Nanocarriers (NCs) have emerged as powerful tools to improve drug solubility, to promote drug transport across membranes, to protect their payload from premature degradation, and to deliver drugs in ...a controlled and targeted manner. Their performance strongly depends on the surface chemistry, which governs their interaction with the biological environment. Bioinert and stealth surface features are advantageous to avoid unintended interactions with endogenous surfaces at off‐target sites and with the immune system, whereas at the target site these carriers should be highly interactive guaranteeing intracellular delivery of their payload. These key surface properties—bioinert and stealth versus interactive at the target site—are in contradiction to each other so that the best compromise between them has to be found. Alternatively, surface structures interacting preferentially with the membrane of target cells can be utilized. Stimuli‐responsive surfaces able to convert from bioinert and stealth to interactive at the target site have been recently introduced. A deepened understanding of how these different approaches influence the performance of NCs in the body is of particular importance in order to improve their efficacy. This review focuses on the surface chemistry of NCs providing the best compromise between bioinert and stealth versus interactive features.
The fate of nanocarriers (NCs) in vivo is mainly determined by their surface chemistry. Various surface modifications are investigated to either prevent or promote the interaction of NCs with the biological environment. However, in future, the potential of NCs lies in smart approaches to balance, combine, or transform inert to interactive NC surfaces along the way to the target site.
Due to thiolation of poly‐ and oligosaccharides numerous favorable properties for tissue engineering and wound healing can be introduced. Poly‐ and oligosaccharides can be thiolated via ...hydroxyl‐to‐thiol conversions or the covalent attachment of sulfhydryl ligands to hydroxyl, carbonic acid or amino groups on them. Since thiolated poly‐ and oligosaccharides can cross‐link via disulfide bonds, they form stable 3D networks with defined microarchitecture, stiffness, elasticity, and degradability. Furthermore, thiol groups can enhance cell adhesion since cells exhibit cysteine‐rich subdomains on their surface that form disulfide bonds with them. Sulfhydryl groups can also participate in cell signaling pathways favoring various cellular processes like proliferation, migration, spreading, and differentiation that are beneficial for tissue engineering and wound healing. In addition, a controlled release of active ingredients such as growth factors being bound via disulfide bonds to thiolated poly‐ and oligosaccharides can be achieved via thiol/disulfide exchange reactions. Over the last two decades, the number of thiolated poly‐ and oligosaccharides such as thiolated hyaluronic acid and thiolated chitosan used for tissue engineering and wound healing has increased tremendously. Within this review, an overview is provided about the chemistry of thiolated poly‐ and oligosaccharides, their key properties, applications and performance in clinical trials and as marketed products.
By thiolation of poly‐ and oligosaccharides numerous favorable properties for tissue engineering and wound healing can be introduced. Within this review an overview about the chemistry of thiolated poly‐ and oligosaccharides, their key properties, applications and performance in clinical trials and as marketed products is provided.
Because of polycationic auxiliary agents such as chitosan, polyethyleneimine and cell penetrating peptides as well as cationic lipids assembling to polycationic systems, drug carriers can tightly ...interact with cell membranes exhibiting a high-density anionic charge. Because of these interactions the cell membrane is depolarized and becomes vulnerable to various uptake mechanisms. On their way to the target site, however, the polycationic character of all these drug carriers is eliminated by polyanionic macromolecules such as mucus glycoproteins, serum proteins, proteoglycans of the extracellular matrix (ECM) and polyanionic surface substructures of non-target cells such as red blood cells. Strategies to overcome this polycation dilemma are focusing on a pH-, redox- or enzyme-triggered charge conversion at the target site. The pH-triggered systems are making use of a slight acidic environment at the target site such as in case of solid tumors, inflammatory tissue and ischemic tissue. Due to a pH shift from 7.2 to slightly acidic mainly amino substructures of polymeric excipients are protonated or shielding groups such as 2,3 dimethylmaleic acid are cleaved off unleashing the underlying cationic character. Redox-triggered systems are utilizing disulfide linkages to bulky side chains such as PEGs masking the polycationic character. Under mild reducing conditions such as in the tumor microenvironment these disulfide bonds are cleaved. Enzyme-triggered systems are targeting enzymes such as alkaline phosphatase, matrix metalloproteinases or hyaluronidase in order to eliminate anionic moieties via enzymatic cleavage resulting in a charge conversion from negative to positive. Within this review an overview about the pros and cons of these systems is provided.
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The past two decades have witnessed a rapid progress in the development of surface charge‐reversible nanoparticles (NPs) for drug delivery and diagnosis. These NPs are able to elegantly address the ...polycation dilemma. Converting their surface charge from negative/neutral to positive at the target site, they can substantially improve delivery of drugs and diagnostic agents. By specific stimuli like a shift in pH and redox potential, enzymes, or exogenous stimuli such as light or heat, charge reversal of NP surface can be achieved at the target site. The activated positive surface charge enhances the adhesion of NPs to target cells and facilitates cellular uptake, endosomal escape, and mitochondrial targeting. Because of these properties, the efficacy of incorporated drugs as well as the sensitivity of diagnostic agents can be essentially enhanced. Furthermore, charge‐reversible NPs are shown to overcome the biofilm formed by pathogenic bacteria and to shuttle antibiotics directly to the cell membrane of these microorganisms. In this review, the up‐to‐date design of charge‐reversible NPs and their emerging applications in drug delivery and diagnosis are highlighted.
Charge‐reversible nanoparticles are drug delivery systems that change their surface charge in response to specific stimuli like the pH, redox‐conditions, enzymes, exogenous stimuli, or a combination of them. This charge reversion from negative to positive enhances cellular uptake and targeted release of the payloads, promising more effective and precise treatments for various diseases.
Cationic and ionizable cationic lipids are broadly applied as auxiliary agents, but their use is associated with adverse effects. If these excipients are rapidly degraded to endogenously occurring ...metabolites such as amino acids and fatty acids, their toxic potential can be minimized. So far, synthesized and evaluated biodegradable cationic and ionizable cationic lipids already showed promising results in terms of functionality and safety. Within this review, an overview about the different types of such biodegradable lipids, the available building blocks, their synthesis and cleavage by endogenous enzymes is provided. Moreover, the relationship between the structure of the lipids and their toxicity is described. Their application in drug delivery systems is critically discussed and placed in context with the lead compounds used in mRNA vaccines. Moreover, their use as preservatives is reviewed, guidance for their design is provided, and an outlook on future developments is given.
Cationic and ionizable cationic lipids are widely used for pharmaceutical formulations. However, their toxicity is seemingly limiting their applicability. Formation of biodegradable cationic lipids overcomes adverse effects while maintaining functionality. The use of natural building blocks provides degradation into safe metabolites. Moreover, endogenous building blocks may improve their efficacy as complexing agents and preservatives.
Since the development of self-emulsifying drug delivery systems (SEDDS) in 1980's, they attract the attention of researchers in order to confront the challenge of poor water-solubility of orally ...given drugs. Within recent years, SEDDS were also discovered for oral administration of hydrophilic macromolecular drugs such as peptides, proteins, polysaccharides and pDNA. Due to hydrophobic ion pairing (HIP) with oppositely charged lipophilic auxiliary agents the resulting complexes can be incorporated in the lipophilic phase of SEDDS. Depending on the solubility of the complex in the SEDDS pre-concentrate and in the release medium drug release can be adjusted on purpose by choosing more or less lipophilic auxiliary agents in appropriate quantities for HIP. Within the oily droplets formed in the GI-tract drugs are protected towards degradation by proteases and nucleases and thiol-disulfide exchange reactions with dietary proteins. The oily droplets can be made mucoadhesive or highly mucus permeating depending on their target site. Furthermore, even their cellular uptake properties can be tuned by adjusting their zeta potential or decorating them with cell penetrating peptides. The potential of SEDDS for oral administration of hydrophilic macromolecular drugs could meanwhile be demonstrated via various in vivo studies showing a bioavailability at least in the single digit percentage range. Owing to these properties advanced SEDDS turned out to be a game changing approach for the oral administration of hydrophilic macromolecular drugs.
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The purpose of this study was to synthesize diaminated starch as a novel mucoadhesive polymer. Starch was tosylated and then reacted with ethylenediamine. The degree of amination was determined by ...2,4,6-trinitrobenzene sulfonic acid assay. Properties of diaminated starch including solubility, cytotoxicity, swelling behavior, and mucoadhesion were compared to chitosan. Diaminated starch displayed 2083 ± 121.6 μmol of diamine substructures/g of polymer. At pH 6, diaminated starch exhibited a ζ potential of 6 mV, whereas it was close to zero in the case of unmodified starch. In addition, diaminated starch displayed water solubility over the entire pH range and minor cytotoxicity. The novel polymer showed pronounced swelling behavior in water increasing its initial weight 18- and 6-fold at pH 5 and 6, respectively. Moreover, diaminated starch exhibited 92-fold higher-mucoadhesivity properties than those of chitosan. According to these results, diaminated starch might be a promising novel excipient for the design of mucoadhesive formulations.
The aim of this study was the development of a novel mucus diffusion model and the approval thereof by self-nanoemulsifying drug delivery systems (SNEDDSs). For diffusion experiments, various SNEDD ...formulations were developed, spiked with fluorescein diacetate, and evaluated for their mucus diffusion behavior through an intestinal mucus layer within the novel setup. In brief, SNEDD formulations resulting in particle sizes of 12.0nm produced 70.3% of diffused model drug through the mucus layer. In comparison, SNEDDSs with particle sizes of 455.5nm led to a permeation of 8.3% only. Apart from this size dependence, two SNEDDS excipients namely Cremophor RH 40 and triacetin were identified to strongly affect the permeation through mucus. Hence, it could be demonstrated that particle size and single excipients can positively influence mucus diffusion of SNEDDSs. Furthermore, it could be shown that the developed mucus diffusion model is a promising tool for pharmaceutical research in comparison with already established systems as it allows an easy handling coupled with the possibility to test different kinds of mucus in parallel within one setup.
This study aims to compare the potential of Polyethylene glycol (PEG‐free and PEG‐based self‐emulsifying drug delivery systems (SEDDS) for the oral administration of insulin glargine (IG). ...Hydrophobic ion pairs (HIPs) of IG are formed using various counterions. HIPs are assessed for log P octanol/water and dissociation behavior. They are incorporated into SEDDS based on polyglycerol (PG) and zwitterionic surfactant (ZW) using response surface methodology and compared to conventional PEG‐SEDDS in size, stability, and log D SEDDS/release medium. Oral IG bioavailability in PG/ZW‐SEDDS and PEG‐SEDDS is evaluated in rats. Among the various counterions studied, IG‐BIS (bis(isotridecyl)sulfosuccinate) HIPs demonstrated the highest log P and an improved dissociation profile. PG/ZW‐SEDDS and PEG‐SEDDS have similar ≈40 nm sizes and are stable over 24 h. Both formulations have log D > 4 in water and >2 in 50 mM phosphate buffer pH 6.8. PG/ZW‐SEDDS yielded an oral bioavailability of 2.13 ± 0.66% for IG, while the employment of PEG‐SEDDS resulted in an oral bioavailability of 1.15 ± 0.35%. This study highlights the prospective utilization of PEG‐free SEDDS involving the concurrent application of PG and ZW surfactants, an alternative to conventional PEG surfactants, for improved oral therapeutic (poly) peptide delivery.
This study presents a novel strategy to boost oral bioavailability of insulin glargine (IG) using polyglycerol/zwitterion‐based self‐emulsifying drug delivery systems (PG/ZW‐SEDDS) as an alternative to polyethylene glycol‐based SEDDS (PEG‐SEDDS). Research focuses on optimizing hydrophobic ion pairing (HIP) complexation, developing a PEG‐free SEDDS, and evaluating its oral IG bioavailability versus PEG‐based SEDDS in rats, advancing diabetes therapeutics.
The aim of the present study was to develop zeta potential-changing polyphosphate nanoparticles (pp-NPs) in order to overcome the diffusion barrier of the mucus gel layer and to provide an enhanced ...cellular uptake. pp-NPs were obtained by in situ gelation between cationic polyethylene imine and anionic polyphosphate. The resulting pp-NPs were characterized with regard to size and zeta potential. Phosphate release studies were carried out by incubation of pp-NPs with isolated as well as cell-associated intestinal alkaline phosphatase (IAP) and quantified by malachite green assay. Correspondingly, change in the zeta potential was measured, and pp-NPs were analyzed by scanning electron microscopy studies. Mucus permeation studies were performed with porcine intestinal mucus via the transwell insert method and rotating tube method. Furthermore, cell viability and cellular uptake were investigated on Caco-2 cells. The resulting pp-NPs displayed a mean size of 269.16 ± 1.12 nm and a zeta potential between −9 and −10 mV in the characterization studies. Within 4 h, a remarkable amount of phosphate was released from pp-NPs incubated with isolated IAP as well as cell-associated IAP and zeta potential raised up from −9.14 ± 0.45 to −1.75 ± 0.46 mV. Compared with dephosphorylated polyphosphate nanoparticles (de-pp-NPs), a significantly enhanced mucus permeation of pp-NPs was observed. Moreover, pp-NPs did not exhibit cytotoxicity. Cellular uptake increased 2.6-fold by conversion of pp-NPs to de-pp-NPs following enzymatic cleavage. Taking the comparatively simple preparation method and the high mucus-permeating properties of pp-NPs and high cellular uptake properties of de-pp-NPs into account, these nanocarriers might be promising novel tools for mucosal drug delivery.
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