Bo Chi

Fast in situ generated ɛ-polylysine-poly (ethylene glycol) hydrogels as tissue adhesives and hemostatic materials using an enzyme-catalyzed method:

In this study, novel bio-inspired in situ hydrogels as tissue adhesives and hemostatic materials were designed and prepared based on ɛ-polylysine-grafted poly(ethylene glycol) and tyramine via enzymatic cross-linking. The enzymatic cross-linked method enabled fast gelation within seconds, which facilitated its therapeutic applications. By changing the cross-linking conditions, the storage modulus of the hydrogels could be tunable and the mechanical strength influenced the tissue adhesiveness of the hydrogels. Besides, the hydrogels showed fine network structures with appropriate pore sizes, which were thought to be a contributing factor to the strong adhesiveness. Benefiting from the strong mechanical properties and fine network structures, the ɛ-polylysine-grafted poly(ethylene glycol) and tyramine hydrogels exhibited superior wound-healing and hemostatic ability compared to conventional and commercially available medical materials. Moreover, indirect cytotoxicity assessment indicated that the ɛ-polylysine-grafted poly(ethylene glycol) and tyramine hydrogels were nontoxic to the L929 cell. These results demonstrated that the enzymatic cross-linked in situ ɛ-polylysine hydrogels hold high potential for tissue sealants and hemostatic materials.

Calcium involved in the poly(γ-glutamic acid)-mediated promotion of Chinese cabbage nitrogen metabolism.

Plant growth can reportedly be promoted by poly(γ-glutamic acid) (γ-PGA). However, the underlying mechanism is unknown. To reveal the mechanism of γ-PGA, we designed an experiment that investigated the effect of γ-PGA on the nitrogen metabolism of Chinese cabbage hydroponic cultured at different calcium (Ca) levels and varied exogenous Ca(2+) inhibitors. The results showed that nitrate reductase (NR), glutamine synthetase (GS), glutamate synthase, and glutamate dehydrogenase activities in leaves and roots were obviously enhanced by γ-PGA at the normal Ca(2+) level (4.0 mM). Meanwhile, γ-PGA increased the content of total nitrogen, soluble protein, and soluble amino acids in leaves. However, the promotional effect of γ-PGA on fresh weight weakened when Ca(2+) was inadequate. Moreover, γ-PGA not only induced the influx of extracellular Ca(2+) and Ca(2+) in organelles into cytoplasm, but also increased the Ca(2+)-ATPase level to modify Ca(2+) homeostasis in plant cells. In addition, exogenous Ca(2+) inhibitors significantly suppressed the γ-PGA-mediated promotion of cytoplasmic free Ca(2+) level, calmodulin (CaM) content, GS and glutamate dehydrogenase activities. In summary, γ-PGA accelerated the nitrogen metabolism of plants through the Ca(2+)/CaM signaling pathway, thereby improving the growth of the plant.

Poly(l-diaminopropionic acid), a novel non-proteinic amino acid oligomer co-produced with poly(ε-l-lysine) by Streptomyces albulus PD-1

Poly(ε-l-lysine) (ε-PL) producer strain Streptomyces albulus PD-1 secreted a novel polymeric substance into its culture broth along with ε-PL. The polymeric substance was purified to homogeneity and identified. Matrix-assisted laser desorption ionization-time of flight mass spectrometry and nuclear magnetic resonance spectroscopy as well as other analytical techniques revealed that the substance was poly(l-diaminopropionic acid) (PDAP). PDAP is an l-α,β-diaminopropionic acid oligomer linking between amino and carboxylic acid functional groups. The molecular weight of PDAP ranged from 500 to 1500 Da, and no co-polymers composed of l-diaminopropionic acid and l-lysine were present in the culture broth. Compared with ε-PL, PDAP exhibited stronger inhibitory activities against yeasts but weaker activities against bacteria. ε-PL and PDAP co-production was also investigated. Both ε-PL and PDAP were synthesized during the stationary phase of growth, and the final ε-PL and PDAP concentration reached 21.7 and 4.8xa0g L-1, respectively, in fed-batch fermentation. Citric acid feeding resulted in a maximum ε-PL concentration of 26.1xa0g L-1 and a decrease in the final concentration of PDAP to 3.8xa0g L-1. No studies on ε-PL and PDAP co-production in Streptomyces albulus have been reported previously, and inhibition of by-products such as PDAP is potentially useful in ε-PL production.

An innovative method for immobilizing sucrose isomerase on ε-poly-L-lysine modified mesoporous TiO2.

Sucrose isomerase (SIase) is the key enzyme in the enzymatic synthesis of isomaltulose. Mesoporous titanium dioxide (M-TiO2) and ε-poly-L-lysine-functionalized M-TiO2 (EPL-M-TiO2) were prepared as carriers for immobilizing SIase. SIase was effectively immobilized on EPL-M-TiO2 (SI-EPL-M-TiO2) with an enzyme activity of 39.41 U/g, and the enzymatic activity recovery rate up to 93.26%. The optimal pH and temperature of immobilized SIase were 6.0 and 30° C, respectively. SI-EPL-M-TiO2 was more stable in pH and thermal tests than SIase immobilized on M-TiO2 and free SIase. K(m) of SI-EPL-M-TiO2 was 204.92 mmol/L, and vmax was 45.7 μmol/L/s. Batch catalysis reaction of sucrose by SI-EPL-M-TiO2 was performed under the optimal conditions. The half-life period of SI-EPL-M-TiO2 under continuous reaction was 114 h, and the conversion rate of sucrose after 16 batches consistently remained at around 95%, which indicates that SI-EPL-M-TiO2 has good operational stability. Thus, SI-EPL-M-TiO2 can be used as a biocatalyst in food industries.

Enzymatically crosslinked epsilon-poly-L-lysine hydrogels with inherent antibacterial properties for wound infection prevention

In this study, in situ forming epsilon-poly-L-lysine (EPL) bioadhesive hydrogels were fabricated for wound infection prevention. The hydrogel precursor polymer consisted of EPL backbone conjugated with phenol groups of hydroxyphenylpropionic acid (HPA). The chemical modification was characterized by 1H NMR and UV spectroscopies. An enzymatic crosslinking method was employed to copolymerize EPL-HPA (EHPA) in the presence of horseradish peroxidase (HRP) and hydrogen peroxide (H2O2). The HRP crosslinking system allows rapid gelation within several seconds. The hydrogel properties, including the gelation rate, the mechanical strength, and the degradation behavior, were adjustable by controlling the concentration of HRP, H2O2, and the polymer. The adhesiveness ranged from 10 kPa to 35 kPa, which is higher than that of fibrin glue. Cytotoxicity assay with L929 fibroblasts revealed that the hydrogels possessed good in vitro biocompatibility. In addition, in vitro antibacterial studies showed that these bioadhesive hydrogels exhibited an impressively wide spectrum of antimicrobial activity against both Gram-negative and Gram-positive bacteria. Furthermore, evaluations of in vivo subcutaneous injection revealed that the hydrogels have a significant in vivo anti-infection effect. These results suggest that the in situ forming EPL-based hydrogels are interesting and promising bioadhesive materials with inherent antibacterial properties for wound infection prevention.

A new L-arabinose isomerase with copper ion tolerance is suitable for creating protein–inorganic hybrid nanoflowers with enhanced enzyme activity and stability

Protein–inorganic hybrid nanoflowers were prepared using Cu2+, PBS buffer, and a copper ion tolerant L-arabinose isomerase that was derived from Paenibacillus polymyxa (PPAI). The expensive rare sugar L-ribulose or D-tagatose was prepared utilizing these nanoflowers with L-arabinose or D-galactose as the substrate, respectively. The PPAI hybrid nanoflowers showed better enzyme stabilities in both thermal and acidic conditions. Meanwhile, long term batch production was successful showing high stability using these hybrid nanoflowers, which achieved a conversion rate of 61.8% from L-arabinose to L-ribulose.

Antimicrobial and biocompatible ε-polylysine–γ-poly(glutamic acid)–based hydrogel system for wound healing:

Biocompatible and antimicrobial wound dressings are important biomaterials for tissue adhesion and healing. Hydrogels derived from natural polyamino acids are ideal wound dressing because of their good water solubility, biocompatibility, and biodegradability. In this study, we introduce poly(amino acid)–based hydrogels as a new type of wound dressing for wound healing. The composite hydrogels were derived from water-soluble ε-polylysine and γ-poly(glutamic acid) cross-linked by 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide and N-hydroxy-succinimide. The gelation is attributed to the reaction between the amino groups of ε-polylysine and carboxyl groups of γ-poly(glutamic acid). Fourier transform infrared spectroscopy was used to characterize the composite hydrogels. The effect of the ratio of ε-polylysine and γ-poly(glutamic acid) on the gelation time, surface morphology, equilibrium swelling, elastic moduli, adhesive strength, and in vitro degradation of composite hydrogels was examined. The hydrogels showed excellent antimicrobial efficacy against Escherichia coli and Staphylococcus aureus. Indirect cytotoxicity assessment indicated that the composite hydrogels were nontoxic to the L929 cell. The potential of the composite hydrogel as wound dressing was demonstrated by applying it in the skin incision. Results demonstrated that the composite hydrogel showed superior healing effects compared with suture, fibrin glue, and compont skin adhesive, while eliciting less inflammatory response. In conclusion, antimicrobial and biocompatible ε-polylysine–γ-poly(glutamic acid) composite may have great application for wound healing.

Injectable hydrogels based on the hyaluronic acid and poly (γ-glutamic acid) for controlled protein delivery

Injectable hydrogels have great potential in minimally invasive delivery. In this work, novel injectable hydrogels were prepared via self-crosslinking of aldehyde hyaluronic acid (HA-CHO) and hydrazide-modified poly (γ-glutamic acid) (γ-PGA-ADH) for proteins delivery. The HA/γ-PGA hydrogels could be formed in situ as fast as 9s with high swelling ratios. Rheological properties illustrated a wide processing range and good mechanical properties, which were reflected by broad linear viscoelastic region and higher threshold shear stress (σc) and storage modulus (G). Meanwhile, the gelation time, swelling ratio, rheological properties, as well as the protein release behavior could be modulated conveniently. Bovine serum albumin (BSA) was designed as a model drug to study the release behavior. We found that the release mechanisms were either diffusion or Case-II relaxation depending on the different hydrogel components. The HA/γ-PGA hydrogels also showed good biocompatibility. Therefore, the HA/γ-PGA hydrogels have great potential as promising injectable biomaterials for controlled protein delivery.

A mussel-inspired poly(γ-glutamic acid) tissue adhesive with high wet strength for wound closure

Injectable hydrogels are promising candidates for adhesives because of their ease of administration, minimal invasion, and biocompatibility. While developing surgical adhesives with strong wet tissue adhesion, controlled degradability and mechanical properties, and excellent biocompatibility have still been a significant challenge. Herein, inspired from nature, we report a novel mussel-inspired tissue-adhesive hydrogel composed of poly(γ-glutamic acid) and dopamine (γ-PGA–DA) that can bond tissues well and stop bleeding in a wet environment by improving its tissue adhesiveness via a horseradish peroxidase-mediated reaction. The hydrogel exhibited 10–12 fold stronger wet tissue adhesion strength (58.2 kPa) over the clinically used fibrin glue and more effective hemostatic ability following liver impalement in animal models (41.2% reduction in the average amount of bleeding compared with fibrin glue). In addition, the hydrogels demonstrated controlled gelation time, swelling ratio, microscopic morphology, biodegradability and tissue-like elastomeric mechanical properties, and exhibited excellent cyto/tissue-compatibility. The overall results suggest that the γ-PGA–DA hydrogels can be considerably applied as promising wet-resistant adhesives and hemostatic materials.

The microbe-secreted isopeptide poly-γ-glutamic acid induces stress tolerance in Brassica napus L. seedlings by activating crosstalk between H 2 O 2 and Ca 2+

Poly-γ-glutamic acid (γ-PGA) is a microbe-secreted isopeptide that has been shown to promote growth and enhance stress tolerance in crops. However, its site of action and downstream signaling pathways are still unknown. In this study, we investigated γ-PGA-induced tolerance to salt and cold stresses in Brassica napus L. seedlings. Fluorescent labeling of γ-PGA was used to locate the site of its activity in root protoplasts. The relationship between γ-PGA-induced stress tolerance and two signal molecules, H2O2 and Ca2+, as well as the γ-PGA-elicited signaling pathway at the whole plant level, were explored. Fluorescent labeling showed that γ-PGA did not enter the cytoplasm but instead attached to the surface of root protoplasm. Here, it triggered a burst of H2O2 in roots by enhancing the transcription of RbohD and RbohF, and the elicited H2O2 further activated an influx of Ca2+ into root cells. Ca2+ signaling was transmitted via the stem from roots to leaves, where it elicited a fresh burst of H2O2, thus promoting plant growth and enhancing stress tolerance. On the basis of these observation, we propose that γ-PGA mediates stress tolerance in Brassica napus seedlings by activating an H2O2 burst and subsequent crosstalk between H2O2 and Ca2+ signaling.