Novel use for polyvinylpyrrolidone as a macromolecular crowder for enhanced extracellular matrix deposition and cell proliferation

Macromolecular crowding (MMC) is a biophysical effect that governs biochemical processes inside and outside of cells. Since standard cell culture media lack this effect, the physiological performance of differentiated and progenitor cells, including extracellular matrix (ECM) deposition, is impaired in vitro. To bring back physiological crowdedness to in vitro systems, we have previously introduced carbohydrate-based macromolecules to culture media and have achieved marked improvements with mixed MMC in terms of ECM deposition and differentiation of mesenchymal stem cells (MSCs). We show here that although this system is successful, it is limited, due to viscosity, to only 33% of the fractional volume occupancy (FVO) of full serum, which we calculated to have an FVO of approximately 54% v/v. We show here that full-serum FVO can be achieved using polyvinylpyrrolidone (PVP) 360 kDa. Under these conditions, ECM deposition in human fibroblasts and MSCs is on par, if not stronger than, with original MMC protocols using carbohydrates, but with a viscosity that is not significantly changed. In addition, we have found that the proliferation rate for bone marrow-derived MSCs and fibroblasts increases slightly in the presence of PVP360, similar to that observed with carbohydrate-based crowders. A palette of MMC compounds is now emerging that enables us to tune the crowdedness of culture media seamlessly from interstitial fluid (9% FVO), in which the majority of tissue cells might be based, to serum environments mimicking intravascular conditions. Despite identical FVO's, individual crowder size effects play a role and different cell types appear to have preferences in terms of FVO and the crowder that this is achieved with. However, in the quest of crowders that we have predicted to have a smoother regulatory approval path, PVP is a highly interesting compound, as it has been widely used in the medical and food industries and shows a novel promising use in cell culture and tissue engineering.

Early detection of biomolecular changes in disrupted porcine cartilage using polarized Raman spectroscopy

We evaluate the feasibility of applying polarized Raman spectroscopy in probing the early biochemical compositions and orientation changes in impacted porcine cartilage explants. We divide 100 fresh tibial cartilage explants into four groups: control (unimpacted) and 3 groups of single impact at 15, 20, and 25 MPa. Each group is examined for biochemical changes using Raman microscopy, cell viability changes using confocal fluorescence microscopy, and histological changes using the modified Mankin score. For the 15-MPa impact group, the modified Mankin score (p>0.05, n=15) and cell viability test (p>0.05, n=5) reveal no significant changes when compared to the control, but polarized Raman spectroscopy detects significant biochemical changes. A significant decrease in the parallel polarized intensity of the pyranose ring band at 1126 cm(-1) suggests a possible decrease in the glycoaminoglycan content in early cartilage damage (one-way analysis of variance with a post hoc Bonferonni test, p<0.05, n=10). For impacts greater than 15 MPa, cell viability and modified Mankin score are consistent with the changes in the observed polarized Raman signals. This suggests that the polarized Raman spectroscopy technique has potential for diagnosis and detection of early cartilage damage at the molecular level.