Peptide-based hydrogels as delivery systems for doxorubicin

Hydrogels (HGs) and nanogels (NGs) have been recently identified as innovative supramolecular materials for many applications in biomedical field such as in tissue engineering, optoelectronic, and local delivery of active pharmaceutical ingredients (APIs). Due to their in vivo biocompatibility, synthetic accessibility, low cost, and tunability, peptides have been used as suitable building blocks for preparation of HGs and NGs formulations. Peptide HGs have shown an outstanding potential to deliver small drugs, protein therapeutics, or diagnostic probes, maintaining the efficacy of their loaded molecules, preventing degradation phenomena, and responding to external physicochemical stimuli. In this review, we discuss the possible use of peptide-based HGs and NGs as vehicles for the delivery of the anticancer drug doxorubicin (Dox). This anthracycline is clinically used for leukemia, stomach, lung, ovarian, breast, and bladder cancer therapy. The loading of Dox into supramolecular systems (liposomes, micelles, hydrogels, and nanogels) allows reducing its cardiotoxicity. According to a primary sequence classification of the constituent peptide, doxorubicin-loaded systems are here classified in short and ultra-short peptide-based HGs, RGD, or RADA-peptide-based HGs and peptide-based NGs.     

Synthesis and characterization of thermo-sensitive semi-IPN hydrogels based on poly(ethylene glycol)-co-poly(ε-caprolactone) macromer, N-isopropylacrylamide, and sodium alginate

Thermo-sensitive semi-IPN hydrogels were prepared via in situ copolymerization of N-isopropylacrylamide (NIPAAm) with poly(ethylene glycol)-co-poly(ε-caprolactone) (PEG-co-PCL) macromer in the presence of sodium alginate by UV irradiation technology. The effects of the sodium alginate content, temperature, and salt on the swelling behavior of the as-obtained hydrogels were studied. The results showed that the swelling ratio of the hydrogels increased with the increasing sodium alginate content at the same temperature, and decreased with the increase in temperature. The salt sensitivity of the semi-IPN hydrogels was dependent on the content of sodium alginate introduced in the hydrogels. The mechanical rheology of the hydrogels and in vitro release behavior of bovine serum albumin (BSA) in situ encapsulated within the hydrogels were also investigated. It was found that the introduction of sodium alginate with semi-IPN structure improved mechanical strength of the hydrogels and the cumulative release percentage of BSA from the hydrogels. Such double-sensitive semi-IPN hydrogel materials could be exploited as potential candidates for drug delivery carriers.     

金特异性结合短肽介导的重组杆状病毒与胶体金构成的纳米复合体

纳米金在生物探针方面的应用技术是重要的研究方向, 这一技术的关键在于纳米金与生物分子有效的结合, 本文通过基因重组策略, 研究杆状病毒表面展示技术与金特异结合肽介导的固定化方法联用以构建生物-无机复合材料的可行性。利用Bac-to-Bac杆状病毒表达系统将合成的金特异结合肽基因融合到杆状病毒BmNPV囊膜糖蛋白gp64的N端信号肽与成熟蛋白之间构成转移质粒载体, 经过转座得到重组穿梭质粒pFB-gp64-Au, 转染Sf9昆虫细胞后收获多角体启动子控制下表达融合蛋白的重组AcMNPV。同时采用硼氢化钠还原法制备得到胶体金, 进行组建病毒 胶体金复合结构的初步研究。结果表明, 成功构建的重组穿梭质粒转染细胞后得到囊膜表面经金无机结合肽修饰的AcMNPV重组病毒, 并通过透射电子显微镜(transmission electron microscopy, TEM)观察到由金特异结合肽所介导的病毒 胶体金的复合结构。这项研究有助于进行生物-无机复合体系构建及纳米材料在生物学领域应用的研究。     

Techniques for RNA extraction from cells cultured in starPEG–heparin hydrogels

Three-dimensional (3D) cell culture models that provide a biologically relevant microenvironment are imperative to investigate cell–cell and cell–matrix interactions in vitro. Semi-synthetic star-shaped poly(ethylene glycol) (starPEG)–heparin hydrogels are widely used for 3D cell culture due to their highly tuneable biochemical and biomechanical properties. Changes in gene expression levels are commonly used as a measure of cellular responses. However, the isolation of high-quality RNA presents a challenge as contamination of the RNA with hydrogel residue, such as polymer or glycosaminoglycan fragments, can impact template quality and quantity, limiting effective gene expression analyses. Here, we compare two protocols for the extraction of high-quality RNA from starPEG–heparin hydrogels and assess three subsequent purification techniques. Removal of hydrogel residue by centrifugation was found to be essential for obtaining high-quality RNA in both isolation methods. However, purification of the RNA did not result in further improvements in RNA quality. Furthermore, we show the suitability of the extracted RNA for cDNA synthesis of three endogenous control genes confirmed via quantitative polymerase chain reaction (qPCR). The methods and techniques shown can be tailored for other hydrogel models based on natural or semi-synthetic materials to provide robust templates for all gene expression analyses.     

Viscoelastic properties of dispersed chitosan/xanthan hydrogels

In this work a gel was formed by complexation of two natural polyelectrolytes, chitosan and xanthan. Changes in the hydrogels rheological properties have been studied in terms of hydrogel concentration (7–10% w/w), chemical media used for the hydrogel dispersion, and ‘test lag time’; i.e., the time between hydrogel dispersion in the chemical media and the start of the rheological test (up to 390 min). The viscoelastic properties of this polysaccharide system were characterized by oscillatory shear measurements under small-deformation conditions and the results show that chitosan/xanthan hydrogels behave like weak gels. The shear modulus increased almost linearly with frequency in the range studied (0.1–65 s⁻¹). The effects of hydrogel concentration and dispersion medium have been related to electrostatic equilibrium and by the presence of counter-ions modifying the internal structure of the hydrogel.     

Preparation of Hydroxy-PAAm Hydrogels for Decoupling the Effects of Mechanotransduction Cues

It is now well established that many cellular functions are regulated by interactions of cells with physicochemical and mechanical cues of their extracellular matrix (ECM) environment. Eukaryotic cells constantly sense their local microenvironment through surface mechanosensors to transduce physical changes of ECM into biochemical signals, and integrate these signals to achieve specific changes in gene expression. Interestingly, physicochemical and mechanical parameters of the ECM can couple with each other to regulate cell fate. Therefore, a key to understanding mechanotransduction is to decouple the relative contribution of ECM cues on cellular functions.Here we present a detailed experimental protocol to rapidly and easily generate biologically relevant hydrogels for the independent tuning of mechanotransduction cues in vitro. We chemically modified polyacrylamide hydrogels (PAAm) to surmount their intrinsically non-adhesive properties by incorporating hydroxyl-functionalized acrylamide monomers during the polymerization. We obtained a novel PAAm hydrogel, called hydroxy-PAAm, which permits immobilization of any desired nature of ECM proteins. The combination of hydroxy-PAAm hydrogels with microcontact printing allows to independently control the morphology of single-cells, the matrix stiffness, the nature and the density of ECM proteins. We provide a simple and rapid method that can be set up in every biology lab to study in vitro cell mechanotransduction processes. We validate this novel two-dimensional platform by conducting experiments on endothelial cells that demonstrate a mechanical coupling between ECM stiffness and the nucleus.     

Enhanced stiffness of silk‐like fibers by loop formation in the corona leads to stronger gels

We study the self‐assembly of protein polymers consisting of a silk‐like block flanked by two hydrophilic blocks, with a cysteine residue attached to the C‐terminal end. The silk blocks self‐assemble to form fibers while the hydrophilic blocks form a stabilizing corona. Entanglement of the fibers leads to the formation of hydrogels. Under oxidizing conditions the cysteine residues form disulfide bridges, effectively connecting two corona chains at their ends to form a loop. We find that this leads to a significant increase in the elastic modulus of the gels. Using atomic force microscopy, we show that this stiffening is due to an increase of the persistence length of the fibers. Self‐consistent‐field calculations indicate a slight decrease of the lateral pressure in the corona upon loop formation. We argue that this small decrease in the repulsive interactions affects the stacking of the silk‐like blocks in the core, resulting in a more rigid fiber.     

Sirtuin 1 evaluation with a novel immunoassay approach based on TiO2–Au label and hyperbranched polymer hybrid

Accurate and highly sensitive evaluation of the sirtuin 1 (SirT1) level is becoming increasingly important for understanding the contribution of SirT1 in metabolism pathways. Here, a novel electrochemical immunoassay of SirT1 based on crosslinked hyperbranched azo-polymer decorated with gold colloids (Au–HAP) as sensing platform and titanium dioxide (TiO₂)–Au nanocomposites to immobilize secondary antibody–horseradish peroxidase (Ab₂–HRP) as electrochemical labels has been designed. Greatly enhanced sensitivity was achieved by exploiting the excellent conductivity of Au nanoparticle, the amplification effect of Au–HAP and TiO₂–Au, and the favorable catalytic ability of HRP. The nanocomposites of Au–HAP and TiO₂–Au could attach numerous capture antibodies on the surface for significant immune recognition efficiency. Meanwhile, the TiO₂–Au-labeled Ab₂–HRP using an HRP–thionine–H₂O₂ (hydrogen peroxide) detection system could further induce signal readout. Under optimal conditions, the signal intensity was linearly related to the concentration of SirT1 in the range of 1–500 ng ml⁻¹, and the limit of detection was 0.28 ng ml⁻¹. The developed biosensor exhibits attractive performance for the analysis of SirT1, with rapid response, high sensitivity, and high accuracy, and could become a promising technique for protein detection.     

Microwave-assisted Functionalization of Poly(ethylene glycol) and On-resin Peptides for Use in Chain Polymerizations and Hydrogel Formation

One of the main benefits to using poly(ethylene glycol) (PEG) macromers in hydrogel formation is synthetic versatility. The ability to draw from a large variety of PEG molecular weights and configurations (arm number, arm length, and branching pattern) affords researchers tight control over resulting hydrogel structures and properties, including Young’s modulus and mesh size. This video will illustrate a rapid, efficient, solvent-free, microwave-assisted method to methacrylate PEG precursors into poly(ethylene glycol) dimethacrylate (PEGDM). This synthetic method provides much-needed starting materials for applications in drug delivery and regenerative medicine. The demonstrated method is superior to traditional methacrylation methods as it is significantly faster and simpler, as well as more economical and environmentally friendly, using smaller amounts of reagents and solvents. We will also demonstrate an adaptation of this technique for on-resin methacrylamide functionalization of peptides. This on-resin method allows the N-terminus of peptides to be functionalized with methacrylamide groups prior to deprotection and cleavage from resin. This allows for selective addition of methacrylamide groups to the N-termini of the peptides while amino acids with reactive side groups (e.g. primary amine of lysine, primary alcohol of serine, secondary alcohols of threonine, and phenol of tyrosine) remain protected, preventing functionalization at multiple sites. This article will detail common analytical methods (proton Nuclear Magnetic Resonance spectroscopy (^;H-NMR) and Matrix Assisted Laser Desorption Ionization Time of Flight mass spectrometry (MALDI-ToF)) to assess the efficiency of the functionalizations. Common pitfalls and suggested troubleshooting methods will be addressed, as will modifications of the technique which can be used to further tune macromer functionality and resulting hydrogel physical and chemical properties. Use of synthesized products for the formation of hydrogels for drug delivery and cell-material interaction studies will be demonstrated, with particular attention paid to modifying hydrogel composition to affect mesh size, controlling hydrogel stiffness and drug release.