The Effects of COVID-19 on General Surgery Residency Programs in the United States.

Introduction: The COVID-19 pandemic impacted multiple aspects of surgical education. This survey delineates steps taken by general surgery residency programs to meet changing patient-care needs while continuing to provide adequate education. Methods: A survey was administered to program directors and coordinators of all United States general surgery residency programs to assess the early effects of the pandemic on residents from March 1 through May 31, 2020. Results: Of 303 programs contacted, 132 (43.6%) completed the survey. Residents were asked to work in areas outside of their specialty at 27.3% of programs. Residency curriculum was changed in 35.6% of programs, and 76.5% of programs changed their academic conferences. Resident schedules were altered at a majority of programs to limit resident-patient exposure, increase ICU coverage, or improve resident utilization. Surgical caseloads decreased at 93.8% of programs; 31.8% of those programs reported concerns regarding residents' achieving the minimum case numbers required to graduate. Conclusions: These results provided insight into the restructuring of general surgery residency programs during a pandemic and may be used to establish future pandemic response plans.

Stability and Thermoelectric Properties of Zn4Sb3 with TiO2 Nanoparticle Inclusions.

ß-Zn4Sb3 is a cheap nontoxic high-performance thermoelectric material, which unfortunately suffers from stability issues because of zinc migration in thermal and electrical gradients. Here, the thermoelectric properties and thermal stability of ß-Zn4Sb3 mixed with varying sizes and weight percentages of TiO2 nanoparticles are investigated. Furthermore, the stability of pressed ß-Zn4Sb3-TiO2 nanocomposite pellets is investigated by measuring high-energy synchrotron powder X-ray diffraction (PXRD) data during operating conditions using the Aarhus thermoelectric operando setup (ATOS). Through these studies, it is determined that TiO2 nanoparticle addition in pressed pellets of ß-Zn4Sb3 does not prevent Zn migration, and even though effects are seen in the thermal conductivity and electrical resistivity, the overall zT remains unchanged regardless of TiO2 nanoinclusions. For the present samples, the Seebeck coefficients are unaffected by the addition of nanoparticles, and thus, there is no observed energy-filtering effect. The operando PXRD data reveal that the TiO2 nanoinclusions lower the degradation rate by up to 75%, but all samples eventually decompose. This is corroborated by long-term stability tests performed using a thermal gradient. In conclusion, TiO2 nanoinclusions do not degrade the excellent thermoelectric properties of ß-Zn4Sb3, but the stabilizing effect is not sufficient for establishing long-term operating stability.

Tuneable local order in thermoelectric crystals.

Although crystalline solids are characterized by their periodic structures, some are only periodic on average and deviate on a local scale. Such disordered crystals with distinct local structures have unique properties arising from both collective and localized behaviour. Different local orderings can exist with identical average structures, making their differences hidden to Bragg diffraction methods. Using high-quality single-crystal X-ray diffuse scattering the local order in thermoelectric half-Heusler Nb1-x CoSb is investigated, for which different local orderings are observed. It is shown that the vacancy distribution follows a vacancy repulsion model and the crystal composition is found always to be close to x = 1/6 irrespective of nominal sample composition. However, the specific synthesis method controls the local order and thereby the thermoelectric properties thus providing a new frontier for tuning material properties.

An Inverse Thermogelling Bioink Based on an ABA-Type Poly(2-oxazoline) Amphiphile.

Hydrogels are key components in several biomedical research areas such as drug delivery, tissue engineering, and biofabrication. Here, a novel ABA-type triblock copolymer comprising poly(2-methyl-2-oxazoline) as the hydrophilic A blocks and poly(2-phenethyl-2-oxazoline) as the aromatic and hydrophobic B block is introduced. Above the critical micelle concentration, the polymer self-assembles into small spherical polymer micelles with a hydrodynamic radius of approx 8-8.5 nm. Interestingly, this specific combination of hydrophilic and hydrophobic aromatic moieties leads to rapid thermoresponsive inverse gelation at polymer concentrations above a critical gelation concentration (20 wt %) into a macroporous hydrogel of densely packed micelles. This hydrogel exhibited pronounced viscoelastic solid-like properties, as well as extensive shear-thinning, rapid structure recovery, and good strain resistance properties. Excellent 3D-printability of the hydrogel at lower temperature opens a wide range of different applications, for example, in the field of biofabrication. In preliminary bioprinting experiments using NIH 3T3 cells, excellent cell viabilities of more than 95% were achieved. The particularly interesting feature of this novel material is that it can be used as a printing support in hybrid bioink systems and sacrificial bioink due to rapid dissolution at physiological conditions.

A model for in situ plan of care for a critically unstable pediatric patient following I-131 MIBG infusion.

Recent clinical trials have moved iodine-131 (I-131) metaiodobenzylguanidine (MIBG) therapy into frontline management of high-risk neuroblastoma. With this expansion, it is reasonable to anticipate the need for intensive care level resuscitations. Radiation exposure remains the greatest risk to health care professionals managing these patients. We combined shock simulation scenario data with actual radiation dosimetry data to create a care model allowing for aggressive, prolonged in situ resuscitation of a critically ill pediatric patient after I-131 MIBG administration. This model will maintain a critical care provider's radiation level below 10% of the annual occupational dose limit (5 mSv, 500 mrem) per patient managed.

Inverse Thermogelation of Aqueous Triblock Copolymer Solutions into Macroporous Shear-Thinning 3D Printable Inks.

Amphiphilic block copolymers that undergo (reversible) physical gelation in aqueous media are of great interest in different areas including drug delivery, tissue engineering, regenerative medicine, and biofabrication. We investigated a small library of ABA-type triblock copolymers comprising poly(2-methyl-2-oxazoline) as the hydrophilic shell A and different aromatic poly(2-oxazoline)s and poly(2-oxazine)s cores B in an aqueous solution at different concentrations and temperatures. Interestingly, aqueous solutions of poly(2-methyl-2-oxazoline)-block-poly(2-phenyl-2-oxazine)-block-poly(2-methyl-2-oxazoline) (PMeOx-b-PPheOzi-b-PMeOx) undergo inverse thermogelation below a critical temperature by forming a reversible nanoscale wormlike network. The viscoelastic properties of the resulting gel can be conveniently tailored by the concentration and the polymer composition. Storage moduli of up to 110 kPa could be obtained while the material retains shear-thinning and rapid self-healing properties. We demonstrate three-dimensional (3D) printing of excellently defined and shape-persistent 24-layered scaffolds at different aqueous concentrations to highlight its application potential, e.g., in the research area of biofabrication. A macroporous microstructure, which is stable throughout the printing process, could be confirmed via cryo-scanning electron microscopy (SEM) analysis. The absence of cytotoxicity even at very high concentrations opens a wide range of different applications for this first-in-class material in the field of biomaterials.

Origin of the low-frequency plateau and the light-scattering slow mode in semidilute poly(ethylene glycol) solutions.

A low-frequency plateau is often found in the rheological spectra of various kinds of semidilute solutions of polymers and other colloids; also, many such solutions have been reported to show slow-modes in their dynamic light scattering autocorrelation functions. Both these observations may lead to the hypothesis of weak associative network structures built by the dissolved polymer chains or colloidal building blocks. To challenge this hypothesis, we conduct a series of comparative studies on semidilute solutions of poly(ethylene glycol) by using classical rheology as well as passive microrheology based on dynamic light scattering, along with structural studies using static light scattering. Although we indeed find a low-frequency plateau using classical shear rheology, even at elevated temperatures where potential polymer aggregates should be broken, no such plateau is observed in any of our microrheology experiments. Also, dynamic and static light scattering studies on the polymer solutions do not confirm the presence of larger structural entities: no slow mode can be detected in the autocorrelation function of the scattering intensity signal, and this signal is angle independent if the samples are purified by a thorough procedure of filtration. Based on these findings, we conclude that the low-frequency plateau in classical rheology results is an instrument effect caused by erroneous recording of the phase angle, although the magnitude of the torque lies well within the resolution of the rheometer. We also conclude that slow modes in dynamic light scattering on solutions of poly(ethylene glycol) are impurity-based artifacts rather than due to actual associated structures.

Molecular cloning, expression and characterization of Pekin duck programmed death-1.

Programmed death-1 (PD-1) has a pivotal role in the attenuation of adaptive immune responses and peripheral tolerance. Here we describe the identification of the Pekin duck programmed death-1 orthologue (duPD-1). The duPD-1 cDNA encodes a 283-amino acid polypeptide that has an amino acid identity of 70%, 32% and 31% with chicken, murine and human PD-1, respectively. The duck PD-1 gene shares five conserved exons with chicken, murine and human PD-1 genes. A cluster of putative regulatory elements within the conserved region B (CR-B) of the basal promotor is conserved. Homology modeling was most compatible with the two ß-sheet IgV domain structure of murine PD-1. Contact residues, shown to be critical for binding of the respective human and murine PD-1 ligands are mostly conserved between avian and mammalian species, whereas residues that define the cytoplasmic immunoreceptor tyrosine-based inhibitory motif (ITIM) and immunoreceptor tyrosine-based switch motif (ITSM) are highly conserved across higher vertebrates and frog. Constitutive expression of duPD-1 transcripts was predominantly found in lymphocyte-rich tissues, and mitogen-stimulation of duck peripheral blood mononuclear cells transiently increased duPD-1 mRNA expression. A soluble duPD-1 protein was expressed and shown to engage the identified duck PD-1 ligands. Our observations show considerable evolutionary conservation between mammalian and avian PD-1 orthologues. This work will facilitate further investigation of the role of PD-1 signaling in adaptive immunity in the Pekin duck, a non-mammalian vertebrate and pathogen host with relevance for human and animal health.

Monocytes Represent One Source of Bacterial Shielding from Antibiotics following Influenza Virus Infection.

Methicillin-resistant Staphylococcus aureus has emerged as a significant contributor to morbidity and mortality associated with influenza infection. In this study, we show in a mouse model that preceding influenza infection promotes S. aureus resistance to killing by antibiotics. This resistance coincides with influenza-induced accumulation of inflammatory monocytes in the lung. CCR type 2 (CCR2) is responsible for pulmonary monocyte recruitment after influenza infection. We found that antibiotic-treated Ccr2-deficient (Ccr2-/-) mice exhibit significantly improved bacterial control and survival from influenza and methicillin-resistant S. aureus coinfection, despite a delay in viral clearance. Mechanistically, our results from in vivo studies indicate that influenza-induced monocytes serve as reservoirs for intracellular S. aureus survival, thereby promoting bacterial resistance to antibiotic treatment. Blocking CCR2 with a small molecular inhibitor (PF-04178903), in conjunction with antibiotic treatment, enhanced lung bacterial clearance and significantly improved animal survival. Collectively, our study demonstrates that inflammatory monocytes constitute an important and hitherto underappreciated mechanism of the conflicting immune requirements for viral and bacterial clearance by hosts, which subsequently leads to exacerbated outcomes of influenza and S. aureus coinfection.

Medical Professional Radiation Dosimeter Usage: Reasons for Noncompliance.

The purpose of this study was to assess the attitudes of occupationally exposed employees at a large teaching hospital about wearing their assigned personal radiation dosimeters. A 16-question multiple-answer survey was used to report the reasons why medical professionals may not wear their dosimetry during procedures involving ionizing radiation. In all, 302 employees responded to the survey. The majority of respondents who reported always or almost always wearing their dosimeters do so because they consider themselves well informed concerning the importance of personal dosimetry measurement and appreciate the importance of federal and state regulations. For respondents who reported not always wearing their dosimeters, the most commonly stated reason was the inconvenience of remembering to bring and wear their dosimeters when working in multiple locations, for which a potential solution would be to provide dosimeters to each affected wearer in each location where they work.

Is RuAs2 a candidate for high temperature thermoelectric applications?

The mineral inspired material RuAs2 shows promise as a thermoelectric material with its high stability and attractive band structure. In order to validate these expectations phase-pure polycrystalline ruthenium arsenide was synthesized and densified using Spark Plasma Sintering. RuAs2 is an n-type semiconductor with an indirect band gap 0.69 eV as estimated from temperature dependent resistivity data, while the band gap calculated with DFT is 0.64 eV. The thermal conductivity and electrical resistivity are both high with room temperature values of 16 W m-1 K-1 and 170 mΩ cm respectively, leading to modest thermoelectric properties for the intrinsic system. Band structure calculations suggest that chemical modification should preferably be done at the As site to improve the intrinsic properties. Synchrotron powder X-ray diffraction and Rietveld structural refinements show RuAs2 to be a stable line phase up to 1000 K in both in air and in vacuum, and both as a powder and as a dense pellet. No indication of preferential orientation or material gradients are observed.

The Pekin duck programmed death ligand-2: cDNA cloning, genomic structure, molecular characterization and expression analysis.

Programmed death-1 (PD-1), upon engagement by its ligands, programmed death ligand-1 (PD-L1) and programmed death ligand-2 (PD-L2), provides signals that attenuate adaptive immune responses. Here we describe the identification of the Pekin duck PD-L2 (duPD-L2) and its gene structure. The duPD-L2 cDNA encodes a 321 amino acid protein that has an amino acid identity of 76% and 35% with chicken and human PD-L2, respectively. Mapping of the duPD-L2 cDNA with duck genomic sequences revealed an exonic structure similar to that of the human Pdcd1lg2 gene. Homology modelling of the duPD-L2 protein was compatible with the murine PD-L2 ectodomain structure. Residues known to be important for PD-1 receptor binding of murine PD-L2 were mostly conserved in duPD-L2 within sheets A and G and partially conserved within sheets C and F. DuPD-L2 mRNA was constitutively expressed in all tissues examined with highest expression levels in lung, spleen, cloaca, bursa, cecal tonsil, duodenum and very low levels of expression in muscle, kidney and brain. Lipopolysaccharide treatment of adherent duck PBMC upregulated duPD-L2 mRNA expression. Our work shows evolutionary conservation of the PD-L2 ectodomain structure and residues important for PD-1 binding in vertebrates including fish. The information provided will be useful for further investigation of the role of duPD-L2 in the regulation of duck adaptive immunity and exploration of PD-1-targeted immunotherapies in the duck hepatitis B infection model.

Protein corona-mediated targeting of nanocarriers to B cells allows redirection of allergic immune responses.

BACKGROUND: Nanoparticle (NP)-based vaccines are attractive immunotherapy tools because of their capability to codeliver antigen and adjuvant to antigen-presenting cells. Their cellular distribution and serum protein interaction ("protein corona") after systemic administration and their effect on the functional properties of NPs is poorly understood. OBJECTIVES: We analyzed the relevance of the protein corona on cell type-selective uptake of dextran-coated NPs and determined the outcome of vaccination with NPs that codeliver antigen and adjuvant in disease models of allergy. METHODS: The role of protein corona constituents for cellular binding/uptake of dextran-coated ferrous nanoparticles (DEX-NPs) was analyzed both in vitro and in vivo. DEX-NPs conjugated with the model antigen ovalbumin (OVA) and immunostimulatory CpG-rich oligodeoxynucleotides were administered to monitor the induction of cellular and humoral immune responses. Therapeutic effects of this DEX-NP vaccine in mouse models of OVA-induced anaphylaxis and allergic asthma were assessed. RESULTS: DEX-NPs triggered lectin-induced complement activation, yielding deposition of activated complement factor 3 on the DEX-NP surface. In the spleen DEX-NPs targeted predominantly B cells through complement receptors 1 and 2. The DEX-NP vaccine elicited much stronger OVA-specific IgG2a production than coadministered soluble OVA plus CpG oligodeoxynucleotides. B-cell binding of the DEX-NP vaccine was critical for IgG2a production. Treatment of OVA-sensitized mice with the DEX-NP vaccine prevented induction of anaphylactic shock and allergic asthma accompanied by IgE inhibition. CONCLUSIONS: Opsonization of lectin-coated NPs by activated complement components results in selective B-cell targeting. The intrinsic B-cell targeting property of lectin-coated NPs can be exploited for treatment of allergic immune responses.

Low-Temperature Anharmonicity in Cesium Chloride (CsCl).

Anharmonic lattice vibrations govern heat transfer in materials, and anharmonicity is commonly assumed to be dominant at high temperature. The textbook cubic ionic defect-free crystal CsCl is shown to have an unexplained low thermal conductivity at room temperature (ca. 1 W/(m K)), which increases to around 13  W/(m K) at 25 K. Through high-resolution X-ray diffraction it is unexpectedly shown that the Cs atomic displacement parameter becomes anharmonic at 20 K.

SiRNA-mediated in vivo gene knockdown by acid-degradable cationic nanohydrogel particles.

Cationic nanohydrogel particles have become an attractive tool for systemic siRNA delivery, but improvement of their in vivo tolerance is desirable, especially to prevent potential long term side effects by tissue and cellular accumulation. Here, we designed novel ketal cross-linked cationic nanohydrogel particles that were assessed for reduced tissue accumulation and robust siRNA delivery in vitro and in vivo. An oligo-amine cross-linker equipped with a ketal moiety in its core was synthesized and applied to nanohydrogel cross-linking of self-assembled reactive ester block copolymers in DMSO. The resulting acid-sensitive cationic nanoparticles spontaneously disassembled over time in acidic milieu, as investigated by dynamic light scattering. Fluorescent correlation spectroscopy showed effective complexation with siRNA as well as its release upon particle degradation at endosomal pH. These properties resulted in an enhanced in vitro gene knockdown for the acid-degradable cationic nanoparticles compared to their non-degradable spermine analogues. In a murine liver fibrosis model enhanced carrier and payload accumulation in the fibrotic tissue facilitated sequence-specific gene knockdown and prevented fibrosis progression. Long-term monitoring of the carrier in the body showed an enhanced clearance for the acid-degradable carrier, even after multiple dosing. Therefore, these acid-degradable cationic nanohydrogel particles can be considered as promising siRNA carriers for in vivo purposes towards therapeutic applications.

Physicochemical and Preclinical Evaluation of Spermine-Derived Surfactant Liposomes for in Vitro and in Vivo siRNA-Delivery to Liver Macrophages.

Herein we report on a liposomal system for siRNA delivery consisting of cholesterol (Chol), distearoylphosphatidylcholine (DSPC), and surfactant TF (1-hydroxy-50-amino-3,4,7,10,13,16,19,22-octaoxa-37,41,45-triaza-pentacontane), a novel spermine derivative (HO-EG8-C12-spermine) which has shown improved siRNA delivery to cells in vitro and in vivo. Predominantly single-walled liposomes with reproducible sizes and moderately broad size distributions were generated with an automated extrusion device. The liposomes remained stable when prepared in the presence of siRNA at N/P ratios of 17-34. However, when mixed with human serum in equal volumes, larger aggregates in the size range of several hundred nanometers were observed by dynamic light scattering. These larger aggregates could potentially limit prolonged in vivo applications. Aggregate formation could be reduced by the addition of a cholesterol-hyperbranched polyglycerol surfactant (hbPG) that sterically shields the liposomal surface against serum induced aggregation. In vitro experiments with murine macrophages utilizing macrophage-specific anti-CD68 siRNA loaded liposomes showed potent and sequence specific reduction of CD68 transcript levels without cytotoxicity. Experiments in mice using intravenous application of CW800 NHS ester labeled liposomes, near-infrared in vivo imaging, and fluorescent assisted cell sorting of inflammatory cells demonstrated an almost quantitative accumulation of these liposomes, with and without hbPG, in the liver and a specific knockdown of CD68 mRNA of up to 70% in liver resident macrophages. It was found that aggregate formation of TF liposomes in serum does not significantly affect in vivo siRNA delivery to these central inflammatory cells of the liver.

Functionalization of Active Ester-Based Polymersomes for Enhanced Cell Uptake and Stimuli-Responsive Cargo Release.

Poly(2,3-dihydroxypropyl methacrylamide) (P(DHPMA))-based amphiphilic block copolymers have recently proven to form polymer vesicles (polymersomes). In this work, we further expand their potential by incorporating (i) units for pH-dependent disintegration into the hydrophobic membrane and (ii) mannose as targeting unit into the hydrophilic block. This last step relies on the use of an active ester prepolymer. We confirm the stability of the polymersomes against detergents like Triton X-100 and their low cytotoxicity. The incorporation of 2-(2,2-dimethyl-1,3-dioxolane-4-yl)ethyl methacrylate into the hydrophobic block (lauryl methacrylate) allows a pH-responsive disintegration for cargo release. Efficient decomposition of the polymersome structure is monitored by dynamic light scattering. It is thus possible to include an active enzyme (glucose oxidase), which gets only active (is set free) after vesicle disintegration. In addition, the introduction of mannose as targeting structure allows enhanced and selective targeting of dendritic cells.

Vaccination with trifunctional nanoparticles that address CD8+ dendritic cells inhibits growth of established melanoma.

AIM: We wanted to assess the potency of a trifunctional nanoparticle (NP) that targeted and activated CD8+ dendritic cells (DC) and delivered an antigen to induce antitumor responses. MATERIALS & METHODS: The DC targeting and activating properties of ferrous NPs conjugated with immunostimulatory CpG-oligonucleotides, anti-DEC205 antibody and ovalbumin (OVA) as a model antigen to induce antigen-specific T-cell responses and antitumor responses were analyzed. RESULTS: OVA-loaded NP conjugated with immunostimulatory CpG-oligonucleotides and anti-DEC205 antibody efficiently targeted and activated CD8+ DC in vivo, and induced strong OVA-specific T-cell activation. Vaccination of B16/OVA tumor-burdened mice with this NP formulation resulted in tumor growth arrest. CONCLUSION: CD8+ DC-targeting trifunctional nanocarriers bear significant potential for antitumor immunotherapy.

Nox2-derived oxidative stress results in inefficacy of antibiotics against post-influenza S. aureus pneumonia.

Clinical post-influenza Staphylococcus aureus pneumonia is characterized by extensive lung inflammation associated with severe morbidity and mortality even after appropriate antibiotic treatment. In this study, we show that antibiotics rescue nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 2 (Nox2)-deficient mice but fail to fully protect WT animals from influenza and S. aureus coinfection. Further experiments indicate that the inefficacy of antibiotics against coinfection is attributable to oxidative stress-associated inflammatory lung injury. However, Nox2-induced lung damage during coinfection was not associated with aggravated inflammatory cytokine response or cell infiltration but rather caused by reduced survival of myeloid cells. Specifically, oxidative stress increased necrotic death of inflammatory cells, thereby resulting in lethal damage to surrounding tissue. Collectively, our results demonstrate that influenza infection disrupts the delicate balance between Nox2-dependent antibacterial immunity and inflammation. This disruption leads to not only increased susceptibility to S. aureus infection, but also extensive lung damage. Importantly, we show that combination treatment of antibiotic and NADPH oxidase inhibitor significantly improved animal survival from coinfection. These findings suggest that treatment strategies that target both bacteria and oxidative stress will significantly benefit patients with influenza-complicated S. aureus pneumonia.

Oxidation-Responsive and "Clickable" Poly(ethylene glycol) via Copolymerization of 2-(Methylthio)ethyl Glycidyl Ether.

Poly(ethylene glycol) (PEG) is a widely used biocompatible polymer. We describe a novel epoxide monomer with methyl-thioether moiety, 2-(methylthio)ethyl glycidyl ether (MTEGE), which enables the synthesis of well-defined thioether-functional poly(ethylene glycol). Random and block mPEG-b-PMTEGE copolymers (Mw/Mn = 1.05-1.17) were obtained via anionic ring opening polymerization (AROP) with molecular weights ranging from 5 600 to 12 000 g·mol(-1). The statistical copolymerization of MTEGE with ethylene oxide results in a random microstructure (rEO = 0.92 ± 0.02 and rMTEG E = 1.06 ± 0.02), which was confirmed by in situ (1)H NMR kinetic studies. The random copolymers are thermoresponsive in aqueous solution, with a wide range of tunable transition temperatures of 88 to 28 °C. In contrast, mPEG-b-PMTEGE block copolymers formed well-defined micelles (Rh ≈ 9-15 nm) in water, studied by detailed light scattering (DLS and SLS). Intriguingly, the thioether moieties of MTEGE can be selectively oxidized into sulfoxide units, leading to full disassembly of the micelles, as confirmed by detection of pure unimers (DLS and SLS). Oxidation-responsive release of encapsulated Nile Red demonstrates the potential of these micelles as redox-responsive nanocarriers. MTT assays showed only minor effects of the thioethers and their oxidized derivatives on the cellular metabolism of WEHI-164 and HEK-293T cell lines (1-1000 µg·mL(-1)). Further, sulfonium PEG polyelectrolytes can be obtained via alkylation or alkoxylation of MTEGE, providing access to a large variety of functional groups at the charged sulfur atom.