Multifunctional Self-Assembled Peptide Hydrogels for Biomedical Applications

Self-assembly is a growth mechanism in nature to apply local interactions forming a minimum energy structure. Currently, self-assembled materials are considered for biomedical applications due to their pleasant features, including scalability, versatility, simplicity, and inexpensiveness. Self-assembled peptides can be applied to design and fabricate different structures, such as micelles, hydrogels, and vesicles, by diverse physical interactions between specific building blocks. Among them, bioactivity, biocompatibility, and biodegradability of peptide hydrogels have introduced them as versatile platforms in biomedical applications, such as drug delivery, tissue engineering, biosensing, and treating different diseases. Moreover, peptides are capable of mimicking the microenvironment of natural tissues and responding to internal and external stimuli for triggered drug release. In the current review, the unique characteristics of peptide hydrogels and recent advances in their design, fabrication, as well as chemical, physical, and biological properties are presented. Additionally, recent developments of these biomaterials are discussed with a particular focus on their biomedical applications in targeted drug delivery and gene delivery, stem cell therapy, cancer therapy and immune regulation, bioimaging, and regenerative medicine.

A Promising Review on Cyclodextrin Conjugated Paclitaxel Nanoparticles for Cancer Treatment

This review presented the unique characteristics of different types of cyclodextrin polymers by non-covalent host–guest interactions to synthesize an inclusion complex. Various cancers are treated with different types of modified cyclodextrins, along with the anticancer drug paclitaxel. PTX acts as a mitotic inhibitor, but due to its low dissolution and permeability in aqueous solutions, it causes considerable challenges for drug delivery system (DDS) designs. To enhance the solubility, it is reformulated with derivatives of cyclodextrins using freeze-drying and co-solvent lyophilization methods. The present supramolecular assemblies involve cyclodextrin as a key mediator, which is encapsulated with paclitaxel and their controlled release at the targeted area is highlighted using different DDS. In addition, the application of cyclodextrins in cancer treatment, which reduces the off-target effects, is briefly demonstrated using various types of cancer cell lines. A new nano-formulation of PTX is used to improve the antitumor activity compared to normal PTX DDS in lungs and breast cancer is well defined in the present review.

Cyclodextrin-based delivery systems in parenteral formulations: a critical update review

Parenteral formulations are indispensable in clinical practice and often are the only option to administer drugs that cannot be administrated through other routes, such as proteins and certain anticancer drugs - which are indispensable to treat some of the most prevailing chronic diseases worldwide (like diabetes and cancer). Additionally, parenteral formulations play a relevant role in emergency care since they are the only ones that provide an immediate action of the drug after its administration. However, the development of parenteral formulations is a complex task owing to the specific quality and safety requirements set for these preparations and the intrinsic properties of the drugs. Amongst all the strategies that can be useful in the development of parenteral formulations, the formation of water-soluble host-guest inclusion complexes with cyclodextrins (CDs) has proven to be one of the most advantageous. CDs are multifunctional pharmaceutical excipients able to form water-soluble host-guest inclusion complexes with a wide variety of molecules, particularly drugs, and thus improve their apparent water-solubility, chemical stability, and bioavailability, to make them suitable for parenteral administration. Besides, CDs can be employed as building blocks of more complex injectable drug delivery systems with enhanced characteristics, such as nanoparticles and supramolecular hydrogels, that has been found particularly beneficial for the delivery of anticancer drugs. However, only a few CDs are considered safe when parenterally administered, and some of these types are already approved to be used in parenteral dosage forms. Therefore, the application of CDs in the development of parenteral formulations has been a more common practice in the last few years, due to their significant worldwide acceptance by the health authorities, promoting the development of safer and more efficient injectable drug delivery systems.

Recent Updates on Supramolecular-Based Drug Delivery - Macrocycles and Supramolecular Gels

Supramolecules-based drug delivery has attracted significant recent research attention as it could enhance drug solubility, retention time, targeting, and stimuli responsiveness. Among the different supramolecules and assemblies, the macrocycles and the supramolecular hydrogels are the two important categories investigated to a greater extent. Here, we provide the most recent advancements in these categories. Under macrocycles, reports on drug delivery by cyclodextrins, cucurbiturils, calixarenes/pillararenes, crown ethers and porphyrins are detailed. The second category discusses the supramolecular hydrogels of macrocycles/polymers and low molecular weight gelators. The updated information provided could be helpful to advance R & D in this vital area.

A long-term controlled drug-delivery with anionic beta cyclodextrin complex in layer-by-layer coating for percutaneous implants devices

This study demonstrated a drug-delivery system with anionic beta cyclodextrin (β-CD) complexes to retain tetracycline (TC) and control its release from multilayers of poly(acrylic acid) (PAA) and poly(l-lysine) (PLL) in a ten double layers ([PAA/PLL]₁₀) coating onto titanium. The drug-delivery capacity of the multilayer system was proven by controlled drug release over 15 days and sustained released over 30 days. Qualitative images confirmed TC retention within the layer-by-layer (LbL) over 30 days of incubation. Antibacterial activity of TC/anionic β-CD released from the LbL was established against Staphylococcus aureus species. Remarkably, [PAA/PLL]₁₀/TC/anionic β-CD antibacterial effect was sustained even after 30 days of incubation. The non-cytotoxic effect of the multilayer system revealed normal human gingival fibroblast growth. It is expected that this novel approach and the chemical concept to improve drug incorporation into the multilayer system will open up possibilities to make the drug release system more applicable to implantable percutaneous devices.

Peptide-based supramolecular hydrogels for bioimaging applications

Peptide-based supramolecular hydrogels have unique merits in bioimaging applications.

Biocompatible Polymers Combined with Cyclodextrins: Fascinating Materials for Drug Delivery Applications

Cyclodextrins (CD) are a group of cyclic oligosaccharides with a cavity/specific structure that enables to form inclusion complexes (IC) with a variety of molecules through non-covalent host-guest interactions. By an elegant combination of CD with biocompatible, synthetic and natural polymers, different types of universal drug delivery systems with dynamic/reversible properties have been generated. This review presents the design of nano- and micro-carriers, hydrogels, and fibres based on the polymer/CD supramolecular systems highlighting their possible biomedical applications. Application of the most prominent hydrophobic aliphatic polyesters that exhibit biodegradability, represented by polylactide and polycaprolactone, is described first. Subsequently, particular attention is focused on materials obtained from hydrophilic polyethylene oxide. Moreover, examples are also presented for grafting of CD on polysaccharides. In summary, we show the application of host-guest interactions in multi-component functional biomaterials for controlled drug delivery.

Azobenzene-grafted carboxymethyl cellulose hydrogels with photo-switchable, reduction-responsive and self-healing properties for a controlled drug release system

In this study, multifunctional hydrogels containing host-guest complex formation between azobenzene-grafted carboxymethyl cellulose (CMC-Azo) and β-cyclodextrin (CD) dimers connected by disulfide bonds with agarose for structural support were prepared. The obtained hydrogels exhibited self-healing properties by host-guest complexation as well as gel-sol phase transition in response to ultraviolet (UV) light and reducing agents. Photo-switchable properties of the hydrogels depend on changes in the complex formation of CD-dimers through the trans(450 nm) to cis(365 nm) photo-isomerization of azobenzene. The tensile and strain sweep tests confirmed that the hydrogel's self-healing ability was 79.44% and 81.59%, respectively. In addition, drug release from the hydrogels was controlled to accelerate to 80% in 3 h using UV light or reducing agent. Since the suggested photo-switchable, reduction-responsive, and self-healable hydrogels are non-cytotoxic, they can be potentially applied as biomedical materials in the development of hydrogel-based drug release systems.

Cyclodextrin Based Nanoparticles for Drug Delivery and Theranostics

Colloidal nanoparticulate technology has been described in the literature as a versatile drug delivery system. But it possesses some inherent lacunae in their formulation. Cyclodextrins (CDs) have been extensively reported for the solubility enhancement of poorly water-soluble drugs. The CDs can cause intervention in aspects related to nanoparticles (NPs) that include improving drug loading in nano-system, improving stability, site-specific/targeted drug delivery, improving solubility profile and absorption of the drug in nanosystem with consequent improvement in bioavailability, with the possibility of controlled release, safety and efficacy. They find application in for simultaneous diagnosis and therapeutics for better treatment procedures. The current communication is focused on the application of CDs to overcome troubles in nanoparticulate formulation and enhancement of their performance. It also envisages the theranostic aspects of CDs.

Biocompatible supramolecular pseudorotaxane hydrogels for controllable release of doxorubicin in ovarian cancer SKOV-3 cells

A series of injectable and biocompatible delivery DOX-loaded supramolecular hydrogels were fabricated by using presynthesized DOX-2N-β-CD, Pluronic F-127 and α-CD through host–guest interactions and cooperative multivalent hydrogen bonding interactions. The compositions and morphologies of these hydrogels were confirmed by PXRD and SEM measurements. Moreover, the Rheological measurements of these hydrogels were studied and the studies found that they showed a unique thixotropic behavior, indicting a fast self-healing property after the continuous oscillatory shear stress. Using α-CD as a capping agent, slow and sustained DOX release was observed at different pH values after 72 h. The amount of DOX released at pH 7.4 was determined to be 49.0% for hydrogel 1, whereas the releasing amount of the DOX was increased to 66.3% for hydrogel 1 during the same period at pH 5.5 (P < 0.05), indicating a higher release rate of the drug under more acidic conditions. Taking hydrogel 1 as a representative material, the toxicities of DOX and hydrogel 1 on ovarian cancer cells (SKOV-3) at different exposure durations were examined. The results revealed that hydrogel 1 was less cytotoxic than free DOX to SKOV-3 cells (P < 0.05), suggesting sustained release by these hydrogels in the presence of ovarian cancer cells. It is anticipated that this exploration can provide a new strategy for preparing drug delivery systems.

A series of injectable and biocompatible delivery DOX-loaded supramolecular hydrogels were fabricated by using presynthesized DOX-2N-β-CD, Pluronic F-127 and α-CD through host–guest interactions and cooperative multivalent hydrogen bonding interactions.

Supramolecular hydrogel containing multi-generation poly(L-lysine) dendrons for sustained co-delivery of docetaxel and matrix metallopeptidase-9 short hairpin RNA plasmid

To obtain an efficient drug and gene co-delivery hydrogel, methoxy polyethylene glycol was reacted with the caprolactone units to form the MPEG-PCL block copolymer through the polymerization reaction, which is amphiphilic and can load the hydrophobic drugs. Then, MPEG-PCL conjugated with a multi-generation poly(L-lysine) dendron to form the guest molecule MPEG-PCL-PLLD. After interacted with α-cyclodextrin through host–guest inclusion, the drug and gene dual carrier of supramolecular hydrogel was obtained. The physical properties of the hydrogel, such as the gelation time, the hydrogel strength, or its shear viscosity, could be modulated by the hose molecule of α-cyclodextrin content. MPEG-PCL-PLLD could co-load the drug and gene effectively. After gelation, the loaded drug and gene could be released sustainedly, and the release rate of them was also modulated by the α-cyclodextrin content. The supramolecular hydrogel showed a sustained effect on tumor cells and could induce the cell apoptosis sustainedly. Moreover, the co-delivery strategy was superior to only drug or gene used in tumor cell inhibition. This supramolecular hydrogel as the high-efficiency and sustained co-delivery system showed a promising application in a long-term tumor therapy.

Injectable Hydrogels for Cancer Therapy over the Last Decade

The interest in injectable hydrogels for cancer treatment has been significantly growing over the last decade, due to the availability of a wide range of starting polymer structures with tailored features and high chemical versatility. Many research groups are working on the development of highly engineered injectable delivery vehicle systems suitable for combined chemo-and radio-therapy, as well as thermal and photo-thermal ablation, with the aim of finding out effective solutions to overcome the current obstacles of conventional therapeutic protocols. Within this work, we have reviewed and discussed the most recent injectable hydrogel systems, focusing on the structure and properties of the starting polymers, which are mainly classified into natural or synthetic sources. Moreover, mapping the research landscape of the fabrication strategies, the main outcome of each system is discussed in light of possible clinical applications.

Injectable thermosensitive hydrogel systems based on functional PEG/PCL block polymer for local drug delivery

Injectable in situ thermosensitive hydrogels have potential applications in tissue engineering and drug delivery. The hydrogel formulations exist as aqueous solutions at room temperature but rapidly solidify into gels at 37 °C in situ, making them highly suitable for administering drugs in a minimally invasive manner to the target organ(s). The hydrogel formed with nanoparticles assembled with amphiphilic polymer blocks of polyethyleneglycol (PEG) and biodegradable polycaprolactone (PCL) have been tested as platforms for targeted and sustained drug delivery, and have shown encouraging results. In this review, we summarize the influence of the molecular weight, PEG/PCL ratio and functional structure of hydrophobic PCL blocks on the critical gelation temperature, gelling behavior and drug release kinetics of the hydrogels. The current studies on the biomedical applications of thermosensitive PEG/PCL hydrogels have also been discussed.

An injectable nanocomposite hydrogel co-constructed with gold nanorods and paclitaxel-loaded nanoparticles for local chemo-photothermal synergetic cancer therapy

A nanocomposite hydrogel, ^AuNR/PTXmPECT^gel, was fabricated for in situ synergetic chemotherapy and photothermal therapy for tumor inhibition.

Cyclodextrin-based biological stimuli-responsive carriers for smart and precision medicine

Spurred on by recent progress in nanotechnology and precision medicine, smart drug carriers are entering an entirely new era. Smart drug carriers have been widely studied in recent years as a result of their ability to control drug release under different microenvironments (such as pH, redox, and enzyme) in vivo. Host-guest interactions based on cyclodextrins have proven to be an efficient tool for fabricating smart drug carriers. Because of the application of host-guest interactions, many kinds of biological molecules or supramolecular building blocks can combine into an organic whole at the molecular level. In this review, the features, mechanisms of action, and potent applications of biological stimuli-responsive drug carriers based on cyclodextrins are discussed. In addition, some personal perspectives on this field are presented.

Self-assembled pH-responsive supramolecular hydrogel for hydrophobic drug delivery

In this study, a novel supramolecular hydrogel system, abbreviated as AGC₁₆/NTS, prepared by molecular self-assembly of cationic gemini surfactant 1,3-bis(N,N-dimethyl-N-cetylammonium)-2-propylacrylatedibromide (AGC₁₆) and anionic aromatic compound trisodium 1,3,6-naphthalenetrisulfonate (NTS), was used to encapsulate hydrophobic model drug curcumin (Cur), constructing a pH-responsive drug delivery system. Cur was effectively encapsulated into the hydrophobic domains of AGC₁₆/NTS through hydrophobic interaction, which was confirmed by ¹H NMR measurement. The effects of Cur on the mechanical strength, phase transition behaviour and morphology of AGC₁₆/NTS were characterized by rheology and cryogenic scanning electron microscopy (cryo-SEM) methods. The pH-responsive release of Cur from AGC₁₆/NTS was obtained and the release amount of Cur ascended with pH value decreasing from 7.4 to 3.0. The hydrodynamic sizes of the released Cur-aggregates determined by dynamic light scattering (DLS) were used to analyse the release process of Cur at different pH. The cell viability assay and cell imaging experiment demonstrated that Cur-loaded hydrogel has much higher cytotoxicity and better cell uptake compared to free Cur. Overall, the AGC₁₆/NTS hydrogel is a prospective material for use in encapsulation and controlled-release of hydrophobic drug molecules.

Supramolecular hydrogel, AGC₁₆/NTS, was used to encapsulate hydrophobic drug curcumin (Cur), constructing a pH-responsive drug delivery system; the uptake of released Cur by cancer cells also occurred.