Structural engineering to control density, conformation, and bioactivity of the poly(ethylene glycol)-grafted poly(urethane urea) scaffolds

Poly(urethane urea) scaffolds were fabricated through combined salt leaching and solvent casting methods. The scaffolds were then functionalized via aminolysis with poly(ethylene glycol) (PEG- g-PUU). To compare its bioactivity, gelatin was also grafted onto the aminolyzed poly(urethane urea) surface (Gel- g-PUU). Chemical changes at the surface were then monitored using quantitative/qualitative methods. Grafting with both gelatin and poly(ethylene glycol) remarkably enhanced the wettability of poly(urethane urea). Proliferation of human adipose–derived mesenchymal stem cells on poly(urethane urea) and the modified poly(urethane urea)s was evaluated by 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide assay. The cell experiment results showed that both the modified poly(urethane urea)s enhanced the attachment and proliferation of human adipose–derived mesenchymal stem cells compared to pure poly(urethane urea). Based on previous reports, while a supportive role is observed at adequate poly(ethylene glycol) graft densities, cell adhesion and proliferation are inhibited at very high grafting densities. To correlate the cell data to poly(ethylene glycol) conformations, the surface tension was measured. Data on human adipose–derived mesenchymal stem cells’ attachment/proliferation and contact angle/surface free energy together showed that the grafting density of poly(ethylene glycol) was regulated by optimizing aminolysis conditions, careful selection of poly(ethylene glycol)’s molecular weight, and bulk properties of the matrix poly(urethane urea). As a result, surface overcrowding and brush conformation of the poly(ethylene glycol) chains were avoided, and human adipose–derived mesenchymal stem cell attachment and proliferation occurred on the PEG- g-PUU scaffold at a comparable level to the Gel- g-PUU.

Improved immobilization of gelatin on a modified polyurethane urea

In this study, polyurethane urea was surface-modified to elevate cell recognition through immobilization of bioactive gelatin. The poly(urethane urea) was synthesized using poly(ε-caprolactone) diol in the absence of a chain extender. The synthesized polyurethane urea was then functionalized with gelatin (gelatin-grafted poly(urethane urea)) via aminolysis. Chemical changes at the polyurethane urea surface were monitored using titration, water contact angle. Fourier transform infrared, and zeta potential measurements. Significantly larger amounts of gelatin were grafted on the polyurethane urea surface compared to those previously reported for poly(ε-caprolactone) diol (three times more) and polyurethanes (two times more), while the mechanical properties were not compromised. Proliferation of human adipose–derived mesenchymal stem cells on the polyurethane urea and the gelatin-grafted polyurethane urea was evaluated through MTT assay. Although both samples enhanced human adipose–derived mesenchymal stem cells’ proliferation, gelatin-grafted polyurethane urea supported human adipose–derived mesenchymal stem cells’ proliferation at a remarkably higher rate.

Synthesis and characterization of biodegradable acrylated polyurethane based on poly(ε-caprolactone) and 1,6-hexamethylene diisocyanate

A series of biodegradable acrylic terminated polyurethanes (APUs) based on poly(ε-caprolactone) diol (PCL), aliphatic 1,6-hexamethylene diisocyanate (HDI) and hydroxyethyl methyl acrylate (HEMA) was synthesized as potential materials for hard tissue biomedical applications. PCLs with low molecular weights of 1000 and 2,000 g/mol were employed to provide different amounts of end capped urethane acrylate in APUs. To control crosslink density, a mixture of two different reactive diluents including mono-functional HEMA and bi-functional ethylene glycol dimethacrylate (EGDMA) with different weight ratios was incorporated into the APUs, called here PUAs. Morphological characteristics and mechanical properties were investigated using X-ray diffraction (XRD), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). DMA results indicated some degree of microphase separation between hard and soft segments; however, the microphase separation is more prominent for PUAs with higher molecular weight PCL. It was also found that the degree of crosslinking dominated greatly the formation of crystalline structure. PUAs with low crosslink density exhibited crystalline microstructure. The results also indicated that the mechanical properties of PUAs were governed considerably by crystalline microstructure, and hard segment content. All PUAs demonstrated hydrophobic behavior and were able to be degraded hydrolytically. The degradation process was closely related to the microstructure and surface tension of PUAs.