Role of Driving Force on Engineering Layer-by-Layer Protein/Polyphenol Coating with Flexible Structures and Properties.

Protein-based coatings are of immense interest due to their rich biological functions. Layer-by-layer (LbL) assembly, as a powerful means of transferring protein functions to the material surface, has received widespread attention. However, the assembly mechanism of protein-based LbL coatings is still far from being explained, not only because of protein structure and function diversity but also characterization limitations. Herein, we monitored in situ the LbL assembly process of tannic acid (TA) and lysozyme (Lyz), a classic pair of polyphenol and protein, by combining quartz crystal microbalance with dissipation monitoring (QCM-D) and spectroscopic ellipsometry (SE). The water content, morphology, mechanical properties, antioxidant activity, and the driving force of TA-Lyz coating engineered under different pH values were analyzed in detail by various techniques. The water content, a key factor in TA-Lyz coatings, increased with increasing assembled pH values, which resulted in a porous morphology, inhomogeneous mechanical distribution, faster assembly growth, and better antioxidant activity in both acellular and cellular levels. In addition, high water content is unfavorable to both entropy and enthalpy changes, and the thermodynamic driving force of TA and Lyz assembly mainly comes from the enthalpy change brought by the noncovalent interaction between TA and Lyz. These results provide new insights into engineering the structure, function, and assembly mechanisms of protein-based coatings.

Layer-by-layer assembly of procyanidin and collagen promotes mesenchymal stem cell proliferation and osteogenic differentiation in vitro and in vivo.

Collagen, commonly used in tissue engineering, is widespread in various tissues. During bone tissue regeneration, collagen can stimulate the cellular response and determine the fate of cells. In this work, we integrated collagen type II with procyanidin (PC) onto an implant coating by applying a layer-by-layer technique to demonstrate that collagen and PC can participate in the construction of new biomaterials and serve as multifunctional components. The effects of PC/collagen multilayers on the viability of cocultured bone marrow mesenchymal stem cells (BMSCs) were analyzed by cell counting kit-8 analysis and phalloidin staining. The reactive oxygen species level of BMSCs was revealed through immunofluorescent staining and flow cytometry. Osteogenesis-related genes were detected, and in vivo experiment was performed to reveal the effect of newly designed material on the osteogenic differentiation of BMSCs. Our data demonstrated that in BMSCs PC/collagen multilayers accelerated the proliferation and osteogenic differentiation through Wnt/ß-catenin signaling pathway and enhanced bone generation around the implant in the bone defect model of rabbit femurs. In summary, combination of collagen and PC provided a new sight for the research and development of implant materials or coatings in the future.

Engineering a mucin coating to promote osteogenic differentiation of BMSCs in vitro and bone formation in vivo through the Wnt/ß-catenin pathway.

Mucin, a family of glycoproteins, is widespread in the inner linings of various lumen organs and plays key roles in protecting epithelial cells from invasion by foreign species and communicating with the external environment. Here, we demonstrated that Mucin could be engineered as a promising building block in biomaterials with unexpected multifunctionalities by codepositing with procyanidin (PC, a kind of flavanol polyphenol) through a layer-by-layer technique. The process of generating PC/Mucin multilayers was well characterized and monitored, which was controllable by the assembly conditions. The behaviors of bone marrow mesenchymal stem cells (BMSCs), including proliferation, antioxidant ability, and expression of vinculin, were investigated to reveal the role of PC/Mucin multilayers on the osteogenic differentiation of BMSCs. Our data showed that PC/Mucin multilayers promoted osteogenesis-related genes (Col1, ON, OCN and RUNX2) in BMSCs in vitro and bone generation in vivo by activating the Wnt/ß-catenin pathway. These findings demonstrate that engineering Mucin might be a new route in the future to implant materials or coatings for bone regeneration.

Universal Strategy to Efficiently Coat Zeolitic Imidazolate Frameworks onto Diverse Substrates.

Anchoring metal-organic framework (MOF) coating has attracted extensive interest due to its wide applications in drug delivery, gas storage and separation, catalysis, and so forth. Here, we reported a flexible strategy on generating ZIF-8 coatings onto diverse substrates in the scale up to hundreds cm2, independent of the geometry of the substrate, with controllable thickness, texture structure, and crystal size of coating. By understanding the mechanism and factors on the formation of ZIF-8 coatings, various zeolitic imidazolate framework coatings were successfully produced. This general strategy and in-depth insights pave the new highway to the design and synthesis of MOF coatings onto diverse substrates.

Material priority engineered metal-polyphenol networks: mechanism and platform for multifunctionalities.

Engineering the surface of materials with desired multifunctionalities is an effective way to fight against multiple adverse factors during tissue repair process. Recently, metal-polyphenol networks (MPNs) have gained increasing attention because of their rapid and simple deposition process onto various substrates (silicon, quartz, gold and polypropylene sheets, etc.). However, the coating mechanism has not been clarified, and multifunctionalized MPNs remain unexplored. Herein, the flavonoid polyphenol procyanidin (PC) was selected to form PC-MPN coatings with Fe3+, and the effects of different assembly parameters, including pH, molar ratio between PC and Fe3+, and material priority during coating formation, were thoroughly evaluated. We found that the material priority (addition sequence of PC and Fe3+) had a great influence on the thickness of the formed PC-MPNs. Various surface techniques (e.g., ultraviolet-visible spectrophotometry, quartz crystal microbalance, X-ray photoelectron spectroscopy, atomic force microscopy, and scanning electron microscopy) were used to investigate the formation mechanism of PC-MPNs. Then PC-MPNs were further engineered with multifunctionalities (fastening cellular attachment in the early stage, promoting long-term cellular proliferation, antioxidation and antibacterial activity). We believe that these findings could further reveal the coating formation mechanism of MPNs and guide the future design of MPN coatings with multifunctionalities, thereby greatly broadening their application prospects, such as in sensors, environments, drug delivery, and tissue engineering.

Secondary Structure-Dominated Layer-by-Layer Growth Mode of Protein Coatings.

Benefiting from the luxury functions of proteins, protein coatings have been extended to various applications, including tissue engineering scaffolds, drug delivery, antimicrobials, sensing and diagnostic equipment, food packaging, etc. Fast construction of protein coatings is always interesting to materials science and significant to industrialization. Here, we report a layer-by-layer (LbL) multilayer-constructed coating of tannic acid (TA) and lysozyme (Lyz), in which the secondary conformations of Lyz dominate the growth rate of the TA/Lyz coating. As well characterized by various techniques (quartz crystal microbalance with dissipation (QCM-D), circular dichroism (CD) spectra, Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), contact angle, etc.), TA-induced conformational transition of Lyz to α-helices occurs at pH 8 from other secondary structures (ß-sheets, ß-turns, and random coils), which leads to the very fast growth of TA/Lyz with a number of deposited bilayers, with thicknesses of more than 90 nm for six bilayers. In contrast to the leading conformation of α-helices at pH 8, Lyz displayed multiple conformations (α-helices, ß-sheets, ß-turns, and random coils) at pH 6, which resulted in coating thicknesses of less than 30 nm for six bilayers. By the addition of NaCl, Tween 20, and urea, we further confirmed that the secondary conformations of Lyz relied greatly on the interactions between TA and Lyz and dominated the growth rate of the multilayers. We believe that these findings will help to understand the transformation of secondary conformations by TA or other polyphenols and inspire a new route to quickly build protein coatings.

Silanization of a Metal-Polyphenol Coating onto Diverse Substrates as a Strategy for Controllable Wettability with Enhanced Performance to Resist Acid Corrosion.

Wettability is a crucial characteristic of materials that plays a vital role in surface engineering. Surface modification is the key to changing the wettability of materials, and a simple and universal modification approach is being extensively pursued by researchers. Recently, metal-phenolic networks (MPNs) have been widely studied because they impart versatility and functionality in surface modification. However, an MPN is not stable for long periods, especially under acidic conditions, and is susceptible to pollution by invasive species. Spurred by the versatility of MPNs and various functionalities achieved by silanization, we introduce a general strategy to fabricate functionally stable coatings with controllable surface wettability by combining the two methods. The formation process of MPN and silane-MPN coatings was characterized by spectroscopic ellipsometry (SE), UV-visible-near-infrared (UV-vis-NIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), water contact angle (WCA), etc. We found that the stability of the MPN was greatly enhanced after silanization, which is attributed to the cross-linking effect that occurs between silane and the MPN, namely, the cross-linking protection produced in this case. Additionally, the wettability of an MPN can be easily changed through our strategy. We trust that our strategy can further extend the applications of MPNs and points toward potential prospects in surface modification.

Medical Applications Based on Supramolecular Self-Assembled Materials From Tannic Acid.

Polyphenol, characterized by various phenolic rings in the chemical structure and an abundance in nature, can be extracted from vegetables, grains, chocolates, fruits, tea, legumes, and seeds, among other sources. Tannic acid (TA), a classical polyphenol with a specific chemical structure, has been widely used in biomedicine because of its outstanding biocompatibility and antibacterial and antioxidant properties. TA has tunable interactions with various materials that are widely distributed in the body, such as proteins, polysaccharides, and glycoproteins, through multimodes including hydrogen bonding, hydrophobic interactions, and charge interactions, assisting TA as important building blocks in the supramolecular self-assembled materials. This review summarizes the recent immense progress in supramolecular self-assembled materials using TA as building blocks to generate different materials such as hydrogels, nanoparticles/microparticles, hollow capsules, and coating films, with enormous potential medical applications including drug delivery, tumor diagnosis and treatment, bone tissue engineering, biofunctional membrane material, and the treatment of certain diseases. Furthermore, we discuss the challenges and developmental prospects of supramolecular self-assembly nanomaterials based on TA.