Biophysical studies of lipid nanodomains using different physical characterization techniques.

For the past 50 years, evidence for the existence of functional lipid domains has been steadily accumulating. Although the notion of functional lipid domains, also known as "lipid rafts," is now widely accepted, this was not always the case. This ambiguity surrounding lipid domains could be partly attributed to the fact that they are highly dynamic, nanoscopic structures. Since most commonly used techniques are sensitive to microscale structural features, it is therefore, not surprising that it took some time to reach a consensus regarding their existence. In this review article, we will discuss studies that have used techniques that are inherently sensitive to nanoscopic structural features (i.e., neutron scatting, nuclear magnetic resonance, and Förster resonance energy transfer). We will also mention techniques that may be of use in the future (i.e., cryoelectron microscopy, droplet interface bilayers, inelastic x-ray scattering, and neutron reflectometry), which can further our understanding of the different and unique physicochemical properties of nanoscopic lipid domains.

Room-Temperature Ferromagnetism at an Oxide-Nitride Interface.

Heterointerfaces have led to the discovery of novel electronic and magnetic states because of their strongly entangled electronic degrees of freedom. Single-phase chromium compounds always exhibit antiferromagnetism following the prediction of the Goodenough-Kanamori rules. So far, exchange coupling between chromium ions via heteroanions has not been explored and the associated quantum states are unknown. Here, we report the successful epitaxial synthesis and characterization of chromium oxide (Cr_{2}O_{3})-chromium nitride (CrN) superlattices. Room-temperature ferromagnetic spin ordering is achieved at the interfaces between these two antiferromagnets, and the magnitude of the effect decays with increasing layer thickness. First-principles calculations indicate that robust ferromagnetic spin interaction between Cr^{3+} ions via anion-hybridization across the interface yields the lowest total energy. This work opens the door to fundamental understanding of the unexpected and exceptional properties of oxide-nitride interfaces and provides access to hidden phases at low-dimensional quantum heterostructures.

Antiferromagnetism of Double Molybdate LiFe(MoO4)2.

The magnetic properties of the spin-5/2 double molybdate LiFe(MoO4)2 have been characterized by heat capacity, magnetic susceptibility, and neutron powder diffraction techniques. Unlike the multiferroic system LiFe(WO4)2 which exhibits two successive magnetic transitions, LiFe(MoO4)2 undergoes only one antiferromagnetic transition at TN ∼ 23.8 K. Its antiferromagnetic magnetic structure with the commensurate propagation vector k = (0, 0.5, 0) has been determined. Density functional theory calculations confirm the antiferromagnetic ground state and provide a numerical estimate of the relevant exchange coupling constants.

Exploiting Symmetry Mismatch to Control Magnetism in a Ferroelastic Heterostructure.

In the bulk, LaCoO_{3} (LCO) is a paramagnet, yet the low-temperature ferromagnetism (FM) is observed in tensile strained thin films, and its origin remains unresolved. Here, we quantitatively measured the distribution of atomic density and magnetization in LCO films by polarized neutron reflectometry (PNR) and found that the LCO layers near the heterointerfaces exhibit a reduced magnetization but an enhanced atomic density, whereas the film's interior (i.e., its film bulk) shows the opposite trend. We attribute the nonuniformity to the symmetry mismatch at the interface, which induces a structural distortion related to the ferroelasticity of LCO. This assertion is tested by systematic application of hydrostatic pressure during the PNR experiments. The magnetization can be controlled at a rate of -20.4% per GPa. These results provide unique insights into mechanisms driving FM in strained LCO films while offering a tantalizing observation that tunable deformation of the CoO_{6} octahedra in combination with the ferroelastic order parameter.

Amyloid Aggregation of Bacillus circulans Xylanase under Native Conditions and its Modulation by ß-Amyloid-Derived Peptide Fragments.

The aggregation of intrinsically disordered proteins into fibrils is implicated in many neurodegenerative diseases. Amyloid aggregation is a generic property of proteins as evidenced by globular proteins that often form amyloid aggregates under partially denaturing conditions. Recently, multiple lines of evidence have suggested that the amyloid aggregation of globular proteins can also occur under native conditions. Unfortunately, amyloid aggregation under native conditions has been demonstrated in only a handful of cases. Engineering a globular protein's amyloid aggregation might benefit from its fusion to an amyloid-derived fragment with reduced aggregation propensity. Unfortunately, the impacts of such fragments on the amyloid aggregation under native conditions have yet to be examined. In this study, we show that a globular protein, Bacillus circulans xylanase (BCX), can aggregate to form amyloid fibrils under native conditions. When BCX was mixed with or fused to the non-self-aggregating fragments, KLVFWAK and ELVFWAE-which were derived from ß-amyloid (Aß)-they modulated the BCX amyloid aggregation to differing extents. This study also provides insight into a correlation between the kinetic stability and amyloid aggregation of BCX, and supports a view that Aß-derived fragments can be useful for the modulating amyloid aggregation of some, though not all, proteins.

Achilles Tendon Rupture in Elite Athletes.

The management of acute Achilles tendon rupture in elite athletes is a current area of clinical controversy. Recent studies have reported near-equivocal outcomes in patients who undergo either nonsurgical or surgical treatment of Achilles tendon rupture; however, similar functional outcomes may not be observed in elite athletes who are at the highest levels of athletic performance and undergo nonsurgical or surgical treatment of Achilles tendon rupture. Surgeons should understand the risks and benefits of nonsurgical and surgical management of acute Achilles tendon rupture. Surgeons also should understand the accelerated rehabilitation protocols; functional nonsurgical and postoperative rehabilitation protocols; as well as the standard open, percutaneous, and minimally invasive surgical techniques for the management of Achilles tendon rupture from the perspective of a sports medicine foot and ankle specialist.

Management of Osteochondral Lesions of the Talus.

Management strategies for symptomatic osteochondral lesions of the talus are primarily surgical. Treatment options for symptomatic osteochondral lesions of the talus most commonly include bone marrow stimulation techniques, osteochondral autograft transplantation, osteochondral allograft transplantation, autologous chondrocyte implantation, matrix-induced autologous chondrocyte implantation, and particulated juvenile articular cartilage. The selection of the most appropriate treatment option should be based on the specifics of a talar lesion, in particular, lesion size.

Lisfranc Injuries in the Elite Athlete.

The management of sports-related Lisfranc injuries is optimized by a detailed understanding of the relevant anatomy, mechanisms of injury, clinical diagnostic maneuvers, imaging, and treatment options for patients with this disabling injury. A lower energy ligamentous variant Lisfranc injury, which was first observed in professional football players, has recently been described. The treatment options for patients with a Lisfranc injury include nonsurgical management, open reduction and internal fixation, suture-button fixation techniques, and arthrodesis.

Lateral Ankle Instability and Peroneal Tendon Pathology.

Surgeons should understand the anatomic, vascular, biomechanical, and predisposing factors related to lateral ankle instability and peroneal tendon injuries, including peroneal tendinitis and tenosynovitis, peroneal tendon tears and ruptures, as well as peroneal tendon subluxation and dislocation. Surgeons should understand the treatment options and recommendations for patients who have lateral ankle instability and peroneal tendon injuries from the perspective of a sports medicine foot and ankle specialist. In addition, surgeons should be aware of arthroscopic approaches and an algorithm for the treatment of patients who have lateral ankle instability and peroneal tendon injuries.

High-Risk Stress Fractures in Elite Athletes.

Surgeons should understand common factors that predispose high-level athletes to stress injuries as well as the importance of vitamin D and specifics related to vascular supply, location of injury, biomechanics, and susceptibility factors in high-level athletes who have stress injuries. Surgeons should be aware of diagnostic- and management-based recommendations for and the outcomes of anterior tibia, medial malleolus, tarsal navicular, and proximal fifth metatarsal stress fractures in professional athletes.

Optimal femoral tunnel positioning in posterior cruciate ligament reconstruction using outside-in drilling.

PURPOSE: The goal of our study was to determine the precise femoral drill guide placement during reconstruction of the anterolateral bundle (ALB) of the posterior cruciate ligament (PCL) femoral footprint that would produce a minimum tunnel length of 25 mm, a maximum graft/femoral tunnel angle of 50°, and a minimum distance of 10 mm between the femoral socket and the subchondral bone of the weight-bearing surface of the medial femoral condyle. METHODS: Using computer navigation, we used synthetic replicas of human femora to create a series of virtual femoral sockets. We then measured the bone tunnel length, angle of the femoral socket relative to the PCL footprint, and distance from the subchondral bone of the weight-bearing surface of the medial femoral condyle to the femoral socket at a series of guide pin sleeve positions. We positioned the guide pin using the following angle combinations: -20°, -10°, 0°, 10°, 20°, 30°, 40°, 50°, and 60° to a line perpendicular to the femoral axis in the coronal plane and -15°, 0°, 15°, 30°, 45°, and 60° to a line parallel to the transepicondylar axis in the axial plane. Using linear regression models, we determined the precise drill guide placement angles that would produce the optimal tunnel length, graft/femoral tunnel angle, and distance to the subchondral bone margin. RESULTS: The results were consistent between small, medium, and large femora. We found that the optimal drilling angles for anatomic reconstruction of the femoral footprint of the ALB of the PCL were 0° to a line perpendicular to the femoral axis in the coronal plane and 15° to a line parallel to the transepicondylar axis in the horizontal or axial plane. CONCLUSIONS: During outside-in drilling for PCL reconstruction, holding the guide pin sleeve at a position 0° to a line perpendicular to the femoral axis in the coronal plane and 15° to a line parallel to the transepicondylar axis in the horizontal or axial plane results in optimal bone tunnel length, graft/tunnel angle, and distance between the femoral socket and the subchondral bone of the weight-bearing surface of the medial femoral condyle. CLINICAL RELEVANCE: We describe a precise femoral tunnel drill guide placement during outside-in PCL reconstruction that ensures an optimal femoral socket with a minimum bone tunnel length of 25 mm, maximum graft/femoral tunnel angle of 50°, and minimum distance of 10 mm between the subchondral bone of the weight-bearing surface of the medial femoral condyle and the femoral socket.

An accurate in vitro model of the E.†coli envelope.

Gram-negative bacteria are an increasingly serious source of antibiotic-resistant infections, partly owing to their characteristic protective envelope. This complex, 20 nm thick barrier includes a highly impermeable, asymmetric bilayer outer membrane (OM), which plays a pivotal role in resisting antibacterial chemotherapy. Nevertheless, the OM molecular structure and its dynamics are poorly understood because the structure is difficult to recreate or study in vitro. The successful formation and characterization of a fully asymmetric model envelope using Langmuir-Blodgett and Langmuir-Schaefer methods is now reported. Neutron reflectivity and isotopic labeling confirmed the expected structure and asymmetry and showed that experiments with antibacterial proteins reproduced published in vivo behavior. By closely recreating natural OM behavior, this model provides a much needed robust system for antibiotic development.

Madura foot: two case reports, review of the literature, and new developments with clinical correlation.

"Madura foot" or pedal mycetoma is a rare destructive infection of the skin and subcutaneous tissues of the foot, progressing to involve muscle and bone. The infection can be caused by both bacteria and fungi. Infection typically follows traumatic implantation of bacteria or fungal spores, which are present in soil or on plant material. Clinically, this entity can be difficult to diagnose and can have an indolent and progressive course. Early diagnosis is important to prevent patient morbidity and mortality. We present two cases of pedal mycetoma, review the literature, review new developments in diagnosis, and discuss magnetic resonance imaging (MRI) features of this unusual entity.

Polymethylmethacrylate (PMMA) Augmentation Enhances the Mechanical Characteristics of Midfoot Beam Constructs in Charcot Neuroarthropathy Cadaver Model.

BACKGROUND: Even with the best conservative care, patients with Charcot neuroarthropathy (CN) of the foot and ankle often ulcerate, increasing their risk of infection, amputation, and death. Surgical fixation has been associated with risk of recurrent ulceration, potentially due to poor bone quality prone to recurrent deformity and ulceration. We propose midfoot beam reconstruction with PMMA augmentation as a novel means of improving fixation. METHODS: A protocol was developed to create characteristic CN midfoot fragmentation both visually and fluoroscopically in each of 12 matched-pair cadaveric feet. Afterward, the pairs were divided into 2 groups: (1) midfoot beam fusion surgery alone, and (2) midfoot beam fusion surgery augmented with PMMA. A solid 7.0-mm beam was placed into the medial column and a solid 5.5-mm beam was placed across the lateral column. In the PMMA group, 8 to 10 mL of PMMA was inserted into the medial column. The hindfoot of each specimen was potted and the metatarsal heads were cyclically loaded for 1800 cycles, followed by load to failure while load and displacement were continually recorded. RESULTS: One specimen in the beam alone group failed before reaching the 1800th cycle and was not included in the failure analysis. The midfoot beam only group demonstrated greater mean displacement during cycle testing compared with the PMMA group, P < .05. The maximum force (N), stiffness (N/mm), and toughness (Nmm) were all significantly greater in the group augmented with PMMA, P < .05. CONCLUSION: In a CN cadaveric model, PMMA augmentation significantly decreased gapping during cyclic loading and nearly doubled the load to failure compared with midfoot beams alone. CLINICAL RELEVANCE: The results of this biomechanical study demonstrate that augmentation of midfoot beams with PMMA increases the strength and stiffness of the fusion construct. This increased mechanical toughness may help reduce the risk of nonunion and infection in patients with neuropathic midfoot collapse.

Hexadecylamine adsorption at the iron oxide-oil interface.

The adsorption behavior of a model additive, hexadecylamine, onto an iron surface from hexadecane oil has been characterized using polarized neutron reflectometry, sum-frequency generation spectroscopy, solution depletion isotherm, and X-ray photoelectron spectroscopy (XPS). The amine showed a strong affinity for the metal surface, forming a dense monolayer at relatively low concentrations; a layer thickness of 16 (±3) Å at low concentrations, increasing to 20 (±3) Å at greater amine concentrations, was determined from the neutron data. These thicknesses suggest that the molecules in the layer are tilted. Adsorption was also indicated by sum-frequency generation spectroscopy and XPS, the latter indicating that the most dominant amine-surface interaction was via electron donation from the nitrogen lone pair to the positively charged iron ions. Sum-frequency generation spectroscopy was used to determine the alkyl chain conformation order and orientation on the surface.

Lateral column length in adult flatfoot deformity.

INTRODUCTION: In adult acquired flatfoot deformity, it is unclear whether the lateral column length shortens with progression of the deformity, whether it is short to begin with, or whether it is short at all. To our knowledge, no previous study has examined the lateral column length of patients with adult acquired flatfoot deformity compared to a control population. The purpose of our study was to compare the lateral column length in patients with and without adult acquired flatfoot deformity to see if there was a significant difference. METHODS: The study was a retrospective radiographic review of 2 foot and ankle fellowship-trained orthopaedic surgeons' patients with adult flatfoot deformity. Our study population consisted of 75 patients, 85 feet (28 male, 57 female) with adult flatfoot deformity with a mean age of 64 (range, 23-93). Our control population consisted of 57 patients and 70 feet (23 male, 47 female) without flatfoot deformity with a mean age of 61 (range, 40-86 years). Weightbearing anteroposterior (AP) and lateral foot radiographs were analyzed for each patient, and the following measurements were made: medial and lateral column lengths, talonavicular uncoverage angle, talus-first metatarsal angle, calcaneal pitch angle, and medial and lateral column heights. An unpaired t test was used to analyze the measurements between the groups. Ten patients' radiographs were remeasured, and correlation coefficients were obtained to assess the reliability of the measuring techniques. RESULTS: For the flatfoot group, the mean medial and lateral column lengths on the AP radiograph were 108.6 mm and 95.8 mm, respectively; the mean talo-navicular uncoverage angle was 26.2 degrees; and the mean talus-first metatarsal angle was 20.0 degrees. In the control group, the mean medial and lateral column lengths on the AP radiograph were 108.8 mm and 96.5 mm, respectively; the mean talo-navicular uncoverage angle was 8.2 degrees; and the mean talus-first metatarsal angle was 7.7 degrees. On the lateral radiograph in the flatfoot group, the mean medial and lateral column lengths were 167.2 mm and 166.6 mm, respectively; the mean medial and lateral column heights were 16.0 mm and 14.7 mm, respectively; the mean calcaneal pitch angle was 15.6 degrees; and the talus-first metatarsal angle was 10.3 degrees and for the control group, the mean medial and lateral column lengths were 165.3 mm and 163.5 mm, respectively; the mean medial and lateral column heights were 22.8 mm and 13.1 mm, respectively; the mean calcaneal pitch angle was 22.4 degrees; and the talus-first metatarsal angle was -3.6 degrees. None of the differences in measurements for medial and lateral column lengths between the flatfoot and control groups achieved statistical significance. However, statistically significant differences between the 2 groups were observed in the measurements for medial and lateral column heights, talo-navicular uncoverage angle, calcaneal pitch angle, and talus-first metatarsal angle. CONCLUSION: There is no difference in lateral column lengths between patients with and without adult flatfoot deformity. The perceived shortened lateral column is likely due to forefoot abduction and hindfoot valgus deformities that are associated with adult flatfoot deformity. LEVEL OF EVIDENCE: Level III, comparative series.

Effect of various hallux valgus reconstruction on sesamoid location: a radiographic study.

BACKGROUND: The correction of sesamoid subluxation is an important component of hallux valgus reconstruction with some surgeons feeling that the sesamoids can be pulled back under the first metatarsal head when imbricating the medial capsule during surgery. The purpose of this study was to radiographically assess the effect of an osteotomy on sesamoid location relative to the second metatarsal. METHODS: This is a retrospective radiographic study review of 165 patients with hallux valgus treated with reconstructive osteotomies. Patients were included if they underwent a scarf or basilar osteotomy for hallux valgus but were excluded if they had inflammatory arthropathy or lesser metatarsal osteotomy. A modified McBride soft tissue procedure was performed in conjunction with the basilar and scarf osteotomies. Each patient's preoperative and postoperative radiographs were evaluated for hallux valgus angle, intermetatarsal 1-2 angle, tibial sesamoid classification, and lateral sesamoid location relative to the second metatarsal. RESULT: The greatest correction of both hallux valgus and intermetatrsal 1-2 angle was achieved in basilar osteotomies (20.6 degrees and 9.7 degrees, respectively), then scarf osteotomies (14.4 degrees and 8.7 degrees, respectively). Basilar and scarf osteotomies both corrected medial sesamoid subluxation relative to the first metatarsal head an average of 2-3 classification stages. All osteotomies had minimal lateral sesamoid location change relative to the second metatarsal. CONCLUSION: The majority of sesamoid correction correlated with the intermetatarsal 1-2 correction. The concept that medial capsular plication pulls the sesamoids beneath the first metatarsal (ie, changes the location of the sesamoids relative to the second metatarsal) was not supported by our results. LEVEL OF EVIDENCE: Level III, retrospective case series.

Ipsilateral intact fibula as a predictor of tibial plafond fracture pattern and severity.

BACKGROUND: The objective of this study was to determine whether there is a difference in fracture pattern and severity of comminution between tibial plafond fractures with and without associated fibular fractures using computed tomography (CT). We hypothesized that the presence of an intact fibula was predictive of increased tibial plafond fracture severity. METHODS: This was a case control, radiographic review performed at a single level I university trauma center. Between November 2007 and July 2011, 104 patients with 107 operatively treated tibial pilon fractures and preoperative CT scans were identified: 70 patients with 71 tibial plafond fractures had associated fibular fractures, and 34 patients with 36 tibial plafond fractures had intact fibulas. Four criteria were compared between the 2 groups: AO/OTA classification of distal tibia fractures, Topliss coronal and sagittal fracture pattern classification, plafond region of greatest comminution, and degree of proximal extension of fracture line. RESULTS: The intact fibula group had greater percentages of AO/OTA classification B2 type (5.5 vs 0, P = .046) and B3 type (52.8 vs 28.2, P = .013). Conversely, the percentage of AO/OTA classification C3 type was greater in the fractured fibula group (53.5 vs 30.6, P = .025). Evaluation using the Topliss sagittal and coronal classifications revealed no difference between the 2 groups (P = .226). Central and lateral regions of the plafond were the most common areas of comminution in fractured fibula pilons (32% and 31%, respectively). The lateral region of the plafond was the most common area of comminution in intact fibula pilon fractures (42%). There was no statistically significant difference (P = .71) in degree of proximal extension of fracture line between the 2 groups. CONCLUSIONS: Tibial plafond fractures with intact fibulas were more commonly associated with AO/OTA classification B-type patterns, whereas those with fractured fibulas were more commonly associated with C-type patterns. An intact fibula may be predictive of less comminution of the plafond. The lateral and central regions of the plafond were the most common areas of comminution in tibial plafond fractures, regardless of fibular status. LEVEL OF EVIDENCE: Level III, case control study.

Accuracy of Pain Tolerance Self-assessment Versus Objective Pressure Sensitivity.

INTRODUCTION: Effective treatment of postoperative pain after elective surgery remains elusive, and the experience of pain can be variable for patients. The patient's intrinsic pain tolerance may contribute to this variability. We sought to identify whether there was a correlation between subjective report of intrinsic pain tolerance and objective measurement of pressure dolorimetry (PD). We also sought to identify whether a correlation existed between PD and Patient Reported Outcome Measurement Information System (PROMIS) scores of pain intensity, physical function, and mood. PD is a validated, objective method to assess pain tolerance. Markers of general mental and physical health are correlated with pain sensitization and may also be linked to pain tolerance. METHODS: PROMIS scores, dolorimetry measurements, and survey data were collected on 40 consecutive orthopaedic foot and ankle surgery patients at the initial clinic visit. Patients were included if they had normal sensation on the plantar foot and no prior surgery or plantar heel source of pain. RESULTS: Objective dolorimetry data reflecting 5/10 pain for the patients were 24 N/cm 2 (±8.9). Patients estimated their pain threshold as 7.3/10 (±2.1). No correlation was found between objective and subjective pain threshold identified. A moderate negative correlation of R = -0.44 was observed regarding PROMIS-M with dolorimetry data ( P < -0.05). PROMIS-M score >60 had a significant decrease in pain threshold to 15.9 ± 8.5 N/cm 2 compared with 25.7 ± 8.9 N/cm 2 for those who were less depressed with a PROMIS<60 ( P < 0.05). CONCLUSION: Subjective pain tolerance is not correlated with the patient's own objective pain threshold or markers of mental health and should not be used to assist clinical decision making. PROMIS-M is inversely correlated with objective pain. Higher PROMIS-M scores are associated with a lower objective pain threshold. LEVEL OF EVIDENCE: Level II-Lesser Quality Randomized Controlled Trial or Prospective Comparative Study.

Emergent Magnetic States and Tunable Exchange Bias at 3d Nitride Heterointerfaces.

Interfacial magnetism stimulates the discovery of giant magnetoresistance (MR) and spin-orbital coupling across the heterointerfaces, facilitating the intimate correlation between spin transport and complex magnetic structures. Over decades, functional heterointerfaces composed of nitrides have seldom been explored due to the difficulty in synthesizing high-quality nitride films with correct compositions. Here, the fabrication of single-crystalline ferromagnetic Fe3 N thin films with precisely controlled thicknesses is reported. As film thickness decreases, the magnetization dramatically deteriorates, and the electronic state changes from metallic to insulating. Strikingly, the high-temperature ferromagnetism is maintained in a Fe3 N layer with a thickness down to 2 u.c. (≈8 Å). The MR exhibits a strong in-plane anisotropy; meanwhile, the anomalous Hall resistivity reverses its sign when the Fe3 N layer thickness exceeds 5 u.c. Furthermore, a sizable exchange bias is observed at the interfaces between a ferromagnetic Fe3 N and an antiferromagnetic CrN. The exchange bias field and saturation moment strongly depend on the controllable bending curvature using the cylinder diameter engineering technique, implying the tunable magnetic states under lattice deformation. This work provides a guideline for exploring functional nitride films and applying their interfacial phenomena for innovative perspectives toward practical applications.