Layer-by-layer assembly as a robust method to construct extracellular matrix mimic surfaces to modulate cell behavior

Three-Dimensional Bioprinting in Vascular Tissue Engineering and Tissue Vascularization of Cardiovascular Diseases

In the 21st century, significant progress has been made in repairing damaged materials through material engineering. However, the creation of large-scale artificial materials still faces a major challenge in achieving proper vascularization. To address this issue, researchers have turned to biomaterials and three-dimensional (3D) bioprinting techniques, which allow for the combination of multiple biomaterials with improved mechanical and biological properties that mimic natural materials. Hydrogels, known for their ability to support living cells and biological components, have played a crucial role in this research. Among the recent developments, 3D bioprinting has emerged as a promising tool for constructing hybrid scaffolds. However, there are several challenges in the field of bioprinting, including the need for nanoscale biomimicry, the formulation of hydrogel blends, and the ongoing complexity of vascularizing biomaterials, which requires further research. On a positive note, 3D bioprinting offers a solution to the vascularization problem due to its precise spatial control, scalability, and reproducibility compared with traditional fabrication methods. This paper aims at examining the recent advancements in 3D bioprinting technology for creating blood vessels, vasculature, and vascularized materials. It provides a comprehensive overview of the progress made and discusses the limitations and challenges faced in current 3D bioprinting of vascularized tissues. In addition, the paper highlights the future research directions focusing on the development of 3D bioprinting techniques and bioinks for creating functional materials.

Robust, Sprayable, and Multifunctional Hydrogel Coating through a Polycation Reinforced (PCR) Surface Bridging Strategy

The sprayable hydrogel coatings that can establish robust adhesion onto diverse materials and devices hold enormous potential; however, a significant challenge persists due to monomer hydration, which impedes even coverage during spraying and induces inadequate adhesion post-gelation. Herein, a polycation-reinforced (PCR) surface bridging strategy is presented to achieve tough and sprayable hydrogel coatings onto diverse materials. The polycations offer superior wettability and instant electrostatic interactions with plasma-treated substrates, facilitating an effective spraying application. This PCR-based hydrogel coatings demonstrate tough adhesion performance to inert PTFE and silicone, including remarkable shear strength (161 ± 49 kPa for PTFE), interfacial toughness (198 ± 27 J m-2 for PTFE), and notable tolerance to cyclic tension (10 000 cycles, 200% strain, silicone). Meanwhile, this method can be applied to various hydrogel formulations, offering diverse functionalities, including underwater adhesion, lubrication, and drug delivery. Furthermore, the PCR concept enables the conformal construction of durable hydrogel coatings onto sophisticated medical devices like cardiovascular stents. Given its simplicity and adaptability, this approach paves an avenue for incorporating hydrogels onto solid surfaces and potentially promotes untapped applications.

Evolution of Hybrid Hydrogels: Next-Generation Biomaterials for Drug Delivery and Tissue Engineering

Hydrogels, being hydrophilic polymer networks capable of absorbing and retaining aqueous fluids, hold significant promise in biomedical applications owing to their high water content, permeability, and structural similarity to the extracellular matrix. Recent chemical advancements have bolstered their versatility, facilitating the integration of the molecules guiding cellular activities and enabling their controlled activation under time constraints. However, conventional synthetic hydrogels suffer from inherent weaknesses such as heterogeneity and network imperfections, which adversely affect their mechanical properties, diffusion rates, and biological activity. In response to these challenges, hybrid hydrogels have emerged, aiming to enhance their strength, drug release efficiency, and therapeutic effectiveness. These hybrid hydrogels, featuring improved formulations, are tailored for controlled drug release and tissue regeneration across both soft and hard tissues. The scientific community has increasingly recognized the versatile characteristics of hybrid hydrogels, particularly in the biomedical sector. This comprehensive review delves into recent advancements in hybrid hydrogel systems, covering the diverse types, modification strategies, and the integration of nano/microstructures. The discussion includes innovative fabrication techniques such as click reactions, 3D printing, and photopatterning alongside the elucidation of the release mechanisms of bioactive molecules. By addressing challenges, the review underscores diverse biomedical applications and envisages a promising future for hybrid hydrogels across various domains in the biomedical field.

Recent Developments in Layer-by-Layer Assembly for Drug Delivery and Tissue Engineering Applications

Surfaces with biological functionalities are of great interest for biomaterials, tissue engineering, biophysics, and for controlling biological processes. The layer-by-layer (LbL) assembly is a highly versatile methodology introduced 30 years ago, which consists of assembling complementary polyelectrolytes or biomolecules in a stepwise manner to form thin self-assembled films. In view of its simplicity, compatibility with biological molecules, and adaptability to any kind of supporting material carrier, this technology has undergone major developments over the past decades. Specific applications have emerged in different biomedical fields owing to the possibility to load or immobilize biomolecules with preserved bioactivity, to use an extremely broad range of biomolecules and supporting carriers, and to modify the film's mechanical properties via crosslinking. In this review, the focus is on the recent developments regarding LbL films formed as 2D or 3D objects for applications in drug delivery and tissue engineering. Possible applications in the fields of vaccinology, 3D biomimetic tissue models, as well as bone and cardiovascular tissue engineering are highlighted. In addition, the most recent technological developments in the field of film construction, such as high-content liquid handling or machine learning, which are expected to open new perspectives in the future developments of LbL, are presented.

Engineering tunable dual peptide hybrid coatings promote osseointegration of implants

Utilizing complementary bioactive peptides is a promising surface engineering strategy for bone regeneration on osteogenesis. In this study, we designed block peptides, (Lysine)6-capped RGD (K6-(linker-RGD)3) and OGP (K6-linker-(YGFGG)2), which were mildly grafted onto PC/Fe-MPNs through supramolecular interactions between K6 and PC residues on the MPNs surface to form a dual peptide coating, named PC/Fe@K6-RGD/OGP. The properties of the block peptides coating, including mechanics, hydrophilicity, chemical composition, etc., were detailly characterized by various techniques (ellipsometry, quartz crystal microbalance, X-ray photoelectron spectroscopy, water contact angle, scanning electronic microscopy and atomic force microscopy). Importantly, the RGD/OGP ratio can be well adjusted, which allowed optimizing the RGD/OGP ratio to endow significantly enhanced osteogenic activity of MC3T3-E1 cells through the Wnt/β-catenin pathway, while also promoting cell adhesion, immune regulation, inhibiting osteoclast differentiation and oxidative stress reduction. In vivo, the optimized RGD/OGP coatings promoted bone regeneration and osseointegration around implants in rats with bone defects. In conclusion, rationally designed PC/Fe@K6-RGD/OGP coating integrated RGD and OGP bioactivities, providing a convenient approach to enhance bioinert implant surfaces for bone regeneration.

Construction of multifunctional coating with cationic amino acid-coupled peptides for osseointegration of implants

Osseointegration is an important indicator of implant success. This process can be improved by coating modified bioactive molecules with multiple functions on the surface of implants. Herein, a simple multifunctional coating that could effectively improve osseointegration was prepared through layer-by-layer self-assembly of cationic amino acids and tannic acid (TA), a negatively charged molecule. Osteogenic growth peptide (OGP) and the arginine-glycine-aspartic acid (RGD) functional polypeptides were coupled with Lys6 (K6), the two polypeptides then self-assembled with TA layer by layer to form a composite film, (TA-OGP@RGD)n. The surface morphology and biomechanical properties of the coating were analyzed in gas and liquid phases, and the deposition process and kinetics of the two peptides onto TA were monitored using a quartz crystal microbalance. In addition, the feeding consistency and adsorption ratios of the two peptides were explored by using fluorescence visualization and quantification. The (TA-OGP@RGD)n composite membrane mediated the early migration and adhesion of cells and significantly promoted osteogenic differentiation and mineralization of the extracellular matrix in vitro. Additionally, the bifunctional peptide exhibited excellent osteogenesis and osseointegration owing to the synergistic effect of the OGP and RGD peptides in vivo. Simultaneously, the (TA-OGP@RGD)n membrane regulated the balance of reactive oxygen species in the cell growth environment, thereby influencing the complex biological process of osseointegration. Thus, the results of this study provide a novel perspective for constructing multifunctional coatings for implants and has considerable application potential in orthopedics and dentistry.

Marine-origin polysaccharides-based free-standing multilayered membranes as sustainable nanoreservoirs for controlled drug delivery

The layer-by-layer (LbL) assembly technology has been widely used to functionalise surfaces and precisely engineer robust multilayered bioarchitectures with tunable structures, compositions, properties, and functions at the nanoscale by resorting to a myriad of building blocks exhibiting complementary interactions. Among them, marine-origin polysaccharides are a sustainable renewable resource for the fabrication of nanostructured biomaterials for biomedical applications owing to their wide bioavailability, biocompatibility, biodegradability, non-cytotoxicity, and non-immunogenic properties. Chitosan (CHT) and alginate (ALG) have been widely employed as LbL ingredients to shape a wide repertoire of size- and shape-tunable electrostatic-driven multilayered assemblies by exploring their opposite charge nature. However, the insolubility of CHT in physiological conditions intrinsically limits the range of bioapplications of the as-developed CHT-based LbL structures. Herein, we report the preparation of free-standing (FS) multilayered membranes made of water-soluble quaternised CHT and ALG biopolymers for controlled release of model drug molecules. The influence of the film structure in the drug release rate is studied by assembling two distinct set-ups of FS membranes, having the model hydrophilic drug fluorescein isothiocyanate-labelled bovine serum albumin (FITC-BSA) either as an intrinsic building block or added as an outer layer after the LbL assembly process. Both FS membranes are characterised for their thickness, morphology, in vitro cytocompatibility, and release profile, with those having FITC-BSA as an intrinsic LbL ingredient denoting a more sustained release rate. This work opens up new avenues for the design and development of a wide array of CHT-based devices for biomedical applications, overcoming the limitations associated with the insolubility of native CHT under physiological conditions.

Chitosan-Based Biomaterials: Insights into Chemistry, Properties, Devices, and Their Biomedical Applications

Chitosan is a marine-origin polysaccharide obtained from the deacetylation of chitin, the main component of crustaceans’ exoskeleton, and the second most abundant in nature. Although this biopolymer has received limited attention for several decades right after its discovery, since the new millennium chitosan has emerged owing to its physicochemical, structural and biological properties, multifunctionalities and applications in several sectors. This review aims at providing an overview of chitosan properties, chemical functionalization, and the innovative biomaterials obtained thereof. Firstly, the chemical functionalization of chitosan backbone in the amino and hydroxyl groups will be addressed. Then, the review will focus on the bottom-up strategies to process a wide array of chitosan-based biomaterials. In particular, the preparation of chitosan-based hydrogels, organic–inorganic hybrids, layer-by-layer assemblies, (bio)inks and their use in the biomedical field will be covered aiming to elucidate and inspire the community to keep on exploring the unique features and properties imparted by chitosan to develop advanced biomedical devices. Given the wide body of literature that has appeared in past years, this review is far from being exhaustive. Selected works in the last 10 years will be considered.

A decade of developing applications exploiting the properties of polyelectrolyte multilayer capsules

Transferring the layer-by-layer (LbL) coating approach from planar surfaces to spherical templates and subsequently dissolving these templates leads to the fabrication of polyelectrolyte multilayer capsules. The versatility of the coatings of capsules and their flexibility upon bringing in virtually any material into the coatings has quickly drawn substantial attention. Here, we provide an overview of the main developments in this field, highlighting the trends in the last decade. In the beginning, various methods of encapsulation and release are discussed followed by a broad range of applications, which were developed and explored. We also outline the current trends, where the range of applications is continuing to grow, including addition of whole new and different application areas.

Artificial Extracellular Matrix Composed of Heparin-Mimicking Polymers for Efficient Anticoagulation and Promotion of Endothelial Cell Proliferation

Heparin-mimicking polymers have emerged as an alternative to heparin to construct effective and safe anticoagulant surfaces. However, the present heparin-mimicking polymers are usually limited to the combinations of glucose and sulfonic acid units, and the structure origin of their anticoagulant properties remains vague. Inspired by the structure of natural heparin, we synthesized a series of novel heparin-mimicking polymers (named GSAs) composed of three units, glucose, sulfonic acid, and carboxylic acid. Then, we constructed artificial extracellular matrices composed of GSAs and two typical cationic polymers, polyethyleneimine and chitosan, to investigate the anticoagulation and endothelialization of GSAs. By changing the ratio of the three units, their functions in the matrices were studied systematically. We found that an increase in the sulfonic acid content enhanced surface anticoagulant activity, an increase in glucose and sulfonic acid content promoted the proliferation of human umbilical vein vascular endothelial cells, and an increase in the carboxylic acid content inhibited the adherence of human umbilical vein vascular smooth muscle cells. This work uncovers the important role of the GSAs structure to the anticoagulation properties, which sheds new light on the design and preparation of heparin-mimicking polymers for practical engineering applications.

Chondrogenic differentiation of mesenchymal stem cells through cartilage matrix-inspired surface coatings

The stem cell niche comprises soluble molecules and extracellular matrix components which provide chemical and mechanical cues that determine the differentiation of stem cells. Here, the effect of polyelectrolyte multilayer (PEM) composition and terminal layer fabricated with layer-by-layer technique (LBL) pairing either hyaluronan [in its native (nHA) and oxidized form (oHA)] or chondroitin sulfate (CS) with type I collagen (Col I) is investigated on chondrogenic differentiation of human umbilical mesenchymal stem cells (hUC-MSCs). Physical studies performed to investigate the establishment and structure of the surface coatings show that PEM composed of HA and Col I show a dominance of nHA or oHA with considerably lesser organization of Col I fibrils. In contrast, distinguished fibrilized Col I is found in nCS-containing PEM. Generally, Col I-terminated PEM promote the adhesion, migration, and growth of hUC-MSCs more than GAG-terminated surfaces due to the presence of fibrillar Col I but show a lower degree of differentiation towards the chondrogenic lineage. Notably, the Col I/nHA PEM not only supports adhesion and growth of hUC-MSCs but also significantly promotes cartilage-associated gene and protein expression as found by histochemical and molecular biology studies, which is not seen on the Col I/oHA PEM. This is related to ligation of HA to the cell receptor CD44 followed by activation of ERK/Sox9 and noncanonical TGF-β signaling-p38 pathways that depends on the molecular weight of HA as found by immune histochemical and western blotting. Hence, surface coatings on scaffolds and other implants by PEM composed of nHA and Col I may be useful for programming MSC towards cartilage regeneration.

pH-Responsive Polyelectrolyte Coatings that Enable Catheter-Mediated Transfer of DNA to the Arterial Wall in Short and Clinically Relevant Inflation Times

We report the design and characterization of pH-responsive polymer coatings that enable catheter balloon-mediated transfer of DNA to arterial tissue in short, clinically relevant inflation times. Our approach exploits the pH-dependent ionization of poly(acrylic acid) (PAA) to promote disassembly and release of plasmid DNA from polyelectrolyte multilayers. We characterized the contact transfer of multilayers composed of PAA, plasmid DNA, and linear poly(ethyleneimine) (LPEI) identified as promising in prior studies on the delivery of DNA to arterial tissue. In contrast to thinner films evaluated previously, we found thicker coatings composed of 32 repeating (LPEI/PAA/LPEI/DNA)_x tetralayers to swell substantially in physiologically relevant media (in PBS; pH = 7.4). In some cases, these coatings also disintegrated or delaminated rapidly from their underlying substrates, suggesting the potential for enhanced balloon-mediated transfer. We developed a technically straightforward agarose gel-based hole-insertion model to characterize factors (inflation time, lumen size, etc.) that influence contact transfer of DNA when film-coated balloons are inflated into contact with soft surfaces. Those studies and the results of in vivo experiments using small animal (rat) and large animal (pig) models of peripheral arterial injury revealed catheters coated with these materials to promote robust contact transfer of DNA to soft hydrogel surfaces and the luminal surfaces of arterial tissue using inflation times as short as 30 s. These short inflation times are relevant in the context of clinical vascular interventions in peripheral arteries. Additional studies demonstrated that contact transfer of DNA using these short times can promote subsequent dissemination and transport of DNA to the medial tissue layer, suggesting the potential for use in therapeutically relevant applications of balloon-mediated gene transfer.

Quenching the Macroporous Collapse of Polyelectrolyte Multilayer Films for Repeated Drug Loading

Macroporous structures can be developed within polyelectrolyte multilayer films for efficient drug loading, but these structures tend to collapse or fracture during conventional drying procedures. Herein, a facile dehydrating method for macroporous polyelectrolyte multilayer films is proposed using solvent exchange to ethanol and then spontaneous evaporation. During these processes, the collapse of the macroporous structures can be effectively avoided, which can be ascribed to a combined effect of two factors. On one hand, capillary pressure during ethanol evaporation is relatively small since the surface tension of ethanol is much lower than that of water. On the other hand, solvent exchange suppresses the interdiffusion of polyelectrolytes and substantially increases the mechanical strength of the macroporous films, more than three orders of magnitude, making the pore walls highly tolerant of the capillary pressure. The stability of macroporous polyelectrolyte films to ethanol enables the repeated wicking from the ethanol solution of drugs, leading to a higher loading beyond previous studies. Such a high loading is favorable for the long-term release of drugs from the surfaces of modified substrates and maintaining a local drug concentration above the minimum effective concentration.

Biomedical polymers: synthesis, properties, and applications

Biomedical polymers have been extensively developed for promising applications in a lot of biomedical fields, such as therapeutic medicine delivery, disease detection and diagnosis, biosensing, regenerative medicine, and disease treatment. In this review, we summarize the most recent advances in the synthesis and application of biomedical polymers, and discuss the comprehensive understanding of their property-function relationship for corresponding biomedical applications. In particular, a few burgeoning bioactive polymers, such as peptide/biomembrane/microorganism/cell-based biomedical polymers, are also introduced and highlighted as the emerging biomaterials for cancer precision therapy. Furthermore, the foreseeable challenges and outlook of the development of more efficient, healthier and safer biomedical polymers are discussed. We wish this systemic and comprehensive review on highlighting frontier progress of biomedical polymers could inspire and promote new breakthrough in fundamental research and clinical translation.

Introduction to bioinspired surfaces engineering for biomaterials

G. Julius Vancso, Jian Ji, Kazuhiko Ishihara, M. Cristina L. Martins and Shaoyi Jiang introduce the Journal of Materials Chemistry B themed collection on bioinspired surfaces engineering for biomaterials.

Cell Adhesion and Migration on Thickness Gradient Bilayer Polymer Brush Surfaces: Effects of Properties of Polymeric Materials of the Underlayer

In the field of tissue engineering and biomaterials, controlling the surface properties and mechanical properties of scaffold materials is crucial and has attracted much attention. Here, two types of bilayer polymer brushes composed of a hydrophilic underlying layer and a cationic surface layer [made of poly(2-aminoethyl methacrylate)] with a thickness gradient were prepared by surface-initiated atom-transfer radical polymerization. To investigate the influence of the stiffness as a mechanical property of the polymer brush on cell behavior, the underlayer was prepared from either 2-methacryloyloxyethyl phosphorylcholine or oligo(ethylene glycol) methyl ether methacrylate, with the bilayers designated as gradient poly(2-methacryloyloxyethyl phosphorylcholine)-block-poly(2-aminoethyl methacrylate) [grad-pMbA] and gradient poly(oligo[ethylene glycol] methyl ether methacrylate)-block-poly(2-aminoethyl methacrylate) [grad-pEGbA], respectively. Characterization of these surfaces was performed by spectroscopic ellipsometry, X-ray reflectivity, and determination of the zeta potential, static contact angle, and force curve. These diblock copolymer brushes with a thickness gradient helped to distinguish the effects of the mechanical and surface properties of the brushes on cell behavior. The attachment and motility of L929 fibroblasts and epithelial MCF 10A cells on the fabricated brushes were then assessed. L929 cells had a round shape on the thin surface layer of grad-pMbA and spread well on thicker areas. In contrast, MCF 10A cells spread well in areas of any thickness of either grad-pMbA or grad-pEGbA. Single MCF 10A cells migrated randomly on grad-pMbA, whereas grouped cells started to climb up along the thickness gradient of grad-pMbA. In contrast, both single and grouped MCF 10A cells migrated randomly on grad-pEGbA. These thickness gradient diblock copolymer brushes are simple, reproducible, and reasonable platforms that can facilitate practical applications of biomaterials, for example, in tissue engineering and biomaterials.

A Versatile Strategy to Coat Individual Cell with Fully/Partially Covered Shell for Preparation of Self-Propelling Living Cells

Coating living cells with a functional shell has been regarded as an effective way to protect them against environmental stress, regulate their biological behaviors, or extend their functionalities. Here, we reported a facile method to prepare fully or partially coated shells on an individual yeast cell surface by visible light-induced graft polymerization. In this strategy, yeast cells that were surface-absorbed with polyethylenimine (PEI) were deposited on the negatively charged glass slide to form a single layer by electrostatic interaction. Then, surface-initiated graft polymerization of poly(ethylene glycol) diacrylate (PEGDA) on yeast cells under visible light irradiation was carried out to generate cross-linked shells on the cells. The process of surface modification had negligible influence on the viability of yeast cells due to the mild reaction condition. Additionally, compared to the native yeast cells, a 17.5 h of delay in division was observed when the graft polymerization was performed under 15 mW/cm² irradiation for 30 min. Introducing artificial shell endowed yeast cells with significant resistance against lyticase, and the protection can be enhanced by increasing the thickness of shell. Moreover, the partially coated yeast cells would be prepared by simply adjusting the reaction condition such as irradiation density and time. By immobilizing urease on the functional patch, the asymmetrically modified yeast cells exhibited self-propelling capability, and the speed of directional movement reached 4 μm/s in the presence of 200 mM urea. This tunable coating individual cell strategy with varying functionality has great potential applications in fields of cell-based drug delivery, cell therapy, biocatalysis, and tissue engineering.

Construction of a Self-Assembled Polyelectrolyte/Graphene Oxide Multilayer Film and Its Interaction with Metal Ions

In this study, a composite multilayer film onto gold was constructed from two charged building blocks, i.e., negatively charged graphene oxide (GO) and a branched polycation (polyethylenimine, PEI) via layer-by-layer (LbL) self-assembly technology, and this process was monitored in situ with quartz crystal microbalance (QCM) under different experimental conditions. This included the differences in frequency (Δf) as well as the changes in dissipation to yield information on the absorbed mass and viscoelastic properties of the formed PEI/GO multilayer films. The experimental conditions were optimized to obtain a high amount of the adsorbed mass of the self-assembled multilayer film. The surface morphology of the PEI/GO multilayer film onto gold was studied with atomic force microscopy (AFM). It was found that the positively charged PEI chains were combined with the oppositely charged GO to form an assembled film on the QCM sensor surface, in a wrapped and curled fashion. Raman and UV-vis spectra also showed that the intensities of the GO-characteristic signals are almost linearly related to the layer number. To explore the films for their use in divalent ion detection, the frequency response of the PEI/GO multilayer-modified QCM sensor to the exposure of aqueous solutions solution of Cu²⁺, Ca²⁺, Zn²⁺, and Sn²⁺ was further studied using QCM. Based on the Sauerbrey equation and the weight of different ions, the number of metal ions adsorbed per unit area on the surface of QCM sensors was calculated. For metal ion concentrations of 40 ppm, the adsorption capacities per unit area of Cu²⁺, Zn²⁺, Sn²⁺, and Ca²⁺ were found to be 1.7, 3.2, 0.7, and 4.9 nmol/cm², respectively. Thus, in terms of the number of adsorbed ions per unit area, the QCM sensor modified by PEI/GO multilayer film shows the largest adsorption capacity of Ca²⁺. This can be rationalized by the relative hydration energies.

Recent developments in mussel-inspired materials for biomedical applications

Over the decades, researchers have strived to synthesize and modify nature-inspired biomaterials, with the primary aim to address the challenges of designing functional biomaterials for regenerative medicine and tissue engineering. Among these challenges, biocompatibility and cellular interactions have been extensively investigated. Some of the most desirable characteristics for biomaterials in these applications are the loading of bioactive molecules, strong adhesion to moist areas, improvement of cellular adhesion, and self-healing properties. Mussel-inspired biomaterials have received growing interest mainly due to the changes in mechanical and biological functions of the scaffold due to catechol modification. Here, we summarize the chemical and biological principles and the latest advancements in production, as well as the use of mussel-inspired biomaterials. Our main focus is the polydopamine coating, the conjugation of catechol with other polymers, and the biomedical applications that polydopamine moieties are used for, such as matrices for drug delivery, tissue regeneration, and hemostatic control. We also present a critical conclusion and an inspired view on the prospects for the development and application of mussel-inspired materials.

Endothelial Cell Migration Regulated by Surface Topography of Poly(ε-caprolactone) Nanofibers

The study of cell migration on biomaterials is of great significance in tissue engineering and regenerative medicine. In recent years, there has been increasing evidence that the physical properties of the extracellular matrix (ECM), such as surface topography, affect various cellular behaviors such as proliferation, adhesion, and migration. However, the biological mechanism of surface topography influencing cellular behavior is still unclear. In this study, we prepared polycaprolactone (PCL) fibrous materials with different surface microstructures by solvent casting, electrospinning, and self-induced crystallization. The corresponding topographical structure obtained is a two-dimensional (2D) flat surface, 2.5-dimensional (2.5D) fibers, and three-dimensional (3D) fibers with a multilevel microstructure. We then investigated the effects of the complex topographical structure on endothelial cell migration. Our study demonstrates that cells can sense the changes of micro- and nanomorphology on the surface of materials, adapt to the physical environment through biochemical reactions, and regulate actin polymerization and directional migration through Rac1 and Cdc42. The cells on the nanofibers are elongated spindles, and the positive feedback of cell adhesion and actin polymerization along the fiber direction makes the plasma membrane continue to protrude, promoting cell polarization and directional migration. This study might provide new insights into the biomaterial design, especially those used for artificial vascular grafts.

Biomimetic Graphene/Spongin Scaffolds for Improved Osteoblasts Bioactivity via Dynamic Mechanical Stimulation

Biomimetics offers excellent prospects for design a novel generation of improved biomaterials. Here the controlled integration of graphene oxide (GO) derivatives with a 3D marine spongin (MS) network is explored to nanoengineer novel smart bio-based constructs for bone tissue engineering. The results point out that 3D MS surfaces can be homogeneously coated by layer-by-layer (LbL) assembly of oppositely charged polyethyleneimine (PEI) and GO. Notably, the GOPEI@MS bionanocomposites present a high structural and mechanical stability under compression tests in wet conditions (shape memory). Dynamic mechanically (2 h of sinusoidal compression cyclic interval (0.5 Hz, 0-10% strain)/14 d) stimulates GOPEI@MS seeded with osteoblast (MC3T3-E1), shows a significant improvement in bioactivity, with cell proliferation being two times higher than under static conditions. Besides, the dynamic assays show that GOPEI@MS bionanocomposites are able to act as mechanical stimulus-responsive scaffolds able to resemble physiological bone extracellular matrix (ECM) requirements by strongly triggering mineralization of the bone matrix. These results prove that the environment created by the system cell-GOPEI@MS is suitable for controlling the mechanisms regulating mechanical stimulation-induced cell proliferation for potential in vivo experimentation.

Microstructured titanium functionalized by naringin inserted multilayers for promoting osteogenesis and inhibiting osteoclastogenesis

Osteoporosis is the most common cause of fractures in middle-aged and elderly people. Fracture repair can be difficult due to the decreased bone volume in osteoporosis patients and implants are often required. In this study, a slow-release system for microstructured titanium (Micro-Ti) was designed to promote osteogenesis and inhibit osteoclastogenesis. Firstly, Micro-Ti was prepared on titanium surfaces by dual acid etching. Micro-Ti was covered with naringin (NA), chitosan (CHI) and gelatin (GEL) multilayers through layer by layer technique, which is denoted as LBL (NA) coated-Ti. Osteoblasts (ME3T3-E1) and macrophages (RAW 264.7) were cultured on untreated and treated titanium surfaces in vitro. Osteoblasts grown on LBL (NA) coated-Ti showed higher alkaline phosphatase (ALP) and mineralization, consistent with qRT-PCR analysis of osteoblast genes including runt-related transcription factor 2 (Runx2), ALP, collagen I (Col I), osteocalcin (OCN), osteopontin (OPN), and osteoprotegerin (OPG). In contrast, acid tartarate-resistant phosphatase activity and the expression of osteoclastic differentiation related genes comprising of cathepsin K (CTSK), nuclear factor of activated T cells (NFAT), tartrate resistant acid phosphatase (TRAP) and V-ATPase (VATP) in osteoclasts were significantly reduced on LBL (NA) coated-Ti surfaces compared with other groups. These results indicate that microstructured titanium functionalized by naringin inserted multilayers enhanced the differentiation of osteoblasts and inhibited osteoclast formation. The proposed approach in this research provides a novel way to modify titanium-based implants for fracture repair in osteoporosis patients.

Bioinstructive Layer-by-Layer-Coated Customizable 3D Printed Perfusable Microchannels Embedded in Photocrosslinkable Hydrogels for Vascular Tissue Engineering

The development of complex and large 3D vascularized tissue constructs remains the major goal of tissue engineering and regenerative medicine (TERM). To date, several strategies have been proposed to build functional and perfusable vascular networks in 3D tissue-engineered constructs to ensure the long-term cell survival and the functionality of the assembled tissues after implantation. However, none of them have been entirely successful in attaining a fully functional vascular network. Herein, we report an alternative approach to bioengineer 3D vascularized constructs by embedding bioinstructive 3D multilayered microchannels, developed by combining 3D printing with the layer-by-layer (LbL) assembly technology, in photopolymerizable hydrogels. Alginate (ALG) was chosen as the ink to produce customizable 3D sacrificial microstructures owing to its biocompatibility and structural similarity to the extracellular matrices of native tissues. ALG structures were further LbL coated with bioinstructive chitosan and arginine–glycine–aspartic acid-coupled ALG multilayers, embedded in shear-thinning photocrosslinkable xanthan gum hydrogels and exposed to a calcium-chelating solution to form perfusable multilayered microchannels, mimicking the biological barriers, such as the basement membrane, in which the endothelial cells were seeded, denoting an enhanced cell adhesion. The 3D constructs hold great promise for engineering a wide array of large-scale 3D vascularized tissue constructs for modular TERM strategies.

Chitosan/gelatin-tannic acid decorated porous tape suture with multifunctionality for tendon healing

The inferior tendon healing after surgery is inextricably linked to the surgical suture. Poor load transfer along the suture often results in a high tendon re-tear rate. Besides, the severe inflammation and infection induced by sutures even cause a second surgery. Herein, to alleviate the above-mentioned issues, a multifunctional suture was fabricated by decorating chitosan/gelatin-tannic acid (CS/GE-TA) on the porous tape suture. The porous tape suture ensured the required mechanical properties and sufficient space for tissue integration. Compared to the pristine suture, the CS/GE-TA decorated suture (TA100) presented a 332% increase in pull-out force from the tendon, indicating potentially decreased re-tear rates. Meanwhile, TA100 showed superior anti-inflammatory and antibacterial performances. In vivo experiments further proved that TA100 could not only reduce inflammatory action but also facilitate collagen deposition and blood vessel formation. These results indicate that the multifunctional sutures are promising candidates for accelerating tendon healing.

Artificial Bioaugmentation of Biomacromolecules and Living Organisms for Biomedical Applications

The synergistic union of nanomaterials with biomaterials has revolutionized synthetic chemistry, enabling the creation of nanomaterial-based biohybrids with distinct properties for biomedical applications. This class of materials has drawn significant scientific interest from the perspective of functional extension via controllable coupling of synthetic and biomaterial components, resulting in enhancement of the chemical, physical, and biological properties of the obtained biohybrids. In this review, we highlight the forefront materials for the combination with biomacromolecules and living organisms and their advantageous properties as well as recent advances in the rational design and synthesis of artificial biohybrids. We further illustrate the incredible diversity of biomedical applications stemming from artificially bioaugmented characteristics of the nanomaterial-based biohybrids. Eventually, we aim to inspire scientists with the application horizons of the exciting field of synthetic augmented biohybrids.

Supramolecular dendrimer-containing layer-by-layer nanoassemblies for bioapplications: current status and future prospects

This review provides a comprehensive and critical overview of the supramolecular dendrimer-containing multifunctional layer-by-layer nanoassemblies driven by a multitude of intermolecular interactions for biological and biomedical applications.

Preparation of AAEK-functionalized cellulose film with antibacterial and anti-adhesion activities

Bacterial adhesion infection caused by medical materials in clinical application has become a serious threat, and it urgently needs new strategies to deal with these clinical challenges. The purpose of this study is to explore the effectiveness of surface-decorated aryl (β-amino) ethyl ketones (AAEK), a promising sorting enzyme A (SrtA) inhibitor of Staphylococcus aureus, to improve the anti-adhesion ability of biomaterials. AAEK was covalently grafted onto cellulose films (CF) via copper-catalyzed azide-alkyne 1, 3-dipolar cycloaddition click reaction. The data of contact angle measurements, ATR-FTIR and XPS proved the successful covalent attachment of AAEK-CF, and the antimicrobial efficacy of AAEK coating was assessed by CFUs, crystal violet staining, scanning electron microscopy and Living/Dead bacteria staining assay. The results illustrated that AAEK-CF exhibited excellent anti-adhesion ability to Staphylococcus aureus, and significantly reduced the number of bacteria adhering to the film. More importantly, AAEK-CF could hinder the formation of bacterial biofilm. Furthermore, AAEK-CF indicated no cytotoxicity to mammalian cells, and the cells could grow normally on the modified surface. Hence, our present work demonstrated that the grafting of the SrtA inhibitor-AAEK onto cellulose films enabled to combat bacterial biofilm formation in biomedical applications.

Electrostatic Assembly Technique for Novel Composites Fabrication

Electrostatic assembly is one of the bottom–up approaches used for multiscale composite fabrication. Since its discovery, this method has been actively used in molecular bioscience as well as materials design and fabrication for various applications. Despite the recent advances and controlled assembly reported using electrostatic interaction, the method still possesses vast potentials for various materials design and fabrication. This review article is a timely revisit of the electrostatic assembly method with a brief introduction of the method followed by surveys of recent advances and applications of the composites fabricated. Emphasis is also given to the significant potential of this method for advanced materials and composite fabrication in line with sustainable development goals. Prospective outlook and future developments for micro-/nanocomposite materials fabrication for emerging applications such as energy-related fields and additive manufacturing are also mentioned.

Ligand Diffusion Enables Force-Independent Cell Adhesion via Activating α5β1 Integrin and Initiating Rac and RhoA Signaling

Cells reside in a dynamic microenvironment in which adhesive ligand availability, density, and diffusivity are key factors regulating cellular behavior. Here, the cellular response to integrin-binding ligand dynamics by directly controlling ligand diffusivity via tunable ligand-surface interactions is investigated. Interestingly, cell spread on the surfaces with fast ligand diffusion is independent of myosin-based force generation. Fast ligand diffusion enhances α5β1 but not αvβ3 integrin activation and initiates Rac and RhoA but not ROCK signaling, resulting in lamellipodium-based fast cell spreading. Meanwhile, on surfaces with immobile ligands, αvβ3 and α5β1 integrins synergistically initiate intracellular-force-based canonical mechanotransduction pathways to enhance cell adhesion and osteogenic differentiation of stem cells. These results indicate the presence of heretofore-unrecognized pathways, distinct from canonical actomyosin-driven mechanisms, that are capable of promoting cell adhesion.

Polyelectrolyte Multilayer Films Modification with Ag and rGO Influences Platelets Activation and Aggregate Formation under In Vitro Blood Flow

Surface functionalization of materials to improve their hemocompatibility is a challenging problem in the field of blood-contacting devices and implants. Polyelectrolyte multilayer films (PEMs), which can mimic functions and structure of an extracellular matrix (ECM), are a promising solution to the urgent need for functional blood-contacting coatings. The properties of PEMs can be easily tuned in order to provide a scaffold with desired physico-chemical parameters. In this study chitosan/chondroitin sulfate (Chi/CS) polyelectrolyte multilayers were deposited on medical polyurethane. Afterwards PEMs were modified by chemical cross-linking and nanoparticles introduction. Coatings with variable properties were tested for their hemocompatibility in the cone-plate tester under dynamic conditions. The obtained results enable the understanding of how substrate properties modulate PEMs interaction with blood plasma proteins and the morphotic elements.

Vat polymerization-based bioprinting-process, materials, applications and regulatory challenges

Over the years, the field of bioprinting has attracted attention for its highly automated fabrication system that enables the precise patterning of living cells and biomaterials at pre-defined positions for enhanced cell-matrix and cell-cell interactions. Notably, vat polymerization (VP)-based bioprinting is an emerging bioprinting technique for various tissue engineering applications due to its high fabrication accuracy. Particularly, different photo-initiators (PIs) are utilized during the bioprinting process to facilitate the crosslinking mechanism for fabrication of high-resolution complex tissue constructs. The advancements in VP-based printing have led to a paradigm shift in fabrication of tissue constructs from cell-seeding of tissue scaffolds (non-biocompatible fabrication process) to direct bioprinting of cell-laden tissue constructs (biocompatible fabrication process). This paper, presenting a first-time comprehensive review of the VP-based bioprinting process, provides an in-depth analysis and comparison of the various biocompatible PIs and highlights the important considerations and bioprinting requirements. This review paper reports a detailed analysis of its printing process and the influence of light-based curing modality and PIs on living cells. Lastly, this review also highlights the significance of VP-based bioprinting, the regulatory challenges and presents future directions to transform the VP-based printing technology into imperative tools in the field of tissue engineering and regenerative medicine. The readers will be informed on the current limitations and achievements of the VP-based bioprinting techniques. Notably, the readers will realize the importance and value of highly-automated platforms for tissue engineering applications and be able to develop objective viewpoints towards this field.

Hollow Alginate-Poly-L-Lysine-Alginate Microspheres Promoted an Epithelial-Mesenchymal Transition in Human Colon Adenocarcinoma Cells

Purpose: Today, there is an urgent need to develop a three-dimentional culture systems mimicking native in vivo condition in order to screen potency of drugs and possibly any genetic alterations in tumor cells. Due to the existence of limitations in animal models, the development of three dimensional systems is highly recommended. To this end, we encapsulated human colon adenocarcinoma cell line HT29 with alginate-poly-L-lysine (Alg-PLL) microspheres and the rate of epithelial-mesenchymal transition was monitored. Methods: Cells were randomly divided into three groups; control, alginate and Alg-PLL. To encapsulate cells, we mixed HT-29 cells (1 × 10⁶ ) with 1 mL of 0.05% PLL and 1% Alg mixture and electrosprayed into CaCl2 solution by using a high-voltage power. Cells from all groups were maintained at 37˚C in a humidified atmosphere containing 5% CO₂ for 7 days. Cell viability was assessed by MTT assay. To monitor the stemness feature, we measured the transcription of genes such as Snail, Zeb, and Vimentin by using real-time PCR analysis. Results: Addition of PLL to Alg in a hallowed state increased the cell survival rate compared to the control and Alg groups (P<0.05). Cells inside Alg-PLL tended to form microcellular aggregates while in Alg microspheres an even distribution of HT-29 cells was found. Real-time PCR analysis showed the up-regulation of Snail, Zeb, and Vimentin in Alg-PLL microspheres compared to the other groups, showing the acquisition of stemness feature (P<0.05). Conclusion: This study showed that hallow Alg-PLL microspheres increased the epithelialmesenchymal transition rate after 7 days in in vitro condition. Such approaches could be touted as appropriate in vitro models for drug screening.

Effect of microenvironment on adhesion and differentiation of murine C3H10T1/2 cells cultured on multilayers containing collagen I and glycosaminoglycans

Polyelectrolyte multilayer coating is a promising tool to control cellular behavior. Murine C3H10T1/2 embryonic fibroblasts share many features with mesenchymal stem cells, which are good candidates for use in regenerative medicine. However, the interactions of C3H10T1/2 cells with polyelectrolyte multilayers have not been studied yet. Hence, the effect of molecular composition of biomimetic multilayers, by pairing collagen I (Col I) with either hyaluronic acid or chondroitin sulfate, based primarily on ion pairing and on additional intrinsic cross-linking was studied regarding the adhesion and differentiation of C3H10T1/2 cells. It was found that the adhesion and osteogenic differentiation of C3H10T1/2 cells were more pronounced on chondroitin sulfate-based multilayers when cultured in the absence of osteogenic supplements, which corresponded to the significant larger amounts of Col I fibrils in these multilayers. By contrast, the staining of cartilage-specific matrixes was more intensive when cells were cultured on hyaluronic acid-based multilayers. Moreover, it is of note that a limited osteogenic and chondrogenic differentiation were detected when cells were cultured in osteogenic or chondrogenic medium. Specifically, cells were largely differentiated into an adipogenic lineage when cultured in osteogenic medium or 100 ng mL-1 bone morphogenic protein 2, and it was more evident on the oxidized glycosaminoglycans-based multilayers, which corresponded also to the higher stiffness of cross-linked multilayers. Overall, polyelectrolyte multilayer composition and stiffness can be used to direct cell-matrix interactions, and hence the fate of C3H10T1/2 cells. However, these cells have a higher adipogenic potential than osteogenic or chondrogenic potential.

Tuning the surface immunomodulatory functions of polyetheretherketone for enhanced osseointegration

The adverse macrophage-mediated immune response elicited by the surface of polyetheretherketone (PEEK) is responsible for the formation of fibrous encapsulation and resulting inferior osseointegration of PEEK implants in the dental and orthopedic fields. Therefore, endowing the PEEK surface with immunomodulatory ability is an appealing strategy to enhance implant-bone integration. Herein, a reliable and cost-effective method to construct adherent films with tunable nanoporous structures on PEEK is described. The functionalized surface not only suppresses the acute inflammatory response of macrophages, but also provides a favorable milieu for osteogenic differentiation of human bone marrow mesenchymal stem cells (hBMSCs). Whole genome expression analysis reveals that the suppression effect arises from synergistic inhibition of focal adhesion, Toll-like receptor, and NOD-like receptor signaling pathways, as well as the attenuating loop through the JAK-STAT and TNF signaling pathways in macrophages. Further in vivo studies confirm that the functionalized surface induces less fibrous capsule formation and an improved bone regeneration. The nanoporous films fabricated on PEEK harmonize the early macrophage-mediated inflammatory response and subsequent hBMSCs-centered osteogenic functions consequently yielding superior osseointegration.