The cumulus cell-oocyte complex (COC) matrix is an extended coat that forms around the oocyte a few hours before ovulation and plays vital roles in oocyte biology. Here, we analyzed the micromechanical response of mouse COC matrix by colloidal-probe atomic force microscopy. We found that the COC matrix is elastic insofar as it does not flow and its original shape is restored after force release. At the same time, the COC matrix is extremely soft. Specifically, the most compliant parts of in vivo and in vitro expanded COC matrices yielded Young's modulus values of 0.5 ± 0.1 Pa and 1.6 ± 0.3 Pa, respectively, suggesting both high porosity and a large mesh size (≥100 nm). In addition, the elastic modulus increased progressively with indentation. Furthermore, using optical microscopy to correlate these mechanical properties with ultrastructure, we discovered that the COC is surrounded by a thick matrix shell that is essentially devoid of cumulus cells and is enhanced upon COC expansion in vivo. We propose that the pronounced nonlinear elastic behavior of the COC matrix is a consequence of structural heterogeneity and serves important functions in biological processes such as oocyte transport in the oviduct and sperm penetration.

The metastatic tumour growing in bone is mechanically distinct from both its surrounding environment and in vitro models.

An important feature necessary for biological stability of gold nanoparticles is resistance to ligand exchange. Here, we design and synthesize self-assembled monolayers of mixtures of small ligands on gold nanoparticles promoting high resistance to ligand exchange. We use as ligands short thiolated peptidols, e.g. H-CVVVT-ol, and ethylene glycol terminated alkane thiols (HS-C11-EG4). We present a straightforward method to evaluate the relative stability of each ligand shell against ligand exchange with small thiolated molecules. The results show that a ligand with a ‘thin’ stem, such as HS-C11-EG4, is an important feature to build a highly packed self-assembled monolayer and provide high resistance to ligand exchange. The greatest resistance to ligand exchange was found for the mixed ligand shells of the pentapeptidols H-CAVLT-ol or H-CAVYT-ol and the ligand HS-C11-EG4 at 30:70 (mole/mole). Mixtures of ligands of very different diameters, such as the peptidol H-CFFFY-ol and the ligand HS-C11-EG4, provide only a slightly lower stability against ligand exchange. These ligand shells are thus likely to be suitable for long-term use in biological environments. The method developed here provides a rapid screening tool to identify nanoparticles likely to be suitable for use in biological and biomedical applications.

Metastatic breast cancer in bone is incurable and there is an urgent need to develop new therapeutic approaches to improve survival. Key to this is understanding the mechanisms governing cancer cell survival and growth in bone, which involves interplay between malignant and accessory cell types. Here, we performed a cellular and molecular comparison of the bone microenvironment in mouse models representing either metastatic indolence or growth, to identify mechanisms regulating cancer cell survival and fate. In vivo, we show that regardless of their fate, breast cancer cells in bone occupy niches rich in osteoblastic cells. As the number of osteoblasts in bone declines, so does the ability to sustain large numbers of breast cancer cells and support metastatic outgrowth. In vitro, osteoblasts protected breast cancer cells from death induced by cell stress and signaling via gap junctions was found to provide important juxtacrine protective mechanisms between osteoblasts and both MDA-MB-231 (TNBC) and MCF7 (ER⁺) breast cancer cells. Combined with mathematical modelling, these findings indicate that the fate of DTCs is not controlled through the association with specific vessel subtypes. Instead, numbers of osteoblasts dictate availability of protective niches which breast cancer cells can colonize prior to stimulation of metastatic outgrowth.

Hyaluronan (HA) is a linear, regular polysaccharide that plays as a chief structural and functional component in peri- and extracellular matrices, thus contributing significantly to many basic cellular processes. To understand more comprehensively the response of the supramolecular organization of HA polymers to changes in their aqueous environment, we study the effects of Ca²⁺concentration and pH on the morphology and rigidity of films of end-grafted HA polymers on planar supports (HA brushes), as a well-definedin vitromodel system of HA-rich matrices, by reflection interference contrast microscopy and quartz crystal microbalance. The thickness and softness of HA brushes decrease significantly with Ca²⁺concentration but do not change with pH, within the physiological ranges of these parameters. The effect of Ca²⁺on HA brush thickness is virtually identical to the effect of Na⁺at 10-fold higher concentrations. Moreover, the thickness and softness of HA brushes decrease appreciably upon HA protonation at pH less than 6. Effects of pH and calcium ions are fully reversible over large parameter ranges. These findings are relevant for understanding the supramolecular organization and dynamics of HA-rich matrices in biological systems and will also benefit the rational design of synthetic HA-rich materials with tailored properties.