Tree gum-based renewable materials: Sustainable applications in nanotechnology,biomedical and environmental fields

The prospective uses of tree gum polysaccharides and their nanostructures in various aspects of food, water, energy, biotechnology, environment and medicine industries, have garnered a great deal of attention recently. In addition to extensive applications of tree gums in food, there are substantial non-food applications of these commercial gums, which have gained widespread attention due to their availability, structural diversity and remarkable properties as ‘green’ bio-based renewable materials. Tree gums are obtainable as natural polysaccharides from various tree genera possessing exceptional properties, including their renewable, biocompatible, biodegradable, and non-toxic nature and their ability to undergo easy chemical modifications. This review focuses on non-food applications of several important commercially available gums (arabic, karaya, tragacanth, ghatti and kondagogu) for the greener synthesis and stabilization of metal/metal oxide NPs, production of electrospun fibers, environmental bioremediation, bio-catalysis, biosensors, coordination complexes of metal–hydrogels, and for antimicrobial and biomedical applications. Furthermore, polysaccharides acquired from botanical, seaweed, animal, and microbial origins are briefly compared with the characteristics of tree gum exudates.     

On the design and efficacy assessment of self‐assembling peptide‐based hydrogel‐glycosaminoglycan mixtures for potential repair of early stage cartilage degeneration

Peptide‐based hydrogels are of interest for their potential use in regenerative medicine. Combining these hydrogels with materials that may enhance their physical and biological properties, such as glycosaminoglycans, has the potential to extend their range of biomedical applications, for example in the repair of early cartilage degeneration. The aim of this study was to combine three self‐assembling peptides (P₁₁‐4, P₁₁‐8, and P₁₁‐12) with chondroitin sulphate at two molar ratios of 1:16 and 1:64 in 130 and 230 mM Na⁺ salt concentrations. The study investigates the effects of mixing self‐assembling peptide and glycosaminoglycan on the physical and mechanical properties at 37°C. Peptide alone, chondroitin sulphate alone, and peptide in combination with chondroitin sulphate were analysed using Fourier transform infrared spectroscopy to determine the β‐sheet percentage, transmission electron microscopy to determine the fibril morphology, and rheology to determine the elastic and viscous modulus of the materials. All of the variables (peptide, salt concentration, and chondroitin sulphate molar ratio) had an effect on the mechanical properties, β‐sheet formation, and fibril morphology of the hydrogels. P₁₁‐4 and P₁₁‐8‐chondroitin sulphate mixtures, at both molar ratios, were shown to have a high β‐sheet percentage, dense entangled fibrillar networks, as well as high mechanical stiffness in both (130 and 230 mM) Na⁺ salt solutions when compared with the P₁₁‐12/chondroitin sulphate mixtures. These peptide/chondroitin sulphate hydrogels show promise for biomedical applications in glycosaminoglycan depleted tissues.     

Molecular design of polymeric materials for biotechnology and medicine

This review describes new polymer materials for biomedical applications developed in the Polymers for Biology Laboratory of the Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences. These include composite rigid sorbents for biochromatography, polymer dispersions for immunoassay, polymer hydrogels for immobilization of enzymes and cells, and polymer ultra thin films as biomembrane models and materials for biosensors. Some general and specific properties of these new materials and models as well as examples of their applications are discussed.     

重金属结合肽（蛋白）的结构分析

金属离子与金属结合肽（蛋白）的相互作用与应用研究,一直是生物无机化学的重点和热点,也是分子间相互作用研究领域的难点。本研究利用ClustalX、BLAST等生物信息技术与方法对大量已知的重金属结合肽进行分析与数据挖掘。确定筛选获得的重金属结合肽常富含His,无Cys,无金属结合肽模式序列,进化不保守;部分氨基酸序列结构（如六肽）可在蛋白数据库中找到相似序列。序列特征主要为Zn^2＋相关的转录因子。本研究为重金属结合蛋白-重金属离子的相互作用分析简化为重金属结合肽-重金属离子的结构模拟与分析提供了重要的理论基础和研究手段。     

纳米材料在生物医学检测中的应用

纳米技术的兴起,对生物医学领域的变革产生了深远的影响。纳米材料是纳米技术发展的重要基础,它具有许多传统材料所不具备的独特的理化性质,因此在生物医学、传感器等重要技术领域有着广泛的应用前景。对几类常见的纳米材料包括纳米金、量子点、磁性纳米粒子、碳纳米管和硅纳米线在蛋白质、DNA、金属离子以及生物相关分子检测方面的应用进行综述。     

DNA-responsive hydrogels that can shrink or swell

Molecule-responsive hydrogels are reputed to be smart materials because of their unique properties. We recently reported that hydrogels containing directly grafted single-stranded (ss) DNA or ssDNA-polyacrylamide conjugate in a semi-interpenetrating network (semi-IPN) manner that "only shrunk" by the addition of ssDNA samples. To date, however, no DNA-responsive hydrogels have been reported capable of "swelling" in response to specific DNAs. Smart materials capable of both shrinking and swelling in response to specific DNAs would be very useful in biochemical and biomedical applications. Here, we show a novel "shrinking or swelling" DNA-responsive mechanism. Novel hybrid hydrogels containing rationally designed ssDNA as the cross-linker were capable of shrinking or swelling in response to ssDNA samples and recognizing a single base difference in the samples. On the basis of the results presented in this paper, it is envisioned that these novel hybrid hydrogels could function and have potential in applications such as DNA-sensing devices and DNA-triggered actuators.     

Recent advances in polysaccharide-based in situ forming hydrogels

Polysaccharides comprise an important class of natural polymers; they are abundant, diverse, polyfunctional, typically benign, and are biodegradable. Using polysaccharides to design in situ forming hydrogels is an attractive and important field of study since many polysaccharide-based hydrogels exhibit desirable characteristics including self-healing, responsiveness to environmental stimuli, and injectability. These characteristics are particularly useful for biomedical applications. This review will discuss recent discoveries in polysaccharide-based in situ forming hydrogels, including network architecture designs, curing mechanisms, physical and chemical properties, and potential applications.     

Three-dimensional biochemical patterning of click-based composite hydrogels via thiolene photopolymerization

Hydrogels formed from (meth)acrylated poly(ethylene glycol) precursors are commonly used in a variety of biomedical applications ranging from tissue engineering to biosensors. While this approach has proven quite diverse, a major limitation to this approach is the heterogeneities and nonidealities that arise in the gels from the chain polymerization process, which increases the difficulty in relating the network structure to the final physical properties of the gel. Here we have exploited the specificity and fidelity of the [3+2] cycloaddition reaction to synthesize hydrogels with controlled architectures and improved mechanical properties. Moreover, we demonstrate a general approach toward the integration of multifunctional photoreactive polypeptide sequences into the network structure that provides a facile way to independently tune the 3D chemical and physical properties of the gel. Standard photolithographic techniques were used to generate a variety of two- and three-dimensional patterns as well as controlled biochemical gradients within existing preformed hydrogels.     

New materials from proteins and peptides

In this review we highlight recent accomplishments in the design of materials from proteins and peptides. Examples include hydrogels made from aggregating designed β-hairpin peptides, whose physical properties respond to small changes in the amino acid composition of the peptide; materials that combine different segments of natural elastomeric proteins - such as elastin, resilin, silk fibroin whose bulk properties are dictated in unanticipated ways by their composition; and hydrogels formed by strings or arrays of protein modules, which are cross-linked by multivalent versions of their peptide ligands, and which may exhibit exquisite stimuli-responsive behavior. The suitability of the unique properties of such new materials for practical applications is also considered.     

Synthesis, swelling behavior, and biocompatibility of novel physically cross-linked polyurethane-block-poly(glycerol methacrylate) hydrogels

Physically cross-linked novel block copolymer hydrogels with tunable hydrophilic properties for biomedical applications were synthesized by controlled radical polymerization of polyurethane macroiniferter and (2,2-dimethyl-1,3-dioxolane) methyl methacrylate. The block copolymers were converted to hydrogels by the selective hydrolysis of poly[(2,2-dimethyl-1,3-dioxolane) methyl methacrylate] block to poly(glycerol methacrylate). The block copolymerization has been monitored by monomer conversion and molecular weight increase as a function of time. It was observed that the polymerization proceeded with a characteristic "living" behavior where both monomer conversion and molecular weight increased linearly, with increasing reaction time. The resulting hydrogels were investigated for their equilibrium water content (EWC), dynamic water contact angles, swelling kinetics, thermodynamic interaction parameters, plasma protein adsorption, and platelet adhesion. Similar to our previous mechanically responsive hydrogels (Mequanint, K.; Sheardown, H. J. Biomater. Sci. Polym. Ed. 2005, 10, 1303-1318), the present results indicated that block copolymer hydrogels have excellent hydrophilicity and swelling behavior with improved modulus of elasticity. The equilibrium swelling was affected by the hydrolysis time, block length of poly(glycerol methacrylate), temperature, and the presence of soluble salts. Fibrinogen adsorption and platelet adhesion were significantly lower for the hydrogels than for the control polyurethane, whereas albumin adsorption increased for the hydrogels in proportion to the contents of poly(glycerol methacrylate). These hydrogels have potential in a number of biomedical applications such as drug delivery and scaffolds for tissue engineering.     

Synthesis and properties of thermo- and pH-sensitive poly(N-isopropylacrylamide)/polyaspartic acid IPN hydrogels

Various interpenetrating polymer network (IPN) hydrogels with sensitivity to temperature and pH were prepared by introducing the pH-sensitive polymer polyaspartic acid (PASP) hydrogel, into the poly(N-isopropylacrylamide) (PNIPAAm) hydrogel system for the purpose of improving its response rate to temperature. The morphologies and thermal behavior of the prepared IPN hydrogels were studied by both scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The IPN hydrogels showed a large and uneven porous network structure, without showing the common PNIPAAm hydrogel structure. The paper moreover studied their swelling properties, such as temperature dependence of equilibrium swelling ratio, shrinking kinetics, re-swelling kinetics and oscillatory swelling behavior in water. The swelling experiment results revealed that IPN hydrogels exhibited much faster shrinking and re-swelling in function of the composition ratio of the two network components. These fast responsive hydrogels foster potential applications in biomedical and biotechnology fields.     

Carbon dioxide induced silk protein gelation for biomedical applications

We present a novel method to fabricate silk fibroin hydrogels using high pressure carbon dioxide (CO(2)) as a volatile acid without the need for chemical cross-linking agents or surfactants. The simple and efficient recovery of CO(2) post processing results in a remarkably clean production method offering tremendous benefit toward materials processing for biomedical applications. Further, with this novel technique we reveal that silk protein gelation can be considerably expedited under high pressure CO(2) with the formation of extensive β-sheet structures and stable hydrogels at processing times less than 2 h. We report a significant influence of the high pressure CO(2) processing environment on silk hydrogel physical properties such as porosity, sample homogeneity, swelling behavior and compressive properties. Microstructural analysis revealed improved porosity and homogeneous composition among high pressure CO(2) specimens in comparison to the less porous and heterogeneous structures of the citric acid control gels. The swelling ratios of silk hydrogels prepared under high pressure CO(2) were significantly reduced compared to the citric acid control gels, which we attribute to enhanced physical cross-linking. Mechanical properties were found to increase significantly for the silk hydrogels prepared under high pressure CO(2), with a 2- and 3-fold increase in the compressive modulus of the 2 and 4 wt % silk hydrogels over the control gels, respectively. We adopted a semiempirical theoretical model to elucidate the mechanism of silk protein gelation demonstrated here. Mechanistically, the rate of silk protein gelation is believed to be a function of the kinetics of solution acidification from absorbed CO(2) and potentially accelerated by high pressure effects. The attractive features of the method described here include the acceleration of stable silk hydrogel formation, free of residual mineral acids or chemical cross-linkers, reducing processing complexity, and avoiding adverse biological responses, while providing direct manipulation of hydrogel physical properties for tailoring toward specific biomedical applications.     

Review: Hydrogels for cell immobilization

Hydrogels are being investigated for mammalian cell immobilization. Their material properties can be engineered for biocompatibility, selective permeability, mechanical and chemical stability, and other requirements as specified by the application including uniform cell distribution and a given membrane thickness or mechanical strength. These aqueous gels are attractive for analytical and tissue engineering applications and can be used with immobilization in therapies for various diseases as well as to generate bioartificial organs. Recent advances have broadened the use of hydrogel cell immobilization in biomedical fields. To provide an overview of available technology, this review surveys the current developments in immobilization of mammalian cells in hydrogels. Discussions cover hydrogel requirements for use in adhesion, matrix entrapment, and microencapsulation, the respective processing methods, as well as current applications. (c) 1996 John Wiley & Sons, Inc.     

Development of a biostable replacement for PEGDA hydrogels

The exceptional tunability of poly(ethylene glycol) (PEG) hydrogel chemical, mechanical, and biological properties enables their successful use in a wide range of biomedical applications. Although PEG diacrylate (PEGDA) hydrogels are often used as nondegradable controls in short-term in vitro studies, it is widely acknowledged that the hydrolytically labile esters formed upon acrylation of the PEG diol make them susceptible to slow degradation in vivo. A PEG hydrogel system that maintains the desirable properties of PEGDA while improving biostability would be valuable in preventing degradation-related failure of gel-based devices in long-term in vivo applications. To this end, PEG diacrylamide (PEGDAA) hydrogels were synthesized and characterized in quantitative comparison to traditional PEGDA hydrogels. It was found that PEGDAA hydrogel modulus and swelling can be tuned over a similar range and to comparable degrees as PEGDA hydrogels with changes in macromer molecular weight and concentration. Additionally, PEGDAA cytocompatibility, low cell adhesion, and capacity for incorporation of bioactivity were analogous to that of PEGDA. In vitro hydrolytic degradation studies showed that the amide-based PEGDAA had significantly increased biostability relative to PEGDA. Overall, these findings indicate that PEGDAA hydrogels are a suitable replacement for PEGDA hydrogels with enhanced hydrolytic resistance. In addition, these studies provide a quantitative measure of the hydrolytic degradation rate of PEGDA hydrogels which was previously lacking in the literature.     

The Binding Ability of a Bicyclic Somatostatin Analogue Towards Cu(II) Ions

Somatostatin (SST) analogues have aroused the interest of scientists for years. This group of compounds is used in the diagnosis and treatment of neuroendocrine tumors. However, new molecules useful as radiopharmaceuticals in targeted therapy are still searched for. Bicyclic peptides seem to be very interesting in this context. These molecules are associated with beneficial properties. In this work, we present studies on the binding ability of the bicyclic analogue of somatostatin toward Cu(II) ions which could potentially be a chelator for copper radionuclides. The research is focused on the analysis of Cu(II) interactions with the metal binding cycle of the ligand and the influence of the receptor binding site on the coordination process. This is a novelty in comparison to the SST analogues used in medicine, where a metal ion is coordinated by a chelator and connected with a bioactive molecule by the linker. In this work, we present the first coordination study for a bicyclic ligand. The obtained results showed that the complexes with only imidazole donors are characterized by significantly higher stability in comparison to the other peptides.     

Sulfated chitin and chitosan as novel biomaterials

Chitin and chitosan are known to be natural polymers and they are non-toxic, biodegradable and biocompatible. Chemical modification of chitin and chitosan with sulfate to generate new bifunctional materials is of interest because the modification would not change the fundamental skeleton of chitin and chitosan, would keep the original physicochemical and biochemical properties and finally would bring new or improved properties. The sulfated chitin and chitosan have a variety of applications, such as, adsorbing metal ions, drug delivery systems, blood compatibility, and antibacterial field. The purpose of this review is to take a closer look about the different synthetic methods and potential applications of sulfated chitin and chitosan. Based on current research and existing products, some new and futuristic approaches in this context area are discussed in detail. From the studies reviewed, we concluded that sulfated chitin and chitosan are promising materials for biomedical applications.     

Hydrogel Nanofilaments via Core-Shell Electrospinning

Recent biomedical hydrogels applications require the development of nanostructures with controlled diameter and adjustable mechanical properties. Here we present a technique for the production of flexible nanofilaments to be used as drug carriers or in microfluidics, with deformability and elasticity resembling those of long DNA chains. The fabrication method is based on the core-shell electrospinning technique with core solution polymerisation post electrospinning. Produced from the nanofibers highly deformable hydrogel nanofilaments are characterised by their Brownian motion and bending dynamics. The evaluated mechanical properties are compared with AFM nanoindentation tests.     

The synthesis and chelation chemistry of DOTA-peptide conjugates

Metal complexes of DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid)-peptide conjugates are increasingly used as targeted imaging and therapeutic radiopharmaceuticals and MRI contrast agents. This review covers the bifunctional derivatives of DOTA, the solution and solid-phase synthesis of DOTA-peptide conjugates, their coordination and chelation chemistry, and the biomedical applications of various DOTA-peptide conjugate metal complexes.     

Enhanced tissue adhesiveness of injectable gelatin hydrogels through dual catalytic activity of horseradish peroxidase

Development of bioadhesives with tunable mechanical strength, high adhesiveness, biocompatibility, and injectability is greatly desirable in all surgeries to replace or complement the sutures and staples. Herein, the dual catalytic activity of horseradish peroxidase is exploited to in situ form the hydroxyphenyl propionic acid‐gelatin/thiolated gelatin (GH/GS) adhesive hydrogels including two alternative crosslinks (phenol‐phenol and disulfide bonds) with fast gelation (few seconds – several minutes) and improved physicochemical properties. Their elastic moduli increase from 6.7 to 10.3 kPa by adding GS polymer that leads to the better stability of GH/GS hydrogels than GH ones. GH/GS adhesive strength is respectively 6.5‐fold and 15.8‐fold higher than GH‐only and fibrin glue that is due to additional disulfide linkages between hydrogels and tissues. Moreover, in vitro cell study with human dermal fibroblast showed the cell‐compatibility of GH/GS hydrogels. Taken together, GH/GS hydrogels can be considered as promising potential adhesive materials for various biomedical applications.     

Facile synthesis of degradable and electrically conductive polysaccharide hydrogels

Degradable and electrically conductive polysaccharide hydrogels (DECPHs) have been synthesized by functionalizing polysaccharide with conductive aniline oligomers. DECPHs based on chitosan (CS), aniline tetramer (AT), and glutaraldehyde were obtained by a facile one-pot reaction by using the amine group of CS and AT under mild conditions, which avoids the multistep reactions and tedious purification involved in the synthesis of degradable conductive hydrogels in our previous work. Interestingly, these one-pot hydrogels possess good film-forming properties, electrical conductivity, and a pH-sensitive swelling behavior. The chemical structure and morphology before and after swelling of the hydrogels were verified by FT-IR, NMR, and SEM. The conductivity of the hydrogels was tuned by adjusting the content of AT. The swelling ratio of the hydrogels was altered by the content of tetraaniline and cross-linker. The hydrogels underwent slow degradation in a buffer solution. The hydrogels obtained by this facile approach provide new possibilities in biomedical applications, for example, biodegradable conductive hydrogels, films, and scaffolds for cardiovascular tissue engineering and controlled drug delivery.