Abstract
This work shows the synthesis of a polyvinylpyrrolidone (PVP) hydrogel by heat-activated polymerization and explores the production of hydrogels with an open porous network by lyophilisation to allow the three-dimensional culture of human oral mucosa stem cells (hOMSCs). The swollen hydrogel showed a storage modulus similar to oral mucosa and elastic solid rheological behaviour without sol transition. A comprehensive characterization of porosity by scanning electron microscopy, mercury intrusion porosimetry and nano-computed tomography (with spatial resolution below 1 μm) showed that lyophilisation resulted in the heterogeneous incorporation of closed oval-like pores in the hydrogel with broad size distribution (5 to 180 μm, d50 = 65 μm). Human oral mucosa biopsies were used to isolate hOMSCs, expressing typical markers of mesenchymal stem cells in more than 95% of the cell population. Direct contact cytotoxicity assay demonstrated that PVP hydrogel have no negative effect on cell metabolic activity, allowing the culture of hOMSCs with normal fusiform morphology. Pore connectivity should be improved in future to allow cell growth in the bulk of the PVP hydrogel.
Highlights
Polyvinylpyrrolidone (PVP) is a synthetic and hydrosoluble polymer produced by free radical polymerization [1,2]
The chemical composition of PVP determined by Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopies was in agreement with previous reports where it was polymerized by different routes [3,4,18,40]
The PVP hydrogel developed in this work presented a storage modulus between keratinized gingiva (20 kPa) and tongue and soft palate (2.5 kPa) [41,42], the main tissues forming the oral mucosa, which is the target of this study to culture and retain undifferentiated the human oral mucosa stem cells (hOMSCs)
Summary
Polyvinylpyrrolidone (PVP) is a synthetic and hydrosoluble polymer produced by free radical polymerization [1,2]. The porous network in the hydrogels is controlled in a variety of pore sizes and shapes that allow the exchange of nutrients and signalling molecules [9,10]. An optimal combination of porosity, pore size, pore connectivity and pore spatial distribution is a critical requirement for proper cell seeding and further homogeneous cell growth in the bulk of the hydrogel [11]. It has been demonstrated that the space between hydrogel polymeric molecules is not suitable for cell migration, leading to heterogeneous distributions of cells [12]. There are several methods for the production of structures with an open porous network in the scale of few hundreds of micrometres, including phase separation [14], porogen leaching [15], gas foaming [16], freeze-thawing [17,18], lyophilisation [19], and cryogelation [20]. Since hydrogels contain more than 50% of water, the frozen water acts as a green and safety porogen for the formation of porous structures (i.e., scaffolds) [12,19,21]
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