Construction of Tough Hydrogel Cross-Linked via Ionic Interaction by Protection Effect of Hydrophobic Domains

Most hydrogels have poor mechanical properties, severely limiting their potential applications, and numerous approaches have been introduced to fabricate more robust and durable examples. However, these systems consist of nonbiodegradable polymers which limit their application in tissue engineering. Herein, we focus on the fabrication and investigate the influence of hydrophobic segments on ionic cross-linking properties for the construction of a tough, biodegradable hydrogel. A biodegradable, poly(γ-glutamic acid) polymer conjugated with a hydrophobic amino acid, l-phenylalanine ethyl ester (Phe), together with an ionic cross-linking group, alendronic acid (Aln) resulting in γ-PGA-Aln-Phe, was initially synthesized. Rheological assessments through time sweep oscillation testing revealed that the presence of hydrophobic domains accelerated gelation. Comparing gels with and without hydrophobic domains, the compressive strength of γ-PGA-Aln-Phe was found to be six times higher and exhibited longer stability properties in ethylenediaminetetraacetic acid solution, lasting for up to a month. Significantly, the contribution of the hydrophobic domains to the mechanical strength and stability of ionic cross-linking properties of the gel was found to be the dominant factor for the fabrication of a tough hydrogel. As a result, this study provides a new strategy for mechanical enhancement and preserves ionic cross-linked sites by the addition of hydrophobic domains. The development of tough, biodegradable hydrogels reported herein will open up new possibilities for applications in the field of biomaterials.

Preparation, Characterization and Drug Delivery Research of γ-Polyglutamic Acid Nanoparticles: A Review

γ-Polyglutamic acid is a kind of biomaterial and environmentally friendly polymer material with the characteristics of water solubility and good biocompatibility. It has a wide range of applications in medicine, food, cosmetics and other fields. This article reviews the preparation, characterization and medical applications of γ-polyglutamic acid nanoparticles. Nanoparticles prepared by using γ- polyglutamic acid not only had the traditional advantages of enhancing drug stability and slow-release effect, but also were simple to prepare without any biological toxicity. The current methods of nanoparticle preparation mainly include the ion gel method and solvent exchange method, which use the total electrostatic force, van der Waals force, hydrophobic interaction force and hydrogen bond force between molecules to embed materials with different characteristics. At present, there are more and more studies on the use of γ-polyglutamic acid to encapsulate drugs, and the research on the mechanism of its encapsulation and sustained release has gradually matured. The development and application of polyglutamic acid nanoparticles have broad prospects.

Poly-γ-glutamic acid nanoparticles as adjuvant and antigen carrier system for cancer vaccination

Vaccination is an innovative strategy for cancer treatment by leveraging various components of the patients' immunity to boost an anti-tumor immune response. Rationally designed nanoparticles are well suited to maximize cancer vaccination by the inclusion of immune stimulatory adjuvants. Also, nanoparticles might control the pharmacokinetics and destination of the immune potentiating compounds. Poly-γ-glutamic acid (γ-PGA) based nanoparticles (NPs), which have a natural origin, can be easily taken up by dendritic cells (DCs), which leads to the secretion of cytokines which ameliorates the stimulation capacity of T cells. The intrinsic adjuvant properties and antigen carrier properties of γ-PGA NPs have been the focus of recent investigations as they can modulate the tumor microenvironment, can contribute to systemic anti-tumor immunity and subsequently inhibit tumor growth. This review provides a comprehensive overview on the potential of γ-PGA NPs as antigen carriers and/or adjuvants for anti-cancer vaccination.

Drug delivery applications of poly-γ-glutamic acid

Background

Poly-γ-glutamic acid (γ-PGA) is a biopolymer of microbial origin, consisting of repeating units of l-glutamic acid and/or D-glutamic acid. The biopolymer has found use in the fields of agriculture, food, wastewater, and medicine, owing to its non-toxic, biodegradable, and biocompatible properties. Due to its biodegradability, γ-PGA is being tipped to dislodge synthetic plastics in drug delivery application. High cost of production, relative to plastics, is however a clog in the wheel of achieving this.

Main body of abstract

This review looked at the production, nanoparticles fabrication, and drug delivery application of γ-PGA. γ-PGA production optimization by modifying the fermentation medium to tailor towards the production of desirable polymer at reduced cost and techniques for the formulation of γ-PGA nanoparticle as well as its characterization were discussed. This review also evaluated the application of γ-PGA and its nanoparticles in the delivery of drugs to action site. Characterization of γ-PGA and its nanoparticles is a crucial step towards determining the applicability of the biopolymer. γ-PGA has been used in the delivery of active agents to action sites.

Conclusion

This review highlights some of the efforts that have been made in the appraisal of γ-PGA and its nanoparticles for drug delivery. γ-PGA is a candidate for future extensive use in drug delivery.

From Residues to Added-Value Bacterial Biopolymers as Nanomaterials for Biomedical Applications

Bacterial biopolymers are naturally occurring materials comprising a wide range of molecules with diverse chemical structures that can be produced from renewable sources following the principles of the circular economy. Over the last decades, they have gained substantial interest in the biomedical field as drug nanocarriers, implantable material coatings, and tissue-regeneration scaffolds or membranes due to their inherent biocompatibility, biodegradability into nonhazardous disintegration products, and their mechanical properties, which are similar to those of human tissues. The present review focuses upon three technologically advanced bacterial biopolymers, namely, bacterial cellulose (BC), polyhydroxyalkanoates (PHA), and γ-polyglutamic acid (PGA), as models of different carbon-backbone structures (polysaccharides, polyesters, and polyamides) produced by bacteria that are suitable for biomedical applications in nanoscale systems. This selection models evidence of the wide versatility of microorganisms to generate biopolymers by diverse metabolic strategies. We highlight the suitability for applied sustainable bioprocesses for the production of BC, PHA, and PGA based on renewable carbon sources and the singularity of each process driven by bacterial machinery. The inherent properties of each polymer can be fine-tuned by means of chemical and biotechnological approaches, such as metabolic engineering and peptide functionalization, to further expand their structural diversity and their applicability as nanomaterials in biomedicine.

Natural bio-based monomers for biomedical applications: a review

In recent years, synthetic and semi-synthetic polymer materials have been widely used in various applications. Especially concerning biomedical applications, their biocompatibility, biodegradability, and non-toxicity have increased the interest of researchers to discover and develop new products for the well-being of humanity. Among the synthetic and semi-synthetic materials, the use of natural bio-based monomeric materials presents a possible novel avenue for the development of new biocompatible, biodegradable, and non-toxic products. The purpose of this article is to review the information on the role of natural bio-based monomers in biomedical applications. Increased eco-friendliness, biocompatibility, biodegradability, non-toxicity, and intrinsic biological activity are some of the attributes which make itaconic, succinic, citric, hyaluronic, and glutamic acids suitable potential materials for biomedical applications. Herein, we summarize the most recent advances in the field over the past ten years and specifically highlight new and interesting discoveries in biomedical applications. Natural origin acid-based bio-monomers for biomedical applications.

Formulation Stability of Amphiphilic Poly(γ-Glutamic Acid) Nanoparticle and Evaluation of Cardiotoxicity of NPs With Human iPSC-Derived 3D-Cardiomyocyte Tissues

We conducted a stability study of biodegradable and amphiphilic nanoparticles (NPs) consisting of phenylalanine-attached poly(γ-glutamic acid) for drug delivery to find the optimal formulation and define the optimal storage conditions using novel quantitative analytical methods. The stability of NP suspension and lyophilized NP powder manufactured by a dimethyl sulfoxide-based and an ethanol-based process was assessed under 5°C, 25°C/60% relative humidity and 40°C/75% relative humidity. The content of phenylalanine-attached poly(γ-glutamic acid), impurities, absolute molecular weight, appearance, clarity of solution, particle size, zeta potential, particle matter, osmolality, water content, and pH were evaluated as parameters of NP stability. Lyophilized NPs with trehalose showed better stability. The lyophilized NP formulation could therefore provide a stable and high-quality product for clinical studies and shows promise as an effective drug delivery system carrier. The cardiotoxicity of prospective impurities contained in NPs and reagents used in the manufacturing process with human-induced pluripotent stem cell-derived 3-dimensional cardiomyocyte tissues by centrifugation layer-by-layer technique was also evaluated. As a result, cardiotoxicity for NPs and reagents was not observed, and it was clarified that the potential risk to human safety from NPs is low. The applicability of the cardiotoxicity evaluation approaches with human-induced pluripotent stem cell-derived 3-dimensional cardiomyocyte tissues will be evaluated by centrifugation layer-by-layer technique.

Biodegradable polymers for modern vaccine development

Most traditional vaccines are composed either of a whole pathogen or its parts; these vaccines, however, are not always effective and can even be harmful. As such, additional agents known as adjuvants are necessary to increase vaccine safety and efficacy. This review summarizes the potential of biodegradable materials, including synthetic and natural polymers, for vaccine delivery. These materials are highly biocompatible and have minimal toxicity, and most biomaterial-based vaccines delivering antigens or adjuvants have been shown to improve immune response, compared to formulations consisting of the antigen alone. Therefore, these materials can be applied in modern vaccine development.

Development of analytical methods for evaluating the quality of dissociated and associated amphiphilic poly(γ-glutamic acid) nanoparticles

A quantitative method of analyzing nanoparticles (NPs) for drug delivery is urgently required by researchers and industry. Therefore, we developed new quantitative analytical methods for biodegradable and amphiphilic NPs consisting of polymeric γ-PGA-Phe [phenylalanine attached to poly(γ-glutamic acid)] molecules. These γ-PGA-Phe NPs were completely dissociated into separate γ-PGA-Phe molecules by adding sodium dodecyl sulfate (SDS). The dissociated NPs were chromatographically separated to analyze parameters such as the γ-PGA-Phe content in the NPs, the impurities present [using reverse-phase (RP) HPLC with an ultraviolet (UV) detector], and the absolute MW [using size-exclusion chromatography (SEC) with refractive index detection (RI) and multiangle light scattering (MALS) detection, i.e., SEC-RI/MALS]. The chromatographic patterns of the NPs were equivalent to those of the component polymer (γ-PGA-Phe), and excellent chromatographic separation for the quantitative evaluation of NPs was achieved. To the best of our knowledge, this is the first report of the quantitative evaluation of NPs in the field of NP-based delivery systems. Furthermore, these methods were applied to optimize and evaluate the NP manufacturing process. The results showed that impurities were effectively removed from the γ-PGA-Phe during the manufacturing process, so the purity of the final γ-PGA-Phe NPs was enhanced. In addition, the appearance, clarity of solution, particle size, zeta potential, particle matter, osmolarity, and pH of the product were evaluated to ensure that the NPs were of the required quality. Our approach should prove useful for product and process characterization and quality control in the manufacture of NPs. γ-PGA-Phe NPs are known to be a powerful vaccine adjuvant, so they are expected to undergo clinical development into a practical drug-delivery system. The analytical methods established in this paper should facilitate the reliable and practical quality testing of NP products, thus aiding the clinical development of γ-PGA-Phe-based drug-delivery systems. Moreover, since these analytical methods employ commonly used reagents and chromatographic systems, the methods are expected to be applicable to other NP-based drug-delivery products too. Graphical abstract NPs were completely dissociated into separate γ-PGA-Phe polymeric molecules, which yielded a similar chromatogram to that seen for the NPs.

Characterization and analytical development for amphiphilic poly(γ-glutamic acid) as raw material of nanoparticle adjuvants

Amphiphilic graft copolymer consisting of poly(γ-glutamic acid) (γ-PGA) as the hydrophilic backbone and L-phenylalanine ethyl ester (Phe) as the hydrophobic side chain is an important biodegradable polymer with great potential in medical applications. In this research, we established analytical methods for the characterization and quality control of γ-PGA-graft-Phe (γ-PGA-Phe), which forms nanoparticles in aqueous solution, as a deployment platform in practical applications for vaccine adjuvants. The SEC-RI/MALS system, which uses size exclusion chromatography (SEC) coupled with a multi_angle light scattering (MALS) detector and refractive index (RI) detector, was developed to evaluate the characteristics of various types of polymers. By this method, it was indicated that absolute molecular weight (MW) should be used to measure the branch polymer. A gradient reversed phase HPLC (RP-HPLC) method was developed for the content of γ-PGA-Phe and the impurity levels to control product quality and safety. This quantitative approach could become key elements for identifying and characterizing γ-PGA-Phe. In addition, the degradation mechanism of γ-PGA-Phe was also identified as cleavage of main-chain of γ-PGA-Phe based on the stability study of γ-PGA-Phe in buffer solution with various pH values. The analytical developments described above will be important for use in both characterization and formulation design of biopolymers. Nanoparticles (NPs) composed of well-characterized biodegradable γ-PGA-Phe are expected to have a variety of potential clinical applications such as their use as drug and vaccine carriers.

Peptide grafted and self-assembled poly(γ-glutamic acid)-phenylalanine nanoparticles targeting camptothecin to glioma

Aim: To synthesize cRGDfK peptide conjugated poly(γ-glutamic acid)-phenylalanine nanoparticles to improve the therapeutic efficacy of camptothecin (CPT) against glioblastoma multiforme. Methods: Peptide-conjugated, drug-loaded nanoparticles (cRGDfK-conjugated camptothecin-loaded PGA–PA nanoparticles [RCPN]) were prepared and physico-chemically characterized using different techniques. Nanoparticles were evaluated for in vitro anticancer activity, cellular uptake, induction of apoptosis and wound healing cell migration against U87MG human glioblastoma cells. Results: RCPN, with a particle size of <100 nm and 65% CPT encapsulation efficiency, exhibited a dose- and time-dependent cytotoxicity to glioblastoma cells. Compared with native CPT or unconjugated nanoparticles, RCPN induced apoptosis, increased reactive oxygen species generation and inhibited U87MG cell migration. Conclusion: cRGDfK-mediated and amphiphilic copolymer-based nanomedicines represent a new approach for improved delivery of anticancer drugs to and treatment of glioblastoma multiforme.

Bacterial-Derived Polymer Poly-y-Glutamic Acid (y-PGA)-Based Micro/Nanoparticles as a Delivery System for Antimicrobials and Other Biomedical Applications

In the past decade, poly-γ-glutamic acid (γ-PGA)-based micro/nanoparticles have garnered remarkable attention as antimicrobial agents and for drug delivery, owing to their controlled and sustained-release properties, low toxicity, as well as biocompatibility with tissue and cells. γ-PGA is a naturally occurring biopolymer produced by several gram-positive bacteria that, due to its biodegradable, non-toxic and non-immunogenic properties, has been used successfully in the medical, food and wastewater industries. Moreover, its carboxylic group on the side chains can offer an attachment point to conjugate antimicrobial and various therapeutic agents, or to chemically modify the solubility of the biopolymer. The unique characteristics of γ-PGA have a promising future for medical and pharmaceutical applications. In the present review, the structure, properties and micro/nanoparticle preparation methods of γ-PGA and its derivatives are covered. Also, we have highlighted the impact of micro/nanoencapsulation or immobilisation of antimicrobial agents and various disease-related drugs on biodegradable γ-PGA micro/nanoparticles.

Size effect of amphiphilic poly(γ-glutamic acid) nanoparticles on cellular uptake and maturation of dendritic cells in vivo

We prepared size-regulated nanoparticles (NPs) composed of amphiphilic poly(γ-glutamic acid) (γ-PGA). In this study, 40, 100 and 200 nm γ-PGA-graft-l-phenylalanine ethylester (γ-PGA-Phe) NPs were employed. The size of NPs significantly influenced the uptake and activation behaviors of antigen-presenting cells (APCs). When 40 nm γ-PGA-Phe NPs were applied to these cells in vitro, they were highly activated compared with 100 and 200 nm NPs, while cellular uptake was size dependent. The size of the γ-PGA-Phe NPs also significantly affected their migration to the lymph nodes and uptake behavior of NPs by dendritic cells (DCs) in vivo. The 40 nm γ-PGA-Phe NPs migrated more rapidly to the lymph nodes and were taken up by a greater number of DCs compared with 100 and 200 nm NPs. On the other hand, when the amount of γ-PGA-Phe NPs taken up per DC was evaluated, it was higher for 100 and 200 nm NPs than for 40 nm NPs, which suggests that the larger γ-PGA-Phe NPs can deliver a large amount of antigen to a single DC compared with smaller NPs. Furthermore, when examined the maturation of DCs in lymph nodes, 40 nm γ-PGA-Phe NPs efficiently stimulated DCs. These results suggest that the activation, uptake behavior by APCs, migration to lymph nodes, and DC maturation can be controlled by the size of γ-PGA-Phe NPs.

Manipulating the antigen-specific immune response by the hydrophobicity of amphiphilic poly(γ-glutamic acid) nanoparticles

The new generation vaccines are safe but poorly immunogenic, and thus they require the use of adjuvants. However, conventional vaccine adjuvants fail to induce potent cellular immunity, and their toxicity and side-effects hinder the clinical use. Therefore, a vaccine adjuvant which is safe and can induce an antigen-specific cellular immunity-biased immune response is urgently required. In the development of nanoparticle-based vaccine adjuvants, the hydrophobicity is one of the most important factors. It could control the interaction between the encapsulated antigens and/or nanoparticles with immune cells. In this study, nanoparticles (NPs) composed of amphiphilic poly(γ-glutamic acid)-graft-L-phenylalanine ethyl ester (γ-PGA-Phe) with various grafting degrees of hydrophobic side chains were prepared to evaluate the effect of hydrophobicity of vaccine carriers on the antigen encapsulation behavior, cellular uptake, activation of dendritic cells (DCs), and induction of antigen-specific cellular immunity-biased immune responses. These NPs could efficiently encapsulate antigens, and the uptake amount of the encapsulated antigen by DCs was dependent on the hydrophobicity of γ-PGA-Phe NPs. Moreover, the activation potential of the DCs and the induction of antigen-specific cellular immunity were correlated with the hydrophobicity of γ-PGA-Phe NPs. By controlling the hydrophobicity of antigen-encapsulated γ-PGA-Phe NPs, the activation potential of DCs was able to manipulate about 5 to 30-hold than the conventional vaccine, and the cellular immunity was about 10 to 40-hold. These results suggest that the hydrophobicity of NPs is a key factor for changing the interaction between NPs and immune cells, and thus the induction of cellular immunity-biased immune response could be achieved by controlling the hydrophobicity of them.

Synergistic stimulation of antigen presenting cells via TLR by combining CpG ODN and poly(γ-glutamic acid)-based nanoparticles as vaccine adjuvants

CpG oligodeoxynucleotide (ODN) encapsulated poly(γ-glutamic acid)-graft-l-phenylalanine ethyl ester (γ-PGA-Phe) nanoparticles (NPs) employing polycations were prepared to develop vaccine delivery and adjuvant systems. The CpG ODN was stably encapsulated into the NPs when protamine was used as the polycation. The CpG ODN-encapsulated γ-PGA-Phe NPs were taken up by macrophages and CpG ODN which was encapsulated into the NPs internalized into endo/lysosomes, where the toll-like receptor (TLR) 9, which recognizes CpG ODN, is expressed. The examination of release behavior in vitro revealed that the encapsulated CpG ODN into NPs was released when these NPs were immersed into the early endosomal environment. Interestingly, CpG ODN-encapsulated γ-PGA-Phe NPs synergistically activated macrophages. This may be due to the multiple stimulation of TLRs by γ-PGA-Phe NPs (TLR4 ligand) and CpG ODN (TLR9 ligand). We previously reported that γ-PGA-Phe NPs are excellent vaccine adjuvants for inducing potent innate and adaptive immune responses via TLR4. Moreover, coencapsulated CpG ODN and antigen in γ-PGA-Phe NPs induced potent antigen-specific cellular immunity at a higher level than the mixture of CpG ODN and antigen which is the conventional vaccine system. These findings suggest that the conjugation strategies of biologically derived adjuvant and polymeric NPs will aid the development of a novel approach for safe and effective vaccine delivery and adjuvant systems.

Multifunctional conjugation of proteins on/into bio-nanoparticles prepared by amphiphilic poly(γ-glutamic acid)

The present study focuses on nanoparticles composed of amphiphilic poly(gamma-glutamic acid) (gamma-PGA) as potential protein carriers. Amphiphilic graft co-polymers composed of y-PGA as the hydrophilic backbone and L-phenylalanine ethylester (L-PAE) as the hydrophobic segment were synthesized by grafting L-PAE to y-PGA using water-soluble carbodiimide (WSC). Due to their amphiphilic properties, the gamma-PGA-graft-L-PAE co-polymer formed monodispersed nanoparticles in water. The particle size of the nanoparticles composed of gamma-PGA-graft-L-PAE (gamma-PGA nanoparticles) was about 200 nm and showed a highly negative zeta potential. To evaluate their potential applications as multifunctional protein carrier, we prepared protein-entrapped gamma-PGA nanoparticles by encapsulation, covalent immobilization or physical adsorption methods. For this purpose, 11 different proteins with various molecular weights and isoelectric points (pI values) were used as model proteins. The encapsulation of the protein into the nanoparticles was observed for all tested proteins. The amount of protein covalently immobilized or adsorbed onto the nanoparticles showed different tends based on the molecular weight and pI of each protein. Positively charged proteins could be adsorbed onto the negatively charged nanoparticles by electrostatic interaction. Moreover, it was found that enzyme-encapsulated nanoparticles showed higher enzymatic activity than surface-immobilized nanoparticles. These results indicated that the enzymatic activity of the enzyme-entrapped nanoparticles was significantly affected by the conjugation method, and that encapsulation was the optimal method for the conjugation of proteins and nanoparticles. It is expected that the y-PGA nanoparticle will have great potential as multifunctional carriers in pharmaceutical and biomedical applications, such as drug and vaccine delivery systems.

Formation of unimer nanoparticles by controlling the self-association of hydrophobically modified poly(amino acid)s

Amphiphilic block or graft copolymers have been demonstrated to form a variety of self-assembled nano/microstructures in selective solvents. In this study, the self-association behavior of biodegradable graft copolymers composed of poly(γ-glutamic acid) (γ-PGA) as the hydrophilic segment and L-phenylalanine (Phe) as the hydrophobic segment in aqueous solution was investigated. The association behavior and unimer nanoparticle formation of these γ-PGA-graft-Phe (γ-PGA-Phe) copolymers in aqueous solution were characterized with a focus on the effect of the Phe grafting degree on the intra- and interpolymer association of γ-PGA-Phe. The particle size and number of polymer aggregates (N(agg)) in one particle of the γ-PGA-Phe depended on the Phe grafting degree. The size of γ-PGA-Phe with 12, 27, 35, or 42% Phe grafting (γ-PGA-Phe-12, -27, -35, or -42) was about 8-14 nm and the N(agg) was about 1, supporting the presence of a unimolecular graft copolymer in PBS. The pyrene fluorescence data indicated that γ-PGA-Phe-35 and -42 have hydrophobic domains formed by the intrapolymer association of Phe attached to γ-PGA. These results suggest that the Phe grafting degree is critical to the association behavior of γ-PGA-Phe and that γ-PGA-Phe-35 and -42 could form unimer nanoparticles. Moreover, when γ-PGA-Phe-42 dissolved in DMSO was added to various concentrations of NaCl solution, the particle size and N(agg) could be easily controlled by changing the NaCl concentration during the formation of the particles. These results suggest that biodegradable γ-PGA-Phe is useful for the fabrication of very small nanoparticles. It is expected that γ-PGA-Phe nanoparticles, including unimer particles, will have great potential as multifunctional carriers for pharmaceutical and biomedical applications, such as drug and vaccine delivery systems.

Nanoliposomes of L-lysine-conjugated poly(aspartic acid) Increase the Generation and Function of Bone Marrow-derived Dendritic Cells

Background

Biodegradable polymers have increasingly been recognized for various biological applications in recent years. Here we examined the immunostimulatory activities of the novel poly(aspartic acid) conjugated with L-lysine (PLA).

Methods

PLA was synthesized by conjugating L-lysine to aspartic acid polymer. PLA-nanoliposomes (PLA-NLs) were prepared from PLA using a microfluidizer. The immunostimulatory activities of PLA-NLs were examined in mouse bone marrow-derived dendritic cells (BM-DCs).

Results

PLA-NLs increased the number of BM-DCs when added to cultures of GM-CSF-induced DC generation on day 4 after the initiation of cultures. Examination of the phenotypic properties showed that BM-DCs generated in the presence of PLA-NLs are more mature in terms of the expression of MHC class II molecules and major co-stimulatory molecules than BM-DCs generated in the absence of PLA-NLs. In addition, the BM-DCs exhibited enhanced capability to produce cytokines, such as IL-6, IL-12, TNF-α and IL-1β. Allogeneic mixed lymphocyte reactions also confirmed that the BMDCs were more stimulatory on allogeneic T cells. PLA- NL also induced further growth of immature BM-DCs that were harvested on day 8.

Conclusion

These results show that PLA-NLs induce the generation and functional activities of BM-DCs, and suggest that PLA-NLs could be immunostimulating agents that target DCs.

pH-dependent disruption of erythrocyte membrane by amphiphilic poly(amino acid) nanoparticles

The efficient cytoplasmic delivery of therapeutic agents is especially important for the induction of a maximal therapeutic effect. Previously, we reported that 200-nm-sized nanoparticles composed of hydrophobically-modified poly(gamma-glutamic acid) (gamma-PGA) showed great potential as protein carriers. Moreover, protein-encapsulated hydrophobic gamma-PGA (gamma-hPGA) nanoparticles efficiently delivered loaded proteins from the endosomes to the cytoplasm in dendritic cells, but the mechanism of the nanoparticle translocation into the cytoplasm remains to be elucidated. In this study, we examined how polymer composition, hydrophobic modification, size, conformation and surface properties of the amphiphilic nanoparticles are related to functional membrane-disruptive activities. To evaluate their potential applications as membrane-disruptive nanoparticles, the nanoparticles were characterized with respect to their hemolytic activity against erythrocytes as a function of pH. The pH-dependent conformation changes of the nanoparticles were studied by Fourier transform infrared (FT-IR) spectroscopy. The gamma-hPGA nanoparticles showed hemolytic activity with decreasing pH from 7 to 5.5, and were membrane-inactive at physiological pH. This activity was dependent on the hydrophobicity of gamma-PGA. The mechanism responsible for the pH-dependent hemolysis by the nanoparticles involved a conformational change of gamma-hPGA and corresponding increase in the surface hydrophobicity. We conclude that gamma-hPGA nanoparticles have significant potential as membrane-disruptive carriers. These results have important implications for the design of endosome-disruptive nanoparticles as drug, protein and DNA delivery systems.

Stabilization of polyion complex nanoparticles composed of poly(amino acid) using hydrophobic interactions

We report the design and preparation of polyion complex (PIC) nanoparticles composed of anionic hydrophobically modified and cationic poly(amino acid) and the effect of hydrophobic interactions on the stability of these PIC nanoparticles under physiological conditions. We selected poly(gamma-glutamic acid) (gamma-PGA) as the biodegradable anionic polymer and poly(epsilon-lysine) (epsilon-PL) as the cationic polymer. Amphiphilic graft copolymers consisting of gamma-PGA and L-phenylalanine (L-Phe) as the hydrophobic side chain were synthesized by grafting L-Phe to gamma-PGA. The PIC nanoparticles were prepared by mixing gamma-PGA-graft-L-Phe (gamma-PGA-Phe) with epsilon-PL in phosphate buffered saline (PBS). The formation and stability of the PIC nanoparticles were investigated by dynamic light scattering (DLS) measurements. Monomodal anionic PIC nanoparticles were obtained using nonstoichiometric mixing ratios. When unmodified gamma-PGA was mixed with epsilon-PL in PBS, the formation of PIC nanoparticles was observed. However, within a few hours after the preparation, the PIC nanoparticles dissolved in the PBS. In contrast, gamma-PGA-Phe/epsilon-PL nanoparticles showed high stability for a prolonged period of time in PBS and over a wide range of pH values. The stability and size of the PIC nanoparticles depended on the gamma-PGA-Phe/epsilon-PL mixing ratio and the hydrophobicity of the gamma-PGA. The improved stability of the PIC nanoparticles was attributed to the formation of hydrophobic domains in the core of the nanoparticles. The fabrication of PIC nanoparticles using hydrophobic interactions was very useful for the stabilization of the nanoparticles. These results will provide a novel concept in the design of carrier systems composed of PIC. It is expected that the gamma-PGA-Phe/epsilon-PL nanoparticles will have great potential as multifunctional carriers for pharmaceutical and biomedical applications, such as drug and vaccine delivery systems.

Preparation of size tunable amphiphilic poly(amino acid) nanoparticles

Size tunable amphiphilic NPs composed of poly(gamma-PGA) and hydrophobic amino acids, such as Phe or Trp, were prepared. To prepare these size-regulated NPs, gamma-PGA-g-Phe or gamma-PGA-g-Trp dissolved in DMSO was added to various concentrations of NaCl solution. The gamma-PGA-Phe and gamma-PGA-Trp formed monodispersed NPs, and the size of NPs can be easily controlled by NaCl concentration. The different-sized NPs showed the same structure. The encapsulation of protein into the different-sized NPs was successfully achieved and the size of protein-encapsulated gamma-PGA-Phe NPs was increased when protein was encapsulated.

Unique size-change behavior of photo-crosslinked cinnamic acid derivative nanoparticles during hydrolytic degradation

A unique size change of photo-crosslinkable poly[(3,4-dihydroxycinnamic acid)-co-(4-hydroxycinnamic acid)] nanoparticles was observed during hydrolytic degradation depending on the crosslinking degree. The diameter of uncrosslinked nanoparticles decreased from 850 to 300 nm during hydrolysis, whereas that of 75% crosslinked nanoparticles increased from 700 to 950 nm. The diameter changes of crosslinked nanoparticles during hydrolysis might be induced by swelling of the crosslinked networks depending on the crosslinking degree. Moreover, the diameter of the uncrosslinked nanoparticle recovered by additional UV irradiation during hydrolysis. These results suggested that the diameter of the nanoparticles could be controlled even during hydrolysis by UV irradiation.