Bo-chao Li

Layer-by-Layer-Assembled Healable Antifouling Films

Healable antifouling films are fabricated by the exponential layer-by-layer assembly of PEGylated branched poly(ethylenimine) and hyaluronic acid followed by post-crosslinking. The antifouling function originates from the grafted PEG and the extremely soft nature of the films. The rapid and multiple healing of damaged antifouling functions caused by cuts and scratches can be readily achieved by immersing the films in normal saline solution.

Direct Adhesion of Endothelial Cells to Bioinspired Poly(dopamine) Coating Through Endogenous Fibronectin and Integrin α5β1

Mussel-inspired poly(dopamine) (PDA) coating is proven to be a simple, versatile, and effective strategy to promote cell adhesion onto various substrates. In this study, the initial adhesive behavior of human umbilical vein endothelial cells (HUVECs) is evaluated on a PDA coating under serum-free conditions. It is found that HUVECs can attach directly to and spread with well-organized cytoskeleton and fibrillar adhesions on the PDA surface, whereas cells adhere poorly to and barely spread on the control polycaprolactone surface. Endogenous fibronectin and α5 β1 integrin are found to be involved in the cell adhesion process. These findings will lead to a better understanding of interactions between cells and PDA coating, paving the way for the further development of PDA.

Substrate Stiffness Combined with Hepatocyte Growth Factor Modulates Endothelial Cell Behavior

Endothelial cells (ECs) play a crucial role in regulating various physiological and pathological processes. The behavior of ECs is modulated by physical (e.g., substrate stiffness) and biochemical cues (e.g., growth factors). However, the synergistic influence of these cues on EC behavior has rarely been investigated. In this study, we constructed poly(l-lysine)/hyaluronan (PLL/HA) multilayer films with different stiffness and exposed ECs to these substrates with and without hepatocyte growth factor (HGF)-supplemented culture medium. We demonstrated that EC adhesion, migration, and proliferation were positively correlated with substrate stiffness and that these behaviors were further promoted by HGF. Interestingly, ECs on the lower stiffness substrates showed stronger responses to HGF in terms of migration and proliferation, suggesting that HGF can profoundly influence stiffness-dependent EC behavior correlated with EC growth. After the formation of an EC monolayer, EC behaviors correlated with endothelial function were evaluated by characterizing monolayer integrity, nitric oxide production, and gene expression of endothelial nitric oxide synthase. For the first time, we demonstrated that endothelial function displayed a negative correlation with substrate stiffness. Although HGF improved endothelial function, HGF was not able to change the stiffness-dependent manner of endothelial functions. Taken together, this study provides insights into the synergetic influence of physical and biochemical cues on EC behavior and offers great potential in the development of optimized biomaterials for EC-based regenerative medicine.

Dynamic stiffness of polyelectrolyte multilayer films based on disulfide bonds for in situ control of cell adhesion

The stiffness of the substrates has been found to have a strong effect on cell behaviors, especially on cell adhesion, which is the first cellular event when cells contact materials. Much effort has been made to develop the materials with controlled stiffness for regulating cell adhesion. However, most available strategies for controlling the stiffness of material surfaces are generally limited to be static, which means that the stiffness is fixed during cell adhesion. Herein, we developed polyelectrolyte multilayer films (PEMs), and their stiffness can be dynamically modulated by mild stimuli. The PEMs were made by alternative deposition of poly-l-lysine (PLL) and thiol group modified hyaluronan (HA-SH) using the layer-by-layer assembly technique. The (PLL/HA-SH) multilayers can be cross-linked via oxidation of thiol groups. After crosslinking, the stiffness was increased and the adhesion of fibroblast cells was promoted. The stiffness of the multilayer films can be down-regulated dynamically by adding glutathione (GSH) in the medium, leading to in situ reduction of cell adhesion. Our study provides a promising strategy for the development of material surfaces with dynamically changeable stiffness, which is of great potential in the field of cell-based biomaterials.

Stiffness of polyelectrolyte multilayer film influences endothelial function of endothelial cell monolayer

Endothelialization has proved to be critical for maintaining long-term success of implantable vascular devices. The formation of monolayer of endothelial cells (ECs) on the implant surfaces is one of the most important factors for the endothelialization. However, endothelial function of regenerated EC monolayer, which plays a much more important role in preventing the complications of post-implantation, has not received enough attention. Here, a vascular endothelial growth factor (VEGF)-incorporated poly(l-lysine)/hyaluronan (PLL/HA) polyelectrolyte multilayer film was fabricated. Through varying the crosslinking degree, stiffness of the film was manipulated, offering either soft or stiff film. We demonstrated that ECs were able to adhere and proliferate on both soft and stiff films, subsequently forming an integrated EC monolayer. Furthermore, endothelial functions were evaluated by characterizing EC monolayer integrity, expression of genes correlated with the endothelial functions, and nitric oxide production. It demonstrated that EC monolayer on the soft film displayed higher endothelial function compared to that on the stiff film. Our study highlights the influence of substrate stiffness on endothelial function, which offers a new criterion for surface design of vascular implants.

Improved Endothelial Function of Endothelial Cell Monolayer on the Soft Polyelectrolyte Multilayer Film with Matrix-Bound Vascular Endothelial Growth Factor.

Endothelialization on the vascular implants is of great importance for prevention of undesired postimplantation symptoms. However, endothelial dysfunction of regenerated endothelial cell (EC) monolayer has been frequently observed, leading to severe complications, such as neointimal hyperplasia, late thrombosis, and neoatherosclerosis. It has significantly impeded long-term success of the therapy. So far, very little attention has been paid on endothelial function of EC monolayer. Bioinspired by the microenvironment of the endothelium in a blood vessel, this study described a soft polyelectrolyte multilayer film (PEM) through layer-by-layer assembly of poly(l-lysine) (PLL) and hyaluronan (HA). The (PLL/HA) PEM was chemically cross-linked and further incorporated with vascular endothelial growth factor. It demonstrated that this approach could promote EC adhesion and proliferation, further inducing formation of EC monolayer. Further, improved endothelial function of the EC monolayer was achieved as shown with the tighter integrity, higher production of nitric oxide, and expression level of endothelial function related genes, compared to EC monolayers on traditional substrates with high stiffness (e.g., glass, tissue culture polystyrene, and stainless steel). Our findings highlighted the influence of substrate stiffness on endothelial function of EC monolayer, giving a new strategy in the surface design of vascular implants.

Substrate-mediated delivery of gene complex nanoparticles via polydopamine coating for enhancing competitiveness of endothelial cells

Substrate-mediated delivery of functional plasmid DNA (pDNA) has been proven to be a promising strategy to promote competitiveness of endothelial cells (ECs) over smooth muscle cells (SMCs), which is beneficial to inducing fast endothelialization of implanted vascular devices. Thus, it is of great importance to develop universal approaches with simplicity and easiness to immobilize DNA complex nanoparticles on substrates. In this study, the bioinspired polydopamine (PDA) coating was employed in immobilization of DNA complex nanoparticles, which were composed of protamine (PrS) and plasmid DNA encoding with hepatocyte growth factor (HGF-pDNA) gene. We demonstrated that the DNA complex nanoparticles can be successfully immobilized onto the PDA surface. Consequently, the HGF expression of both ECs and SMCs were significantly improved when they cultured on the DNA complex nanoparticles-immobilized substrates. Furthermore, EC proliferation was specifically promoted due to bioactivity of HGF, leading to an enhancement of EC competitiveness over SMCs. Our findings demonstrated the substrate-mediated functional gene nanoparticle delivery through PDA coating as a simple and efficient approach. It may hold great potential in the field of interventional cardiovascular implants.

Mechanical Adaptability of the MMP-Responsive Film Improves the Functionality of Endothelial Cell Monolayer

&NA; Extracellular matrix and cells are inherent in coordinating and adapting to each other during all physiological and pathological processes. Synthetic materials, however, show rarely reciprocal and spatiotemporal responses to cells, and lacking self‐adapting properties as well. Here, a mechanical adaptability based on the matrix metalloproteinase (MMPs) sensitive polyelectrolyte film is reported. Poly‐lysine (PLL) and methacrylated hyaluronic acid (HA‐MA) nanolayers are employed to build the thin film through the layer‐by‐layer assembly, and it is further crosslinked using MMP sensitive peptides, which endows the films with changeable mechanical properties in response to MMPs. It is demonstrated that stiffness of the (PLL/HA‐MA) films increases with the crosslinking, and then decreases in response to a treatment of enzyme. Consequently, the crosslinked (PLL/HA‐MA) films reveal effective growth of endothelial cells (ECs), leading to fast formation of EC monolayer. Importantly, significantly improved endothelial function of the EC monolayer, which is characterized by integrity, biomolecules release, expression of function related gene, and antithrombotic properties, is achieved along with the decrosslinking of the film because of EC‐secreted MMPs. These results suggest that mechanical adaptability of substrate in Youngs modulus plays a significant role in endothelial progression, which shows great application potential in tissue engineering, regenerative medicine, and organ‐on‐a‐chip.