Development of American Society for Gastrointestinal Endoscopy standards for training in advanced endoscopy within dedicated advanced endoscopy fellowship programs.

BACKGROUND AND AIMS: Training in interventional endoscopy is offered by nonaccredited advanced endoscopy fellowship programs (AEFPs). The number of these programs has increased dramatically with a concurrent increase in the breadth and complexity of interventional endoscopy procedures. Accreditation is governed by competency-based education, yet what constitutes a "high-quality" nonaccredited AEFP has not been defined. Using an evidence-based consensus process, we aimed to establish standards for AEFPs. METHODS: The RAND UCLA appropriateness method, a well-described modified Delphi process to develop quality indicators, was used. A task force established by the American Society for Gastrointestinal Endoscopy drafted potential quality indicators (structure, process, and outcome) in 6 categories: activity preceding training; structure of AEFPs; training in ERCP, EUS, and EMR; and luminal stent placement. Three rounds of iterative feedback from 20 experts were conducted. Round 0 involved discussion of project details. In round 1, experts independently ranked proposed quality indicators on a 9-point interval scale ranging from highly inappropriate (1) to highly appropriate (9). Next, proposed quality indicators were discussed and reworded in a group meeting followed by round 2, in which experts independently reranked proposed quality indicators and provided benchmarks (when applicable). The median score for each quality indicator was calculated. Mean absolute deviation from the median was calculated, and appropriateness of potential quality indicators was assessed using the BIOMED concerted action on appropriateness definition, P value method, and interpercentile range adjusted for symmetry definition. A quality indicator was deemed appropriate if the median score was ≥7 and met criteria for appropriateness using all 3 defined statistical methods. RESULTS: Of 89 proposed quality indicators, 37 statements met criteria as appropriate for a quality indicator (activity preceding training, 2; structure of AEFPs, 10; training in ERCP, 7; training in EUS, 8; training in EMR, 7; luminal stent placement, 3). Minimum thresholds were defined for 19 relevant quality indicators for number of trainers, procedures during fellowship, and procedures before assessment of competence. Among the final appropriate quality indicators were that all trainees should undergo qualitative and quantitative competence assessments using validated tools at least quarterly with documented feedback throughout the training period and that trainees should track outcomes and relevant quality metrics for specific procedures. CONCLUSIONS: This consensus process using validated methodology established standards for an AEFP in an effort to ensure adequate training in the most commonly taught interventional endoscopic procedures (ERCP, EUS, EMR, and luminal stent placement) during fellowship. An important component of an AEFP is the use of competency-based assessments that are compliant with the Accreditation Council for Graduate Medical Education's Next Accreditation System, with the goal of ensuring that trainees achieve specific milestones in their progression to achieving cognitive and technical competency.

Photoclick Chemistry: A Bright Idea.

At its basic conceptualization, photoclick chemistry embodies a collection of click reactions that are performed via the application of light. The emergence of this concept has had diverse impact over a broad range of chemical and biological research due to the spatiotemporal control, high selectivity, and excellent product yields afforded by the combination of light and click chemistry. While the reactions designated as "photoclick" have many important features in common, each has its own particular combination of advantages and shortcomings. A more extensive realization of the potential of this chemistry requires a broader understanding of the physical and chemical characteristics of the specific reactions. This review discusses the features of the most frequently employed photoclick reactions reported in the literature: photomediated azide-alkyne cycloadditions, other 1,3-dipolarcycloadditions, Diels-Alder and inverse electron demand Diels-Alder additions, radical alternating addition chain transfer additions, and nucleophilic additions. Applications of these reactions in a variety of chemical syntheses, materials chemistry, and biological contexts are surveyed, with particular attention paid to the respective strengths and limitations of each reaction and how that reaction benefits from its combination with light. Finally, challenges to broader employment of these reactions are discussed, along with strategies and opportunities to mitigate such obstacles.

Burden of early hospitalization after simultaneous liver-kidney transplantation: Results from the US Multicenter SLKT Consortium.

The burden of early hospitalization (within 6 months) following simultaneous liver-kidney transplant (SLKT) is not known. We examined risk factors associated with early hospitalization after SLKT and their impact on patient mortality conditional on 6-month survival. We used data from the US Multicenter SLKT Consortium cohort study of all adult SLKT recipients between 2002 and 2017 who were discharged alive following SLKT. We used Poisson regression to model rates of early hospitalizations after SLKT. Cox regression was used to identify risk factors associated with mortality conditional on survival at 6 months after SLKT. Median age (N = 549) was 57.7 years (interquartile range [IQR], 50.6-63.9) with 63% males and 76% Whites; 33% had hepatitis C virus, 20% had non-alcohol-associated fatty liver disease, 23% alcohol-associated liver disease, and 24% other etiologies. Median body mass index (BMI) and Model for End-Stage Liver Disease-sodium scores were 27.2 kg/m2 (IQR, 23.6-32.2 kg/m2 ) and 28 (IQR, 23-34), respectively. Two-thirds of the cohort had at least one hospitalization within the first 6 months of SLKT. Age, race, hospitalization at SLKT, diabetes mellitus, BMI, and discharge to subacute rehabilitation (SAR) facility after SLKT were independently associated with a high incidence rate ratio of early hospitalization. Number of hospitalizations within the first 6 months did not affect conditional survival. Early hospitalizations after SLKT were very common but did not affect conditional survival. Although most of the risk factors for early hospitalization were nonmodifiable, discharge to SAR after initial SLKT was associated with a significantly higher incidence rate of early hospitalization. Efforts and resources should be focused on identifying SLKT recipients at high risk for early hospitalization to optimize their predischarge care, discharge planning, and long-term follow-up.

Renal Outcomes After Simultaneous Liver-Kidney Transplantation: Results from the US Multicenter Simultaneous Liver-Kidney Transplantation Consortium.

Simultaneous liver-kidney transplantation (SLKT) is increasingly common in the United States. However, little is known about the renal-related outcomes following SLKT, which are essential to maximize the health of these allografts. We examined the factors impacting renal function following SLKT. This is an observational multicenter cohort study from the US Multicenter SLKT Consortium consisting of recipients of SLKT aged ≥18 years of transplantations performed between February 2002 and June 2017 at 6 large US centers in 6 different United Network for Organ Sharing regions. The primary outcome was incident post-SLKT stage 4-5 chronic kidney disease (CKD) defined as <30 mL/minute/1.73 m2 or listing for kidney transplant. The median age of the recipients (n = 570) was 58 years (interquartile range, 51-64 years), and 37% were women, 76% were White, 33% had hepatitis C virus infection, 20% had nonalcoholic steatohepatitis (NASH), and 23% had alcohol-related liver disease; 68% developed ≥ stage 3 CKD at the end of follow-up. The 1-year, 3-year, and 5-year incidence rates of post-SLKT stage 4-5 CKD were 10%, 12%, and 16%, respectively. Pre-SLKT diabetes mellitus (hazard ratio [HR], 1.45; 95% CI, 1.00-2.15), NASH (HR, 1.58; 95% CI, 1.01-2.45), and delayed kidney graft function (HR, 1.72; 95% CI, 1.10-2.71) were the recipient factors independently associated with high risk, whereas the use of tacrolimus (HR, 0.44; 95% CI, 0.22-0.89) reduced the risk. Women (ß = -6.22 ± 2.16 mL/minute/1.73 m2 ; P = 0.004), NASH (ß = -7.27 ± 3.27 mL/minute/1.73 m2 ; P = 0.027), and delayed kidney graft function (ß = -7.25 ± 2.26 mL/minute/1.73 m2 ; P = 0.007) were independently associated with low estimated glomerular filtration rate at last follow-up. Stage 4-5 CKD is common after SLKT. There remains an unmet need for personalized renal protective strategies, specifically stratified by sex, diabetes mellitus, and liver disease, to preserve renal function among SLKT recipients.

Are There Upper Limits in Tumor Burden for Down-Staging of Hepatocellular Carcinoma to Liver Transplant? Analysis of the All-Comers Protocol.

Patients with hepatocellular carcinoma (HCC) within the University of California, San Francisco down-staging (UCSF-DS) criteria (one lesion > 5 cm and ≤ 8 cm; two to three lesions each ≤ 5 cm; or four to five lesions each ≤ 3 cm with total tumor diameter ≤ 8 cm) who achieved successful down-staging (DS) to Milan criteria had similar outcomes after liver transplantation (LT) compared with HCC initially meeting the Milan criteria. Nevertheless, little is known about the outcome of DS in patients with initial tumor burden exceeding the UCSF-DS criteria, defined as "all-comers" (AC). We compared the intention-to-treat (ITT) outcomes of DS in 74 patients in the AC group and 133 patients in the UCSF-DS group. Successful DS to Milan was observed in 64.8% of the AC group versus 84.2% of the UCSF-DS group (P < 0.001). The sum of tumor number and largest tumor diameter was significantly associated with successful DS (hazard ratio [HR] 0.87, P < 0.05). The cumulative probability of dropout within 1 year and 3 years was 53.5% and 80.0%, respectively, for AC versus 25.0% and 36.1%, respectively, for UCSF-DS (P < 0.0001). Factors predicting dropout included sum of tumor number and largest tumor diameter greater than 8 (HR 1.79, P = 0.049) and Child class B and C (HR 2.54, P = 0.001). The AC group also had a significantly lower liver transplant (LT) rate (13.5% versus 59.0%, P < 0.001). ITT survival at 1 year and 5 years was 77.4% and 21.1%, respectively, in AC versus 85.5% and 56.0%, respectively, in UCSF-DS (P < 0.001). Three of 10 patients in the AC group who underwent LT developed HCC recurrence. Conclusion: We observed a significantly lower LT probability and inferior ITT survival with DS in the AC group versus the UCSF-DS group. Our results suggest that an upper limit in tumor burden exists beyond which successful LT after DS becomes an unrealistic goal.

Click Nucleic Acid-DNA Binding Behavior: Dependence on Length, Sequence, and Ionic Strength.

Click nucleic acids (CNAs) are a new, low-cost class of xeno nucleic acid (XNA) oligonucleotides synthesized by an efficient and scalable thiol-ene polymerization. In this work, a thorough characterization of oligo(thymine) CNA-oligo(adenine) DNA ((dA)20) hybridization was performed to guide the future implementation of CNAs in applications that rely on sequence-specific interactions. Microscale thermophoresis provided a convenient platform to rapidly and systematically investigate the effects of several factors (i.e., sequence, length, and salt concentration) on the CNA-DNA dissociation constant (Kapp). Because CNAs have limited water solubility, all studies were performed in aqueous-DMSO mixtures. CNA-DNA hybrids between oligo(thymine) CNA (average length of 16 bases) and (dA)20 DNA have good stability despite the high organic content, a favorable attribute for many emerging applications of XNAs. In particular, the Kapp of CNA-DNA hybrids in 65 vol % DMSO with 10 mM sodium chloride (NaCl) was 0.74 ± 0.1 µM, whereas the Kapp for (dT)20-(dA)20 DNA-DNA was found to be 45 ± 2 µM in a buffer without DMSO but at the same NaCl concentration. CNA hybridized with DNA following Watson-Crick base pairing with excellent sequence specificity, discriminating even a single-base-pair mismatch, with Kapp values of 0.74 ± 0.1 and 3.7 ± 0.6 µM for complementary and single-base-pair mismatch sequences, respectively. As with dsDNA, increasing CNA length led to more stable hybrids as a result of increased base pairing, where Kapp decreased from 5.6 ± 0.8 to 0.27 ± 0.1 µM as the CNA average length increased from 7 to 21 bases. However, unlike DNA-DNA duplexes, which are largely unstable at low salt concentrations, the CNA-DNA stability does not depend on salt concentration, with Kapp remaining consistent between 1.0 and1.9 µM over a NaCl concentration range of 1.25-30 mM.

Sequence-Controlled Synthesis of Advanced Clickable Synthetic Oligonucleotides.

Through thiol-ene photopolymerization of presynthesized oligomers, advanced clickable nucleic acids (CNA-2G) are synthesized with sequence-controlled repeating units. As examples, poly(thymine-adenine) (polyTA) CNA-2G and poly(thymine-thymine-cytosine) CNA-2G are synthesized by polymerizing thiol-ene heterofunctional dimers with pendant thymine-adenine nucleobases and trimer with pendant thymine-thymine-cytosine nucleobases. Based on size exclusion chromatography (SEC) analysis, polyTA and polyTTC have number average molecular weights of 2000 and 1800, respectively, which contain 7-8 pendant nucleobases. Based on the different behavior of the CNA-2G monomers and CNA-2G oligomers with two or more pendant nucleobases in photopolymerization, an unusual thiol-ene chain-growth propagation mechanism is observed for the former and a common thiol-ene step-growth propagation mechanism for the latter. The uncommon thiol-ene chain-growth propagation is hypothesized to rely on a six-membered ring mediated intramolecular hydrogen atom transfer process.

Thiol-Anhydride Dynamic Reversible Networks.

The reaction of thiols and anhydrides to form ring opened thioester/acids is shown to be highly reversible and it is accordingly employed in the fabrication of covalent adaptable networks (CANs) that possess tunable dynamic covalent chemistry. Maleic, succinic, and phthalic anhydride derivatives were used as bifunctional reactants in systems with varied stoichiometries, catalyst, and loadings. Dynamic characteristics such as temperature-dependent stress relaxation, direct reprocessing and recycling abilities of a range of thiol-anhydride elastomers, glasses, composites and photopolymers are discussed. Depending on the catalyst strength, 100 % of externally imposed stresses were relaxed in the order of minutes to 2 hours at mild temperatures (80-120 °C). Pristine properties of the original materials were recovered following up to five cycles of a hot-press reprocessing technique (1 h/100 °C).

Rational Design of Efficient Amine Reductant Initiators for Amine-Peroxide Redox Polymerization.

Amine-peroxide redox polymerization (APRP) has been highly prevalent in industrial and medical applications since the 1950s, yet the initiation mechanism of this radical polymerization process is poorly understood so that innovations in the field are largely empirically driven and incremental. Through a combination of computational prediction and experimental analysis, we elucidate the mechanism of this important redox reaction between amines and benzoyl peroxide for the ambient production of initiating radicals. Our calculations show that APRP proceeds through SN2 attack by the amine on the peroxide but that homolysis of the resulting intermediate is the rate-determining step. We demonstrate a correlation between the computationally predicted initiating rate and the experimentally measured polymerization rate with an R2 = 0.80. The new mechanistic understanding was then applied to computationally predict amine reductant initiators with faster initiating kinetics. This led to our discovery of N-(4-methoxyphenyl)pyrrolidine (MPP) as amine reductant, which we confirmed significantly outperforms current state-of-the-art tertiary aromatic amines by ∼20-fold, making it the most efficient amine-peroxide redox initiator to date. The application of amines with superior kinetics such as MPP in APRP could greatly accelerate existing industrial processes, facilitate new industrial manufacturing methods, and improve biocompatibility in biomedical applications conducted with reduced initiator concentrations yet higher overall efficiency.

Adherence to quality indicators and best practices in surveillance endoscopy of Barrett's esophagus: A video-based assessment.

Background and study aims Adherence to quality indicators (QIs) and best practices (BPs) for endoscopic surveillance of Barrett's esophagus (BE) is low based on clinical documentation which is an inaccurate representation of events occurring during procedures. This study aimed to assess adherence to measurable QI and BP using video evaluation. Methods We performed a single center video-based retrospective review of surveillance endoscopies performed for BE ≥1 cm between March 1, 2018 and October 1, 2020. Adherence to QIs and BPs was assessed through video review and documentation. Videos were evaluated by five gastroenterologists. Interrater variability was determined using 10 videos before reviewing the remaining 128 videos. A generalized linear regression model was used to determine predictors of adherence to QIs and BPs. Results There were 138 endoscopies reviewed. Inspection with virtual chromoendoscopy (VC) occurred in 75 cases (54%) on video review with documentation in 50 of these cases (67%). Adherence to the Seattle protocol (SP) occurred in 74 cases (54%) on video review with documentation in 28 of these cases (38%). Use of VC or the SP was documented but not observed on video review in 16 (12%) and 30 (22%) cases, respectively. Length of BE was associated with increased use of the Prague classification (odds ratio [OR] 1.21, 95% confidence interval [CI] 1.07-1.37) while years in practice was associated with a decreased likelihood of VC use (OR 0.93, 95% CI 0.88-0.99). Conclusions This study validates prior data demonstrating poor adherence to QIs and BPs and highlights discrepancies between clinical documentation and events occurring during procedures.

Photochemical Control of Network Topology in PEG Hydrogels.

Hydrogels are often synthesized through photoinitiated step-, chain-, and mixed-mode polymerizations, generating diverse network topologies and resultant material properties that depend on the underlying network connectivity. While many photocrosslinking reactions are available, few afford controllable connectivity of the hydrogel network. Herein, a versatile photochemical strategy is introduced for tuning the structure of poly(ethylene glycol) (PEG) hydrogels using macromolecular monomers functionalized with maleimide and styrene moieties. Hydrogels are prepared along a gradient of topologies by varying the ratio of step-growth (maleimide dimerization) to chain-growth (maleimide-styrene alternating copolymerization) network-forming reactions. The initial PEG content and final network physical properties (e.g., modulus, swelling, diffusivity) are tailored in an independent manner, highlighting configurable gel mechanics and reactivity. These photochemical reactions allow high-fidelity photopatterning and 3D printing and are compatible with 2D and 3D cell culture. Ultimately, this photopolymer chemistry allows facile control over network connectivity to achieve adjustable material properties for broad applications.

Factors associated with cardiovascular events after simultaneous liver-kidney transplant from the US Multicenter Simultaneous Liver-Kidney Transplant Consortium.

Cardiovascular disease is a leading complication after both liver and kidney transplantation. Factors associated with and rates of cardiovascular events (CVEs) after simultaneous liver-kidney transplant (SLKT) are unknown. This was a retrospective cohort study of adult SLKT recipients between 2002 and 2017 at six centers in six United Network for Organ Sharing regions in the US Multicenter SLKT Consortium. The primary outcome was a CVE defined as hospitalization due to acute coronary syndrome, arrhythmia, congestive heart failure, or other CV causes (stroke or peripheral vascular disease) within 1 year of SLKT. Among 515 SLKT subjects (mean age ± SD, 55.4 ± 10.6 years; 35.5% women; 68.1% White), 8.7% had a CVE within 1 year of SLKT. The prevalence of a CVE increased from 3.3% in 2002-2008 to 8.9% in 2009-2011 to 14.0% in 2012-2017 ( p  = 0.0005). SLKT recipients with a CVE were older (59.9 vs. 54.9 years, p < 0.0001) and more likely to have coronary artery disease (CAD) (37.8% vs. 18.4%, p  = 0.002) and atrial fibrillation (AF) (27.7% vs. 7.9%, p  = 0.003) than those without a CVE. There was a trend toward older age by era of SLKT ( p  = 0.054). In multivariate analysis adjusted for cardiac risk factors at transplant, age (odds ratio [OR], 1.06; 95% confidence interval [CI], 1.02, 1.11), CAD (OR, 3.62; 95% CI, 1.60, 8.18), and AF (OR, 2.36; 95% CI, 1.14, 4.89) were associated with a 1-year CVE after SLKT. Conclusion : Among SLKT recipients, we observed a 4-fold increase in the prevalence of 1-year CVEs over time. Increasing age, CAD, and AF were the main potential explanatory factors for this trend independent of other risk factors. These findings suggest that CV risk protocols may need to be tailored to this high-risk population.

Predictors of Length of Stay and Mortality During Simultaneous Liver-Kidney Transplant Index Admission: Results From the US-Multicenter SLKT Consortium.

Length of stay (LOS) during index solid organ transplant impacts morbidity and healthcare costs. To date, there are no studies evaluating characteristics and outcomes of simultaneous liver-kidney transplant (SLKT) index hospitalization. We examined factors associated with LOS and mortality during index SLKT admission. Methods: Adult SLKT recipients between 2002 and 2017 at 6 transplant centers across 6 UNOS regions were retrospectively enrolled in the US-Multicenter SLKT Consortium. Multivariable regression analyses assessed predictors of SLKT LOS and death during index admission. Results: Median age of cohort (N = 570) was 58 y (interquartile range: 51-64); 63% male, 75% White, 32.3% hepatitis C, 23.3% alcohol-related, 20.1% nonalcoholic steatohepatitis with median MELD-Na at SLKT 28 (23-34). Seventy-one percent were hospitalized at the time of SLKT with median LOS pretransplant of 10 d. Majority of patients were discharged alive (N = 549; 96%)' and 36% were discharged to subacute rehab facility. LOS for index SLKT was 19 d (Q1: 10, Q3: 34 d). Female sex (P = 0.003), Black race (P = 0.02), advanced age (P = 0.007), ICU admission at time of SLKT (P = 0.03), high MELD-Na (P = 0.003), on cyclosporine during index hospitalization (P = 0.03), pre-SLKT dialysis (P < 0.001), and kidney delayed graft function (P < 0.001) were the recipient factors associated with prolonged LOS during index SLKT hospitalization. Prolonged LOS also contributed to overall mortality (HR = 1.007; P = 0.03). Conclusions: Despite excellent survival, index SLKT admission was associated with high-resource utilization with more than half the patients with LOS >2 wk and affected overall patient survival. Further investigation is needed to optimize healthcare resources for these patients in a financially strained healthcare landscape.

Visible-Light Photoinitiation of (Meth)acrylate Polymerization with Autonomous Post-conversion.

Conversion plateaus rapidly in radical photopolymerizations (RPPs) following discontinuation of irradiation due to rapid termination of reactive radicals, which restricts the wider use of RPPs in applications that involve nonuniform light access including those with attenuated light transmission or irregular surfaces. Based on our recent report of a radical dark-curing photoinitiator (DCPI) that continues polymerization beyond the cessation of irradiation by enabling latent redox initiation with photo-released amine in the presence of a suitable oxidant, we developed a new DCPI with an absorption spectrum that extends well into the visible range. Our design process involved a series of computational investigations of candidate molecules, including a systematic study of substituents and their position-dependent effects on absorption characteristics, electronic transitions, and the photochemical mechanism and its associated energetics. Our quantum chemical computations identified the target compound 5,7-dimethoxy-6-bromo-3-aroylcoumarin-DMPT/BPh4 and predicted that it would facilitate the dark-curing mechanism by concurrent photo-radical generation and photo-induced release of an efficient redox reductant under visible irradiation. This reductant-tethered chromophore was then synthesized and optically characterized with UV-vis spectroscopy that revealed its strong visible-light absorption with a molar absorptivity of 5710 M-1 cm-1 at 405 nm and 50 M-1 cm-1 at 455 nm. We then demonstrated extensive dark-curing of >35% additional conversion over 25 min following brief activation of the shelf-stable one-part system by irradiation with a 455 nm LED that was ceased at 20% conversion. In contrast, shuttering irradiation of the control formulation at that same point resulted in immediate cessation of conversion, which plateaued at 20%. We determined a remarkable initiator efficiency of 2.82 that results from the additional redox-generated radicals with a 77% photo-reductant generation quantum yield. The combination of superior photo- and dark-curing efficiencies of this new visible DCPI is expected to open new application opportunities in RPP, especially those involving resins that are highly light attenuating, surfaces that possess irregular features that produce uneven irradiance, and production lines where continued dark-curing downstream of the light activation step enhances line efficiencies.

High Refractive Index Photopolymers by Thiol-Yne "Click" Polymerization.

A scalable synthesis of high refractive index, optically transparent photopolymers from a family of low-viscosity multifunctional thiol and alkyne monomers via thiol-yne "click" is described herein. The monomers designed to incorporate high refractive index cores consisting of aryl and sulfide groups with high intrinsic molar refraction were synthesized starting from commercially available low-cost raw materials. The low-viscosity (<500 cP) thiol-yne resins formulated with these new multifunctional monomers and a phosphine oxide photoinitiator underwent efficient thiol-yne polymerizations upon exposure to 405 nm light at 30 mW/cm2. In contrast to the previously reported thiol-ene systems, the kinetic profile of these photopolymerizations showed significant dependence on the nature of the thiol and alkyne monomers. However, the ability of the thiol-yne reaction to introduce a large number of sulfide linkages compared to that of thiol-ene systems yielded cross-linked high optical quality photopolymers with a polymer refractive index that exceeds 1.68 (nD/20 °C). Interestingly, the photopolymer formed from the least sterically hindered alkynyl thioether monomer 2b with flexible thioether core and the dithiol 1a exhibited unprecedented difference in the polymer refractive index as compared to that of the resin with polymerization-induced changes reaching up to 0.08. Furthermore, the implementation of these low-viscosity thiol-yne resins was demonstrated by preparing two-stage photopolymeric holographic materials with a dynamic range of ∼0.02 and haze < 1.5% in two-dimensional high refractive index structures.

Effects of network structures on the tensile toughness of copper-catalyzed azide-alkyne cycloaddition (CuAAC)-based photopolymers.

In the present study, the photo-initiated copper-catalyzed azide-alkyne cycloaddition (CuAAC) polymerization was utilized to form structurally diverse glassy polymer networks. Systematic alterations in the monomer backbone rigidity (e.g., cyclic or aliphatic groups with a different length of backbone) and the reactive functional group density (e.g., tetra-, tri-, di-, and mono-functional azide and alkyne monomers) were used to provide readily tailorable network structures with crosslink densities (estimated from the rubbery modulus) varying by a factor of over 20. All eight of the resultant networks exhibited glass transition temperatures (Tg) between 50 and 80 °C with tensile toughness ranging from 28 to 61 MJ m-3. A nearly linear dependence of yield stress and elongation at break (broadly defined as strength and ductility, respectively) on the Tg and rubbery modulus was established in these triazole networks. When a flexible di-alkyne monomer (5 carbon spacing between alkynes) was incorporated in a network composed of a tri-alkyne and di-azide monomer, the elongation at break was improved from 166 to 300 %, while the yield stress was reduced from 36 to 23 MPa. Additionally, the polymer ductility was also varied by incorporating mono-functional azides as chain ends in the network - replacing a sterically hindered stiff mono-azide with a more flexible mono-azide increased the elongation at break from 24 to 185 % and the tensile toughness from 6 to 28 MJ m-3.

Determining Michael Acceptor Reactivity from Kinetic, Mechanistic, and Computational Analysis for the Base-catalyzed Thiol-Michael Reaction.

A combined experimental and computational study of the reactivities of seven commonly used Michael acceptors paired with two thiols within the framework of photobase-catalyzed thiol-Michael reactions is reported. The rate coefficients of the propagation (kP), reverse propagation (k-P), chain-transfer (kCT), and overall reaction (koverall) were experimentally determined and compared with the well-accepted electrophilicity parameters of Mayr and Parr, and DFT-calculated energetics. Both Mayr's and Parr's electrophilicity parameters predict the reactivities of these structurally varying vinyl functional groups well, covering a range of overall reaction rate coefficients from 0.5 to 6.2 s-1. To gain insight into the individual steps, the relative energies have been calculated using DFT for each of the stationary points along this step-growth reaction between ethanethiol and the seven alkenes. The free energies of the individual steps reveal the underlying factors that control the reaction barriers for propagation and chain transfer. Both the propagation and chain transfer steps are under kinetic control. These results serve as a useful guide for Michael acceptor selection to design and predict thiol-Michael-based materials with appropriate kinetic and material properties.

Efficient cellular uptake of click nucleic acid modified proteins.

Efficient intracellular delivery of biomacromolecules such as proteins continues to remain a challenge despite its potential for medicine. In this work, we show that mScarlet, a non cytotoxic red fluorescent protein (RFP) conjugated to Click Nucleic Acid (CNA), a synthetic analog of DNA, undergo cell uptake significantly more than either native proteins or proteins conjugated with similar amounts of DNA in MDA-MB-468 cells. We further demonstrate that the process of cell uptake is metabolically driven and that scavenger receptors and caveolae mediated endocytosis play a significant role. Co-localization studies using anti-scavenger receptor antibodies suggest that scavenger receptors are implicated in the mechanism of uptake of CNA modified proteins.

Messenger RNA enrichment using synthetic oligo(T) click nucleic acids.

Enrichment of mRNA is a key step in a number of molecular biology techniques, particularly in the rapidly growing field of transcriptomics. Currently, mRNA is isolated using oligo(thymine) DNA (oligo(dT)) immobilized on solid supports, which binds to the poly(A) tail of mRNA to pull the mRNA out of solution through the use of magnets or centrifugal filters. Here, a simple method to isolate mRNA by complexing it with synthetic click nucleic acids (CNAs) is described. Oligo(T) CNA bound efficiently to mRNA, and because of the insolubility of CNA in water, >90% of mRNA was readily removed from solution using this method. Simple washing, buffer exchange, and heating steps enabled mRNA's enrichment from total RNA, with a yield of 3.1 ± 1.5% of the input total RNA by mass, comparable to the yield from commercially available mRNA enrichment beads. Further, the integrity and activity of mRNA after CNA-facilitated pulldown and release was evaluated through two assays. In vitro translation of EGFP mRNA confirmed the translatability of mRNA into functional protein and RT-qPCR was used to amplify enriched mRNA from total RNA extracts and compare gene expression to results obtained using commercially available products.