Polysaccharides based hydrogels for biological applications

Polysaccharides based hydrogels show several peculiar properties which can be so reassumed: • Capability to absorb a great amount of water once immersed in biological fluids, assuming, consequently, a structure similar to extracellular matrix or biological tissue • Tissotropic property, i.e. possibility to be injected through a needle without lose of their rheological properties. These fundamental properties make them ideal materials for several biomedical applications, such as cellular scaffold, coatings for biomedical disposals, treatments for different diseases, controlled release of drugs, etc. Hyaluronane, Carboxymethyl cellulose and Alginic acid based 50% hydrogels (i.e. 50% of the carboxylate groups present in the macromolecule chain were involved in the cross-linking reaction) are synthesised. Their effectiveness in promoting cells adhesion and proliferation was verified. Furthermore the possibility of injecting and sterilising hydrogels permitted to test the effect of Hyal 50% in the osteoarthritis therapy. It was found that the in vivo effect of Hyal 50% in the treatment of surgically created chondral defect in the rabbit knee was positive. These materials can be both chemically and morphologically modified. In fact, the insertion of sulphate groups increase their hemocompatibility as demonstred by the increase of TT (time necessary to turn the fibrinogen to thrombin). Furthermore microporous hydrogels were obtained and tested as drug controlled release systems.     

Self-assembled small molecular weight hydrogels of prodrugs

Prodrugs as building unit for construction of various hydrogelator in response to different stimulus (e.g., temperature, enzyme, pH value, ion).     

Electroactive self-assembled monolayers that permit orthogonal control over the adhesion of cells to patterned substrates

This article describes an electroactive substrate that displays two independent dynamic functions for controlling the adhesion of cells. The approach is based on self-assembled monolayers on gold that are patterned into regions presenting the Arg-Gly-Asp peptide cell adhesion ligand. The patterned regions differ in the electrochemical properties of the linkers that tether the peptides to the monolayer. In this work, three distinct chemistries are employed that provide for release of the ligand on application of a negative potential, release of the ligand on application of a positive potential, and no change in response to a potential. Cells were allowed to attach to a monolayer patterned into circular regions comprising the three chemistries. Treatment with electric potentials of 650 or -650 mV resulted in the selective release of adherent cells only from regions that display the relevant electroactive groups. This example establishes the preparation of dynamic substrates with multiple functions and will be important to preparing model cultures derived from multiple cell types, with control over the temporal interactions of each cell population.     

Strong and Injectable Hydrogels Based on Multivalent Metal Ion-Peptide Cross-linking

Injectable hydrogels are ideal biomaterials for delivering cells, growth factors and drugs specifically to localized lesions and subsequent controlled release. Many factors can affect the efficacy of injectable hydrogels. To avoid potential damage to encapsulated cells or drugs, injectable hydrogels should be highly dynamic so that they can undergo shear-thinning at low strain rates and rapidly reform after injection. However, dynamic hydrogels are often mechanically weak, leading to the leakage of encapsulated cells or drugs. Here we demonstrated a convenient method to improve the mechanical strength without jeopardizing the dynamic properties of hydrogels by using metal ion-peptide crosslinkers containing multiple metal ion-ligand bonds. We showed that the dynamic properties of the hydrogels correlated with the intrinsic dynamics of the metal-ligand bonds and were not affected by the formation of multivalent binding. Yet, the mechanical stability of the hydrogels was significantly improved due to the increased thermodynamic stability of the crosslinkers. We further showed that the drug release rates were slowed down by the formation of multivalent crosslinkers. Our results highlight the importance of ligand valency to the mechanical response of hydrogels and provide a universal route to rationally tune the dynamic and mechanical properties of injectable hydrogels.     

A Molecular Toolkit for the Functionalization of Titanium‐Based Biomaterials That Selectively Control Integrin‐Mediated Cell Adhesion

We present a click chemistry‐based molecular toolkit for the biofunctionalization of materials to selectively control integrin‐mediated cell adhesion. To this end, α5β1‐selective RGD peptidomimetics were covalently immobilized on Ti‐based materials, and the capacity to promote the selective binding of α5β1 was evaluated using a solid‐phase integrin binding assay. This functionalization strategy yielded surfaces with a nine‐fold increased affinity for α5β1, in comparison to control samples, and total selectivity against the binding of the closely related integrin αvβ3. Moreover, our methodology allowed the screening of several phosphonic acid containing anchoring units to find the best spacer–anchor moiety required for establishing an efficient binding to titanium and to promote selective integrin binding. The integrin subtype specificity of these biofunctionalized surfaces was further examined in vitro by inducing selective adhesion of genetically modified fibroblasts, which express exclusively the α5β1 integrin. The versatility of our molecular toolkit was proven by shifting the cellular specificity of the materials from α5β1‐ to αvβ3‐expressing fibroblasts by using an αvβ3‐selective peptidomimetic as coating molecule. The results shown here represent the first functionalization of Ti‐based materials with α5β1‐ or αvβ3‐selective peptidomimetics that allow an unprecedented control to discriminate between α5β1‐ and αvβ3‐mediated adhesions. The role of these two integrins in different biological events is still a matter of debate and is frequently discussed in literature. Thus, such bioactive titanium surfaces will be of great relevance for the study of integrin‐mediated cell adhesion and the development of new biomaterials targeting specific cell types.     

PEG作为成孔剂对聚(N-异丙基丙烯酰胺-co-丙烯酸)水凝胶性能的影响

以PEG400,1000,6000为成孔剂,合成了一系列聚(N-异丙基丙烯酰胺co丙烯酸)水凝胶,研究了成孔剂分子量和数量对凝胶性能的影响.结果表明,聚乙二醇(PEG)分子充当成孔剂,不参与反应.PEG分子量越大,投料越多,所得凝胶孔的孔径越大,孔数目越多,在室温时可以容纳更多的水分子,因而溶胀率也越大.凝胶的大孔结构有利于水分子的进出,所以响应速率比普通共聚凝胶快.随着PEG分子量增大,孔数目增多,响应速率相应变快.     

Light‐Triggered Multifunctionality at Surfaces Mediated by Photolabile Protecting Groups

Photoremovable protecting groups (PRPGs) are applied to organic surfaces, thin polymer films, and hydrogels to achieve light‐based remote control of their (bio)chemical and physical properties. These can be localized (i.e. patterned), tunable by exposure dose, and generated on‐demand. Using PRPGs with independent response to different wavelengths, multifunctional materials with a number of individually addressable functional states can be generated. Light‐triggered polymerization, crosslinking, and degradation processes as well as release of attached molecules can be realized. Light‐responsive surfaces and materials based on PRPGs open interesting possibilities for the next generation of instructive materials for cell culture and tissue regeneration.     

Build in seconds: Small-molecule hydrogels of self-assembled tryptophan derivatives

Small-molecule hydrogels based on amino acid derivatives have promising applications in many biological fields, including cell culture, drug delivery, and tissue engineering. Although these hydrogels have been widely reported to have low cytotoxicity, biocompatibility, and tunable bioactivity, problems such as harsh preparation conditions and complex material design hinder their application. Herein, by adjusting pH to induce non-covalent interactions between small-molecule tryptophan derivatives (N-[(phenylmethoxy)carbonyl]-l-tryptophan, Mw: 338.35), we developed a self-assembled three-dimensional network hydrogel that can be rapidly formed in seconds. And the supramolecular self-assembly mechanism of the hydrogels was also investigated in detail through experimental characterizations and density functional theory calculation. As-prepared hydrogels also exhibit reversible pH-stimulated response and self-healing properties. This study details a research process for the simple and rapid preparation of tryptophan derivative-based hydrogels, which provides more reference ideas for the future development of materials based on other amino acid derivatives.     

Biomimetic Strain-Stiffening Self-Assembled Hydrogels

Supramolecular structures with strain-stiffening properties are ubiquitous in nature but remain rare in the lab. Herein, we report on strain-stiffening supramolecular hydrogels that are entirely produced through the self-assembly of synthetic molecular gelators. The involved gelators self-assemble into semi-flexible fibers, which thereby crosslink into hydrogels. Interestingly, these hydrogels are capable of stiffening in response to applied stress, resembling biological intermediate filaments system. Furthermore, strain-stiffening hydrogel networks embedded with liposomes are constructed through orthogonal self-assembly of gelators and phospholipids, mimicking biological tissues in both architecture and mechanical properties. This work furthers the development of biomimetic soft materials with mechanical responsiveness and presents potentially enticing applications in diverse fields, such as tissue engineering, artificial life, and strain sensors.     

Helical assembly of azobenzene-conjugated carbohydrate hydrogelators with specific affinity for lectins

Carbohydrate-mediated interactions are involved in various biological processes via specific molecular assembly and recognition. Such interactions are enhanced by multivalent effects of the sugar moieties, and thus supramolecular sugar-assembly, i.e., spontaneous association of glycoamphiphiles, is a promising approach to tailor glycocluster formation. In this study, novel sugar-decorated nanofibers were successfully prepared by self-assembly of low molecular weight hydrogelators composed of azobenzene and disaccharide lactones. Circular dichroism measurement of the as-prepared hydrogels indicated that the azobenzene amphiphile containing a lactose moiety possessed (R)-chirality, while the maltose-azobenzene conjugate exhibited (S)-chirality, even though the cellobiose-conjugated azobenzene existed in an achiral form. This suggests that the chiral orientation of the chromophoric azobenzene depended on both the glycosidic linkages and the steric arrangement of hydroxyl groups in the conjugated carbohydrates. Lectin-binding and cell adhesion assays revealed that the nonreducing ends of the conjugated sugar moieties were exposed on the surfaces of self-assembled nanofibrous hydrogels, allowing them to be effectively recognized by the corresponding lectins. In addition, photoisomerization of azobenzene under ultraviolet irradiation induced the sol-gel transitions of the hydrogels. These results demonstrate that the reversibly transformed fibrous glycohydrogels show potential for application as carbohydrate-decorated scaffolds for cell culture engineering.     

Spatiotemporal control of cell adhesion on a self-assembled monolayer having a photocleavable protecting group

Control of cell adhesion is a key technology for cell-based drug screening and for analyses of cellular processes. We developed a method to spatiotemporally control cell adhesion using a photochemical reaction. We prepared a cell-culturing substrate by modifying the surface of a glass coverslip with a self-assembled monolayer of an alkylsiloxane having a photocleavable 2-nitrobenzyl group. Bovine serum albumin (BSA) was adsorbed onto the substrate to make the surface inert to cell adhesion. When exposed to UV light, the alkylsiloxane underwent a photocleavage reaction, leading to the release of BSA from the surface. Fibronectin, a protein promoting cell adhesion, was added to cover the irradiated regions and made them cell-adhesive. Seeding of cells on this substrate resulted in their selective adhesion to the illuminated regions. By controlling the sizes of the illuminated regions, we formed cell-adhesive spots smaller than single cells and located focal adhesions of the cells. Moreover, by subsequently illuminating the region alongside the cells patterned on the substrate in advance, we released their geometrical confinements and induced migration and proliferation. These manipulations were conducted under a conventional fluorescence microscope without any additional instruments. The present method of cell manipulation will be useful for cell biological studies as well as for the formation of cell arrays.     

Bioresponsive DNA-co-polymer hydrogels for fabrication of sensors

Bioresponsive hydrogels that include DNA within a non-DNA network (DNA-co-polymer hydrogels) constitute a group of soft materials possessing selective recognition ability hosted by the included DNA structure. They are furthermore characterized by the changes to the hydrogel properties which follow the recognition of the biological analyte. Such hydrogels can be synthesized with desired recognition ability through the selection of particular nucleotide sequence that is recognizing or binding ions, small molecules, biomolecules or parts of larger entities. The binding of the label-free analyte triggers a response of the hydrogel, such as changes in its swelling volume, mass, optical or mechanical properties. The hydrogel response is mediated by changes in network parameters such as charge density, crosslinking density or a combination of these associated with the interaction with the analyte. Bioresponsive DNA polymer hydrogels have found wide application in biosensors due to their versatile nature.     

Head group modulated pH-responsive hydrogel of amino acid-based amphiphiles: entrapment and release of cytochrome c and vitamin B12

The present study describes the rational design and synthesis of amino acid-based amphiphilic hydrogelators, which were systemically fine-tuned at the head group to develop pH-responsive hydrogels. To understand the basic structural requirements of a low molecular weight amphiphilic hydrogelator, 10 analogous amphiphiles based on L-phenylalanine and L-tyrosine with structurally related head group were synthesized. Among them, three with quaternary ammonium substitution at the head group formed transparent hydrogels at room temperature while others were unable to gelate water. To establish correlations between the head group architecture of the gelators and their supramolecular arrangements, a variety of spectroscopic and microscopic techniques were investigated that showed that a balance between hydrophilicity and hydrophobicity is required to achieve hydrogelation. Interestingly, the gelator with tyrosinate in its head group showed remarkable response toward external pH. All hydrogels including the pH-responsive one were used in the controlled and/or pH-triggered release of entrapped (with in hydrogels) vitamin B12 and cytochrome c at different pHs. Since the hydrogels were formed at room temperature without heating, this could be very important during the entrapment of biomolecules such as proteins because of their heat sensitivity. At biological pH (7.4), the release of entrapped biomolecules from all three hydrogels was caused by diffusion through the gel structure, but at endosomal pH (approximately 5.5) and further lower pH, the release rate of biomolecules from the pH-responsive hydrogel with tyrosinate head group (pKa approximately equal to 7.2) increased by 9-10-fold compared to that observed at physiological pH, because of gel dissolution. Retention of the structure and activity of released biomolecule has established the prospect of the hydrogel as an efficient drug delivery vehicle.     

Synthetic Layered Silicate as a Carrier for Liquid Ingredients for the Rubber- and Tire Industry

We propose the use of novel materials based on synthetic calcium silicate hydrate (C S H) for the rubber- and tire industry. We found that the synthetic silicate belongs to the family of layered calcium silicate hydrates. Due to its layered structure and inert surface it easily adsorbs liquid components of rubber compounds, such as bis(triethoxysilylpropyl) tetrasulfide (TESPT) and liquid polysulfide (LP). Then, in processing, the C S H can smoothly release these components. The water, trapped in the material's gallery layers, plays the role of a catalyst in the silane coupling on silica's surface. In addition, we used this silicate as a component in promoter systems in order to improve adhesion stability between a brass-coated steel cord and rubber. The application of the calcium silicate hydrate as an inert substrate for the promoter system allowed the development of materials that have comparable adhesion strength with most commercial promoters.     

Biomimetic Strain‐Stiffening Self‐Assembled Hydrogels

Supramolecular structures with strain‐stiffening properties are ubiquitous in nature but remain rare in the lab. Herein, we report on strain‐stiffening supramolecular hydrogels that are entirely produced through the self‐assembly of synthetic molecular gelators. The involved gelators self‐assemble into semi‐flexible fibers, which thereby crosslink into hydrogels. Interestingly, these hydrogels are capable of stiffening in response to applied stress, resembling biological intermediate filaments system. Furthermore, strain‐stiffening hydrogel networks embedded with liposomes are constructed through orthogonal self‐assembly of gelators and phospholipids, mimicking biological tissues in both architecture and mechanical properties. This work furthers the development of biomimetic soft materials with mechanical responsiveness and presents potentially enticing applications in diverse fields, such as tissue engineering, artificial life, and strain sensors.     

Engineering of Covalently Immobilized Gradients of RGD Peptides on Hydrogel Scaffolds: Effect on Cell Behaviour

Summary: The aim of this study has been to design a system for the preparation of Polyethylene-glycol (PEG) based hydrogels with a controlled spatial distribution of covalently immobilised RGD adhesion signals in order to control and guide cell response for tissue engineering application. Gradients of immobilised RGD peptides were characterized by confocal microscopy analysis. Moreover, the effect of RGD spatial distribution on cell behaviour was evaluated by using mouse embryo fibroblasts NIH3T3. In particular, we observed cell adhesion and migration of fibroblasts seeded on RGD gradient compared to cells on control hydrogels having an uniform distribution of RGD. Our data suggest that a linear gradient of covalently immobilised adhesion signals affects cell behaviour. In particular, cells feel RGD gradient and oriented themselves and move along gradient direction.     

Polymethacrylate Networks as Substrates for Cell Culture

Summary: methacrylate networks have a long history of applications in medical technology and much is known of their non-fouling properties. However, in recent times it has become clear that the swollen nature of these materials may provide some advantages if they are used as scaffolds in tissue engineering. In general however these hydrogels are resistant to protein adsorption and human cells do not easily adhere. In this work we provide an overview of several strategies that are designed to improve the cell-adhesive properties of hydrogels while maintaining their useful properties, mainly ease of diffusion of nutrients and growth factors. We describe our early attempts at modifying hydrogels based on 2,3-propandiol -1-methacrylate, with either hydrophobic units or acid groups. Modification with lauryl methacrylate produced an improvement but acid modification failed to provide surfaces that were conducive to cell culture. Much better scaffolds were prepared by amination of epoxy functional 2,3-propandiol-1-methacrylate networks. Optimized materials in this class were shown to be good substrates for the co-culture of bovine keratocytes with human corneal epithelial cells. We also describe the synthesis and biological properties of methacrylate conetworks, which phase separate during synthesis to give porous amphiphilic materials. Optimization of these materials produces materials that perform as well as tissue culture plastic so that confluent sheets of human dermal fibroblasts can be produced using standard culture techniques.     

Recent advances on bioprinting of hydrogels containing carbon materials

The intrinsic properties and versatility of carbon materials (CMs) have recently raised a growing interest in their combination with hydrogels towards the development of advanced materials for biomedical applications. The increasing demand for biomimetic constructs that closely mimic the intricate composition and structure of native tissues has boosted the interest in using three-dimensional (3D) bioprinting technologies for the processing of CMs-containing hydrogels into specialized and more complex constructs capable of steering cell behavior. This review summarizes the progress on the bioprinting of 3D hydrogels containing CMs, focusing on the role of CMs on biomaterial ink design and their impact on both the printing process and the biological function of fabricated constructs. Recent findings demonstrate that CMs are versatile materials that have been mostly used to (1) tune the rheological properties of biomaterial inks, (2) improve the mechanical properties of hydrogels, and/or (3) confer new physical features to hydrogels, such as shape memory, roughness, and thermal and electrical conductivity, which have been shown to modulate the biological response of bioprinted constructs.     

Rapid and precise release from nano-tracted poly(N-isopropylacrylamide) hydrogels containing linear poly(acrylic acid)

We investigated the rapid and precise molecular release from hydrogels in response to dual stimuli. To achieve precise on/off drug release using thermoresponsive poly(N-isopropylacrylamide) hydrogels, we prepared nano-structured semi-IPNs, which consisted of thermosensitive PNIPAAm networks penetrated by pH-responsive poly(acrylic acid) (PAAc) linear chains and perforated to create nano-tracts as a molecular pathway. The present nano-tracted semi-IPNs show a rapid deswelling response to both temperature and pH. Model drug releases were investigated when simultaneous changes in temperature and pH were applied. We observed that the cationic drug was rapidly released and then abruptly discontinued from the nano-tracted semi-IPNs in response to the dual stimuli, and clear release and stopping cycles were repeatedly observed on successive steps. Moreover, the release rates and amount of drug released were controllable by the deswelling speed of the gels and the PAAc content inside the gels. This novel release system using the nano-tracted semi-IPNs may be useful for the high performance, pulsed release of molecules.     

pH敏感型聚谷氨酸/透明质酸基互穿网络医用水凝胶的制备及表征

生物材料是推动生物医学领域日新月异变化的基石,医用水凝胶作为重要成员,近年来表现出蓬勃发展的态势。文章介绍了一种新型可注射的、以生物相容性方法交联的聚谷氨酸(Poly (γ-glutamic acid), PGA)/透明质酸(Hyaluronic acid, HA)复合水凝胶。研究首先采用EDC/NHS方法合成了酪胺(Tyramine,Ty)接枝聚谷氨酸的PGA-Ty前体大分子及半胱胺(Cysteamine, CA)修饰透明质酸的HA-CA前体大分子。两种前体大分子的结构分别使用核磁和红外进行了确证。得到的两种前体大分子在低浓度双氧水和辣根过氧化物酶(Horseradish Peroxidase, HRP)的共同作用下,于水相中交联得到互穿网络(Interpenetrating Network, IPN)水凝胶。实验对IPN水凝胶样品的系列性能,如平衡含水量、内部形貌、酶降解速率以及力学性能等进行了测试,并选取了盐酸四环素为药物模型对凝胶的体外药物释放行为、体外抗菌效果进行了测评。凝胶材料的细胞毒性及凝胶支架对细胞3D培养的效果证明其生物相容性优异,体外包埋的细胞经72h培养,未表现出明显细胞毒性。系列数据证明,该种水凝胶可以设计成为pH敏感型的药物控释载体材料,并因其良好的生物相容性,也有作为细胞支架、创伤辅料等其它生物医用材料的潜力。