Regulating the Thermodynamics and Thermal Properties of Depolymerizable Polycyclooctenes through Substituent Effects.

Chemical recycling to monomer (CRM) is a promising route for transitioning to a circular polymer economy. To develop new CRM systems with useful properties, it is important to understand the effects of monomer structure on polymerization/depolymerization behavior. In earlier work, this group demonstrated chemically recyclable polymers prepared by ring-opening metathesis polymerization of trans-cyclobutane fused cyclooctenes (tCBCO). Here, it is investigated how different substituents on cyclobutane impact the thermodynamics and thermal properties of tCBCO polymers. Introducing additional substituents to a cis-diester functionalized tCBCO is found to favor the conversion of polymerization; increased polymerization conversion is also observed when the cis-diester is isomerized into its trans counterpart. The effects of these structural features on the thermal properties are also studied. These findings can provide important insights into designing next-generation CRM polymers.

Comparison of the differentiation of dental pulp stem cells and periodontal ligament stem cells into neuron-like cells and their effects on focal cerebral ischemia.

Recent studies have reported an increasing incidence of ischemic stroke, particularly in younger age groups. Dental pulp stem cells (DPSCs) and periodontal ligament stem cells (PDLSCs) are the most common stem cells acquired from the teeth of adults, even elderly people. However, there are no detailed reports on whether DPSCs or PDLSCs are suitable for the treatment of ischemic stroke. In this study, the in vitro differentiation of DPSCs and PDLSCs into neuron-like cells was evaluated. Then, we established a rat model of cerebral ischemia. DPSCs or PDLSCs were administered to animals, and the therapeutic effects of these two types of cells were investigated. The results showed that PDLSCs had a higher differentiation rate than DPSCs. Immunofluorescence studies showed that the expression of the neuronal differentiation marker Thy-1 was higher in PDLSCs than in DPSCs, and other gene markers of neuronal differentiation showed corresponding trends, which were confirmed by western blot analysis. In this process, the Notch and Wnt signaling pathways were inhibited and activated, respectively. Finally, rats with transient occlusion of the right middle cerebral artery were used as a model to assess the therapeutic effect of PDLSCs and DPSCs on ischemia. The results showed that rats in the PDLSC-treated group emitted significantly greater red fluorescence signal than the DPSC-treated group. PDLSC transplantation promoted the recovery of neurological function more effectively than DPSC transplantation. Hence, PDLSCs represent an autogenous source of adult mesenchymal stem cells with desirable biological properties and may be an ideal candidate for clinical applications.

Mechanochemically accessing a challenging-to-synthesize depolymerizable polymer.

Polymers with low ceiling temperatures (Tc) are highly desirable as they can depolymerize under mild conditions, but they typically suffer from demanding synthetic conditions and poor stability. We envision that this challenge can be addressed by developing high-Tc polymers that can be converted into low-Tc polymers on demand. Here, we demonstrate the mechanochemical generation of a low-Tc polymer, poly(2,5-dihydrofuran) (PDHF), from an unsaturated polyether that contains cyclobutane-fused THF in each repeat unit. Upon mechanically induced cycloreversion of cyclobutane, each repeat unit generates three repeat units of PDHF. The resulting PDHF completely depolymerizes into 2,5-dihydrofuran in the presence of a ruthenium catalyst. The mechanochemical generation of the otherwise difficult-to-synthesize PDHF highlights the power of polymer mechanochemistry in accessing elusive structures. The concept of mechanochemically regulating the Tc of polymers can be applied to develop next-generation sustainable plastics.

Depolymerizable Olefinic Polymers Based on Fused-Ring Cyclooctene Monomers.

The growing consumption of synthetic polymers and the accumulation of polymer waste have led to a pressing need for new routes to sustainable materials. Achieving a closed-loop polymer economy via chemical recycling to monomer (CRM) is one such promising route. Our group recently reported a new CRM system based on polymers prepared by ring-opening metathesis polymerization (ROMP) of trans-cyclobutane fused cyclooctene (tCBCO) monomers. This system offers several key advantages, including the ease of polymerization at ambient temperatures, quantitative depolymerization to monomers under mild conditions, and a broad range of functionalities and thermomechanical properties. Here, we outline detailed protocols for the preparation of tCBCO-based monomers and their corresponding polymers, including the preparation of elastic polymer networks and compression molding of linear thermoplastic polymers. We also outline the preparation of high ring strain E-alkene tCBCO monomers and their living polymerization. Finally, the procedures for the depolymerization of linear polymers and polymer networks are also demonstrated.

Gastric Residual Volume after Split-Dose Bowel Preparation versus Conventional Single-Dose Regimen before Anesthetic Colonoscopy.

The aim of this study was to compare gastric residual volume (GRV) in patients given a split-dose versus a conventional single-dose of polyethylene glycol (PEG) preparation before undergoing anesthetic colonoscopy. Methods. In a prospective observational study, we assessed GRV in outpatients undergoing same-day anesthetic gastroscopy and colonoscopy between October 8 and December 30 of 2016. Outpatients were assigned to the split-dose (1 L PEG in the prior evening and 1 L PEG 2-4 h before endoscopy) or single-dose (ingestion of 2 L PEG ≥ 6 h before endoscopy) regimen randomly. Bowel cleansing quality was assessed with the Boston Bowel Preparation Scale (BBPS). Results. The median GRV in the split-dose group (17 ml, with a range of 0-50 ml; N = 65) was significantly lower than that in the single-dose group (22 ml, with a range of 0-62 ml; N = 64; p = 0.005), with a better bowel cleansing quality (BBPS score 8.05 ± 0.82 versus 7.64 ± 1.21; p = 0.028). GRV was not associated with diabetes or the use of medications. Conclusions. GRV after a split-dose preparation and fasting for 2-4 hours is not larger than that after a conventional single-dose preparation and fasting for 6-8 hours. The data indicates that the split-dose bowel preparation might not increase the risk of aspiration.

Establishment and application of enzyme immunoassay for saliva cortisol in Taiwanese context.

Saliva steroid assay is an upcoming area of research, with much potential for growth and progress. Expensive, varying results with commercial kits and the disadvantages of radioimmunoassay have forced researchers to develop their own system of enzyme immunoassay (EIA). A modification from our established EIA system was used to develop a saliva cortisol (F) assay system. The system sensitivity (>90pg/mL) was checked by various experiments, including comparison of data with a commercial kit obtained from Salimetrics. The assay system was employed to investigate the saliva F level in a young Taiwanese population, and compared with the total and free serum levels of F.