Biofabrication and Monitoring of a 3D Printed Skin Model for Melanoma.

There is an unmet need for in vitro cancer models that emulate the complexity of human tissues. 3D-printed solid tumor micromodels based on decellularized extracellular matrices (dECMs) recreate the biomolecule-rich matrix of native tissue. Herein a 3D in vitro metastatic melanoma model that is amenable for drug screening purposes and recapitulates features of both the tumor and the skin microenvironment is described. Epidermal, basement membrane, and dermal biocompatible inks are prepared by means of combined chemical, mechanical, and enzymatic processes. Bioink printability is confirmed by rheological assessment and bioprinting, and bioinks are subsequently combined with melanoma cells and dermal fibroblasts to build complex 3D melanoma models. Cells are tracked by confocal microscopy and surface-enhanced Raman spectroscopy (SERS) mapping. Printed dECMs and cell tracking allow modeling of the initial steps of metastatic disease, and may be used to better understand melanoma cell behavior and response to drugs.

Dynamic 3D in vitro lung models: applications of inorganic nanoparticles for model development and characterization.

Being a vital organ exposed to the external environment, the lung is susceptible to a plethora of pathogens and pollutants. This is reflected in high incidences of chronic respiratory diseases, which remain a leading cause of mortality world-wide and pose a persistent global burden. It is thus of paramount importance to improve our understanding of these pathologies and provide better therapeutic options. This necessitates the development of representative and physiologically relevant in vitro models. Advances in bioengineering have enabled the development of sophisticated models that not only capture the three-dimensional architecture of the cellular environment but also incorporate the dynamics of local biophysical stimuli. However, such complex models also require novel approaches that provide reliable characterization. Within this review we explore how 3D bioprinting and nanoparticles can serve as multifaceted tools to develop such dynamic 4D printed in vitro lung models and facilitate their characterization in the context of pulmonary fibrosis and breast cancer lung metastasis.

A Scaffold-Assisted 3D Cancer Cell Model for Surface-Enhanced Raman Scattering-Based Real-Time Sensing and Imaging.

Despite recent advances in the development of scaffold-based three-dimensional (3D) cell models, challenges persist in imaging and monitoring cell behavior within these complex structures due to their heterogeneous cell distribution and geometries. Incorporating sensors into 3D scaffolds provides a potential solution for real-time, in situ sensing and imaging of biological processes such as cell growth and disease development. We introduce a 3D printed hydrogel-based scaffold capable of supporting both surface-enhanced Raman scattering (SERS) biosensing and imaging of 3D breast cancer cell models. The scaffold incorporates plasmonic nanoparticles and SERS tags, for sensing and imaging, respectively. We demonstrate the scaffold's adaptability and modularity in supporting breast cancer spheroids, thereby enabling spatial and temporal monitoring of tumor evolution.

3D bioprinted breast tumor-stroma models for pre-clinical drug testing.

The use of three-dimensional (3D) bioprinting has been proposed for the reproducible production of 3D disease models that can be used for high-throughput drug testing and personalized medicine. However, most such models insufficiently reproduce the features and environment of real tumors. We report the development of bioprinted in vitro 3D tumor models for breast cancer, which physically and biochemically mimic important aspects of the native tumor microenvironment, designed to study therapeutic efficacy. By combining a mix of breast decellularized extracellular matrix and methacrylated hyaluronic acid with tumor-derived cells and non-cancerous stromal cells of biological relevance to breast cancer, we show that biological signaling pathways involved in tumor progression can be replicated in a carefully designed tumor-stroma environment. Finally, we demonstrate proof-of-concept application of these models as a reproducible platform for investigating therapeutic responses to commonly used chemotherapeutic agents.

Remodeling arteries: studying the mechanical properties of 3D-bioprinted hybrid photoresponsive materials.

3D-printed cell models are currently in the spotlight of medical research. Whilst significant advances have been made, there are still aspects that require attention to achieve more realistic models which faithfully represent the in vivo environment. In this work we describe the production of an artery model with cyclic expansive properties, capable of mimicking the different physical forces and stress factors that cells experience in physiological conditions. The artery wall components are reproduced using 3D printing of thermoresponsive polymers with inorganic nanoparticles (NPs) representing the outer tunica adventitia, smooth muscle cells embedded in extracellular matrix representing the tunica media, and finally a monolayer of endothelial cells as the tunica intima. Cyclic expansion can be induced thanks to the inclusion of photo-responsive plasmonic NPs embedded within the thermoresponsive ink composition, resulting in changes in the thermoresponsive polymer hydration state and hence volume, in a stimulated on-off manner. By changing the thermoresponsive polymer composition, the transition temperature and pulsatility can be efficiently tuned. We show the direct effect of cyclic expansion and contraction on the overlying cell layers by analyzing transcriptional changes in mechanoresponsive mesenchymal genes associated with such microenvironmental physical cues. The technique described herein involving stimuli-responsive 3D printed tissue constructs, also described as four- dimensional (4D) printing, offers a novel approach for the production of dynamic biomodels.

Ag2 S Biocompatible Ensembles as Dual OCT Contrast Agents and NIR Ocular Imaging Probes.

Ag2 S nanoparticles (NPs) emerge as a unique system that simultaneously features in vivo near-infrared (NIR) imaging, remote heating, and low toxicity thermal sensing. In this work, their capabilities are extended into the fields of optical coherence tomography (OCT), as contrast agents, and NIR probes in both ex vivo and in vivo experiments in eyeballs. The new dual property for ocular imaging is obtained by the preparation of Ag2 S NPs ensembles with a biocompatible amphiphilic block copolymer. Rather than a classical ligand exchange, where surface traps may arise due to incomplete replacement of surface sites, the use of this polymer provides a protective extra layer that preserves the photoluminescence properties of the NPs, and the procedure allows for the controlled preparation of submicrometric scattering centers. The resulting NPs ensembles show extraordinary colloidal stability with time and biocompatibility, enhancing the contrast in OCT with simultaneous NIR imaging in the second biological window.

Hybrid core-shell nanoparticles for cell-specific magnetic separation and photothermal heating.

Hyperthermia, as the process of heating a malignant site above 42 °C to trigger cell death, has emerged as an effective and selective cancer therapy strategy. Various modalities of hyperthermia have been proposed, among which magnetic and photothermal hyperthermia are known to benefit from the use of nanomaterials. In this context, we introduce herein a hybrid colloidal nanostructure comprising plasmonic gold nanorods (AuNRs) covered by a silica shell, onto which iron oxide nanoparticles (IONPs) are subsequently grown. The resulting hybrid nanostructures are responsive to both external magnetic fields and near-infrared irradiation. As a result, they can be applied for the targeted magnetic separation of selected cell populations - upon targeting by antibody functionalization - as well as for photothermal heating. Through this combined functionality, the therapeutic effect of photothermal heating can be enhanced. We demonstrate both the fabrication of the hybrid system and its application for targeted photothermal hyperthermia of human glioblastoma cells.

Multifunctional plasmonic-magnetic nanoparticles for bioimaging and hyperthermia.

Multicompartment nanoparticles have raised great interest for different biomedical applications, thanks to the combined properties of different materials within a single entity. These hybrid systems have opened new avenues toward diagnosis and combination therapies, thus becoming preferred theranostic agents. When hybrid nanoparticles comprise magnetic and plasmonic components, both magnetic and optical properties can be achieved, which are potentially useful for multimodal bioimaging, hyperthermal therapies and magnetically driven selective delivery. Nanostructures comprising iron oxide and gold are usually selected for biomedical applications, as they display size-dependent properties, biocompatibility, and unique physical and chemical characteristics that can be tuned through highly precise synthetic protocols. We provide herein an overview of the most recent synthetic protocols to prepare magnetic-plasmonic nanostructures made of iron oxide and gold, to then highlight the progress made on multifunctional magnetic-plasmonic bioimaging and heating-based therapies. We discuss the advantages and limitations of the various systems in these directions.

Combination of Live Cell Surface-Enhanced Raman Scattering Imaging with Chemometrics to Study Intracellular Nanoparticle Dynamics.

Surface-enhanced Raman scattering (SERS)-encoded nanoparticles are used for bioimaging, on account of their well-defined Raman spectra and biocompatibility, which allow long incubation times with high signal stability and no cytotoxicity. However, reliable analysis of SERS bioimaging requires quantification of the amount of encoded nanoparticles that have been taken up by cells and the effect of subsequent dilution due to cellular division (mitosis). Although methods such as elemental analysis and flow cytometry can be used to quantify nanoparticle uptake, these are both end-point measurements in which a cell population is screened rather than looking at individual cells. In contrast, SERS imaging can be applied at multiple timepoints to the same individual cells without damaging the biological sample. We present the application of both supervised and unsupervised multivariate analyses, to quantify the intracellular amount of SERS tags in individual MCF7 living cells, toward the characterization of cellular uptake in vitro. The obtained results from both methodologies were validated by standard elemental analysis techniques.

SERS and Fluorescence-Active Multimodal Tessellated Scaffolds for Three-Dimensional Bioimaging.

With the ever-increasing use of 3D cell models toward studying bio-nano interactions and offering alternatives to traditional 2D in vitro and in vivo experiments, methods to image biological tissue in real time and with high spatial resolution have become a must. A suitable technique therefore is surface-enhanced Raman scattering (SERS)-based microscopy, which additionally features reduced photocytotoxicity and improved light penetration. However, optimization of imaging and postprocessing parameters is still required. Herein we present a method to monitor cell proliferation over time in 3D, using multifunctional 3D-printed scaffolds composed of biologically inert poly(lactic-co-glycolic acid) (PLGA) as the base material, in which fluorescent labels and SERS-active gold nanoparticles (AuNPs) can be embedded. The combination of imaging techniques allows optimization of SERS imaging parameters for cell monitoring. The scaffolds provide anchoring points for cell adhesion, so that cell growth can be observed in a suspended 3D matrix, with multiple reference points for confocal fluorescence and SERS imaging. By prelabeling cells with SERS-encoded AuNPs and fluorophores, cell proliferation and migration can be simultaneously monitored through confocal Raman and fluorescence microscopy. These scaffolds provide a simple method to follow cell dynamics in 4D, with minimal disturbance to the tissue model.

Nd3+-Doped Lanthanum Oxychloride Nanocrystals as Nanothermometers.

The development of optical nanothermometers operating in the near-infrared (NIR) is of high relevance toward temperature measurements in biological systems. We propose herein the use of Nd3+-doped lanthanum oxychloride nanocrystals as an efficient system with intense photoluminescence under NIR irradiation in the first biological transparency window and emission in the second biological window with excellent emission stability over time under 808 nm excitation, regardless of Nd3+ concentration, which can be considered as a particular strength of our system. Additionally, surface passivation through overgrowth of an inert LaOCl shell around optically active LaOCl/Nd3+ cores was found to further enhance the photoluminescence intensity and also the lifetime of the 1066 nm, 4F3/2 to 4I11/2 transition, without affecting its (ratiometric) sensitivity toward temperature changes. As required for biological applications, we show that the obtained (initially hydrophobic) nanocrystals can be readily transferred into aqueous solvents with high, long-term stability, through either ligand exchange or encapsulation with an amphiphilic polymer.

Live-Cell Surface-Enhanced Raman Spectroscopy Imaging of Intracellular pH: From Two Dimensions to Three Dimensions.

Visualization of intracellular pH (i-pH) using surface-enhanced Raman spectroscopy (SERS) plays an important role toward understanding of cellular processes including their interactions with nanoparticles. However, conventional two-dimensional SERS imaging often fails to take into consideration changes occurring in the whole-cell volume. We therefore aimed at obtaining a comprehensive i-pH profile of living cells by means of three-dimensional (3D) SERS imaging, thereby visualizing dynamic i-pH distribution changes in a single cell. We devised here a biocompatible and highly stable SERS pH probe, comprising plasmonic gold nanostars functionalized with a pH-sensitive Raman reporter tag-4-mercaptobenzoic acid-and protected by a cationic biocompatible polymer, poly-l-arginine hydrochloride (PA). The positively charged PA coating plays a double role in enhancing cell uptake and providing chemical and colloidal stability in cellular environments. The SERS-active pH probe allowed visualization of local changes in i-pH, such as acidification during nanoparticle (NP) endocytosis. We provide evidence of i-pH changes during NP endocytosis via high-resolution 3D SERS imaging, thereby opening new avenues toward the application of SERS to intracellular studies.

Shielded Silver Nanorods for Bioapplications.

Silver is arguably the best plasmonic material in terms of optical performance. However, wide application of Ag and Ag-containing nanoparticles is usually hindered by two major drawbacks, namely, chemical degradation and cytotoxicity. We report herein a synthetic method for highly monodisperse polymer-coated Ag nanorods, which are thereby protected against external stimuli (oxidation, light, heat) and are noncytotoxic to various cell lines. The monodispersity of Ag nanorods endows them with narrow plasmon bands, which are tunable into the near-infrared biological transparency window, thus facilitating application in bioanalytical and therapeutic techniques. We demonstrate intracellular surface-enhanced Raman scattering (SERS) imaging using Ag nanorods encoded with five different Raman reporter molecules. Encoded Ag nanorods display long-term stability in terms of size, shape, optical response, and SERS signal. Our results help eliminate concerns of instability and cytotoxicity in the application of Ag-containing nanoparticles with enhanced optical response, toward the development of bioapplications.

SERS-based immunoassay for monitoring cortisol-related disorders.

As a natural response to a stressful situation, the human body produces cortisol. For this reason, cortisol is also called "the stress hormone" and is considered to be the principal stress biomarker. Although cortisol response to stress is essential for survival, abnormal levels in biological fluids may represent serious health risks. In this work, we present a cortisol biosensor which relies on a highly sensitive technique (surface-enhanced Raman spectroscopy, SERS) and a specific recognition (immunoassay). Gold nanostars were used as SERS nanotags, since they provided a better response than nanorods or nanospheres. Using the same concept, two different immunoassay modalities were evaluated, using either magnetic beads or gold-coated glass slides decorated with cortisol antibodies as the capture substrates. The magnetically-assisted SERS immunoassay presented a better performance and was therefore selected to quantify cortisol content in biological fluids (urine and serum). Significant advantages of this assay were found over standard methods such as Ultra Performance Liquid Chromatography-Mass Spectrometry (UPLC-MS) and Enzyme-Linked Immunosorbent Assay (ELISA), including higher sensitivity and repeatability, minimum sample preparation, simplicity, and portability. Therefore, the proposed SERS immunoassay might be implemented as a highly efficient tool for in situ monitoring of human stress levels and cortisol-related disorders (e.g. Cushing's syndrome and Addison's disease).

Present and Future of Surface-Enhanced Raman Scattering.

The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article.

Surface-Enhanced Raman Scattering Tags for Three-Dimensional Bioimaging and Biomarker Detection.

We have recently witnessed a major improvement in the quality of nanoparticles encoded with Raman-active molecules (SERS tags). Such progress relied mainly on a major improvement of fabrication methods for building-blocks, resulting in widespread application of this powerful tool in various fields, with the potential to replace commonly used techniques, such as those based on fluorescence. We present hereby a brief Perspective on surface enhanced Raman scattering (SERS) tags, regarding their composition, morphology, and structure, and describe our own selection from the current state-of-the-art. We then focus on the main bioimaging applications of SERS tags, showing a gradual evolution from two-dimensional studies to three-dimensional analysis. Recent improvements in sensitivity and multiplexing ability have enabled great advancements toward in vivo applications, e.g., highlighting tumor boundaries to guide surgery. In addition, the high level of biomolecule sensitivity reached by SERS tags promises an expansion toward biomarker detection in cases for which traditional methods offer limited reliability, as a consequence of the frequently low analyte concentrations.

Composite Polymer Colloids for SERS-Based Applications.

Polymers and nanoparticles can be combined into different materials with applications in various fields like catalysis, biotechnology, or drug delivery, to cite just a few. Colloidal composites may vary significantly, ranging from a single nanoparticle stabilized by a polymer shell through a polymeric carrier decorated with hundreds of particles. We review here composite colloids comprising gold nanoparticles, with an emphasis in systems with potential application in surface enhanced Raman scattering (SERS). The focus is on selected strategies for synthesis and functionalization, such as: encapsulation of gold nanoparticles by amphiphilic polymers, polymeric matrices as nanoparticle carriers and smart polymer based composites. We stress the benefits derived from the combination of polymers and metal particles toward SERS, such as chemical and colloidal stabilization in complex environments, and collective optical effects through hot spot generation for optimized SERS enhancement or improved imaging tags.

Involvement of two uptake mechanisms of gold and iron oxide nanoparticles in a co-exposure scenario using mouse macrophages.

Little is known about the simultaneous uptake of different engineered nanoparticle types, as it can be expected in our daily life. In order to test such co-exposure effects, murine macrophages (J774A.1 cell line) were incubated with gold (AuNPs) and iron oxide nanoparticles (FeO x NPs) either alone or combined. Environmental scanning electron microscopy revealed that single NPs of both types bound within minutes on the cell surface but with a distinctive difference between FeO x NPs and AuNPs. Uptake analysis studies based on laser scanning microscopy, transmission electron microscopy, and inductively coupled plasma optical emission spectrometry revealed intracellular appearance of both NP types in all exposure scenarios and a time-dependent increase. This increase was higher for both AuNPs and FeO x NPs during co-exposure. Cells treated with endocytotic inhibitors recovered after co-exposure, which additionally hinted that two uptake mechanisms are involved. Cross-talk between uptake pathways is relevant for toxicological studies: Co-exposure acts as an uptake accelerant. If the goal is to maximize the cellular uptake, e.g., for the delivery of pharmaceutical agents, this can be beneficial. However, co-exposure should also be taken into account in the case of risk assessment of occupational settings. The demonstration of co-exposure-invoked pathway interactions reveals that synergetic nanoparticle effects, either positive or negative, must be considered for nanotechnology and nanomedicine in particular to develop to its full potential.

Janus plasmonic-magnetic gold-iron oxide nanoparticles as contrast agents for multimodal imaging.

The design of compact nanoprobes for multimodal bioimaging is a current challenge and may have a major impact on diagnostics and therapeutics. Multicomponent gold-iron oxide nanoparticles have shown high potential as contrast agents in numerous imaging techniques due to the complementary features of iron oxide and gold nanomaterials. In this paper we describe novel gold-iron oxide Janus magnetic-plasmonic nanoparticles as versatile nanoprobes for multimodal imaging. The nanoparticles are characterized as contrast agents for different imaging techniques, including X-ray computed tomography (CT), T2-weighted nuclear magnetic resonance imaging (MRI), photoacoustic imaging (PA), dark-field and bright-field optical microscopy, transmission electron microscopy (TEM), and surface enhanced Raman spectroscopy (SERS). We discuss the effect of particle size and morphology on their performance as contrast agents and show the advantage of a Janus configuration. Additionally, the uptake of nanoparticles by cells can be simultaneously visualized in dark- and bright-field optical microscopy, SERS mapping, and electron microscopy. These complementary techniques allow a complete view of cell uptake in an artifact-free manner, with multiplexing capabilities, and with extra information regarding the nanoparticles' fate inside the cells. Altogether, the results obtained with these non-invasive techniques show the high versatility of these nanoparticles, the advantages of a Janus configuration, and their high potential in multipurpose biomedical applications.

Colloidal Gold Nanoparticles Induce Changes in Cellular and Subcellular Morphology.

Exposure of cells to colloidal nanoparticles (NPs) can have concentration-dependent harmful effects. Mostly, such effects are monitored with biochemical assays or probes from molecular biology, i.e., viability assays, gene expression profiles, etc., neglecting that the presence of NPs can also drastically affect cellular morphology. In the case of polymer-coated Au NPs, we demonstrate that upon NP internalization, cells undergo lysosomal swelling, alterations in mitochondrial morphology, disturbances in actin and tubulin cytoskeleton and associated signaling, and reduction of focal adhesion contact area and number of filopodia. Appropriate imaging and data treatment techniques allow for quantitative analyses of these concentration-dependent changes. Abnormalities in morphology occur at similar (or even lower) NP concentrations as the onset of reduced cellular viability. Cellular morphology is thus an important quantitative indicator to verify harmful effects of NPs to cells, without requiring biochemical assays, but relying on appropriate staining and imaging techniques.