Hyaluronic acid hydrogel immobilized with RGD peptides for brain tissue engineering

In this paper, hyaluronic acid hydrogels with open porous structure have been developed for scaffold of brain tissue engineering. A short peptide sequence of arginine–glycine–aspartic acid (RGD) was immobilized on the backbone of the hydrogels. Both unmodified hydrogels and those modified with RGD were implanted into the defects of cortex in rats and evaluated for their ability to improve tissue reconstruction. After 6 and 12 weeks, sections of brains were processed for DAB and Glees staining. They were also labeled with GFAP and ED1 antibodies, and observed under the SEM for ultrastructral examination. After implanting into the lesion of cortex, the porous hydrogels functioned as a scaffold to support cells infiltration and angiogenesis, simultaneously inhibitting the formation of glial scar. In addition, HA hydrogels modified with RGD were able to promote neurites extension. Our experiments showed that the hyaluronic acid-RGD hydrogel provided a structural, three-dimensional continuity across the defect and favoured reorganization of local wound-repair cells, angiogenesis and axonal growth into the hydrogel scaffold, while there was little evidence of axons regeneration in unmodified hydrogel.     

Hydrogels of collagen/chondroitin sulfate/hyaluronan interpenetrating polymer network for cartilage tissue engineering

The network structure of a three-dimensional hydrogel scaffold dominates its performance such as mechanical strength, mass transport capacity, degradation rate and subsequent cellular behavior. The hydrogels scaffolds with interpenetrating polymeric network (IPN) structure have an advantage over the individual component gels and could simulate partly the structure of native extracellular matrix of cartilage tissue. In this study, to develop perfect cartilage tissue engineering scaffolds, IPN hydrogels of collagen/chondroitin sulfate/hyaluronan were prepared via two simultaneous processes of collagen self-assembly and cross linking polymerization of chondroitin sulfate-methacrylate (CSMA) and hyaluronic acid-methacrylate. The degradation rate, swelling performance and compressive modulus of IPN hydrogels could be adjusted by varying the degree of methacrylation of CSMA. The results of proliferation and fluorescence staining of rabbit articular chondrocytes in vitro culture demonstrated that the IPN hydrogels possessed good cytocompatibility. Furthermore, the IPN hydrogels could upregulate cartilage-specific gene expression and promote the chondrocytes secreting glycosaminoglycan and collagen II. These results suggested that IPN hydrogels might serve as promising hydrogel scaffolds for cartilage tissue engineering.     

物理/化学复合交联水凝胶的结构形态和温敏性

以等质量的物理交联剂锂皂石(hectorite)和化学交联剂亚甲基双丙烯酰胺(MBA)共同作为交联剂制备了聚异丙基丙烯酰胺水凝胶。该复合交联剂改善了仅用MBA交联制备的水凝胶的脆性和透光性,储能模量(E′)约为单独使用亚甲基双丙烯酰胺(MBA)和hectorite制备的水凝胶的储能模量之和的一半,体积相转变温度(VPTT)仍在32℃左右,和单独使用MBA和hectorite制备的水凝胶的VPTT相一致,但内部形态和溶胀度更多地取决于化学交联剂MBA的使用。     

物理/化学复合交联剂配比对凝胶温敏性的影响

采用化学交联剂亚甲基双丙烯酰胺(MBA)和物理交联剂无机纳米黏土硅酸镁锂(LMSH)复配制备聚异丙基丙烯酰胺(PNIPAM)水凝胶。随m(MBA)∶m(LMSH)的质量比由9∶1降至为1∶9,水凝胶的透光度和溶胀度增加。凝胶的内部形态取决于交联剂配比,孔洞尺寸随LMSH含量增加而增加。当m(MBA)∶m(LMSH)的质量比为9∶1和1∶9时,温度脉冲响应性最好,但m(MBA)∶m(LMSH)的质量比为1∶9时凝胶对温度的响应最为敏感,20℃下的储能模量最高。DSC结果表明体积相转变温度(VPTT)均在33℃左右,但VPTT范围随LMSH含量增加而窄化。     

Mechanical properties and in vitro behavior of nanofiber-hydrogel composites for tissue engineering applications

Hydrogel-based biomaterial systems have great potential for tissue reconstruction by serving as temporary scaffolds and cell delivery vehicles for tissue engineering (TE). Hydrogels have poor mechanical properties and their rapid degradation limits the development and application of hydrogels in TE. In this study, nanofiber reinforced composite hydrogels were fabricated by incorporating electrospun poly(ε-caprolactone) (PCL)/gelatin 'blend' or 'coaxial' nanofibers into gelatin hydrogels. The morphological, mechanical, swelling and biodegradation properties of the nanocomposite hydrogels were evaluated and the results indicated that the moduli and compressive strengths of the nanofiber reinforced hydrogels were remarkably higher than those of pure gelatin hydrogels. By increasing the amount of incorporated nanofibers into the hydrogel, the Young's modulus of the composite hydrogels increased from 3.29 ± 1.02 kPa to 20.30 ± 1.79 kPa, while the strain at break decreased from 66.0 ± 1.1% to 52.0 ± 3.0%. Compared to composite hydrogels with coaxial nanofibers, those with blend nanofibers showed higher compressive strength and strain at break, but with lower modulus and energy dissipation properties. Biocompatibility evaluations of the nanofiber reinforced hydrogels were carried out using bone marrow mesenchymal stem cells (BM-MSCs) by cell proliferation assay and immunostaining analysis. The nanocomposite hydrogel with 25 mg ml(-1) PCL/gelatin 'blend' nanofibers (PGB25) was found to enhance cell proliferation, indicating that the 'nanocomposite hydrogels' might provide the necessary mechanical support and could be promising cell delivery systems for tissue regeneration.     

Synthesis, characterization, and in vitro evaluation of a hydrogel-based corneal onlay

Blindness due to opacity of the cornea is treated by corneal transplantation with donor tissue. Due to the limited supply of suitable donor corneas, the need for synthetic corneal equivalents is clear. Herein we report the design and in vitro characterization of a hydrogel-based implant; this implant will serve as a permanent, transparent, space-filling onlay with a two-layer design that mimics the native corneal stratification to support surface epithelialization and foster integration with the surrounding tissue. The top layer of the implant was composed of a 2-hydroxyethylmethacrylate hydrogel containing methacrylic acid as the co-monomer (HEMA-co-MAA) with tunable dimensions and compressive modulus ranging from 700-1000 kPa. The bottom layer, which constitutes the bulk of the implant and is designed to provide integration with the corneal stroma, is a dendrimer hydrogel with high water content and compressive modulus ranging from 500-1200 kPa. Both hydrogels were found to possess optical and diffusion properties similar to those of the human cornea. In addition, composite implants with uniform and structurally sound interfaces were formed when the gels were sequentially injected and cross-linked in the same mold. HEMA-co-MAA hydrogels were covalently modified with type I collagen to enable corneal epithelial cell adhesion and spreading that was dependent upon the collagen coating density but independent of hydrogel stiffness. Similarly, dendrimer hydrogels supported the adhesion and spreading of corneal fibroblasts upon modification with the adhesion ligand arginine-glycine-aspartic acid (RGD). Fibroblast adhesion was not dependent upon dendrimer hydrogel stiffness for the formulations studied and, after in vitro culture for 4 weeks, fibroblasts remained able to adhere to and conformally coat the hydrogel surface. In conclusion, the tunable physical properties and structural integrity of the laminated interface suggests that this design is suitable for further study. The judicious tuning of material properties and inclusion of bioactive moieties is a promising strategy for promotion of implant epithelialization and tissue integration.     

Thermoresponsive hyperbranched copolymer with multi acrylate functionality for in situ cross-linkable hyaluronic acid composite semi-IPN hydrogel

Thermoresponsive polymers have been widely used for in situ formed hydrogels in drug delivery and tissue engineering as they are easy to handle and their shape can easily conform to tissue defects. However, non-covalent bonding and mechanical weakness of these hydrogels limit their applications. In this study, a physically and chemically in situ cross-linkable hydrogel system was developed from a novel thermoresponsive hyperbranched PEG based copolymer with multi acrylate functionality, which was synthesized via an ‘one pot and one step’ in situ deactivation enhanced atom transfer radical co-polymerization of poly(ethylene glycol) diacrylate (PEGDA, M_n = 258 g mol⁻¹), poly(ethylene glycol) methyl ether methacrylate (PEGMEMA, M_n = 475 g mol⁻¹) and (2-methoxyethoxy) ethyl methacrylate (MEO₂MA). This hyperbranched copolymer was tailored to have the lower critical solution temperature to form physical gelation around 37°C. Meanwhile, with high level of acrylate functionalities, a chemically cross-linked gel was formed from this copolymer using thiol functional cross-linker of pentaerythritol tetrakis (3-mercaptopropionate) (QT) via thiol-ene Michael addition reaction. Furthermore, a semi-interpenetrated polymer networks (semi-IPN) structure was developed by combining this polymer with hyaluronic acid (HA), leading to an in situ cross-linkable hydrogel with significantly increased porosity, enhanced swelling behavior and improved cell adhesion and viability both in 2D and 3D cell culture models.     

PNIPAAm/CMC半互穿网络水凝胶的合成及性质

以N-马来酰化壳聚糖为交联剂,N-异丙基丙烯酰胺(NIPAAm)为单体,羧甲基纤维素钠(CMC)为半互穿材料,在水溶液中通过自由基聚合制备了PNIPAAm/CMC半互穿网络水凝胶.所合成的水凝胶的低临界溶解温度(LCST)在33℃左右,CMC的加入对水凝胶的LCST无显著影响,但随着CMC用量的增加,水凝胶的温度敏感性...     

Novel PAAm/Laponite clay nanocomposite hydrogels with improved cationic dye adsorption behavior

A nanocomposite (NC) hydrogel was prepared by incorporating the nanoclay (Laponite (Lap) XLS) into a poly(acrylamide) (PAAm) hydrogel by the in situ polymerization method without any organic cross-linker. The parameters pertaining to the swelling (Q) and diffusion (D) of water for the PAAm/Lap NC hydrogels were estimated. The crystal violet (CV) dye adsorption properties of the PAAm/Lap NC hydrogels were investigated. The adsorption of CV dye by the hydrogel increases as the concentration of the dye increases. The cationic dye adsorption ability of the NC hydrogel increased with increasing clay content in the NC hydrogel. The NC hydrogels containing CV dye were characterized by FT-IR. A sigmoidal type of adsorption isotherm was observed for the CV-NC hydrogels. The effects of heat treatment on the dye adsorption behavior of the NC hydrogels were studied.     

Ⅰ型胶原/海藻酸钠/透明质酸复合水凝胶用于血管组织工程细胞负载与3D培养EI北大核心CSCD

胶原、海藻酸钠和透明质酸是天然来源的高分子材料,具有良好的细胞相容性与生物安全性,在细胞培养、组织工程、药物负载等方面具有广泛应用。单纯的胶原力学性能较差,将胶原与海藻酸钠制备成复合水凝胶材料后,可以通过调节海藻酸钠与Ca^(2+)交联程度来改变水凝胶支架的力学性能和孔隙率,模拟细胞培养的力学环境和细胞微环境。本研究通过PIUMA纳米压痕仪和DHR流变仪表征Ⅰ型胶原/海藻酸钠/透明质酸水凝胶的杨氏模量和溶胶-凝胶转变温度。并将内皮细胞与间充质干细胞在水凝胶微环境内进行3D培养,倒置荧光显微镜观察细胞培养0,3,5,7 d时细胞的活力情况,表征Ⅰ型胶原/海藻酸钠/透明质酸水凝胶的细胞相容性,并在内皮细胞与间充质干细胞培养0,1,4,6 d时,观察内皮细胞的迁移、成血管情况,在培养1,6,9 d时,观察内皮细胞的生长扩散情况。结果表明:水凝胶杨氏模量为(600±81)Pa,水凝胶的溶胶-凝胶转变温度为23.2℃。细胞培养0,3,5,7 d时,活力持续增强,培养4,6 d时,观测到共培养下内皮细胞的迁移,培养1,6,9 d时,水凝胶内的内皮细胞球体持续生长扩散。本工作表明,Ⅰ型胶原/海藻酸钠/透明质酸水凝胶对内皮细胞与间充质干细胞具有良好的细胞相容性,可用于细胞3D培养的理想支架材料。水凝胶的杨氏模量和溶胶-凝胶转变温度对细胞活力无损害,可作为研究血管新生的相关体外模型,在血管组织工程研究中具有重要的应用前景。     

Chemistry between crosslinks affects the properties of peptide hydrogels

Protein hydrogels were prepared by substituting ovalbumin with different concentrations of ethyl vinyl sulfone (EVS) or acrylic acid (AA) and crosslinking with divinyl sulfone (DVS). Fourier transform-infrared (FT-IR) spectroscopic studies confirmed the addition of EVS, AA, and DVS onto the protein. Swelling was assessed as a function of pH in the range of 2.5 to 9.4 and ionic strength. The elastic modulus of the gels was determined in shear and compression. Stress relaxation was assessed in compression. The substituent highly affected swelling and modulus with both hydrogels displaying non-Gaussian behavior in the range of hydrogel environments studied. Acrylic acid substituted ovalbumin exhibited a decreasing modulus with increasing swelling behaving as a polyelectrolyte with low added salt content. Ethyl vinyl sulfone substituted ovalbumin displayed an increasing modulus with swelling originating in the finite extensibility of the highly swollen chains. AA-substituted ovalbumin showed higher modulus and reduced swelling compared to EVS-substituted ovalbumin because of its ability to hydrogen and ionic bond to other molecules.     

Facile preparation of low swelling,high strength,self-healing and pH-responsive hydrogels based on the triple-network structure

A polyacrylic acid(PAA)/gelatin(Gela)/polyvinyl alcohol(PVA)hydrogel was prepared by copolymerization,cooling,and freezing/thawing methods.This triplenetwork(TN)structure hydrogel displayed superior mechanical properties,low swelling ratio and self-healing properties,The superior mechanical properties are attributed to the triple helix association of Gela and PVA crystallites by reversible hydrogen bonding.The characterization results indicated that the fracture stress and the strain were 808 kPa and 370% respectively,while the compression strength could reach 4443 kPa and the compressive modulus was up to 39 MPa under the deformation of 90%.The hydrogen bonding in PVA contributed to maintain and improve the self-healing ability of hydrogels.Every type of hydrogels exhibited a higher swelling ratio under alkaline conditions,and the swelling ratios of PAA,PAA/PVA and PAA/Gela hydrogels were 27.71,12.30 and 9.09,respectively.The PAA/Gela/PVA TN hydrogel showed the lowest swelling ratio(6.57)among these hydrogels.These results indicate that the novel TN hydrogels possess good environmental adaptability and have potential applications in the biomedical engineering and sensor field.     

Non-destructive characterization of hydrogels

Hydrogels have been prepared by a freezing–thawing procedure and investigations made of the effect of both number of freezing–thawing cycles and different content of hyaluronic acid (HA) on the mechanical properties of the PVA-HA hydrogels using non-destructive testing. The bulk elastic modulus K of hydrogels has been determined by pulse-echo measurements. It is noted that hydrogel elastic properties improve with the number of the cycles in PVA-HA 100/0; on the other hand samples with a high HA (1000000 molecular weight) content, beyond the third cycle, seem to be unaffected by the number of cycles. A bulk elastic modulus fall-off is then observed in samples submitted to an additional overnight freezing between two subsequent cycles. K increases in hydrogels with the highest HA content, when samples undergo pulse-echo measurements soon after their preparation. When hydrogels reach equilibrium, after having been kept in deionized water for 12 h, K values are lower, showing a nearly constant behaviour with different PVA-HA ratios and cycles. Furthermore, by means of scanning laser acoustic microscopy (SLAM) defects have been detected in the hydrogels. In samples which have reached equilibrium, SLAM images show that these defects disappear in PVA-HA hydrogels.     

3D cell growth and proliferation on a RGD functionalized nanofibrillar hydrogel based on a conformationally restricted residue containing dipeptide

Three-dimensional (3D) hydrogels incorporating a compendium of bioactive molecules can allow efficient proliferation and differentiation of cells and can thus act as successful tissue engineering scaffolds. Self-assembled peptide-based hydrogels can be worthy candidates for such applications as peptides are biocompatible, biodegradable and can be easily functionalized with desired moieties. Here, we report 3D growth and proliferation of mammalian cells (HeLa and L929) on a dipeptide hydrogel chemically functionalized with a pentapeptide containing Arg-Gly-Asp (RGD) motif. The method of functionalization is simple, direct and can be adapted to other functional moieties as well. The functionalized gel was noncytotoxic, exhibited enhanced cell growth promoting properties, and promoted 3D growth and proliferation of cells for almost 2 weeks, with simultaneous preservation of their metabolic activities. The presence of effective cell growth supporting properties in a simple and easy to functionalize dipeptide hydrogel is unique and makes it a promising candidate for tissue engineering and cell biological applications.     

Adhesive Hemostatic Conducting Injectable Composite Hydrogels with Sustained Drug Release and Photothermal Antibacterial Activity to Promote Full‐Thickness Skin Regeneration During Wound Healing

Developing injectable nanocomposite conductive hydrogel dressings with multifunctions including adhesiveness, antibacterial, and radical scavenging ability and good mechanical property to enhance full‐thickness skin wound regeneration is highly desirable in clinical application. Herein, a series of adhesive hemostatic antioxidant conductive photothermal antibacterial hydrogels based on hyaluronic acid‐graft‐dopamine and reduced graphene oxide (rGO) using a H₂O₂/HPR (horseradish peroxidase) system are prepared for wound dressing. These hydrogels exhibit high swelling, degradability, tunable rheological property, and similar or superior mechanical properties to human skin. The polydopamine endowed antioxidant activity, tissue adhesiveness and hemostatic ability, self‐healing ability, conductivity, and NIR irradiation enhanced in vivo antibacterial behavior of the hydrogels are investigated. Moreover, drug release and zone of inhibition tests confirm sustained drug release capacity of the hydrogels. Furthermore, the hydrogel dressings significantly enhance vascularization by upregulating growth factor expression of CD31 and improve the granulation tissue thickness and collagen deposition, all of which promote wound closure and contribute to a better therapeutic effect than the commercial Tegaderm films group in a mouse full‐thickness wounds model. In summary, these adhesive hemostatic antioxidative conductive hydrogels with sustained drug release property to promote complete skin regeneration are an excellent wound dressing for full‐thickness skin repair.     

Swelling and mechanical behaviors of carbon nanotube/poly(vinyl alcohol) hybrid hydrogels

In this paper, carbon nanotubes (CNTs) were added into poly(vinyl alcohol) (PVA) hydrogels to modify their mechanical properties. A series of CNT/PVA hybrid hydrogels were prepared by freezing/thawing method. The mechanical and swelling properties of all hybrid hydrogels are better than those of the original PVA hydrogel. Especially, for CNTP-0.5 specimen with 0.5% w/w CNTs, its tensile modulus, tensile strength and strain at break are increased by 78.2%, 94.3% and 12.7%, respectively. And its swelling behavior is different from that of the pure PVA hydrogel. Its final swelling ratios at room temperature and 310 K are increased by 35.7% and 44.9%, respectively.     

Fabrication and characterization of hyaluronic-acid-based antigen sensitive degradable hydrogel

Biomolecule sensitive hydrogel, as an important part of intelligent materials, has extensive applications in the biochemical and biomedical fields. In this paper, an antigen sensitive degradable hydrogel based on hyaluronic acid (HA) has been prepared. Antigen and antibody were covalently attached to the hydrogel simultaneous, while HA was cross-linked used adipic dihydrazide (ADH) as cross-linking agent primarily. We describe the synthesis, characteristics, and the antigen sensitive behavior of the hydrogel. The hydrogel can exhibit a reversible swelling behavior while the native antigen is present or not. This property of the antigen sensitive hydrogel may be applied as novel drug delivery system, which can release drug by the presence of native antigen.     

新型胶原/聚丙烯酸互穿网络pH敏感水凝胶的制备及性能研究

以Bis为交联剂,采用互穿网络(IPN)技术制备胶原/聚丙烯酸pH敏感水凝胶.研究了不同配比的水凝胶的溶胀动力学、pH敏感性及pH溶胀-退胀特性,并利用傅里叶变换红外光谱法(FTIR)和差示量热扫描法(DSC)对其结构进行表征.结果显示:制备的水凝胶具有较快的溶胀速率,在13min时吸水率可达93%左右;水凝胶有明显的pH敏感性且pH溶胀-退胀可逆性良好.FTIR和DSC结果表明,在保持胶原三股螺旋结构的同时,材料间形成了互穿网络,材料的热稳定性显著提高,从而扩大了材料的应用范围.     

交联方式对半乳糖基温敏凝胶结构和性能的影响

为改善传统化学交联水凝胶的低力学性能、透明度、溶胀度和生物相容性, 以无机纳米粒子硅酸镁锂(LMSH)作为物理交联剂, 半乳糖氨基化的丙烯酸衍生物(GAC)作为生物相容性单体, N-异丙基丙烯酰胺(NIPAM)为功能单体, 采用原位自由基聚合制备得到兼具温度敏感性和生物相容性的纳米复合水凝胶poly(NIPAM-LMSH-GAC)。结果表明: LMSH在水凝胶基体中被完全剥离, 并起到交联作用; 相比于传统化学交联剂制备的此类水凝胶, 所得物理交联的纳米复合水凝胶具有更高的溶胀度、良好的温敏性、优异的脉冲响应性, 但鼠成纤细胞(L929)在纳米复合水凝胶表面的细胞数量略低; 物理交联剂LMSH的使用和一定量的GAC的使用并没有明显改变水凝胶的体积相转变温度(VPTT), 仍保持在33℃左右。     

Fabrication and characterization of hyaluronic-acid-based antigen sensitive degradable hydrogel

Biomolecule sensitive hydrogel, as an important part of intelligent materials, has extensive applications in the biochemical and biomedical fields. In this paper, an antigen sensitive degradable hydrogel based on hyaluronic acid (HA) has been prepared. Antigen and antibody were covalently attached to the hydrogel simultaneous, while HA was cross-linked used adipic dihydrazide (ADH) as cross-linking agent primarily. We describe the synthesis, characteristics, and the antigen sensitive behavior of the hydrogel. The hydrogel can exhibit a reversible swelling behavior while the native antigen is present or not. This property of the antigen sensitive hydrogel may be applied as novel drug delivery system, which can release drug by the presence of native antigen.