Second harmonic generation confocal microscopy of collagen type I from rat tendon cryosections

Extraction of collagen morphological features from second-harmonic generation microscopy images via GLCM and CT analyses: A cross-laboratory study

Second-harmonic generation (SHG) microscopy provides a high-resolution label-free approach for noninvasively detecting collagen organization and its pathological alterations. Up to date, several imaging analysis algorithms for extracting collagen morphological features from SHG images-such as fiber size and length, order and anisotropy-have been developed. However, the dependence of extracted features on experimental setting represents a significant obstacle for translating the methodology in the clinical practice. We tackled this problem by acquiring SHG images of the same kind of collagenous sample in various laboratories using different experimental setups and imaging conditions. The acquired images were analyzed by commonly used algorithms, such as gray-level co-occurrence matrix or curvelet transform; the extracted morphological features were compared, finding that they strongly depend on some experimental parameters, whereas they are almost independent from others. We conclude with useful suggestions for comparing results obtained in different labs using different experimental setups and conditions.

On the quantitative analysis of lamellar collagen arrangement with second-harmonic generation imaging

Second harmonic generation (SHG) allows for the examination of collagen structure in collagenous tissues. Collagen is a fibrous protein found in abundance in the human body, present in bones, cartilage, the skin, and the cornea, among other areas, providing structure, support, and strength. Its structural arrangement is deeply intertwined with its function. For instance, in the cornea, alterations in collagen organization can result in severe visual impairments. Using SHG imaging, various metrics have demonstrated the potential to study collagen organization. The discrimination between healthy, keratoconus, and crosslinked corneas, assessment of injured tendons, or the characterization of breast and ovarian tumorous tissue have been demonstrated. Nevertheless, these metrics have not yet been objectively evaluated or compared. A total of five metrics were identified and implemented from the literature, and an additional approach adapted from texture analysis was proposed. In this study, we analyzed their effectiveness on a ground-truth set of artificially generated fibrous images. Our investigation provides the first comprehensive assessment of the performance of multiple metrics, identifying both the strengths and weaknesses of each approach and providing valuable insights for future applications of SHG imaging in medical diagnostics and research.

Spheroids as a 3D in vitro model to study bone and bone mineralization

Traumas, fractures, and diseases can severely influence bone tissue. Insight into bone mineralization is essential for the development of therapies and new strategies to enhance bone regeneration. 3D cell culture systems, in particular cellular spheroids, have gained a lot of interest as they can recapitulate crucial aspects of the in vivo tissue microenvironment, such as the extensive cell-cell and cell-extracellular matrix (ECM) interactions found in tissue. The potential of combining spheroids and various classes of biomaterials opens also new opportunities for research within bone tissue engineering. Characterizing cellular organization, ECM structure, and ECM mineralization is a fundamental step for understanding the biological processes involved in bone tissue formation in a spheroid-based model system. Still, many experimental techniques used in this field of research are optimized for use with monolayer cell cultures. There is thus a need to develop new and improving existing experimental techniques, for applications in 3D cell culture systems. In this review, bone composition and spheroids properties are described. This is followed by an insight into the techniques that are currently used in bone spheroids research and how these can be used to study bone mineralization. We discuss the application of staining techniques used with optical and confocal fluorescence microscopy, molecular biology techniques, second harmonic imaging microscopy, Raman spectroscopy and microscopy, as well as electron microscopy-based techniques, to evaluate osteogenic differentiation, collagen production and mineral deposition. Challenges in the applications of these methods in bone regeneration and bone tissue engineering are described. STATEMENT OF SIGNIFICANCE: 3D cell cultures have gained a lot of interest in the last decades as a possible technique that can be used to recreate in vitro in vivo biological process. The importance of 3D environment during bone mineralization led scientists to use this cell culture to study this biological process, to obtain a better understanding of the events involved. New and improved techniques are also required for a proper analysis of this cell model and the process under investigation. This review summarizes the state of the art of the techniques used to study bone mineralization and how 3D cell cultures, in particular spheroids, are tested and analysed to obtain better resolved results related to this complex biological process.

Primary radiation damage in bone evolves via collagen destruction by photoelectrons and secondary emission self-absorption

X-rays are invaluable for imaging and sterilization of bones, yet the resulting ionization and primary radiation damage mechanisms are poorly understood. Here we monitor in-situ collagen backbone degradation in dry bones using second-harmonic-generation and X-ray diffraction. Collagen breaks down by cascades of photon-electron excitations, enhanced by the presence of mineral nanoparticles. We observe protein disintegration with increasing exposure, detected as residual strain relaxation in pre-stressed apatite nanocrystals. Damage rapidly grows from the onset of irradiation, suggesting that there is no minimal 'safe' dose that bone collagen can sustain. Ionization of calcium and phosphorous in the nanocrystals yields fluorescence and high energy electrons giving rise to structural damage that spreads beyond regions directly illuminated by the incident radiation. Our findings highlight photoelectrons as major agents of damage to bone collagen with implications to all situations where bones are irradiated by hard X-rays and in particular for small-beam mineralized collagen fiber investigations.

Two-Photon Imaging for Non-Invasive Corneal Examination

Two-photon imaging (TPI) microscopy, namely, two-photon excited fluorescence (TPEF), fluorescence lifetime imaging (FLIM), and second-harmonic generation (SHG) modalities, has emerged in the past years as a powerful tool for the examination of biological tissues. These modalities rely on different contrast mechanisms and are often used simultaneously to provide complementary information on morphology, metabolism, and structural properties of the imaged tissue. The cornea, being a transparent tissue, rich in collagen and with several cellular layers, is well-suited to be imaged by TPI microscopy. In this review, we discuss the physical principles behind TPI as well as its instrumentation. We also provide an overview of the current advances in TPI instrumentation and image analysis. We describe how TPI can be leveraged to retrieve unique information on the cornea and to complement the information provided by current clinical devices. The present state of corneal TPI is outlined. Finally, we discuss the obstacles that must be overcome and offer perspectives and outlooks to make clinical TPI of the human cornea a reality.

Tunable optical activities in chiral transition metal oxide nanoparticles

Chiral transition metal oxides (TMOs) are widely used in various optoelectronic devices. However, the currently poor understanding of how the optical activities of TMOs can be regulated considerably hinders their applications. We have synthesized a series of chiral TMO nanoparticles (NPs), i.e., MoO_x (x = 2, 2.4 and 2.5) and Co₃O₄. Compared with TMO NPs with L-/D-cysteine molecules as the capping ligand, L-/D-histidine-capped TMO NPs possess larger anisotropic factors (g_abs), which are as high as ∼0.01 and ∼0.02 for L-/D-histidine-capped MoO_2.5 and Co₃O₄ NPs, respectively. A nondegenerate coupled oscillator (NDCO) theoretical calculation confirms that L-/D-histidine molecules can generate a smaller electric dipole moment and thus induce higher optical activity than L-/D-cysteine molecules. Impressively, the chiral NPs exhibit broadband second harmonic generation. This work indicates that chiral TMO NPs have potential for application in nonlinear optical devices.

Investigation into self-assembled collagen arrays guided by the surface properties of polyimide films

The mechanism of highly-oriented collagen (Col) fibril arrays on rubbed polyimide (PI) films was investigated in order to understand the interfacial Col-PI interactions. It was found that the orientation of the surface functional groups of the rubbed PI films was most effectively controlled and optimized by the rubbing conditions. In particular, nano-grooves with a width of 100-600 nm and a depth of 2-10 nm were formed on the rubbed PI films at a rubbing strength of 2.4 m, leading to the formation of the highest density of the Col fibril array. Moreover, highly-oriented Col fibrils were formed inside the nano-grooves by the formation of hydrogen bonds between the CO of the imide groups (@ rubbed PI films) and the N-H of the amino groups (@ β-Sheets of Col molecules), resulting in the orientation of the Col molecules and subsequent assembly to the fibrils. Thus, the orientation and density of the fibril arrays on the rubbed PI films were successfully controlled by the interfacial interactions between the β-Sheet component of Col and the nano-groove surfaces of the rubbed PI films. Therefore, the novel technology of this study will provide an effective method to fabricate the one-directional fibrous nanostructures and to understand how to control the orientation of biomolecules in vitro.

Structurally abnormal collagen fibrils in abdominal aortic aneurysm resist platelet adhesion

BACKGROUND

Platelet adhesion to the subendothelial collagen fibrils is one of the first steps in hemostasis. Understanding how structural perturbations in the collagen fibril affect platelet adhesion can provide novel insights into disruption of hemostasis in various diseases. We have recently identified the presence of abnormal collagen fibrils with compromised D-periodic banding in the extracellular matrix remodeling present in abdominal aortic aneurysms (AAA).

OBJECTIVE

In this study, we employed multimodal microscopy approaches to characterize how collagen fibril structure impacts platelet adhesion in clinical AAA tissues.

METHODS

Ultrastructural atomic force microscopy (AFM) analysis was performed on tissue sections after staining with fluorescently labeled collagen hybridizing peptide (CHP) to recognize degraded collagen. Second harmonic generation (SHG) microscopy was used on CHP-stained sections to identify regions of intact versus degraded collagen. Finally, platelet adhesion was identified via SHG and indirect immunofluorescence on the same tissue sections.

RESULTS

Our results indicate that ultrastructural features characterizing collagen fibril abnormalities coincide with CHP staining. SHG signal was absent from CHP-positive regions. Additionally, platelet binding was primarily localized to regions with SHG signal. Abnormal collagen fibrils present in AAA (in SHG negative regions) were thus found to inhibit platelet adhesion compared to normal fibrils.

CONCLUSIONS

Our investigations reveal how the collagen fibril structure in the vessel wall can serve as another regulator of platelet-collagen adhesion. These results can be broadly applied to understand the role of collagen fibril structure in regulating thrombosis or bleeding disorders.

Membrane curvature and connective fiber alignment in guinea pig round window membrane

The round window membrane (RWM) covers an opening between the perilymph fluid-filled inner ear space and the air-filled middle ear space. As the only non-osseous barrier between these two spaces, the RWM is an ideal candidate for aspiration of perilymph for diagnostics purposes and delivery of medication for treatment of inner ear disorders. Routine access across the RWM requires the development of new surgical tools whose design can only be optimized with a thorough understanding of the RWM's structure and properties. The RWM possesses a layer of collagen and elastic fibers so characterization of the distribution and orientation of these fibers is essential. Confocal and two-photon microscopy were conducted on intact RWMs in a guinea pig model to characterize the distribution of collagen and elastic fibers. The fibers were imaged via second-harmonic-generation, autofluorescence, and Rhodamine B staining. Quantitative analyses of both fiber orientation and geometrical properties of the RWM uncovered a significant correlation between mean fiber orientations and directions of zero curvature in some portions of the RWM, with an even more significant correlation between the mean fiber orientations and linear distance along the RWM in a direction approximately parallel to the cochlear axis. The measured mean fiber directions and dispersions can be incorporated into a generalized structure tensor for use in the development of continuum anisotropic mechanical constitutive models that in turn will enable optimization of surgical tools to access the cochlea. STATEMENT OF SIGNIFICANCE: The Round Window Membrane (RWM) is the only non-osseous barrier separating the middle and inner ear spaces, and thus is an ideal portal for medical access to the cochlea. An understanding of RWM structure and mechanical response is necessary to optimize the design of surgical tools for this purpose. The RWM geometry and the connective fiber orientation and dispersion are measured via confocal and 2-photon microscopy. A region of the RWM geometry is characterized as a hyperbolic paraboloid and another region as a tapered parabolic cylinder. Predominant fiber directions correlate well with directions of zero curvature in the hyperbolic paraboloid region. Overall fiber directions correlate well with position along a line approximately parallel to the central axis of the cochlea's spiral.

Development of Fluorescently Labeled, Functional Type I Collagen Molecules

While de novo collagen fibril formation is well-studied, there are few investigations into the growth and remodeling of extant fibrils, where molecular collagen incorporation into and erosion from the fibril surface must delicately balance during fibril growth and remodeling. Observing molecule/fibril interactions is difficult, requiring the tracking of molecular dynamics while, at the same time, minimizing the effect of the observation on fibril structure and assembly. To address the observation-interference problem, exogenous collagen molecules are tagged with small fluorophores and the fibrillogenesis kinetics of labeled collagen molecules as well as the structure and network morphology of assembled fibrils are examined. While excessive labeling significantly disturbs fibrillogenesis kinetics and network morphology of assembled fibrils, adding less than ≈1.2 labels per collagen molecule preserves these characteristics. Applications of the functional, labeled collagen probe are demonstrated in both cellular and acellular systems. The functional, labeled collagen associates strongly with native fibrils and when added to an in vitro model of corneal stromal development at low concentration, the labeled collagen is incorporated into a fine extracellular matrix (ECM) network associated with the cells within 24 h.

Study of collagen remodeling in structural disorders of the temporomandibular joint using second-harmonic generation microscopy

Structural disorder of the temporomandibular joint (TMJ) is a progressive disease with poor prognosis due to its physiological three-dimensional anatomical position and the complicated relationship among muscles, ligaments, and cartilage. The lack of detection methods for changes in the collagen structure of the TMJ disc makes the diagnosis untimely and unclear. This work aimed to explore the feasibility of using a promising detection technique, second-harmonic generation (SHG), to characterize collagen fibers in a TMJ disc with structural disorders. The TMJ discs with structural disorder were observed using SHG microscopy, and assessment of collagen orientation was conducted by analyzing digitized images. The SHG images were also compared with the scanning electron microscopy images and microscopic images acquired after hematoxylin and eosin and Masson's trichrome staining. The SHG imaging showed that the collagen fibers in diseased TMJ were distributed in a disorderly manner, and pixel intensities in diseased TMJ discs were significantly different from those acquired in healthy TMJs. Moreover, the three dimensions of collagen fibers and dynamic images acquired by SHG nonlinear optical microscopy showed the structural disorder of the collagen fibers in a diseased TMJ. In summary, SHG imaging could provide three-dimensional and quantitative data, with dynamic and critical pathological information for clinical diagnosis, showing its potential value in the diagnosis and evaluation of structural disorders of the TMJ disc.

Extracellular matrix and cellular senescence in venous leg ulcers

High prevalence of non-healing chronic wounds contributes to a huge healthcare burden across the world. Early treatment interventions for non-healing wounds are vital. It was previously shown that accumulation of 15% or more of senescent cells in a chronic wound edge is an indicator that the wound is unlikely to heal. However, determining the presence of senescent cells would require invasive procedures such as tissue biopsies to be taken. In this study, we found a strong correlation between decreased collagen area and presence of senescent cells in human chronic wounds i.e. venous leg ulcer (VLU), diabetic foot ulcer (DFU) and pressure ulcer (PRU). We also report that the lowest collagen levels were found in VLU patients less than 60 years of age, with a persistent wound of > 24 months. Elevated levels of senescent cells were also found in VLU of males. Second harmonic imaging of collagen at the edge of chronic wounds with a handheld multiphoton device could be used to predict the number of senescent cells, indicating if the wound is on a healing trajectory or not. Our data support the use of collagen imaging in cutaneous wound assessment for a faster and non-invasive method to predict cellular senescence and determining wound trajectory of healing.

A quality optimization approach to image Achilles tendon microstructure by phase-contrast enhanced synchrotron micro-tomography

Achilles tendons are mechanosensitive, and their complex hierarchical structure is in part the result of the mechanical stimulation conveyed by the muscles. To fully understand how their microstructure responds to mechanical loading a non-invasive approach for 3D high resolution imaging suitable for soft tissue is required. Here we propose a protocol that can capture the complex 3D organization of the Achilles tendon microstructure, using phase-contrast enhanced synchrotron micro-tomography (SR-PhC-μCT). We investigate the effects that sample preparation and imaging conditions have on the resulting image quality, by considering four types of sample preparations and two imaging setups (sub-micrometric and micrometric final pixel sizes). The image quality is assessed using four quantitative parameters. The results show that for studying tendon collagen fibers, conventional invasive sample preparations such as fixation and embedding are not necessary or advantageous. Instead, fresh frozen samples result in high-quality images that capture the complex 3D organization of tendon fibers in conditions as close as possible to natural. The comprehensive nature of this innovative study by SR-PhC-μCT breaks ground for future studies of soft complex biological tissue in 3D with high resolution in close to natural conditions, which could be further used for in situ characterization of how soft tissue responds to mechanical stimuli on a microscopic level.

Loss of Nitric Oxide Induces Fibrogenic Response in Organotypic 3D Co-Culture of Mammary Epithelia and Fibroblasts-An Indicator for Breast Carcinogenesis

Simple Summary

Fibrosis, which is often caused by chronic diseases and environmental substances, is closely associated with cancer. Thus, the development of a robust method allowing for deep studies of the linkage between fibrosis and cancer is essential. Here, we tested whether our novel three-dimensional (3D) co-culture of breast epithelia and fibroblasts would be a suitable model for that purpose. We compared the phenotypic effects of L-NAME, an inhibitor of nitric oxide (NO) production, on 3D mono- and co-cultures. We previously reported that prolonged NO depletion with L-NAME caused fibrosis and tumorigenesis in mouse mammary glands. Such in vivo effects of L-NAME were well recapitulated in 3D co-cultures, but not in 3D mono-cultures of epithelia and fibroblasts. These results support not only the essential roles of the presence of the stroma in cancer development, but also the utility of this co-culture in studying the causal relationship between fibrosis and cancer.

Abstract

Excessive myofibroblast activation, which leads to dysregulated collagen deposition and the stiffening of the extracellular matrix (ECM), plays pivotal roles in cancer initiation and progression. Cumulative evidence attests to the cancer-causing effects of a number of fibrogenic factors found in the environment, diseases and drugs. While identifying such factors largely depends on epidemiological studies, it would be of great importance to develop a robust in vitro method to demonstrate the causal relationship between fibrosis and cancer. Here, we tested whether our recently developed organotypic three-dimensional (3D) co-culture would be suitable for that purpose. This co-culture system utilizes the discontinuous ECM to separately culture mammary epithelia and fibroblasts in the discrete matrices to model the complexity of the mammary gland. We observed that pharmaceutical deprivation of nitric oxide (NO) in 3D co-cultures induced myofibroblast differentiation of the stroma as well as the occurrence of epithelial–mesenchymal transition (EMT) of the parenchyma. Such in vitro response to NO deprivation was unique to co-cultures and closely mimicked the phenotype of NO-depleted mammary glands exhibiting stromal desmoplasia and precancerous lesions undergoing EMT. These results suggest that this novel 3D co-culture system could be utilized in the deep mechanistic studies of the linkage between fibrosis and cancer.

Giant Optical Activity and Second Harmonic Generation in 2D Hybrid Copper Halides

Hybrid organic-inorganic metal halides have emerged as highly promising materials for a wide range of applications in optoelectronics. Incorporating chiral organic molecules into metal halides enables the extension of their unique optical and electronic properties to chiral optics. By using chiral (R)- or (S)-methylbenzylamine (R-/S-MBA) as the organic component, we synthesized chiral hybrid copper halides, (R-/S-MBA)₂ CuCl₄ , and investigated their optical activity. Thin films of this material showed a record anisotropic g-factor as high as approximately 0.06. We discuss the origin of the giant optical activity observed in (R-/S-MBA)₂ CuCl₄ by theoretical modeling based on density functional theory (DFT) and demonstrate highly efficient second harmonic generation (SHG) in these samples. Our study provides insight into the design of chiral materials by structural engineering, creating a new platform for chiral and nonlinear photonic device applications of the chiral hybrid copper halides.

Tailoring the assembly of collagen fibers in alginate microspheres

The application of microspheres instead of bulk hydrogels in cell-laden biomaterials offers multiple advantages such as a high surface-to-volume-ratio and, consequently, a better nutrition and oxygen transfer to and from cells. The preparation of inert alginate microspheres is facile, quick, and well-established and the fabrication of alginate-collagen microspheres has been previously reported. However, no detailed characterization of the collagen fibrillogenesis in the alginate matrix is available. We use second-harmonic imaging microscopy reflection confocal microscopy and turbidity assay to study the assembly of collagen in alginate microspheres. We show that the assembly of collagen fibers in a gelled alginate matrix is a complex process that can be aided by addition of small polar molecules, such as glycine and by a careful selection of the gelling buffer used to prepare alginate hydrogels.

Tendon Extracellular Matrix Assembly, Maintenance and Dysregulation Throughout Life

In his Lissner Award medal lecture in 2000, Stephen Cowin asked the question: "How is a tissue built?" It is not a new question, but it remains as relevant today as it did when it was asked 20 years ago. In fact, research on the organization and development of tissue structure has been a primary focus of tendon and ligament research for over two centuries. The tendon extracellular matrix (ECM) is critical to overall tissue function; it gives the tissue its unique mechanical properties, exhibiting complex non-linear responses, viscoelasticity and flow mechanisms, excellent energy storage and fatigue resistance. This matrix also creates a unique microenvironment for resident cells, allowing cells to maintain their phenotype and translate mechanical and chemical signals into biological responses. Importantly, this architecture is constantly remodeled by local cell populations in response to changing biochemical (systemic and local disease or injury) and mechanical (exercise, disuse, and overuse) stimuli. Here, we review the current understanding of matrix remodeling throughout life, focusing on formation and assembly during the postnatal period, maintenance and homeostasis during adulthood, and changes to homeostasis in natural aging. We also discuss advances in model systems and novel tools for studying collagen and non-collagenous matrix remodeling throughout life, and finally conclude by identifying key questions that have yet to be answered.

A Tenon's capsule/bulbar conjunctiva interface biomimetic to model fibrosis and local drug delivery

Glaucoma filtration surgery is one of the most effective methods for lowering intraocular pressure in glaucoma. The surgery efficiently reduces intra-ocular pressure but the most common cause of failure is scarring at the incision site. This occurs in the conjunctiva/Tenon’s capsule layer overlying the scleral coat of the eye. Currently used antimetabolite treatments to prevent post-surgical scarring are non-selective and are associated with potentially blinding side effects. Developing new treatments to target scarring requires both a better understanding of wound healing and scarring in the conjunctiva, and new means of delivering anti-scarring drugs locally and sustainably. By combining plastic compression of collagen gels with a soft collagen-based layer, we have developed a physiologically relevant model of the sub-epithelial bulbar conjunctiva/Tenon’s capsule interface, which allows a more holistic approach to the understanding of subconjunctival tissue behaviour and local drug delivery. The biomimetic tissue hosts both primary human conjunctival fibroblasts and an immune component in the form of macrophages, morphologically and structurally mimicking the mechanical proprieties and contraction kinetics of ex vivo porcine conjunctiva. We show that our model is suitable for the screening of drugs targeting scarring and/or inflammation, and amenable to the study of local drug delivery devices that can be inserted in between the two layers of the biomimetic. We propose that this multicellular-bilayer engineered tissue will be useful to study complex biological aspects of scarring and fibrosis, including the role of inflammation, with potentially significant implications for the management of scarring following glaucoma filtration surgery and other anterior ocular segment scarring conditions. Crucially, it uniquely allows the evaluation of new means of local drug delivery within a physiologically relevant tissue mimetic, mimicking intraoperative drug delivery in vivo.

The heterogeneous morphology of networked collagen in distal colon and rectum of mice quantified via nonlinear microscopy

Visceral pain from the distal colon and rectum (colorectum) is a major complaint of patients with irritable bowel syndrome. Mechanotransduction of colorectal distension/stretch appears to play a critical role in visceral nociception, and further understanding requires improved knowledge of the micromechanical environments at different sub-layers of the colorectum. In this study, we conducted nonlinear imaging via second harmonic generation to quantify the thickness of each distinct through-thickness layer of the colorectum, as well as the principal orientations, corresponding dispersions in orientations, and the distributions of diameters of collagen fibers within each of these layers. From C57BL/6 mice of both sexes (8-16 weeks of age, 25-35 g), we dissected the distal 30 mm of the large bowel including the colorectum, divided these into three even segments, and harvested specimens (~8 × 8 mm²) from each segment. We stretched the specimens either by colorectal distension to 20 mmHg (reference) or 80 mmHg (deformed) or by biaxial stretch to 10 mN (reference) or 80 mN (deformed), and fixed them with 4% paraformaldehyde. We then conducted SHG imaging through the wall thickness and analyzed post-hoc using custom-built software to quantify the orientations of collagen fibers in all distinct layers. We also quantified the thickness of each layer of the colorectum, and the corresponding distributions of collagen density and diameters of fibers. We found collagen concentrated in the submucosal layer. The average diameter of collagen fibers was greatest in the submucosal layer, followed by the serosal and muscular layers. Collagen fibers aligned with muscle fibers in the two muscular layers, whereas their orientation varied greatly with location in the serosal layer. In colonic segments, thick collagen fibers in the submucosa presented two major orientations aligned approximately ±30° to the axial direction, and form a patterned network. Our results indicate the submucosa is likely the principal passive load-bearing structure of the colorectum. In addition, afferent endings in those collagen-rich regions present likely candidates of colorectal nociceptors to encode noxious distension/stretch.

Hyperthermia affects collagen fiber architecture and induces apoptosis in pancreatic and fibroblast tumor hetero-spheroids in vitro

Desmoplasia, an aberrant production of extracellular matrix (ECM), is considered as one predictive marker of malignancy of pancreatic cancer. In this paper, we study the effect of mild hyperthermia on fibrillary collagen architecture in murine Achilles tendons and in a pancreatic cancer model, in vitro, i.e. 3D hetero-type tumor spheroids, consisting of pancreatic cancer (Panc-1) cells and fibroblasts (WI-38), producing collagen fibers. We clearly demonstrate that i) mild hyperthermia (40 °C, 42 °C) damages the collagen architecture in murine Achilles tendons. ii) Mild extrinsic (hot air) and iron oxide nanoparticle based magnetic hyperthermia reduce the level of collagen fiber architecture in the generated hetero-type tumor spheroids. iii) Mild magnetic hyperthermia reduces cell vitality mainly through apoptotic and necrotic processes in the generated tumor spheroids. In conclusion, hetero-type 3D tumor spheroids are suitable for studying the effect of hyperthermia on collagen fibers, in vitro.

Reduced Basal Nitric Oxide Production Induces Precancerous Mammary Lesions via ERBB2 and TGFβ

One third of newly diagnosed breast cancers in the US are early-stage lesions. The etiological understanding and treatment of these lesions have become major clinical challenges. Because breast cancer risk factors are often linked to aberrant nitric oxide (NO) production, we hypothesized that abnormal NO levels might contribute to the formation of early-stage breast lesions. We recently reported that the basal level of NO in the normal breast epithelia plays crucial roles in tissue homeostasis, whereas its reduction contributes to the malignant phenotype of cancer cells. Here, we show that the basal level of NO in breast cells plummets during cancer progression due to reduction of the NO synthase cofactor, BH₄, under oxidative stress. Importantly, pharmacological deprivation of NO in prepubertal to pubertal animals stiffens the extracellular matrix and induces precancerous lesions in the mammary tissues. These lesions overexpress a fibrogenic cytokine, TGFβ, and an oncogene, ERBB2, accompanied by the occurrence of senescence and stem cell-like phenotype. Consistently, normalization of NO levels in precancerous and cancerous breast cells downmodulates TGFβ and ERBB2 and ameliorates their proliferative phenotype. This study sheds new light on the etiological basis of precancerous breast lesions and their potential prevention by manipulating the basal NO level.

3,3'-thiodipropanol as a versatile refractive index-matching mounting medium for fluorescence microscopy

High resolution fluorescence microscopy requires optimization of the protocols for biological sample preparation. The optical and chemical characteristics of mounting media are among the things that could be modified to achieve optimal image formation. In our search for chemical substances that could perform as mounting media, 3,3'-thiodipropanol (TDP) emerged as a sulfide with potentially interesting characteristics. In this work, several tests of its performance as a mounting medium for fluorescence microscopy of biological samples were performed, including the labeling of filamentous actin with fluorescent phalloidins. The refractive index dispersion curve of pH-adjusted TDP was experimentally obtained in the visible range and compared to the dispersion curves of commercial and lab-made mounting media. The effects on the fluorescence of commonly used dyes were tested by using TDP as a solvent and measuring the relative fluorescence quantum yield of the dyes. By being able to mix TDP in any concentration with water and 2,2'-thiodiethanol (TDE), it was possible not only to fine-tune the refractive index of the resulting solution, but also to preserve the compatibility of TDP with the most popular and efficient fluorescent actin staining used in biological microscopy.

Tissue effects of intra-tissue refractive index shaping (IRIS): insights from two-photon autofluorescence and second harmonic generation microscopy

Intra-tissue refractive index shaping (IRIS) is a novel, non-ablative form of vision correction by which femtosecond laser pulses are tightly focused into ocular tissues to induce localized refractive index (RI) change via nonlinear absorption. Here, we examined the effects of Blue-IRIS on corneal microstructure to gain insights into underlying mechanisms. Three-layer grating patterns were inscribed with IRIS ~180 µm below the epithelial surface of ex vivo rabbit globes using a 400 nm femtosecond laser. Keeping laser power constant at 82 mW in the focal volume, multiple patterns were written at different scan speeds. The largest RI change induced in this study was + 0.011 at 20 mm/s. After measuring the phase change profile of each inscribed pattern, two-photon excited autofluorescence (TPEF) and second harmonic generation (SHG) microscopy were used to quantify changes in stromal structure. While TPEF increased significantly with induced RI change, there was a noticeable suppression of SHG signal in IRIS treated regions. We posit that enhancement of TPEF was due to the formation of new fluorophores, while decreases in SHG were most likely due to degradation of collagen triple helices. All in all, the changes observed suggest that IRIS works by inducing a localized, photochemical change in collagen structure.

Near-infrared probe-based confocal microendoscope for deep-tissue imaging

In this work, a near-infrared probe-based confocal microendoscope (pCM) with a 785 nm laser source, a long working distance, and a probe with diameter of 2.6 mm that can be compatible with a conventional endoscope is demonstrated to produce deep-tissue images at cellular resolutions with enhanced contrast and signal-to-noise ratio. Theoretical simulations and experiments confirm that near-infrared light can optimize the image quality. Abundant details of mouse esophagus obtained at different depths demonstrate the system's ability to image deep tissues at cellular resolutions, which makes it possible to diagnose diseases in the digestive tract in real time, laying a solid foundation for clinical applications.

Quantitative assessment of radiation-induced changes of bladder and rectum collagen structure using optical methods

The objective of the study is the quantitative analysis of the dose-time dependences of changes occurring in collagen of bladder and rectum after gamma-irradiation using optical methods [nonlinear microscopy in a second harmonic generation (SHG) detection regime and cross-polarization optical coherence tomography (CP OCT)]. For quantitative assessment of the collagen structure, regions of interest on the SHG-images of two-dimensional (2-D) distribution of SHG signal intensity of collagen were chosen in the submucosa. The mean SHG signal intensity and its standard deviation were calculated by ImageJ 1.39p (NIH). For quantitative analysis of CP OCT data, an integral depolarization factor (IDF) was calculated. Quantitative calculation of the SHG signal intensity and the IDF can provide additional information about the processes of the collagen radiation-induced degradation and subsequent remodeling. High positive correlation between the mean SHG signal intensity and the mean IDF of bladder and rectum demonstrates that CP OCT can be used as an "optical biopsy" in the grading of collagen radiation damage.

Assessment of the metabolism and morphology of the porcine cornea, lens and retina by 2-photon imaging

Two-photon imaging is a noninvasive imaging technique with increasing importance in the biological and medical fields since it allows intratissue cell imaging with high resolution. We demonstrate the feasibility of using a single 2-photon instrument to evaluate the cornea, the crystalline lens and the retina based on their autofluorescence (AF). Image acquisition was performed using a custom-built 2-photon microscope for 5-dimensional microscopy with a near infrared broadband sub-15 femtosecond laser centered at 800 nanometers. Signals were detected using a spectral photomultiplier tube. The spectral ranges for the analysis of each tissue/layer AF were determined based on the spectra of each tissue as well as of pure endogenous fluorophores. The cornea, lens and retina are characterized at multiple depths with subcellular resolution based on their morphology and AF lifetime. Additionally, the AF lifetime of NAD(P)H was used to assess the metabolic activity of the cornea epithelium, endothelium and keratocytes. The feasibility to evaluate the metabolic activity of lens epithelial cells was also demonstrated, which may be used to further investigate the pathogenesis of cataracts. The results illustrate the potential of multimodal multiphoton imaging as a novel ophthalmologic technique as well as its potential as a diagnostic tool.

Enabling second harmonic generation as a contrast mechanism for optical projection tomography (OPT) and scanning laser optical tomography (SLOT)

Volumetric imaging of connective tissue provides insights into the structure of biological tissue. Second harmonic generation (SHG) microscopy has become a standard method to image collagen rich tissue like skin or cornea. Due to the non-centrosymmetric architecture, no additional label is needed and tissue can be visualized noninvasively. Thus, SHG microscopy enables the investigation of collagen associated diseases, providing high resolution images and a field of view of several hundreds of μm. However, the in toto visualization of larger samples is limited to the working distance of the objective and the integration time of the microscope setup, which can sum up to several hours and days. A faster imaging technique for samples in the mesoscopic range is scanning laser optical tomography (SLOT), which provides linear fluorescence, scattering and absorption as intrinsic contrast mechanisms. Due to the advantages of SHG and the reduced measurement time of SLOT, the integration of SHG in SLOT would be a great extension. This way SHG measurements could be performed faster on large samples, providing isotropic resolution and simultaneous acquisition of all other contrast mechanisms available, such as fluorescence and absorption. SLOT is based on the principle of computed tomography, which requires the rotation of the sample. The SHG signal, however, depends strongly on the sample orientation and the polarization of the laser, which results in SHG intensity fluctuation during sample rotation and prevents successful 3D reconstruction. In this paper we investigate the angular dependence of the SHG signal by simulation and experiment and found a way to eliminate reconstruction artifacts caused by this angular dependence in SHG-SLOT data. This way, it is now possible to visualize samples in the mesoscopic range using SHG-SLOT, with isotropic resolution and in correlation to other contrast mechanisms as absorption, fluorescence and scattering.

Controlling the orientation of a cell-synthesized extracellular matrix by using engineered gelatin-based building blocks

Surface micropatterned gelatin building blocks clearly increment the alignment degree of collagen-based microtissues synthesized by human dermal fibroblasts.

Three-Dimensional Adult Cardiac Extracellular Matrix Promotes Maturation of Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes

Pluripotent stem cell-derived cardiomyocytes (CMs) have great potential in the development of new therapies for cardiovascular disease. In particular, human induced pluripotent stem cells (iPSCs) may prove especially advantageous due to their pluripotency, their self-renewal potential, and their ability to create patient-specific cell lines. Unfortunately, pluripotent stem cell-derived CMs are immature, with characteristics more closely resembling fetal CMs than adult CMs, and this immaturity has limited their use in drug screening and cell-based therapies. Extracellular matrix (ECM) influences cellular behavior and maturation, as does the geometry of the environment-two-dimensional (2D) versus three-dimensional (3D). We therefore tested the hypothesis that native cardiac ECM and 3D cultures might enhance the maturation of iPSC-derived CMs in vitro. We demonstrate that maturation of iPSC-derived CMs was enhanced when cells were seeded into a 3D cardiac ECM scaffold, compared with 2D culture. 3D cardiac ECM promoted increased expression of calcium-handling genes, Junctin, CaV1.2, NCX1, HCN4, SERCA2a, Triadin, and CASQ2. Consistent with this, we find that iPSC-derived CMs in 3D adult cardiac ECM show increased calcium signaling (amplitude) and kinetics (maximum upstroke and downstroke) compared with cells in 2D. Cells in 3D culture were also more responsive to caffeine, likely reflecting an increased availability of calcium in the sarcoplasmic reticulum. Taken together, these studies provide novel strategies for maturing iPSC-derived CMs that may have applications in drug screening and transplantation therapies to treat heart disease.

Comparison of second harmonic microscopy images of collagen-based ocular tissues with 800 and 1045 nm

Second harmonic generation (SHG) imaging is a well-suited multiphoton technique allowing visualization of biological tissues mainly composed of collagen with submicron resolution. Despite its inherent confocal properties, imaging of deeper layers within thick samples has still some limitations. Although the use of longer wavelengths might help to overcome this, the dependence between SHG signals and wavelength is still under discussion. We report here on the dependence with wavelength of SHG signals from collagen-based ocular tissues. The quality of SHG images for two commonly used excitation wavelengths (800 and 1045 nm) is studied. The analysis of the collagen structural information reveals that the information provided by both wavelengths is similar. It was also found that, independently of the depth location, 1045-nm SHG images presented always lower signal levels than those acquired with 800 nm. However, the contrast of the former images was higher, what may improve the visualization of certain features of interest.

A new mode of contrast in biological second harmonic generation microscopy

Enhanced image contrast in biological second harmonic imaging microscopy (SHIM) has previously been reported via quantitative assessments of forward- to epi-generated signal intensity ratio and by polarization analysis. Here we demonstrate a new form of contrast: the material-specific, wavelength-dependence of epi-generated second harmonic generation (SHG) excitation efficiency, and discriminate collagen and myosin by ratiometric epi-generated SHG images at 920 nm and 860 nm. Collagen shows increased SHG intensity at 920 nm, while little difference is detected between the two for myosin; allowing SHIM to characterize different SHG-generating components within a complex biological sample. We propose that momentum-space mapping of the second-order non-linear structure factor is the source of this contrast and develop a model for the forward and epi-generated SHG wavelength-dependence. Our model demonstrates that even very small changes in the assumed material fibrillar structure can produce large changes in the wavelength-dependency of epi-generated SHG. However, in the case of forward SHG, although the same changes impact upon absolute intensity at a given wavelength, they have very little effect on wavelength-dependency beyond the expected monotonic fall. We also propose that this difference between forward and epi-generated SHG provides an explanation for many of the wavelength-dependency discrepancies in the published literature.

Imaging Collagen in Scar Tissue: Developments in Second Harmonic Generation Microscopy for Biomedical Applications

The ability to respond to injury with tissue repair is a fundamental property of all multicellular organisms. The extracellular matrix (ECM), composed of fibrillar collagens as well as a number of other components is dis-regulated during repair in many organs. In many tissues, scaring results when the balance is lost between ECM synthesis and degradation. Investigating what disrupts this balance and what effect this can have on tissue function remains an active area of research. Recent advances in the imaging of fibrillar collagen using second harmonic generation (SHG) imaging have proven useful in enhancing our understanding of the supramolecular changes that occur during scar formation and disease progression. Here, we review the physical properties of SHG, and the current nonlinear optical microscopy imaging (NLOM) systems that are used for SHG imaging. We provide an extensive review of studies that have used SHG in skin, lung, cardiovascular, tendon and ligaments, and eye tissue to understand alterations in fibrillar collagens in scar tissue. Lastly, we review the current methods of image analysis that are used to extract important information about the role of fibrillar collagens in scar formation.

Changes in the extracellular matrix surrounding human chronic wounds revealed by 2-photon imaging

Chronic wounds are a growing problem worldwide with no effective therapeutic treatments available. Our objective was to understand the composition of the dermal tissue surrounding venous leg ulcers and diabetic foot ulcers (DFU). We used novel 2-photon imaging techniques alongside classical histology to examine biopsies from the edges of two common types of chronic wound, venous leg ulcers and DFU. Compared to normal intact skin, we found that collagen levels are significantly reduced throughout the dermis of venous leg ulcer biopsies and DFU, with a reduction in both fibril thickness and abundance. Both wound types showed a significant reduction in elastin in the upper dermis, but in DFU, the loss was throughout the dermis. Loss of extracellular matrix correlated with high levels of CD68- and CD18-positive leukocytes. 2-photon imaging of the extracellular matrix in the intact tissue surrounding a chronic wound with a hand-held device may provide a useful clinical indicator on the healing progression or deterioration of these wounds.

Circular Dichroism Spectroscopy of Collagen Fibrillogenesis: A New Use for an Old Technique

Type-I collagen assembles in a stepwise, hierarchic fashion from the folding of the triple helix to the assembly of fibrils into fibers. The mature assembled fibers are crucial for tissue structure and mechanics, cell interactions, and other functions in vivo. Although triple helix folding can be followed with the use of optical methods such as circular dichroism (CD) spectroscopy, fibrillogenesis is typically measured by alternative methods such as turbidity, rheology, and microscopy. Together, these approaches allow for investigation of the mechanical properties and architectures of collagen-based scaffolds and excised tissues. Herein, we demonstrate that CD spectroscopy, a technique that is used primarily to evaluate the secondary structure of proteins, can also be employed to monitor collagen fibrillogenesis. Type-I collagen suspensions demonstrated a strong, negative ellipticity band between 204 and 210 nm under conditions consistent with fibrillogenesis. Deconvolution of CD spectra before, during, and after fibrillogenesis identified a unique fibril spectrum distinct from triple helix and random coil conformations. The ability to monitor multiple states of collagen simultaneously in one experiment using one modality provides a powerful platform for studying this complex assembly process and the effects of other factors, such as collagenases, on fibrillogenesis and degradation.

Imaging the Nonlinear Susceptibility Tensor of Collagen by Nonlinear Optical Stokes Ellipsometry

Nonlinear optical Stokes ellipsometric (NOSE) microscopy was demonstrated for the analysis of collagen-rich biological tissues. NOSE is based on polarization-dependent second harmonic generation imaging. NOSE was used to access the molecular-level distribution of collagen fibril orientation relative to the local fiber axis at every position within the field of view. Fibril tilt-angle distribution was investigated by combining the NOSE measurements with ab initio calculations of the predicted molecular nonlinear optical response of a single collagen triple helix. The results were compared with results obtained previously by scanning electron microscopy, nuclear magnetic resonance imaging, and electron tomography. These results were enabled by first measuring the laboratory-frame Jones nonlinear susceptibility tensor, then extending to the local-frame tensor through pixel-by-pixel corrections based on local orientation.

Wavelength-Dependent Second Harmonic Generation Circular Dichroism for Differentiation of Col I and Col III Isoforms in Stromal Models of Ovarian Cancer Based on Intrinsic Chirality Differences

Extensive remodeling of the extracellular matrix (ECM) occurs in many epithelial cancers. For example, in ovarian cancer, upregulation of collagen isoform type III has been linked to invasive forms of the disease, and this change may be a potential biomarker. To examine this possibility, we implemented wavelength-dependent second harmonic generation circular dichroism (SHG-CD) imaging microscopy to quantitatively determine changes in chirality in ECM models comprised of different Col I/Col III composition. In these models, Col III was varied between 0 and 40%, and we found increasing Col III results in reduced net chirality, consistent with structural biology studies of Col I and III in tissues where the isoforms comingle in the same fibrils. We further examined the wavelength dependence of the SHG-CD to both optimize the response and gain insight into the underlying mechanism. We found using shorter SHG excitation wavelengths resulted in increased SHG-CD sensitivity, where this is consistent with the electric-dipole-coupled oscillator model suggested previously for the nonlinear chirality response from thin films. Moreover, the sensitivity is further consistent with the wavelength dependency of SHG intensity fit to a two-state model of the two-photon absorption in collagen. We also provide experimental calibration protocols to implement the SHG-CD modality on a laser scanning microscope. We last suggest that the technique has broad applicability in probing a wide range of diseased states with changes in collagen molecular structure.

Optical second-harmonic images of sacran megamolecule aggregates

We have detected a second-order nonlinear optical response from aggregates of the ampholytic megamolecular polysaccharide sacran extracted from cyanobacterial biomaterials by using optical second-harmonic-generation (SHG) microscopy. The SHG images of sacran cotton-like lump, fibers, and cast films showed SHG intensity microspots of several tens of micrometers in size. The dependence of the SHG spot intensity on an excitation light polarization angle was observed to illustrate sacran molecular orientation in these microdomains. We also observed SHG signals around a special region of the cast film edges of sacran. These results show that sacran megamolecules aggregate in several different ways.

Unified Theory for Polarization Analysis in Second Harmonic and Sum Frequency Microscopy

A unified theoretical framework for the recovery of second-order nonlinear susceptibility tensors and sample orientations from polarization-dependent second harmonic generation and sum frequency generation microscopy was developed. Jones formalism was extended to nonlinear optics and was used to bridge the experimental observables and the local-frame tensor elements. Four commonly used experimental architectures were explicitly explored, including polarization rotation with no postsample optics, polarization-in polarization-out measurement, and polarization modulation with and without postsample optics. Polarization-dependent second harmonic generation measurement was performed on Z-cut quartz and the local-frame tensor elements were calculated. The recovered tensor elements agree with the expected values dictated by symmetry.

Connexin 43 is overexpressed in human fetal membrane defects after fetoscopic surgery

OBJECTIVE

We examined whether surgically induced membrane defects elevate connexin 43 (Cx43) expression in the wound edge of the amniotic membrane (AM) and drives structural changes in collagen that affects healing after fetoscopic surgery.

METHOD

Cell morphology and collagen microstructure was investigated by scanning electron microscopy and second harmonic generation in fetal membranes taken from women who underwent fetal surgery. Immunofluoresence and real-time quantitative polymerase chain reaction was used to examine Cx43 expression in control and wound edge AM.

RESULTS

Scanning electron microscopy showed dense, helical patterns of collagen fibrils in the wound edge of the fetal membrane. This arrangement changed in the fibroblast layer with evidence of collagen fibrils that were highly polarised along the wound edge but not in control membranes. Cx43 was increased by 112.9% in wound edge AM compared with controls (p < 0.001), with preferential distribution in the fibroblast layer compared with the epithelial layer (p < 0.01). In wound edge AM, mesenchymal cells had a flattened morphology, and there was evidence of poor epithelial migration across the defect. Cx43 and COX-2 expression was significantly increased in wound edge AM compared with controls (p < 0.001).

CONCLUSION

Overexpression of Cx43 in the AM after fetal surgery induces morphological and structural changes in the collagenous matrix that may interfere with normal healing mechanisms. © 2016 The Authors. Prenatal Diagnosis published by John Wiley & Sons, Ltd.

Inverse focusing inside turbid media by creating an opposite virtual objective

Limited by the penetration depth, imaging of thick bio-tissues can be achieved only by epi-detection geometry. Applications based on forward-emitted signals or bidirectional illumination are restricted by lack of an opposite objective. A method for creating an opposite virtual objective inside thick media through phase conjugation was first proposed. Under forward illumination, the backward scattering light from the media was collected to generate a phase conjugate wave, which was sent back to the media and formed an inverse focusing light. Samples combined with a diffuser or a mouse skin were used as specimens. Inverse focusing was successfully demonstrated by applying holography-based optical phase conjugation with a BaTiO3. This result indicates the capability to create an opposite virtual objective inside live tissues. The proposed method is compatible with current coherent imaging and super-resolution imaging technologies. It creates a possible way for forward-emitted signals collection and bidirectional illumination in thick specimens.

Inflammation Drives Retraction, Stiffening, and Nodule Formation via Cytoskeletal Machinery in a Three-Dimensional Culture Model of Aortic Stenosis

In calcific aortic valve disease, the valve cusps undergo retraction, stiffening, and nodular calcification. The inflammatory cytokine, tumor necrosis factor (TNF)-α, contributes to valve disease progression; however, the mechanisms of its actions on cusp retraction and stiffening are unclear. We investigated effects of TNF-α on murine aortic valvular interstitial cells (VICs) within three-dimensional, free-floating, compliant, collagen hydrogels, simulating their natural substrate and biomechanics. TNF-α increased retraction (percentage of diameter), stiffness, and formation of macroscopic, nodular structures with calcification in the VIC-laden hydrogels. The effects of TNF-α were attenuated by blebbistatin inhibition of myosin II-mediated cytoskeletal contraction. Inhibition of actin polymerization with cytochalasin-D, but not inhibition of Rho kinase with Y27632, blocked TNF-α-induced retraction in three-dimensional VIC hydrogels, suggesting that actin stress fibers mediate TNF-α-induced effects. In the hydrogels, inhibitors of NF-κB blocked TNF-α-induced retraction, whereas simultaneous inhibition of c-Jun N-terminal kinase was required to block TNF-α-induced stiffness. TNF-α also significantly increased collagen deposition, as visualized by Masson's trichrome staining, and up-regulated mRNA expression of discoidin domain receptor tyrosine kinase 2, fibronectin, and α-smooth muscle actin. In human aortic valves, calcified cusps were stiffer and had more collagen deposition than noncalcified cusps. These findings suggest that inflammation, through stimulation of cytoskeletal contractile activity, may be responsible for valvular cusp retraction, stiffening, and formation of calcified nodules.

In Vitro Enzymatic Degradation of Tissue Grafts and Collagen Biomaterials by Matrix Metalloproteinases: Improving the Collagenase Assay

Matrix metalloproteinase-1 and -8 are active during the wound healing and remodelling processes, degrading native extracellular matrix and implantable devices. However, traditional in vitro assays utilize primarily matrix metalloproteinase-1 to mimic the in vivo degradation microenvironment. Herein, we assessed the influence of various concentrations of matrix metalloproteinase- 1 and 8 (50, 100, and 200 U/mL) as a function of pH (5.5 and 7.4) and time (3, 6, 9, 12, and 24 h) on the degradation profile of three tissue grafts (chemically cross-linked Permacol, nonchemically cross-linked Permacol and nonchemically cross-linked Strattice) and a collagen biomaterial (nonchemically cross-linked collagen sponge). Chemically cross-linked and nonchemically cross-linked Permacol samples exhibited the highest resistance to enzymatic degradation, while nonchemically cross-linked collagen sponges exhibited the least resistance to enzymatic degradation. Qualitative and quantitative degradation analysis of all samples revealed a similar degradation profile over time, independently of the matrix metalloproteinase used and its respective concentration and pH. These data indicate that matrix metalloproteinase-1 and matrix metalloproteinase-8 exhibit similar degradation profile in vitro, suggesting that matrix metalloproteinase-8 should be used for collagenase assay.

Enabling Multiphoton and Second Harmonic Generation Imaging in Paraffin-Embedded and Histologically Stained Sections

Nonlinear microscopy, namely multiphoton imaging and second harmonic generation (SHG), is an established noninvasive technique useful for the imaging of extracellular matrix (ECM). Typically, measurements are performed in vivo on freshly excised tissues or biopsies. In this article, we describe the effect of rehydrating paraffin-embedded sections on multiphoton and SHG emission signals and the acquisition of nonlinear images from hematoxylin and eosin (H&E)-stained sections before and after a destaining protocol. Our results reveal that bringing tissue sections to a physiological state yields a significant improvement in nonlinear signals, particularly in SHG. Additionally, the destaining of sections previously processed with H&E staining significantly improves their SHG emission signals during imaging, thereby allowing sufficient analysis of collagen in these sections. These results are important for researchers and pathologists to obtain additional information from paraffin-embedded tissues and archived samples to perform retrospective analysis of the ECM or gain additional information from rare samples.

Two-photon spectral fluorescence lifetime and second-harmonic generation imaging of the porcine cornea with a 12-femtosecond laser microscope

Five dimensional microscopy with a 12-fs laser scanning microscope based on spectrally resolved two-photon autofluorescence lifetime and second-harmonic generation (SHG) imaging was used to characterize all layers of the porcine cornea. This setup allowed the simultaneous excitation of both metabolic cofactors, NAD(P)H and flavins, and their discrimination based on their spectral emission properties and fluorescence decay characteristics. Furthermore, the architecture of the stromal collagen fibrils was assessed by SHG imaging in both forward and backward directions. Information on the metabolic state and the tissue architecture of the porcine cornea were obtained with subcellular resolution, and high temporal and spectral resolutions.

The use of optical trap and microbeam to investigate the mechanical and transport characteristics of tunneling nanotubes in tumor spheroids

The use of optical trap and microbeam for investigating mechanical and transport properties of inter cellular tunneling nanotubes (TnTs) in tumor spheroids has been demonstrated. TnTs in tumor spheroids have been visualized by manipulating TnT connected cells using optical tweezers. Functionality of the TnTs for transferring cytoplasmic vesicles and injected dye molecules by optoporation method has been studied. Further, the TnTs could be longitudinally stretched by manipulating the connected cells and their elastic response was studied. Manipulation of cells at the surface of tumor spheroid using optical tweezers and injection of fluorescent dye into a trapped cell using optoporation technique.

Automated biphasic morphological assessment of hepatitis B-related liver fibrosis using second harmonic generation microscopy

Liver fibrosis assessment by biopsy and conventional staining scores is based on histopathological criteria. Variations in sample preparation and the use of semi-quantitative histopathological methods commonly result in discrepancies between medical centers. Thus, minor changes in liver fibrosis might be overlooked in multi-center clinical trials, leading to statistically non-significant data. Here, we developed a computer-assisted, fully automated, staining-free method for hepatitis B-related liver fibrosis assessment. In total, 175 liver biopsies were divided into training (n = 105) and verification (n = 70) cohorts. Collagen was observed using second harmonic generation (SHG) microscopy without prior staining, and hepatocyte morphology was recorded using two-photon excitation fluorescence (TPEF) microscopy. The training cohort was utilized to establish a quantification algorithm. Eleven of 19 computer-recognizable SHG/TPEF microscopic morphological features were significantly correlated with the ISHAK fibrosis stages (P < 0.001). A biphasic scoring method was applied, combining support vector machine and multivariate generalized linear models to assess the early and late stages of fibrosis, respectively, based on these parameters. The verification cohort was used to verify the scoring method, and the area under the receiver operating characteristic curve was >0.82 for liver cirrhosis detection. Since no subjective gradings are needed, interobserver discrepancies could be avoided using this fully automated method.