Functionalized poly(γ-Glutamic Acid) fibrous scaffolds for tissue engineering

Functional hemostatic hydrogels: design based on procoagulant principles

Uncontrolled hemorrhage results in various complications and is currently the leading cause of death in the general population. Traditional hemostatic methods have drawbacks that may lead to ineffective hemostasis and even the risk of secondary injury. Therefore, there is an urgent need for more effective hemostatic techniques. Polymeric hemostatic materials, particularly hydrogels, are ideal due to their biocompatibility, flexibility, absorption, and versatility. Functional hemostatic hydrogels can enhance hemostasis by creating physical circumstances conducive to hemostasis or by directly interfering with the physiological processes of hemostasis. The procoagulant principles include increasing the concentration of localized hemostatic substances or establishing a physical barrier at the physical level and intervention in blood cells or the coagulation cascade at the physiological level. Moreover, synergistic hemostasis can combine these functions. However, some hydrogels are ineffective in promoting hemostasis or have a limited application scope. These defects have impeded the advancement of hemostatic hydrogels. To provide inspiration and resources for new designs, this review provides an overview of the procoagulant principles of hemostatic hydrogels. We also discuss the challenges in developing effective hemostatic hydrogels and provide viewpoints.

Biomimetic, self-coacervating adhesive with tough underwater adhesion for ultrafast hemostasis and infected wound healing

Massive bleeding and wound infection due to severe traumas pose a huge threat to the life and health of sufferers; therefore, it is of clinical importance to fabricate adhesives with rapid hemostatic and superior antibacterial capabilities. However, the weak wet adhesion and insufficient function of existing bioadhesives limits their practical application. In this study, a sandcastle worm protein inspired polyelectrolyte self-coacervate adhesive of poly-γ-glutamic acid (PGA) and lysozyme (LZM) was developed. The adhesive exhibited strong underwater adhesion to various surfaces (>250 kPa for solid plates and >50 kPa for soft tissues) and maintained a 80 kPa even when soaked in water for 7 days. Rat liver and tail defect bleeding models revealed that the hemostatic efficiency was superior to that of commercial samples. The in vitro antimicrobial tests showed that the bacterial inhibition to Staphylococcus aureus and Escherichia coli reached almost 100%. Additionally, the infected wound regeneration model demonstrated that the healing rate of the adhesive group was about 100% within 15 days, which was greater than that of the control group. In vitro and in vivo experiments proved that this facilely prepared adhesive will be a promising material to fulfil the integration functions for rapid wound closure and facilitating wound healing.

In situ forming injectable γ-poly(glutamic acid)/PEG adhesive hydrogels for hemorrhage control

Rapidly in situ forming adhesive hydrogels are promising candidates for efficient hemostasis due to their easy administration and minimal invasion. However, development of biocompatible and high-performance hemostatic hydrogels without any additional toxic agents remains a challenge. Herein, a series of novel injectable adhesive hydrogels based on N-hydroxysuccinimide (NHS) modified γ-poly(glutamic acid) (γPGA-NHS) and tetra-armed poly(ethylene glycol) amine (Tetra-PEG-NH₂) were developed. Among all samples, PGA₁₀-PEG₁₅ and PGA₁₀-PEG₂₀ hydrogels with higher PEG contents exhibited rapid gelation time (<20 s), strong mechanical strength (compression modulus up to ∼75 kPa), good adhesive properties (∼15 kPa), and satisfactory burst pressure (∼18-20 kPa). As a result, PGA₁₀-PEG₁₅ and PGA₁₀-PEG₂₀ hydrogels showed a remarkable reduction in hemostasis time and blood loss compared with gauze and fibrin glue. More importantly, the PGA₁₀-PEG₂₀ hydrogel was also successfully used to seal femoral arterial trauma. Subcutaneous implantation experiments indicated a good biocompatibility of the hydrogels in vivo. All these results strongly support that the developed PGA-PEG hydrogels could serve as promising hemostatic agents in emergency and clinical situations.

Development and Advantages of Biodegradable PHA Polymers Based on Electrospun PHBV Fibers for Tissue Engineering and Other Biomedical Applications

Biodegradable polymeric biomaterials offer a significant advantage in disposable or fast-consuming products in medical applications. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is an example of a polyhydroxyalkanoate (PHA), i.e., one group of natural polyesters that are byproducts of reactions taking place in microorganisms in conditions with an excess carbon source. PHA polymers are a promising material for the production of everyday materials and biomedical applications. Due to the high number of monomers in the group, PHAs permit modifications enabling the production of copolymers of different compositions and with different proportions of individual monomers. In order to change and improve the properties of polymer fibers, PHAs are combined with either other natural and synthetic polymers or additives of inorganic phases. Importantly, electrospun PHBV fibers and mats showed an enormous potential in both the medical field (tissue engineering scaffolds, plasters, wound healing, drug delivery systems) and industrial applications (filter systems, food packaging). This Review summarizes the current state of the art in processing PHBV, especially by electrospinning, its degradation processes, and biocompatibility studies, starting from a general introduction to the PHA group of polymers.

Injectable adaptive self-healing hyaluronic acid/poly (γ-glutamic acid) hydrogel for cutaneous wound healing

The most significant challenge in designing wound dressings is to mimic the tissue microenvironment because of the pro-regenerative structural and functional properties of skin. Herein, we developed a type of bionic extracellular matrix (ECM) hydrogels based on thiol-modified poly (γ-glutamic acid) (γ-PGA-SH) and oxidized hyaluronic acid (HA-CHO). The rapid and reversible thiol-aldehyde addition reaction of thiols in γ-PGA-SH and aldehyde groups in HA-CHO provided hydrogels with a dynamic covalent network and endowed them with properties of adaptability and self-healing capability, which are conducive for initial wound coverage and for prolonging the lifespan of the dressing. Interestingly, these hydrogels also showed typical viscoelastic characteristics similar to those of natural ECM, degradation property in vitro and in vivo, and free radical scavenging capability. In addition, the gelation time, rheological behavior, mechanical property, porous structure, and degradation process of the hydrogels could be tuned by adjusting polymer content. Furthermore, the ECM-inspired hydrogels significantly enhanced the wound healing process in vivo in a full-thickness skin defect model compared to those by commercial dressing (Tegaderm™) by facilitating angiogenesis and promoting collagen deposition. The successful application of the multifunctional hydrogel as an antioxidant wound dressing for wound treatment significantly exhibited its great application potential for biomedical areas. STATEMENT OF SIGNIFICANCE: The application of tissue engineering techniques to repair full-thickness skin wounds remains a great challenge in clinical trials. Among the recent approaches used for wound healing, in situ forming injectable hydrogels have gained much attention, and few of them have shown satisfactory overall performance, such as integration into the wound bed, biodegradability, immunocompatibility, vascularization, and recapitulation of the structure and function of skin. In the present study, we designed a simple and convenient in situ forming injectable adaptable self-healing hydrogels with biodegradability and antioxidative properties, which could substantially improve wound healing quality at an affordable cost. The hydrogel-based wound dressing is expected to solve the abovementioned problems and help in promoting cutaneous wound healing.

Injectable Hyaluronic Acid/Poly(γ-glutamic acid) Hydrogel with Step-by-step Tunable Properties for Soft Tissue Engineering

Injectable hydrogels as an important class of biomaterials have gained much attention in tissue engineering. However, their crosslinking degree is difficult to be controlled after being injected into body. As we all know, the crosslinking degree strongly influences the physicochemical properties of hydrogels. Therefore, developing an injectable hydrogel with tunable crosslinking degree in vivo is important for tissue engineering. Herein, we present a dual crosslinking strategy to prepare injectable hydrogels with step-by-step tunable crosslinking degree using Schiff base reaction and photopolymerization. The developed hyaluronic acid/poly(γ-glutamic acid) (HA/γ-PGA) hydrogels exhibit step-by-step tunable swelling behavior, enzymatic degradation behavior and mechanical properties. Mechanical performance tests show that the storage moduli of HA/γ-PGA hydrogels are all less than 2000 Pa and the compressive moduli are in kilopascal, which have a good match with soft tissue. In addition, NIH 3T3 cells encapsulated in HA/γ-PGA hydrogel exhibit a high cell viability, indicating a good cytocompatibility of HA/γ-PGA hydrogel. Therefore, the developed HA/γ-PGA hydrogel as an injectable biomaterial has a good potential in soft tissue engineering.

Recent Advances in Bioplastics: Application and Biodegradation

The success of oil-based plastics and the continued growth of production and utilisation can be attributed to their cost, durability, strength to weight ratio, and eight contributions to the ease of everyday life. However, their mainly single use, durability and recalcitrant nature have led to a substantial increase of plastics as a fraction of municipal solid waste. The need to substitute single use products that are not easy to collect has inspired a lot of research towards finding sustainable replacements for oil-based plastics. In addition, specific physicochemical, biological, and degradation properties of biodegradable polymers have made them attractive materials for biomedical applications. This review summarises the advances in drug delivery systems, specifically design of nanoparticles based on the biodegradable polymers. We also discuss the research performed in the area of biophotonics and challenges and opportunities brought by the design and application of biodegradable polymers in tissue engineering. We then discuss state-of-the-art research in the design and application of biodegradable polymers in packaging and emphasise the advances in smart packaging development. Finally, we provide an overview of the biodegradation of these polymers and composites in managed and unmanaged environments.

Poly(N-Isopropyl-Acrylamide)/Poly(γ-Glutamic Acid) Thermo-Sensitive Hydrogels Loaded with Superoxide Dismutase for Wound Dressing Application

INTRODUCTION

Chronic trauma repair is an important issue affecting people's healthy lives. Thermo-sensitive hydrogel is injectable in situ and can be used to treat large-area wounds. In addition, antioxidants play important roles in promoting wound repair.

METHODS

The purpose of this research was to prepare a novel thermo-sensitive hydrogel-poly(N-isopropyl-acrylamide)/poly(γ-glutamic acid) (PP) loaded with superoxide dismutase (SOD) to improve the effect for trauma treatment. The micromorphology of the hydrogel was observed by scanning electron microscope and the physical properties were measured. The biocompatibility of hydrogel was evaluated by MTT experiment, and the effect of hydrogel on skin wound healing was evaluated by in vivo histological staining.

RESULTS

Gelling behavior and differential scanning calorimeter outcomes showed that the PP hydrogels possessed thermo-sensitivity at physiological temperature and the phase transformation temperature was 28.2°C. The high swelling rate and good water retention were conducive to wound healing. The activity of SOD in vitro was up to 85% at 10 h, which was advantageous to eliminate the superoxide anion. MTT assay revealed that this hydrogel possessed good biocompatibility. Dressings of PP loaded with SOD (SOD-PP) had a higher wound closure rate than other treatments in vivo in diabetic rat model.

DISCUSSION

The SOD-PP thermo-sensitive hydrogels can effectively promote wound healing and have good application prospects for wound repair.

Covalent conjugation of bioactive peptides to graphene oxide for biomedical applications

Graphene is a valuable material in biomedical implant applications due to its mechanical integrity, long-range order, and conductivity; but graphene must be chemically modified to increase biocompatibility and maximize functionality in the body. Here, we developed a foundational synthetic method for covalently functionalizing a reduced GO with bioactive molecules, focusing on synthetic peptides that have shown osteogenic or neurogenic capability as a prototypical example. X-ray photoelectron spectroscopy provides evidence that the peptide is covalently linked to the graphenic backbone. These peptide-graphene (Pep-G) conjugate materials can be processed into mechanically robust, three-dimensional constructs. Differences in their electrostatic charges allow the Pep-G conjugates to form self-assembled, layer-by-layer coatings. Further, the Pep-G conjugates are cytocompatible and electrically conductive, leading us to investigate their potential as regenerative scaffolds, as conductive surfaces can stimulate bone and nerve regeneration. Notably, PC12 cells grown on an electrically stimulated Pep-G scaffold demonstrated enhanced adhesion and neurite outgrowth compared to the control. The functionalization strategy developed here can be used to conjugate a wide variety of bioactive molecules to graphene oxide to create cell-instructive surfaces for biomedical scaffold materials.

Bionic Poly(γ-Glutamic Acid) Electrospun Fibrous Scaffolds for Preventing Hypertrophic Scars

Hypertrophic scarring (HS) remains a great challenge in wound dressing. Although various bionic extracellular matrix (ECM) biomaterials have been designed towards HS treatment, not all biomaterials can synergize biological functions and application functions in wound repair. Bionic scar-inhibiting scaffolds, loaded with biomolecules or drugs, become promising strategies for scarless skin regeneration. In this work, inspired by the physicochemical environment of ECM, a versatile fabrication of poly(γ-glutamic acid) based on electrospun photocrosslinkable hydrogel fibrous scaffolds incorporated with ginsenoside Rg3 (GS-Rg3) is developed for tissue repair and wound therapy. Decorated with adhesive peptide, bionic fibrous scaffolds can accelerate fibroblasts to sprout and grow, forming organized space-filling basement that gradually fills a depression before wound close up in the early stage. Additionally, by sustained release of GS-Rg3 in late stage, fibrous scaffolds promote scarless wound healing in vivo as evidenced by the promotion of cell communication and skin regeneration, as well as the subsequent decrease of angiogenesis and collagen accumulation. These ECM-inspired fibrous scaffolds, therefore, offer new perspectives on accelerated wound healing and tissue regeneration.

In situ photocrosslinked hyaluronic acid and poly (γ-glutamic acid) hydrogels as injectable drug carriers for load-bearing tissue application

Due to the syringeability of precursor solution and convenience of open surgical treatment, injectable hydrogels have gained growing attention in drug delivery application. For load-bearing tissue, the excellent mechanical property is an important requirement for delivery vehicles to resist external stress and loads. Herein, we prepared mechanically robust injectable hydrogels (HA/γ-PGA hydrogels for short) using methacrylate-functionalized hyaluronic acid and poly (γ-glutamic acid) via photopolymerization. The HA/γ-PGA hydrogels showed outstanding anti-compression ability and could suffer a more than 80% strain. Meanwhile, after 5 cycles of compression, HA/γ-PGA hydrogels could still recover quickly against external stress, showing excellent shape recovery capability. Moreover, the mechanical properties could be modulated easily by changing the molar ratio of HA to γ-PGA. The drug release behavior was also evaluated and the drug-loaded HA/γ-PGA hydrogels showed a weak burst release and sustained release behavior. Additionally, HA/γ-PGA hydrogels also exhibited superior biocompatibility. Therefore, HA/γ-PGA hydrogels have great potential as injectable drug carriers for load-bearing tissue application.

Design of functional electrospun nanofibers for cancer cell capture applications

The review reports recent advances in the design of functional electrospun nanofibers for cancer cell capture applications.

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 (σ_c) 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.

Development of Jerusalem artichoke resource for efficient one-step fermentation of poly-(γ-glutamic acid) using a novel strain Bacillus amyloliquefaciens NX-2S

This study aimed to develop non-food fermentation for the cost-effective production of poly-(γ-glutamic acid) (γ-PGA) using a novel strain of Bacillus amyloliquefaciens NX-2S. The new isolate assimilated inulin more efficiently than other carbohydrates from Jerusalem artichoke, without hydrolytic treatment. To investigate the effect of inulin on γ-PGA production, the transcript levels of γ-PGA synthetase genes (pgsB, pgsC, pgsA), regulatory genes (comA, degQ, degS), and the glutamic acid biosynthesis gene (glnA) were analyzed; inulin addition upregulated these key genes. Without exogenous glutamate, strain NX-2S could produce 6.85±0.22g/L of γ-PGA during fermentation. Exogenous glutamate greatly enhances the γ-PGA yield (39.4±0.38g/L) and productivity (0.43±0.05g/L/h) in batch fermentation. Our study revealed a potential method of non-food fermentation to produce high-value products.

Self-Healing, Self-Assembled β-Sheet Peptide-Poly(γ-glutamic acid) Hybrid Hydrogels

Self-assembled biomaterials are an important class of materials that can be injected and formed in situ. However, they often are not able to meet the mechanical properties necessary for many biological applications, losing mechanical properties at low strains. We synthesized hybrid hydrogels consisting of a poly(γ-glutamic acid) polymer network physically cross-linked via grafted self-assembling β-sheet peptides to provide non-covalent cross-linking through β-sheet assembly, reinforced with a polymer backbone to improve strain stability. By altering the β-sheet peptide graft density and concentration, we can tailor the mechanical properties of the hydrogels over an order of magnitude range of 10-200 kPa, which is in the region of many soft tissues. Also, due to the ability of the non-covalent β-sheet cross-links to reassemble, the hydrogels can self-heal after being strained to failure, in most cases recovering all of their original storage moduli. Using a combination of spectroscopic techniques, we were able to probe the secondary structure of the materials and verify the presence of β-sheets within the hybrid hydrogels. Since the polymer backbone requires less than a 15% functionalization of its repeating units with β-sheet peptides to form a hydrogel, it can easily be modified further to incorporate specific biological epitopes. This self-healing polymer-β-sheet peptide hybrid hydrogel with tailorable mechanical properties is a promising platform for future tissue-engineering scaffolds and biomedical applications.

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

A novel mussel-inspired γ-PGA–DA tissue-adhesive hydrogel via a horseradish peroxidase-mediated reaction with robust tissue adhesive strength and hemostasis performance when wet.

Injectable in situ forming poly(l-glutamic acid) hydrogels for cartilage tissue engineering

Injectable, in situ forming hydrogels have exhibited many advantages in regenerative medicine. Herein, we present the novel design of poly(l-glutamic acid) injectable hydrogels via the self-crosslinking of adipic dihydrazide (ADH)-modified poly(l-glutamic acid) (PLGA-ADH) and aldehyde-modified poly(l-glutamic acid) (PLGA-CHO), and investigate their potential in cartilage tissue engineering. Both the hydrazide modification degree of PLGA-ADH and oxidation degree of PLGA-CHO can be adjusted by the amount of activators and sodium periodate, respectively. Experiments reveal that the solid content of the hydrogels, -NH₂/-CHO molar ratio, and oxidation degree of PLGA-CHO have a great effect on the gelation time, equilibrium swelling, mechanical properties, microscopic morphology, and in vitro degradation of the hydrogels. Encapsulation of rabbit chondrocytes within the hydrogels showed viability of the entrapped cells and cytocompatibility of the injectable hydrogels. A preliminary study exhibits injectability and rapid in vivo gel formation, as well as mechanical stability, cell ingrowth, and ectopic cartilage formation. These results suggest that the PLGA hydrogel has potential as an injectable cell delivery carrier for cartilage regeneration and could serve as a new biomaterial for tissue engineering.

Preparation and characterization of foamy poly(γ-benzyl-l-glutamate-co-l-phenylalanine)/bioglass composite scaffolds for bone tissue engineering

Novel foamy scaffolds of poly(γ-benzyl-l-glutamate) and poly(γ-benzyl-l-glutamate-co-l-phenylalanine) were fabricated via a combination of a sintered NaCl templating method and ring-opening polymerization of α-amino acid N-carboxyanhydrides.

Peptide-directed spatial organization of biomolecules in dynamic gradient scaffolds

Specific binding peptides are used to spatially organize biomolecule gradients within an electrospun fiber scaffold. Different biomolecule-binding peptide-polymer conjugates are sequentially co-electrospun with a fiber-forming host polymer to generate opposing gradients of peptide functionalization. The binding peptides specifically and non-covalently guide the spatial arrangement of biomolecules into dynamic gradients within the scaffold, mimicking biological gradients found in native tissues.

Cancer-specific gene silencing through therapeutic siRNA delivery with B vitamin-based nanoassembled low-molecular-weight hydrogelators

This paper describes the synthesis, characterization, and in vitro and in vivo siRNA transfection ability of B vitamin-based cationic clickable bolaamphiphiles (VBs). Our VBs derived from vitamins B₂, B₃, B₅, B₆, and B₇ formed nanoassembled low-molecular-weight hydrogelators (LMWGs, vitagels). The vitagels VB2, VB6, and VB7 (derived from vitamins B₂, B₆, and B₇, respectively) facilitated delivery of small interfering RNAs (siRNA), efficiently silencing gene expression specifically into cancer cell lines; in addition, the LMWGs derived from vitamins B₃, B₅, and B₆ were biocompatible. An ex vivo study in a mouse model revealed that the siRNA delivered by the vitagel VB7 was located primarily at the site of the tumor. The gene silencing efficiency of vascular endothelial growth factor siRNA delivered by vitagels was dependent on the nature of the vitamin headgroup, the N/P ratio, and, interestingly, the hydrogelation properties of the VBs.

Poly(amidoamine) dendrimer-enabled simultaneous stabilization and functionalization of electrospun poly(γ-glutamic acid) nanofibers

We report a facile and general approach to using generation 2 (G2) poly(amidoamine) (PAMAM) dendrimers for simultaneous stabilization and functionalization of electrospun poly(γ-glutamic acid) nanofibers (γ-PGA NFs). In this study, uniform γ-PGA NFs with a smooth morphology were generated using electrospinning technology. In order to endow the NFs with good water stability, amine-terminated G2.NH2 PAMAM dendrimers were utilized to crosslink the γ-PGA NFs via 1-ethyl-3-(3-dimethylami-nopropyl) carbodiimide coupling chemistry. Under the optimized crosslinking conditions, G2.NH2 dendrimers partially modified with fluorescein isothiocyanate (FI) or folic acid (FA) were used to crosslink γ-PGA NFs. Our results reveal that G2.NH2-FI is able to simultaneously render the NFs with good water stability and fluorescence property, while G2.NH2-FA is able to simultaneously endow the NFs with water stability and the ability to capture FA receptor-overexpressing cancer cells in vitro via ligand-receptor interaction. With the tunable dendrimer surface chemistry, multifunctional water-stable γ-PGA-based NFs may be generated via a dendrimer crosslinking approach, thereby providing diverse applications in the areas of biosensing, tissue engineering, drug delivery, and environmental sciences.

Responsive poly (γ-glutamic acid) fibres for biomedical applications

A novel responsive system using a protein-based biopolymer was designed to undergo structural, geometric, and chemical changes upon temperature change or solvent interaction. Poly(γ-glutamic acid) (γ-PGA) is an attractive candidate for various biomedical applications as it is naturally produced, biocompatible and enzymatically degradable. The responsive material was fabricated using an electrospun modified γ-PGA to create a sub-micron fibrous mat. By modulating the environment responsive behaviour in a controlled manner, exciting applications such as wound dressing, compression materials and self-tightening knots are envisaged.

Electrospinning covalently cross-linking biocompatible hydrogelators

Many hydrogel materials of interest are homogeneous on the micrometer scale. Electrospinning, the formation of sub-micrometer to micrometer diameter fibers by a jet of fluid formed under an electric field, is one process being explored to create rich microstructures. However, electrospinning a hydrogel system as it reacts requires an understanding of the gelation kinetics and corresponding rheology near the liquid-solid transition. In this study, we correlate the structure of electrospun fibers of a covalently cross-linked hydrogelator with the corresponding gelation transition and kinetics. Polyethylene oxide (PEO) is used as a carrier polymer in a chemically cross-linking poly(ethylene glycol)-high molecular weight heparin (PEG-HMWH) hydrogel. Using measurements of gelation kinetics from multiple particle tracking microrheology (MPT), we correlate the material rheology with the the formation of stable fibers. An equilibrated, cross-linked hydrogel is then spun and the PEO is dissolved. In both cases, microstructural features of the electrospun fibers are retained, confirming the covalent nature of the network. The ability to spin fibers of a cross-linking hydrogel system ultimately enables the engineering of materials and microstructural length scales suitable for biological applications.