Poly(glutamic acid) for biomedical applications

Poly (γ) glutamic acid: a unique microbial biopolymer with diverse commercial applicability

Microbial biopolymers have emerged as promising solutions for environmental pollution-related human health issues. Poly-γ-glutamic acid (γ-PGA), a natural anionic polymeric compound, is composed of highly viscous homo-polyamide of D and L-glutamic acid units. The extracellular water solubility of PGA biopolymer facilitates its complete biodegradation and makes it safe for humans. The unique properties have enabled its applications in healthcare, pharmaceuticals, water treatment, foods, and other domains. It is applied as a thickener, taste-masking agent, stabilizer, texture modifier, moisturizer, bitterness-reducing agent, probiotics cryoprotectant, and protein crystallization agent in food industries. γ-PGA is employed as a biological adhesive, drug carrier, and non-viral vector for safe gene delivery in tissue engineering, pharmaceuticals, and medicine. It is also used as a moisturizer to improve the quality of hair care and skincare cosmetic products. In agriculture, it serves as an ideal stabilizer, environment-friendly fertilizer synergist, plant-growth promoter, metal biosorbent in soil washing, and animal feed additive to reduce body fat and enhance egg-shell strength.

Disposable biosensor based on ionic liquid, carbon nanofiber and poly(glutamic acid) for tyramine determination

In this study, an electrochemical biosensor based on carbon nanofibers (CNF), ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (IL), poly(glutamic acid) (PGA) and tyrosinase (Tyr) modified screen printed carbon electrode (SPE) was constructed for tyramine determination. Optimum experimental parameters such as CNF and IL amount, polymerization conditions of glutamic acid, enzyme loading, pH of test solution and operating potential were explored. The construction steps of the Tyr/PGA/CNF-IL/SPE were pursued by scanning electron microscopy and cyclic voltammetry. The Tyr/PGA/CNF-IL/SPE biosensor exhibited linear response to tyramine in the range of 2.0 × 10-7 - 4.8 × 10-5 M with a low detection limit of 9.1 × 10-8 M and sensitivity of 302.6 μA mM-1. The other advantages of Tyr/PGA/CNF-IL/SPE include its high reproducibility, good stability and anti-interference ability. The presented biosensor was also applied for tyramine determination in malt drink and pickle juice samples and mean analytical recoveries of spiked tyramine were calculated as 100.6% and 100.4% respectively.

An injectable bioactive poly(γ-glutamic acid) modified magnesium phosphate bone cement for bone regeneration

As potential alternatives for calcium phosphate bone cements, magnesium phosphate bone cements (MPC) have attracted considerable attention in recent years. However, their several defects, such as rapid setting times, highly hydration temperature and alkaline pH due to the part of the unreacted phosphate, restricted their applications in human body. With aim to overcome these defects, a novel polypeptite poly(γ-glutamic acid) (γ-PGA) modified MPC were developed. Effect of γ-PGA content on the injectability, anti-washout ability, setting times, hydration temperature, mechanical compressive strength, in vitro bioactivity and degradation were investigated. Moreover, in vitro cyto-compatibility was evaluated using MC3T3-E1 cells by CCK-8 and Live/Dead staining. All these results indicated that the 10%PGA-MPC with an improved handling performances, low hydration temperature, high mechanical compressive strength, and good cyto-compatibility hold a great potential for bone repair and regeneration.

Label free flexible electrochemical DNA biosensor for selective detection of Shigella flexneri in real food samples

An effective tool for early-stage selective detection of the foodborne bacterial pathogen Shigella flexneri (S. flexneri) is essential for diagnosing infectious diseases and controlling outbreaks. Here, a label-free electrochemical DNA biosensor for monitoring S. flexneri is developed. To fabricate the biosensor, detection probe (capture probe) is immobilized on the surface of poly melamine (P-Mel) and poly glutamic acid (PGA), and disuccinimidyl suberate (DSS) functionalized flexible indium tin oxide (ITO) electrode. Anthraquinone-2-sulfonic acid monohydrate sodium salt (AQMS) is used as a signal indicator for the detection of S. flexneri. The proposed DNA biosensor exhibits a wide dynamic range with concentration of the targets ranging from 1 × 10^-6 to 1 × 10^-21 molL^-1 with a limit of detection (LOD) of 7.4 × 10^-22 molL^-1 in the complementary linear target of S. flexneri, and a detection range of 8 × 10¹⁰-80 cells/ml with a LOD of 10 cells/ml in real S. flexneri sample. The proposed flexible biosensor provides high specificity for the detection of S. flexneri compared to other target signals such as discrete base mismatches and different bacterial species. The developed biosensor displayed excellent recoveries in detecting S. flexneri in spiked food samples. Therefore, the proposed biosensor can serve as a model methodology for the detection of other pathogens in a broad span of industries.

Online measurement of the viscosity in shake flasks enables monitoring of γ-PGA production in depolymerase knockout mutants of Bacillus subtilis with the phosphate-starvation inducible promoter Ppst

Poly-γ-glutamic acid (γ-PGA) is a biopolymer with a wide range of applications, mainly produced using Bacillus strains. The formation and concomitant secretion of γ-PGA increases the culture broth viscosity, while enzymatic depolymerisation and degradation of γ-PGA decreases the culture broth viscosity. In this study, the recently published ViMOS (Viscosity Monitoring Online System) is applied for optical online measurements of broth viscosity in eight parallel shake flasks. It is shown that the ViMOS is suitable to monitor γ-PGA production and degradation online in shake flasks. This online monitoring enables the detailed analysis of the P_pst promoter and γ-PGA depolymerase knockout mutants in genetically modified Bacillus subtilis 168. The P_pst promoter becomes active under phosphate starvation. The different single depolymerase knockout mutants are ∆ggt, ∆pgdS, ∆cwlO and a triple knockout mutant. An increase in γ-PGA yield in g_γ-PGA /g_glucose of 190% could be achieved with the triple knockout mutant compared to the P_pst reference strain. The single cwlO knockout also increased γ-PGA production, while the other single knockouts of ggt and pgdS showed no impact. Partial depolymerisation of γ-PGA occurred despite the triple knockout. The online measured data are confirmed with offline measurements. The online viscosity system directly reflects γ-PGA synthesis, γ-PGA depolymerisation, and changes in the molecular weight. Thus, the ViMOS has great potential to rapidly gain detailed and reliable information about new strains and cultivation conditions. The broadened knowledge will facilitate the further optimization of γ-PGA production.

Efficient molasses utilization for low-molecular-weight poly-γ-glutamic acid production using a novel Bacillus subtilis stain

Background

Poly-γ-glutamic acid (γ-PGA) is a biopolymer and has various applications based on its biocompatibility, non-toxicity, and edibility. Low-molecular-weight (Mw)-γ-PGA has promising applications in agriculture and pharmaceuticals. It is traditionally produced by enzymatic hydrolysis. Cost-effective bioproduction of low-Mw-γ-PGA is essential for commercial application of γ-PGA.

Results

Bacillus subtilis 242 is a newly isolated low-Mw-γ-PGA-producing strain. To develop cost-effective production of γ-PGA using this newly isolated strain, cane molasses and corn steep liquor were used to produce γ-PGA. The concentration of cane molasses was optimized and 100 g/L cane molasses resulted in high γ-PGA production. The effects of yeast extract and corn steep liquor on γ-PGA yield were investigated. High concentration of γ-PGA was obtained in the medium with corn steep liquor. A concentration of 32.14 g/L γ-PGA was achieved in fed-batch fermentation, with a productivity of 0.67 g/L/h and a percentage yield (g_γ-PGA/g_glutamate) of 106.39%. The Mw of γ-PGA was 27.99 kDa.

Conclusion

This study demonstrated the potential application of B. subtilis 242 for cost-effective production of low-Mw-γ-PGA from cane molasses.

Multivalent γ-PGA-Exendin-4 conjugates to target pancreatic β-cells

Targeting of glucagon‐like peptide 1 receptor (GLP‐1R), expressed on the surface of pancreatic β‐cells, is of great interest for the development of advanced therapies for diabetes and diagnostics for insulinoma. We report the conjugation of exendin‐4 (Ex‐4), an approved drug to treat type 2 diabetes, to poly‐γ‐glutamic acid (γ‐PGA) to obtain more stable and effective GLP‐1R ligands. Exendin‐4 modified at Lysine‐27 with PEG4‐maleimide was conjugated to γ‐PGA functionalized with furan, in different molar ratios, exploiting a chemoselective Diels‐Alder cycloaddition. The γ‐PGA presenting the highest number of conjugated Ex‐4 molecules (average 120 per polymeric chain) showed a double affinity towards GLP‐1R with respect to exendin per se, paving the way to improved therapeutic and diagnostic applications.

Recent Advances in Microbial Synthesis of Poly-γ-Glutamic Acid: A Review

Poly-γ-glutamic acid (γ-PGA) is a natural, safe, non-immunogenic, biodegradable, and environmentally friendly glutamic biopolymer. γ-PGA has been regarded as a promising bio-based materials in the food field, medical field, even in environmental engineering field, and other industrial fields. Microbial synthesis is an economical and effective way to synthesize γ-PGA. Bacillus species are the most widely studied producing strains. γ-PGA biosynthesis involves metabolic pathway of racemization, polymerization, transfer, and catabolism. Although microbial synthesis of γ-PGA has already been used extensively, productivity and yield remain the major constraints for its industrial application. Metabolic regulation is an attempt to solve the above bottleneck problems and meet the demands of commercialization. Therefore, it is important to understand critical factors that influence γ-PGA microbial synthesis in depth. This review focuses on production strains, biosynthetic pathway, and metabolic regulation. Moreover, it systematically summarizes the functional properties, purification procedure, and industrial application of γ-PGA.

Polypeptoids and Peptoid-Peptide Hybrids by Transition Metal Catalysis

Peptoids have attracted attention for application in biomedicine due to their advantageous properties as compared to peptides. The structural analogues are typically resistant to protease degradation and offer improved biocompatibility. Chemical routes to an impressive variety of short-chain, low-molecular-weight peptoids are well-established. However, synthetic methods for well-defined, high-molecular-weight polypeptoids with side chain diversity are still in their infancy. Here, we report a facile method for synthesis of polypeptoids via transition-metal-catalyzed controlled, living polymerization of N-substituted N-carboxyanhydrides. Our method is amenable to hydrophilic and hydrophobic side chains and yields high-molecular-weight linear polypeptoids of predictable length and low dispersity. Further, the polymer end groups can be tuned for biological targeting, and polypeptide-polypeptoid hybrids are readily prepared in one pot. Our materials are indeed resistant to common proteases and are well-tolerated by human cells. Overall, this work represents a significant stride toward access to tunable polypeptoids.

Rehardening and the Protective Effect of Gamma-Polyglutamic Acid/Nano-Hydroxyapatite Paste on Surface-Etched Enamel

Many revolutionary approaches are on the way pertaining to the high occurrence of tooth decay, which is an enduring challenge in the field of preventive dentistry. However, an ideal dental care material has yet to be fully developed. With this aim, this research reports a dramatic enhancement in the rehardening potential of surface-etched enamels through a plausible synergistic effect of the novel combination of γ-polyglutamic acid (γ-PGA) and nano-hydroxyapatite (nano-HAp) paste, within the limitations of the study. The percentage of recovery of the surface microhardness (SMHR%) and the surface parameters for 9 wt% γ-PGA/nano-HAp paste on acid-etched enamel were investigated with a Vickers microhardness tester and an atomic force microscope, respectively. This in vitro study demonstrates that γ-PGA/nano-HAp treatment could increase the SMHR% of etched enamel to 39.59 ± 6.69% in 30 min. To test the hypothesis of the rehardening mechanism and the preventive effect of the γ-PGA/nano-HAp paste, the surface parameters of mean peak spacing (Rsm) and mean arithmetic surface roughness (Ra) were both measured and compared to the specimens subjected to demineralization and/or remineralization. After the treatment of γ-PGA/nano-HAp on the etched surface, the reduction in Rsm from 999 ± 120 nm to 700 ± 80 nm suggests the possible mechanism of void-filling within a short treatment time of 10 min. Furthermore, ΔRa-I, the roughness change due to etching before remineralization, was 23.15 ± 3.23 nm, while ΔRa-II, the roughness change after remineralization, was 11.99 ± 3.90 nm. This statistically significant reduction in roughness change (p < 0.05) implies a protective effect against the demineralization process. The as-developed novel γ-PGA/nano-HAp paste possesses a high efficacy towards tooth microhardness rehardening, and a protective effect against acid etching.

Polyamide/Poly(Amino Acid) Polymers for Drug Delivery

Polymers have always played a critical role in the development of novel drug delivery systems by providing the sustained, controlled and targeted release of both hydrophobic and hydrophilic drugs. Among the different polymers, polyamides or poly(amino acid)s exhibit distinct features such as good biocompatibility, slow degradability and flexible physicochemical modification. The degradation rates of poly(amino acid)s are influenced by the hydrophilicity of the amino acids that make up the polymer. Poly(amino acid)s are extensively used in the formulation of chemotherapeutics to achieve selective delivery for an appropriate duration of time in order to lessen the drug-related side effects and increase the anti-tumor efficacy. This review highlights various poly(amino acid) polymers used in drug delivery along with new developments in their utility. A thorough discussion on anticancer agents incorporated into poly(amino acid) micellar systems that are under clinical evaluation is included.

Effect of Polymer Hydrophilicity and Molar Mass on the Properties of the Protein in Protein-Polymer Conjugates: The Case of PPEylated Myoglobin

Polyphosphoesters (PPEs), a versatile class of biodegradable and biocompatible polymers, have been proposed as alternatives to poly(ethylene glycol) (PEG), which is suspected to be responsible for anaphylactic reactions in some patients after the administration of PEGylated compounds, e.g., in the current Covid-19 vaccines. We present the synthesis and characterization of a novel set of protein-polymer conjugates using the model protein myoglobin and a set of PPEs with different hydrophilicity and molar mass. We report an extensive evaluation of the (bio)physical properties of the protein within the conjugates, studying its conformation, residual activity, and thermal stability by complementary techniques (UV-vis spectroscopy, nano-differential scanning calorimetry, and fluorometry). The data underline the systematic influence of polymer hydrophilicity on protein properties. The more hydrophobic polymers destabilize the protein, the more hydrophilic PPEs protect against thermally induced aggregation and proteolytic degradation. This basic study aims at guiding the design of future PPEylated drugs and protein conjugates.

A novel and disposable GP- based impedimetric biosensor using electropolymerization process with PGA for highly sensitive determination of leptin: Early diagnosis of childhood obesity

This study presents a novel, single-use electrochemical biosensor for the leptin biomarker, which may have potential use for early diagnosis of childhood obesity. The graphite paper working electrode was used for the first time in impedimetric biosensors. All immobilization procedure, investigation of the optimal parameters and characterization of biosensors were followed and evaluated using Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry (CV). The Scanning Electron Microscope (SEM) was utilized to visualize the morphology of the electrode surface during the immobilization steps of the immunosensor. Moreover, the characterization of the interactions between anti-leptin and leptin was investigated by using Single Frequency Technique (SFI). The applicability of the designed biosensor for real serum samples was tested for clinical use. It was observed that the biosensor allows high sensitivity in the analyte detection (leptin) in real serum samples. Moreover, it was suggested that the developed biosensor presents advantages such as long shelf life (5% loss of activity after 8 weeks and 60% loss after 10 weeks), ability to determine analyte concentrations at picogram level (0.2 pg mL^-1 -20 pg mL^-1), low limit of detection (0.00813 pg mL^{- 1}), reproducibility, reusability (12 times) and high sensitivity.

A rapid and rapid method to quantify poly (γ-glutamic acid) content via copper ion complexation

Presently, there have been some limitations in most of methods to determine poly (γ-glutamic acid) (γ-PGA) content because of many impurities in test specimens. It is necessary to establish a rapid and accurate method to quantify γ-PGA content. In this work, γ-PGA and some impurities commonly seen in fermented broth like glucose, glutamic acid and proteins were used to complex with copper ions. The results show that only γ-PGA can make copper ion precipitated, which content linearly correlates with the precipitate amount. From the study on the validity of the method, it is found that the accuracy and precision are 95.82% and 99.29%, much higher than the ones of method UV and weighing. Therefore, the method via the complexation of copper ion will be popularized to determine γ-PGA content in crude biological samples.

Current applications and prospects of nanoparticles for antifungal drug delivery

Currently, the significance of fungi as human pathogens is not medically concealed in the world. Consequently, suitable recognition and treatment of such infections are of great importance and necessitate the need for comprehensive information in this regard. The introduction of new antifungals and their use today, especially in the last two decades, have revolutionized the treatment of fungal infections. On the other hand, increasing drug resistance in the world has overshadowed such developments. The use of NPs results in the treatment of fungal infections and owing to their specific properties, these particles, unlike the pure antibiotics, can exert a greater inhibitory power although with less concentration compared with conventional drugs. Important reasons that have led to the use of antifungal drugs in delivery systems include reduced drug efficacy, limited penetration through tissue, poor aqueous solubility, decreased bioavailability, and poor drug pharmacokinetics. It is therefore hoped that unfavorable properties of antifungal drugs be mitigated via their incorporation into different types of NPs. This review summarizes the different types of NPs as delivery systems of antifungal as well as their advantages over pure drugs.

Hybrid Curdlan Poly(γ -Glutamic Acid) Nanoassembly for Immune Modulation in Macrophage

A nanoformulation composed of curdlan, a linear polysaccharide of 1,3-β-linked d-glucose units, hydrogen bonded to poly(γ -glutamic acid) (PGA), was developed to stimulate macrophage. Curdlan/PGA nanoparticles (C-NP) are formulated by physically blending curdlan (0.2 mg mL^-1 in 0.4 m NaOH) with PGA (0.8 mg mL^-1 ). Forster resonance energy transfer (FRET) analysis demonstrates a heterospecies interpolymer complex formed between curdlan and PGA. The ¹ H-NMR spectra display significant peak broadening as well as downfield chemical shifts of the hydroxyl proton resonances of curdlan, indicating potential intermolecular hydrogen bonding interactions. In addition, the cross peaks in ¹ H-¹ H 2D-NOESY suggest intermolecular associations between the OH-2/OH-4 hydroxyl groups of curdlan and the carboxylic-/amide-groups of PGA via hydrogen bonding. Intracellular uptake of C-NP occurs over time in human monocyte-derived macrophage (MDM). Furthermore, C-NP nanoparticles dose-dependently increase gene expression for TNF-α, IL-6, and IL-8 at 24 h in MDM. C-NP nanoparticles also stimulate the release of IL-lβ, MCP-1, TNF-α, IL-8, IL-12p70, IL-17, IL-18, and IL-23 from MDM. Overall, this is the first demonstration of a simplistic nanoformulation formed by hydrogen bonding between curdlan and PGA that modulates cytokine gene expression and release of cytokines from MDM.

Renewable polymers and plastics: Performance beyond the green

Renewable bio-based polymers are one of the effective answers that the bioeconomy offers to solve the environmental emergency connected to plastics and more specifically fossil-based plastics. Previous studies have shown that more than 70 % of the natural capital cost associated with plastic derives from the extraction and processing of fossil raw materials and that the price of fossil plastic would be on average 44 % higher if such impact was fully paid by businesses. The disclosure of the hidden costs of plastics will contribute to dispelling the myth of the expensiveness of renewable polymers. Nevertheless, the adoption of bio-based plastics in the market must be motivated by their functional properties and not merely by their green credentials. This article highlights some successful examples of synergies between chemistry and biotechnology in achieving a new generation of bio-based monomers and polymers. Their success is justified by the combination of scientific advances with positive environmental and social fallouts.

Biomedical and Pharmacological Uses of Fluorescein Isothiocyanate Chitosan-Based Nanocarriers

Chitosan-based nanocarriers (ChNCs) are considered suitable drug carriers due to their ability to encapsulate a variety of drugs and cross biological barriers to deliver the cargo to their target site. Fluorescein isothiocyanate-labeled chitosan-based NCs (FITC@ChNCs) are used extensively in biomedical and pharmacological applications. The main advantage of using FITC@ChNCs consists of the ability to track their fate both intra and extracellularly. This journey is strictly dependent on the physico-chemical properties of the carrier and the cell types under investigation. Other applications make use of fluorescent ChNCs in cell labeling for the detection of disorders in vivo and controlling of living cells in situ. This review describes the use of FITC@ChNCs in the various applications with a focus on understanding their usefulness in labeled drug-delivery systems.

Properties of Poly-γ-Glutamic Acid Producing-Bacillus Species Isolated From Ogi Liquor and Lemon-Ogi Liquor

Poly-γ-glutamic acid (γPGA) is a natural and promising biopolymer synthesized by Bacillus spp. during fermentation. This study isolated Bacillus spp. from ogi steep liquor (OSL) and lemon-ogi steep liquor (LOSL) using standard methods and determined the γPGA-producing ability. The antimicrobial and angiotensin-converting enzyme (ACE) inhibitory activities of γPGA polymer were evaluated and isolates were sequenced. Four isolates (TA004, TA006, TA011, TA012) selected based on phenotypic characterization and stickiness (<15 cm) showed antibacterial activity against different pathogens with the highest activity found in TA004 (22.5 mm) and least in TA011 (16.6 mm). Furthermore, time-kill assay showed that the combined γPGA polymer was more effective and demonstrated bactericidal activity over individual γPGA which are bacteriostatic in nature. All γPGA polymer exhibited ACE properties except TA011. The highest IC50 was observed in TA006 (0.11 mg/ml) and least in TA004 (0.35 mg/ml). TA004 had the highest molecular weight (261 kDa) while TA011 had the least (194.97 kDa). In addition, all γPGA exhibited characteristic peaks at 3413-3268 cm-1 and 1722-1664 cm-1 that corresponded to amine N-H stretching intensities and C = O stretching in COOH. Bacillus isolates were identified as TA004 (B. subtilis-GenBank: MH782061), TA006 (B. amyloliquefaciens- GenBank: MH782075), TA011 (B. subtilis- GenBank: MH782088), TA012 (B. subtilis- GenBank: MH782083). OSL and LOSL have the potential for developing functional foods with a valuable effect on health.

Multicomponent peptide assemblies

Self-assembled peptide nanostructures have been increasingly exploited as functional materials for applications in biomedicine and energy. The emergent properties of these nanomaterials determine the applications for which they can be exploited. It has recently been appreciated that nanomaterials composed of multicomponent coassembled peptides often display unique emergent properties that have the potential to dramatically expand the functional utility of peptide-based materials. This review presents recent efforts in the development of multicomponent peptide assemblies. The discussion includes multicomponent assemblies derived from short low molecular weight peptides, peptide amphiphiles, coiled coil peptides, collagen, and β-sheet peptides. The design, structure, emergent properties, and applications for these multicomponent assemblies are presented in order to illustrate the potential of these formulations as sophisticated next-generation bio-inspired materials.

Conformations and molecular interactions of poly-γ-glutamic acid as a soluble microbial product in aqueous solutions

Soluble microbial products (SMPs) are of significant concern in the natural environment and in engineered systems. In this work, poly-γ-glutamic acid (γ-PGA), which is predominantly produced by Bacillus sp., was investigated in terms of pH-induced conformational changes and molecular interactions in aqueous solutions; accordingly, its sedimentation coefficient distribution and viscosity were also elucidated. Experimental results indicate that pH has a significant impact on the structure and molecular interactions of γ-PGA. The conformation of the γ-PGA acid form (γ-PGA-H) is rod-like while that of the γ-PGA sodium form (γ-PGA-Na) is sphere-like. The transformation from α-helix to random coil in the γ-PGA secondary structure is primarily responsible for this shape variation. The intramolecular hydrogen bonds in the γ-PGA-H structure decrease and intramolecular electrostatic repulsion increases as pH increases; however, the sedimentation coefficient distributions of γ-PGA are dependent on intermolecular interactions rather than intramolecular interactions. Concentration has a more substantial effect on intermolecular electrostatic repulsion and chain entanglement at higher pH values. Consequently, the sedimentation coefficient distributions of γ-PGA shift significantly at pH 8.9 from 0.1 to 1.0 g/L, and the viscosity of γ-PGA (5% w/v) significantly increases as pH increases from 2.3 to 6.0.

Improving solubility, stability, and cellular uptake of resveratrol by nanoencapsulation with chitosan and γ-poly (glutamic acid)

Resveratrol (RES), a polyphenolic compound found in grape skins, is a potent antioxidant with broad health benefits. However, its utilization in food has been limited by its poor water solubility, instability, and low bioavailability. The purpose of this study is to improve the solubility, stability, and cellular uptake of RES by nanoencapsulation using chitosan (CS) and γ-poly (glutamic acid) (γ-PGA). The size of nanoparticles significantly decreases with a decrease in the CS/γ-PGA ratio (p<0.05). The nanoparticle size with CS/γ-PGA ratio of 5 was 100-150nm. The entrapment efficiency and UV-light protection effect significantly increases (p<0.05), with an increase in the CS and γ-PGA concentration. The solubility of RES increases 3.2 and 4.2 times before and after lyophilization by nanoencapsulation, respectively. Compared with non-nanoencapsulated RES, the nanoencapsulated RES tends to maintain its solubility and antioxidant activity during storage. CS/γ-PGA nanoencapsulation was able to significantly enhance the transport of RES across a Caco-2 cell monolayer (p<0.05). The highest cellular uptake was found for nanoparticles prepared with 0.5mg/mL CS and 0.1mg/mL γ-PGA, which showed the highest solubility and antioxidant activity during storage. Therefore, CS/γ-PGA nanoencapsulation is found to be a potentially valuable technique for improving the solubility, stability, and cellular uptake of RES.

Dressing with epigallocatechin gallate nanoparticles for wound regeneration

Several reagents have been studied to overcome the problems encountered with antiseptic use, such as moderate cutaneous wound cytotoxicity and skin thinning. We successfully prepared a gelatin/chitosan/epigallocatechin gallate nanoparticle incorporated in a poly(γ-glutamic acid)/gelatin hydrogel, which comprised activated carbon fibers with gentamicin, to fabricate a sandwiched dressing to enhance wound regeneration. The inner layer of activated carbon fibers with gentamicin was designed to prevent bacterial infection, and the outer layer of gelatin/chitosan/epigallocatechin gallate nanoparticles incorporated in a poly(γ-glutamic acid)/gelatin hydrogel was designed to prevent inflammation and facilitate reepithelialization. An in vitro study demonstrated that the dressing effectively inhibited target microorganisms, and scanning electron microscope and confocal laser scanning microscope indicated that the nanoparticles were homogeneously dispersed and migrated into the hydrogel. The in vivo study reported that the sandwiched dressing, comprising the poly(γ-glutamic acid)/gelatin hydrogel, was easy to remove from the wound and facilitated wound tissue regeneration and accelerated healing process.

Reprint of: Review of bioactive glass: From Hench to hybrids

Bioactive glasses are reported to be able to stimulate more bone regeneration than other bioactive ceramics but they lag behind other bioactive ceramics in terms of commercial success. Bioactive glass has not yet reached its potential but research activity is growing. This paper reviews the current state of the art, starting with current products and moving onto recent developments. Larry Hench's 45S5 Bioglass® was the first artificial material that was found to form a chemical bond with bone, launching the field of bioactive ceramics. In vivo studies have shown that bioactive glasses bond with bone more rapidly than other bioceramics, and in vitro studies indicate that their osteogenic properties are due to their dissolution products stimulating osteoprogenitor cells at the genetic level. However, calcium phosphates such as tricalcium phosphate and synthetic hydroxyapatite are more widely used in the clinic. Some of the reasons are commercial, but others are due to the scientific limitations of the original Bioglass 45S5. An example is that it is difficult to produce porous bioactive glass templates (scaffolds) for bone regeneration from Bioglass 45S5 because it crystallizes during sintering. Recently, this has been overcome by understanding how the glass composition can be tailored to prevent crystallization. The sintering problems can also be avoided by synthesizing sol-gel glass, where the silica network is assembled at room temperature. Process developments in foaming, solid freeform fabrication and nanofibre spinning have now allowed the production of porous bioactive glass scaffolds from both melt- and sol-gel-derived glasses. An ideal scaffold for bone regeneration would share load with bone. Bioceramics cannot do this when the bone defect is subjected to cyclic loads, as they are brittle. To overcome this, bioactive glass polymer hybrids are being synthesized that have the potential to be tough, with congruent degradation of the bioactive inorganic and the polymer components. Key to this is creating nanoscale interpenetrating networks, the organic and inorganic components of which have covalent coupling between them, which involves careful control of the chemistry of the sol-gel process. Bioactive nanoparticles can also now be synthesized and their fate tracked as they are internalized in cells. This paper reviews the main developments in the field of bioactive glass and its variants, covering the importance of control of hierarchical structure, synthesis, processing and cellular response in the quest for new regenerative synthetic bone grafts. The paper takes the reader from Hench's Bioglass 45S5 to new hybrid materials that have tailorable mechanical properties and degradation rates.

An interferon-γ-delivery system based on chitosan/poly(γ-glutamic acid) polyelectrolyte complexes modulates macrophage-derived stimulation of cancer cell invasion in vitro

Macrophages represent a large component of the tumour microenvironment and are described to establish interactions with cancer cells, playing crucial roles in several stages of cancer progression. The functional plasticity of macrophages upon stimulation from the environment makes them susceptible to the influence of cancer cells and also renders them as promising therapeutic targets. In this work, we describe a drug delivery system to modulate the phenotype of macrophages, converting them from the pro-tumour M2 phenotype to the anti-tumour M1 phenotype, based on the incorporation of a pro-inflammatory cytokine (interferon-γ) in chitosan (Ch)/poly(γ-glutamic acid) (γ-PGA) complexes. Ch is a biocompatible cationic polysaccharide extensively studied and γ-PGA is a biodegradable, hydrophilic and negatively charged poly-amino acid. These components interact electrostatically, due to opposite charges, resulting in self-assembled structures that can be designed to deliver active molecules such as drugs and proteins. Ch and γ-PGA were self-assembled into polyelectrolyte multilayer films (PEMs) of 371nm thickness, using the layer-by-layer method. Interferon-γ (IFN-γ) was incorporated within the Ch layers at 100 and 500ng/mL. Ch/γ-PGA PEMs with IFN-γ were able to modulate the phenotype of IL-10-treated macrophages at the cell cytoskeleton and cytokine profile levels, inducing an increase of IL-6 and a decrease of IL-10 production. More interestingly, the pro-invasive role of IL-10-treated macrophages was hindered, as their stimulation of gastric cancer cell invasion in vitro decreased from 4 to 2-fold, upon modulation by Ch/γ-PGA PEMs with IFN-γ. This is the first report proposing Ch/γ-PGA PEMs as a suitable strategy to incorporate and release bioactive IFN-γ with the aim of modulating macrophage phenotype, counteracting their stimulating role on gastric cancer cell invasion.

Cisplatin-Induced Formation of Biocompatible and Biodegradable Polypeptide-Based Vesicles for Targeted Anticancer Drug Delivery

Novel cisplatin (CDDP)-loaded, polypeptide-based vesicles for the targeted delivery of cisplatin to cancer cells have been prepared. These vesicles were formed from biocompatible and biodegradable maleimide-poly(ethylene oxide)114-b-poly(L-glutamic acid)12 (Mal-PEG114-b-PLG12) block copolymers upon conjugation with the drug itself. CDDP conjugation forms a short, rigid, cross-linked, drug-loaded, hydrophobic block in the copolymer, and subsequently induces self-assembly into hollow vesicle structures with average hydrodynamic diameters (Dh) of ∼ 270 nm. CDDP conjugation is critical to the formation of the vesicles. The reactive maleimide-PEG moieties that form the corona and inner layer of the vesicles were protected via formation of a reversible Diels-Alder (DA) adduct throughout the block copolymer synthesis so as to maintain their integrity. Drug release studies demonstrated a low and sustained drug release profile in systemic conditions (pH = 7.4, [Cl(-)] = 140 mM) with a higher "burst-like" release rate being observed under late endosomal/lysosomal conditions (pH = 5.2, [Cl(-)] = 35 mM). Further, the peripheral maleimide functionalities on the vesicle corona were conjugated to thiol-functionalized folic acid (FA) (via in situ reduction of a novel bis-FA disulfide, FA-SS-FA) to form an active targeting drug delivery system. These targeting vesicles exhibited significantly higher cellular binding/uptake into and dose-dependent cytotoxicity toward cancer cells (HeLa) compared to noncancerous cells (NIH-3T3), which show high and low folic acid receptor (FR) expression, respectively. This work thus demonstrates a novel approach to polypeptide-based vesicle assembly and a promising strategy for targeted, effective CDDP anticancer drug delivery.

Entrapment of methyl parathion hydrolase in cross-linked poly(γ-glutamic acid)/gelatin hydrogel

Methyl parathion hydrolase (MPH) is an important enzyme in hydrolyzing toxic organophosphorus (OP) compounds. However, MPH is easily deactivated when subjected to extreme environmental conditions and is difficult to recover from the reaction system for reuse, thereby limiting its practical application. To address these shortcomings, we examined the entrapment of MPH in an environment-friendly, biocompatible and biodegradable cross-linked poly(γ-glutamic acid)/gelatin hydrogel. The cross-linked poly(γ-glutamic acid)/gelatin hydrogels were prepared with different gelatin/poly(γ-glutamic acid) mass ratios using water-soluble carbodiimide as the cross-linking agent. The MPH-entrapped cross-linked poly(γ-glutamic acid)/gelatin hydrogel (CPE-MPH) not only possessed improved thermostability, pH stability, and reusability but also exhibited enhanced efficiency in hydrolyzing OP compounds. Furthermore, CPE-MPH possesses high water-absorbing and water-retaining capabilities. We believe that the cross-linked poly(γ-glutamic acid)/gelatin hydrogels are an attractive carrier for the entrapment of diverse enzymes, affording a new approach for enzyme entrapment.

Buffer-stable chitosan-polyglutamic acid hybrid nanoparticles for biomedical applications

In spite of their attractive features, widespread biomedical applications of CS nanoparticles are yet to be realized due to their poor stability in physiological conditions, such as in buffer system at pH 7.4. Buffer-stable chitosan-based hybrid NPs (HNPs) are reported and characterized. Buffer stability is achieved by introducing polyglutamic acid to chitosan. The effect of PGA to CS molar ratio and crosslinking on HNP integrity, buffer stability, and biodegradability are studied. Preliminary in vitro studies are carried out to evaluate targeted uptake efficiency of folate conjugated HNPs. Successful demonstration of buffer stability and cancer cell targeting by HNPs achieves important milestones for chitosan-based nanoparticle technology.

Review of bioactive glass: from Hench to hybrids

Bioactive glasses are reported to be able to stimulate more bone regeneration than other bioactive ceramics but they lag behind other bioactive ceramics in terms of commercial success. Bioactive glass has not yet reached its potential but research activity is growing. This paper reviews the current state of the art, starting with current products and moving onto recent developments. Larry Hench's 45S5 Bioglass® was the first artificial material that was found to form a chemical bond with bone, launching the field of bioactive ceramics. In vivo studies have shown that bioactive glasses bond with bone more rapidly than other bioceramics, and in vitro studies indicate that their osteogenic properties are due to their dissolution products stimulating osteoprogenitor cells at the genetic level. However, calcium phosphates such as tricalcium phosphate and synthetic hydroxyapatite are more widely used in the clinic. Some of the reasons are commercial, but others are due to the scientific limitations of the original Bioglass 45S5. An example is that it is difficult to produce porous bioactive glass templates (scaffolds) for bone regeneration from Bioglass 45S5 because it crystallizes during sintering. Recently, this has been overcome by understanding how the glass composition can be tailored to prevent crystallization. The sintering problems can also be avoided by synthesizing sol-gel glass, where the silica network is assembled at room temperature. Process developments in foaming, solid freeform fabrication and nanofibre spinning have now allowed the production of porous bioactive glass scaffolds from both melt- and sol-gel-derived glasses. An ideal scaffold for bone regeneration would share load with bone. Bioceramics cannot do this when the bone defect is subjected to cyclic loads, as they are brittle. To overcome this, bioactive glass polymer hybrids are being synthesized that have the potential to be tough, with congruent degradation of the bioactive inorganic and the polymer components. Key to this is creating nanoscale interpenetrating networks, the organic and inorganic components of which have covalent coupling between them, which involves careful control of the chemistry of the sol-gel process. Bioactive nanoparticles can also now be synthesized and their fate tracked as they are internalized in cells. This paper reviews the main developments in the field of bioactive glass and its variants, covering the importance of control of hierarchical structure, synthesis, processing and cellular response in the quest for new regenerative synthetic bone grafts. The paper takes the reader from Hench's Bioglass 45S5 to new hybrid materials that have tailorable mechanical properties and degradation rates.

Development of fibroblast culture in three-dimensional activated carbon fiber-based scaffold for wound healing

This work developed a novel bi-layer wound dressing composed of 3D activated carbon fibers that allows facilitates fibroblast cell growth and migration to a wound site for tissue reconstruction, and the gentamicin is incorporated into a poly(γ-glutamic acid)/gelatin membrane to prevent bacterial infection. In an in vitro, field emission scanning electron microscopy shows that rat skin fibroblasts appeared and spread on the surface of activated carbon fibers, and penetrated the interior and exterior of the 3D activated carbon fiber construct to a depth of roughly 200 μm. An in vivo analysis shows that fibroblast cells containing the proposed 3D scaffold had the potential of a biologically functionalized dressing to accelerate wound closure. Additionally, fibroblasts migrated to the wound site in a bi-layer wound dressing containing fibroblasts, enhancing fibronectin and type I collagen expression, resulting in faster skin regeneration than that achieved with a Tegaderm™ hydrocolloid dressing or gauze.