Polymers and Thermodynamics

Classic thermodynamic equilibrium considerations, supported by simple molecular models, may lead to useful predictions about phase relationships in partially miscible systems that contain polymers. How quantitative the prediction is depends on the amount of experimental information, as well as, on the complexity of the system. The solubility parameter and group contribution approaches present the first LeveL and allow a qualitative judgement whether a system is miscible or not. On this level, the entropy of mixing is not considered though it is higly important. A second, higher level of prediction is supplied by the Flory-Huggins-Staverman equation which permits estimations of the temperature and chain length dependence on the location of miscibility gaps. On this level the concentration ranges of partial miscibility are not well covered. Taking account of the ever present disparity in size and shape between molecules and repeat units improves the situation considerably and represents a third level of prediction. On this level the influence of pressure can reasonably accurately b~ dealt with. If predictions of a high precision are required, the present-day theory fails, even in the simple case of a linear, apolar homopolymer solution. Extensive measurements then remain needed to determine the many empirical and theoretical parameters. Predictions on such a high level have amore than academic value, since they may supply better mathematical frameworks to be applied in less demanding calculations

A cost-effectiveness analysis of iStent inject combined with phacoemulsification cataract surgery in patients with mild-to-moderate open-angle glaucoma in France

OBJECTIVE: To investigate the cost-effectiveness of implementing iStent inject trabecular bypass stent (TBS) in conjunction with cataract surgery (Cat Sx) in patients with mild-to-moderate glaucoma from a societal perspective in France. The secondary objective was to explore the economic impact of iStent inject TBS in patients who comply to different degrees with their anti-glaucoma medications. METHODS: A previously published Markov model was adapted to estimate the cost-effectiveness of treatment with iStent inject TBS + Cat Sx versus Cat Sx alone over a lifetime time horizon in patients with mild-to-moderate open-angle glaucoma in France. Progression was modeled by health states reflecting increasing stages of vision loss. Disease progression was obtained from the two-year randomized clinical trial assessing safety and effectiveness of both interventions. French specific health-state utilities and costs were obtained through a targeted literature review. Model structure and inputs were validated by French ophthalmologists. Outcomes were expressed as incremental cost per quality-adjusted life-year (QALY) gained. The robustness of results was tested through sensitivity analyses. RESULTS: iStent inject TBS + Cat Sx reduced the number of medications needed and risk of blindness. Incremental cost and QALYs were euro75 and 0.065 leading to an incremental cost-effectiveness ratio (ICER) of euro1,154/QALY gained. ICER ranged from dominating for non-persistent patients to euro31,127 patients fully persistent with their medication regime. Results from one-way sensitivity analysis had a maximum ICER of euro29,000 when varying input parameters. iStent inject TBS + Cat Sx had an 86% chance of being cost-effective at a willingness-to-pay threshold of euro30,000 per QALY gained. CONCLUSION: Results demonstrate that iStent inject TBS + Cat Sx is a cost-effective intervention for intraocular pressure reduction when compared to Cat Sx alone in France