Genipin-cross-linked poly(L-lysine)-based hydrogels: synthesis, characterization, and drug encapsulation

Genipin prevents alpha-synuclein aggregation and toxicity by affecting endocytosis, metabolism and lipid storage

Parkinson's Disease (PD) is a common neurodegenerative disorder affecting millions of people worldwide for which there are only symptomatic therapies. Small molecules able to target key pathological processes in PD have emerged as interesting options for modifying disease progression. We have previously shown that a (poly)phenol-enriched fraction (PEF) of Corema album L. leaf extract modulates central events in PD pathogenesis, namely α-synuclein (αSyn) toxicity, aggregation and clearance. PEF was now subjected to a bio-guided fractionation with the aim of identifying the critical bioactive compound. We identified genipin, an iridoid, which relieves αSyn toxicity and aggregation. Furthermore, genipin promotes metabolic alterations and modulates lipid storage and endocytosis. Importantly, genipin was able to prevent the motor deficits caused by the overexpression of αSyn in a Drosophila melanogaster model of PD. These findings widens the possibility for the exploitation of genipin for PD therapeutics.

Recent developments in mussel-inspired materials for biomedical applications

Over the decades, researchers have strived to synthesize and modify nature-inspired biomaterials, with the primary aim to address the challenges of designing functional biomaterials for regenerative medicine and tissue engineering. Among these challenges, biocompatibility and cellular interactions have been extensively investigated. Some of the most desirable characteristics for biomaterials in these applications are the loading of bioactive molecules, strong adhesion to moist areas, improvement of cellular adhesion, and self-healing properties. Mussel-inspired biomaterials have received growing interest mainly due to the changes in mechanical and biological functions of the scaffold due to catechol modification. Here, we summarize the chemical and biological principles and the latest advancements in production, as well as the use of mussel-inspired biomaterials. Our main focus is the polydopamine coating, the conjugation of catechol with other polymers, and the biomedical applications that polydopamine moieties are used for, such as matrices for drug delivery, tissue regeneration, and hemostatic control. We also present a critical conclusion and an inspired view on the prospects for the development and application of mussel-inspired materials.

Superabsorbent polymers: A state-of-art review on their classification, synthesis, physicochemical properties, and applications

Superabsorbent polymers (SAP) and modified natural polymer hydrogels are widely and increasingly used in agriculture, health care textiles, effluent treatment, drug delivery, tissue engineering, civil concrete structure, etc. However, not many comprehensive reviews are available on this class of novel polymers. A review covering all the viable applications of SAP will be highly useful for researchers, industry persons, and medical, healthcare, and agricultural purposes. Hence, an attempt has been made to review SAPs with reference to their classifications, synthesis, modification by crosslinking, and physicochemical characterization such as morphology, swellability, thermal and mechanical properties, lifetime prediction, thermodynamics of swelling, absorption, release and transport kinetics, quantification of hydrophilic groups, etc. Besides, the possible methods of fine-tuning their structures for improving their absorption capacity, fast absorption kinetics, mechanical strength, controlled release features, etc. were also addressed to widen their uses. This review has also highlighted the biodegradability, commercial viability and market potential of SAPs, SAP composites, the feasibility of using biomass as raw materials for SAP production, etc. The challenges and future prospects of SAP, their safety, and environmental issues are also discussed.

Poly(α-l-lysine)-based nanomaterials for versatile biomedical applications: Current advances and perspectives

Poly(α-l-lysine) (PLL) is a class of water-soluble, cationic biopolymer composed of α-l-lysine structural units. The previous decade witnessed tremendous progress in the synthesis and biomedical applications of PLL and its composites. PLL-based polymers and copolymers, till date, have been extensively explored in the contexts such as antibacterial agents, gene/drug/protein delivery systems, bio-sensing, bio-imaging, and tissue engineering. This review aims to summarize the recent advances in PLL-based nanomaterials in these biomedical fields over the last decade. The review first describes the synthesis of PLL and its derivatives, followed by the main text of their recent biomedical applications and translational studies. Finally, the challenges and perspectives of PLL-based nanomaterials in biomedical fields are addressed.

Evaluation of Composition Effects on the Physicochemical and Biological Properties of Polypeptide-Based Hydrogels for Potential Application in Wound Healing

In this study, the effect of crosslinking and concentration on the properties of a new library of low-concentration poly(Lys₆₀-ran-Ala₄₀)-based hydrogels for potential application in wound healing was investigated in order to correlate the hydrogel composition with the desired physicochemical and biofunctional properties to expand the assortment of poly-l-lysine (PLL)-based hydrogels suitable for wound healing. Controlled ring-opening polymerization (ROP) and precise hydrogel compositions were used to customize the physicochemical and biofunctional properties of a library of new hydrogels comprising poly(l-lysine-ran-l-alanine) and four-arm poly(ethylene glycol) (P(KA)/4-PEG). The chemical composition and degree of crosslinking via free amine quantification were analyzed for the P(KA)/4-PEG hydrogels. In addition, the rheological properties, pore morphology, swelling behavior and degradation time were characterized. Subsequently, in vitro cell studies for evaluation of the cytotoxicity and cell adhesion were performed. The 4 wt% 1:1 functional molar ratio hydrogel with P(KA) concentrations as low as 0.65 wt% demonstrated low cytotoxicity and desirable cell adhesion towards fibroblasts and thus displayed a desirable combination of properties for wound healing application.

Antibacterial polypeptide/heparin composite hydrogels carrying growth factor for wound healing

We report an efficient growth factor delivering system based on polypeptide/heparin composite hydrogels for wound healing application. Linear and star-shaped poly(l-lysine) (l-PLL and s-PLL) were chosen due to not only their cationic characteristics, facilitating the efficient complexation of negatively charged heparin, but also the ease to tune the physical and mechanical properties of as-prepared hydrogels simply by varying polypeptide topology and chain length. The results showed that polymer topology can be an additional parameter to tune hydrogel properties. Our experimental data showed that these composite hydrogels exhibited low hemolytic activity and good cell compatibility as well as excellent antibacterial activity, making them ideal as wound dressing materials. Unlike other heparin-based hydrogels, these composite hydrogels with heparin densely deposited on the surface can increase the stabilization and concentration of growth factor, which can facilitate the healing process as confirmed by our in vivo animal model. We believe that these PLL/heparin composite hydrogels are promising wound dressing materials and may have potential applications in other biomedical fields.

Dual Regulations of Thermosensitive Heparin-Poloxamer Hydrogel Using ε-Polylysine: Bioadhesivity and Controlled KGF Release for Enhancing Wound Healing of Endometrial Injury

Hydrogel was not only used as an effective support matrix to prevent intrauterine adhesion after endometrial injury but also served as scaffold to sustain release of some therapeutics, especially growth factor. However, because of the rapid turnover of the endometrial mucus, the poor retention and bad absorption of therapeutic agents in damaged endometrial cavity were two important factors hindering their pharmacologic effect. Herein, a mucoadhesive hydrogel was described by using heparin-modified poloxamer (HP) as the matrix material and ε-polylysine (EPL) as functional excipient. Various EPL-HP hydrogels formulations are screened by rheological evaluation and mucoadhesion studies. It was found that the rheological and mucoadhesive properties of EPL-HP hydrogels were easily controlled by changing the amount of EPL in formulation. The storage modulus of EPL-HP hydrogel with 90 μg/mL of EPL (EPL-HP-90) was elevated to be 1.9 × 10⁵ Pa, in accordance with the adhesion force rising to 3.18 N (10-fold higher than HP hydrogels). Moreover, in vitro release of model drug keratinocyte growth factor (KGF) from EPL-HP hydrogel was significantly accelerated by adding EPL in comparison with HP hydrogel. Both strong mucoadhesive ability and the accelerated drug release behavior for EPL-HP-90 made more of the encapsulated KGF absorbed by the uterus basal layer and endometrial glands after 8 h of administration in uterus cavity. Meanwhile, the morphology of endometrium in the injured uterus was repaired well after 3 d of treatment with KGF-EPL-HP-90 hydrogels. Compared with KGF-HP group, not only proliferation of endometrial epithelial cell and glands but also angiogenesis in the regenerated endometrium was obviously enhanced after treatment with KGF-EPL-HP-90 hydrogels. Alternatively, the cellular apoptosis in the damaged endometrium was significantly inhibited after treatment with KGF-EPL-HP-90 hydrogels. Overall, the mucoadhesive EPL-HP hydrogel with a suitable KGF release profile may be a more promising approach than HP hydrogel alone to repair the injured endometrium.

Multiresponsive and biocompatible self-healing hydrogel: its facile synthesis in water, characterization and properties

Multiresponsive and biocompatible self-healing ε-PL/A-Pul/BPEI hydrogels were prepared in aqueous solution by Schiff base reaction with aldehyded pullulan (A-Pul), ε-poly-l-lysine (ε-PL) and branched polyethyleneimine (BPEI) as materials. The imine bonds were rapidly cross-linked into a hydrogel network within 80 s. Scanning electron microscopy images showed that the hydrogels exhibited a cross-linked structure with the average pore size from 58 to 82 μm. Rheology tests indicated that the hydrogels maintained good mechanical properties. Water contact angles and swelling studies suggested that the hydrogels could swell in water, with a max swell ratio of 1559%, and pH and temperature had an influence on the equilibrium swelling ratio. The hydrogels could be injected either before or after gelation, and they displayed a self-healing process in ddH₂O at room temperature based on the dynamic uncoupling and recoupling of the imine bonds. The MTT assays implied that the hydrogels were non-cytotoxic on mice bone marrow mesenchymal stem cells. Therefore, the hydrogels showed potential application in biomedical fields, and consequently further work was performed using the self-healing hydrogels as drug carriers in in vitro/vivo antitumor studies.

Synthesis, characterization, and anti-microbial activity of superabsorbents based on agar–poly(methacrylic acid-glycine)

In this study, poly(methacrylic acid-glycine)-grafted agar-based hydrogels with optimized process parameters were synthesized via a two-step green-radiation induced grafting process using microwave heating. Poly(methacrylic acid) chains were graft copolymerized onto an agar backbone using ammonium persulfate as a free radical initiator and N,N′-methylene-bis-acrylamide as a cross-linking means using microwave heating. The influence of different reaction parameters was investigated on the percentage swelling behavior of the cross-linked hydrogel networks. The prepared hydrogel networks with optimum percentage swelling were characterized by Fourier transform infrared spectroscopy, time-of-flight secondary ion mass spectrometry, scanning electron microscopy, X-ray diffraction, and thermogravimetric analysis, using agar as a reference. The anti-bacterial activities of the prepared hydrogels against Gram-positive Staphylococcus aureus bacteria and Gram-negative Escherichia coli bacteria were investigated. Staphylococcus aureus was found to be more susceptible to the compounds compared to Escherichia coli. These results indicate that the prepared hydrogels have the potential to be applied as anti-bacterial agents.

A photo-polymerized poly(Nε-acryloyl l-lysine) hydrogel for 3D culture of MCF-7 breast cancer cells

The most common in vitro cell culture platform, standard two-dimensional (2D) monolayer cell culture, often fails to mimic the tumor microenvironment, while animal models complicate research on the effect of individual factors on cell behaviors. Both are unsatisfactory in the research of molecular mechanisms of tumor development and progression and the discovery and development of anticancer drugs. In vitro three-dimensional (3D) cell culture can partially simulate in vivo conditions and 3D-cultured cancer cells can recapture many essential features of native tumor tissues. In this study, to mimic the in vivo breast tumor microenvironment, novel reduction-responsive poly(N_ε-acryloyl l-lysine) (pLysAAm) hydrogels were synthesized by rapid photo-polymerization of N_ε-acryloyl l-lysine and using N,N'-bis(acryloyl)-(l)-cystine as a crosslinker, and their physicochemical properties were characterized systemically. The results showed that the pLysAAm hydrogels were formed within 93 s under UV irradiation and exhibited almost total elastic recovery from compressions as high as 75%. The lyophilized hydrogel samples displayed a highly porous structure with interconnected pores, had an equilibrium swelling ratio of about 20, and were degraded faster in a glutathione-containing solution than in PBS solution. The biological versatility of the pLysAAm hydrogels was demonstrated by both in vitro MCF-7 cell culture and in vivo tumor formation. Compared to cells cultured as 2D monolayers, the 3D-cultured cells presented 3D cell morphology, exhibited better cell viability, expressed higher levels of pro-angiogenic factors, and showed significantly greater migration and invasion abilities. The results from assay of tumorigenicity in nude mice and histologic analysis demonstrated the enhanced tumorigenic and angiogenic capabilities of the MCF-7 cells pre-cultured in pLysAAm hydrogels. These findings suggest that pLysAAm hydrogels may be used to bridge the gap between standard in vitro cell cultures and living tissues, aid breast cancer research, and help researchers to develop novel anticancer therapeutics.

Preparation and properties of EDC/NHS mediated crosslinking poly (gamma-glutamic acid)/epsilon-polylysine hydrogels

In this paper, a novel pH-sensitive poly (amino acid) hydrogel based on poly γ-glutamic acid (γ-PGA) and ε-polylysine (ε-PL) was prepared by carbodiimide (EDC) and N-hydroxysuccinimide (NHS) mediated polymerization. The influence of PGA/PL molar ratio and EDC/NHS concentration on the structure and properties was studied. Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) proved that hydrogels were crosslinked through amide bond linkage, and the conversion rate of a carboxyl group could reach 96%. Scanning electron microscopy (SEM) results showed a regularly porous structure with 20 μm pore size in average. The gelation time in the crosslink process of PGA/PL hydrogels was within less than 5 min. PGA/PL hydrogels had excellent optical performance that was evaluated by a novel optotype method. Furthermore, PGA/PL hydrogels were found to be pH-sensitive, which could be adjusted to the pH of swelling media intelligently. The terminal pH of swelling medium could be controlled at 5 ± 1 after equilibrium when the initial pH was within 3-11. The swelling kinetics was found to follow a Voigt model in deionized water but a pseudo-second-order model in normal saline and phosphate buffer solution, respectively. The differential swelling degrees were attributed to the swelling theory based on the different ratio of -COOH/-NH2 and pore size in hydrogels. The results of mechanical property indicated that PGA/PL hydrogels were soft and elastic. Moreover, PGA/PL hydrogels exhibited excellent biocompatibility by cell proliferation experiment. PGA/PL hydrogels could be degraded in PBS solution and the degradation rate was decreased with the increase of the molar ratio of PL. Considering the simple preparation process and pH-sensitive property, these PGA/PL hydrogels might have high potential for use in medical and clinical fields.

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.

Size and medium conductivity dependence on dielectrophoretic behaviors of gas core poly-L-lysine shell nanoparticles

Dynamic (dis)assembly of biocompatible nanoparticles into 3D, packed structures would benefit drug delivery, films, and diagnostics. Dielectrophoretic (DEP) microdevices can rapidly assemble and manipulate polarizable particles within nonuniform electric fields. DEP has primarily discerned micrometer particles since nanoparticles experience smaller forces. This work examines conductivity and size DEP dependencies of previously unexplored spherical core-shell nanoparticle (CSnp) into 3D particle assemblies. Poly-L-lysine shell material was custom synthesized around a gas core to form CSnps. DEP frequencies from 1 kHz to 80 MHz at fixed 5 volts peak-to-peak and medium conductivities of 10(-5) and 10(-3) S/m were tested. DEP responses of ∼220 and ∼400 nm poly-L-lysine CSnps were quantified via video intensity densitometry at the microdevice's quadrapole electrode center for negative DEP (nDEP) and adjacent to electrodes for positive DEP. Intensity densitometry was then translated into a relative DEP response curve. An unusual nDEP peak occurred at ∼57 MHz with 25-80 times greater apparent nDEP force. All electrical circuit components were then impedance matched, which changed the observed response to weak positive DEP at low frequencies and consistently weak nDEP from ∼100 kHz to 80 MHz. This impedance-matched behavior agrees with conventional Clausius-Mossotti DEP signatures taking into account the gas core's contributions to the polarization mechanisms. This work describes a potential pitfall when conducting DEP at higher frequencies in microdevices and concurrently demonstrates nDEP behavior for a chemically and structurally distinct particle system. This work provides insight into organic shell material properties in nanostructures and strategies to facilitate dynamic nanoparticle assemblies.

Shell and core cross-linked poly(L-lysine)/poly(acrylic acid) complex micelles

We report the versatility of polyion complex (PIC) micelles for the preparation of shell and core cross-linked (SCL and CCL) micelles with their surface properties determined by the constituent polymer composition and cross-linking agent. The negatively and positively charged PIC micelles with their molecular structure and properties depending on the mixing weight percentage and polymer molecular weight were first prepared by mixing the negatively and positively charged polyions, poly(acrylic acid) (PAA) and poly(L-lysine) (PLL). The feasibility of preparing SCL micelles was demonstrated by cross-linking the shell of the negatively and positively charged micelles using cystamine and genipin, respectively. The core of the micelles can be cross-linked by silica deposition to stabilize the assemblies. The shell and/or core cross-linked micelles exhibited excellent colloid stability upon changing solution pH. The drug release from the drug-loaded SCL micelles revealed that the controllable permeability of the SCL micelles can be achieved by tuning the cross-linking degree and the SCL micelles exhibited noticeable pH-responsive behavior with accelerated release under acidic conditions. With the versatility of cross-linking strategies, it is possible to prepare a variety of SCL and CCL micelles from PIC micelles.