Surface charge and wettability, the two prominent physical factors governing protein adsorption and cell adhesion, have been extensively investigated in the literature. However, a comparison between these driving forces in terms of their independent and cooperative effects in affecting adhesion is rarely explored on a systematic and quantitative level. Herein, we formulate a protocol that features two-dimensional control over both surface charge and wettability with limited cross-parameter influence. This strategy is implemented by controlling both the polyion charge density in the layer-by-layer (LbL) assembly process and the polyion side-chain chemical structures. The 2D property matrix spans surface isoelectric points ranging from 5 to 9 and water contact angles from 35 to 70°, with other interferential factors (e.g., roughness) eliminated. The interplay between these two surface variables influences protein (bovine serum albumin, lysozyme) adsorption and 3T3 fibroblast cell adhesion. For proteins, we observe the presence of thresholds for surface wettability and electrostatic driving forces necessary to affect adhesion. Beyond these thresholds, the individual effects of electrostatic forces and wettability are observed. For fibroblast, both surface charge and wettability have an effect on its adhesion. The combined effects of positive charge and hydrophilicity lead to the highest cell adhesion, whereas negative charge and hydrophobicity lead to the lowest cell adhesion. Our design strategy can potentially form the basis for studying the distinct behaviors of electrostatic force or wettability driven interfacial phenomena and serve as a reference in future studies assessing protein adsorption and cell adhesion to surfaces with known charge and wettability within the property range studied here.

Cross-linking of polysaccharide electrospun constructs using currently available techniques results in poor scaffold structural stability. In general, cross-linked substrates lose their nanofibrous architecture within a short time under physiological conditions. In this study, we introduce an in situ cross-linking electrospinning technique to fabricate and stabilize pullulan/dextran fibres. Pullulan/dextran (4:1 weight ratio, 16.7 and 20 wt%) solutions were preloaded with the chemical cross-linker, trisodium trimetaphosphate (STMP), to enable cross-linking during electrospinning. By increasing STMP from 4 to 16 wt%, the average diameter of electrospun fibres increased significantly from 268 ± 35 nm to 416 ± 74 nm (P < 0.05). Additionally, the enhanced cross-linking effectively decreased the swelling extent of the scaffolds. In particular, in the presence of 10 wt% gelatin, a significant decrease in scaffold swelling ratio was observed (208.5 ± 31.3% at 4 wt% STMP vs 133.1 ± 9.1% at 16 wt% STMP, P < 0.05). In vitro stability studies demonstrated the retention of scaffold fibrous morphology and negligible weight loss in all samples after 28 days. Environmental SEM analysis revealed that at least 16 wt% STMP was required in order to retain the nanofibrous structure of the scaffolds under hydrated conditions. Compared with hydrogels of similar chemical content, the nanofibrous architecture of electrospun scaffolds significantly enhanced human dermal fibroblast (HDF) viability at days 3 and 7 (P < 0.05). The incorporation of gelatin and the increase in scaffold cross-linking density favoured HDF cell attachment and spreading. In particular, 16 wt% STMP promoted actin stress fibre formation. Taken together, the results support the promise of using STMP in situ cross-linking for long-term stabilization of polysaccharide electrospun fibres and the advantage of polysaccharide nanofibrous constructs for tissue engineering.

Dopamine (DA) protected by an o-nitrobenzyl functionality on its phenolic group was synthesized as a photolabile catecholamine derivative. This compound, o-nitrobenzyl dopamine (NBDA), was more stable than DA in basic solution at pH 8.5 and will not self-polymerize when protected from light. UV irradiation of a methanolic solution of NBDA at 365 nm for 40 min induced ca. 85% deprotection. Taking advantage of the stability of NBDA, a one-pot spray coating technique for modifying surfaces with polydopamine (PDA) was developed. Using ethylene glycol with Tris buffer (pH 8.5) as the solvent for this technique, stainless steel substrates can be coated with a robust PDA layer. Silver was deposited on the PDA-coated surface after treatment with silver nitrate solution, and >80% of the deposited silver remained on the surface after 1 week immersion in water. The NBDA-Ag surface was highly effective in inhibiting Staphylococcus aureus (S. aureus) biofilm formation.

The potential of electrospun pullulan/dextran (P/D) nanofibers (average diameter = 323 nm) for vascular tissue engineering applications is explored. The mechanical properties of the nanofibers are of the same order of magnitude as that of human arteries (Young's modulus ≈0.88 MPa; tensile strength ≈0.35 MPa). It is demonstrated that the nanofiber topography enables cell adhesion and that the endothelial phenotype is maintained on the nanofibers. Moreover, P/D nanofibers support a stable confluent monolayer of endothelial cells over 14 d. SMCs seeded on nanofibers display similar levels of alpha smooth muscle actin and a lower proliferation rate than cells on 2D cultures. The observations suggest that nanofibers promote a shift to a quiescent contractile phenotype in SMCs.

The bifunctional comonomer 4‐(3‐butenyl) styrene was used to synthesize crosslinked polystyrene microspheres (c‐PS) with pendant butenyl groups on their surface via suspension copolymerization. Polyethylene chains were grafted onto the surface of c‐PS microspheres (PS‐g‐PE) via ethylene copolymerizing with the pendant butenyl group on the surface of the c‐PS microspheres under the catalysis of metallocene catalyst. The composition and morphology of the PS‐g‐PE microspheres were characterized by means of Fourier transform infrared spectroscopy, Fourier transform Raman spectroscopy, X‐ray photoelectron spectroscopy, and field‐emission scanning electron microscopy. It is possible to control the content of PE grafted onto the surface of c‐PS microspheres by varying the polymerization time or the initial quantity of pendant butenyl group on the surface of c‐PS microspheres. Investigation on the morphology and crystallization behavior of grafted PE chains showed that different surface patterns could be formed under various crystallization conditions. Moreover, the crystallization temperature of PE chains grafted on the surface of c‐PS microspheres was 6 °C higher than that of pure PE. The c‐PS microspheres decorated by PE chains had a better compatibility with PE matrix. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4477–4486, 2007