Photoresponsive crosslinked hyperbranched polyglycerols as smart nanocarriers for guest binding and controlled release

Characterization of an ester-based core-multishell (CMS) nanocarrier for the topical application at the oral mucosa

OBJECTIVES

Topical drug administration is commonly applied to control oral inflammation. However, it requires sufficient drug adherence and a high degree of bioavailability. Here, we tested the hypothesis whether an ester-based core-multishell (CMS) nanocarrier is a suitable nontoxic drug-delivery system that penetrates efficiently to oral mucosal tissues, and thereby, increase the bioavailability of topically applied drugs.

MATERIAL AND METHODS

To evaluate adhesion and penetration, the fluorescence-labeled CMS 10-E-15-350 nanocarrier was applied to ex vivo porcine masticatory and lining mucosa in a Franz cell diffusion assay and to an in vitro 3D model. In gingival epithelial cells, potential cytotoxicity and proliferative effects of the nanocarrier were determined by MTT and sulphorhodamine B assays, respectively. Transepithelial electrical resistance (TEER) was measured in presence and absence of CMS 10-E-15-350 using an Endohm-12 chamber and a volt-ohm-meter. Cellular nanocarrier uptake was analyzed by laser scanning microscopy. Inflammatory responses were determined by monitoring pro-inflammatory cytokines using real-time PCR and ELISA.

RESULTS

CMS nanocarrier adhered to mucosal tissues within 5 min in an in vitro model and in ex vivo porcine tissues. The CMS nanocarrier exhibited no cytotoxic effects and induced no inflammatory responses. Furthermore, the physical barrier expressed by the TEER remained unaffected by the nanocarrier.

CONCLUSIONS

CMS 10-E-15-350 adhered to the oral mucosa and adhesion increased over time which is a prerequisite for an efficient drug release. Since TEER is unaffected, CMS nanocarrier may enter the oral mucosa transcellularly.

CLINICAL RELEVANCE

Nanocarrier technology is a novel and innovative approach for efficient topical drug delivery at the oral mucosa.

Approaches for the synthesis of o-nitrobenzyl and coumarin linkers for use in photocleavable biomaterials and bioconjugates and their biomedical applications

Photocleavable biomaterials and bioconjugates are particularly interesting because light sources are easy to obtain and the responsiveness of materials is convenient to control. In recent years, various photocleavable biomaterials and bioconjugates have been synthesized for the control of payload release, regulation of biomolecule activity, 3D cell culture, and investigation of molecular mechanisms. Photocleavable linkers are crucial components of photocleavable biomaterials, which significantly influence the photoresponsive capabilities of materials. Photosensitive molecules, such as o-nitrobenzyls and coumarins, have been extensively developed as photocleavable linkers. In the present review, we provide comprehensive knowledge regarding the synthetic strategies of o-nitrobenzyl and coumarin derived linkers with various functional groups and their applications for the construction of photocleavable biomaterials and bioconjugates. Finally, the biomedical applications of o-nitrobenzyl and coumarin-based photocleavable biomaterials and bioconjugates will be summarized and discussed.

Intramolecularly Cross-Linked Polymers: From Structure to Function with Applications as Artificial Antibodies and Artificial Enzymes

Cross-linking of polymers significantly alters their physical properties, greatly expanding their everyday utility. Indeed, the polymeric networks resulting from linkages between polymer chains are found in everyday materials from soft contact lenses and automobile tires to enamel coatings and high-performance adhesives. In contrast, intramolecularly cross-linked polymers have received far less attention until recent years, in large part because they are synthetically more challenging to prepare. In this Account, we trace our own efforts to develop the chemistry of intramolecularly cross-linked macromolecules, starting with dendrimers. Dendrimers provided an excellent starting point for investigating intramolecular cross-linking because they are single molecular entities. We showed that the end groups of dendrimers can be extensively cross-linked using the ring-closing metathesis reaction and that the discrete structure of the dendrimer provides unique opportunities for characterizing the number and location of the cross-links as well as some physical properties of the macromolecule such as its size and rigidity. Increasing the number of ring-closing metathesis reactions correlated with a reduction in size and an increase in rigidity. The general strategy applied to dendrimers was extended to star polymers and hyperbranched polyglycerols. Each of these macromolecules has a core or an initiating group from which the branches emanate. Linking the end groups or branches of these polymers presents a unique opportunity to chemically remove the core of the cross-linked macromolecule in a process that is reminiscent of that used to produce covalent molecular imprinted polymers. Recognizing this analogy, we sought a compelling application for cross-linked dendrimers, the first example of unimolecular imprinting, where a single polymer contains a single molecular imprint. The quality of the imprinting was mixed but pointed to an alternative general strategy for molecular imprinting in polymers. The effort also focused attention on synthetic antibodies and the general biomimicry provided by this class of macromolecules. Indeed, cross-linking of polymers either covalently or non-covalently bears a loose resemblance to folding of proteins into defined three-dimensional shapes. The synthesis and study of cross-linked linear polymers, often called single-chain nanoparticles (SCNPs), has emerged as a very active area of research in the past few years. Our experience with the cross-linking of branched polymers combined with an interest in performing organic synthesis within living cells led us to develop copper-containing SCNPs as artificial clickases. These polymeric clickases exhibit all of the hallmarks of enzymatic catalysis. One clickase containing a polyacrylamide backbone performs low-concentration copper-assisted alkyne-azide click reactions at unprecedented rates. Another performs click reactions within living cells. Other organic transformations can be performed intracellularly, and some of the most advanced SCNPs engage in concurrent and tandem catalysis with a naturally occurring biocatalyst. By tracing our own efforts, this Account provides a few entry points into the broader literature and also points to both the remaining challenges and overall promising future envisioned for this unique class of functional macromolecules.

Molecular Precision and Enzymatic Degradation: From Readily to Undegradable Polymeric Micelles by Minor Structural Changes

Studying the enzymatic degradation of synthetic polymers is crucial for the design of suitable materials for biomedical applications ranging from advanced drug delivery systems to tissue engineering. One of the key parameters that governs enzymatic activity is the limited accessibility of the enzyme to its substrates that may be collapsed inside hydrophobic domains. PEG-dendron amphiphiles can serve as powerful tools for the study of enzymatic hydrolysis of polymeric amphiphiles due to the monodispersity and symmetry of the hydrophobic dendritic block, which significantly simplifies kinetic analyses. Using these hybrids, we demonstrate how precise, minor changes in the hydrophobic block are manifested into tremendous changes in the stability of the assembled micelles toward enzymatic degradation. The obtained results emphasize the extreme sensitivity of self-assembly and its great importance in regulating the accessibility of enzymes to their substrates. Furthermore, the demonstration that the structural differences between readily degradable and undegradable micelles are rather minor, points to the critical roles that self-assembly and polydispersity play in designing biodegradable materials.

Photo-irradiation paradigm: Mapping a remarkable facile technique used for advanced drug, gene and cell delivery

Undoubtedly, the progression of photo-irradiation technique has provided a smart engineering tool for the state-of-the-art biomaterials that guide the biomedical and therapeutic domains for promoting the modern pharmaceutical industry. Many investigators had exploited such a potential technique to create/ameliorate numerous pharmaceutical carriers. These carriers show promising applications that vary from small drug to therapeutic protein delivery and from gene to living cell encapsulation design. Harmony between the properties of precisely engineered precursors and the formed network structure broadens the investigator's intellect for both brilliant creations and effective applications. As well, controlling photo-curing at the formulation level, through manipulating the absorption of light stimuli, photoinitiator system and photo-responsive precursor, facilitates the exploration of novel distinctive biomaterials. Discussion of utilizing different photo-curing procedures in designing/formulation of different pharmaceutical carriers is the main emphasis of this review. In addition, recent applications of these intelligent techniques in targeted, controlled, and sustained drug delivery with understanding of photo-irradiation concept and mechanism are illustrated.

Dendritic nanocarriers based on hyperbranched polymers

The use of hyperbranched polymers as an alternative to perfect dendrimers as nanocarrier systems for drugs, dyes and other guest molecules is covered. Different types of hyperbranched polymers are discussed with regard to aspects like synthesis, functionalisation and encapsulation properties but also their degradation.

Bioapplications of hyperbranched polymers

The recent research progress in biological and biomedical applications of hyperbranched polymers has been summarized in this review.

Hyperbranched polymers: advances from synthesis to applications

This review summarizes the advances in hyperbranched polymers from the viewpoint of structure, click synthesis and functionalization towards their applications in the last decade.

Organic nanoparticles composed of Fréchet-type dendrons: synthesis, characterization, self-assembly and reversible guest encapsulation

Novel organic nanoparticles composed of Fréchet-type dendrons have been synthesized by a simple one-pot reaction, which involved etching off the gold core in a first generation gold nanoparticle-cored dendrimer (AuG₁). Dissolution of the Au core leads to the generation of numerous dendron radicals in a small volume, which underwent very fast coupling and addition reactions to form the Fréchet-type dendron nanoparticles (FDNs). The FDNs were found to be nearly monodispersed with an average size of 3 nm. NMR, TEM and MALDI-TOF analysis suggested that the FDNs are extremely dense organic structures made up of Fréchet-type dendrons. Although the FDNs do not contain any self-assembling motifs, such as hydrogen bonding moieties, they exhibited time and concentration dependent morphological transformations, leading to the formation of larger spherical aggregates and fibrous networks. Morphological transformations were probed using TEM, AFM and DLS studies. The self-assembly was found to be reversible. The morphological transformation of FDNs was exploited for the encapsulation and on-demand release of guest molecules.

Synthesis of photodegradable macromers for conjugation and release of bioactive molecules

Hydrogel scaffolds are used in biomedicine to study cell differentiation and tissue evolution, where it is critical to control the delivery of chemical cues both spatially and temporally. While large molecules can be physically entrapped in a hydrogel, moderate molecular weight therapeutics must be tethered to the hydrogel network through a labile linkage to allow controlled release. We synthesized and characterized a library of polymerizable ortho-nitrobenzyl (o-NB) macromers with different functionalities at the benzylic position (alcohol, amine, BOC-amine, halide, acrylate, carboxylic acid, activated disulfide, N-hydroxysuccinyl ester, biotin). This library of polymerizable macromers containing o-NB groups should allow direct conjugation of nearly any type of therapeutic agent and its subsequent controlled photorelease from a hydrogel network. As proof-of-concept, we incorporated the N-hydroxysuccinyl ester macromer into hydrogels and then reacted phenylalanine with the NHS ester. Upon exposure to light (λ = 365 nm; 10 mW/cm(2), 10 min), 81.3% of the phenylalanine was released from the gel. Utilizing the photodegradable macromer incorporating an activated disulfide, we conjugated a cell-adhesive peptide (GCGYGRGDSPG), a protein that exhibits enzymatic activity (bovine serum albumin (BSA)), and a growth factor (transforming growth factor-β1 (TGF-β1)) into hydrogels, controlled their release with light (λ = 365 nm; 10 mW/cm(2), 0-20 min), and verified the bioactivity of the photoreleased molecules. The photoreleasable peptide allows real-time control over cell adhesion. BSA maintains full enzymatic activity upon sequestration and release from the hydrogel. Photoreleased TGF-β1 is able to induce chondrogenic differentiation of human mesenchymal stem cells comparable to native TGF-β1. Through this approach, we have demonstrated that photodegradable tethers can be used to sequester peptides and proteins into hydrogel depots and release them in an externally controlled, predictable manner without compromising biological function.

Molecular plasmonics for biology and nanomedicine

The optical excitation of surface plasmons in metal nanoparticles leads to nanoscale spatial confinement of electromagnetic fields. The confined electromagnetic fields can generate intense, localized thermal energy and large near-field optical forces. The interaction between these effects and nearby molecules has led to the emerging field known as molecular plasmonics. Recent advances in molecular plasmonics have enabled novel optical materials and devices with applications in biology and nanomedicine. In this article, we categorize three main types of interactions between molecules and surface plasmons: optical, thermal and mechanical. Within the scope of each type of interaction, we will review applications of molecular plasmonics in biology and nanomedicine. We include a wide range of applications that involve sensing, spectral analysis, imaging, delivery, manipulation and heating of molecules, biomolecules or cells using plasmonic effects. We also briefly describe the physical principles of molecular plasmonics and progress in the nanofabrication, surface functionalization and bioconjugation of metal nanoparticles.

Stimuli-responsive polymeric nanocarriers for the controlled transport of active compounds: concepts and applications

The use of polymeric nanocarriers to transport active compounds like small-molecular drugs, peptides, or genes found an increased attention throughout the different fields of natural sciences. Not only that these nanocarriers enhance the properties of already existing drugs in terms of solubility, bioavailability, and prolonged circulation times, furthermore they can be tailor-made in such a manner that they selectively release their cargo at the desired site of action. For the triggered release, these so-called smart drug delivery systems are designed to react on certain stimuli like pH, temperature, redox potential, enzymes, light, and ultrasound. Some of these stimuli are naturally occurring in vivo, for example the difference in pH in different cellular compartments while others are caused by the disease, which is to be treated, like differences in pH and temperature in some tumor tissues. Other external applied stimuli, like light and ultrasound, allow the temporal and spatial control of the release, since they are not triggered by any biological event. This review gives a brief overview about some types of stimuli-responsive nanocarriers with the main focus on organic polymer-based systems. Furthermore, the different stimuli and the design of corresponding responsive nanocarriers will be discussed with the help of selected examples from the literature.

Stimuli-responsive polymers and their applications in nanomedicine

This review focuses on smart nano-materials built of stimuli-responsive (SR) polymers and will discuss their numerous applications in the biomedical field. The authors will first provide an overview of different stimuli and their corresponding, responsive polymers. By introducing myriad functionalities, SR polymers present a wide range of possibilities in the design of stimuli-responsive devices, making use of virtually all types of polymer constructs, from self-assembled structures (micelles, vesicles) to surfaces (polymer brushes, films) as described in the second section of the review. In the last section of this review the authors report on some of the most promising applications of stimuli-responsive polymers in nanomedicine. In particular, we will discuss applications pertaining to diagnosis, where SR polymers are used to construct sensors capable of selective recognition and quantification of analytes and physical variables, as well as imaging devices. We will also highlight some examples of responsive systems used for therapeutic applications, including smart drug delivery systems (micelles, vesicles, dendrimers...) and surfaces for regenerative medicine.

Photoresponsive hydrogels for biomedical applications

Hydrogels are soft materials composed of a three-dimensional network which contain a high percentage of water similar to body tissue and are therefore regarded as a biocompatible material. Hydrogels have various potential applications in the biomedical field such as drug delivery and as scaffold for tissue engineering. Control over the physical properties of a hydrogel by an external stimulus is highly desirable and is therefore actively studied. Light is a particularly interesting stimulus to manipulate the properties of a hydrogel as it is a remote stimulus that can be controlled spatially and temporally with great ease and convenience. Therefore in recent years photoresponsive hydrogels have been investigated as an emerging biomaterial. Here we will review recent developments and discuss these new materials, and their applications in the biomedical field.

Self-assembly of hyperbranched polymers and its biomedical applications

Hyperbranched polymers (HBPs) are highly branched macromolecules with a three-dimensional dendritic architecture. Due to their unique topological structure and interesting physical/chemical properties, HBPs have attracted wide attention from both academia and industry. In this paper, the recent developments in HBP self-assembly and their biomedical applications have been comprehensively reviewed. Many delicate supramolecular structures from zero-dimension (0D) to three-dimension (3D), such as micelles, fibers, tubes, vesicles, membranes, large compound vesicles and physical gels, have been prepared through the solution or interfacial self-assembly of amphiphilic HBPs. In addition, these supramolecular structures have shown promising applications in the biomedical areas including drug delivery, protein purification/detection/delivery, gene transfection, antibacterial/antifouling materials and cytomimetic chemistry. Such developments promote the interdiscipline researches among surpramolecular chemistry, biomedical chemistry, nano-technology and functional materials.

Construction and application of a pH-sensitive nanoreactor via a double-hydrophilic multiarm hyperbranched polymer

A double-hydrophilic multiarm hyperbranched polymer with a hyperbranched poly(amidoamine) (HPAMAM) core and many poly(ethylene glycol) monomethyl ether (MPEG) arms connected by pH-sensitive acylhydrazone bonds (HPAMAM-g-MPEG) was successfully prepared. Benefiting from the cationic dendritic core and PEGylation shell, the double-hydrophilic multiarm hyperbranched polymer was used as a nanoreactor for CdS quantum dots (CdS QDs) synthesis in aqueous solution. The obtained HPAMAM-g-MPEG and CdS/HPAMAM-g-MPEG nanocomposites were carefully characterized by (1)H NMR, (13)C NMR, Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible absorption spectroscopy (UV-vis), fluorescence spectroscopy (FL), dynamic light scattering (DLS), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and electronic dispersive X-ray spectroscopy (EDS) analysis. Both (1)H NMR and fluorescence spectroscopy investigations confirmed that the acylhydrazone linkage between the dendritic core and linear arms was readily broken under acidic condition (pH <5.5). When MPEG arms departed from the HPAMAM core, the fluorescence intensity of CdS/HPAMAM-g-MPEG nanocomposites greatly increased. Such pH-responsive behavior of CdS/HPAMAM-g-MPEG nanocomposites was utilized as an exploration of a novel fluorescence probe in an acidic lysosome exemplified by COS-7 cells.

Dendritic polyglycerols for biomedical applications

The application of nanotechnology in medicine and pharmaceuticals is a rapidly advancing field that is quickly gaining acceptance and recognition as an independent area of research called "nanomedicine". Urgent needs in this field, however, are biocompatible and bioactive materials for antifouling surfaces and nanoparticles for drug delivery. Therefore, extensive attention has been given to the design and development of new macromolecular structures. Among the various polymeric architectures, dendritic ("treelike") polymers have experienced an exponential development due to their highly branched, multifunctional, and well-defined structures. This Review describes the diverse syntheses and biomedical applications of dendritic polyglycerols (PGs). These polymers exhibit good chemical stability and inertness under biological conditions and are highly biocompatible. Oligoglycerols and their fatty acid esters are FDA-approved and are already being used in a variety of consumer applications, e.g., cosmetics and toiletries, food industries, cleaning and softening agents, pharmaceuticals, polymers and polymer additives, printing photographing materials, and electronics. Herein, we present the current status of dendritic PGs as functional dendritic architectures with particular focus on their application in nanomedicine, in drug, dye, and gene delivery, as well as in regenerative medicine in the form of non-fouling surfaces and matrix materials.