Endocytic capsule sensors for probing cellular internalization

A decade of developing applications exploiting the properties of polyelectrolyte multilayer capsules

Transferring the layer-by-layer (LbL) coating approach from planar surfaces to spherical templates and subsequently dissolving these templates leads to the fabrication of polyelectrolyte multilayer capsules. The versatility of the coatings of capsules and their flexibility upon bringing in virtually any material into the coatings has quickly drawn substantial attention. Here, we provide an overview of the main developments in this field, highlighting the trends in the last decade. In the beginning, various methods of encapsulation and release are discussed followed by a broad range of applications, which were developed and explored. We also outline the current trends, where the range of applications is continuing to grow, including addition of whole new and different application areas.

Bioinspired core-shell silica nanoparticles monitoring extra- and intra-cellular drug release

Förster resonance energy transfer (FRET) has been widely used for monitoring drug release from nanoparticles (NPs). To understand the drug release from bioinspired drug-core silica-shell NPs, we synthesised two types of NPs using the dual-functional peptide SurSi via biosilicification for the first time, i.e., silica NP conjugated with FRET (Cy3 and Cy5) molecules, and FRET-core (DiO and DiI) silica-shell NP with different shell thicknesses (18 and 41 nm). The release kinetics of these two types of NPs were investigated under different conditions, including fetal bovine serum (FBS) and in cells, to mimic the drug release during blood circulation and intracellularly. Two different drug release mechanisms were identified. Cargo diffusion dominated the release during circulation, while the degradation of silica shell played a key role in drug release intracellularly.

Classification of analytics, sensorics, and bioanalytics with polyelectrolyte multilayer capsules

Polyelectrolyte multilayer (PEM) capsules, constructed by LbL (layer-by-layer)-adsorbing polymers on sacrificial templates, have become important carriers due to multifunctionality of materials adsorbed on their surface or encapsulated into their interior. They have been also been used broadly used as analytical tools. Chronologically and traditionally, chemical analytics has been developed first, which has long been synonymous with all analytics. But it is not the only development. To the best of our knowledge, a summary of all advances including their classification is not available to date. Here, we classify analytics, sensorics, and biosensorics functionalities implemented with polyelectrolyte multilayer capsules and coated particles according to the respective stimuli and application areas. In this classification, three distinct categories are identified: (I) chemical analytics (pH; K⁺, Na⁺, and Pb²⁺ ion; oxygen; and hydrogen peroxide sensors and chemical sensing with surface-enhanced Raman scattering (SERS)); (II) physical sensorics (temperature, mechanical properties and forces, and osmotic pressure); and (III) biosensorics and bioanalytics (fluorescence, glucose, urea, and protease biosensing and theranostics). In addition to this classification, we discuss also principles of detection using the above-mentioned stimuli. These application areas are expected to grow further, but the classification provided here should help (a) to realize the wealth of already available analytical and bioanalytical tools developed with capsules using inputs of chemical, physical, and biological stimuli and (b) to position future developments in their respective fields according to employed stimuli and application areas. Graphical abstract.

pH and glutathione dual-triggered supramolecular assemblies as synergistic and controlled drug release carriers

Illustration of the formation of β-CD-g-OX-HA/ADA-CPT supramolecular inclusion micelles and their selective release of CPT in tumor cells.

Innovation in Layer-by-Layer Assembly

Methods for depositing thin films are important in generating functional materials for diverse applications in a wide variety of fields. Over the last half-century, the layer-by-layer assembly of nanoscale films has received intense and growing interest. This has been fueled by innovation in the available materials and assembly technologies, as well as the film-characterization techniques. In this Review, we explore, discuss, and detail innovation in layer-by-layer assembly in terms of past and present developments, and we highlight how these might guide future advances. A particular focus is on conventional and early developments that have only recently regained interest in the layer-by-layer assembly field. We then review unconventional assemblies and approaches that have been gaining popularity, which include inorganic/organic hybrid materials, cells and tissues, and the use of stereocomplexation, patterning, and dip-pen lithography, to name a few. A relatively recent development is the use of layer-by-layer assembly materials and techniques to assemble films in a single continuous step. We name this "quasi"-layer-by-layer assembly and discuss the impacts and innovations surrounding this approach. Finally, the application of characterization methods to monitor and evaluate layer-by-layer assembly is discussed, as innovation in this area is often overlooked but is essential for development of the field. While we intend for this Review to be easily accessible and act as a guide to researchers new to layer-by-layer assembly, we also believe it will provide insight to current researchers in the field and help guide future developments and innovation.

Probing cell internalisation mechanics with polymer capsules

We report polymer capsule-based probes for quantifying the pressure exerted by cells during capsule internalisation (P_in). Poly(methacrylic acid) (PMA) capsules with tuneable mechanical properties were fabricated through layer-by-layer assembly. The P_in was quantified by correlating the cell-induced deformation with the ex situ osmotically induced deformation of the polymer capsules. Ultimately, we found that human monocyte-derived macrophage THP-1 cells exerted up to approximately 360 kPa on the capsules during internalisation.

Nanoengineered Templated Polymer Particles: Navigating the Biological Realm

Nanoengineered materials offer tremendous promise for developing the next generation of therapeutics. We are transitioning from simple research questions, such as "can this particle eradicate cancer cells?" to more sophisticated ones like "can we design a particle to preferentially deliver cargo to a specific cancer cell type?" These developments are poised to usher in a new era of nanoengineered drug delivery systems. We primarily work with templating methods for engineering polymer particles and investigate their biological interactions. Templates are scaffolds that facilitate the formation of particles with well-controlled size, shape, structure, stiffness, stability, and surface chemistry. In the past decade, breakthroughs in engineering new templates, combined with advances in coating techniques, including layer-by-layer (LbL) assembly, surface polymerization, and metal-phenolic network (MPN) coordination chemistry, have enabled particles with specific physicochemical properties to be engineered. While materials science offers an ever-growing number of new synthesis techniques, a central challenge of therapeutic delivery has become understanding how nanoengineered materials interact with biological systems. Increased collaboration between chemists, biologists, and clinicians has resulted in a vast research output on bio-nano interactions. Our understanding of cell-particle interactions has grown considerably, but conventional in vitro experimentation provides limited information, and understanding how to bridge the in vitro/in vivo gap is a continuing challenge. As has been demonstrated in other fields, there is now a growing interest in applying computational approaches to advance this area. A considerable knowledge base is now emerging, and with it comes new and exciting opportunities that are already being capitalized on through the translation of materials into the clinic. In this Account, we outline our perspectives gained from a decade of work at the interface between polymer particle engineering and bio-nano interactions. We divide our research into three areas: (i) biotrafficking, including cellular association, intracellular transport, and biodistribution; (ii) biodegradation and how to achieve controlled, responsive release of therapeutics; and (iii) applications, including drug delivery, controlling immunostimulatory responses, biosensing, and microreactors. There are common challenges in these areas for groups developing nanoengineered therapeutics. A key "lesson-learned" has been the considerable challenge of staying informed about the developments relevant to this field. There are a number of reasons for this, most notably the interdisciplinary nature of the work, the large numbers of researchers and research outputs, and the limited standardization in technique nomenclature. Additionally, a large body of work is being generated with limited central archiving, other than vast general databases. To help address these points, we have created a web-based tool to organize our past, present, and future work [Bio-nano research knowledgebase, http://bionano.eng.unimelb.edu.au/knowledge_base/ (accessed May 2, 2016)]. This tool is intended to serve as a first step toward organizing results in this large, complex area. We hope that this will inspire researchers, both in generating new ideas and also in collecting, collating, and sharing their experiences to guide future research.

Ratiometric Organic Fibers for Localized and Reversible Ion Sensing with Micrometer-Scale Spatial Resolution

A fundamental issue in biomedical and environmental sciences is the development of sensitive and robust sensors able to probe the analyte of interest, under physiological and pathological conditions or in environmental samples, and with very high spatial resolution. In this work, novel hybrid organic fibers that can effectively report the analyte concentration within the local microenvironment are reported. The nanostructured and flexible wires are prepared by embedding fluorescent pH sensors based on seminaphtho-rhodafluor-1-dextran conjugate. By adjusting capsule/polymer ratio and spinning conditions, the diameter of the fibers and the alignment of the reporting capsules are both tuned. The hybrid wires display excellent stability, high sensitivity, as well as reversible response, and their operation relies on effective diffusional kinetic coupling of the sensing regions and the embedding polymer matrix. These devices are believed to be a powerful new sensing platform for clinical diagnostics, bioassays and environmental monitoring.

Quantification of endocytosis using a folate functionalized silica hollow nanoshell platform

A quantification method to measure endocytosis was designed to assess cellular uptake and specificity of a targeting nanoparticle platform. A simple N -hydroxysuccinimide ester conjugation technique to functionalize 100-nm hollow silica nanoshell particles with fluorescent reporter fluorescein isothiocyanate and folate or polyethylene glycol (PEG) was developed. Functionalized nanoshells were characterized using scanning electron microscopy and transmission electron microscopy and the maximum amount of folate functionalized on nanoshell surfaces was quantified with UV-Vis spectroscopy. The extent of endocytosis by HeLa cervical cancer cells and human foreskin fibroblast (HFF-1) cells was investigated in vitro using fluorescence and confocal microscopy. A simple fluorescence ratio analysis was developed to quantify endocytosis versus surface adhesion. Nanoshells functionalized with folate showed enhanced endocytosis by cancer cells when compared to PEG functionalized nanoshells. Fluorescence ratio analyses showed that 95% of folate functionalized silica nanoshells which adhered to cancer cells were endocytosed, while only 27% of PEG functionalized nanoshells adhered to the cell surface and underwent endocytosis when functionalized with 200 and 900  μg , respectively. Additionally, the endocytosis of folate functionalized nanoshells proved to be cancer cell selective while sparing normal cells. The developed fluorescence ratio analysis is a simple and rapid verification/validation method to quantify cellular uptake between datasets by using an internal control for normalization.

Advances in Use of Capsule-Based Fluorescent Sensors for Measuring Acidification of Endocytic Compartments in Cells with Altered Expression of V-ATPase Subunit V1G1

Acidification of eukaryotic cell compartments is accomplished by vacuolar H+-ATPases (V-ATPases), large multisubunit complexes able to pump protons into the lumen of organelles or in the extracellular medium. V-ATPases are involved in a number of physiological cellular processes, and thus regulation of V-ATPase activity is of crucial importance for the cell. Indeed, dysfunction of V-ATPase or alterations of acidification have been recently recognized as key factors in a variety of human diseases. In this study, we applied capsule-based pH sensors and a real-time tracking method for investigating the role of the V1G1 subunit of V-ATPases in regulating the activity of the proton pump. We first constructed stable cell lines overexpressing or silencing the subunit V1G1. Second, we used fluorescent capsule-based pH sensors to monitor acidification before and during internalization by modified and control living cells. By using a simple real-time method for tracking capsule internalization, we were able to identify different capsule acidification levels with respect to each analyzed cell and to establish the kinetics for each. The intracellular pH measurements indicate a delay in acidification in either V1G1-overexpressing or V1G1-silenced cells compared to controls. Finally, in an independent set of experiments, we applied transmission electron microscopy and confocal fluorescence microscopy to further investigate the internalization of the capsules. Both analyses confirm that capsules are engulfed in acidic vesicular structures in modified and control cell lines. The use of capsule-based pH sensors allowed demonstration of the importance of the V1G1 subunit in V-ATPase activity concerning intravesicular acidification. We believe that the combined use of these pH-sensor system and such a real-time method for tracking their internalization path would contribute to systematically measure the proton concentration changes inside the endocytic compartments in various cell systems. This approach would provide fundamental information regarding molecular mechanisms and factors that regulate intracellular acidification, vesicular trafficking, and cytoskeletal reorganizations.

Interfacing materials science and biology for drug carrier design

Over the last ten years, there has been considerable research interest in the development of polymeric carriers for biomedicine. Such delivery systems have the potential to significantly reduce side effects and increase the bioavailability of poorly soluble therapeutics. The design of carriers has relied on harnessing specific variations in biological conditions, such as pH or redox potential, and more recently, by incorporating specific peptide cleavage sites for enzymatic hydrolysis. Although much progress has been made in this field, the specificity of polymeric carriers is still limited when compared with their biological counterparts. To synthesize the next generation of carriers, it is important to consider the biological rationale for materials design. This requires a detailed understanding of the cellular microenvironments and how these can be harnessed for specific applications. In this review, several important physiological cues in the cellular microenvironments are outlined, with a focus on changes in pH, redox potential, and the types of enzymes present in specific regions. Furthermore, recent studies that use such biologically inspired triggers to design polymeric carriers are highlighted, focusing on applications in the field of therapeutic delivery.