Direct Adhesion of Endothelial Cells to Bioinspired Poly(dopamine) Coating Through Endogenous Fibronectin and Integrin α5 β1

Preparation and Immobilization Mechanism on a Novel Composite Carrier PDA-CF/PUF to Improve Cells Immobilization and Xylitol Production

The preparation of a novel composite carrier of polydopamine-modified carbon fiber/polyurethane foam (PDA-CF/PUF) was proposed to improve cell immobilization and the fermentation of xylitol, which is an important food sweetener and multifunctional food additive. Candida tropicalis was immobilized on the composite carrier by adsorption and covalent binding. The properties and immobilization mechanism of the composite carrier and its effect on immobilized cells were investigated. It showed that the modification of PDA enhanced the loading of CF on the PUF surface and the adhesion of cells on the composite carrier surface. Also, the biocompatibility of carriers to cells was improved. In addition, the introduction of PDA increased the active groups on the surface of the carrier, enhanced the hydrophilicity, promoted the cells immobilization, and increased the xylitol yield. It was also found that expression of the related gene XYL1 in cells was significantly increased after the immobilization of the PDA-CF/PUF composite carrier during the fermentation. The PDA-CF/PUF was an immobilized carrier with the excellent biocompatibility and immobilization performance, which has great development potential in the industrial production of xylitol.

Bovine serum albumin-modified 3D printed alginate dialdehyde-gelatin scaffolds incorporating polydopamine/SiO2-CaO nanoparticles for bone regeneration

Three-dimensional (3D) printing allows precise manufacturing of bone scaffolds for patient-specific applications and is one of the most recently developed and implemented technologies. In this study, bilayer and multimaterial alginate dialdehyde-gelatin (ADA-GEL) scaffolds incorporating polydopamine (PDA)/SiO2-CaO nanoparticle complexes were 3D printed using a pneumatic extrusion-based 3D printing technology and further modified on the surface with bovine serum albumin (BSA) for application in bone regeneration. The morphology, chemistry, and in vitro bioactivity of PDA/SiO2-CaO nanoparticle complexes were characterized (n = 3) and compared with those of mesoporous SiO2-CaO nanoparticles. Successful deposition of the PDA layer on the surface of the SiO2-CaO nanoparticles allowed better dispersion in a liquid medium and showed enhanced bioactivity. Rheological studies (n = 3) of ADA-GEL inks consisting of PDA/SiO2-CaO nanoparticle complexes showed results that may indicate better injectability and printability behavior compared to ADA-GEL inks incorporating unmodified nanoparticles. Microscopic observations of 3D printed scaffolds revealed that PDA/SiO2-CaO nanoparticle complexes introduced additional topography onto the surface of 3D printed scaffolds. Additionally, the modified scaffolds were mechanically stable and elastic, closely mimicking the properties of natural bone. Furthermore, protein-coated bilayer scaffolds displayed controllable absorption and biodegradation, enhanced bioactivity, MC3T3-E1 cell adhesion, proliferation, and higher alkaline phosphatase (ALP) activity (n = 3) compared to unmodified scaffolds. Consequently, the present results confirm that ADA-GEL scaffolds incorporating PDA/SiO2-CaO nanoparticle complexes modified with BSA offer a promising approach for bone regeneration applications.

Development and Future Trends of Protective Strategies for Magnesium Alloy Vascular Stents

Magnesium alloy stents have been extensively studied in the field of biodegradable metal stents due to their exceptional biocompatibility, biodegradability and excellent biomechanical properties. Nevertheless, the specific in vivo service environment causes magnesium alloy stents to degrade rapidly and fail to provide sufficient support for a certain time. Compared to previous reviews, this paper focuses on presenting an overview of the development history, the key issues, mechanistic analysis, traditional protection strategies and new directions and protection strategies for magnesium alloy stents. Alloying, optimizing stent design and preparing coatings have improved the corrosion resistance of magnesium alloy stents. Based on the corrosion mechanism of magnesium alloy stents, as well as their deformation during use and environmental characteristics, we present some novel strategies aimed at reducing the degradation rate of magnesium alloys and enhancing the comprehensive performance of magnesium alloy stents. These strategies include adapting coatings for the deformation of the stents, preparing rapid endothelialization coatings to enhance the service environment of the stents, and constructing coatings with self-healing functions. It is hoped that this review can help readers understand the development of magnesium alloy cardiovascular stents and solve the problems related to magnesium alloy stents in clinical applications at the early implantation stage.

Mechanomorphological Guidance of Colloidal Gel Regulates Cell Morphogenesis

Microstructural morphology of the extracellular matrix guides the organization of cells in 3D. However, current biomaterials-based matrices cannot provide distinct spatial cues through their microstructural morphology due to design constraints. To address this, colloidal gels are developed as 3D matrices with distinct microstructure by aggregating ionic polyurethane colloids via electrostatic screening. Due to the defined orientation of interconnected particles, positively charged colloids form extended strands resulting in a dense microstructure whereas negatively charged colloids form compact aggregates with localized large voids. Chondrogenesis of human mesenchymal stem cells (MSCs) and endothelial morphogenesis of human endothelial cells (ECs) are examined in these colloidal gels. MSCs show enhanced chondrogenic response in dense colloidal gel due to their spatial organization achieved by balancing the cell-cell and cell-matrix interactions compared to porous gels where cells are mainly clustered. ECs tend to form relatively elongated cellular networks in dense colloidal gel compared to porous gels. Additionally, the role of matrix stiffness and viscoelasticity in the morphogenesis of MSCs and ECs are analyzed with respect to microstructural morphology. Overall, these results demonstrate that colloidal gels can provide spatial cues through their microstructural morphology and in correlation with matrix mechanics for cell morphogenesis.

A versatile and tunable bio-patterning platform for the construction of various cell array biochips

In this work, we report a versatile and tunable platform for the construction of various cell array biochips using a simple soft lithographic approach to pattern polydopamine (PDA) arrays via microcontact printing (μCP). Instead of direct polymerization of PDA on the polydimethylsiloxane (PDMS) tips, dopamine monomers were first printed on the substrate followed by a self-oxidative polymerization step facilitated by ammonia vapor to grow PDA in situ, which greatly reduced the reaction time and prevented the PDMS tips from damaging. The improved robustness and utility of the PDMS tips allows the formation of tunable PDA array chips with controllable PDA feature size and shape. As a result, single cell, multi-cells and cell line arrays can be constructed. The obtained cell array chips showed high single cell capture efficiency, providing a standardized single cell array analysis platform. Meanwhile, the adhered cells can maintain excellent viability and proliferation ability on the PDA chips. Moreover, a cytotoxicity sensor with single cell resolution was enabled on the single cell array chip. This work provides a promising cell array biochip platform for high-throughput cellular analysis and cell screening.

Alginate-based biomaterial-mediated regulation of macrophages in bone tissue engineering

Many studies in the bone tissue engineering field have focused on the interactions between materials and bone marrow stem cells. With the development of osteoimmunology, the immune cells' essential role in biomaterial-mediated osteogenesis has increasingly been recognized. As a promising therapeutic candidate for bone defects due to their prominent biocompatibility, tuneability, and versatility, it is necessary to develop alginate-based biomaterials that can regulate immune cells, especially macrophages. Moreover, modified alginate-based biomaterials may facilitate better regulation of macrophage phenotypes by the newly endowed physicochemical properties, including stiffness, porosity, hydrophilicity, and electrical properties. This review summarizes the role of macrophages in bone regeneration and the recent research progress related to the effects of alginate-based biomaterials on macrophages applied in bone tissue engineering. This review also emphasizes the strategies adopted by material design to regulate macrophage phenotypes, the corresponding macrophage responses, and their contribution to osteogenesis.

Polydopamine Incorporation Enhances Cell Differentiation and Antibacterial Properties of 3D-Printed Guanosine-Borate Hydrogels for Functional Tissue Regeneration

Tissue engineering focuses on the development of materials as biosubstitutes that can be used to regenerate, repair, or replace damaged tissues. Alongside this, 3D printing has emerged as a promising technique for producing implants tailored to specific defects, which in turn increased the demand for new inks and bioinks. Especially supramolecular hydrogels based on nucleosides such as guanosine have gained increasing attention due to their biocompatibility, good mechanical characteristics, tunable and reversible properties, and intrinsic self-healing capabilities. However, most existing formulations exhibit insufficient stability, biological activity, or printability. To address these limitations, we incorporated polydopamine (PDA) into guanosine-borate (GB) hydrogels and developed a PGB hydrogel with maximal PDA incorporation and good thixotropic and printability qualities. The resulting PGB hydrogels exhibited a well-defined nanofibrillar network, and we found that PDA incorporation increased the hydrogel's osteogenic activity while having no negative effect on mammalian cell survival or migration. In contrast, antimicrobial activity was observed against the Gram-positive bacteria Staphylococcus aureus and Staphylococcus epidermidis. Thus, our findings suggest that our PGB hydrogel represents a significantly improved candidate as a 3D-printed scaffold capable of sustaining living cells, which may be further functionalized by incorporating other bioactive molecules for enhanced tissue integration.

Polydopamine-mediated graphene oxide and nanohydroxyapatite-incorporated conductive scaffold with an immunomodulatory ability accelerates periodontal bone regeneration in diabetes

Regenerating periodontal bone tissues in the aggravated inflammatory periodontal microenvironment under diabetic conditions is a great challenge. Here, a polydopamine-mediated graphene oxide (PGO) and hydroxyapatite nanoparticle (PHA)-incorporated conductive alginate/gelatin (AG) scaffold is developed to accelerate periodontal bone regeneration by modulating the diabetic inflammatory microenvironment. PHA confers the scaffold with osteoinductivity and PGO provides a conductive pathway for the scaffold. The conductive scaffold promotes bone regeneration by transferring endogenous electrical signals to cells and activating Ca²⁺ channels. Moreover, the scaffold with polydopamine-mediated nanomaterials has a reactive oxygen species (ROS)-scavenging ability and anti-inflammatory activity. It also exhibits an immunomodulatory ability that suppresses M1 macrophage polarization and activates M2 macrophages to secrete osteogenesis-related cytokines by mediating glycolytic and RhoA/ROCK pathways in macrophages. The scaffold induces excellent bone regeneration in periodontal bone defects of diabetic rats because of the synergistic effects of good conductive, ROS-scavenging, anti-inflammatory, and immunomodulatory abilities. This study provides fundamental insights into the synergistical effects of conductivity, osteoinductivity, and immunomodulatory abilities on bone regeneration and offers a novel strategy to design immunomodulatory biomaterials for treatment of immune-related diseases and tissue regeneration.

•

The conductive PGO-PHA-AG scaffold can activate Ca²⁺ channels.

•The PGO-PHA-AG scaffold had ROS-scavenging and anti-inflammatory activities.

•The scaffold exhibited an immunomodulatory ability.

•The scaffold induced excellent periodontal bone regeneration in diabetes.

Stretchable and Electroactive Crosslinked Gelatin for Biodevice and Cell Culture Applications

Biomimetic substrates that incorporate functionality such as electroactivity and mechanical flexibility, find utility in a variety of biomedical applications. Toward these uses, nature-derived materials such as gelatin offer inherent biocompatibility and sustainable sourcing. However, issues such as high swelling, poor mechanical properties, and lack of stability at biological temperatures limit their use. The enzymatic crosslinking of gelatin via microbial transglutaminase (mTG) yields flexible and robust large area substrates that are stable under physiological conditions. Here, we demonstrate the fabrication and characterization of strong, stretchable, conductive mTG crosslinked gelatin thin films. Incorporation of the conductive polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate in the gel matrix with a bioinspired polydopamine surface coating is used to enable conductivity with enhanced mechanical properties such as extensibility and flexibility, in comparison to plain gelatin or crosslinked gelatin films. The electroconductive substrates are conducive to cell growth, supporting myoblast cell adhesion, viability, and proliferation and could find use in creating active cell culture systems incorporating electrical stimulation. The substrates are responsive to motion such as stretching and bending while being extremely handleable and elastic, making them useful for applications such as electronic skin and flexible bioelectronics. Overall, this work presents facile, yet effective development of bioinspired conductive composites as substrates for bio-integrated devices and functional tissue engineering.

Mussel-inspired polydopamine decorated alginate dialdehyde-gelatin 3D printed scaffolds for bone tissue engineering application

This study utilized extrusion-based 3D printing technology to fabricate calcium-cross-linked alginate dialdehyde-gelatin scaffolds for bone regeneration. The surface of polymeric constructs was modified with mussel-derived polydopamine (PDA) in order to induce biomineralization, increase hydrophilicity, and enhance cell interactions. Microscopic observations revealed that the PDA layer homogeneously coated the surface and did not appear to induce any distinct change in the microstructure of the scaffolds. The PDA-functionalized scaffolds were more mechanically stable (compression strength of 0.69 ± 0.02 MPa) and hydrophilic (contact angle of 26) than non-modified scaffolds. PDA-decorated ADA-GEL scaffolds demonstrated greater durability. As result of the 18-days immersion in simulated body fluid solution, the PDA-coated scaffolds showed satisfactory biomineralization. Based on theoretical energy analysis, it was shown that the scaffolds coated with PDA interact spontaneously with osteocalcin and osteomodulin (binding energy values of −35.95 kJ mol⁻¹ and −46.39 kJ mol⁻¹, respectively), resulting in the formation of a protein layer on the surface, suggesting applications in bone repair. PDA-coated ADA-GEL scaffolds are capable of supporting osteosarcoma MG-63 cell adhesion, viability (140.18% after 7 days), and proliferation. In addition to increased alkaline phosphatase secretion, osteoimage intensity also increased, indicating that the scaffolds could potentially induce bone regeneration. As a consequence, the present results confirm that 3D printed PDA-coated scaffolds constitute an intriguing novel approach for bone tissue engineering.

Polydopamine Biomaterials for Skin Regeneration

Designing biomaterials capable of biomimicking wound healing and skin regeneration has been receiving increasing attention recently. Some biopolymers behave similarly to the extracellular matrix (ECM), supporting biointerfacial adhesion and intrinsic cellular interactions. Polydopamine (PDA) is a natural bioadhesive and bioactive polymer that endows high chemical versatility, making it an exciting candidate for a wide range of biomedical applications. Moreover, biomaterials based on PDA and its derivatives have near-infrared (NIR) absorption, excellent biocompatibility, intrinsic antioxidative activity, antibacterial activity, and cell affinity. PDA can regulate cell behavior by controlling signal transduction pathways. It governs the focal adhesion behavior of cells at the biomaterials interface. These features make melanin-like PDA a fascinating biomaterial for wound healing and skin regeneration. This paper overviews PDA-based biomaterials' synthesis, properties, and interactions with biological entities. Furthermore, the utilization of PDA nano- and microstructures as a constituent of wound-dressing formulations is highlighted.

Optimization of a PDMS-Based Cell Culture Substrate for High-Density Human-Induced Pluripotent Stem Cell Adhesion and Long-Term Differentiation into Cardiomyocytes under a Xeno-Free Condition

Despite the numerous advantages of PDMS-based substrates in various biomedical applications, they are limited by their highly hydrophobic surface that does not optimally interact with cells for attachment and growth. Hence, the lack of lengthy and straightforward procedures for high-density cell production on the PDMS-based substrate is one of the significant challenges in cell production in the cell therapy field. In this study, we found that the PDMS substrate coated with a combination of polydopamine (PDA) and laminin-511 E8 fragments (PDA + LME8-coated PDMS) can support human-induced pluripotent stem cell (hiPSC) attachment and growth for the long term and satisfy their demands of differentiation into cardiomyocytes (iCMs). Compared with prior studies, the density of hiPSCs and their adhesion time on the PDMS surface were increased during iCM production. Although the differentiated iCMs beat and produce mechanical forces, which disturb cellular attachments, the iCMs on the PDA + LME8-coated PDMS substrate showed dramatically better attachment than the control condition. Further, the substrate required less manipulation by enabling one-step seeding throughout the process in iCM formation from hiPSCs under animal-free conditions. In light of the results achieved, the PDA + LME8-coated PDMS substrate will be an up-and-coming tool for cardiomyocyte production for cell therapy and tissue engineering, microfluidics, and organ-on-chip platforms.

A Facile and Scalable Hydrogel Patterning Method for Microfluidic 3D Cell Culture and Spheroid-in-Gel Culture Array

Incorporation of extracellular matrix (ECM) and hydrogel in microfluidic 3D cell culture platforms is important to create a physiological microenvironment for cell morphogenesis and to establish 3D co-culture models by hydrogel compartmentalization. Here, we describe a simple and scalable ECM patterning method for microfluidic cell cultures by achieving hydrogel confinement due to the geometrical expansion of channel heights (stepped height features) and capillary burst valve (CBV) effects. We first demonstrate a sequential "pillar-free" hydrogel patterning to form adjacent hydrogel lanes in enclosed microfluidic devices, which can be further multiplexed with one to two stepped height features. Next, we developed a novel "spheroid-in-gel" culture device that integrates (1) an on-chip hanging drop spheroid culture and (2) a single "press-on" hydrogel confinement step for rapid ECM patterning in an open-channel microarray format. The initial formation of breast cancer (MCF-7) spheroids was achieved by hanging a drop culture on a patterned polydimethylsiloxane (PDMS) substrate. Single spheroids were then directly encapsulated on-chip in individual hydrogel islands at the same positions, thus, eliminating any manual spheroid handling and transferring steps. As a proof-of-concept to perform a spheroid co-culture, endothelial cell layer (HUVEC) was formed surrounding the spheroid-containing ECM region for drug testing studies. Overall, this developed stepped height-based hydrogel patterning method is simple to use in either enclosed microchannels or open surfaces and can be readily adapted for in-gel cultures of larger 3D cellular spheroids or microtissues.

Rational Design of Thermoresponsive Microgel Templates with Polydopamine Surface Coating for Microtissue Applications

Functional microgels provide a versatile basis for synthetic in vitro platforms as alternatives to animal experiments. The tuning of the physical, chemical, and biological properties of synthetic microgels can be achieved by blending suitable polymers and formulating them such to reflect the heterogenous and complex nature of biological tissues. Based on this premise, this paper introduces the development of volume-switchable core-shell microgels as 3D templates to enable cell growth for microtissue applications, using a systematic approach to tune the microgel properties based on a deep conceptual and practical understanding. Microscopic microgel design, such as the tailoring of the microgel size and spherical shape, is achieved by droplet-based microfluidics, while on a nanoscopic scale, a thermoresponsive polymer basis, poly(N-isopropylacrylamide) (PNIPAAm), is used to provide the microgel volume switchability. Since PNIPAAm has only limited cell-growth promoting properties, the cell adhesion on the microgel is further improved by surface modification with polydopamine, which only slightly affects the microgel properties, thereby simplifying the system. To further tune the microgel thermoresponsiveness, different amounts of N-hydroxyethylacrylamide are incorporated into the PNIPAAm network. In a final step, cell growth on the microgel surface is investigated, both at a single microgel platform and in spheroidal cell structures.

Investigation of human adipose-derived stem-cell behavior using a cell-instructive polydopamine-coated gelatin-alginate hydrogel

Hydrogels can be fabricated and designed to exert direct control over stem cells' adhesion and differentiation. In this study, we have investigated the use of polydopamine (pDA)-treatment as a binding platform for bioactive compounds to create a versatile gelatin-alginate (Gel-Alg) hydrogel for tissue engineering applications. Precisely, pDA was used to modify the surface properties of the hydrogel and better control the adhesion and osteogenic differentiation of human adipose-derived stem cells (hASCs). pDA enabled the adsorption of different types of bioactive molecules, including a model osteoinductive drug (dexamethasone) as well as a model pro-angiogenic peptide (QK). The pDA treatment efficiently retained the drug and the peptide compared to the untreated hydrogel and proved to be effective in controlling the morphology, cell area, and osteogenic differentiation of hASCs. Overall, the findings of this study confirm the efficacy of pDA treatment as a valuable strategy to modulate the biological properties of biocompatible Gel-Alg hydrogels and further extend their value in regenerative medicine.

Evaluation of human umbilical vein endothelial cells growth onto heparin-modified electrospun vascular grafts

One of the main challenges of cardiovascular tissue engineering is the development of bioresorbable and compliant small-diameter vascular grafts (SDVG) for patients where autologous grafts are not an option. In this work, electrospun bilayered bioresorbable SDVG based on blends of poly(L-lactic acid) (PLLA) and segmented polyurethane (PHD) were prepared and evaluated. The inner layer of these SDVG was surface-modified with heparin, following a methodology involving PHD urethane functional groups. Heparin was selected as anticoagulant agent, and also due to its ability to promote human umbilical vein endothelial cells (HUVECs) growth and to inhibit smooth muscle cells over-proliferation, main cause of neointimal hyperplasia and restenosis. Immobilized heparin was quantified and changes in SDVG microstructure were investigated through SEM. Tensile properties of the heparin-functionalized SDVG resembled those of saphenous vein. Vascular grafts were seeded with HUVECs and cultured on a flow-perfusion bioreactor to analyze the effect of heparin on graft endothelization under simulated physiological-like conditions. The analysis of endothelial cells attachment and gene expression (Real-Time PCR) pointed out that the surface functionalization with heparin successfully promoted a stable and functional endothelial cell layer.

Surface Modification of PDMS-Based Microfluidic Devices with Collagen Using Polydopamine as a Spacer to Enhance Primary Human Bronchial Epithelial Cell Adhesion

Polydimethylsiloxane (PDMS) is a silicone-based synthetic material used in various biomedical applications due to its properties, including transparency, flexibility, permeability to gases, and ease of use. Though PDMS facilitates and assists the fabrication of complicated geometries at micro- and nano-scales, it does not optimally interact with cells for adherence and proliferation. Various strategies have been proposed to render PDMS to enhance cell attachment. The majority of these surface modification techniques have been offered for a static cell culture system. However, dynamic cell culture systems such as organ-on-a-chip devices are demanding platforms that recapitulate a living tissue microenvironment's complexity. In organ-on-a-chip platforms, PDMS surfaces are usually coated by extracellular matrix (ECM) proteins, which occur as a result of a physical and weak bonding between PDMS and ECM proteins, and this binding can be degraded when it is exposed to shear stresses. This work reports static and dynamic coating methods to covalently bind collagen within a PDMS-based microfluidic device using polydopamine (PDA). These coating methods were evaluated using water contact angle measurement and atomic force microscopy (AFM) to optimize coating conditions. The biocompatibility of collagen-coated PDMS devices was assessed by culturing primary human bronchial epithelial cells (HBECs) in microfluidic devices. It was shown that both PDA coating methods could be used to bind collagen, thereby improving cell adhesion (approximately three times higher) without showing any discernible difference in cell attachment between these two methods. These results suggested that such a surface modification can help coat extracellular matrix protein onto PDMS-based microfluidic devices.

Poly-dopamine, poly-levodopa, and poly-norepinephrine coatings: Comparison of physico-chemical and biological properties with focus on the application for blood-contacting devices

Thanks to its simplicity, versatility, and secondary reactivity, dopamine self-polymerized coatings (pDA) have been widely used in surface modification of biomaterials, but the limitation in secondary molecular grafting and the high roughness restrain their application in some special scenarios. Therefore, some other catecholamine coatings analog to pDA have attracted more and more attention, including the smoother poly-norepinephrine coating (pNE), and the poly-levodopa coating (pLD) containing additional carboxyl groups. However, the lack of a systematic comparison of the properties, especially the biological properties of the above three catecholamine coatings, makes it difficult to give a guiding opinion on the application scenarios of different coatings. Herein, we systematically studied the physical, chemical, and biological properties of the three catecholamine coatings, and explored the feasibility of their application for the modification of biomaterials, especially cardiovascular materials. Among them, the pDA coating was the roughest, with the largest amount of amino and phenolic hydroxyl groups for molecule grafting, and induced the strongest platelet adhesion and activation. The pLD coating was the thinnest and most hydrophilic but triggered the strongest inflammatory response. The pNE coating was the smoothest, with the best hemocompatibility and histocompatibility, and with the strongest cell selectivity of promoting the proliferation of endothelial cells while inhibiting the proliferation of smooth muscle cells. To sum up, the pNE coating may be a better choice for the surface modification of cardiovascular materials, especially those for vascular stents and grafts, but it is still not widely recognized.

Superhydrophilic Polyurethane/Polydopamine Nanofibrous Materials Enhancing Cell Adhesion for Application in Tissue Engineering

The use of nanofibrous materials in the field of tissue engineering requires a fast, efficient, scalable production method and excellent wettability of the obtained materials, leading to enhanced cell adhesion. We proposed the production method of superhydrophilic nanofibrous materials in a two-step process. The process is designed to increase the wettability of resulting scaffolds and to enhance the rate of fibroblast cell adhesion. Polyurethane (PU) nanofibrous material was produced in the solution blow spinning process. Then the PU fibers surface was modified by dopamine polymerization in water solution. Two variants of the modification were examined: dopamine polymerization under atmospheric oxygen (V-I) and using sodium periodate as an oxidative agent (V-II). Hydrophobic PU materials after the treatment became highly hydrophilic, regardless of the modification variant. This effect originates from polydopamine (PDA) coating properties and nanoscale surface structures. The modification improved the mechanical properties of the materials. Materials obtained in the V-II process exhibit superior properties over those from the V-I, and require shorter modification time (less than 30 min). Modifications significantly improved fibroblasts adhesion. The cells spread after 2 h on both PDA-modified PU nanofibrous materials, which was not observed for unmodified PU. Proposed technology could be beneficial in applications like scaffolds for tissue engineering.

Bio-surface coated titanium scaffolds with cancellous bone-like biomimetic structure for enhanced bone tissue regeneration

In view of the fact that titanium (Ti)-based implants still face the problem of loosening and failure of the implants caused by the slow biological response, the low osseointegration rate and the implant bacterial infection in clinical application, we designed a cancellous bone-like biomimetic Ti scaffold using the template accumulated by sugar spheres as a pore-forming agent. And based on a modified surface mineralization process and mussel-like adhesion mechanism, a silicon-doped calcium phosphate composite coating (Van-pBNPs/pep@pSiCaP) with Vancomycin (Van)-loaded polydopamine (pDA)-modified albumin nanoparticles (Van-pBNPs) and cell adhesion peptides (GFOGER) was constructed on the surface of Ti scaffold for mimicking the extracellular matrix (ECM) microenvironment of natural bone matrix to induce greater tissue regeneration. The in vitro study demonstrated that this porous Ti scaffold with functional bio-surface could distinctly facilitate cell early adhesion and spreading, and activate the expression of α2β1 integrin receptor on the cell membrane through promoting the formation of focal adhesions (FAs) in bone marrow stromal cells (BMSCs), thus mediating greater osteogenic cell differentiation. And it could also effectively inhibit the adhesion and growth of Staphylococcus epidermidis, exhibiting good antibacterial properties. Moreover, the Van-pBNPs/pep@pSiCaP-Ti scaffolds showed enhanced in vivo bone-forming ability due to the contributions of bioactive chemical components and the natural cancellous bone-like macrostructure. This work offers a promising structural and functional bio-inspired strategy for designing metal implants with desirable ability of osteoinduction synergistically with antibacterial efficacy for promoting bone regeneration and infection prevention simultaneously. STATEMENT OF SIGNIFICANCE: This manuscript describes a new method for making porous Ti scaffolds with a natural cancellous bone-like structure. Besides, a functional bio-surface was constructed on the bionic structure, mimicking some of the functions of the collagen-rich organic matrix and inorganic CaP nanocrystallites of native ECM of bone in chemical components and biological activities. This interconnected inter-pore opening structure encouraged the migration of cells among open macro-pores within the scaffold. In addition, the functionalized surface not only improved early cell adhesion, spreading, stimulated greater osteogenic differentiation of bone-forming cells, but also endowed the scaffold with excellent antibacterial effect. The biomimetic metal implant with multiple biomedical functions designed in this study has a great clinical application potential. This study represents a feasible method for the preparation of biomimetic structure of metal implants and the improvement of their surface biological activity.

Elucidating structure–function relationships governing the interfacial response of human mesenchymal stem cells to polydopamine coatings

Deposition of mussel-inspired polydopamine (PDA) has rapidly emerged as a simple yet effective strategy to functionalize the surface of biomaterials.

Rapid and Robust Coating Method to Render Polydimethylsiloxane Surfaces Cell-Adhesive

Polydimethylsiloxane (PDMS) is a synthetic material with excellent properties for biomedical applications because of its easy fabrication method, high flexibility, permeability to oxygen, transparency, and potential to produce high-resolution structures in the case of lithography. However, PDMS needs to be modified to support homogeneous cell attachments and spreading. Even though many physical and chemical methods, like plasma treatment or extracellular matrix coatings, have been developed over the last decades to increase cell-surface interactions, these methods are still very time-consuming, often not efficient enough, complex, and can require several treatment steps. To overcome these issues, we present a novel, robust, and fast one-step PDMS coating method using engineered anchor peptides fused to the cell-adhesive peptide sequence (glycine-arginine-glycine-aspartate-serine, GRGDS). The anchor peptide attaches to the PDMS surface predominantly by hydrophobic interactions by simply dipping PDMS in a solution containing the anchor peptide, presenting the GRGDS sequence on the surface available for cell adhesion. The binding performance and kinetics of the anchor peptide to PDMS are characterized, and the coatings are optimized for efficient cell attachment of fibroblasts and endothelial cells. Additionally, the applicability is proven using PDMS-based directional nanotopographic gradients, showing a lower threshold of 5 μm wrinkles for fibroblast alignment.

Functionalization of Silk Fibroin Electrospun Scaffolds via BMSC Affinity Peptide Grafting through Oxidative Self-Polymerization of Dopamine for Bone Regeneration

Electrospun scaffolds have been broadly studied to enhance bone regeneration because of the ability to simulate the structure and biological functions of the extracellular matrix. Polydopamine (PDA) is used to coat various surfaces at a slightly basic pH (8-8.5) and spontaneously reacts with nucleophilic functional groups. It is suitable for surface modifications of scaffolds correlated with bone formation. E7 is a newly discovered peptide with specific affinity for bone marrow mesenchymal stem cells (BMSCs). It can be useful for recruiting stem cells. Here, electrospun silk fibroin (SF) scaffolds were fabricated, and PDA was used for surface modification followed by grafting E7 (SF-PDA-E7). These composite SF-PDA-E7 electrospun scaffolds improved hydrophilicity, facilitated cell proliferation and adhesion, and boosted the osteogenic differentiation of BMSCs by creating osteoinduction conditions under the synergistic effects of PDA and E7. Moreover, the scaffolds showed high efficiency for recruiting BMSCs induced by E7 both in vitro and in vivo, which was associated with the SDF-1α/CXCR4 axis and the p38, extracellular signal-related kinase, and Akt signal transduction pathways. These functionalized electrospun scaffolds promoted regeneration of bone in the rat calvarial bone defect model. In general, this study verified that PDA could be a simple and efficient method for surface modification, and E7-grafted PDA-modified SF electrospun scaffolds were suitable for bone tissue engineering.

Redox State of PDA Directs Cellular Responses through Preadsorbed Protein

Polydopamine (PDA) is capable of adhering on nearly all kinds of surfaces and shows good biocompatibility. Moreover, its surface state could be switched between oxidation and reduction states under different electrical stimulation. In this work, the effects of PDA redox states on protein adsorption, as well as the subsequent effects on cellular responses were characterized and evaluated. It was found that the electrical treatment changed the redox states of PDA, which in turn changed the state of preadsorbed protein molecules and eventually affected the cellular responses. BSA preadsorbed PDA film was found to be beneficial for cell proliferation when PDA was changed into reduction state (RPDA), while BMP-2 preadsorbed PDA film showed promotion on cell differentiation when PDA was changed into oxidation state (OPDA). It was found that the transitions of PDA to RPDA and OPDA greatly changed the secondary structure of protein preadsorbed on it. This work provides a deeper insight on changes of protein molecules between cells and PDA surfaces with different redox states, which is important for both optimization of cell-material interactions and application of PDA as a functional coating for biomedical engineering.

Glutathione Responsive β-Cyclodextrin Conjugated S-Nitrothiols as a Carrier for Intracellular Delivery of Nitric Oxide

Nitric oxide (NO) exerts multiple functions in many life processes and was of great significance in a variety of biomedical scenarios. However, the mismatches between releasing locations and NO active sites seriously limited the available NO at areas of interest and greatly dampen the overall efficiency of delivery systems. Therefore, in the present study, a NO donor was developed to achieve intracellular delivery and release of NO to overcome the aforementioned challenges. Enhanced uptake and effective intracellular release of NO were realized via β-cyclodextrin (β-CD) mediated endocytosis and high level glutathione (GSH) inside cells, respectively. We demonstrated that intracellularly delivered NO would exert stronger bioeffects than premature release of NO outside targeted cells. Besides, β-CD assisted cellular uptake proved indispensable in maximizing the influence of NO in modulating cellular behavior. These results demonstrated the significance of intracellular delivery and release of NO in improving its bioutilization. The carrier could efficiently inhibit proliferation of SMCs, while promoting the growth of ECs. Such cell-type-differed physiological effects were advantageous in re-endothelialization and might hold great potential in cardiovascular applications.

Titanium discs coated with 3,4-dihydroxy-l-phenylalanine promote osteogenic differentiation of human bone mesenchymal stem cells in vitro

The bioinspired material 3,4-dihydroxy-l-phenylalanine (DOPA) is commonly used as a basic layer in surface modification for osteogenesis; however, its effects on bone remodeling and the underlying mechanisms remain unclear. Here, we investigated the effect of DOPA-coated surfaces on human bone marrow-derived mesenchymal stem cells in vitro. Cells cultured on DOPA-modified titanium discs exhibited enhanced cellular adhesion and spreading compared with cells on non-treated surfaces. Moreover, DOPA-coating promoted greater cell proliferation and osteogenic differentiation, as determined using cell counting kit-8 (CCK-8) assay, alkaline phosphatase activity test and quantitative mineralization measurements. Furthermore, microarray analysis revealed that genes participating in focal adhesion were upregulated on DOPA-coated surfaces. Our results indicate that the application of a simple DOPA coating can promote osteogenic differentiation of osteoprogenitor cells, improving new bone formation and bone remodeling around implantable devices in tissue engineering.

Titanium discs with simple 3,4-dihydroxy-l-phenylalanine coating enhanced BM-MSC adhesion, spreading, proliferation and differentiation, and upregulated expression of genes involved in focal adhesion in vitro.

Mussel-inspired injectable hydrogel and its counterpart for actuating proliferation and neuronal differentiation of retinal progenitor cells

Biomaterials-mediated retinal progenitor cell (RPC)-based transplantation therapy has shown substantial potential for retinal degeneration (RD), but it is limited by the poor RPC survival, proliferation and differentiation. Herein, the gelatin-hyaluronic acid (Gel-HA)-based hydrogels formed via moderate Michael-type addition reaction with or without the introduction of mussel-inspired polydopamine (PDA), i.e. Gel-HA-PDA and its counterpart Gel-HA hydrogels are developed, and their effects on the biological behaviour of RPCs, including adhesion, survival, proliferation, differentiation, delivery and migration are investigated. The hybrid hydrogels can adopt the intricate structure of the retina with suitable mechanical strength, degradation rate and biological activity to support cellular adhesion, survival and delivery. Meanwhile, Gel-HA hydrogel can remarkably promote RPC proliferation with much larger cell clusters, while Gel-HA-PDA hydrogel significantly enhances RPC adhesion and migration, and directs RPCs to preferentially differentiate toward retinal neurons such as photoreceptors (the most crucial cell-type for RD treatment), which is mainly induced by the activation of integrin α5β1-phosphatidylinositol-3-kinase (PI3K) pathway. This study demonstrates that Gel-HA hydrogel possesses great potential for RPC proliferation, while mussel-inspired PDA-modified Gel-HA hydrogel with superior biocompatibility can significantly promote RPC neuronal differentiation, providing new insights for developing biomedical materials applied for RPC-based transplantation therapy.

Advanced capability of radially aligned fibrous scaffolds coated with polydopamine for guiding directional migration of human mesenchymal stem cells

In a large tissue defect, faster migration of adjacent tissue toward the defect shortens the tissue regeneration time. Little has been explored on guiding of directional migration from all fronts of the defect boundary towards the center in tissue engineering. This paper demonstrates the effect of radially aligned fibrous scaffolds (RAFSs) coated with polydopamine in order to guide directional migration of human mesenchymal stem cells (hMSCs). RAFSs were electrospun using a collector with a set of electrodes, each constructed with a metallic ring and a point. The polydopamine was then coated by dipping the scaffolds in a dopamine solution (PD-RAFS). The RAFSs exhibited radial distribution of the fibers from the peripheral region toward the center, and polydopamine was uniformly coated over the entire surface by presenting characteristics of the aromatic ring from dopamine. When hMSCs were seeded on the scaffolds, cells grew in an elongated form toward the center along the fiber direction. In particular, the polydopamine coating improved adhesion and spreading of hMSCs on the scaffolds while preserving initial cell orientation. The hMSCs migrated toward the center of the scaffolds at the border of the seeded area; it was enhanced in the order of PD-RAFS > RAFS > random fibrous scaffolds. Therefore, PD-RAFSs can be utilized as an alternate scaffold that can lead to fast and directional migration of cells for finally facilitating tissue regeneration.

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.

Facile Cell Sheet Harvest and Translocation Mediated by a Thermally Expandable Hydrogel with Controlled Cell Adhesion

Facile cell sheet translocation system is developed based on a thermally expandable hydrogel with modular cell adhesion favorable for both robust cell sheet formation and harvest. Efficient translocation is achieved at moderate cell-substrate interaction, which can be tuned by two-step reactions of mussel-inspired coating.

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.

Surface modification of strontium-doped porous bioactive ceramic scaffolds via poly(DOPA) coating and immobilizing silk fibroin for excellent angiogenic and osteogenic properties

For bioceramic scaffolds employed in clinical applications, excellent bioactivity and tenacity were of great importance. Modifying inorganic SCPP scaffolds with biological macromolecules could obviously improve its bioactivity and eliminate its palpable brittleness. However, it was hard to execute directly due to extremely bad interfacial compatibility between them. In this research, dopamine (DOPA) was introduced onto strontium-doped calcium polyphosphate (SCPP) scaffolds, subsequently the preliminary material was successfully further modified by silk fibroin (SF). SCPP/D/SF possessed suitable biomechanical properties, ability to stimulate angiogenic factor secretion and excellent biocompatibility. Biomechanical examination demonstrated that SCPP/D/SF scaffolds yielded better compressive strength because of improved interfacial compatibility. MTT assay and CLSM observation showed that SCPP/D/SF scaffolds had good cytocompatibility and presented better inducing-cell-migration potential than pure SCPP scaffolds. Meanwhile, its ability to stimulate angiogenic factor secretion was measured through the ELISA assay and immunohistological analysis in vitro and in vivo respectively. The results revealed, superior to SCPP, SCPP/D/SF could effectively promote VEGF and bFGF expression, possibly leading to enhancing angiogenesis and osteogenesis. In a word, SCPP/D/SF could serve as a potential bone tissue engineering scaffold for comparable biomechanical properties and excellent bioactivity. It provided a novel idea for modification of inorganic materials to prepare promising bone tissue engineering scaffolds with the ability to accelerate bone regeneration and vascularization.

Mussel adhesive protein inspired coatings on temperature-responsive hydrogels for cell sheet engineering

A cell sheet translocation system is developed based on a temperature-responsive hydrogel with modular cell adhesion properties by a mussel-inspired polydopamine coating.

Evaluation of the direct effects of poly(dopamine) on the in vitro response of human osteoblastic cells

Functional poly(dopamine) coatings promise to become an efficient strategy to endow biomaterials with enhanced bioactive properties.

Rat liver sinusoidal surface N-linked glycoproteomic analysis by affinity enrichment and mass spectrometric identification

Glycosylation in liver is one of the most biologically important protein modifications. It plays critical roles in many physiological and pathological processes by virtue of its unique location at the blood-tissue interface, including angiogenesis, liver cancer, cirrhosis, and fibrosis. To analyze glycosylation of plasma membrane proteins in liver sinusoidal endothelial cells (LSEC), N-glycopeptides of the LSEC surface were enriched using a filter-assisted sample preparation-based lectin affinity capture method and subsequently identified with mass spectrometry. In total, 225 unique N-glycosylation sites on 152 glycoproteins were identified, of which 119 (53%) sites had not previously been determined experimentally. Among the glycoproteins, 53% were classified as plasma membrane proteins and 47 (31%) as signaling proteins and receptors. Moreover, 23 cluster of differentiation antigens with 49 glycopeptides were detected within the membrane glycoproteins of the liver sinusoidal surface. Furthermore, bioinformatics analysis revealed that the majority of identified glycoproteins have an impact on processes of LSEC. Therefore, N-glycoproteomic analysis of the liver sinusoidal surface may provide useful information on liver regeneration and facilitate liver disease diagnosis.

Mussel inspired coating of a biocompatible cyclodextrin based polymer onto CoCr vascular stents

During the past decade, drug-eluting stents (DES) have been widely used for the treatment of occlusive coronary artery diseases. They are supposed to reduce the incidence of early in-stent restenosis by the elution of highly hydrophobic antiproliferative drugs. Nevertheless, the absence of long-term activity of these devices is responsible for late acute thrombosis probably due to the delayed re-endothelialization of the arterial wall over the bare metallic stent struts. Thus, a new generation of DES with a sustained release of therapeutic agents is required to improve long-term results of these devices. In this article, we report an original functionalization of CoCr vascular devices with a hydrophilic, biocompatible and biodegradable cyclodextrins based polymer which acts as a reservoir for lipophilic drugs allowing the sustained release of antiproliferative drugs. In this setting, polydopamine (PDA), a strong adhesive biopolymer, was applied as a first coating layer onto the surface of the metallic CoCr device in order to promote the strong anchorage of a cyclodextrin polymer. This polymer was generated "in situ" from the methylated cyclodextrins and citric acid as a cross-linking agent through a polycondensation reaction. After optimization of the grafting process, the amount of cyclodextrin polymer coated onto the CoCr device was quantified by colorimetric titrations and the resulting film was characterized by scanning electron microscopy (SEM) investigations. The cytocompatibility of the resulting coated film was assessed by cell proliferation and vitality tests. Finally, the ability of this coated device to act as a drug-eluting system was evaluated with paclitaxel, a strong hydrophobic antiproliferative drug, a reference drug used in current vascular drug-eluting stents.

Microfluidic generation of polydopamine gradients on hydrophobic surfaces

Engineered surface-bound molecular gradients are of great importance for a range of biological applications. In this paper, we fabricated a polydopamine gradient on a hydrophobic surface. A microfluidic device was used to generate a covalently conjugated gradient of polydopamine (PDA), which changed the wettabilty and the surface energy of the substrate. The gradient was subsequently used to enable the spatial deposition of adhesive proteins on the surface. When seeded with human adipose mesenchymal stem cells, the PDA-graded surface induced a gradient of cell adhesion and spreading. The PDA gradient developed in this study is a promising tool for controlling cellular behavior and may be useful in various biological applications.

Synthesis of polydopamine-coated magnetic graphene for Cu(2+) immobilization and application to the enrichment of low-concentration peptides for mass spectrometry analysis

In this work, Cu(2+)-immobilized magnetic graphene@polydopamine (magG@PDA@Cu(2+)) composites were synthesized for the first time. Magnetic graphene prepared via a hydrothermal reaction were easily encapsulated by a layer of polydopamine through the oxidative polymerization of dopamine in alkaline buffer, and it was conveniently modified with Cu(2+) ions afterward. The as-prepared magG@PDA@Cu(2+) composites were endowed with strong magnetic responsivness, excellent dispersibility and biological compatibility. We applied the novel nanocomposites to the enrichment and identification of low-concentration standard peptides, peptides in standard protein digestions, endogenous peptides in human urine and serum. The enriched peptides were eluted and analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The magG@PDA@Cu(2+) composites were proved to exhibit great affinity to both hydrophobic and hydrophilic peptides, thus providing a rapid and facile approach to the extraction of low-concentration peptides. Notably, peptides at an extremely low concentration of 10 pM could be detected by MALDI-TOF MS after enrichment with magG@PDA@Cu(2+) composites. The results demonstrated that the magG@PDA@Cu(2+) composite is a promising candidate for the enrichment of low-abundance peptides for mass spectrometry analysis.