size F5-ProTaper instrument. In the experimental groups, F5-ProTaper fragments were fractured in the coronal, middle and apical one-thirds, and then removed ultrasonically. The time required for removal was recorded. Roots were reweighed, and canals were shaped to a size F5-ProTaper and filled with GuttaFlow. After incubation, roots underwent a vertical fracture test in which the force at fracture was recorded. The difference in root mass before and after treatment (fractured file removal or canal preparation) was calculated. Data were analysed using the Kruskal-Wallis, Mann-Whitney post-hoc and regression tests at P < 0.05. The highest root-mass loss was recorded when fragments were removed from the apical one-third (46.04 mg) followed by the middle and coronal (27.7 and 13.5 mg, respectively); these differences were significant (P < 0.05). There were significant differences in the force required for vertical fracture amongst the experimental groups (P < 0.05) with the lowest mean force recorded in the apical-third group (107.1 N) followed by the middle and coronal (152.6 and 283.3 N, respectively). The highest mean force was recorded in the control group (301.5 N) which was not significantly different from that in the coronal group (P = 1.00). A negative exponential correlation (r = 0.669) existed between the root-mass loss and the force required to fracture the roots. Whilst removal of fractured instruments from the coronal one-third of the root canal can be considered as a safe procedure, removal from deeper locations renders the root less resistant to vertical fracture.

Strength of wired sternotomy closures: effect of number of wire twists

The objective of this study was to investigate the effect of the number of wire twists on the strength of wired sternotomy closures. A custom-built test rig, fitted to a materials testing machine, was used to apply an increasing tension to wire closures, until they failed. The number of twists in the wire closure was varied between one and ten. Stainless steel wires of diameter 0.7 mm (No. 5) and 0.9 mm (No. 7) were tested. Initially, there is an increase in the maximum strength of the wire closure with increasing number of wire twists. After three wire twists greater strength is not achieved with increasing the number of wire twists. The highest mean force taken by the 0.7 mm diameter wire was 613 N (approximately 63 kg), at nine wire twists, whereas the highest force taken by the 0.9 mm diameter wire was 887 N (approximately 90 kg), at eight wire twists. However, by three wire twists, 80% and 88% of the maximum force has been achieved for the 0.7 and 0.9 mm diameter wire, respectively. Twisting wires many times in a sternotomy closure does not result in increased strength. Three or four twists would appear sufficient to sustain the forces across a sternotomy.

Feasibility of measuring antigen–antibody interaction forces using a scanning force microscope

The molecular affinity scanning force microscopy (MASFM) described in this study was developed in an effort to test the possibility of antigen–antibody binding measurement using force-separation distance profiles. The MASFM configuration was comprised of a spherical glass bead as an MASFM probe, to which the fluorescein antigen has been covalently attached, and a silicon dioxide-based substrate, to which the antifluorescyl IgG antibody was covalently bound. The bead was glued to the tip of a commercial SFM cantilever. Adhesion forces have been measured between two different specific antigen–antibody pairs and between nonspecific surfaces bearing only glycidoxypropylsilane immobilization chemistry. In force-separation (F-s) measurements, nonspecific forces displayed relatively few force discontinuities and mean adhesion forces lower than those found for specific antigen–antibody measurements. Force-separation profiles measured between specific antigen–antibody pairs showed many discontinuities and had higher mean forces. Positive controls revealed that the mean forces were slightly reduced by the addition of free ligand. The magnitude of mean forces did not correlate with the respective activation enthalpies of the proteins, as would be expected. At lower force values the force histograms for the specific pairs and for positive controls were indistinguishable. None of the force-separation data sets could fit a Poisson discrete-force model. This statistical analysis showed a large relative contribution from nonspecific interactions. It is concluded that the use of the large sphere as an SFM probe is counterproductive: while the large sphere does sample a larger number of specific interactions during each measurement, it also samples at the same time a large proportion of nonspecific forces. The presence of the nonspecific force contributions is likely due to the deformation of the polymerized GPS spacer layer which is thought to be delaminated from the surface upon the application of tension across the specific antigen–antibody bonds.