Dynamic Introduction of Cell Adhesive Factor via Reversible Multicovalent Phenylboronic Acid/cis-Diol Polymeric Complexes

RAFT polymerization of a RGD peptide-based methacrylamide monomer for cell adhesion

The present study provides a robust method for the preparation of RGD peptide-based polymers that has important implications in the synthesized biomaterials that support cell adhesion.

POSS-enhanced thermosensitive hybrid hydrogels for cell adhesion and detachment

Thermosensitive poly(N-isopropylacrylamide) (PNIPAM)-based substrates have presented great promise in cell sheet engineering. However, non-functionalized PNIPAM cannot be well applied for cell cultivation, due to the low cell adhesion. Herein, to enhance PNIPAM-based substrates and to promote cell proliferation and detachment, a polyhedral oligomeric silsesquioxane (POSS) nanoscale inorganic enhanced agent has been introduced into PNIPAM matrices to construct POSS-containing hybrid hydrogels. The hydrogels were facilely prepared using POSS as a cross-linker via one-pot crosslinking reaction under UV irradiation. The swelling behavior, thermal stability and the mechanical properties of POSS–PNIPAM hybrid hydrogels have been evaluated and they are all dependent on the content of POSS. The in vitro experiment confirms that human amniotic mesenchymal stem cells (hAMSCs) exhibit clearly enhanced adhesion and proliferation on the substrates of POSS–PNIPAM hybrid hydrogels in comparison to the pure PNIPAM hydrogel without POSS. Based on the thermal-responsiveness of PNIPAM, the proliferated cells are easily released without damage from the surface of hybrid hydrogels. Therefore, POSS-enhanced PNIPAM hybrid hydrogels provide a unique approach for harvesting anchorage dependent stem cells.

Thermosensitive poly(N-isopropylacrylamide) (PNIPAM)-based substrates have presented great promise in cell sheet engineering.

PAMA–Arg brush-functionalized magnetic composite nanospheres for highly effective enrichment of phosphorylated biomolecules

A novel polymer brush-functionalized magnetic composite nanosphere was successfully prepared, exhibiting large enrichment capacity, extremely high detection sensitivity, and high enrichment recovery in phosphorylated biomolecule enrichment.

Dual-sensitive chitosan derivative micelles for site-specific drug release in the treatment of chicken coccidiosis

Here, we report a “dual-sensitive” drug delivery platform packaged with anti-coccidia drug diclazuril (DIC) applied in the field of intestinal-targeted administration.

An Epitope-Imprinted Biointerface with Dynamic Bioactivity for Modulating Cell-Biomaterial Interactions

In this study, an epitope-imprinting strategy was employed for the dynamic display of bioactive ligands on a material interface. An imprinted surface was initially designed to exhibit specific affinity towards a short peptide (i.e., the epitope). This surface was subsequently used to anchor an epitope-tagged cell-adhesive peptide ligand (RGD: Arg-Gly-Asp). Owing to reversible epitope-binding affinity, ligand presentation and thereby cell adhesion could be controlled. As compared to current strategies for the fabrication of dynamic biointerfaces, for example, through reversible covalent or host-guest interactions, such a molecularly tunable dynamic system based on a surface-imprinting process may unlock new applications in in situ cell biology, diagnostics, and regenerative medicine.

Nanopatterned Adhesive, Stretchable Hydrogel to Control Ligand Spacing and Regulate Cell Spreading and Migration

Spatial molecular patterning enables the regulation of adhesion receptor clustering and can thus play a pivotal role in multiple biological activities such as cell adhesion, viability, proliferation, and differentiation. A wide range of nanopatterned, adhesive interfaces have been designed to decipher the essence of molecular-scale interactions between cells and the adhesive interface. Although an interligand spacing of less than 70 nm is a proven prerequisite for the formation of stable focal adhesions, there is a paucity of data concerning how cells behave on substrates featuring heterogeneous adhesiveness. In this study, a stretchable hydrogel functionalized with a quasi-hexagonally arranged nanoarray was stretched along one direction, resulting in ligands periodically arranged in a pattern resembling a centered rectangular lattice with an interligand spacing smaller than 70 nm in one direction and greater than 70 nm in the orthogonal direction. This substrate was utilized to modulate interligand spacing and investigate cell adhesion and migration. An interligand spacing larger than 70 nm-even in just one direction-prevented the establishment of stable focal adhesions. The stretched interface promoted dynamic remodeling at cell contacts, resulting in higher cellular mobility. Our nanopatterned stretchable hydrogel permits reversible control over cell adhesion and migration on nanopatterned ligand interfaces.

Fluorescent Cell-Conjugation by a Multifunctional Polymer: A New Application of the Hantzsch Reaction

Multicomponent reactions (MCRs) can form unique structures with interesting functions, therefore, multifunctional polymers might be simply prepared using MCRs as coupling tools to simultaneously link and generate different functional groups. To verify this concept, a new fluorescent polymer containing phenylboronic acid has been facilely prepared via a one pot method by combining the Hantzsch reaction with reversible addition-fragmentation chain transfer (RAFT) polymerization. The Hantzsch-RAFT system has been found robust to smoothly achieve predesigned multifunctional polymer, which can be used for cell conjugation through the interaction between phenylboronic acid and glycoprotein on cell membrane. The conjugated cells could be directly observed due to the fluorescent Hantzsch moiety in the polymer chain, demonstrating a new application of the old Hantzsch reaction (>130 years) outside organic chemistry. Meanwhile, the conjugated cells remained excellent dispersity in the presence of coagulation protein (lectin), implying that multifunctional polymer a possible anticoagulant for cell separation. We believe that the current research paves a new way to exploit new applications of MCRs in interdisciplinary fields and might prompt the development of other multifunctional polymers based on different MCRs.

Dynamically Tunable Cell Culture Platforms for Tissue Engineering and Mechanobiology

Human tissues are sophisticated ensembles of many distinct cell types embedded in the complex, but well-defined, structures of the extracellular matrix (ECM). Dynamic biochemical, physicochemical, and mechano-structural changes in the ECM define and regulate tissue-specific cell behaviors. To recapitulate this complex environment in vitro, dynamic polymer-based biomaterials have emerged as powerful tools to probe and direct active changes in cell function. The rapid evolution of polymerization chemistries, structural modulation, and processing technologies, as well as the incorporation of stimuli-responsiveness, now permit synthetic microenvironments to capture much of the dynamic complexity of native tissue. These platforms are comprised not only of natural polymers chemically and molecularly similar to ECM, but those fully synthetic in origin. Here, we review recent in vitro efforts to mimic the dynamic microenvironment comprising native tissue ECM from the viewpoint of material design. We also discuss how these dynamic polymer-based biomaterials are being used in fundamental cell mechanobiology studies, as well as towards efforts in tissue engineering and regenerative medicine.

Antibacterial activity and osseointegration of silver-coated poly(ether ether ketone) prepared using the polydopamine-assisted deposition technique

PEEK-PDA-Ag substrates may be a promising orthopaedic implant material due to the outstanding biocompatibility and antibacterial properties.

Smart Thin Hydrogel Coatings Harnessing Hydrophobicity and Topography to Capture and Release Cancer Cells

Smart thin hydrogel coatings are fabricated to capture and release targeted cancer cells by simultaneously tuning surface hydrophobicity and topography. At physiological temperature, the targeted cancer cells are captured on the hydrophobic and wrinkled coating surface. At room temperature, the captured cells are released from the hydrophilic and smooth coating surface.

pH-Activated Targeting Drug Delivery System Based on the Selective Binding of Phenylboronic Acid

Phenylboronic acid (PBA) is a tumor-targeting molecule, but its nonspecific interaction with normal cells or other components containing cis-diol residues undoubtedly limits its potential application in tumor-targeting drug delivery. Herein, we developed fructose-coated mixed micelles via PBA-terminated polyethylene glycol monostearate (PBA-PEG-C18) and Pluronic P123 (PEG20-PPG70-PEG20) to solve this problem, as the stability of borate formed by PBA and fructose was dramatically dependent on pH. The fluorescence spectroscopic results indicated that the borate formed by PBA and fructose decomposed at a decreased pH, and better binding between PBA and sialic acid (SA) was observed at a low pH. These results implied that the fructose groups decorated on the surface of the micelles could be out-competed by SA at a low pH. In vitro uptake and cytotoxicity studies demonstrated that the fructose coating on the mixed micelles improved the endocytosis and enhanced the cytotoxicity of drug-loaded mixed micelles in HepG2 cells but reduced the cytotoxicity in normal cells. These results demonstrate that a simple decorating strategy may facilitate PBA-targeted nanoparticles for tumor-specific drug delivery.

Cells Cultured on Core-Shell Photonic Crystal Barcodes for Drug Screening

The development of effective drug screening platforms is an important task for biomedical engineering. Here, a novel methacrylated gelatin (GelMA) hydrogel-encapsulated core-shell photonic crystal (PhC) barcode particle was developed for three-dimensional cell aggregation culture and drug screening. The GelMA shells of the barcode particles enable creation of a three-dimensional extracellular matrix (ECM) microenvironment for cell adhesion and growth, while the PhC cores of the barcode particles provide stable diffraction peaks that can encode different cell spheroids during culture and distinguish their biological response during drug testing. The applicability of this cell spheroids-on-barcodes platform was investigated by testing the cytotoxic effect of tegafur (TF), a prodrug of 5-fluorouracil (5-FU), on barcode particle-loaded liver HepG2 and HCT-116 colonic tumor cell spheroids. The cytotoxicity of TF against the HCT-116 tumor cell spheroids was enhanced in systems using cocultures of HepG2 and NIH-3T3 cells, indicating the effectiveness of this multiple cell spheroids-on-barcodes platform for drug screening.

Simultaneous expression and transportation of insulin by supramolecular polysaccharide nanocluster

Drug/gene transportation systems with stimuli-responsive release behaviors are becoming research hotspots in biochemical and biomedical fields. In this work, a glucose-responsive supramolecular nanocluster was successfully constructed by the intermolecular complexation of phenylboronic acid modified β-cyclodextrin with adamantane modified polyethylenimine, which could be used as a biocompatible carrier for insulin and pCMV3-C-GFPSpark-Ins DNA which could express insulin co-delivery. Benefiting from the response capability of phenylboronic acid moiety toward glucose, the encapsulated insulin could be specifically released and the corresponding targeted DNA could efficiently express insulin in HepG2 cell, accompanied by the high-level insulin release in vitro. Our results demonstrate that the simultaneous insulin drug delivery and insulin gene transfection in a controlled mode may have great potential in the clinical diabetes treatments.

Fast and Tight Boronate Formation for Click Bioorthogonal Conjugation

A new click bioorthogonal reaction system was devised to enable the fast ligation (k(ON) ≈340 m(-1)  s(-1)) of conjugatable derivatives of a rigid cyclic diol (nopoldiol) and a carefully optimized boronic acid partner, 2-methyl-5-carboxymethylphenylboronic acid. Using NMR and fluorescence spectroscopy studies, the corresponding boronates were found to form reversibly within minutes at low micromolar concentration in water, providing submicromolar equilibrium constant (K(eq) ≈10(5) -10(6) m(-1)). Efficient protein conjugation under physiological conditions was demonstrated with model proteins thioredoxin and albumin, and characterized by mass spectrometry and gel electrophoresis.

The design of reversible hydrogels to capture extracellular matrix dynamics

The extracellular matrix (ECM) is a dynamic environment that constantly provides physical and chemical cues to embedded cells. Much progress has been made in engineering hydrogels that can mimic the ECM, but hydrogel properties are, in general, static. To recapitulate the dynamic nature of the ECM, many reversible chemistries have been incorporated into hydrogels to regulate cell spreading, biochemical ligand presentation and matrix mechanics. For example, emerging trends include the use of molecular photoswitches or biomolecule hybridization to control polymer chain conformation, thereby enabling the modulation of the hydrogel between two states on demand. In addition, many non-covalent, dynamic chemical bonds have found increasing use as hydrogel crosslinkers or tethers for cell signalling molecules. These reversible chemistries will provide greater temporal control of adhered cell behaviour, and they allow for more advanced in vitro models and tissue-engineering scaffolds to direct cell fate.

Engineering Dynamic Biointerfaces

Recent advances in dynamic biointerfaces enable spatiotemporal control over cell position and migration after attachment using substrates that employ chemical, optical, thermal, or electrical triggers. This review focuses on flexible and accessible methods for the fabrication of cellular arrays or co cultures for fundamental studies of cell biology or regenerative medicine.

Switching biological functionalities of biointerfaces via dynamic covalent bonds

We construct a stimuli responsive biointerface via a dynamic covalent bond that could switch its surface biofunctionalities on demand. The switchability is achieved via reversible attaching/detaching of aldehyde end-functionalized biomacromolecules.

Photoresponsive Cucurbit[8]uril-Mediated Adhesion of Bacteria on Supported Lipid Bilayers

In this work, the development of a photoresponsive platform for the presentation of bioactive ligands to study receptor-ligand interactions has been described. For this purpose, supramolecular host-guest chemistry and supported lipid bilayers (SLBs) have been combined in a microfluidic device. Quartz crystal microbalance with dissipation monitoring (QCM-D) studies on methyl viologen (MV)-functionalized oligo ethylene glycol-based self-assembled monolayers, gel and liquid-state SLBs have been compared for their nonfouling properties in the case of ConA and bacteria. In combination with bacterial adhesion test, negligible nonspecific bacterial adhesion is observed only in the case of methyl-viologen-modified liquid-state SLBs. Therefore, liquid-state SLBs have been identified as most suitable for studying specific cell interactions when MV is incorporated as a guest on the surface. The photoswitchable supramolecular ternary complex is formed by assembling cucurbit[8]uril (CB[8]) and an azobenzene-mannose conjugate (Azo-Man) onto MV-functionalized liquid-state SLBs and the assembly process has been characterized using QCM-D and fluorescence techniques. Mannose has been found to enable binding of E. coli via cell-surface receptors on the nonfouling supramolecular SLBs. Optical switching of the azobenzene moiety allows us to "erase" the bioactive surface after bacterial binding, providing the potential to develop reusable sensors. Localized photorelease of bacterial cells has also been shown indicating the possibility of optically guiding cellular growth, migration, and intercellular interactions.

CH-π Interaction Driven Macroscopic Property Transition on Smart Polymer Surface

Life systems have evolved to utilize weak noncovalent interactions, particularly CH-π interaction, to achieve various biofunctions, for example cellular communication, immune response, and protein folding. However, for artificial materials, it remains a great challenge to recognize such weak interaction, further transform it into tunable macroscopic properties and realize special functions. Here we integrate monosaccharide-based CH-π receptor capable of recognizing aromatic peptides into a smart polymer with three-component "Recognition-Mediating-Function" design, and report the CH-π interaction driven surface property switching on smart polymer film, including wettability, adhesion, viscoelasticity and stiffness. Detailed studies indicate that, the CH-π interaction induces the complexation between saccharide unit and aromatic peptide, which breaks the initial amphiphilic balance of the polymer network, resulting in contraction-swelling conformational transition for polymer chains and subsequent dramatic switching in surface properties. This work not only presents a new approach to control the surface property of materials, but also points to a broader research prospect on CH-π interaction at a macroscopic level.

A rationally designed peptidomimetic biosensor for sialic acid on cell surfaces

We have developed peptidomimetic sialic acid (Sia) biosensors using boronic acid and arginine groups on the peptide backbone. The designed peptides were conjugated to fluorescent streptavidin via biotin enabling the optical labeling of cells. This approach provides unique opportunities to detect Sia composition on the cell surfaces and filopodia.

Responsive cell–material interfaces

Major design aspects for novel biomaterials are driven by the desire to mimic more varied and complex properties of a natural cellular environment with man-made materials. The development of stimulus responsive materials makes considerable contributions to the effort to incorporate dynamic and reversible elements into a biomaterial. This is particularly challenging for cell–material interactions that occur at an interface (biointerfaces); however, the design of responsive biointerfaces also presents opportunities in a variety of applications in biomedical research and regenerative medicine. This review will identify the requirements imposed on a responsive biointerface and use recent examples to demonstrate how some of these requirements have been met. Finally, the next steps in the development of more complex biomaterial interfaces, including multiple stimuli-responsive surfaces, surfaces of 3D objects and interactive biointerfaces will be discussed.

Dynamic biointerfaces: from recognition to function

The transformation of recognition signals into regulating macroscopic behaviors of biological entities (e.g., biomolecules and cells) is an extraordinarily challenging task in engineering interfacial properties of artificial materials. Recently, there has been extensive research for dynamic biointerfaces driven by biomimetic techniques. Weak interactions and chirality are two crucial routes that nature uses to achieve its functions, including protein folding, the DNA double helix, phospholipid membranes, photosystems, and shell and tooth growths. Learning from nature inspires us to design dynamic biointerfaces, which usually take advantage of highly selective weak interactions (e.g., synergetic chiral H-bonding interactions) to tailor their molecular assemblies on external stimuli. Biomolecules can induce the conformational transitions of dynamic biointerfaces, then drive a switching of surface characteristics (topographic structure, wettability, etc.), and eventually achieve macroscopic functions. The emerging progresses of dynamic biointerfaces are reviewed and its role from molecular recognitions to biological functions highlighted. Finally, a discussion is presented of the integration of dynamic biointerfaces with the basic biochemical processes, possibly solving the big challenges in life science.

Saccharides and temperature dual-responsive hydrogel layers for harvesting cell sheets

A novel non-invasive approach for harvesting cell sheets was demonstrated just by adding saccharide biomolecules into cell culture medium and without reduction of the temperature.

Facile synthesis of guanidyl-functionalized magnetic polymer microspheres for tunable and specific capture of global phosphopeptides or only multiphosphopeptides

The highly selective and efficient capture of heterogeneous types of phosphopeptides is critical for comprehensive and in-depth phosphoproteome analysis, but it still remains a challenge since the lack of affinity material with large binding capacity and controllable specificity. Here, a new affinity material was prepared to improve the enrichment capacity and endue the tunable specificity by introducing guanidyl onto poly(glycidyl methacrylate) (PGMA) modified Fe3O4 microsphere (denoted as Fe3O4@PGMA-Guanidyl). The thick polymer shell endows the composite microsphere with large amount of guanidyl and is beneficial to enhancing the affinity interaction between phosphopeptides and the material. Interestingly, the Fe3O4@PGMA-Guanidyl possesses tunable enriching ability for global phosphopeptides or only multiphosphopeptides through simple regulation of buffer composition. The composite has large enrichment capacity (200 mg g(-1)), extremely high detection sensitivity (0.5 fmol), high enrichment recovery (91.30%), great specificity, and rapid magnetic separation. Moreover, the result of the application to capture of phosphopeptides from tryptic digest of nonfat milk has demonstrated the great potential of Fe3O4@PGMA-Guanidyl in detection and identification of low-abundance phosphopeptides of interest in biological sample.