Polyurethanes Crosslinked with Poly(vinyl alcohol) as a Slowly-Degradable and Hydrophilic Materials of Potential Use in Regenerative Medicine

Abstract

Novel, slowly-degradable and hydrophilic materials with proper mechanical properties and surface characteristics are in great demand within the biomedical field. In this paper, the design, synthesis, and characterization of polyurethanes (PUR) crosslinked with poly(vinyl alcohol) (PVA) as a new proposition for regenerative medicine is described. PVA-crosslinked PURs were synthesized by a two-step polymerization performed in a solvent (dimethylsulfoxide, DMSO). The raw materials used for the synthesis of PVA-crosslinked PURs were poly(ε-caprolactone) (PCL), 1,6-hexamethylene diisocyanate (HDI), and PVA as a crosslinking agent. The obtained materials were studied towards their physicochemical, mechanical, and biological performance. The tests revealed contact angle of the materials surface between 38-47° and tensile strength in the range of 41-52 MPa. Mechanical characteristics of the obtained PURs was close to the characteristics of native human bone such as the cortical bone (T_Sb = 51-151 MPa) or the cancellous bone (T_Sb = 10-20 MPa). The obtained PVA-crosslinked PURs did not show significant progress of degradation after 3 months of incubation in a phosphate-buffered saline (PBS). Accordingly, the obtained materials may behave similar to slowly-degradable materials, which can provide long-term physical support in, for example, tissue regeneration, as well as providing a uniform calcium deposition on the material surface, which may influence, for example, bone restoration. A performed short-term hemocompatibility study showed that obtained PVA-crosslinked PURs do not significantly influence blood components, and a cytotoxicity test performed with the use of MG 63 cell line revealed the great cytocompatibility of the obtained materials. According to the performed studies, such PVA-crosslinked PURs may be a suitable proposition for the field of tissue engineering in regenerative medicine.

Keywords: bone tissue engineering; crosslinking; degradation; hydrophilicity; poly(vinyl alcohol); polyurethane; surface.

Figure 1

Scheme of PUR synthesis.

Figure 2

The FTIR spectra of non-crosslinked (black) and PVA-crosslinked PURs (blue and red respectively for 1 wt % and 2 wt % of PVA) in the range between 500–4000 cm⁻¹ (a) and in the range of 1000–2000 cm⁻¹ (b).

Figure 3

Tensile strength (T_Sb) (a), percent of elongation at break (%) (ε_b) (b); and hardness (c) of obtained non-crosslinked and PVA-crosslinked PURs.

Figure 4

Canola oil sorption noted for PU-I, PU-II-1, PU-II-2 after 24 h of incubation.

Figure 5

Distilled water (a) and PBS (b) sorption of obtained PURs after selected incubation time-points.

Figure 6

Microscopic images of the PUR surfaces before and after long-term interactions study performed in PBS.

Figure 7

Selected SEM images of non-crosslinked (PU-I) and PVA-crosslinked (PU-II-1, PU-II-2) before and after calcification study.

Figure 8

The EDX spectra of non-crosslinked and PVA-crosslinked PURs before and after calcification study.

Figure 9

Selected results of PVA-crosslinked and non-crosslinked PURs hemocompatibility. APTT (a); Fibrynogen (b); Hb (c); RBC (d); and WBC (e).

Figure 10

The effect of polymer extracts on the in vitro cell growth of MG 63 studied by MTT assay after 24 h, 48 h and 72 h.

Figure 11

The cell attachment to the selected samples surface: PU-I (a) and PU-II-2 (b) after 72 h of the test. Cells were simultaneously stained with DAPI (blue) for nucleus visualization and Phalloidin TRITC (red) for actin viability.