Gelatin-siloxane nanoparticles to deliver nitric oxide for vascular cell regulation: synthesis, cytocompatibility, and cellular responses.

Nitric oxide (NO) is an important mediator in cardiovascular system to regulate vascular tone and maintain tissue homeostasis. Its role in vascular cell regulation makes it promising to address the post-surgery restenosis problem. However, the application of NO is constrained by its high reactivity. Here, we developed a novel NO-releasing gelatin-siloxane nanoparticle (GS-NO NP) to deliver NO effectively for vascular cell regulation. Results showed that gelatin-siloxane nanoparticles (GS NPs) could be synthesized via sol-gel chemistry with a diameter of ∼200 nm. It could be modified into GS-NO NPs via S-nitrosothiol (RSNO) modification. The synthesized GS-NO NPs could release a total of ∼0.12 µmol/mg NO sustainably for 7 days following a first-order exponential profile. They showed not only excellent cytocompatibility, but also rapid intracellularization within 2 h. GS-NO NPs showed inhibition of human aortic smooth muscle cell (AoSMC) proliferation and promotion of human umbilical vein endothelial cell (HUVEC) proliferation in a dose-dependent manner, which is an important approach to prevent restenosis. With GS-NO NP dose at 100 µg/mL, the proliferation of AoSMCs could be slowed down whereas the growth of HUVECs was significantly promoted. We concluded that GS-NO NPs could have potential to be used as a promising nano-system to deliver NO for vascular cell regulation.

Biomimetic three-dimensional anisotropic geometries by uniaxial stretching of poly(ε-caprolactone) films: degradation and mesenchymal stem cell responses.

Geometric cues have been used for a variety of cell regulation and tissue regenerative applications. While the function of geometric cues is being recognized, their stability and degradation behaviors are not well known. Here, we studied the influence of degradation on uniaxial-stretch-induced poly(ε-caprolactone) (UX-PCL) ridge/groove arrays and further cellular responses. Results from accelerated hydrolysis in vitro showed that UX-PCL ridge/groove arrays followed a surface-controlled erosion, with an overall geometry remained even at ∼45% film weight loss. Compared to unstretched PCL flat surfaces and/or ridge/groove arrays, UX-PCL ridge/groove arrays achieved an enhanced morphological stability against degradation. Over the degradation period, UX-PCL ridge/groove arrays exhibited an "S-shape" behavior of film weight loss, and retained more stable surface hydrophilicity and higher film mechanical properties than those of unstretched PCL surfaces. Human mesenchymal stem cells (MSCs) aligned better toward UX-PCL ridge/groove arrays when the geometries were remained intact, and became sensitive with gradually declined nucleus alignment and elongation to the geometric degradation of ridges. We speculate that uniaxial stretching confers UX-PCL ridge/groove arrays with enhanced stability against degradation in erosive environment. This study provides insights of how degradation influences geometric cues and further cell responses, and has implications for the design of biomaterials with stability-enhanced geometric cues for long-term tissue regeneration.

Biomimetic three-dimensional anisotropic geometries by uniaxial stretch of poly(ε-caprolactone) films for mesenchymal stem cell proliferation, alignment, and myogenic differentiation.

Anisotropic geometries are critical for eliciting cell alignment to dictate tissue microarchitectures and biological functions. Current fabrication techniques are complex and utilize toxic solvents, hampering their applications for translational research. Here, we present a novel simple, solvent-free, and reproducible method via uniaxial stretching for incorporating anisotropic topographies on bioresorbable films with ambitions to realize stem cell alignment control. Uniaxial stretching of poly(ε-caprolactone) (PCL) films resulted in a three-dimensional micro-ridge/groove topography (inter-ridge-distance: ~6 µm; ridge-length: ~90 µm; ridge-depth: 200-900 nm) with uniform distribution and controllable orientation by the direction of stretch on the whole film surface. When stretch temperature (Ts) and draw ratio (DR) were increased, the inter-ridge-distance was reduced and ridge-length increased. Through modification of hydrolysis, increased surface hydrophilicity was achieved, while maintaining the morphology of PCL ridge/grooves. Upon seeding human mesenchymal stem cells (hMSCs) on uniaxial-stretched PCL (UX-PCL) films, aligned hMSC organization was obtained. Compared to unstretched films, hMSCs on UX-PCL had larger increase in cellular alignment (>85%) and elongation, without indication of cytotoxicity or reduction in cellular proliferation. This aligned hMSC organization was homogenous and stably maintained with controlled orientation along the ridges on the whole UX-PCL surface for over 2 weeks. Moreover, the hMSCs on UX-PCL had a higher level of myogenic genes' expression than that on the unstretched films. We conclude that uniaxial stretching has potential in patterning film topography with anisotropic structures. The UX-PCL in conjunction with hMSCs could be used as "basic units" to create tissue constructs with microscale control of cellular alignment and elongation for tissue engineering applications.