In vitro and in vivo investigation of thermosensitive chitosan hydrogels containing silica nanoparticles for vaccine delivery

Functionalized nanomaterials targeting NLRP3 inflammasome driven immunomodulation: Friend or Foe

The advancement in drug delivery systems in recent times has significantly enhanced therapeutic effects by enabling site-specific targeting through nanocarriers. These nanocarriers serve as invaluable tools for pharmacotherapeutic advancements against various disorders that enhance the effectiveness of encapsulated drugs by reducing their toxicity and increasing the efficacy of less potent drugs, thereby improving the therapeutic index. Inflammasomes, protein complexes located in the activated immune cell cytoplasm, regulate the activation of caspases involved in inflammation. However, aberrant activation of inflammasomes can result in uncontrolled tissue responses, contributing to the development of various diseases. Therefore, achieving a precise balance between inflammasome inhibition and activation is crucial for effectively treating inflammatory disorders through targeted functionalized nanocarriers. Despite the wealth of available data on the relevance of functionalized nanocarriers in inflammatory disorders, the nanotechnological potential to modulate inflammasomes has not been adequately explored. In this comprehensive review, we highlight the latest research on the modulation of the inflammasome cascade, both upregulating and downregulating its function, using nanocarriers in the context of inflammatory disorders. The utilization of nanocarriers as a therapeutic strategy holds immense potential for researchers aiming to effectively target and modulate inflammasomes in the treatment of inflammatory disorders, thus improving disease severity outcomes.

Single Hydrogel Particle Mechanics and Dynamics Studied by Combining Capillary Micromechanics with Osmotic Compression

Hydrogels can exhibit a remarkably complex response to external stimuli and show rich mechanical behavior. Previous studies of the mechanics of hydrogel particles have generally focused on their static, rather than dynamic, response, as traditional methods for measuring single particle response at the microscopic scale cannot readily measure time-dependent mechanics. Here, we study both the static and the time-dependent response of a single batch of polyacrylamide (PAAm) particles by combining direct contact forces, applied by using Capillary Micromechanics, a method where particles are deformed in a tapered capillary, and osmotic forces are applied by a high molecular weight dextran solution. We found higher values of the static compressive and shear elastic moduli for particles exposed to dextran, as compared to water (KDex≈63 kPa vs. Kwater≈36 kPa, and GDex≈16 kPa vs. Gwater≈7 kPa), which we accounted for, theoretically, as being the result of the increased internal polymer concentration. For the dynamic response, we observed surprising behavior, not readily explained by poroelastic theories. The particles exposed to dextran solutions deformed more slowly under applied external forces than did those suspended in water (τDex≈90 s vs. τwater≈15 s). The theoretical expectation was the opposite. However, we could account for this behaviour by considering the diffusion of dextran molecules in the surrounding solution, which we found to dominate the compression dynamics of our hydrogel particles suspended in dextran solutions.

From Synthetic Route of Silica Nanoparticles to Theranostic Applications

The advancements in nanotechnology have quickly developed a new subject with vast applications of nanostructured materials in medicine and pharmaceuticals. The enormous surface-to-volume ratio, ease of surface modification, outstanding biocompatibility, and, in the case of mesoporous nanoparticles, the tunable pore size make the silica nanoparticles (SNPs) a promising candidate for nano-based medical applications. The preparation of SNPs and their contemporary usage as drug carriers, contrast agents for imaging, carrier of photosensitizers (PS) in photodynamic, as well as photothermal treatments are intensely discussed in this review. Furthermore, the potential harmful responses of silica nanoparticles are reviewed using data obtained from in vitro and in vivo experiments conducted by several studies. Moreover, we showcase the engineering of SNPs for the theranostic applications that can address several intrinsic limitations of conventional therapeutics and diagnostics. In the end, a personal perspective was outlined to state SNPs’ current status and future directions, focusing on SNPs’ significant potentiality and opportunities.

Vaccine implants: current status and recent advancements

Implants have long been used in the field of drug delivery as controlled release vehicles and are now being investigated as single-shot vaccine technologies. Implants have shown great promise, minimizing the need for multiple immunizations while stimulating potent immune responses with reduced doses of vaccine. Synchronous release of vaccine components from implants over an appropriate period of time is important in order to avoid issues including immune tolerance, sequestration or deletion. Traditionally, implants require surgical implantation and removal, which can be a barrier to their widespread use. Degradable and in situ implants are now being developed that can be administered using minimally invasive subcutaneous or intramuscular injection techniques. Injectable hydrogels remain the most commonly studied approach for sustained vaccine delivery due to their ease of administration and tunable degradation properties. Despite exciting advancements in the field of vaccine implants, few technologies have progressed to clinical trials. To increase the likelihood of clinical translation of vaccine implants, strategic testing of disease-relevant antigens in appropriate species is essential. In this review, the significance of vaccine implants and the different types of implants being developed to deliver vaccines are discussed.

Improvement of antithrombotic activity of red ginseng extract by nanoencapsulation using chitosan and antithrombotic cross-linkers: polyglutamic acid and fucodian

Background

Red ginseng (RG) extract, especially ginsenoside Rg1 and Rb1 fractions has been reported to have antithrombotic activities. However, gastric instability and low intestinal permeability are considered to be obstacles to its oral administration. We hypothesized that stability, permeability, and activities of RG might be improved by encapsulation within nanoparticles (NPs) prepared with antithrombotic coating materials.

Methods

RG-loaded chitosan (CS) NPs (PF-NPs) were prepared by complex ionic gelation with the antithrombotic wall materials, polyglutamic acid (PGA), and fucoidan (Fu). The concentrations of PGA (mg/mL, X₁) and Fu (mg/mL, X₂) were optimized for the smallest particle size by response surface methodology. Antithrombotic activities of RG and PF-NPs were analyzed using ex vivo and in vivo antiplatelet activities, in vivo carrageenan-induced mouse tail, and arteriovenous shunt rat thrombosis models.

Results

In accordance with a quadratic regression model, the smallest PF-NPs (286 ± 36.6 nm) were fabricated at 0.628 mg/mL PGA and 0.081 mg/mL Fu. The inhibitory activities of RG on ex vivo and in vivo platelet aggregation and thrombosis in in vivo arteriovenous shunt significantly (p < 0.05) increased to approximately 66.82%, 35.42%, and 38.95%, respectively, by encapsulation within PF-NPs. For an in vivo carrageenan-induced mouse tail thrombosis model, though RG had a weaker inhibitory effect, PF-NPs reduced thrombus significantly due to the presence of PGA and Fu.

Conclusion

PF-NPs contributed to improve the activities of RG not only by nanoencapsulation but also by antithrombotic coating materials. Therefore, PG-NPs can be suggested as an efficient delivery system for oral administration of RG.

Quaternized Chitosan Nanoparticles in Vaccine Applications

Different natural and synthetic biodegradable polymers have been used in vaccine formulations as adjuvant and delivery system but have faced various limitations. Chitosan is a new delivery system with the potential to improve development of nano vaccines and drugs. However, chitosan is only soluble in acidic solutions of low concentration inorganic acids such as dilute acetic acid and dilute hydrochloric acid and in pure organic solvents, which greatly limits its application. Chemical modification of chitosan is an important way to improve its weak solubility. Quaternized chitosan not only retains the excellent properties of chitosan, but also improves its water solubility for a wider application. Recently, quaternized chitosan nanoparticles have been widely used in biomedical field. This review focuses on some quaternized chitosan nanoparticles, and points out the advantages and research direction of quaternized chitosan nanoparticles. As shown by the applications of quaternized chitosan nanoparticles as adjuvant and delivery carrier in vaccines, quaternized chitosan nanoparticles have promising potential in application for the development of nano vaccines in the future.

EspA-loaded mesoporous silica nanoparticles can efficiently protect animal model against enterohaemorrhagic E. coli O157: H7

In the present study, the application of mesoporous silica nanoparticles (MSNPs) loaded with recombinant EspA protein, an immunogen of enterohaemorrhagic E. coli, was investigated in the case of BALB/c mice immunization against the bacterium. MSNPs of 96.9 ± 15.9 nm in diameter were synthesized using template removing method. The immunization of mice was carried out orally and subcutaneously. Significant immune responses to the antigen were observed for the immunized mice when rEspA-loaded MSNPs were administered in both routes in comparison to that of the antigen formulated using a well-known adjuvant, i.e. Freund's. According to the titretitre of serum IL-4, the most potent humoral responses were observed when the mice were immunized subcutaneously with antigen-loaded MSNPs (244, 36 and 14 ng/dL of IL-4 in the serum of mice immunized subcutaneously or orally by antigen-loaded MSNPs, and subcutaneously by Freund's adjuvant formulated-antigen, respectively). However, the difference in serum IgG and serum IgA was not significant in mice subcutaneously immunized with antigen-loaded MSNPs and mice immunized with Freund's adjuvant formulated-antigen. Finally, the immunized mice were challenged orally by enterohaemorrhagic E. coli cells. The amount of bacterial shedding was significantly reduced in faecesfaeces of the animals immunized by antigen-loaded MSNPs in both subcutaneous and oral routes.

Synthesis and compatibility evaluation of versatile mesoporous silica nanoparticles with red blood cells: an overview

Protean mesoporous silica nanoparticles are propitious candidates over decades for nanoscale drug delivery systems due to their unique characteristics, including changeable pore size, mesoporosity, high drug loading capacity and biodegradability.

Novel application of trimethyl chitosan as an adjuvant in vaccine delivery

The application of natural carbohydrate polysaccharides for antigen delivery and its adjuvanation potential has garnered interest in the scientific community in the recent years. These biomaterials are considered favorable candidates for adjuvant development due to their desirable properties like enormous bioavailability, non-toxicity, biodegradability, stability, affordability, and immunostimulating ability. Chitosan is the one such extensively studied natural polymer which has been appreciated for its excellent applications in pharmaceuticals. Trimethyl chitosan (TMC), a derivative of chitosan, possesses these properties. In addition it has the properties of high aqueous solubility, high charge density, mucoadhesive, permeation enhancing (ability to cross tight junction), and stability over a range of ionic conditions which makes the spectrum of its applicability much broader. It has also been seen to perform analogously to alum, complete Freund’s adjuvant, incomplete Freund’s adjuvant, and cyclic guanosine monophosphate adjuvanation, which justifies its role as a potent adjuvant. Although many review articles detailing the applications of chitosan in vaccine delivery are available, a comprehensive review of the applications of TMC as an adjuvant is not available to date. This article provides a comprehensive overview of structural and chemical properties of TMC which affect its adjuvant characteristics; the efficacy of various delivery routes for TMC antigen combination; and the recent advances in the elucidation of its mechanism of action.

Poloxamer 407-chitosan grafted thermoresponsive hydrogels achieve synchronous and sustained release of antigen and adjuvant from single-shot vaccines

Sustained-release vaccine delivery systems may enhance the immunogenicity of subunit vaccines and reduce the need for multiple vaccinations. The aim of this study was to develop a thermoresponsive hydrogel using poloxamer 407-chitosan (CP) grafted copolymer as a delivery system for single-shot sustained-release vaccines. The CP copolymer was synthesized using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide and N-hydroxysuccinimide chemistry. The CP copolymer was a free flowing solution at ambient temperature and transformed rapidly into a gel at body temperature. The hydrogels were loaded with vaccine antigen and adjuvants or the vaccine components were encapsulated in poly (lactic-co-glycolic acid) nanoparticles in order to ensure synchronous release. The CP hydrogels were stable for up to 18 days in vitro. Release of both nanoparticles and the individual components was complete, with release of the individual components being modulated by incorporation into nanoparticles. In vivo, a single dose of CP hydrogel vaccine induced strong, long lasting, cellular and humoral responses that could protect against the development of tumors in a murine melanoma model.

Preparation, characterization, and cellular uptake of resveratrol-loaded trimethyl chitosan nanoparticles

The aim of the study was to encapsulate resveratrol (RV) in trimethyl chitosan (TMC) nanoparticles cross-linked with tripolyphosphate (TPP) and/or alginate to achieve controlled release and improved cellular uptake. TMC (degree of quaternization of 78%) was prepared by reacting purified chitosan with iodomethane. Three types of RV-loaded TMC nanoparticles were prepared: TMC-TPP (TP-NPs), TMC-alginate (TA-NPs), and TMC-alginate-TPP (TAP-NPs). TA-NPs and TAP-NPs showed lower particle size and encapsulation efficiency (EE), better distribution, and more sustained release than TP-NPs due to the high molecular weight and viscous property of alginate. Caco-2 cellular uptake of RV was improved by TMC nanoencapsulation, and TP-NPs showed the highest uptake due to its significantly higher EE. Compared with TAP-NPs, TA-NPs with higher positive surface charge showed higher cellular uptake. Moreover, Caco-2 cell growth-inhibiting activity of RV was significantly increased by TMC nanoencapsulation and TP-NPs showed the significantly highest activity with a good agreement with the permeability results.

Preliminary evaluation of a thermosensitive chitosan hydrogel for Echinococcus granulosus vaccine delivery

The EG95 vaccine is effective in protecting grazing animals from infection with Echinococcus granulosus. Six male lambs were used in the study, two were each vaccinated subcutaneously with 50μg EG95/1mg Quil-A, two animals were each vaccinated with 50μg EG95/1mg Quil-A in 1% chitosan thermolabile gel subcutaneously, and two animals served as non-vaccinated controls. Two vaccinations were given at a 7 week interval. Two vaccinations induced a significantly higher antibody titre in the chitosan group compared with the Quil-A only group. The chitosan vaccine group also had a significantly higher antibody titre compared with a positive control sera from vaccinated and challenged sheep. Incorporating the EG95/Quil-A vaccine in a thermo-responsive chitosan sol-gel stimulated, after the second injection, a high level of antibody absorbance which remained high for at least one year. This response was significantly greater than the response to vaccine without the gel.

A Review of Injectable Polymeric Hydrogel Systems for Application in Bone Tissue Engineering

Biodegradable, stimuli-responsive polymers are essential platforms in the field of drug delivery and injectable biomaterials for application of bone tissue engineering. Various thermo-responsive hydrogels display water-based homogenous properties to encapsulate, manipulate and transfer its contents to the surrounding tissue, in the least invasive manner. The success of bioengineered injectable tissue modified delivery systems depends significantly on their chemical, physical and biological properties. Irrespective of shape and defect geometry, injectable therapy has an unparalleled advantage in which intricate therapy sites can be effortlessly targeted with minimally invasive procedures. Using material testing, it was found that properties of stimuli-responsive hydrogel systems enhance cellular responses and cell distribution at any site prior to the transitional phase leading to gelation. The substantially hydrated nature allows significant simulation of the extracellular matrix (ECM), due to its similar structural properties. Significant current research strategies have been identified and reported to date by various institutions, with particular attention to thermo-responsive hydrogel delivery systems, and their pertinent focus for bone tissue engineering. Research on future perspective studies which have been proposed for evaluation, have also been reported in this review, directing considerable attention to the modification of delivering natural and synthetic polymers, to improve their biocompatibility and mechanical properties.

Vaccination of Sheep with a Methanogen Protein Provides Insight into Levels of Antibody in Saliva Needed to Target Ruminal Methanogens

Methane is produced in the rumen of ruminant livestock by methanogens and is a major contributor to agricultural greenhouse gases. Vaccination against ruminal methanogens could reduce methane emissions by inducing antibodies in saliva which enter the rumen and impair ability of methanogens to produce methane. Presently, it is not known if vaccination can induce sufficient amounts of antibody in the saliva to target methanogen populations in the rumen and little is known about how long antibody in the rumen remains active. In the current study, sheep were vaccinated twice at a 3-week interval with a model methanogen antigen, recombinant glycosyl transferase protein (rGT2) formulated with one of four adjuvants: saponin, Montanide ISA61, a chitosan thermogel, or a lipid nanoparticle/cationic liposome adjuvant (n = 6/formulation). A control group of sheep (n = 6) was not vaccinated. The highest antigen-specific IgA and IgG responses in both saliva and serum were observed with Montanide ISA61, which promoted levels of salivary antibodies that were five-fold higher than the second most potent adjuvant, saponin. A rGT2-specific IgG standard was used to determine the level of rGT2-specific IgG in serum and saliva. Vaccination with GT2/Montanide ISA61 produced a peak antibody concentration of 7 × 10¹⁶ molecules of antigen-specific IgG per litre of saliva, and it was estimated that in the rumen there would be more than 10⁴ molecules of antigen-specific IgG for each methanogen cell. Both IgG and IgA in saliva were shown to be relatively stable in the rumen. Salivary antibody exposed for 1–2 hours to an in vitro simulated rumen environment retained approximately 50% of antigen-binding activity. Collectively, the results from measuring antibody levels and stablility suggest a vaccination-based mitigation strategy for livestock generated methane is in theory feasible.

Nanoencapsulation of Red Ginseng Extracts Using Chitosan with Polyglutamic Acid or Fucoidan for Improving Antithrombotic Activities

The potential of nanoencapsulation using bioactive coating materials for improving antithrombotic activities of red ginseng extract (RG) was examined. RG-loaded chitosan (CS) nanoparticles were prepared using antithrombotic materials, polyglutamic acid (PGA) or fucoidan (Fu). Both CS-PGA (P-NPs, 360 ± 67 nm) and CS-Fu nanoparticles (F-NPs, 440 ± 44 nm) showed sustained ginsenoside release in an acidic environment and improved ginsenoside solubility by approximately 122.8%. Both in vitro rabbit and ex vivo rat platelet aggregation of RG (22.3 and 41.5%) were significantly (p < 0.05) decreased within P-NPs (14.4 and 30.0%) and F-NPs (12.3 and 30.3%), respectively. Although RG exhibited no effect on in vivo carrageenan-induced mouse tail thrombosis, P-NPs and F-NPs demonstrated significant effects, likely the anticoagulation activity of PGA and Fu. Moreover, in the in vivo rat arteriovenous shunt model, P-NPs (156 ± 6.8 mg) and F-NPs (160 ± 3.2 mg) groups showed significantly lower thrombus formation than that of RG (190 ± 5.5 mg). Therefore, nanoencapsulation using CS, PGA, and Fu is a potential for improving the antithrombotic activity of RG.

Novel Injectable Pentablock Copolymer Based Thermoresponsive Hydrogels for Sustained Release Vaccines

The need for multiple vaccinations to enhance the immunogenicity of subunit vaccines may be reduced by delivering the vaccine over an extended period of time. Here, we report two novel injectable pentablock copolymer based thermoresponsive hydrogels made of polyethyleneglycol-polycaprolactone-polylactide-polycaprolactone-polyethyleneglycol (PEG-PCL-PLA-PCL-PEG) with varying ratios of polycaprolactone (PCL) and polylactide (PLA), as single shot sustained release vaccines. Pentablock copolymer hydrogels were loaded with vaccine-encapsulated poly lactic-co-glycolic acid nanoparticles (PLGA-NP) or with the soluble vaccine components. Incorporation of PLGA-NP into the thermoresponsive hydrogels increased the complex viscosity of the gels, lowered the gelation temperature, and minimized the burst release of antigen and adjuvants. The two pentablock hydrogels stimulated both cellular and humoral responses. The addition of PLGA-NP to the hydrogels sustained immune responses for up to 49 days. The polymer with a higher ratio of PCL to PLA formed a more rigid gel, induced stronger immune responses, and stimulated effective anti-tumor responses in a prophylactic melanoma tumor model.

Immune-enhancing effect of nano-DNA vaccine encoding a gene of the prME protein of Japanese encephalitis virus and BALB/c mouse granulocyte-macrophage colony-stimulating factor

Plasmid-encoded granulocyte-macrophage colony-stimulating factor (GM-CSF) is an adjuvant for genetic vaccines; however, how GM-CSF enhances immunogenicity remains to be elucidated. In the present study, it was demonstrated that injection of a plasmid encoding the premembrane (prM) and envelope (E) protein of Japanese encephalitis virus and mouse GM-CSF (pJME/GM-CSF) into mouse muscle recruited large and multifocal conglomerates of macrophages and granulocytes, predominantly neutrophils. During the peak of the infiltration, an appreciable number of immature dendritic cells (DCs) appeared, although no T and B-cells was detected. pJME/GM-CSF increased the number of splenic DCs and the expression of major histocompatibility complex class II (MHCII) on splenic DC, and enhanced the antigenic capture, processing and presentation functions of splenic DCs, and the cell-mediated immunity induced by the vaccine. These findings suggested that the immune-enhancing effect by pJME/GM-CSF was associated with infiltrate size and the appearance of integrin αx (CD11c)+cells. Chitosan-pJME/GM-CSF nanoparticles, prepared by coacervation via intramuscular injection, outperformed standard pJME/GM-CSF administrations in DC recruitment, antigen processing and presentation, and vaccine enhancement. This revealed that muscular injection of chitosan-pJME/GM-CSF nanoparticles may enhance the immunoadjuvant properties of GM-CSF.

Effective polymer adjuvants for sustained delivery of protein subunit vaccines

We have synthesized thermogelling cationic amphiphilic pentablock copolymers that have the potential to act as injectable vaccine carriers and adjuvants that can simultaneously provide sustained delivery and enhance the immunogenicity of released antigen. While these pentablock copolymers have shown efficacy in DNA delivery in past studies, the ability to deliver both DNA and protein for subunit vaccines using the same polymeric carrier can provide greater flexibility and efficacy. We demonstrate the ability of these pentablock copolymers, and the parent triblock Pluronic copolymers to slowly release structurally intact and antigenically stable protein antigens in vitro, create an antigen depot through long-term injection-site persistence and enhance the in vivo immune response to these antigens. We show release of the model protein antigen ovalbumin in vitro from the thermogelling block copolymers with the primary, secondary and tertiary structures of the released protein unchanged compared to the native protein, and its antigenicity preserved upon release. The block copolymers form a gel at physiological temperatures that serves as an antigenic depot and persists in vivo at the site of injection for over 50days. The pentablock copolymers show a significant fivefold enhancement in the immune response compared to soluble protein alone, even 6weeks after the administration, based on measurement of antibody titers. These results demonstrate the potential of these block copolymers hydrogels to persist for several weeks and sustain the release of antigen with minimal effects on protein stability and antigenicity; and their ability to be used simultaneously as a sustained delivery device as well as a subunit vaccine adjuvant platform.

Chitosan hydrogel vaccine generates protective CD8 T cell memory against mouse melanoma

CD8(+) T cells are important in the control of viral infections and cancers because of their cytolytic activity. A vaccine able to generate these cells could be beneficial in the prevention or treatment of these diseases. Chitosan hydrogel is a promising vaccine formulation that has previously been shown to generate effector CD8(+) T cells in a mouse model. This vaccine promotes sustained release of antigen and adjuvant, which generates a robust effector response. For longer lasting immunity, a memory population of these CD8(+) T cells is required to control further disease. We found that vaccination with chitosan hydrogel or dendritic cells using ovalbumin protein as a model antigen and Quil-A adjuvant provided protection in a subcutaneous melanoma challenge 30 days later. Ovalbumin-specific memory CD8(+) T cells were detectable following vaccination with the chitosan hydrogel but not the dendritic cell vaccine and an in vivo cytotoxicity assay demonstrated specific lysis of target cells in chitosan hydrogel vaccinated mice but not those receiving dendritic cell vaccination. These results demonstrate that vaccination with chitosan hydrogel is equally effective as dendritic cell vaccination in tumour protection but has more readily detectable immune correlates of protection. This may be advantageous in predetermining protection in vaccinated individuals.

Hypoxia-induced angiogenesis is increased by the controlled release of deferoxiamine from gelatin hydrogels

The objective of this study is to design biodegradable hydrogels for the controlled release of deferoxiamine (DFO) and evaluate their biological activity. When the DFO was added to human umbilical vein endothelial cells cultured in 5.0% O2, the level of hypoxia-inducible factor-1α and vascular endothelial growth factor significantly increased compared with that without DFO. The expression of angiogenesis-related genes was accordingly increased by the DFO addition. An aqueous solution of mixed gelatin and DFO was freeze-dried, and dehydrothermally treated at 140°C for 24h to prepare a gelatin hydrogel incorporating DFO. In the release test with phosphate-buffered saline solution (PBS) at 37°C, an initial DFO release of 60% was observed, followed by no release. When placed in PBS containing collagenase, the hydrogel was enzymatically degraded with time, and consequently released DFO in a degradation-dependent manner. After the hydrogel incorporating DFO was injected intramuscularly into a mouse model of hind limb ischemia, the number of new blood vessels formed was significantly higher than that with free DFO and DFO-free hydrogel. It is concluded that the DFO-containing hydrogel shows promising for inducing angiogenesis locally.

Bioactive factor delivery strategies from engineered polymer hydrogels for therapeutic medicine

Polymer hydrogels have been widely explored as therapeutic delivery matrices because of their ability to present sustained, localized and controlled release of bioactive factors. Bioactive factor delivery from injectable biopolymer hydrogels provides a versatile approach to treat a wide variety of diseases, to direct cell function and to enhance tissue regeneration. The innovative development and modification of both natural-(e.g., alginate (ALG), chitosan, hyaluronic acid (HA), gelatin, heparin (HEP), etc.) and synthetic-(e.g., polyesters, polyethyleneimine (PEI), etc.) based polymers has resulted in a variety of approaches to design drug delivery hydrogel systems from which loaded therapeutics are released. This review presents the state-of-the-art in a wide range of hydrogels that are formed though self-assembly of polymers and peptides, chemical crosslinking, ionic crosslinking and biomolecule recognition. Hydrogel design for bioactive factor delivery is the focus of the first section. The second section then thoroughly discusses release strategies of payloads from hydrogels for therapeutic medicine, such as physical incorporation, covalent tethering, affinity interactions, on demand release and/or use of hybrid polymer scaffolds, with an emphasis on the last 5 years.

Activation of the NLRP3 inflammasome is not a feature of all particulate vaccine adjuvants

Particulate vaccine formulations, designed to improve the delivery of antigens to antigen-presenting cells (APCs) and to stimulate an immune response, have been shown to activate the NLRP3 inflammasome. This leads to the processing and secretion of interleukin (IL)-1β, which supports the recruitment of pro-inflammatory immune cells into the tissue and can therefore be beneficial for vaccine potency. Recent work suggested that this may be a common mechanism of action for all particulate formulations. The aim of this study was to investigate whether the activation of the NLRP3 inflammasome was common to many delivery systems. We prepared polymer-based chitosan nanoparticles (CNPs), lipid-based cubosomes, a water in oil emulsion of incomplete Freund's adjuvant (IFA) and alum formulations and examined inflammasome activation in vitro using murine bone-marrow-derived dendritic cells and human peripheral blood mononuclear cells and in vivo in mice. The formulations differed in their morphology, size and zeta-potential. Only the positively charged particles (CNPs and alum) were able to activate the inflammasome and increase the secretion of IL-1β. A decrease in the activation of the inflammasome with these particulates was observed when cathepsin B-mediated effects were blocked, implying a role of lysosomal rupture in the activation process. These findings demonstrate a role for the surface charge of particulates in the activation of the NLRP3 inflammasome, which should be considered when designing a novel vaccine formulation.

Recent development of silica nanoparticles as delivery vectors for cancer imaging and therapy

In spite of significant advances in early detection and combined treatments, a number of cancers are often diagnosed at advanced stages and thereby carry a poor prognosis. Developing novel prognostic biomarkers and targeted therapies may offer alternatives for cancer diagnosis and treatment. Recent rapid development of nanomaterials, such as silica based nanoparticles (SiNPs), can just render such a promise. In this article, we attempt to summarize the recent progress of SiNPs in tumor research as a novel delivery vector. SiNP-assisted imaging techniques are used in cancer diagnosis both in vitro and in vivo. Meanwhile, SiNP-mediated drug delivery can efficiently treat tumor by carrying chemotherapeutic agents, photosensitizers, photothermal agents, siRNA, and gene therapeutic agents. Finally, SiNPs that contain at least two different functional agents may be more powerful for both tumor imaging and therapy.

FROM THE CLINICAL EDITOR

This paper summarizes recent progress on the field of silica nanoparticles research as novel delivery vectors for cancer-specific imaging as well as drug delivery of chemotherapeutics, photosensitizers, photothermal agents, siRNA, and gene therapy agents.

Thermosensitive chitosan/glycerophosphate-based hydrogel and its derivatives in pharmaceutical and biomedical applications

INTRODUCTION

Thermogelling chitosan (CS)/glycerophosphate (GP) solutions have been reported as a new type of parenteral in situ forming depot system. These free-flowing solutions at ambient temperature turn into semi-solid hydrogels after parenteral administration.

AREAS COVERED

Formulation parameters such as CS physico-chemical characteristics, CS/gelling agent ratio or pH of the system, were acknowledged as key parameters affecting the solution stability, the sol/gel transition behavior and/or the final hydrogel structure. We discuss also the use of the standard CS/GP thermogels for various biomedical applications, including drug delivery and tissue engineering. Furthermore, this manuscript reviews the different strategies implemented to improve the hydrogel characteristics such as combination with carrier particles, replacement of GP, addition of a second polymer and chemical modification of CS.

EXPERT OPINION

The recent advances in the formulation of CS-based thermogelling systems already overcame several challenges faced by the standard CS/GP system. Dispersion of drug-loaded carrier particles into the thermogels allowed achieving prolonged release profiles for low molecular weight drugs; incorporation of an additional polymer enabled to strengthen the network, while the use of chemically modified CS led to enhanced pH sensitivity or biodegradability of the matrix.

In vivo evaluation of chitosan as an adjuvant in subcutaneous vaccine formulations

Vaccines utilising pure antigens instead of whole pathogens and alternative administration routes require the use of potent adjuvants and effective antigen delivery systems. Chitosan has been reported to act as both an adjuvant as well as a matrix for delivery systems. Chitosan is a natural product produced predominantly from crab shell and commercially available preparations vary in molecular weight, degree of deacetylation and purity. In this study, the impact of chitosan characteristics (molecular weight, degree of deacetylation, particle size, viscosity and impurities) on adjuvant activity were examined. It could be shown that the degree of immune response differed if different chitosan qualities were used and this could be attributed to different characteristics of the chitosan qualities: the immunoadjuvant effect of chitosan probably is a result of an interplay between chemical properties such as molecular weight and degree of deacetylation and physical properties such as particle size and preparation technique, which impacts characteristics such as solubility and viscosity. Hence, the chitosan quality to be used as adjuvant in vaccine preparations needs to be selected carefully.

Preparation of chitosan/mesoporous silica nanoparticle composite hydrogels for sustained co-delivery of biomacromolecules and small chemical drugs

We have developed composite hydrogels of chitosan (CS) and mesoporous silica nanoparticles (MSNs) in this study. The gelation rate, gel strength, drug delivery behavior and chondrocyte proliferation properties were investigated. The introduction of MSNs into CS accelerated the gelation process at body temperature and also increased the elastic modulus G' from 1000 to 1800 Pa. When we used gentamicin (GS) and bovine serum albumin (BSA) as model small chemical drugs and biomacromolecules, respectively, the CS/MSN hydrogels released GS and BSA in a sustained manner simultaneously, but the CS hydrogels only showed sustained BSA release. Furthermore, in vitro chondrocyte culture showed that the CS/MSN composite hydrogels indeed performed much better in supporting chondrocyte growth and maintaining chondrocytic phenotype compared to the CS hydrogels. Therefore, the results suggest that the CS/MSN composite hydrogels can be potentially very useful for cartilage regeneration.

Nanocomposite thermogel for controlled release of small proteins

A nanocomposite thermogel composed of Pluronic®-based multiblock copolymer and laponite nanoclay was developed to sustain delivery of low-molecular-weight proteins. The rapid release of low-molecular-weight proteins from multiblock copolymer thermogels has been a problem for sustained delivery but was solved by using nanocomposite thermogel. Lysozyme (Mw = 14,700), a relatively low-molecular-weight protein, was successfully loaded into and released from nanocomposite thermogel. In addition, interactions among multiblock copolymer, laponite, and lysozyme were studied in terms of gelation, micellization, particle size, and zeta potential. Critical micellization temperatures and sol–gel transition temperatures of multiblock copolymer solutions were lowered with laponite addition. Positively charged lysozyme was adsorbed onto anionic surface of laponite, which increased with an increase in the lysozyme concentration. Particle size and zeta potential of the laponite–lysozyme complex were also dependent on the lysozyme concentration. The nanocomposite thermogel sustained lysozyme release to 40 days, whereas lysozyme release from multiblock copolymer thermogel lasted for only 18 days. The structural stability of released lysozyme was confirmed by circular dichroism spectroscopy and differential scanning calorimetry.