Yoon Jeong Choi

Effects of cross-linking molecular weights in a hyaluronic acid–poly(ethylene oxide) hydrogel network on its properties

We examined the effects of cross-linking molecular weights on the properties of a hyaluronic acid (HA)-poly(ethylene oxide) (PEO) hydrogel. Swelling behaviors, mechanical strength and rheological behaviors of the HA-PEO hydrogel were evaluated by employing different cross-linking molecular weights (100 kDa and 1.63 mDa) of the HAs in the hydrogel networks. The low molecular weight of HA was obtained in advance by treating high molecular weight HA with a hydrogen chloride solution. Methacrylation of HA was obtained by grafting aminopropylmethacrylate to its caroboxylic acid functional groups. While reduction of the HA molecular weights was confirmed by gel permeation chromatography, the degree of methacrylate grafting to the HA was measured by (1)H-nuclear magnetic resonance. Synthesis of the HA-PEO hydrogel was successfully achieved via the Michael-type addition reaction between the methacrylate arm groups in the HA and the six thiol groups in PEO. The hydrogel formation was not dependent upon the HA molecular weights and its gelation behaviors were markedly different. Compared to the properties of the high molecular weight HA-based PEO one, the low molecular weight HA-based hydrogel induced quicker hydrogelation, as observed from the behaviors of the elastic and viscous modulus. Furthermore, the low molecular weight HA-based hydrogel demonstrated stronger mechanical properties as measured with a texture analyzer, lower water absorption as measured with a microbalance and smaller pore sizes on its surface and cross section as observed with scanning electron microscopy. The information about the effects of the cross-linking molecular weights of the gel network on the properties of the HA-based PEO hydrogel may lead to better design of hydrogels, especially in tissue engineering applications.

Characterizations of the TiO(2-x) films synthesized by e-beam evaporation for endovascular applications.

Different chemical states of titanium oxide films were deposited on commercially pure Ti (CP Ti) by electron-beam evaporation at different oxygen flow rates to examine a possibility of their applications to endovascular stents. The surface morphology, chemical composition and crystal structure of the obtained titanium oxide films were analyzed by FE-SEM, XPS and XRD, respectively. As a function of the deposition parameters employed, the obtained titanium oxide films demonstrated different mixtures of anatase phase, Ti2O3 and TiO. By the formation of titanium oxide film on the CP Ti plate, the contact angle was decreased and the cellular activity of porcine aortic smooth muscle cells was increased. Post-deposition annealing was also found to be an important factor to achieve advantageous biocompatibility. When haemocompatibility was investigated by observing adhesion of blood platelets from platelet-rich plasma, less platelet adhesion was observed on titanium oxide films. These results indicated that titanium oxide film synthesized by e-beam evaporation could be applicable to coronary stents.

The Impact of Medicare Part D on the Proportion of Out-of-Pocket Prescription Drug Costs Among Older Adults With Diabetes

OBJECTIVE The purpose of this study was to evaluate the impact of Medicare Part D on reducing the financial burden of prescription drugs in older adults with diabetes. RESEARCH DESIGN AND METHODS Using Medical Expenditure Panel Survey data (2000–2011), interrupted time series and difference-in-difference analyses were used to examine out-of-pocket costs for prescription drugs in 4,664 Medicare beneficiaries (≥65 years of age) compared with 2,938 younger, non-Medicare adults (50–60 years) with diabetes and to estimate the causal effects of Medicare Part D. RESULTS Part D enrollment of Medicare beneficiaries with diabetes gradually increased from 45.7% (2006) to 52.4% (2011). Compared with years 2000–2005, out-of-pocket pharmacy costs decreased by 13.5% (SE 2.1) for all Medicare beneficiaries with diabetes following Part D implementation; on average, Part D beneficiaries had 5.3% (0.8) lower costs compared with those without Part D. Compared with a younger group with diabetes, out-of-pocket pharmacy costs decreased by 19.4% (1.7) for Medicare beneficiaries after Part D. Part D beneficiaries with diabetes who experienced the coverage gap decreased from 60.1% (2006) to 40.9% (2011) over this period. CONCLUSIONS These findings demonstrate that although Medicare Part D has been effective in reducing the out-of-pocket cost burden of prescription drugs, approximately two out of five Part D beneficiaries with diabetes experienced the coverage gap in 2011. Future research is needed to examine the impact of Affordable Care Act provisions to close the coverage gap on the cost burden of prescription drugs for Medicare beneficiaries with diabetes.

Evaluation of the Hemodynamics of a Tissue-engineered Hybrid Graft

We evaluated the hemodynamics of tissue-engineered hybrid graft in vivo. The hybrid expanded polytetrafluoroethylene (ePTFE) scaffold was fabricated by coating the ePTFE graft with poly (lactide-co-glycolide) (PLGA) solution. This scaffold was turned into an engineered hybrid graft by culturing smooth muscle cells on its surface. Both the ePTFE (n = 6) and the engineered hybrid grafts (n = 8) were implanted in the carotid arteries of mongrel dogs. The length of intima in the engineered hybrid graft was greater than the ePTFE. The neoarterial thickness in the engineered hybrid group was greater, and the foreign body reaction was more severe. We compared the hemodynamics (diameter, flow rate, pulsatile index, mean velocity, shear stress, resistance index, and systolic/diastolic ratio) of the native arteries in the distal anastmosis. The shear rate in the engineered hybrid group was higher immediately after implantation, and the resistance index was lower, but there was no significant difference after 4 weeks. The engineered grafts demonstrated similar hemodynamics with the ePTFE grafts after 4 weeks implantation.

Tissue Regeneration of a Hybrid Vascular Graft Composed of Biodegradable Layers and Non-Biodegradable Layer by Static and Pulsatile Flows

Clinical applications of expanded polytetrafluoroethylene (ePTFE) as a small diameter graft have been limited due to its limited patency rates, even though its demands are high. After fabricating the biodegradable PLGA layers on both the inside and outside of ePTFE, long-term in vitro smooth muscle cell culture was performed on the luminal scaffold surface. The fabricated hybrid ePTFE scaffolds were designed to have three distinctive layers and porous structures in the biodegradable layers generated by gas-foaming of the ammonium bicarbonate porogens, i.e. two layers of poly(lactide-co-glycolide) (PLGA) as biodegradable layers for tissue engineering and an ePTFE layer in the middle as a non-biodegradable layer. We evaluated the regenerated vascular tissues after applying either static or pulstile flow on a smooth muscle cells-seeded hybrid scaffold. Analysis of the engineered tissues was performed with SEM for morphological observation and H&E staining for observation of tissue development dependent upon a mode of culture system, flow patterns and scaffold species.

Factors Associated With Medication Engagement Among Older Adults With Diabetes: Systematic Review and Meta-Analysis:

Purpose The purpose of this systematic review and meta-analysis is to explore the factors associated with medication engagement among older adults (≥60 years) with diabetes. Methods Five databases (PubMed, Embase, Cumulative Index to Nursing and Allied Health Literature, PsycINFO, and Scopus) were systematically searched to identify studies examining the association between factors and medication engagement among older diabetes patients. A study met inclusion for meta-analysis if the prevalence of medication engagement or factor was reported in ≥2 studies and the frequency or strength of association was either reported or able to be computed. Quality appraisal was performed with the Downs and Black tool. Results Of 538 retrieved studies, 33 (20 cohort and 13 cross-sectional) were included for systematic review; of these, 22 met criteria for meta-analysis. Findings from meta-analysis show that women (odds ratio [OR], 0.92; 95% CI, 0.86-0.97), those with depression (OR, 0.73; 95% CI, 0.62-0.87), and those with higher out-of-pocket spending for prescription drugs (OR, 0.87; 95% CI, 0.80-0.94) were less likely to take diabetes medication when compared with men, those without depression, and those with lower out-of-pocket costs, respectively. Older age (OR, 1.13; 95% CI, 1.00-1.27) was associated with better engagement to diabetes medication. Conclusions Of 4 identified factors, 2 are modifiable. Recent policy efforts to decrease the cost burden of prescribed medication for older adults, such as Medicare Part D, may remove this barrier to medication engagement. Routine screening for depression among older adults with diabetes should be included as part of usual care to facilitate an integrated treatment approach.

CD133-induced TM4SF5 expression promotes sphere growth via recruitment and blocking of protein tyrosine phosphatase receptor type F (PTPRF)

CD133 is a surface marker of liver cancer stem cells. Transmembrane 4u202fL six family member 5 (TM4SF5) promotes sphere growth and circulation. However, it is unknown how CD133 and TM4SF5 cross-talk with each other for cancer stem cell properties. Here, we investigated the significance of inter-relationships between CD133, TM4SF5, CD44, and protein tyrosine phosphatase receptor type F (PTPRF) in a three-dimensional (3D) sphere growth system. We found that CD133 upregulated TM4SF5 and CD44, whereas TM4SF5 and CD44 did not affect CD133 expression. Signaling activity following CD133 phosphorylation caused TM4SF5 expression and sphere growth. TM4SF5 bound to CD133 and promoted c-Src activity for CD133 phosphorylation as a positive feedback loop, leading to CD133-mediated sphere growth that was inhibited by TM4SF5 inhibition or suppression. TM4SF5 also bound PTPRF and promoted paxillin phosphorylation. Decreased sphere growth upon CD133 suppression was recovered by TM4SF5 expression and partially by PTPRF suppression. TM4SF5 inhibition enhanced PTPRF levels and abolished PTPRF suppression-mediated sphere growth. Altogether, CD133-induced TM4SF5 expression and function were important for liver cancer sphere growth and may be a promising target to block metastasis.

Evaluation of acid-treated hyaluronic acid-based hydrogelation

Though hyaluronic acid (HA)-based hydrogel has drawn great attention in biomedical society, it’s long molecular weights sometimes have been problematic due to its difficulty in handling. After reduction of its high molecular weight into smaller sizes with various concentrations of hydrogen chloride solutions, its chemical and biological properties have been examined by changes in viscosity, FTIR spectroscopy and gel permeation chromatography as well as cellular interactions. While FTIR analysis indicated maintenance of its original chemical structures, its viscosity has been remarkably reduced and its extent was dependent upon the employment of acid concentrations. After controlling its molecular weight to approximately 100 kDa and coupling of aminopropymethacrylate to the treated HA, we evaluated in vitro cellular interactions and cell proliferations of the HA-poly(ethylene oxide) (PEO) hydrogel.

Characterization of Hyaluronic Acid-Poly(Ethylene Oxide) Hydrogel Dependent upon Poly(Ethylene Oxide)

Characterization of an hyaluronic acid (HA)-poly(ethylene oxide) (PEO) hydrogel was performed by changing the number of side arms in a PEO molecule. Verification of grafting chemistry and mechanical strength, as well as swelling behaviors and surface morphologies of the HA-PEO hydrogels were analyzed by employing different x-linking molecular weights (MW) of PEO ranging from 1.7 to 5.0 kDa at a fixed low MW HA in the hydrogel network. Methacrylation to the HA successfully obtained via Michael type reaction between the methacrylate arm groups in HA and the thiol end groups in PEO was observed by XPS. Hydrogel formation was markedly dependent upon the numbers of thiol groups in the PEO molecule. Furthermore the lower MW PEO-based HA hydrogel demonstrated stronger mechanical properties but lower water absorption and the smaller pore sizes on its surface and cross section.