Colloidally stable polypeptide‐based nanogel: Study of enzyme‐mediated nanogelation in inverse miniemulsion

Robust Protocol for the Synthesis of BSA Nanohydrogels by Inverse Nanoemulsion for Drug Delivery

In a highly efficient and reproducible process, bovine serum albumin (BSA) nanogels are prepared from inverse nanoemulsions. The concept of independent nanoreactors of the individual droplets in the nanoemulsions allows high protein concentrations of up to 0.6% in the inverse total system. The BSA gel networks are generated by the 1-ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride coupling strategy widely used in protein chemistry. In a robust work-up protocol, the hydrophobic continuous phase of the inverse emulsion is stepwise replaced by water without compromising the colloidal stability and non-toxicity of the nanogel particles. Further, the simple process allows the loading of the nanogels with various cargos like a dye (Dy-495), a drug (ibuprofen), another protein [FMN-binding fluorescent protein (EcFbFP)], and oligonucleotides [plasmid DNA for enhanced GFP expression in mammalian cells (pEGFP c3) and a synthetic anti-Pseudomonas aeruginosa aptamer library]. These charged nanoobjects work efficiently as carriers for staining and transfection of cells. This is exemplarily shown for a phalloidin dye and a plasmid DNA as cargo with adenocarcinomic human alveolar basal epithelial cells (A549), a cell revertant of the SV-40 cancer rat cell line SV-52 (Rev2), and human breast carcinoma cells (MDA-MB-231), respectively.

The Dual Modification of PNIPAM and β-Cyclodextrin Grafted on Hyaluronic Acid as Self-Assembled Nanogel for Curcumin Delivery

Curcumin is an extract of turmeric (Curcuma longa) which possesses anti-inflammatory, anti-cancer and wound-healing effects and has been used as an active compound in biomedical research for many years. However, its poor solubility presents challenges for its use in drug delivery systems. A modified nanogel delivery system, with PNIPAM and β-cyclodextrin grafted onto hyaluronic acid (PNCDHA), was utilized to enhance the solubility. The polymer was characterized by NMR, and the inclusion complex between curcumin and β-cyclodextrin was confirmed by FTIR. The potential of this PNCDHA polymer complex as a drug delivery vehicle was supported by a curcumin encapsulation efficiency of 93.14 ± 5.6% and the release of encapsulated curcumin at 37 °C. At a concentration of 0.5% w/v in water, PNCDHA nanogels were biocompatible with fibroblast cell line (L929) up to a curcumin concentration of 50 µM. There was a direct concentration between curcumin loading and cellular internalization. A more detailed study of the cellular internalization of PNCDHA nanogel should be considered in order to clarify cellular delivery mechanisms and to assess how its viability as a carrier may be optimized.

Stimuli-responsive polypeptide nanogels for trypsin inhibition

A new type of hydrophilic, biocompatible, and biodegradable polypeptide nanogel depots loaded with the natural serine protease inhibitor α1-antitrypsin (AAT) was applied for the inhibition of the inflammatory mediator trypsin. Two types of nanogels were prepared from linear synthetic polypeptides based on biocompatible and biodegradable poly[N ⁵-(2-hydroxyethyl)-ʟ-glutamine-ran-N ⁵-propargyl-ʟ-glutamine-ran-N ⁵-(6-aminohexyl)-ʟ-glutamine]-ran-N ⁵-[2-(4-hydroxyphenyl)ethyl)-ʟ-glutamine] (PHEG-Tyr) or biocompatible N ^α-ʟ-lysine-grafted α,β-poly[(2-propyne)-ᴅ,ʟ-aspartamide-ran-(2-hydroxyethyl)-ᴅʟ-aspartamide-ran-(2-(4-hydroxyphenyl)ethyl)-ᴅʟ-aspartamide] (N ^α-Lys-NG). Both nanogels were prepared by HRP/H₂O₂-mediated crosslinking in inverse miniemulsions with pH and temperature-stimuli responsive behavior confirmed by dynamic light scattering and zeta potential measurements. The loading capacity of PHEG-Tyr and N ^α-Lys-NG nanogels and their release profiles were first optimized with bovine serum albumin. The nanogels were then used for loading and release of AAT. PHEG-Tyr and N ^α-Lys-NG nanogels showed different loading capacities for AAT with the maximum (20%) achieved with N ^α-Lys-NG nanogel. In both cases, the nanogel depots demonstrated a burst release of AAT during the first 6 h, which could be favorable for quick inhibition of trypsin. A consequent pilot in vitro inhibition study revealed that both PHEG-Tyr and N ^α-Lys-NG nanogels loaded with AAT successfully inhibited the enzymatic activity of trypsin. Furthermore, the inhibitory efficiency of the AAT-loaded nanogels was higher than that of only AAT. Interestingly, also non-loaded PHEG-Tyr and N ^α-Lys-NG nanogels were shown to effectively inhibit trypsin because they contain suitable amino acids in their structures that effectively block the active site of trypsin.

Bio-Orthogonal Nanogels for Multiresponsive Release

Responsive nanogel systems are interesting for the drug delivery of bioactive molecules due to their high stability in aqueous media. The development of nanogels that are able to respond to biochemical cues and compatible with the encapsulation and the release of large and sensitive payloads remains challenging. Here, multistimuli-responsive nanogels were synthesized using a bio-orthogonal and reversible reaction and were designed for the selective release of encapsulated cargos in a spatiotemporally controlled manner. The nanogels were composed of a functionalized polysaccharide cross-linked with pH-responsive hydrazone linkages. The effect of the pH value of the environment on the nanogels was fully reversible, leading to a reversible control of the release of the payloads and a “stop-and-go” release profile. In addition to the pH-sensitive nature of the hydrazone network, the dextran backbone can be degraded through enzymatic cleavage. Furthermore, the cross-linkers were designed to be responsive to oxidoreductive cues. Disulfide groups, responsive to reducing environments, and thioketal groups, responsive to oxidative environments, were integrated into the nanogel network. The release of model payloads was investigated in response to changes in the pH value of the environment or to the presence of reducing or oxidizing agents.

Enzymatically Cross-linked Hydrogels Based on Synthetic Poly(α-amino acid)s Functionalized with RGD Peptide for 3D Mesenchymal Stem Cell Culture

Injectable hydrogel scaffolds combined with stem cell therapy represent a promising approach for minimally invasive surgical tissue repair. In this study, we developed and characterized a fully synthetic, biodegradable poly(N⁵-(2-hydroxyethyl)-l-glutamine)-based injectable hydrogel modified with integrin-binding arginine-glycine-aspartic acid (RGD) peptide (PHEG-Tyr-RGD). The biodegradable hydroxyphenyl polymer precursor derivative of PHEG-Tyr was enzymatically cross-linked to obtain injectable hydrogels with different physicochemical properties. The gelation time, gel yield, swelling behavior, and storage modulus of the PHEG-Tyr hydrogels were tuned by varying the concentrations of the PHEG-Tyr precursors and horseradish peroxidase as well as the n_H2O2/n_Tyr ratio. The mechanical properties and gelation time of the PHEG-Tyr hydrogel were optimized for the encapsulation of rat mesenchymal stem cells (rMSCs). We focused on the 2D and 3D spreading and viability of rMSCs within the PHEG-Tyr-RGD hydrogels with different physicochemical microenvironments in vitro. Encapsulation of rMSCs shows long-term survival and exhibits cell-matrix and cell-cell interactions reflective of both the RGD concentration and hydrogel stiffness. The presented biomaterial represents a suitable biological microenvironment to guide 3D spreading and may act as a promising 3D artificial extracellular matrix for stem cell therapy.

Biocompatible polypeptide nanogel: Effect of surfactants on nanogelation in inverse miniemulsion, in vivo biodistribution and blood clearance evaluation

Horseradish peroxidase (HRP)/H₂O₂-mediated crosslinking of polypeptides in inverse miniemulsion is a promising approach for the development of next-generation biocompatible and biodegradable nanogels. Herein, we present a fundamental investigation of the effects of three surfactants and their different concentrations on the (HRP)/H₂O₂-mediated nanogelation of poly[N⁵-(2-hydroxyethyl)-l-glutamine-ran-N⁵-propargyl-l-glutamine-ran-N⁵-(6-aminohexyl)-l-glutamine]-ran-N⁵-[2-(4-hydroxyphenyl)ethyl)-l-glutamine] (PHEG-Tyr) in inverse miniemulsion. The surfactants sorbitan monooleate (SPAN 80), polyoxyethylenesorbitan trioleate (TWEEN 85), and dioctyl sulfosuccinate sodium salt (AOT) were selected and their influence on the nanogel size, size distribution, and morphology was evaluated. The most effective nanogelation stabilization was achieved with 20 wt% nonionic surfactant SPAN 80. The diameter of the hydrogel nanoparticles was 230 nm (dynamic light scattering, DLS) and was confirmed also by nanoparticle tracking analysis (NTA) which showed the diameters ranging from 200 to 300 nm. Microscopy and image analyses showed that the nanogel in the dry state was spherical in shape and had number-average diameter D_n = 26 nm and dispersity Р= 1.91. In the frozen-hydrated state, the nanogel appeared porous and was larger in size with D_n = 182 nm and Р= 1.52. Our results indicated that the nanogelation of the polymer precursor required a higher concentration of surfactant than classical inverse miniemulsion polymerization to ensure effective stabilization. The developed polypeptide nanogel was radiolabeled with ¹²⁵I, and in vivo biodistribution and blood clearance evaluations were performed. We found that the ¹²⁵I-labeled nanogel was well-biodistributed in the bloodstream, cleared from mouse blood during 48 h by renal and hepatic pathways and did not provoke any sign of toxic effects.

Ring opening polymerization of α-amino acids: advances in synthesis, architecture and applications of polypeptides and their hybrids

This review provides a comprehensive overview of the latest advances in the synthesis, architectural design and biomedical applications of polypeptides and their hybrids.