Marrow-Derived Stem Cell Motility in 3D Synthetic Scaffold Is Governed by Geometry Along With Adhesivity and Stiffness

Author Manuscript 2012 May 21.Design of 3D scaffolds that can facilitate proper survival, proliferation, and differentiation of progenitor cells is a challenge for clinical applications involving large connective tissue defects. Cell migration within such scaffolds is a critical process governing tissue integration. Here, we examine effects of scaffold pore diameter, in concert with matrix stiffness and adhesivity, as independently tunable parameters that govern marrow-derived stem cell motility. We adopted an “inverse opal” processing technique to create synthetic scaffolds by crosslinking poly(ethylene glycol) at different densities (controlling matrix elastic moduli or stiffness) and small doses of a heterobifunctional monomer (controlling matrix adhesivity) around templating beads of different radii. As pore diameter was varied from 7 to 17 µm (i.e., from significantly smaller than the spherical cell diameter to approximately cell diameter), it displayed a profound effect on migration of these stem cells—including the degree to which motility was sensitive to changes in matrix stiffness and adhesivity. Surprisingly, the highest probability for substantive cell movement through pores was observed for an intermediate pore diameter, rather than the largest pore diameter, which exceeded cell diameter. The relationships between migration speed, displacement, and total path length were found to depend strongly on pore diameter. We attribute this dependence to convolution of pore diameter and void chamber diameter, yielding different geometric environments experienced by the cells within. Bioeng. 2011; 108:1181–1193(National Institute of General Medical Sciences (U.S.) (NRSA Fellowship GM083472)National Institutes of Health (U.S.) (National Institute of General Medical Sciences (U.S.) Cell Migration Consortium Grant GM064346)National Science Foundation (U.S.) (CAREER CBET-0644846

Writing-to-teach: A new pedagogical approach to elicit explanative writing in undergraduate chemistry students

Contemporary strategies in STEM education focus on developing pedagogies that more actively engage students in their own learning. A method that has proven effective to this end has been peer instruction and discussion, particularly those in which participating students must organize information in such a way as to be able to verbally articulate it to others. The success of peer learning raises the question of what other communicative activities could lead to similar learning gains. Writing is a reasonable choice for such an activity, as there is strong historical evidence of the value of writing in facilitating student learning. Presented here is “writing-to-teach”; a fusion of writing and peer instruction that is rooted in the theories of meaningful learning and situated cognition as well as research on student-generated explanatory knowledge. Writing-to-teach activities were designed and implemented in an introductory physical chemistry course and evaluated using student surveys. In addition, a novel expert-ranking methodology was employed to evaluate the quality of explanatory writing produced by students engaging in writing-to-teach activities. Lastly, suggestions are given on how writing-to-teach can be implemented more broadly in other STEM classrooms