Taolei Sun

Functional biointerface materials inspired from nature

Controlling the interfacial chemical and physical properties, and thus modulating the behaviours of cells and biomolecules on material surfaces, form an important foundation for the development of high-performance biomaterials and devices. Biological systems in nature exhibit unique features in this aspect. The first one is that the superior properties of natural biomaterials are normally not determined by their bulk properties, but more related to the multi-scale micro- and nanostructures on the surface; the second is that biological systems usually utilize highly specific weak interactions (e.g. hydrogen bonding interaction, hydrophobic interaction, etc.) to solve the problems of biomolecule interactions; the third is that the biomolecules in nature are often chiral molecules and show high preference for one specific enantiomorphous configuration, suggesting a distinctive chiral recognition mechanism in biological systems. These features bring much inspiration to design novel biointerface materials with special functionalities, e.g. structural biointerface materials, smart biointerface materials and chiral biointerface materials. The purpose of this critical review is to give a brief introduction of recent advances in these aspects (90 references).

Biomimetic Smart Interface Materials for Biological Applications

Controlling the surface chemical and physical properties of materials and modulating the interfacial behaviors of biological entities, e.g., cells and biomolecules, are central tasks in the study of biomaterials. In this context, smart polymer interface materials have recently attracted much interest in biorelated applications and have broad prospects due to the excellent controllability of their surface properties by external stimuli. Among such materials, poly(N-isopropylacrylamide) and its copolymer films are especially attractive due to their reversible hydrogen-bonding-mediated reversible phase transition, which mimics natural biological processes. This platform is promising for tuning surface properties or to introduce novel biofunctionalities via copolymerization with various functional units and/or combination with other materials. Important progress in this field in recent years is highlighted.

How Many Lithium Ions Can Be Inserted onto Fused C6 Aromatic Ring Systems

A fundamental and persistent problem in the study of carbonbased electrode materials for lithium ion batteries is the question of how many lithium ions can be inserted onto a C6 aromatic ring. Although different empirical models of Lix/C6 (x< 3) have been proposed, the question remains unresolved. Herein we employ 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA), an aromatic compound containing a naphthalene ring system (fused C6 aromatic rings), to demonstrate that each carbon in a C6 ring can accept a Li ion to form a Li6/C6 additive complex through a reversible electrochemical lithium addition reaction. This process results in Li ion insertion capacities of up to nearly 2000 mAhg , depending on the exact molecular structure. This value is several times higher than any other organic electrode material previously reported and can be fully released under certain conditions. Our experiments and theoretical calculations indicate that the anhydride groups on the sides of the aromatic system are crucial for this process, which provides a promising strategy for the design of novel high-performance organic electrode materials. Organic molecules are intriguing candidates for electrode materials for use in rechargeable Li ion batteries. The application of such species has aroused much interest recently, owing to the obvious advantages of such a system: no need for rare metals, low safety risks compared to transition metal oxides, and design flexibility at the molecular level. However, organic molecules are usually considered to possess relatively poor specific energies and cycling properties, as compared to those of inorganic materials, and these factors greatly limit their practical application. Recently, studies on aromatic carbonyl derivatives showed that organic materials can possess outstanding electrochemical performance comparable to, or even superior to, inorganic materials. Furthermore, the wide diversity of organic redox systems, as well as the excellent flexibility in their molecular design, suggest even greater prospects for these materials, and this has inspired the exploration of new organic Li ion insertion systems with improved performance. Aromatic C6 rings are the basic structural units of graphite and other carbon-based electrode materials, which are the most commonly used anodes in commercial Li ion batteries owing to their high electric conductivity and low cost. It has traditionally been believed that each C6 ring can accept one Li ion to form an intercalated Li/C6 complex, giving a relatively low theoretical capacity of 372 mAhg . Recently, studies on graphene, nanographene, and their derivatives reveal that, through the reduction of size and dimensionality, these materials exhibit unique electric and electrochemical properties superior to those of conventional graphitic materials; thus, these materials are currently a hot research topic. In studies of electrode materials for Li ion batteries, these derivatives also exhibit high reversible capacities of up to almost twice the theoretical value of graphite, although the detailed mechanism is still unclear. This leads to a fundamental question in the study of carbonbased electrode materials: How many Li ions can actually be inserted onto each C6 aromatic ring? Multi-ring aromatics (for example, naphthalene, NTCDA, perylene, etc.) and their derivatives have planar C6 ring structures similar to graphene or nanographene. NTCDA is a typical example; it has a naphthalene-like ring structure consisting of two C6 rings fused together along with two cyclic anhydride groups (Figure 1a). NTCDA is a well-known organic semiconductor with good crystallinity and has been extensively studied for use in molecular electric devices. It provides an ideal model to study Li ion insertion onto C6 rings owing to the minimal number of C6 rings it possesses, which guarantees the necessary insolubility of the electrode materials in the commonly used electrolyte solution (ethylene carbonate/dimethyl carbonate/LiPF6) for Li ion batteries. NTCDA also possesses the necessary degree of conductivity for electron transport among molecules. We investigated the electrochemical Li ion insertion/deinsertion properties of NTCDA using model test cells with Li metal as the counter electrode. The working electrode consisted of NTCDA, acetylene black (AB), and polytetrafluoroethylene binders in a weight ratio of about 60:35:5. The cells were initially cycled by discharging (Li ion insertion) and charging (Li ion deinsertion) repeatedly in a potential range of 0.001–3.0 V vs. Li/Li at a moderate current rate of 100 mAg . Figure 1b shows selected discharge/charge curves (the 1st, 2nd, 3rd, and 8th cycles) for NTCDA. Figure 1c shows the corresponding discharge and charge capacities of NTCDA versus the cycle number. The first discharge and charge capacities are 1273 and 724 mAhg , respectively, showing a coulombic efficiency [*] X. Han, G. Qing, T. Sun State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology Wuhan, 430070 (China) E-mail: suntaolei@iccas.ac.cn

Polymer‐Based Stimuli‐Responsive Recyclable Catalytic Systems for Organic Synthesis

The introduction of stimuli-responsive polymers into the study of organic catalysis leads to the generation of a new kind of polymer-based stimuli-responsive recyclable catalytic system. Owing to their reversible switching properties in response to external stimuli, these systems are capable of improving the mass transports of reactants/products in aqueous solution, modulating the chemical reaction rates, and switching the catalytic process on and off. Furthermore, their stimuli-responsive properties facilitate the separation and recovery of the active catalysts from the reaction mixtures. As a fascinating approach of the controllable catalysis, these stimuli-responsive catalytic systems including thermoresponsive, pH-responsive, chemo-mechano-chemical, ionic strength-responsive, and dual-responsive, are reviewed in terms of their nanoreactors and mechanisms.

Nucleotide-Responsive Wettability on a Smart Polymer Surface

A smart copolymer film that is sensitive to nucleotide species in solution was developed. The film exhibits ann excellent reversible wettability response to nucleotide solutions, which is accompanied by a phase change and the corresponding swell and shrinkage of the copolymer.

Chirality‐Triggered Wettability Switching on a Smart Polymer Surface

IO N Chiral recognition and enantioselective interactions of biomolecules are of fundamental importance in biological processes in nature, [ 1–3 ] and also for various applications in biochemistry, medicine, and industry. [ 4 , 5 ] For different chiral molecular species, many synthetic chiral recognition systems have been developed, [ 6–8 ] with applications such as chiral detection and separation, and asymmetric catalysis, etc. However, recognition is usually only the fi rst step, and a more appealing task is to translate the chiral signals into other processes or macroscopic properties and functions of materials, [ 9 ] which will bring great advantages to applications, but is quite challenging for chemists. Here we report the chirality-triggered wettability switching on smart copolymer fi lms containing dipeptide units. Monosaccharide enantiomers stereoselectively interact with L -dipeptide units, which is translated into differential conformational changes of copolymer chains by a cooperative hydrogen-bonding interaction. It results in discrepant wettability responses with a contact angle difference larger than 90 ° on a textured substrate, being accompanied by changes of other fi lm properties, e.g., volume. This work points to a promising direction for developing novel chirality-responsive materials, which fi nd broad applications in controllable chiral separation, chiral medicine, smart bio-devices, etc. Smart surfaces [ 10–13 ] can change their surface properties conveniently according to external stimuli, thus have aroused much interest recently. Directing the chiral recognition of biomolecules onto smart surfaces to develop chirality-responsive surfaces may open up new avenues for studies of both chiral and smart materials. As a typical example of a smart surface material, a poly( N -isopropylacrylamide) (PNIPAAm) fi lm can change its wettability and volume readily with changes of environmental temperature. [ 13 , 14 ] The responsiveness originates from the reversible contraction and stretching of PNIPAAm chains that is induced by the tunable hydrogenbonding interaction surrounding them. [ 15 ] On the other hand, hydrogen bonding is also one of the most important forces driving biomolecule interactions in natural systems. Based on

Stereochemistry triggered differential cell behaviours on chiral polymer surfaces

One of the distinct biochemical signatures of life is the high chiral preference of biomolecules that compose the organisms, e.g.L-amino acids, D-sugars, L-phospholipids. As a result, many biological and physiological processes are greatly influenced by the chirality of biomolecules. This inspires the introduction of chiral effects into biomaterials research. For this purpose, we developed a novel chiral polymer brush film system containing amino acid units and report that the stereochemistry of the polymer films significantly influences the cell/substrate interaction. With two adhesive cell lines—COS-7 and bEnd.3 as examples, here we report a study of differential cell behaviors on chiral polymer film. We show that the cells can adhere, grow, spread, and assemble much better on the L-amino acid based polymer film than on the corresponding D film, although their chemical and other physical properties are all the same, indicating that the L configuration of the polymer film has better cytocompatibility than the D configuration. It not only implies a novel strategy for the design of new generation of biomaterials and devices based on the chiral effect, but may also add important knowledge to the understanding the origin of chiral preference in biosystems.

Chiral effect at protein/graphene interface: a bioinspired perspective to understand amyloid formation.

Protein misfolding to form amyloid aggregates is the main cause of neurodegenerative diseases. While it has been widely acknowledged that amyloid formation in vivo is highly associated with molecular surfaces, particularly biological membranes, how their intrinsic features, for example, chirality, influence this process still remains unclear. Here we use cysteine enantiomer modified graphene oxide (GO) as a model to show that surface chirality strongly influences this process. We report that R-cysteine modification suppresses the adsorption, nucleation, and fiber elongation processes of Aβ(1-40) and thus largely inhibits amyloid fibril formation on the surface, while S-modification promotes these processes. And surface chirality also greatly influences the conformational transition of Aβ(1-40) from α-helix to β-sheet. More interestingly, we find that this effect is highly related to the distance between chiral moieties and GO surface, and inserting a spacer group of about 1-2 nm between them prevents the adsorption of Aβ(1-40) oligomers, which eliminates the chiral effect. Detailed study stresses the crucial roles of GO surface. It brings novel insights for better understanding the amyloidosis process on surface from a biomimetic perspective.

Modulating Cell Behaviors on Chiral Polymer Brush Films with Different Hydrophobic Side Groups

Chirality is one of the significant biochemical signatures of life. Nearly all biological polymers are homochiral as they usually show high preference toward one specific enantiomer. This phenomenon inspires us to design biomaterials with chiral units and study their interactions with cells and other biological entities. In this article, through adopting three pairs of aliphatic amino acids with different hydrophobic side groups as chiral species, and using two adhesive cell lines as examples, we show that the chirality of polymer brushes can trigger differential cell behaviors on the enantiomorphous surfaces, and more interestingly, such chiral effect on cellular behaviors can be modulated in a certain extent by varying the hydrophobic side groups of the chiral moieties composing the polymers. This work not only proves the versatility of the chiral effect at the cell level but also demonstrates a method to bridge the gap between organic signal molecules and biomaterials. It thus points out a promising approach for designing novel biomaterials based on the chiral effect, which will be an important complement for conventional strategies in the study of biomaterials.

One-Step Controllable Synthesis for High-Quality Ultrafine Metal Oxide Semiconductor Nanocrystals via a Separated Two-Phase Hydrolysis Reaction

A one-step synthesis method is described to prepare high-quality ultrafine inorganic semiconductor nanocrystals via a two-phase interface hydrolysis reaction under hydrothermal conditions. With the synthesis of ZrO2 quantum dots as an example, we show that the prepared nanocrystals have good monodispersity and high crystallinity, as well as other related superior properties, e.g., strong photoluminescence and excellent photocatalytic activities. Also the crystal size can be conveniently adjusted in the range below 10 nm through controlling the reaction temperature. Besides that, this method also shows other distinct advantages compared with other methods reported previously. First, the preparation process is simple and cheap and does not contain any complicated posttreatment procedure. Second, products (without coating) can be collected from the organic phase which effectively avoids grain aggregation induced by the capillary concentration in the water environment. Third, the production yield is very high (almost 100%) and the organic and water phases after reaction can be easily recycled for next reaction. Therefore, it provides a promising strategy for the large-scale industrial production of different kinds of high-quality inorganic nanocrystals.