Differential regulation of osteogenic differentiation of stem cells on surface roughness gradients

Tissue engineering using scaffold-cell constructs holds the potential to develop functional strategies to regenerate bone. The interface of orthopedic implants with the host tissues is of great importance for its later performance. Thus, the optimization of the implant surface in a way that could stimulate osteogenic differentiation of mesenchymal stem cells (MSCs) is of significant therapeutic interest. The effect of surface roughness of polycaprolactone (PCL) on the osteogenic differentiation of human bone-marrow MSCs was investigated. We prepared surface roughness gradients of average roughness (Ra) varying from the sub-micron to the micrometer range (~0.5e4.7 mm), and mean distance between peaks (RSm) gradually varying from ~214 mm to 33 mm. We analyzed the degree of cytoskeleton spreading, expression of alkaline phosphatase, collagen type 1 and mineralization. The response of cells to roughness divided the gradient into three groups of elicited stem cell behavior: 1) faster osteogenic commitment and strongest osteogenic expression; 2) slower osteogenic commitment but strong osteogenic expression, and 3) similar or inferior osteogenic potential in comparison to the control material. The stem-cell modulation by specific PCL roughness surfaces highlights the potential for creating effective solutions for orthopedic applications featuring a clinically relevant biodegradable material.This work was supported by the Portuguese Foundation for Science and Technology for the PhD grant of Faia-Torres AB (SFRH/BD136476/2007) We are also grateful to the Competence Center for Materials Science and Technology (CCMX) and the Swiss National Science Foundation (SNF) grant PA00P3_142120/1 for providing funds to MC

Regulation of Human Mesenchymal Stem Cell Osteogenesis by Specific Surface Density of Fibronectin: a Gradient Study

The success of synthetic bone implants requires good interface between the material and the host tissue. To study the biological relevance of fibronectin (FN) density on the osteogenic commitment of human bone marrow mesenchymal stem cells (hBM-MSCs), human FN was adsorbed in a linear density gradient on the surface of PCL. The evolution of the osteogenic markers alkaline phosphatase and collagen 1 alpha 1 was monitored by immunohistochemistry, and the cytoskeletal organization and the cell-derived FN were assessed. The functional analysis of the gradient revealed that the lower FN-density elicited stronger osteogenic expression and higher cytoskeleton spreading, hallmarks of the stem cell commitment to the osteoblastic lineage. The identification of the optimal FN density regime for the osteogenic commitment of hBM-MSCs presents a simple and versatile strategy to significantly enhance the surface properties of polycaprolactone as a paradigm for other synthetic polymers intended for bone-related applications

Measuring the Metabolic Activity of Mature Mycobacterial Biofilms Using Isothermal Microcalorimetry

Measuring metabolic activity and response of biofilm to different conditions or compounds is of general interest but is also expected to help in developing new antibiofilm compounds and potentially new treatments. Current culture-based and microscopic methods although of much use have several drawbacks. Isothermal calorimetry can be useful in this context by allowing measurements of the metabolic activity of biofilm grown and maintained on solid medium. Biofilms prepared on membranes were placed in calorimetry vials containing solid medium. Sealed vials were introduced in an isothermal calorimeter, and the rate of metabolic heat production was monitored over time. We chose mycobacteria as an example for this paper as working with mycobacterial biofilms is notoriously difficult