Injectable system and its potential application for the delivery of biomolecules by using thermosensitive poly(γ-glutamic acid)-based physical hydrogel

Preparation, thermal response mechanisms and biomedical applications of thermosensitive hydrogels for drug delivery

INTRODUCTION

Drug treatment is one of the main ways of coping with disease today. For the disadvantages of drug management, thermosensitive hydrogel is used as a countermeasure, which can realize the simple sustained release of drugs and the controlled release of drugs in complex physiological environments.

AREAS COVERED

This paper talks about thermosensitive hydrogels that can be used as drug carriers. The common preparation materials, material forms, thermal response mechanisms, characteristics of thermosensitive hydrogels for drug release and main disease treatment applications are reviewed.

EXPERT OPINION

When thermosensitive hydrogels are used as drug loading and delivery platforms, desired drug release patterns and release profiles can be tailored by selecting raw materials, thermal response mechanisms, and material forms. The properties of hydrogels prepared from synthetic polymers will be more stable than natural polymers. Integrating multiple thermosensitive mechanisms or different kinds of thermosensitive mechanisms on the same hydrogel is expected to realize the spatiotemporal differential delivery of multiple drugs under temperature stimulation. The industrial transformation of thermosensitive hydrogels as drug delivery platforms needs to meet some important conditions.

Injectable poly(γ-glutamic acid)-based biodegradable hydrogels with tunable gelation rate and mechanical strength

Polypeptide-based hydrogels have potential applications in polymer therapeutics and regenerative medicine. However, designing reliable polypeptide-based hydrogels with a rapid injection time and controllable stiffness for clinical applications remains a challenge. Herein, a class of injectable poly(γ-glutamic acid) (PGA)-based hydrogels were constructed using furfurylamine and tyramine-modified PGA (PGA-Fa-Tyr) and the crosslinker dimaleimide poly(ethylene glycol) (MAL-PEG-MAL), through a facile strategy combining enzymatic crosslinking and Diels-Alder (DA) reaction. The injectable hydrogels could be quickly gelatinized and the gelation time, ranging from 10 to 95 s, could be controlled by varying the hydrogen peroxide (H2O2) concentration. Compared with hydrogels formed by single enzymatic crosslinking, the compressive stress and strain of the injectable hydrogels were remarkably enhanced because of the occurrence of the subsequent DA reaction in the hydrogels, suggesting the DA network imparted an outstanding toughening effect on the hydrogels. Furthermore, the mechanical strength, swelling ratio, pore size, and degradation behavior of the injectable hydrogels could be easily controlled by changing the molar ratios of H2O2/Tyr or furan/maleimide. More importantly, injectable hydrogels encapsulating bovine serum albumin exhibited sustained release behavior. Thus, the developed hydrogels hold great potential for applications in biomedical fields, such as tissue engineering and cell/drug delivery.

Polysaccharide-Based Materials Created by Physical Processes: From Preparation to Biomedical Applications

Polysaccharide-based materials created by physical processes have received considerable attention for biomedical applications. These structures are often made by associating charged polyelectrolytes in aqueous solutions, avoiding toxic chemistries (crosslinking agents). We review the principal polysaccharides (glycosaminoglycans, marine polysaccharides, and derivatives) containing ionizable groups in their structures and cellulose (neutral polysaccharide). Physical materials with high stability in aqueous media can be developed depending on the selected strategy. We review strategies, including coacervation, ionotropic gelation, electrospinning, layer-by-layer coating, gelation of polymer blends, solvent evaporation, and freezing-thawing methods, that create polysaccharide-based assemblies via in situ (one-step) methods for biomedical applications. We focus on materials used for growth factor (GFs) delivery, scaffolds, antimicrobial coatings, and wound dressings.

Incorporation of VEGF-and bFGF-loaded alginate oxide particles in acellular collagen-alginate composite hydrogel to promote angiogenesis

BACKGROUND

The use of growth factors in tissue engineering is often challenging due to their instability and short half-life. The delivery of growth factors with nanocarriers can eliminate these problems. In the present study, we introduced an alginate oxide particle in acellular collagen-alginate composite hydrogel platform for the immobilization and controlled release of VEGF and bFGF to promote angiogenesis.

METHODS

The particles were prepared by the oxidation of sodium alginate. Then, they were embedded in collagen-alginate hydrogel. Cytocompatibility of the construct with the human umbilical vein endothelial cells was analyzed through a live/dead assay and scanning electron microscopy. In vitro evaluation of VEGF and bFGF Release Kinetics was done. Moreover, the function of the constructs was confirmed through the chick chorioallantoic membrane assay.

RESULTS

The engineered constructs maintained the human umbilical vein endothelial cells viability, which indicates the non-toxicity of the tested constructs. The presence of VEGF-loaded particles could improve the Total Branching Points in the chick chorioallantoic membrane assay. In this regard, Total Branching Points was significantly improved in the VEGF group compared to the control group (p = 0.010) and FGF group (p = 0.023).

CONCLUSION

The results demonstrated the potential role of these particles in regenerative medicine to improve angiogenesis.

Preliminary investigation on a new natural based poly(gamma-glutamic acid)/Chitosan bioink

The study aims to investigate a novel bioink made from Chitosan (Cs)/ poly(gamma-glutamic acid) (Gamma-PGA) hydrogel that takes advantage of the two biodegradable and biocompatible polymers meeting most of the requirements for biomedical applications. The bioink could be an alternative to other materials commonly used in 3D-bioprinting such as gelatin or alginate. Cs/ Gamma-PGA hydrogel was prepared by double extrusion of Gamma-PGA and Cs solutions, where 2 × 10⁵ human adult fibroblasts per ml Cs solution had been loaded, through Cellink 3D-Bioprinter at 37°C. A computer aided design model was used to get 3D-bioprinting of a four layers grid hydrogel construct with 70% infill. Hydrogel characterization involved rheology, FTIR analysis, stability study (mass loss [ML], fluid uptake [FU]), and cell retaining ability into hydrogel. 3D-bioprinted hydrogel gelation time resulted to be <60 s, hydrogel structure was maintained up to 36.79 Pa shear stress, FTIR analysis demonstrated Gamma-PGA/Cs interpolyelectrolyte complex formation. The 3D-bioprinted hydrogel was stable for 35 days (35% ML) in cell culture medium, with increasing FU. Cell loaded 3D-bioprinted Cs 6% hydrogel was able to retain 70% of cells which survived to printing process and cell viability was maintained during 14 days incubation.

Metabolic engineering of Bacillus amyloliquefaciens LL3 for enhanced poly-γ-glutamic acid synthesis

Poly-γ-glutamic acid (γ-PGA) is a biocompatible and biodegradable polypeptide with wide-ranging applications in foods, cosmetics, medicine, agriculture and wastewater treatment. Bacillus amyloliquefaciens LL3 can produce γ-PGA from sucrose that can be obtained easily from sugarcane and sugar beet. In our previous work, it was found that low intracellular glutamate concentration was the limiting factor for γ-PGA production by LL3. In this study, the γ-PGA synthesis by strain LL3 was enhanced by chromosomally engineering its glutamate metabolism-relevant networks. First, the downstream metabolic pathways were partly blocked by deleting fadR, lysC, aspB, pckA, proAB, rocG and gudB. The resulting strain NK-A6 synthesized 4.84 g l-1 γ-PGA, with a 31.5% increase compared with strain LL3. Second, a strong promoter PC 2up was inserted into the upstream of icd gene, to generate strain NK-A7, which further led to a 33.5% improvement in the γ-PGA titre, achieving 6.46 g l-1 . The NADPH level was improved by regulating the expression of pgi and gndA. Third, metabolic evolution was carried out to generate strain NK-A9E, which showed a comparable γ-PGA titre with strain NK-A7. Finally, the srf and itu operons were deleted respectively, from the original strains NK-A7 and NK-A9E. The resulting strain NK-A11 exhibited the highest γ-PGA titre (7.53 g l-1 ), with a 2.05-fold improvement compared with LL3. The results demonstrated that the approaches described here efficiently enhanced γ-PGA production in B. amyloliquefaciens fermentation.

Charged polymeric additives affect the nucleation of lysozyme crystals

Charged polymers (PGA and PL) interact with lysozyme and then promote the heterogeneous nucleation of the crystals.