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To present a theoretical framework that rigorously defines and analyzes key concepts and quantities for velocity selective arterial spin labeling (VSASL). An expression for the VSASL arterial delivery function is derived based on (1) labeling and saturation profiles as a function of velocity and (2) physiologically plausible approximations of changes in acceleration and velocity across the vascular system. The dependence of labeling efficiency on the amplitude and effective bolus width of the arterial delivery function is defined. Factors that affect the effective bolus width are examined, and timing requirements to minimize quantitation errors are derived. The model predicts that a flow-dependent negative bias in the effective bolus width can occur when velocity selective inversion (VSI) is used for the labeling module and velocity selective saturation (VSS) is used for the vascular crushing module. The bias can be minimized by choosing a nominal labeling cutoff velocity that is lower than the nominal cutoff velocity of the vascular crushing module. The elements of the model are specified in a general fashion such that future advances can be readily integrated. The model can facilitate further efforts to understand and characterize the performance of VSASL and provide critical theoretical insights that can be used to design future experiments and develop novel VSASL approaches.

Mitochondrial dysfunction plays an important role in the aging process. However, the mechanism by which this dysfunction causes aging is not fully understood. The accumulation of mutations in the mitochondrial genome (or "mtDNA") has been proposed as a contributor. One compelling piece of evidence in support of this hypothesis comes from the PolgD257A/D257A mutator mouse (Polgmut/mut ). These mice express an error-prone mitochondrial DNA polymerase that results in the accumulation of mtDNA mutations, accelerated aging, and premature death. In this paper, we have used the Polgmut/mut model to investigate whether the age-related biological effects observed in these mice are triggered by oxidative damage to the DNA that compromises the integrity of the genome. Our results show that mutator mouse has significantly higher levels of 8-oxoguanine (8-oxoGua) that are correlated with increased nuclear DNA (nDNA) strand breakage and oxidative nDNA damage, shorter average telomere length, and reduced mtDNA integrity. Based on these results, we propose a model whereby the increased level of reactive oxygen species (ROS) associated with the accumulation of mtDNA mutations in Polgmut/mut mice results in higher levels of 8-oxoGua, which in turn lead to compromised DNA integrity and accelerated aging via increased DNA fragmentation and telomere shortening. These results suggest that mitochondrial play a central role in aging and may guide future research to develop potential therapeutics for mitigating aging process.

Complex coacervation driven liquid-liquid phase separation (LLPS) of biopolymers has been attracting attention as a novel phase in living cells. Studies of LLPS in this context are typically of proteins harboring chemical and structural complexity, leaving unclear which properties are fundamental to complex coacervation versus protein-specific. This study focuses on the role of polyethylene glycol (PEG)-a widely used molecular crowder-in LLPS. Significantly, entropy-driven LLPS is recapitulated with charged polymers lacking hydrophobicity and sequence complexity, and its propensity dramatically enhanced by PEG. Experimental and field-theoretic simulation results are consistent with PEG driving LLPS by dehydration of polymers, and show that PEG exerts its effect without partitioning into the dense coacervate phase. It is then up to biology to impose additional variations of functional significance to the LLPS of biological systems.

A set of functionalized nanoparticles (PEGylated dendrimers, d = 2.8-11 nm) was used to probe the structural heterogeneity in Na+/K+ induced κ-carrageenan gels. The self-diffusion behavior of these nanoparticles as observed by 1H pulsed-field gradient NMR, fluorescence recovery after photobleaching, and raster image correlation spectroscopy revealed a fast and a slow component, pointing toward microstructural heterogeneity in the gel network. The self-diffusion behavior of the faster nanoparticles could be modeled with obstruction by a coarse network (average mesh size

Hydration water on the surface of a protein is thought to mediate the thermodynamics of protein-ligand interactions. For hydration water to play a role beyond modulating global protein solubility or stability, the thermodynamic properties of hydration water must reflect on the properties of the heterogeneous protein surface and thus spatially vary over the protein surface. A potent read-out of local variations in thermodynamic properties of hydration water is its equilibrium dynamics spanning picosecond to nanosecond time scales. In this study, we employ Overhauser dynamic nuclear polarization (ODNP) to probe the equilibrium hydration water dynamics at select sites on the surface of Chemotaxis Y (CheY) in dilute solution. ODNP reports on site-specific hydration water dynamics within 5-10 Å of a label tethered to the biomolecular surface on two separate time scales of motion, corresponding to diffusive water (DW) and protein-water coupled motions, referred to as bound water (BW). We find DW dynamics to be highly heterogeneous across the surface of CheY. We identify a significant correlation between DW dynamics and the local hydropathy of the CheY protein surface, empirically determined by molecular dynamics (MD) simulations, and find the more hydrophobic sites to be hydrated with slower diffusing water. Furthermore, we compare the hydration water dynamics on different polypeptides and liposome surfaces and find the DW dynamics on globular proteins to be significantly more heterogeneous than on intrinsically disordered proteins (IDPs), peptides, and liposomes. The heterogeneity in the hydration water dynamics suggests that structured proteins have the capacity to encode information into the surrounding hydration shell.

We report here on the implementation of arbitrary waveform generation (AWG) capabilities at ∼200GHz into an Electron Paramagnetic Resonance (EPR) and Dynamic Nuclear Polarization (DNP) instrument platform operating at 7T. This is achieved with the integration of a 1GHz, 2 channel, digital to analog converter (DAC) board that enables the generation of coherent arbitrary waveforms at Ku-band frequencies with 1ns resolution into an existing architecture of a solid state amplifier multiplier chain (AMC). This allows for the generation of arbitrary phase- and amplitude-modulated waveforms at 200GHz with >150mW power. We find that the non-linearity of the AMC poses significant difficulties in generating amplitude-modulated pulses at 200GHz. We demonstrate that in the power-limited regime of ω110MHz) spin manipulation in incoherent (inversion), as well as coherent (echo formation) experiments. Highlights include the improvement by one order of magnitude in inversion bandwidth compared to that of conventional rectangular pulses, as well as a factor of two in improvement in the refocused echo intensity at 200GHz.

The necessary resonator employed in pulse electron paramagnetic resonance (EPR) rings after the excitation pulse and creates a finite detector dead-time that ultimately prevents the detection of signal from fast relaxing spin systems, hindering the application of pulse EPR to room temperature measurements of interesting chemical or biological systems. We employ a recently available high bandwidth arbitrary waveform generator (AWG) to produce a cancellation pulse that precisely destructively interferes with the resonant cavity ring-down. We find that we can faithfully detect EPR signal at all times immediately after, as well as during, the excitation pulse. This is a proof of concept study showcasing the capability of AWG pulses to precisely cancel out the resonator ring-down, and allow for the detection of EPR signal during the pulse itself, as well as the dead-time of the resonator. However, the applicability of this approach to conventional EPR experiments is not immediate, as it hinges on either (1) the availability of low-noise microwave sources and amplifiers to produce the necessary power for pulse EPR experiment or (2) the availability of very high conversion factor micro coil resonators that allow for pulse EPR experiments at modest microwave power.

We present arbitrary control over a homogenous spin system, demonstrated on a simple, home-built, electron paramagnetic resonance (EPR) spectrometer operating at 8-10 GHz (X-band) and controlled by a 1 GHz arbitrary waveform generator (AWG) with 42 dB (i.e. 14-bit) of dynamic range. Such a spectrometer can be relatively easily built from a single DAC (digital to analog converter) board with a modest number of stock components and offers powerful capabilities for automated digital calibration and correction routines that allow it to generate shaped X-band pulses with precise amplitude and phase control. It can precisely tailor the excitation profiles "seen" by the spins in the microwave resonator, based on feedback calibration with experimental input. We demonstrate the capability to generate a variety of pulse shapes, including rectangular, triangular, Gaussian, sinc, and adiabatic rapid passage waveforms. We then show how one can precisely compensate for the distortion and broadening caused by transmission into the microwave cavity in order to optimize corrected waveforms that are distinctly different from the initial, uncorrected waveforms. Specifically, we exploit a narrow EPR signal whose width is finer than the features of any distortions in order to map out the response to a short pulse, which, in turn, yields the precise transfer function of the spectrometer system. This transfer function is found to be consistent for all pulse shapes in the linear response regime. In addition to allowing precise waveform shaping capabilities, the spectrometer presented here offers complete digital control and calibration of the spectrometer that allows one to phase cycle the pulse phase with 0.007° resolution and to specify the inter-pulse delays and pulse durations to ≤ 250 ps resolution. The implications and potential applications of these capabilities will be discussed.

Subscapularis management and repair are crucial during total shoulder arthroplasty to maximize outcomes. Bioinductive implants have been used to aid in repair of tendons in a variety of surgical techniques. In this surgical technique, we demonstrate our technique of subscapularis repair augmentation with a bioinductive implant during anatomic total shoulder arthroplasty. [Display omitted] [ABSTRACT FROM AUTHOR]

Hip arthroscopy is rapidly increasing in case volume annually in the United States. However, it remains a challenging surgery with a steep learning curve. Labral repair is commonly performed to preserve the labrum rather than labral debridement or reconstruction. Many techniques have been described for labral repair. In this technical note, we describe our technique for a modified loop suture technique for arthroscopic labral repair of the hip. [Display omitted] [ABSTRACT FROM AUTHOR]

Knee arthrocentesis can be performed by landmark (LM) or ultrasound (US) guidance. The goal of performing knee arthrocentesis is to obtain synovial fluid, however, it is also important to consider the number of attempts required and accidental bone contacts that occur. This study evaluates procedural success without bone contact in knee arthrocentesis and compares both LM and US guided techniques in a cadaver model. This was a randomized crossover study comparing US vs LM guidance for arthrocentesis in a single academic center. Volunteers were randomized to perform both LM and US guided knee arthrocentesis on cadavers. The primary outcome was procedural success, defined as first attempt aspiration of synovial fluid without bone contact. Secondary outcomes included number of attempts, number of bone contacts, time to aspiration, and confidence. Sixty-one participants completed the study with a total of 122 procedures performed. Procedural success without bone contact was greater in the US group (84% vs 64% p = 0.02). Time to aspiration was longer for US (38.75 s vs 25.54 s p = 0.004). Participants were more confident with US compared to LM both before the procedure on a Visual Analog Scale from 1 to 100 (29 vs 21 p = 0.03) as well as after the procedure (83 vs 69 p = 0.0001). Participants had a greater median increase in confidence with US following training (44 vs 26 p = 0.01). Study participants had greater procedural success without bone contact when US guidance was used. The increase in confidence following training was greater for US guidance than the LM method. Use of US guidance may offer a benefit by allowing for better needle control and avoidance of sensitive structures for clinicians performing knee arthrocentesis. [ABSTRACT FROM AUTHOR]

Radial meniscus tears occur commonly as traumatic tears in younger patients, as well as in association with concomitant degenerative changes. Traditional management of these tears has centered around partial meniscectomy; however, there has been a more recent trend toward preserving the meniscus and attempting repair. Because of the gapping and displacement that frequently occurs with these tears, repair is often challenging and is done under high amounts of tension. The following article describes a technique using a traction suture to aid in maintaining reduction throughout repair. This is followed by the use of a combination of techniques to form a "super-hashtag" configuration of both vertical and horizontal mattress sutures, leading to a secure repair under little tension. [Display omitted] [ABSTRACT FROM AUTHOR]

Horizontal cleavage meniscus tears occur more frequently in older patient populations with degenerative changes within the meniscus. Traditionally, they have been managed with nonsurgical interventions or with partial meniscectomy. As increasing evidence demonstrates the link between partial meniscectomy and progressive osteoarthritis with these types of tears, as well as worse long-term outcomes and reduced cost savings, surgical repair of horizontal cleavage meniscal tears has increased in appropriate patients. This technique article highlights the evaluation, indications, and preferred repair technique for horizontal cleavage tears in appropriately selected patients. [Display omitted] [ABSTRACT FROM AUTHOR]

Meniscus root tears are tears that occur within 1 cm of the meniscus root attachment to the tibia. If not repaired, root tears will lead to altered knee biomechanics and accelerated degenerative changes in the knee. In this surgical technique, we demonstrate repair of a meniscus root tear with an all-inside suture repair of the posterior meniscus that is then passed through 2 transtibial tunnels and then fixed with an anchor. After surgery, patients are non-weightbearing for 4 weeks and can return to activity by 6 months. [Display omitted] [ABSTRACT FROM AUTHOR]

Without the benefit of having experienced many years of teaching, it is hard to emulate the experienced colleagues one admires. In her second year of teaching, the author seems to have captured some of the wisdom that comes with many years of teaching. Her advice reveals many of the practices that distinguish veterans from newcomers. Teachers who have been practicing their craft for many years exude confidence borne of an awareness of the resources in the school and the possibilities for pedagogical options. They have rebounded from mistakes and disappointments, and they have found ways to contend with the workload that comes with an endlessly demanding job. In this article, the author reveals some key characteristics of a "stayer" in the classroom: (1) a commitment to the mission of schools; (2) a determination to plan for growth and improvement; and (3) a strong sense of humor. The need to mentor a newer teacher and the importance of staying connected to colleagues within a school and among other schools remains into the second year of teaching and well beyond.

Gluteal tendon tears are a common cause of hip pain. Most commonly, tears occur in the gluteus medius and minimus, and there are well-established nonoperative or operative treatment pathways. In this Technical Note, we describe our technique for repair of a full-thickness gluteus maximus tendon tear using anchor fixation. [Display omitted] [ABSTRACT FROM AUTHOR]