High-throughput spectroscopic imaging applied to permeation through the skin

Skin models of cutaneous toxicity, transdermal transport and wound repair

Skin is widely used as a drug delivery route due to its easy access and the possibility of using relatively painless methods for the administration of bioactive molecules. However, the barrier properties of the skin, along with its multilayer structure, impose severe restrictions on drug transport and bioavailability. Thus, bioengineered models aimed at emulating the skin have been developed not only for optimizing the transdermal transport of different drugs and testing the safety and toxicity of substances but also for understanding the biological processes behind skin wounds. Even though in vivo research is often preferred to study biological processes involving the skin, in vitro and ex vivo strategies have been gaining increasing relevance in recent years. Indeed, there is a noticeably increasing adoption of in vitro and ex vivo methods by internationally accepted guidelines. Furthermore, microfluidic organ-on-a-chip devices are nowadays emerging as valuable tools for functional and behavioural skin emulation. Challenges in miniaturization, automation and reliability still need to be addressed in order to create skin models that can predict skin behaviour in a robust, high-throughput manner, while being compliant with regulatory issues, standards and guidelines. In this review, skin models for transdermal transport, wound repair and cutaneous toxicity will be discussed with a focus on high-throughput strategies. Novel microfluidic strategies driven by advancements in microfabrication technologies will also be revised as a way to improve the efficiency of existing models, both in terms of complexity and throughput.

Quantitative two-photon microscopy imaging analysis of human skin to evaluate enhanced transdermal delivery by hybrid-type multi-lamellar nanostructure

Transdermal skin delivery is a method to transport various topical formulations to a deeper skin layer non-invasively. Permeability analysis of many delivering agents has been mostly conducted by a simple tape stripping method. However, it cannot reveal a detailed depth-dependent distribution profile of transdermally delivered agents in the skin. In this work, we achieved a cellular-level depth-defined visualization of fluorophore-labelled human epidermal growth factor (EGF) transdermally delivered to human skin by using encapsulation with common liposomes and newly fabricated multi-lamellar nanostructures using a custom-design two-photon microscopy system. It was able to generate 3D reconstructed images displaying the distribution of human EGF inside the human skin sample with high-resolution. Based on a depthwise fluorescence intensity profile showing the permeation of human EGF, a quantitative analysis was performed to assess the transdermal delivery efficacy achieved by each formulation, showing a significant improvement of the efficacy with the utilization of multi-lamellar nanostructure.

Attenuated total reflection Fourier-transform infrared (ATR-FTIR) imaging of tissues and live cells

FTIR spectroscopic imaging is a label-free, non-destructive and chemically specific technique that can be utilised to study a wide range of biomedical applications such as imaging of biopsy tissues, fixed cells and live cells, including cancer cells. In particular, the use of FTIR imaging in attenuated total reflection (ATR) mode has attracted much attention because of the small, but well controlled, depth of penetration and corresponding path length of infrared light into the sample. This has enabled the study of samples containing large amounts of water, as well as achieving an increased spatial resolution provided by the high refractive index of the micro-ATR element. This review is focused on discussing the recent developments in FTIR spectroscopic imaging, particularly in ATR sampling mode, and its applications in the biomedical science field as well as discussing the future opportunities possible as the imaging technology continues to advance.

High-definition Fourier Transform Infrared (FT-IR) spectroscopic imaging of human tissue sections towards improving pathology

High-definition Fourier Transform Infrared (FT-IR) spectroscopic imaging is an emerging approach to obtain detailed images that have associated biochemical information. FT-IR imaging of tissue is based on the principle that different regions of the mid-infrared are absorbed by different chemical bonds (e.g., C=O, C-H, N-H) within cells or tissue that can then be related to the presence and composition of biomolecules (e.g., lipids, DNA, glycogen, protein, collagen). In an FT-IR image, every pixel within the image comprises an entire Infrared (IR) spectrum that can give information on the biochemical status of the cells that can then be exploited for cell-type or disease-type classification. In this paper, we show: how to obtain IR images from human tissues using an FT-IR system, how to modify existing instrumentation to allow for high-definition imaging capabilities, and how to visualize FT-IR images. We then present some applications of FT-IR for pathology using the liver and kidney as examples. FT-IR imaging holds exciting applications in providing a novel route to obtain biochemical information from cells and tissue in an entirely label-free non-perturbing route towards giving new insight into biomolecular changes as part of disease processes. Additionally, this biochemical information can potentially allow for objective and automated analysis of certain aspects of disease diagnosis.

Recent applications of ATR FTIR spectroscopy and imaging to proteins

Attenuated Total Reflection (ATR) Fourier Transform Infrared (FTIR) spectroscopy is a label-free, non-destructive analytical technique that can be used extensively to study a wide variety of different molecules in a range of different conditions. The aim of this review is to discuss and highlight the recent advances in the applications of ATR FTIR spectroscopic imaging to proteins. It briefly covers the basic principles of ATR FTIR spectroscopy and ATR FTIR spectroscopic imaging as well as their advantages to the study of proteins compared to other techniques and other forms of FTIR spectroscopy. It will then go on to examine the advances that have been made within the field over the last several years, particularly the use of ATR FTIR spectroscopy for the understanding and development of protein interaction with surfaces. Additionally, the growing potential of Surface Enhanced Infrared Spectroscopy (SEIRAS) within this area of applications will be discussed. The review includes the applications of ATR FTIR imaging to protein crystallisation and for high-throughput studies, highlighting the future potential of the technology within the field of protein structural studies and beyond.

Attenuated total reflectance Fourier-transform infrared spectroscopic imaging for breast histopathology

Histopathology forms the gold standard for the diagnosis of breast cancer. Fourier Transform Infrared (FT-IR) spectroscopic imaging has been proposed to be a potentially powerful adjunct to current histopathological techniques. Most studies using FT-IR imaging for breast tissue analysis have been in the transmission or transmission-reflection mode, in which the wavelength and optics limit the data to a relatively coarse spatial resolution (typically, coarser than 5 μm × 5 μm per pixel). This resolution is insufficient to examine many histologic structures. Attenuated Total Reflectance (ATR) FT-IR imaging incorporating a Germanium optic can allow for a four-fold increase in spatial resolution due to the material's high refractive index in the mid-IR. Here, we employ ATR FT-IR imaging towards examining cellular and tissue structures that constitute and important component of breast cancer diagnosis. In particular, we resolve and chemically characterize endothelial cells, myoepithelial cells and terminal ductal lobular units. Further extending the ability of IR imaging to examine sub-cellular structures, we report the extraction of intact chromosomes from a breast cancer cells and their spatially localized analysis as a novel approach to understand changes associated with the molecular structure of DNA in breast cancer.

Chemical imaging of protein adsorption and crystallization on a wettability gradient surface

The use of self-assembled monolayers is an established method to study the effect of surface properties on proteins and other biological materials. The generation of a monolayer with a gradient of chemical properties allows for the study of multiple surface properties simultaneously in a high throughput manner. Typically, in order to detect the presence of proteins or biological material on a surface, the use of additional dyes or tags is required. Here we present a novel method of studying the effect of gradient surface properties on protein adsorption and crystallization in situ through the use of ATR-FTIR spectroscopic imaging, which removes the need for additional labeling. We describe the successful application of this technique to the measurement of the growth of a gradient monolayer of octyltrichlorosilane across the surface of a silicon ATR element. ATR-FTIR imaging was also used to study the adsorption of lysozyme, as a model protein, onto the modified surface. The sensitivity of measurements obtained with a focal plane array (FPA) detector were improved though the use of pixel averaging which allowed small absorption bands to be detected with minimal effect on the spatial resolution along the gradient. Study of the effect of surface hydrophobicity on both adsorption of lysozyme to the element and lysozyme crystallization revealed that more lysozyme adsorbed to the hydrophobic side of the ATR element and more lysozyme crystals formed in the same region. These findings strongly suggest a correlation exists between surface protein adsorption and protein crystallization. This method could be applied to the study of other proteins and whole cells.

Rapid prototyping of microfluidic devices for integrating with FT-IR spectroscopic imaging

A versatile approach for the rapid prototyping of microfluidic devices suitable for use with FT-IR spectroscopic imaging is introduced. Device manufacture is based on the direct printing of paraffin onto the surface of an infrared transparent substrate, followed by encapsulation. Key features of this approach are low running costs, rapid production times, simplicity of design modifications and suitability for integration with FT-IR spectroscopic measurements. In the current experiments, the minimum width of channel walls was found to be approximately 120 mum and approximately 200 when a 25 mum and 12 mum spacer is used, respectively. Water and poly(ethylene glycol) are used as model fluids in a laminar flow regime, and are imaged in both transmission and attenuated total reflection (ATR) modes. It is established that adoption of transmission mode measurements yields superior sensitivity whilst the ATR mode is more suitable for quantitative analysis using strong spectral absorption bands. Results indicate that devices manufactured using this approach are suitable for use with in situ FT-IR spectroscopic imaging.

Characterization of tumor progression in engineered tissue using infrared spectroscopic imaging

Engineered tissues can provide models for imaging and disease progression and the use of such models is becoming increasingly prevalent. While structural characterization of these systems is documented, a combination of biochemical and structural knowledge is often helpful. Here, we apply Fourier transform infrared (FT-IR) spectroscopic imaging to examine an engineered tissue model of melanoma. We first characterize the biochemical properties and spectral changes in different layers of growing skin. Second, we introduce malignant melanocytes to simulate tumor formation and growth. Both cellular changes associated with tumor formation and growth can be observed. In particular, chemical changes associated with tumor-stromal interactions are observed during the course of tumor growth and appear to influence a 50-100 microm region. The development of this analytical approach combining engineered tissue with spectroscopy, imaging and computation will allow for quality control and standardization in tissue engineering and novel scientific insight in cancer progression.

Micro- and macro-attenuated total reflection Fourier transform infrared spectroscopic imaging. Plenary Lecture at the 5th International Conference on Advanced Vibrational Spectroscopy, 2009, Melbourne, Australia

Fourier transform infrared (FT-IR) spectroscopic imaging has become a very powerful method in chemical analysis. In this review paper we describe a variety of opportunities for obtaining FT-IR images using the attenuated total reflection (ATR) approach and provide an overview of fundamental aspects, accessories, and applications in both micro- and macro-ATR imaging modes. The advantages and versatility of both ATR imaging modes are discussed and the spatial resolution of micro-ATR imaging is demonstrated. Micro-ATR imaging has opened up many new areas of study that were previously precluded by inadequate spatial resolution (polymer blends, pharmaceutical tablets, cross-sections of blood vessels or hair, surface of skin, single live cells, cancerous tissues). Recent applications of ATR imaging in polymer research, biomedical and forensic sciences, objects of cultural heritage, and other complex materials are outlined. The latest advances include obtaining spatially resolved chemical images from different depths within a sample, and surface-enhanced images for macro-ATR imaging have also been presented. Macro-ATR imaging is a valuable approach for high-throughput analysis of materials under controlled environments. Opportunities exist for chemical imaging of dynamic aqueous systems, such as dissolution, diffusion, microfluidics, or imaging of dynamic processes in live cells.