Randomized clinical trial on the effect of intermittent vibrational force application during orthodontic treatment with aligners on RANKL and OPG concentrations in crevicular fluid.

Application of intermittent forces by vibration is proposed as an easy-to-use accelerator of dental movement. The purpose of this study was to determine the effect of intermittent vibrational force application during orthodontic aligner treatment on receptor activator of nuclear factor-kappa B ligand (RANKL) and osteoprotegerin (OPG) concentrations in crevicular fluid as markers of bone remodeling. This three-arm parallel randomized clinical trial included 45 candidates for malocclusion treatment with aligners, randomly assigned to: Group A (vibrational forces from onset of treatment); Group B (vibrational forces at 6 weeks after treatment onset); or Group C (no vibration). The frequency of aligner adjustment also differed among groups. At different time points, a paper tip was used to draw crevicular fluid samples from a moving lower incisor for RANKL and OPG analysis using ELISA kits. Mixed-model ANOVA found no significant differences in RANKL (A: p = 0.31, B: p = 0.8, C: p = 0.49) or OPG (A: p = 0.24, B: p = 0.58, C: p = 0.59) over time in any group or as a function of the application/non-application of vibration or the frequency of aligner adjustments. Application of this accelerator device did not significantly affect bone remodeling in patients undergoing orthodontic treatment with aligners. However, a nonsignificant improvement in biomarker concentrations was observed when aligners were changed every 7 days and vibration was also applied. Further research is warranted to establish protocols for the application of vibration and the timing of aligner adjustments.

Partial Bell-State Measurement with Type-II Parametric Down Conversion: Extracting Phase Information from the Zeropoint Field (I).

In this paper, the nexus between the Bell-state measurement and extracting phase information from the zeropoint field is investigated. For this purpose, the Wigner representation in the Heisenberg picture is applied in a Bell-type experiment in which the polarisation-entangled photon pairs generated in a type-II parametric down-conversion do not overlap. The signal intensities at the detectors are calculated in a four-mode approximation, being expressed as functions of the modules and phases of the four zeropoint amplitudes entering the crystal. A general criterion for identifying the correlated detectors is proposed based on the equality of the signal intensities, and without involving the calculation of the joint detection probabilities. In addition, from the analyses in the rectilinear and diagonal basis, it is shown that the distinguishability of the polarisation Bell states, which is in direct correspondence with the joint detection events in each experiment, can be related to the knowledge of the phases of the vacuum field entering the entanglement source, and giving rise to correlated detections. To this purpose, it is conjectured that a detection event is associated with a maximum value of the signal intensity averaged in the modules of the zeropoint amplitudes, as a function of the vacuum phases.

Experimental verification of fiber coupling characteristics for FSO downlinks from the International Space Station.

Free-space optical (FSO) systems are compulsory to realize high capacity and interference-free communication links from low-Earth orbit (LEO) satellite constellations as well as spacecraft and space stations to the Earth. To be integrated with high-capacity ground networks, the collected portion of the incident beam should be coupled into an optical fiber. To accurately evaluate the signal-to-noise ratio (SNR) and bit-error rate (BER) performance metrics, the probability density function (PDF) of fiber coupling efficiency (CE) must be determined. Previous studies have experimentally verified the CE PDF for a single-mode fiber, however, there is no such investigation for the CE PDF of a multi-mode fiber (MMF) in a LEO-to-ground FSO downlink. In this paper, for the first time, the CE PDF for a 200-µm MMF is experimentally investigated using data from an FSO downlink from the Small Optical Link for International Space Station (SOLISS) terminal to a 40-cm sub-aperture optical ground station (OGS) supported by a fine-tracking system. An average CE of 5.45 dB was also achieved given that the alignment between SOLISS and OGS was not optimal. In addition, using the angle-of-arrival (AoA) and received power data, the statistical characteristics such as channel coherence time, power spectral density, spectrogram, and PDFs of AoA, beam misalignments, and atmospheric turbulence-induced fluctuations are revealed and compared with the state-of-the-art theoretical background.

Survival and Recurrence of Endocarditis following Mechanical vs. Biological Aortic Valve Replacement for Endocarditis in Patients Aged 40 to 65 Years: Data from the INFECT-Registry.

BACKGROUND: Infective endocarditis (IE) is a serious disease, and in many cases, surgery is necessary. Whether the type of prosthesis implanted for aortic valve replacement (AVR) for IE impacts patient survival is a matter of debate. The aim of the present study is to quantify differences in long-term survival and recurrence of endocarditis AVR for IE according to prosthesis type among patients aged 40 to 65 years. METHODS: This was an analysis of the INFECT-REGISTRY. Trends in proportion to the use of mechanical prostheses versus biological ones over time were tested by applying the sieve bootstrapped t-test. Confounders were adjusted using the optimal full-matching propensity score. The difference in overall survival was compared using the Cox model, whereas the differences in recurrence of endocarditis were evaluated using the Gray test. RESULTS: Overall, 4365 patients were diagnosed and operated on for IE from 2000 to 2021. Of these, 549, aged between 40 and 65 years, underwent AVR. A total of 268 (48.8%) received mechanical prostheses, and 281 (51.2%) received biological ones. A significant trend in the reduction of implantation of mechanical vs. biological prostheses was observed during the study period (p < 0.0001). Long-term survival was significantly higher among patients receiving a mechanical prosthesis than those receiving a biological prosthesis (hazard ratio [HR] 0.546, 95% CI: 0.322-0.926, p = 0.025). Mechanical prostheses were associated with significantly less recurrent endocarditis after AVR than biological prostheses (HR 0.268, 95%CI: 0.077-0.933, p = 0.039). CONCLUSIONS: The present analysis of the INFECT-REGISTRY shows increased survival and reduced recurrence of endocarditis after a mechanical aortic valve prosthesis implant for IE in middle-aged patients.

Prognostic value of SARS-CoV-2 on patients undergoing cardiac surgery.

OBJECTIVE: To analyze Italian Cardiac Surgery experience during the pandemic of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) identifying risk factors for overall mortality according to coronavirus disease 2019 (COVID-19) status. METHODS: From February 20 to May 31, 2020, 1354 consecutive adult patients underwent cardiac surgery at 22 Italian Centers; 589 (43.5%), patients came from the red zone. Based on COVID-19 status, 1306 (96.5%) were negative to SARS-CoV-2 (COVID-N), and 48 (3.5%) were positive to SARS-CoV-2 (COVID-P); among the COVID-P 11 (22.9%) and 37 (77.1%) become positive, before and after surgery, respectively. Surgical procedures were as follows: 396 (29.2%) isolated coronary artery bypass grafting (CABG), 714 (52.7%) isolated non-CABG procedures, 207 (15.3%) two associate procedures, and three or more procedures in 37 (2.7%). Heart failure was significantly predominant in group COVID-N (10.4% vs. 2.5%, p = .01). RESULTS: Overall in-hospital mortality was 1.6% (22 cases), being significantly higher in COVID-P group (10 cases, 20.8% vs. 12, 0.9%, p < .001). Multivariable analysis identified COVID-P condition as a predictor of in-hospital mortality together with emergency status. In the COVID-P subgroup, the multivariable analysis identified increasing age and low oxygen saturation at admission as risk factors for in-hospital mortality. CONCLUSION: As expected, SARS-CoV-2 infection, either before or soon after cardiac surgery significantly increases in-hospital mortality. Moreover, among COVID-19-positive patients, older age and poor oxygenation upon admission seem to be associated with worse outcomes.

The day after tomorrow: cardiac surgery and coronavirus disease-2019.

The impact of the coronavirus disease-2019 (COVID-19) pandemic forced the governments worldwide to deal with an unprecedented health crisis. The aim of this review is to summarize what happened to cardiac surgery worldwide during the first wave of this pandemic. A literature search was performed to extrapolate key concepts regarding guidelines and reorganization of cardiac surgery wards during COVID-19. Supporting literature was also included to discuss the hot topics related to COVID-19 and cardiac surgery. Hence, both official documents from national scientific societies and single- or multiple-center experiences during the pandemics are reviewed and discussed. In Italy, the first western country hit by the pandemic, two different models were proposed to cope with the need for ICU/ward beds and to reallocate cardiac surgical services: Hub-and-Spoke system ('Hubs', dedicated to perform urgent and nondeferrable surgery, and 'Spokes', turned into COVID centers) and/or a progressive reduction in surgical activity. Worldwide, several guidelines/consensus statements were published, suggesting how to deal with the outbreak. Two different approaches for stratifying surgical indications were proposed: dynamic, based on the number of hospitalized COVID-19 patients; static, based only on the severity of the cardiovascular disease. Moreover, the importance of personal protective equipment was stressed. Several measures should have been adopted to deal with an unprecedented need for healthcare resources allocation to care for COVID-19 patients, putting the healthcare systems under serious stress. Cardiac surgery has, as have most surgical activities, been asked to reduce its own activity, giving priority to emergency and nondeferrable cases.

Midterm outcomes of transaortic and transapical TAVI in patients with unsuitable vascular anatomy for femoral access: A propensity score inverse probability weight study.

AIMS: Transaortic (TAo) and transapical (TA) implantation can be used in transcatheter aortic valve implantation (TAVI) when the transfemoral (TF) approach is precluded. We compare the safety and efficacy of these alternative techniques. METHODS: From October 2007 to February 2016, TAo and TA patients' data were collected. Propensity score inverse probability of treatment weight (IPTW) method was employed to minimize the impact of no-randomization bias. RESULTS: From our single-center non-TF-TAVI registry, 282 patients were included: 235 (83.3%) underwent TAo and 47 (16.7%) TA. Differences in baseline characteristics were statistically significant in age, sex, risk profile according to logistic-EuroSCORE, and previous cardiac surgery. No difference in hospital morbidity and mortality, but lower stroke-rate in TAo (1.27% vs. 8.5% p < .01) was observed. This was confirmed at logistic regression after IPTW adjustment (odds ratio [OR]: 0.16, 95% CI 0.03-0.71, p = .01), together with reduced risk of the paravalvular leak (PVL) (OR: 0.14, 95% confidence interval [CI]: 0.02-0.81, p = .02). Kaplan-Meier estimates did not demonstrate differences in long-term mortality among access routes (logrank test p = .13). At the IPTW-Cox regression model, long-term mortality was related to New York Heart Association III-IV (hazard ratio [HR]: 2.92, 95% CI: 1.15-7.40, p = .026), chronic renal failure (HR: 3.25; 95% CI: 1.02-10.32 p = .046), previous transient ischemic attack/stroke (HR: 2.29, 95% CI: 1.25-4.20 p = .007). Sapien-3 device resulted to be a protective factor, reducing long-term mortality (HR: 0.18, 95% CI 0.04- 0.90 p = .03). CONCLUSIONS: TAo is safe and feasible in case of contraindication to femoral approach demonstrating comparable midterm outcomes to TA, thus representing a central access alternative, to increase the overall safety of high-risk TAVI procedures.

Long-Term Survival and Outcomes According to VARC-2 Criteria for Subclavian, Direct Aortic, Femoral, and Apical Implantation: An 8-Year United Kingdom TAVI Surgical Experience.

OBJECTIVES: The use of transcatheter aortic valve implantation (TAVI) has expanded as an alternative to aortic valve replacement, and more than 500,000 patients have been treated worldwide since April, 2002. The aim of this study was to compare complications and morbidity/mortality associated with different TAVI approaches as alternatives to a surgical-femoral approach. METHODS: From January 2007 to January 2015, 2,863 patients underwent TAVI surgery in 36 United Kingdom TAVI centers. Primary outcomes were complications according to VARC-2 criteria. The secondary outcome was long-term survival. RESULTS: The enrolled patients were distributed as follows: 1,150 in the surgical-femoral (SF) group, 1,216 in the trans-apical (TA) group, 207 in the direct-aortic (DA) group, and 290 in the subclavian (SC) group. There were no differences in the rates of acute myocardial infarction, emergency valve-in-valve, cardiac tamponade, or TIA among the groups. The rates of stroke and renal replacement therapy, as well as in-hospital stay, in-hospital death, and 30-day and 12-month mortality in DA and TA were higher than those in SC and SF. The rates of paravalvular leak and balloon post-dilatation in SC and DA were higher than those in TA and SF. The rates of vascular injuries and permanent pacemaker implantation in SC and SF were higher than those in DA and TA. SF provided the best long term-survival (p = 0.008). CONCLUSIONS: This was a large study that compared outcomes and long-term survival among different TAVI surgical approaches in a national real-world setting. According to our results, SF provided the best survival. While SC provided worse survival than SF, it was still better than TA and DA, and thus may represent the safest non-femoral access if use of the femoral approach is precluded.

Mortality in trials on transcatheter aortic valve implantation versus surgical aortic valve replacement: a pooled meta-analysis of Kaplan-Meier-derived individual patient data.

OBJECTIVES: This meta-analysis of Kaplan-Meier-estimated individual patient data was designed to evaluate the effects of transcatheter aortic valve implantation (TAVI) and surgical aortic valve replacement (SAVR) on the long-term all-cause mortality rate, to examine the potential time-varying effect and to model their hazard ratios (HRs) over time. Moreover, we sought to compare traditional meta-analytic tools and estimated individual patient data meta-analyses. METHODS: Trials comparing TAVI versus SAVR were identified through Medline, Embase, Cochrane databases and specialist websites. The primary outcome was death from any cause at follow-up. Enhanced secondary analyses of survival curves were performed estimating individual patient time-to-event data from published Kaplan-Meier curves. Treatments were compared with the random effect Cox model in a landmark framework and fully parametric models. RESULTS: We identified 6 eligible trials that included 6367 participants, randomly assigned to undergo TAVI (3252) or SAVR (3115). According to the landmark analysis, the incidence of death in the first year after implantation was significantly lower in the TAVI group [risk-profile stratified HR 0.85, 95% confidence interval (CI) 0.73-0.99; P = 0.04], whereas there was a reversal of the HR after 40 months (risk-profile stratified HR 1.31, 95% CI 1.01-1.68; P = 0.04) favouring SAVR over TAVI. This time-varying trend of HRs was also confirmed by a fully parametric time-to-event model. Traditional meta-analytic tools were shown to be biased because they did not intercept heterogeneity and the time-varying effect. CONCLUSIONS: The mortality rates in trials of TAVI versus SAVR are affected by treatments with a time-varying effect. TAVI is related to better survival in the first months after implantation whereas, after 40 months, it is a risk factor for all-cause mortality.

Main Risk Factor in Long-Term Postoperative Aortic Root Enlargement After Aortic Valve Surgery Associated with Ascending Aorta Replacement.

AIM: Dilatation of the aortic root (AR) after aortic valve surgery associated with ascending aorta replacement (AVS+AAR) is an important concern in long-term follow-up (FU). This study aimed to identify factors that may be associated with this late complication. MATERIAL AND METHODS: Two-hundred-sixteen consecutive patients (150 males and 66 females) who underwent AVS+AAR from June 2009 to April 2018 at a single center were retrospectively analyzed. The mean trans-thoracic echocardiographic (TTE) FU was 44.9 ± 22.2 months. An increase of 10% in AR size compared to the pre-operative baseline was the outcome variable. The Student t-test or chi-square test was used as appropriate. For a survival analysis, a Kaplan-Meier curve was computed and a log-rank p-value was calculated. Cox's regression model was used to assess the predictive value of variables over time. A p-value < 0.05 was significant. RESULTS: No significant differences were observed among patients who underwent aortic valve repair and those who underwent aortic valve replacement (log-rank = 0.917). In patients who underwent valve replacement, AR enlargement was associated with the difference between the diameter of the prosthetic valve and the diameter of the straight vascular prosthesis (OR 0.87, P = 0.024). Based on the difference in diameter between vascular and valve prosthesis, we arbitrarily classified the patients into two groups: a small group (S) (n = 52), in which the difference was ≤ 5 mm, and a large group (L) (n = 34), in which the difference was > 5 mm. Significant AR enlargement was observed in 30.8 % of the S group and 14.7 % of the L group (log-rank = 0.026). A difference of more than 5 mm between the aortic valve prosthesis and the vascular prosthesis protected against AR enlargement in the long-term FU (OR 12.31, P = 0.033), even after adjusting for age and sex (OR 00.32, P = 0.043). CONCLUSION: According to our findings, a difference between the size of the aortic valve prosthesis and the vascular prosthesis of less than or equal to 5 mm was the only factor that increased the risk of AR enlargement after AVS+AAR in long-term FU.

LEO-to-ground polarization measurements aiming for space QKD using Small Optical TrAnsponder (SOTA).

Quantum communication, and more specifically Quantum Key Distribution (QKD), enables the transmission of information in a theoretically secure way, guaranteed by the laws of quantum physics. Although fiber-based QKD has been readily available since several years ago, a global quantum communication network will require the development of space links, which remains to be demonstrated. NICT launched a LEO satellite in 2014 carrying a lasercom terminal (SOTA), designed for in-orbit technological demonstrations. In this paper, we present the results of the campaign to measure the polarization characteristics of the SOTA laser sources after propagating from LEO to ground. The most-widely used property for encoding information in free-space QKD is the polarization, and especially the linear polarization. Therefore, studying its behavior in a realistic link is a fundamental step for proving the feasibility of space quantum communications. The results of the polarization preservation of two highly-polarized lasers are presented here, including the first-time measurement of a linearly-polarized source at λ = 976 nm and a circularly-polarized source at λ = 1549 nm from space using a realistic QKD-like receiver, installed in the Optical Ground Station at the NICT Headquarters, in Tokyo, Japan.

Feasibility of utilizing Cherenkov Telescope Array gamma-ray telescopes as free-space optical communication ground stations.

The signals that will be received on Earth from deep-space probes in future implementations of free-space optical communication will be extremely weak, and new ground stations will have to be developed in order to support these links. This paper addresses the feasibility of using the technology developed in the gamma-ray telescopes that will make up the Cherenkov Telescope Array (CTA) observatory in the implementation of a new kind of ground station. Among the main advantages that these telescopes provide are the much larger apertures needed to overcome the power limitation that ground-based gamma-ray astronomy and optical communication both have. Also, the large number of big telescopes that will be built for CTA will make it possible to reduce costs by economy-scale production, enabling optical communications in the large telescopes that will be needed for future deep-space links.

Reversible and oriented immobilization of ferrocene-modified proteins.

Adopting supramolecular chemistry for immobilization of proteins is an attractive strategy that entails reversibility and responsiveness to stimuli. The reversible and oriented immobilization and micropatterning of ferrocene-tagged yellow fluorescent proteins (Fc-YFPs) onto ß-cyclodextrin (ßCD) molecular printboards was characterized using surface plasmon resonance (SPR) spectroscopy and fluorescence microscopy in combination with electrochemistry. The proteins were assembled on the surface through the specific supramolecular host-guest interaction between ßCD and ferrocene. Application of a dynamic covalent disulfide lock between two YFP proteins resulted in a switch from monovalent to divalent ferrocene interactions with the ßCD surface, yielding a more stable protein immobilization. The SPR titration data for the protein immobilization were fitted to a 1:1 Langmuir-type model, yielding K(LM) = 2.5 × 10(5) M(-1) and K(i,s) = 1.2 × 10(3) M(-1), which compares favorably to the intrinsic binding constant presented in the literature for the monovalent interaction of ferrocene with ßCD self-assembled monolayers. In addition, the SPR binding experiments were qualitatively simulated, confirming the binding of Fc-YFP in both divalent and monovalent fashion to the ßCD monolayers. The Fc-YFPs could be patterned on ßCD surfaces in uniform monolayers, as revealed using fluorescence microscopy and atomic force microscopy measurements. Both fluorescence microscopy imaging and SPR measurements were carried out with the in situ capability to perform cyclic voltammetry and chronoamperometry. These studies emphasize the repetitive desorption and adsorption of the ferrocene-tagged proteins from the ßCD surface upon electrochemical oxidation and reduction, respectively.

Supramolecularly oriented immobilization of proteins using cucurbit[8]uril.

A supramolecular strategy is used for oriented positioning of proteins on surfaces. A viologen-based guest molecule is attached to the surface, while a naphthol guest moiety is chemoselectively ligated to a yellow fluorescent protein. Cucurbit[8]uril (CB[8]) is used to link the proteins onto surfaces through specific charge-transfer interactions between naphthol and viologen inside the CB cavity. The assembly process is characterized using fluorescence and atomic force microscopy, surface plasmon resonance, IR-reflective absorption, and X-ray photoelectron spectroscopy measurements. Two different immobilization routes are followed to form patterns of the protein ternary complexes on the surfaces. Each immobilization route consists of three steps: (i) attaching the viologen to the glass using microcontact chemistry, (ii) blocking, and (iii) either incubation or microcontact printing of CB[8] and naphthol guests. In both cases uniform and stable fluorescent patterns are fabricated with a high signal-to-noise ratio. Control experiments confirm that CB[8] serves as a selective linking unit to form stable and homogeneous ternary surface-bound complexes as envisioned. The attachment of the yellow fluorescent protein complexes is shown to be reversible and reusable for assembly as studied using fluorescence microscopy.

Reabsorción condilar poscirugía ortognática. Revisión de la literatura / Post orthognathic surgery condylar resorption. A literature review

Objetivo: Entre las posibles complicaciones que pueden surgir tras una cirugía ortognática, se ha descrito la reabsorción condilar, en la que los cóndilos se reabsorben parcial o totalmente, provocando una disminución de la altura condilar y una alteración de la morfología maxilofacial y de la oclusión. El objetivo de este trabajo es esclarecer cuáles son los factores de riesgo, el diagnóstico y los tratamientos utilizados, así como diseñar un protocolo de prevención de la reabsorción condilar poscirugía ortognática (RCPO).Material y métodos: Se han identificado y revisado los estudios publicados entre 1990 y 2011 relacionados con la RCPO en las siguientes bases de datos: PubMed, MedLine, EMBASE, TESEO y Cochrane. Las palabras clave utilizadas han sido: orthognathic surgery, condylar resorption, condylar atrophy, dysfunctional remodelling y condylysis. También se ha hecho una búsqueda en estos artículos para identificar otros posibles estudios. Resultados: Los principales factores de riesgo con los que se asocia la RCPO son: patrón dolicofacial, cóndilos pequeños o inclinados posteriormente, desplazamiento discal, ser mujer, desarreglos hormonales y compresión o alteración del torque condilar posquirúrgico. Los tratamientos propuestos son: estabilizar la posición condilar y disminuir su carga con el uso de férulas interdentales; mejorar la homeostasis fibrocartilaginosa de la articulación temporomandibular mediante farmacoterapia, infiltraciones o artrocentesis y cirugía de la articulación temporomandibular (artroscopia, revascularización condilar, meniscopexia, condilectomía y reconstrucción autógena o aloplástica).Conclusiones: La RCPO es un proceso complejo y todo él muy controvertido, según se refleja en los numerosos trabajos publicados (AU)

Objective: Condylar resorption has been described as a possible complication of orthognathic surgery. in this condition, condyles are partially or completely reabsorbed, with a consequent shortening of condylar height and an alteration in maxillofacial morphology and occlusion. The aim of this review was to clarify risk factors for condylar resorption, its diagnosis and the treatments used, and to design a protocol for the prevention of post-orthognathic surgery condylar resorption (POCR).Materials and methods: Studies related to POCR published between 1990 and 2011 were identified and reviewed in the following databases: PubMed, MedLine, EMBASE, TESEO and Cochrane. The key words used were orthognathic surgery, condylar resorption, condylar atrophy, dysfunctional remodeling and condylysis. A manual search was carried out to identify other possible studies.Results: The main risk factors associated with POCR were dolichofacial growth pattern, small or posteriorly inclined condyles, disk displacement, being female, hormonal disorders, and compression or postsurgical condylar torque. Proposed treatments consisted of stabilizing condylar position and decreasing condylar loading; improving fibrocartilaginous homeostasis with drug therapy, infiltrations or arthrocentesis; and temporomandibular joint surgery (arthroscopy, condylar revascularization, discal reposition, condylectomy and autogenic or alloplastic reconstruction).Conclusions: POCR is a complex condition and a highly controversial issue, as reflected in the numerous articles published (AU)

Interlaboratory round robin on cantilever calibration for AFM force spectroscopy.

Single-molecule force spectroscopy studies performed by Atomic Force Microscopes (AFMs) strongly rely on accurately determined cantilever spring constants. Hence, to calibrate cantilevers, a reliable calibration protocol is essential. Although the thermal noise method and the direct Sader method are frequently used for cantilever calibration, there is no consensus on the optimal calibration of soft and V-shaped cantilevers, especially those used in force spectroscopy. Therefore, in this study we aimed at establishing a commonly accepted approach to accurately calibrate compliant and V-shaped cantilevers. In a round robin experiment involving eight different laboratories we compared the thermal noise and the Sader method on ten commercial and custom-built AFMs. We found that spring constants of both rectangular and V-shaped cantilevers can accurately be determined with both methods, although the Sader method proved to be superior. Furthermore, we observed that simultaneous application of both methods on an AFM proved an accurate consistency check of the instrument and thus provides optimal and highly reproducible calibration. To illustrate the importance of optimal calibration, we show that for biological force spectroscopy studies, an erroneously calibrated cantilever can significantly affect the derived (bio)physical parameters. Taken together, our findings demonstrated that with the pre-established protocol described reliable spring constants can be obtained for different types of cantilevers.

Recognition properties of cucurbit[7]uril self-assembled monolayers studied with force spectroscopy.

Specific (host-guest) and unspecific (substrate-guest) interactions between self-assembled monolayers of cucurbit[7]uril (CB[7]) on gold (Au) substrates and neutral adamantyl (Ad) guests were resolved by studying these interactions at the single molecule level using dynamic force spectroscopy. The dissociation rate constants of the Ad-Au and the Ad-CB[7] interactions were 0.3 s(-1) and 0.03 s(-1), respectively, indicating that the specific binding is more stable. The probability of observing a specific interaction (40 ± 9%) is similar to the reported surface coverages of CB[7] monolayers on Au substrates. The higher strength and stability of the Ad-CB[7] interactions explains why, although presenting an imperfect coverage, CB[n] monolayers can be used successfully as a platform for surface immobilization.

Probing multivalent interactions in a synthetic host-guest complex by dynamic force spectroscopy.

Multivalency is present in many biological and synthetic systems. Successful application of multivalency depends on a correct understanding of the thermodynamics and kinetics of this phenomenon. In this Article, we address the stability and strength of multivalent bonds with force spectroscopy techniques employing a synthetic adamantane/ß-cyclodextrin model system. Comparing the experimental findings to theoretical predictions for the rupture force and the kinetic off-rate, we find that when the valency of the complex is increased from mono- to di- to trivalent, there is a transition from quasi-equilibrium, with a constant rupture force of 99 pN, to a kinetically dependent state, with loading-rate-dependent rupture forces from 140 to 184 pN (divalent) and 175 to 210 pN (trivalent). Additional binding geometries, parallel monovalent ruptures, single-bound divalent ruptures, and single- and double-bound trivalent ruptures are identified. The experimental kinetic off-rates of the multivalent complexes show that the stability of the complexes is significantly enhanced with the number of bonds, in agreement with the predictions of a noncooperative multivalent model.

Gradient-driven motion of multivalent ligand molecules along a surface functionalized with multiple receptors.

The kinetics of multivalent (multisite) interactions at interfaces is poorly understood, despite its fundamental importance for molecular or biomolecular motion and molecular recognition events at biological interfaces. Here, we use fluorescence microscopy to monitor the spreading of mono-, di- and trivalent ligand molecules on a receptor-functionalized surface, and perform multiscale computer simulations to understand the surface diffusion mechanisms. Analogous to chemotaxis, we found that the spreading is directional (along a developing gradient of vacant receptor sites) and is strongly dependent on ligand valency and concentration of a competing monovalent receptor in solution. We identify multiple surface diffusion mechanisms, which we call walking, hopping and flying. The study shows that the interfacial behaviour of multivalent systems is much more complex than that of monovalent ones.