Flexible Flap Research Articles

A new approach for spatio-temporal interface treatment in fluid–solid interaction using artificial neural networks employing coupled partitioned fluid–solid solvers

Partitioned fluid–solid interaction (FSI) problems involving non-conforming grids pose formidable challenge in interface treatment, especially for information exchange, interface tracking, and field variable interpolation between solvers in both space and time. These demand special considerations for accurate and efficient simulations. This paper presents an application of artificial neural networks (ANN) for the interface treatment in a coupled FSI problem employing partitioned solvers. A shallow time-series ANN (nonlinear auto-regressive model with exogenous inputs, NARX) scheme is proposed to handle the exchange of Neumann/Dirichlet information at the coupling interface. This scheme involves two interface treatment models that were developed and analysed. The proposed models interpolate and transfer loads from the fluid to the solid domains, and conversely, displacements from the solid to the fluid domains between non-collocated grids. To validate this approach, we tested it on a 3D FSI problem, which involved damped oscillations of a flexible flap submerged in a fluid cavity. Adequately trained NARX interface models demonstrate reliable input–output mapping and accurate prediction of transient behaviour at the interface. Additionally, we explored the concept of reduced-order modelling (ROM) in the time domain. This allowed us to reduce the model’s complexity by half. Different training algorithms were evaluated to enhance the efficiency and performance of the proposed scheme. The study demonstrates that NARX networks trained with Bayesian Regularization (BR) and Levenberg–Marquardt (LM) algorithms exhibit the best accuracy, while the scaled conjugate gradient (SCG)-based training method provides better computational efficiency with acceptable accuracy. Overall, the NARX interface models provide precise performance and offer a viable potential for applications in FSI problems requiring accurate and faster computations.

Nonlinear flow control mechanism of two flexible flaps with fluid-structure interaction

Nonlinear flow control mechanism of two flexible flaps with fluid-structure interaction

Experimental investigation of rear flexible flaps interacting with the wake dynamics behind a squareback Ahmed body

We have conducted an experimental study on the use of rear flexible vertical flaps as adaptive solutions to reduce the drag of a squareback Ahmed body, and on the fluid–structure interaction mechanisms at the turbulent wake. To that aim, wind tunnel experiments were conducted to compare the performance of various configurations including the baseline body, the body with rigid flaps and with flexible flaps. These configurations were tested under different aligned and cross-flow conditions. The results reveal that the flexible adaptive devices effectively reduce the drag within for low values of the dimensionless stiffness quantified through the Cauchy number, Ca. Thus, the two-dimensional deformation of the flexible flaps, which undergo progressive inwards reconfiguration (with an averaged tip deflection angle of Θ≃4°), reduces the bluffness of the flow separation at the body base, thus shrinking the recirculation region. This reconfiguration leads to increased base pressure, resulting into a 8.3% decrease in the global drag, CD, under aligned conditions. Similar drag reductions are observed under yawed conditions.Two regimes are identified in terms of the coupled fluid–structure dynamics. For low Ca, the passive reconfiguration of the flaps include small amplitude, periodic oscillations corresponding to the first free deformation mode of a cantilevered beam. Alongside these weak oscillations, the flaps are deformed guided by the changes in the value of the horizontal base pressure gradient, depicting bi-stable behavior which is caused by the synchronization between the Reflectional Symmetry Breaking (RSB) mode, typically present in the wake of three-dimensional bluff bodies, and the flaps deformation. For higher values of Ca, the flexible flaps deflect inwardly by about Θ≃20° on average, but exhibit vigorous oscillations combining the first and second free deformation modes of a cantilevered beam. These large amplitude oscillations excite the flow separation at the model’s trailing edges, leading to significant fluctuations in the separated shear layers and a consequent 31% increase in the global drag. Under yawed conditions, the flaps responses for large values of Ca are different due to the asymmetry of the corresponding recirculation region.

Elbow coverage by the descending superficial radial artery flap: a clinical series and literature review.

Soft tissue coverage of the posterior aspect of the elbow requires thin and flexible flaps to adapt to movements without constraining them. The authors report a clinical series of reconstruction by the descending superficial radial artery (DSRA) flap, a proximal forearm perforator flap which use is rarely reported in the literature. Seven patients with a mean age of 50years (range 24-88years) were treated for a posterior elbow defect using the DSRA flap with an adipofascial pedicle. The flap was tunneled to the defect in the subcutaneous tissue or raised using the racket-like technique to avoid any pedicle compression. The mean follow-up was 3.3months (range 1-12months). A partial necrosis of the skin paddle occurred in an 88-year-old patient. In the other cases, the flap evolution was straightforward. At the last follow-up, the appearance of the flaps was satisfactory in terms of color, texture, and thickness. No complications were observed at the donor site. The DSRA flap with an adipofascial pedicle is a simple, reliable, and reproducible method for reconstruction of small to moderate-sized defect on the posterior aspect of the elbow. Its use is easier for defects on the posterolateral side, but it can reach the medial olecranon.

EFFECT OF FLEXIBLE FLAP LENGTH ON FLOW GENERATION BY AN AIRFOIL PITCHING IN QUIESCENT FLUID

We experimentally investigate the effect of the length of a chordwise flexible surface (flap) attached to the trailing edge of a symmetric rigid airfoil purely pitching in quiescent fluid on flow, and thus thrust generation. We aim to identify the optimum length of the flexible appendage necessary for coherent, orderly jet generation in a situation relating to hovering. To this end, we consider a flexible flap of a 50 μm thick polyethylene sheet. We systematically vary the length of the flexible flap (<i>c<sub>f</sub></i>) over a wide range, from <i>c<sub>f</sub></i> = 0.5 c to 4 c, where c is a rigid foil chord. Moreover, we explore the effect of pitching amplitude and frequency for each flap length. Based on length, the flaps are categorized as short (<i>c<sub>f</sub></i> ≤ 1), moderate length (1 < <i>c<sub>f</sub></i> ≤ 2), and long (<i>c<sub>f</sub></i> > 2) flaps. Detailed particle visualization study reveals that flap length has the predominant effect onflow generation. We find that for small amplitude-frequency pitching, flaps with moderate length generate narrow and coherent jets, while short and long flaps generate spread out and deflected jets. For moderate amplitude-frequency pitching, flexible flaps of all lengths, except the short flaps, generate coherent and aligned jet. However, for large amplitude-frequency pitching, only a few long flaps produce a narrow jet and thrust along the centerline. Results suggest that optimum flap length is a strong function of pitching kinematics. Interestingly, we also find that more than one optimal flap length exists for moderate and large pitching parameters which generate the orderly jet with small/minimum width.

Kinetic and structural details of urease inactivation by thiuram disulphides

This paper reports on the molecular details of the reactivity of urease, a nickel-dependent enzyme that catalyses the last step of organic nitrogen mineralization, with thiuram disulphides, a class of molecules known to inactivate the enzyme with high efficacy but for which the mechanism of action had not been yet established. IC50 values of tetramethylthiuram disulphide (TMTD or Thiram) and tetraethylthiuram disulphide (TETD or Disulfiram) in the low micromolar range were determined for plant and bacterial ureases. The X-ray crystal structure of Sporosarcina pasteurii urease inactivated by Thiram, determined at 1.68 Å resolution, revealed the presence of a covalent modification of the catalytically essential cysteine residue. This is located on the flexible flap that modulates the size of the active site channel and cavity. Formation of a Cys-S-S-C(S)-N(CH3)2 functionality responsible for enzyme inactivation was observed. Quantum-mechanical calculations carried out to rationalise the large reactivity of the active site cysteine support the view that a conserved histidine residue, adjacent to the cysteine in the active site flap, modulates the charge and electron density along the thiol SH bond by shifting electrons towards the sulphur atom and rendering the thiol proton more reactive. We speculate that this proton could be transferred to the nickel-coordinated urea amide group to yield a molecule of ammonia from the generated Curea-NH3+ functionality during catalysis.

Unsteady flow control mechanisms of a bio-inspired flexible flap with the fluid–structure interaction

Recently, the development of bio-inspired aircrafts has broad application prospects. However, the flow separation in the boundary layer of the bio-inspired wing under low Reynolds number becomes a great challenge for the design of a novel bio-inspired aircraft. It is worth noting that birds in nature can easily control flow separation, thanks to the flap-like flexible plumes attached to their wing surfaces. In this paper, the unsteady flow control of the flexible flap is studied by the immersed boundary-lattice Boltzmann-finite element method (IB-LB-FEM). The mechanism of flow separation on the airfoil surface at a bio-inspired large angle of attack (AOA) is suggested. The effects of the flexible flap position and its material properties on the unsteady flow control of the airfoil at large AOA are systematically discussed. The deformation law of the flexible flap with fluid–structure interaction (FSI) is revealed, and its influence on unsteady aerodynamics of the airfoil is discussed. The results show that with the increase in the AOA, the aerodynamic characteristics of the airfoil change with time from “periodic state” to “chaotic state” to “quasi-periodic state,” which is closely related to the unsteady flow separation on the airfoil upper surface. The new induced vortex is formed at the end of the flexible flap because of the FSI, which enhances or weakens the strength of vortices on the airfoil surface, affecting the aerodynamics of the airfoil. The flow control mechanism of the flexible flap proposed in this paper will provide a new design idea for the novel bio-inspired aircraft.

Flexible and Slim Device Switching Air Blowing and Suction by a Single Airflow Control

This study proposes a soft robotic device with a slim and flexible body that switches between air blowing and suction with a single airflow control. Suction is achieved by jet flow entraining surrounding air, and blowing is achieved by blocking and reversing jet flow. The thin and flexible flap gate enables the switching. Air flow is blocked while the gate is closed and passes through while the gate is open. The opening and closing of the flap gate are controlled by the expansion of the inflatable chambers installed near the gate. The extent of expansion is determined by the upstream static pressure. Therefore, the gate can be controlled by the input airflow rate. The dimensions of the flap gate are introduced as a design parameter, and we show that the parameter contributes to the blowing and suction capacities. We also experimentally demonstrate that the proposed device is available for a variable friction system and an end effector for picking up a thin object covered with dust.

Nectar feeding beyond the tongue: hummingbirds drink using phase-shifted bill opening, flexible tongue flaps and wringing at the tips.

Hummingbirds are the most speciose group of vertebrate nectarivores and exhibit striking bill variation in association with their floral food sources. To explicitly link comparative feeding biomechanics to hummingbird ecology, deciphering how they move nectar from the tongue to the throat is as important as understanding how this liquid is collected. We employed synced, orthogonally positioned, high-speed cameras to describe the bill movements, and backlight filming to track tongue and nectar displacements intraorally. We reveal that the tongue base plays a central role in fluid handling, and that the bill is neither just a passive vehicle taking the tongue inside the flower nor a static tube for the nectar to flow into the throat. Instead, we show that the bill is actually a dynamic device with an unexpected pattern of opening and closing of its tip and base. We describe three complementary mechanisms: (1) distal wringing: the tongue is wrung out as soon as it is retracted and upon protrusion, near the bill tip where the intraoral capacity is decreased when the bill tips are closed; (2) tongue raking: the nectar filling the intraoral cavity is moved mouthwards by the tongue base, leveraging flexible flaps, upon retraction; (3) basal expansion: as more nectar is released into the oral cavity, the bill base is open (phase-shifted from the tip opening), increasing the intraoral capacity to facilitate nectar flow towards the throat.

Retalho miocutâneo infra-hióideo em defeitos de cabeça e pescoço: experiência de uma única instituição

ABSTRACT Introduction: The infrahyoid flap is a pedicled flap with a simple harvesting technique. It may be an alternative for free flaps in elderly or patients with multiple comorbidities. This article evaluates 15 patients submitted to reconstruction of head and neck defects. Case report: Case series of patients submitted to infrahyoid flap reconstruction in a referral center. We evaluate surgical and functional outcomes associated with reconstruction with infrahyoid flap from November of 2013 to May of 2017. Conclusion: Infrahyoid flap is a thin and flexible flap with low rates of complications and does not require another surgical team. The majority of the patients had complete functional rehabilitation. Keywords: Reconstructive Surgical Procedures. Myocutaneous Flap. Surgical Flaps. Head and Neck Neoplasms.

Use of the double-paddle anterolateral thigh flap for locally advanced tongue carcinoma requiring second site reconstruction

BackgroundAdvanced oral tongue carcinoma can present with extension beyond the oral cavity. Operative defects after resection may involve multiple anatomical sites and significantly impact speech and swallowing. Dependence on long-term enteral feeding is not uncommon for these patients. The anterolateral thigh (ALT) flap is one of the most reliable and flexible flaps used in the reconstruction of total and subtotal tongue defects. The double-paddle flap modification may be a more suitable option for complex oral tongue defects after advanced tumor ablation. MethodsCase series of 31 patients with oral tongue squamous cell carcinoma that were classified as stage IV. The age of patients ranged from 32 to 63 years. We designed the double-paddle ALT flaps to reconstruct the two-site surgical defects (tongue defect and pharynx or neck skin defect). Postoperative viability of the flap was checked by clinical observation. The last examination was performed at 3-months after the completion of adjuvant chemoradiotherapy. The functional capacity of our patients was evaluated by three physicians (Head and Neck Surgeon, Radiation Oncologist, and Physiatrist) using a Speech Intelligibility Score and the Functional Oral Intake Scale. ResultsA total of 31 patients with surgical defects after total or subtotal tongue resection for cancer underwent double-paddle ALT flaps for reconstruction from March 2018 to December 2019. The dimension of flaps from 8 × 12 cm to 10 × 18 cm were divided into double-paddle from 8 × 5 cm to 10 × 10 cm. There was one case of pedicle thrombosis, one case of postoperative bleeding, three cases of neck infection, and six cases of salivary fistula. Our patients were seen in follow up from 6 to 36 months, with median follow-up of 23.5 months. The survival rate of ALT flap was 100%. All of our patients achieved an oral diet by 9 months after surgery. The mean score speech intelligibility was 2.74 ± 0.68 (4-point ordinal scale). The 2-year disease-free survival rate was 61.3%. ConclusionsThe double-paddle ALT flap is a reliable flap suitable for oral defects involving multiple subsites after ablative procedures. The majority of patients demonstrated acceptable functional rehabilitation. Clinical question/ level of evidenceTherapeutic, IV.

Anatomical Mechanism for Protecting the Airway in Whales Involves Interlocking the Larynx

The mammalian respiratory and digestive tracts are configured to enable simultaneous function of both systems, while preventing accidental choking on food. This protection is critical in mysticetes (baleen whales), especially as feeding involves large pressures and potential inundation of water.Dissections were performed on 43 specimens representing 8 mysticete species: fin, blue, sei, minke, humpback, gray, right, and pygmy right whales. 36 specimens were necropsied as whole carcasses, 5 were obtained as whole heads, 2 were whole fetuses. All were recovered post mortem from US beach strandings. Dissections focused on hyolaryngeal anatomy, soft palate, and nasopharynx.Results indicate that the mysticete larynx retains an intranarial position during feeding, swallowing, breathing, and sound production. The soft palate forms a muscular ring that keeps the larynx interlocked into the nasopharynx. The epiglottis overlaps the soft palate extensively, nesting rostrally over a shelf that forms a pocket lined by nasopharyngeal pits. The soft palate articulates tightly with the epiglottic base, and lateral portions arc around larynx to meet in the caudal midline. Posteriorly, the soft palate forms another smaller shelf that interlocks with the caudally curling paired corniculate cartilages. These two points of interlocking keep the larynx intranarially positioned during deglutition. The paired lateral food channels (piriform sinuses) pass on either side of the epiglottis and corniculate cartilages and unite caudally to form the esophagus. Food can easily pass around the interlocked larynx using these lateral food channels.Suprahyoid muscles elevate the oral floor, squeezing out water and pushing the tongue towards the oral roof to compress the food bolus and force it through the oropharyngeal inlet. The oropharyngeal inlet appears regulated by muscles that likely relax to allow dilation. Suprahyoid muscles also ensure the larynx‐soft palate interlock, as the epiglottis is pushed rostrally to maximally overlap the soft palate. Food encountering the interlocked soft palate‐epiglottis is diverted laterally into paired lateral food channels. Infrahyoid muscles retract the larynx caudally, returning it to its rest position with moderate soft palate overlap. Continued contraction would allow the long epiglottis to slide along its overlap with the soft palate, giving mobility to enlarge the depth of the lateral food channels if necessary, without unlocking the larynx. This interlock preserves the protection of the airway.Unlocking the epiglottis necessitates elevating the soft palate while withdrawing the epiglottis. This may occur to channel air into the oral cavity for bubble cloud production. However, the larynx is at risk of inundation from water in this position, as it forms a very poor seal with the corniculate cartilages and their flexible flaps. The rigid epiglottis could not be folded caudally manually to meet the corniculates. No muscles were noted that could retract the epiglottis towards the corniculates. Similarly, no muscles were found that could rigidify the corniculate flaps or cause them to seal in opposition. Therefore, the sealing mechanism of the larynx is limited to opposition of the arytenoid cartilages supporting the U‐shaped vocal fold.

Resurfacing the complex finger defect and sensation reconstruction with the free distal ulnar artery perforator flap: a self-controlled case series study.

BackgroundThe purpose of this clinical research is to report our results using the free distal ulnar artery perforator flap for resurfacing complex tissue defects in the finger, and to provide empirical reference for the treatment of subsequent clinical cases.MethodsIn our research, eight patients with complex skin defects were treated with free distal ulnar artery perforator flaps. There were 4 index, 3 long, and 2 ring fingers. All the flaps were raised from the ipsilateral ulnar lateral wrist. The donor sites were covered with a full thickness skin graft or closed by direct suture.ResultsComprehensive analysis of the clinical treatment process of eight patients, all flaps survived completely without any necrosis during the 6–18 months follow-up. The patients were satisfied with the finger mobility, the sensation function, and the aesthetic appearance.ConclusionsResurfacing complex tissue defects in the finger using the free perforator flap in a single stage, especially when the defect is medium in size and accompanied by digit nerve loss, is a valuable technique to achieve satisfaction in both sensation and aesthetic appearance. The ulnar artery perforator flap seems to be a reliable and flexible flap for addressing complex hand injuries with tissue loss.

A free flexible flap in channel flow

Fine fibre immersed in different flows is ubiquitous. For a fibre in shear flows, most motion modes appear in the flow-gradient plane. Here the two-dimensional behaviours of an individual flexible flap in channel flows are studied. The nonlinear coupling of the fluid inertia ( $\textit {Re}$ ), flexibility of the flap ( $K$ ) and channel width ( $W$ ) is discovered. Inside a wide channel (e.g. $W=4$ ), as $K$ decreases, the flap adopts rigid motion, springy motion, snake turn and complex mode in sequence. It is found that the fluid inertia tends to straighten the flap. Moreover, $\textit {Re}$ significantly affects the lateral equilibrium location $y_{eq}$ , therefore affecting the local shear rate and the tumbling period $T$ . For a rigid flap in a wide channel, when $\textit {Re}$ exceeds a threshold, the flap stays inclined instead of tumbling. As $\textit {Re}$ further increases, the flap adopts swinging mode. In addition, there is a scaling law between $T$ and $\textit {Re}$ . For the effect of $K$ , through the analysis of the torque generated by surrounding fluid, we found that a smaller $K$ slows down the tumbling of the flap even if $y_{eq}$ is comparable. As $W$ decreases, the wall confinement effect makes the flap easier to deform and closer to the centreline. The tumbling period would increase and the swinging mode would be more common. When $W$ further decreases, the flaps are constrained to stay inclined, parabolic-like or one-end bending configurations moving along with the flow. Our study may shed some light on the behaviours of a free fibre in flows.

Ritonavir and xk263 Binding-Unbinding with HIV-1 Protease: Pathways, Energy and Comparison.

Understanding non-covalent biomolecular recognition, which includes drug–protein bound states and their binding/unbinding processes, is of fundamental importance in chemistry, biology, and medicine. Fully revealing the factors that govern the binding/unbinding processes can further assist in designing drugs with desired binding kinetics. HIV protease (HIVp) plays an integral role in the HIV life cycle, so it is a prime target for drug therapy. HIVp has flexible flaps, and the binding pocket can be accessible by a ligand via various pathways. Comparing ligand association and dissociation pathways can help elucidate the ligand–protein interactions such as key residues directly involved in the interaction or specific protein conformations that determine the binding of a ligand under certain pathway(s). Here, we investigated the ligand unbinding process for a slow binder, ritonavir, and a fast binder, xk263, by using unbiased all-atom accelerated molecular dynamics (aMD) simulation with a re-seeding approach and an explicit solvent model. Using ritonavir-HIVp and xk263-HIVp ligand–protein systems as cases, we sampled multiple unbinding pathways for each ligand and observed that the two ligands preferred the same unbinding route. However, ritonavir required a greater HIVp motion to dissociate as compared with xk263, which can leave the binding pocket with little conformational change of HIVp. We also observed that ritonavir unbinding pathways involved residues which are associated with drug resistance and are distal from catalytic site. Analyzing HIVp conformations sampled during both ligand–protein binding and unbinding processes revealed significantly more overlapping HIVp conformations for ritonavir-HIVp rather than xk263-HIVp. However, many HIVp conformations are unique in xk263-HIVp unbinding processes. The findings are consistent with previous findings that xk263 prefers an induced-fit model for binding and unbinding, whereas ritonavir favors a conformation selection model. This study deepens our understanding of the dynamic process of ligand unbinding and provides insights into ligand–protein recognition mechanisms and drug discovery.

Correction: Reiswich et al. Effect of Flexible Flaps on Lift and Drag of Laminar Profile Flow. Energies 2020, 13, 1077

The authors wish to make the following corrections to their paper [...]

Clinical effects of partially de-epithelized local flaps in repairing tubercular chest wall defects

Objective: To explore the clinical effects of partially de-epithelized local flaps in repairing tubercular chest wall defects. Methods: A retrospective observational study was conducted. From April 2010 to February 2021, twelve patients who met the inclusion criteria were admitted to the Department of Burns and Plastic Surgery of the Eighth Medical Center of PLA General Hospital, including 9 males and 3 females with age of (42±18) years. The sizes of tubercular chest wall defects of patients were ranged from 4 cm×3 cm×2 cm to 16 cm×8 cm×5 cm, which were all repaired with partial de-epithelized local flaps. The widths of flaps were equal to the widths of the defects, and the lengths of flaps were 2 cm longer than those of the defects. In one patient, the local flap was too large to close the donor site directly by suturing, so an autologous back free medium thickness skin graft was used for repair. In other patients, the collection areas of local flaps were small, and the donor areas of flaps were directly closed. The duration of operation, intraoperative bleeding, and postoperative drainage volume and indwelling time of drainage tube were observed and recorded. In two weeks after operation, the survival, color, and texture of flaps, the presence of subcutaneous hydrops and skin ulcer, and donor site healing including wound disruption, local infection, hematoma were observed. Chest X-ray, CT scan, or nuclear magnetic resonance imaging was performed in one month after operation to check whether new local hydrops and bone destruction occurred in the chest wall defects and the concomitant tuberculose focus of patients. All patients were followed up for more than 6 months to record whether the surgical incisions of the chest wall defects of the patients were complicated by hypertrophic scar, redness, swelling, and sinus. Results: In surgery, the patient had (104±18) min of operation duration, (119±53) mL of intraoperative bleeding, (134±49) mL of cumulative drainage of drainage tube, and (5.3±1.7) days of drainage tube indwelling time. In two weeks after operation, all the grafted local flaps survived, and the color and texture of flaps were similar to the surrounding normal skin. One patient had fluid leakage from the incision of chest wall defect area with the incision partially dehisced, which healed well after a phase Ⅱ operation; no wound infection, subcutaneous hydrops, or wound rupture occurred in other patients. The incisions of donor sites in all the patients healed well and no wound disruption, local infection, or hematoma occurred. One month after operation, no new bone destruction was observed in the operative region by chest imaging examination. Patients were followed up for 6 to 96 months, with one patient having wound swelling, ulceration, and sinus in the operative area of the chest wall defect in 12 months after surgery, which healed after phase Ⅱ operation; the incisions of chest wall defect wounds in other patients healed well and had no scar, redness and swelling, or sinus. Conclusions: Partially de-epithelized local flap could be used in repairing tubercular chest wall defect wounds, with the advantages of flexible flap design, minimal donor site injury, and good postoperative wound healing.

Distal Brachial Artery Perforator flap: a new chimeric option for complex hand and digits defects

Reconstruction of fingers pose unique challenges, as a thin and flexible flap is needed in order to guarantee a good functional outcome. For the first time, in this report, we present the DBAp (distal brachial artery perforator) flap, based on the distal perforator closer to the medial epicondyle. The DBAp flap was used to reconstruct complex digit defects as free flap, and to cover an elbow defect while raised as a propeller. Four patients underwent finger reconstruction (free flaps): two patients presented an unstable finger scar following previous surgery, whereas the other two patients presented a terminalized finger at the level of the middle phalanx. A further patient presented a post-traumatic loss of substance at the elbow and was reconstructed using a perforator propeller DBAP flap. Loss of tissues included skin and subcutaneous tissue in all patients and in one patient it included a bone component. Flap dimensions ranged from 48 to 18 cm2 (average: 32 cm2). Among complications, patient n.2 flap presented a marginal flap necrosis requiring a small skin graft after necrosis debridement. The DBAp flap provides a slim, glabrous and pliable skin tissue with a well-hidden donor site scar and thanks to the anatomic location of the distal perforator can be designed to include a vascularized bone graft from the medial epicondyle. Despite the low number of cases, we believe that this flap should be considered as a dependable and effective source for complex reconstructions of both soft tissue and bone in fingers.

The importance of a lifeboat-median artery forearm flap in Goldenhar Syndrome

We present a case of a 32-year-old male with left-sided Goldenhar Syndrome and delta phalanx of the thumb, who was offered free tissue transfer from the forearm to address an intra-oral soft tissue deficiency. Despite the presence of appropriately developed right radial artery, used in previous facial reconstruction, the left radial artery occurred to be hypoplastic. He ultimately underwent free flap transfer based on the anomalous persistent left median artery. We suggest that in face of an unusual hand anatomy, flexible flap creation techniques that allow a lifeboat strategy of adjusting flap design should be considered preoperatively. Level of evidence: Level V, therapeutic study.

Revertant mutation V48G alters conformational dynamics of highly drug resistant HIV protease PRS17

Drug resistance is a serious problem for controlling the HIV/AIDS pandemic. Current antiviral drugs show several orders of magnitude worse inhibition of highly resistant clinical variant PRS17 of HIV-1 protease compared with wild-type protease. We have analyzed the effects of a common resistance mutation G48V in the flexible flaps of the protease by assessing the revertant PRS17V48G for changes in enzyme kinetics, inhibition, structure, and dynamics. Both PRS17 and the revertant showed about 10-fold poorer catalytic efficiency than wild-type enzyme (0.55 and 0.39 μM−1min−1 compared to 6.3 μM−1min−1). Clinical inhibitors, amprenavir and darunavir, showed 2-fold and 8-fold better inhibition, respectively, of the revertant than of PRS17, although the inhibition constants for PRS17V48G were still 25 to 1,200-fold worse than for wild-type protease. Crystal structures of inhibitor-free revertant and amprenavir complexes with revertant and PRS17 were solved at 1.3–1.5 Å resolution. The amprenavir complexes of PRS17V48G and PRS17 showed no significant differences in the interactions with inhibitor, although changes were observed in the conformation of Phe53 and the interactions of the flaps. The inhibitor-free structure of the revertant showed flaps in an open conformation, however, the flap tips do not have the unusual curled conformation seen in inhibitor-free PRS17. Molecular dynamics simulations were run for 1 μs on the two inhibitor-free mutants and wild-type protease. PRS17 exhibited higher conformational fluctuations than the revertant, while the wild-type protease adopted the closed conformation and showed the least variation. The second half of the simulations captured the transition of the flaps of PRS17 from a closed to a semi-open state, whereas the flaps of PRS17V48G tucked into the active site and the wild-type protease retained the closed conformation. These results suggest that mutation G48V contributes to drug resistance by altering the conformational dynamics of the flaps.