Investigations on the melting and bending modulus of polymer grafted bilayers using dissipative particle dynamics

Understanding the influence of polymer grafted bilayers on the physicomechanical properties of lipid membranes is important while developing liposomal based drug delivery systems. The melting characteristics and bending moduli of polymer grafted bilayers are investigated using dissipative particle dynamics simulations as a function of the amount of grafted polymer and lipid tail length. Simulations are carried out using a modified Andersen barostat, whereby the membrane is maintained in a tensionless state. For lipids made up of four to six tail beads, the transition from the low temperature L(β) phase to the L(α) phase is lowered only above a grafting fraction of G(f)=0.12 for polymers made up of 20 beads. Below G(f)=0.12 small changes are observed only for the HT(4) bilayer. The bending modulus of the bilayers is obtained as a function of G(f) from a Fourier analysis of the height fluctuations. Using the theory developed by Marsh et al. [Biochim. Biophys. Acta 1615, 33 (2003)] for polymer grafted membranes, the contributions to the bending modulus due to changes arising from the grafted polymer and bilayer thinning are partitioned. The contributions to the changes in κ from bilayer thinning were found to lie within 11% for the lipids with four to six tail beads, increasing to 15% for the lipids containing nine tail beads. The changes in the area stretch modulus were also assessed and were found to have a small influence on the overall contribution from membrane thinning. The increase in the area per head group of the lipids was found to be consistent with the scalings predicted by self-consistent mean field results.     

Beyond the student teaching seminar: examining transformative learning through arts-based approaches**

This qualitative study examined the question: How can arts-based approaches facilitate transformative learning in a student teaching seminar? Two teacher educators facilitated a supplemental and voluntary arts-based ST seminar that comprised six, two-hour sessions. Thirty-four student teachers participated over five semesters making use of Theater of the Oppressed and other arts-based activities to process dilemmas they faced in their student teaching contexts. Data included video recordings, photographs, journal reflection, participant artwork, and transcribed focus group interviews. Data analysis employed line-by-line coding to identify critical incidents. We offer examples where pre-service student teachers worked with a dilemma, examined their assumptions, engaged in perspective-taking, and in the process explored new possibilities. Engaging in embodied reflections, naming, imagining, and critically reflecting provided rich opportunity for constructing new ways of thinking and feeling, which could lead to transformative learning. Issues relating to the seminar environment like safety, starting with participants’ dilemmas, and willingness to take risks and ownership in the learning process supported transformative learning in an arts-based student teaching seminar.