Structural variations of collagen in normal and pathological tissues: role of electron microscopy

Orientation-dependent indentation reveals the crosslink-mediated deformation mechanisms of collagen fibrils

The spatial arrangement and interactions of the extracellular matrix (ECM) components control the mechanical behavior of tissue at multiple length scales. Changes in microscale deformation mechanisms affect tissue function and are often hallmarks of remodeling and disease. Despite their importance, the deformation mechanisms that modulate the mechanical behavior of collagenous tissue, particularly in indentation and compression modes of deformation, remain poorly understood. Here, we develop an integrated computational and experimental approach to investigate the deformation mechanisms of collagenous tissue at the microscale. While the complex deformation arising from indentation with a spherical probe is often considered a pitfall rather than an opportunity, we leverage this orientation-dependent deformation to examine the shear-regulated interactions of collagen fibrils and the role of crosslinks in modulating these interactions. We specifically examine tendon and cervix, two tissues rich in collagen with quite different microstructures and mechanical functions. We find that interacting, crosslinked collagen fibrils resist microscale longitudinal compressive forces, while widely used constitutive models fail to capture this behavior. The reorientation of collagen fibrils tunes the compressive stiffness of complex tissues like cervix. This study offers new insights into the mechanical behavior of collagen fibrils during indentation, and more generally, under longitudinal compressive forces, and illustrates the mechanisms that contribute to the experimentally observed orientation-dependent mechanical behavior. STATEMENT OF SIGNIFICANCE: Remodeling and disease can affect the deformation and interaction of tissue constituents, and thus mechanical function of tissue. Yet, the microscale deformation mechanisms are not well characterized in many tissues. Here, we develop a combined experimental-computational approach to infer the microscale deformation mechanisms of collagenous tissues with very different functions: tendon and cervix. Results show that collagen fibrils resist microscale forces along their length, though widely-used constitutive models do not account for this mechanism. This deformation process partially modulates the compressive stiffness of complex tissues such as cervix. Computational modeling shows that crosslink-mediated shear deformations are central to this unexpected behavior. This study offers new insights into the deformation mechanisms of collagenous tissue and the function of collagen crosslinkers.

Biomechanics and mechanobiology of the bone matrix

The bone matrix plays an indispensable role in the human body, and its unique biomechanical and mechanobiological properties have received much attention. The bone matrix has unique mechanical anisotropy and exhibits both strong toughness and high strength. These mechanical properties are closely associated with human life activities and correspond to the function of bone in the human body. None of the mechanical properties exhibited by the bone matrix is independent of its composition and structure. Studies on the biomechanics of the bone matrix can provide a reference for the preparation of more applicable bone substitute implants, bone biomimetic materials and scaffolds for bone tissue repair in humans, as well as for biomimetic applications in other fields. In providing mechanical support to the human body, bone is constantly exposed to mechanical stimuli. Through the study of the mechanobiology of the bone matrix, the response mechanism of the bone matrix to its surrounding mechanical environment can be elucidated and used for the health maintenance of bone tissue and defect regeneration. This paper summarizes the biomechanical properties of the bone matrix and their biological significance, discusses the compositional and structural basis by which the bone matrix is capable of exhibiting these mechanical properties, and studies the effects of mechanical stimuli, especially fluid shear stress, on the components of the bone matrix, cells and their interactions. The problems that occur with regard to the biomechanics and mechanobiology of the bone matrix and the corresponding challenges that may need to be faced in the future are also described.

Polarized Microscopic Analysis of Picrosirius Red Stained Salivary Gland Pathologies: An Observational Study

OBJECTIVE

 Salivary gland diseases and their pathologies may affect the glandular structure including collagen, a major stromal component, in response to tissue damage or diseases. This study aimed to examine the changes in collagens in different salivary gland diseases using polarized picrosirius red staining.

MATERIALS AND METHODS

 The submandibular gland samples diagnosed as sialadenitis, chronic sclerosing sialadenitis, pleomorphic adenoma, adenoid cystic carcinoma, and mucoepidermoid carcinoma were stained with picrosirius red, Masson's trichrome, and anticollagen I staining. The quantity of collagens was examined and reported as a percentage of positive picrosirius red area. The maturity of collagens was studied with polarized light microscope and reported as a percentage of orange-red and yellow-green polarized collagens, representing the mature and immature collagens, respectively.

STATISTICAL ANALYSIS

 The % positive areas for picrosirius red representing the collagen amount among salivary gland diseases were analyzed by one-way analysis of variance with Tukey's test. The % orange-red and % yellow-green polarized areas representing the collagen maturity were analyzed by Kruskal-Wallis test and Mann-Whitney U test.

RESULTS

 The malignant tumors, adenoid cystic carcinoma (29.92) and mucoepidermoid carcinoma (26.59), had higher significant percentage of positive picrosirius red area, compared with the benign tumor (14.56), chronic sclerosing sialadenitis (10.61), and sialadenitis (7.22) (p < 0.05). The percentages of orange-red polarized areas are 48.07, 39.6, 62.67, 83.75, and 76.05 in sialadenitis, chronic sclerosing sialadenitis, pleomorphic adenoma, adenoid cystic carcinoma, and mucoepidermoid carcinoma, respectively. This percentage tended to increase in the benign and malignant lesions with statistical difference, compared with the inflammatory lesions (p < 0.05). There was no statistical difference in the percentages of yellow-green polarized areas among various salivary gland diseases. In addition, the results of Masson's trichrome and anticollagen I staining are corresponding to that of picrosirius red among various salivary gland diseases.

CONCLUSIONS

 Polarized picrosirius red demonstrated the most amounts of collagen in the malignant lesion, and represented the different maturity of collagens in each lesion group. Studying the amounts and maturity of collagen with picrosirius red for extracellular matrix alteration in salivary gland diseases along with routine hematoxylin and eosin, Masson's trichrome, and immunohistochemistry may provide a better understanding in different salivary gland pathologies.

Segment-Long-Spacing (SLS) and the Polymorphic Structures of Fibrillar Collagen

The diverse and complex functions of collagen during the development of an organism are closely related to the polymorphism of its supramolecular structures in the extracellular matrix. SLS (segment-long-spacing) is one of the best understood alternative structures of collagen. SLS played an instrumental role in the original studies of collagen more than half a century ago that laid the foundation of nearly everything we know about collagen today. Despite being used mostly under in vitro conditions, the natural occurrence of SLS in tissues has also been reported. Here we will provide a brief overview of the major findings of the SLS and other structures of collagen based on a wealth of work published starting from the 1940s. We will discuss the factors that determine the stability and the structural specificity of the different molecular assemblies of collagen in light of the new studies using designed fibril forming collagen peptides. At the end of the chapter, we will summarize some recent discoveries of the alternative structures of collagen in tissues, especially those involved in pathogenic states. A revisit of SLS will likely inspire new understandings concerning the range of critical roles of fibrillar collagen in terms of its organizational diversity in the extracellular matrix.

Amianthoid transformation of costal cartilage matrix in children with pectus excavatum and pectus carinatum

Background

It is unclear if amianthoid transformation (AT) of costal cartilage extracellular matrix (ECM) has an impact on the development of pectus excavatum (PE) and pectus carinatum (PC).

Methods

AT foci were examined in intrasurgical biopsy specimens of costal cartilages of children (8–17 years old) with PE (n = 12) and PC (n = 12) and in age-matching autopsy control samples (n = 10) using histological and immunohistochemical staining, atomic force and nonlinear optical microscopy, transmission and scanning electron microscopy, morphometry and statistics.

Results

AT areas were identified in the costal cartilage ECM in children with normal chest, PE and PC. Each type of the AT areas (“canonical”, “intertwined”, “fine-fibred” and “intralacunary”) had a unique morphological pattern of thickness and alignment of amianthoid fibers (AFs). AFs were formed via lateral aggregation of collagen type II fibrils in the intact ECM. Foci of the AT were observed significantly more frequently in the PE and PC groups. The AT areas had unique quantitative features in each study group.

Conclusion

AT is a structurally diverse form of ECM alteration present in healthy and pathological costal cartilage. PE and PC are associated with specific AT disorders.

Clinical and Cone-Beam Computed Tomography Features of Orthokeratinized Odontogenic Cysts and Odontogenic Keratocysts in the Mandible

PURPOSE

The aim of the study was to compare the clinical and cone-beam computed tomography features of orthokeratinized odontogenic cysts (OOCs) and odontogenic keratocysts (OKCs) and to fully understand features of these 2 odontogenic cysts.

MATERIALS AND METHODS

This retrospective cross-sectional study included patients with mandibular OOCs and OKCs. The predictor variables included age at the time of diagnosis, sex, anatomical location of the cysts, lesion size, cortical bone expansion rate, and presence of cortical bone destruction, impacted tooth, tooth displacement, and root resorption. The outcome variable was the type of cystic lesion. A 1-way analysis of variance test was used to analyze the differences among the cases of OOCs and OKCs. The specificity and sensitivity of the radiological features were calculated to differentiate OOCs from OKCs.

RESULT

The sample was composed of 12 patients with OOCs and 36 patients with OKCs. The mean ages of the patients with OOCs (30.50 ± 6.14 years) and OKCs (38.39 ± 19.44 years) were concentrated in the third decade. The cystic lesions occurring in areas II and III accounted for 66.67 and 52.78% of the OOC and OKC cases, respectively. The cortical bone expansion rate of the OOC was larger than that of the unilocular OKC (OOC, 2.20 ± 1.05; OKC, 1.48 ± 0.50; P < .05). The specificity and sensitivity of unilocular or multiocular cysts to differentiate OOC from OKC were 100%, 42%, 95% confidence interval of 0.1479 to 0.3892 (P < .05) and tooth displacement were 100%, 3%, 95% confidence interval of 0.1479 to 0.3892 (P < .05).

CONCLUSIONS

The results of this study suggest clinical and radiological features of OOCs and OKCs mostly overlap, but OOC has distinctive characteristics. Most cystic lesions of OOC are unilocular cysts, rarely accompanied by tooth displacement. The cortical bone expansion rate is larger than that of unilocular cysts of OKC.

Distinct Expression Patterns of Fibrillar Collagen Types I, III, and V in Association with Mammary Gland Remodeling during Pregnancy, Lactation and Weaning

The mammary gland structurally and functionally remodels during pregnancy, during lactation and after weaning. There are three types of fibrillar collagens, types I, III, and V, in mammary stromal tissue. While the importance of the fibrillar structure of collagens for mammary morphogenesis has been suggested, the expression patterns of each type of fibrillar collagen in conjunction with mammary remodeling remain unclear. In this study, we investigated their expression patterns during pregnancy, parturition, lactation and involution. Type I collagen showed a well-developed fibril structure during pregnancy, but the fibrillar structure of type I collagen then became sparse at parturition and during lactation, which was concurrent with the downregulation of its mRNA and protein levels. The well-developed fibrillar structure of type I collagen reappeared after weaning. On the other hand, type V collagen showed a well-developed fibrillar structure and upregulation in the lactation period but not in the periods of pregnancy and involution. Type III collagen transiently developed a dense fibrillar network at the time of parturition and exhibited drastic increases in mRNA expression. These results indicate that each type of fibrillar collagen is distinctly involved in structural and functional remodeling in mammary glands during pregnancy, parturition, lactation, and involution after weaning. Furthermore, in vitro studies of mammary epithelial cells showed regulatory effects of type I collagen on cell adhesion, cell proliferation, ductal branching, and β-casein secretion. Each type of fibrillar collagen may have different roles in defining the cellular microenvironment in conjunction with structural and functional mammary gland remodeling.

[Costal cartilage structural and functional changes in children with a funnel or keeled chest]

Congenital chest wall deformities (CCWDs) in children are severe diseases leading to cosmetic defects and diseases of the respiratory and cardiovascular systems. The most common of these deformities are funnel-shaped (pectus excavatum, FD) and keeled (pectus carinatum, KD) ones. The pathogenesis of CCWDs and the role of costal cartilage structural and functional changes in their pathogenesis have now been not well studied, which makes it difficult to elaborate pathogenetic approaches to correcting these diseases. Analysis of the literature has shown that structural and functional changes occur in the matrix and chondrocytes from the costal cartilage in FD. Similar costal cartilage changes are observed in KD. It is still unknown exactly which pathological processes are present in the costal cartilage and how they result in the development of one or other type of CCWDs. The role of amianthoid transformation (AT) of costal cartilages in these processes is also unknown. It is not improbable that it is AT drastically changing the native cartilage matrix, which is one of the key mechanisms leading to changes in its properties and to the subsequent development of FD or KD.

Acetic acid and pepsin result in high yield, high purity and low macrophage response collagen for biomedical applications

Collagen based devices are frequently associated with foreign body response. Although several pre- (e.g. species, state of animal, tissue) and post- (e.g. cross-linking, scaffold architecture) extraction method factors have a profound effect on foreign body response, little is known about which and how during the extraction process factors mediate foreign body response. In this study, we assessed the influence of acetic acid and hydrochloric acid and the utilisation or not of pepsin or salt precipitation during collagen extraction on the yield, purity, free amines, denaturation temperature, resistance to collagenase degradation and macrophage response. Acetic acid/pepsin extracted collagen exhibited the highest yield, purity and free amine content and the lowest denaturation temperature. No differences in resistance to collagenase digestion were detected between the groups. Although all treatments exhibited similar macrophage morphology comprised of round cells (M1 phenotype), elongated cells (M2 phenotype) and cell aggregates (foreign body response), significantly more elongated cells were observed on HC films. Although no differences in metabolic activity were observed between the groups, the DNA concentration was significantly lower for the hydrochloric acid treatments. Further, cytokine analysis revealed that hydrochloric acid treatments induced significantly higher IL-1β and TNF-α release with respect to acetic acid treatments. Salt precipitation did not influence the parameters assessed. Collectively, these data suggest that during the collagen extraction process variables should also be monitored as, evidently, they affect the physicochemical and biological properties of collagen preparations.

Directional Matrix Nanotopography with Varied Sizes for Engineering Wound Healing

Topographic features play a crucial role in the regulation of physiologically relevant cell and tissue functions. Here, an analysis of feature-size-dependent cell-nanoarchitecture interactions is reported using an array of scaffolds in the form of uniformly spaced ridge/groove structures for engineering wound healing. The ridge and groove widths of nanopatterns are varied from 300 to 800 nm and the nanotopography features are classified into three size ranges: dense (300-400 nm), intermediate (500-600 nm), and sparse (700-800 nm). On these matrices, fibroblasts demonstrate a biphasic trend of cell body and nucleus elongation showing the maximum at intermediate feature density, whereas maximum migration speed is observed at the dense case with monotonic decrease upon increasing feature size. The directional organization of cell-synthesized fibronectin fibers can be regulated differently via the nanotopographical features. In an in vitro wound healing model, the covering rate of cell-free regions is maximized on the dense nanotopography and decreased with increasing feature size, showing direct correlation with the trend of migration speed. It is demonstrated that the properties of repaired tissue matrices in the process of wound healing may be controlled via the feature-size-dependent cell-nanoarchitecture interactions, which can be an important consideration for designing tissue engineering scaffolds.

[The morphological and morphometric study of amianthoid transformation of the costal cartilage in health and in keeled chest deformity in children]

Amianthoid transformation (AT) is the accumulations of abnormal collagen structures (amianthoid fibers) in the hyaline cartilages, tumors, and tendons. Neither functional value of costal cartilage matrix AT, nor its role in the pathogenesis of congenital chest deformities is known now.

AIM

to examine the morphological features of AT in the costal cartilage of children with the normal and keeled chest.

SUBJECTS AND METHODS

Costal cartilages were studied in 6 children with the normal chest (autopsy material) and in 5 ones with keeled chest (surgical material). Tissue fragments were fixed in 10% neutral formalin and embedded in compacted paraffin. The sections were stained with hematoxylin and eosin, picrofuchsin by van Gieson, with picrosirius, toluidine blue and by the Malaurie method modified by Gallego. The specimens were examined by light, phase-contrast, dark-field, fluorescence, and polarization microscopy. The frequency of AT sites and their area were morphometrically studied and the findings were then statistically processed.

RESULTS

Various types of AT in the costal cartilages were described as both the normal and keeled chest. According to their morphological features, classic, fine-fiber, twisted, and intralacunar types were identified. There were statistically significant increases in the incidence of all types (except the intralacunar one) and in the area of the fine-fiber AT type in keeled chest deformity as compared to health. There were positive correlations between the area of classic, intralacunar, and twisted types in both groups and between the area of a classic type and age in the controls.

CONCLUSION

A classification of AT areas varying in structures in health and disease has been given for the first time; their relation to each other and to the presence of keeled deformity shown, which, in our opinion, suggests that AT is implicated in the pathogenesis of the disease.

The collagen type I segment long spacing (SLS) and fibrillar forms: Formation by ATP and sulphonated diazo dyes

The collagen type I segment long spacing (SLS) crystallite is a well-ordered rod-like molecular aggregate, ∼300nm in length, which is produced in vitro under mildly acidic conditions (pH 2.5-3.5) in the presence of 1mM ATP. The formation of the SLS crystallite amplifies the inherent linear structural features of individual collagen heterotrimers, due to the punctate linear distribution and summation of the bulkier amino acid side chains along the length of individual collagen heterotrimers. This can be correlated structurally with the 67nm D-banded collagen fibril that is found in vivo, and formed in vitro. Although first described many years ago, the range of conditions required for ATP-induced SLS crystallite formation from acid-soluble collagen have not been explored extensively. Consequently, we have addressed biochemical parameters such as the ATP concentration, pH, speed of formation and stability so as to provide a more complete structural understanding of the SLS crystallite. Treatment of collagen type I with 1mM ATP at neutral and higher pH (6.0-9.0) also induced the formation of D-banded fibrils. Contrary to previous studies, we have shown that the polysulphonated diazo dyes Direct red (Sirius red) and Evans blue, but not Congo red and Methyl blue, can also induce the formation of SLS-like aggregates of collagen, but under markedly different ionic conditions to those employed in the presence of ATP. Specifically, pre-formed D-banded collagen fibrils, prepared in a higher than the usual physiological NaCl concentration (e.g. 500mM NaCl, 20mM Tris-HCl pH7.4 or x3 PBS), readily form SLS aggregates when treated with 0.1mM Direct red and Evans blue, but this did not occur at lower NaCl concentrations. These new data are discussed in relation to the anion (Cl(-)) and polyanion (phosphate and sulphonate) binding by the collagen heterotrimer and their likely role in collagen fibrillogenesis and SLS formation.

Collagen Matrix Remodeling in Stented Pulmonary Arteries after Transapical Heart Valve Replacement

The use of valved stents for minimally invasive replacement of semilunar heart valves is expected to change the extracellular matrix and mechanical function of the native artery and may thus impair long-term functionality of the implant. Here we investigate the impact of the stent on matrix remodeling of the pulmonary artery in a sheep model, focusing on matrix composition and collagen (re)orientation of the host tissue. Ovine native pulmonary arteries were harvested 8 (n = 2), 16 (n = 4) and 24 (n = 2) weeks after transapical implantation of self-expandable stented heart valves. Second harmonic generation (SHG) microscopy was used to assess the collagen (re)orientation of fresh tissue samples. The collagen and elastin content was quantified using biochemical assays. SHG microscopy revealed regional differences in collagen organization in all explants. In the adventitial layer of the arterial wall far distal to the stent (considered as the control tissue), we observed wavy collagen fibers oriented in the circumferential direction. These circumferential fibers were more straightened in the adventitial layer located behind the stent. On the luminal side of the wall behind the stent, collagen fibers were aligned along the stent struts and randomly oriented between the struts. Immediately distal to the stent, however, fibers on both the luminal and the adventitial side of the wall were oriented in the axial direction, demonstrating the stent impact on the collagen structure of surrounding arterial tissues. Collagen orientation patterns did not change with implantation time, and biochemical analyses showed no changes in the trend of collagen and elastin content with implantation time or location of the vascular wall. We hypothesize that the collagen fibers on the adventitial side of the arterial wall and behind the stent straighten in response to the arterial stretch caused by oversizing of the stent. However, the collagen organization on the luminal side suggests that stent-induced remodeling is dominated by contact guidance.

Cutaneous collagenous vasculopathy: a new case series with clinicopathologic and ultrastructural correlation, literature review, and insight into the pathogenesis

Cutaneous collagenous vasculopathy (CCV) is a rare distinct idiopathic microangiopathy of the superficial cutaneous vasculature. Seven new cases are reported (6 females and 1 male) ranging in age from 42 to 85 years, with some showing unusual clinical and histopathological findings. All presented with macular telangiectases starting on the lower extremities and spreading progressively in 5 cases and were suspected to have generalized essential telangiectasia. Two cases had a history of over 20 years. One case had lesions in the abdominal striae, and 1 was markedly ecchymotic. All skin biopsies showed the characteristic features of CCV with dilatation and marked thickening of the walls of superficial dermal blood vessels displaying reduplication of the basement membrane on periodic acid-Schiff-diastase stain and deposition of hyaline collagenous material immunostaining as collagen type IV, and showing decreased or absent actin staining. However, the changes were subtle and only seen focally in some biopsies. Few lymphoid cells were present around occasional vessels. Electron microscopy showed increased basement membrane lamellae with marked deposition of normal and some abnormal collagen (Luse-like bodies) and focal endothelial damage, suggesting reparative perivascular fibrosis resulting from repeated endothelial injury. These cases (and all 18 previously reported ones) are of a wide age range and no gender predilection. This disorder is underdiagnosed, and it is likely that some cases clinically suspected to be generalized essential telangiectasia may actually represent CCV. Better recognition by dermatologists may lead to more biopsies from patients with generalized telangiectasia and a further understanding of the pathogenesis of CCV and its relationship to other cutaneous vascular disorders.

Absolute polarity determination of teeth cementum by phase sensitive second harmonic generation microscopy

The absolute sign of local polarity in relation to the biological growth direction has been investigated for teeth cementum using phase sensitive second harmonic generation microscopy (PS-SHGM) and a crystal of 2-cyclooctylamino-5-nitropyridine (COANP) as a nonlinear optic (NLO) reference material. A second harmonic generation (SHG) response was found in two directions of cementum: radial (acellular extrinsic fibers that are oriented more or less perpendicular to the root surface) and circumferential (cellular intrinsic fibers that are oriented more or less parallel to the surface). A mono-polar state was demonstrated for acellular extrinsic cementum. However, along the different parts of cementum in circumferential direction, two corresponding domains were observed featuring an opposite sign of polarity indicative for a bi-polar microscopic state of cellular intrinsic cementum. The phase information showed that the orientation of radial collagen fibrils of cementum is regularly organized with the donor (D) groups pointing to the surface. Circumferential collagen molecules feature orientational disorder and are oriented up and down in random manner showing acceptor or donor groups at the surface of cementum. Considering that the cementum continues to grow in thickness throughout life, we can conclude that the cementum is growing circumferentially in two opposite directions and radially in one direction. A Markov chain type model for polarity formation in the direction of growth predicts D-groups preferably appearing at the fiber front.

Characterization of collagen fibrils after equine suspensory ligament injury: an ultrastructural and biochemical approach

Suspensory ligament (SL) injuries are an important cause of lameness in horses. The mechanical properties of connective tissue in normal and pathological ligaments are mainly related to fibril morphology, as well as collagen content and types. The purpose of this study was to evaluate, using biochemical and ultrastructural approaches, the alterations in collagen fibrils after injury. Eight Warmblood horses with visible signs of injury in only one forelimb SL were selected and specimens were examined by transmission electron microscope (TEM). Collagen types I, III and V were purified by differential salt precipitation after collagen extraction with acetic acid containing pepsin. TEM revealed abnormal organization as well as alterations in the diameter and shape of fibrils after SL injury. The bands corresponding to types I, III and V collagen were assessed by densitometry after sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Densitometric analysis indicated that the proportions of type III and type V collagen were higher (P < 0.001) in damaged tissues compared with normal tissues with a mean increase of 20.9% and 17.3%, respectively. Concurrently, a decrease (P < 0.001) in type I collagen within damaged tissues was recorded with a mean decrease of 15.2%. These alterations could be the hallmark of a decrease in the tissue quality and mechanical properties of the ligament. The findings provide new insight for subsequent research on tissue regeneration that may lead to the development of future treatment strategies for SL injury.

Imaging collagen type I fibrillogenesis with high spatiotemporal resolution

Fibrillar collagens, such as collagen type I, belong to the most abundant extracellular matrix proteins and they have received much attention over the last five decades due to their large interactome, complex hierarchical structure and high mechanical stability. Nevertheless, the collagen self-assembly process is still incompletely understood. Determining the real-time kinetics of collagen type I formation is therefore pivotal for better understanding of collagen type I structure and function, but visualising the dynamic self-assembly process of collagen I on the molecular scale requires imaging techniques offering high spatiotemporal resolution. Fast and high-speed scanning atomic force microscopes (AFM) provide the means to study such processes on the timescale of seconds under near-physiological conditions. In this study we have applied fast AFM tip scanning to study the assembly kinetics of fibrillar collagen type I nanomatrices with a temporal resolution reaching eight seconds for a frame size of 500 nm. By modifying the buffer composition and pH value, the kinetics of collagen fibrillogenesis can be adjusted for optimal analysis by fast AFM scanning. We furthermore show that amplitude-modulation imaging can be successfully applied to extract additional structural information from collagen samples even at high scan rates. Fast AFM scanning with controlled amplitude modulation therefore provides a versatile platform for studying dynamic collagen self-assembly processes at high resolution.

Multimodal optical characterisation of collagen photodegradation by femtosecond infrared laser ablation

Collagen is a structural component of the human body, as a connective tissue it can become altered as a result of pathophysiological conditions. Although the collagen degradation mechanism is not fully understood, it plays an important role in ageing, disease progression and applications in therapeutic laser treatments. To fully understand the mechanism of collagen alteration, in our study photo-disruptive effects were induced in collagen I matrix by point-irradiation with a femtosecond Ti-sapphire laser under controlled laser ablation settings. This was followed by multi-modal imaging of the irradiated and surrounding areas to analyse the degradation mechanism. Our multi-modal methodology was based on second harmonic generation (SHG), scanning electron microscope (SEM), autofluorescence (AF) average intensities and the average fluorescence lifetime. This allowed us to quantitatively characterise the degraded area into four distinct zones: (1) depolymerised zone in the laser focal spot as indicated by the loss of SHG signal, (2) enhanced crosslinking zone in the inner boundary of the laser induced cavity as represented by the high fluorescence ring, (3) reduced crosslinking zone formed the outer boundary of the cavity as marked by the increased SHG signal and (4) native collagen. These identified distinct zones were in good agreement with the expected photochemical changes shown using Raman spectroscopy. In addition, imaging using polarisation-resolved SHG (p-SHG) revealed both a high degree of fibre re-orientation and a SHG change in tensor ratios around the irradiation spot. Our multi-modal optical imaging approach can provide a new methodology for defining distinct zones that can be used in a clinical setting to determine suitable thresholds for applying safe laser treatments without affecting the surrounding tissues. Furthermore this technique can be extended to address challenges observed in collagen based tissue engineering and used as a minimally invasive diagnostic tool to characterise diseased and non-diseased collagen rich tissues.

Effect of tear size, corticosteroids and subacromial decompression surgery on the hierarchical structural properties of torn supraspinatus tendons

OBJECTIVES

The effects of disease progression and common tendinopathy treatments on the tissue characteristics of human rotator cuff tendons have not previously been evaluated in detail owing to a lack of suitable sampling techniques. This study evaluated the structural characteristics of torn human supraspinatus tendons across the full disease spectrum, and the short-term effects of subacromial corticosteroid injections (SCIs) and subacromial decompression (SAD) surgery on these structural characteristics.

METHODS

Samples were collected inter-operatively from supraspinatus tendons containing small, medium, large and massive full thickness tears (n = 33). Using a novel minimally invasive biopsy technique, paired samples were also collected from supraspinatus tendons containing partial thickness tears either before and seven weeks after subacromial SCI (n = 11), or before and seven weeks after SAD surgery (n = 14). Macroscopically normal subscapularis tendons of older patients (n = 5, mean age = 74.6 years) and supraspinatus tendons of younger patients (n = 16, mean age = 23.3) served as controls. Ultra- and micro-structural characteristics were assessed using atomic force microscopy and polarised light microscopy respectively.

RESULTS

Significant structural differences existed between torn and control groups. Differences were identifiable early in the disease spectrum, and increased with increasing tear size. Neither SCI nor SAD surgery altered the structural properties of partially torn tendons seven weeks after treatment.

CONCLUSIONS

These findings may suggest the need for early clinical intervention strategies for torn rotator cuff tendons in order to prevent further degeneration of the tissue as tear size increases. Further work is required to establish the long-term abilities of SCI and SAD to prevent, and even reverse, such degeneration. Cite this article: Bone Joint Res 2014;3:252-61.

Convergence of nanotechnology and cancer prevention: are we there yet?

Nanotechnology is emerging as a promising modality for cancer treatment; however, in the realm of cancer prevention, its full utility has yet to be determined. Here, we discuss the potential of integrating nanotechnology in cancer prevention to augment early diagnosis, precision targeting, and controlled release of chemopreventive agents, reduced toxicity, risk/response assessment, and personalized point-of-care monitoring. Cancer is a multistep, progressive disease; the functional and acquired characteristics of the early precancer phenotype are intrinsically different from those of a more advanced anaplastic or invasive malignancy. Therefore, applying nanotechnology to precancers is likely to be far more challenging than applying it to established disease. Frank cancers are more readily identifiable through imaging and biomarker and histopathologic assessment than their precancerous precursors. In addition, prevention subjects routinely have more rigorous intervention criteria than therapy subjects. Any nanopreventive agent developed to prevent sporadic cancers found in the general population must exhibit a very low risk of serious side effects. In contrast, a greater risk of side effects might be more acceptable in subjects at high risk for cancer. Using nanotechnology to prevent cancer is an aspirational goal, but clearly identifying the intermediate objectives and potential barriers is an essential first step in this exciting journey.

Selective modulation of cell response on engineered fractal silicon substrates

A plethora of work has been dedicated to the analysis of cell behavior on substrates with ordered topographical features. However, the natural cell microenvironment is characterized by biomechanical cues organized over multiple scales. Here, randomly rough, self-affinefractal surfaces are generated out of silicon,where roughness Ra and fractal dimension Df are independently controlled. The proliferation rates, the formation of adhesion structures, and the morphology of 3T3 murine fibroblasts are monitored over six different substrates. The proliferation rate is maximized on surfaces with moderate roughness (Ra ~ 40 nm) and large fractal dimension (Df ~ 2.4); whereas adhesion structures are wider and more stable on substrates with higher roughness (Ra ~ 50 nm) and lower fractal dimension (Df ~ 2.2). Higher proliferation occurson substrates exhibiting densely packed and sharp peaks, whereas more regular ridges favor adhesion. These results suggest that randomly roughtopographies can selectively modulate cell behavior.

Role of cytokine receptor-like factor 1 in hepatic stellate cells and fibrosis

AIM

To elucidate the role of cytokine receptor-like factor 1 (CRLF1) in hepatic stellate cells and liver fibrosis.

METHODS

Rat hepatic stellate cells (HSCs) were isolated by Nykodenz gradient centrifugation and activated by culturing in vitro. Differentially expressed genes in quiescent and culture activated HSCs were identified using microarrays. Injections of carbon tetrachloride (CCl(4)) for 4 wk were employed to induce liver fibrosis. The degree of fibrosis was assessed by Sirius red staining. Adenovirus expressing CRLF1 was injected through tail vein into mice to achieve overexpression of CRLF1 in the liver. The same adenovirus was used to overexpress CRLF1 in quiescent HSCs cultured in vitro. Expression of CRLF1, CLCF1 and ciliary neurotrophic factor receptor (CNTFR) in hepatic stellate cells and fibrotic livers was analyzed by semi-quantitative reverse transcription-polymerase chain reaction and Western blotting. Expression of profibrotic cytokines and collagens was analyzed by the same method.

RESULTS

CRLF1 is a secreted cytokine with unknown function. Human mutations suggested a role in development of autonomous nervous system and a role of CRLF1 in immune response was implied by its similarity to interleukin (IL)-6. Here we show that expression of CRLF1 was undetectable in quiescent HSCs and was highly upregulated in activated HSCs. Likewise, expression of CRLF1 was very low in normal livers, but was highly upregulated in fibrotic livers, where its expression correlated with the degree of fibrosis. A cofactor of CLRF1, cardiotrophin-like cytokine factor 1 (CLCF1), and the receptor which binds CRLF1/CLCF1 dimer, the CNTFR, were expressed to similar levels in quiescent and activated HSCs and in normal and fibrotic livers, indicating a constitutive expression. Overexpression of CLRF1 alone in the normal liver did not stimulate expression of profibrotic cytokines, suggesting that the factor itself is not pro-inflammatory. Ectopic expression in quiescent HSCs, however, retarded their activation into myofibroblasts and specifically decreased expression of type III collagen. Inhibition of type III collagen expression by CRLF1 was also seen in the whole liver. Our results suggest that CLRF1 is the only component of the CRLF1/CLCF1/CNTFR signaling system that is inducible by a profibrotic stimulus and that activation of this system by CLRF1 may regulate expression of type III collagen in fibrosis.

CONCLUSION

By regulating activation of HSCs and expression of type III collagen, CRLF1 may have an ability to change the composition of extracellular matrix in fibrosis.

Effect of processing methods for transmission electron microscopy on corneal collagen fibrils diameter and spacing

INTRODUCTION

The corneal tissue was processed in fixatives and embedded in resin for transmission electron microscopy to observe the ultrastructure of the collagen fibrils (CFs). The effect of these processing methods on the CF diameter and the interfibrillar spacing was studied.

METHODS

Four normal human corneal buttons were used for this study. A part of each cornea was fixed in 2.5% glutaraldehyde containing cuprolinic blue in sodium acetate buffer and embedded in spurr's resin (SpurrCB). A second part of each cornea was fixed in 2.5% glutaraldehyde + osmium tetroxide and embedded spurr's resin (SpurrOsm). The third part of each cornea was fixed in paraformaldehyde (4%) and embedded in LR White at 4°C (LRWhite). Ultrathin sections were stained with uranyl acetate and lead citrate.

RESULTS

In the tissue, fixed in SpurrCB, the diameter was 38.4 ± 5.9 nm and spacing between CF was 52.5 ± 5.3 nm. In the tissue fixed in SpurrOsm, the diameter was 28.37 ± 5.84 nm and spacing between CF was 45 ± 4.57 nm. In the tissue fixed in LR White, the CF diameter was 24 ± 2.3 nm and spacing between CF was 39.0 ± 4.2 nm. The diameters and interfibrillar spacing of the tissue processed by SpurrCB, SpurrOsm, and LRWhite were significantly different (P < 0.001) from one another.

CONCLUSION

Our study shows that there is a variation in the CF diameter and spacing depending on the method of fixation and embedding resins used. This needs to be considered when comparative studies using different methods are done.

Prostaglandins in cancer cell adhesion, migration, and invasion

Prostaglandins exert a profound influence over the adhesive, migratory, and invasive behavior of cells during the development and progression of cancer. Cyclooxygenase-2 (COX-2) and microsomal prostaglandin E₂ synthase-1 (mPGES-1) are upregulated in inflammation and cancer. This results in the production of prostaglandin E₂ (PGE₂), which binds to and activates G-protein-coupled prostaglandin E_1–4 receptors (EP_1–4). Selectively targeting the COX-2/mPGES-1/PGE₂/EP_1–4 axis of the prostaglandin pathway can reduce the adhesion, migration, invasion, and angiogenesis. Once stimulated by prostaglandins, cadherin adhesive connections between epithelial or endothelial cells are lost. This enables cells to invade through the underlying basement membrane and extracellular matrix (ECM). Interactions with the ECM are mediated by cell surface integrins by “outside-in signaling” through Src and focal adhesion kinase (FAK) and/or “inside-out signaling” through talins and kindlins. Combining the use of COX-2/mPGES-1/PGE₂/EP_1–4 axis-targeted molecules with those targeting cell surface adhesion receptors or their downstream signaling molecules may enhance cancer therapy.

Spectroscopic and histological evaluation of wound healing progression following Low Level Laser Therapy (LLLT)

The present study focuses on the evaluation of the effect of He-Ne laser on tissue regeneration by monitoring collagen synthesis in wound granulation tissues in Swiss albino mice using analysis of laser induced fluorescence (LIF) and light microscopy techniques. The spectral analyses of the wound granulation tissues have indicated a dose dependent increase in collagen levels during the post-wounding days. The histological examinations on the other hand have also shown a significant increase in collagen deposition along with the reduced edema, leukocytes, increased granulation tissue, and fibroblast number in the optimal laser dose treated group compared to the non-illuminated controls.

Assessment of collagen fibril spacing in relation to selected region of interest (ROI) on electron micrographs--application to the mammalian corneal stroma

AIMS

To evaluate measurements of collagen fibril spacing using different shaped regions of interest (ROI) on transmission electron micrograph (TEM) images of rabbit corneal stroma.

METHODS

Following glutaraldehyde fixation and phosphotungstic acid staining, TEM images of collagen fibrils in cross section were projected at a final magnification close to 250,000 × to obtain overlays. Interfibril distances (IFDs; center-to-center spacing) were measured within different ROIs of the same nominal area (0.25 μm(2) ) but different shape (with the length to width, L:W, ratio from 1:1 to 6:1). The IFD distribution was analyzed, and the 2D organization assessed using a radial distribution analysis.

RESULTS

The fibrils had an average diameter of 35.3 ± 3.8 (SD) nm, packing density of 393 ± 4 fibrils / μm(2) and a fibril volume fraction of 0.39 ± 0.02. IFDs ranged from 29 to 1400 nm depending on the shape of the ROI, with average values ranging from 263 to 443 nm. By artificially selecting IFD data only to a radial distance of 250 nm, the average IFDs were just 145-157 nm. The radial distributions, to 250 nm, all showed a nearest neighbors first peak which shifted slightly from predominantly at 45-54 nm with more rectangular ROIs. The radial distribution profiles could be shown to be statistically different if the ROI L:W ratio was 2:1 or greater.

CONCLUSION

Selection of an ROI for assessment of packing density and interfibril distances should be standardized for comparative assessments of TEMs of collagen fibrils.

Structural changes in mixed Col I/Col V collagen gels probed by SHG microscopy: implications for probing stromal alterations in human breast cancer

Second Harmonic Generation (SHG) microscopy has been previously used to describe the morphology of collagen in the extracellular matrix (ECM) in different stages of invasion in breast cancer. Here this concept is extended by using SHG to provide quantitative discrimination of self-assembled collagen gels, consisting of mixtures of type I (Col I) and type V (Col V) isoforms which serve as models of changes in the ECM during invasion in vivo. To investigate if SHG is sensitive to changes due to Col V incorporation into Col I fibrils, gels were prepared with 0-20% Col V with the balance consisting of Col I. Using the metrics of SHG intensity, fiber length, emission directionality, and depth-dependent intensities, we found similar responses for gels comprised of 100% Col I, and 95% Col I/5% Col V, where these metrics were all significantly different from those of the 80% Col I/20% Col V gels. Specifically, the gels of lower Col V content produce brighter SHG, are characterized by longer fibers, and have a higher forward/backward emission ratio. These attributes are all consistent with more highly organized collagen fibrils/fibers and are in agreement with previous TEM characterization as well as predictions based on phase matching considerations. These results suggest that SHG can be developed to discriminate Col I/Col V composition in tissues to characterize and follow breast cancer invasion.

Morphometric analysis of human sciatic nerve perineurial collagen type IV content

OBJECTIVES

Aging is the process which unavoidably alters structure and function of the basal membranes in humans. Though, collagen type IV presents the most prominent component of the basal membranes, we estimated its presence in the perineurium of the human sciatic nerve samples during the aging process.

MATERIALS AND METHODS

Material was 12 sciatic nerve samples, obtained from cadavers whose age ranged from 36 to 84 years. Cadavers were classified into three age groups: first which age ranged from 35 to 54 years, second which age ranged from 55 to 74 years and third which included cases older than 75 years. Tissue slices were further stained by labeled streptavidin-biotin method with collagen type IV monoclonal antibody and analyzed with light microscope under 100× lens magnification with oil immersion. Digital images of sciatic nerve perineurium were further processed and analyzed with ImageJ software.

RESULTS

Our results showed that there is statistically significant increase of perineurial area, perimeter, collagen type IV area, and collagen type IV area per perineurial perimeter unit in the third age group. These parameters also increased in the second age group, but this increase was not significant. Multiple regression analysis showed that beside fascicular size, age more significantly predict perineurial collagen type IV content.

CONCLUSIONS

Results of morphometric and statistical analysis pointed to the conclusion that there is significant increase of sciatic nerve perineurial thickness during the aging process. This increase might represent the consequence of perineurial collagen type IV deposition with aging.

Stromal Elements for Tumor Diagnosis: A Brief Review of Diagnostic Electron Microscopic Features

Tumor diagnosis mainly depends on the appearance of the tumor cells in recapitulating the appearance of primordial cells from which they arise. However, certain tumors may present with specific stromal changes that may assist/enhance the diagnosis. In this presentation, diagnostic stromal features have been reviewed. The cytoplasm is enclosed by a unit membrane, which serves as a barrier to, as well as an interface with, surrounding structures. Epithelial cells usually show characteristic basal-apical orientation. In mesenchymal tissue, different types of interface can be found in different types of mesenchymal tissue. External lamina can be defined as an anatomic structure, which encloses anatomic functional units. In epithelial tissue, cells in a functional unit are enclosed within a well-defined external lamina (EL). In malignant epithelial tumors, EL can become increasingly indistinct as tumors become less differentiated, and one has to look for it diligently. Within the external lamina, epithelial cells are closely packed with closely apposed cell membranes and cell attachment junctions. In contrast to epithelial tissue, mesenchymal tissue is usually characterized by the stromal elements they produce. Individual cells are embedded in the stroma, and individual mesenchymal cells represent the functional unit. Vascular endothelial cells are an exception since their relationship to stroma resembles to that of epithelial cells. Thus, tumors deriving from mesenchymal cells known to have external lamina such as muscle cells and Schwann cells tend to show total enclosure of cells by external lamina. In malignant muscle tumors, external lamina production can be focally present and found only by diligent search. In Schwann cell tumors, the presence of EL is prominent in low-grade tumors and more irregular and variable in malignant tumors. In the latter, stromal aggregation of scrolls of external lamina can be characteristic. Similar features are seen in ossifying fibromyxoid tumors. Fibronexus junctions (composed of extracellular fibronectin fillements linking intracellular 5-nm filaments) is claimed to be typical of myofbroblasts. Finding them in spindle cell tumors justifies a diagnosis of myofibroblastomas. There have been several stromal changes diagnostic for certain tumors found only by electron microscopy. Fibrous long-spaced collagen (known as Luse bodies) is diagnostic for peripheral nerve sheath tumors, but they can rarely be found in other tumors. Luse bodies usually appear as focally as crystallized aggregates apart from the regular collagenous interstitial stroma. They should be distinguished from other nonspecific long-spaced collagen changes. The changes are diffusely stromal in contrast to Luse bodies. Spiny collagen and amianthoid fibers are interesting collagen fibrils and their diagnostic value is questionable. Skeinoid fibers (SF) are short-spaced collagen of 41- to 45-nm banding so-named because of their peculiar appearance by electron microscopy simulating skeins of yarn. They were originally described in neurogenic tumors and small intestinal stromal tumors with features of gastrointestinal autonomic nerve tumors (GANT). Although there have been a few sporadic case reports of the presence of skeinoid fibers in nonneurogenic tumors, the frequent presence of SF in spindle cell tumors signifies their neurogenic nature in this authors' experience. An exception to this is that SF can be a constant element of rare ciliary body tumors known as ciliary mesectodermal leiomyomas, in which tumor cells show some resemblance to smooth muscle as well as Schwann cells. In addition to SF, several other types of peculiar crystallized collagen were observed in GANT tumors, particularly those with multiple tumor syndromes such as neurofibromatosis and Carney's triad. They simulate the appearance of railroad tracks or centrosomes. The reason for this is not known. The authors speculate that such collagen crystallization may be caused by genetic alterations involving collagenosis. Further studies will be necessary to clarify their pathogenesis. Another peculiar stromal change is electron-dense stromal filamentous aggregates with extra-long banding of > 250-nm periodicity previously described in Ewing sarcomas. This stromal change simulating a tiger skin pattern is also seen in primitive neuroectodermal tumors and malignant melanomas. In view of continually new discoveries of stromal changes that can be used for the differential diagnosis of tumors, the importance of close evaluation of stromal elements of tumors, and diligent application of electron microscopy in tumor diagnosis cannot be overemphasized.

Bruch's membrane changes in transgenic mice overexpressing the human biglycan and apolipoprotein b-100 genes

Age-Related Macular Degeneration (AMD) is characterized by the accumulation of lipid- and protein-rich deposits in Bruch's Membrane (BrM). A consequent decrease in hydraulic conductivity and impairment of transport through BrM may play a central role in the pathogenesis of AMD. The mechanism of deposit formation in AMD had been suggested to show similarities to the formation of atherosclerotic plaques in which the interactions of extracellular matrix proteoglycans with apolipoprotein-B 100 (apoB-100) play an important role. A prime candidate for this interaction is the small leucin-rich proteoglycan biglycan. The aim of our study was to test the effect of the simultaneous overexpression of human apoB-100 and biglycan genes in combination with a high-cholesterol diet on BrM morphology in transgenic mice. Six-weeks-old homozygous apoB-100 or biglycan, hemizygous apoB-100/biglycan transgenic and wild-type C57Bl/6 mice were fed either a standard chow or a diet supplemented with 2% cholesterol for 17 weeks. Animals were sacrificed, serum lipid levels were measured and eyes were processed for transmission electron microscopy (TEM) according to standard protocol. Morphometric analysis of digitally acquired TEM images of BrM showed that in apoB-100 and double transgenic animals fed a high-cholesterol diet, the BrM thickness was significantly increased compared to wild-type animals. Both groups had electron-lucent profiles in clusters, scattered throughout the collagenous layers of BrM, and focal nodules of an amorphous material of intermediate electron-density between the plasma and basement membranes of the retinal pigment epithelium (RPE). BrM thickness in these two groups correlated well with elevated cholesterol levels. Unexpectedly, animals overexpressing biglycan alone showed a marked, diet-independent increase in BrM thickness associated with a layer of a basement membrane-like material in outer BrM. The effects of biglycan overexpression are intriguing and further investigations are needed to elucidate the underlying mechanisms.

Quantification of the second-order nonlinear susceptibility of collagen I using a laser scanning microscope

Characteristic changes in the organization of fibrillar collagen can potentially serve as an early diagnostic marker in various pathological processes. Tissue types containing collagen I can be probed by pulsed high-intensity laser radiation, thereby generating second harmonic light that provides information about the composition and structure at a microscopic level. A technique was developed to determine the essential second harmonic generation (SHG) parameters in a laser scanning microscope setup. A rat-tail tendon frozen section was rotated in the xy-plane with the pulsed laser light propagating along the z-axis. By analyzing the generated second harmonic light in the forward direction with parallel and crossed polarizer relative to the polarization of the excitation laser beam, the second-order nonlinear optical susceptibilities of the collagen fiber were determined. Systematic variations in SHG response between ordered and less ordered structures were recorded and evaluated. A 500 microm-thick z-cut lithiumniobate (LiNbO(3)) was used as reference. The method was applied on frozen sections of malignant melanoma and normal skin tissue. Significant differences were found in the values of d(22), indicating that this parameter has a potential role in differentiating between normal and pathological processes.

Light scattering from collagen fiber networks: micro-optical properties of normal and neoplastic stroma

Development of epithelial precancer and cancer leads to well-documented molecular and structural changes in the epithelium. Recently, it has been recognized that stromal biology is also altered significantly with preinvasive disease. We used the finite-difference time-domain method, a popular technique in computational electromagnetics, to model light scattering from heterogeneous collagen fiber networks and to analyze how neoplastic changes alter stromal scattering properties. Three-dimensional optical images from the stroma of fresh normal and neoplastic oral-cavity biopsies were acquired using fluorescence confocal microscopy. These optical sections were then processed to create realistic three-dimensional collagen networks as model input. Image analysis revealed that the volume fraction of collagen fibers in the stroma decreases with precancer and cancer progression, and fibers tend to be shorter and more disconnected in neoplastic stroma. The finite-difference time-domain modeling results showed that neoplastic fiber networks have smaller scattering cross sections compared to normal networks. Computed scattering-phase functions indicate that high-angle scattering probabilities tend to be higher for neoplastic networks. These results provide valuable insight into the micro-optical properties of normal and neoplastic stroma. Characterization of optical signals obtained from epithelial tissues can aid in development of optical spectroscopic and imaging techniques for noninvasive monitoring of early neoplastic changes.

Dense tissue-like collagen matrices formed in cell-free conditions

A new protocol was developed to produce dense organized collagen matrices hierarchically ordered on a large scale. It consists of a two stage process: (1) the organization of a collagen solution and (2) the stabilization of the organizations by a sol-gel transition that leads to the formation of collagen fibrils. This new protocol relies on the continuous injection of an acid-soluble collagen solution into glass microchambers. It leads to extended concentration gradients of collagen, ranging from 5 to 1000 mg/ml. The self-organization of collagen solutions into a wide array of spatial organizations was investigated. The final matrices obtained by this procedure varied in concentration, structure and density. Changes in the liquid state of the samples were followed by polarized light microscopy, and the final stabilized gel states obtained after fibrillogenesis were analyzed by both light and electron microscopy. Typical organizations extended homogeneously by up to three centimetres in one direction and several hundreds of micrometers in other directions. Fibrillogenesis of collagen solutions of high and low concentrations led to fibrils spatially arranged as has been described in bone and derm, respectively. Moreover, a relationship was revealed between the collagen concentration and the aggregation of and rotational angles between lateral fibrils. These results constitute a strong base from which to further develop highly enriched collagen matrices that could lead to substitutes that mimic connective tissues. The matrices thus obtained may also be good candidates for the study of the three-dimensional migration of cells.

The TEM characterization of the lamellar structure of osteoporotic human trabecular bone

The lamellar structure of osteoporotic human trabecular bone was characterized experimentally by means of transmission electron microscopy (TEM). More specifically, the TEM was used to determine if trabecular bone exhibits similar lamellar structural motifs as cortical bone by analyzing unmineralized, mineralized and demineralized bone, and to study the influence of the osteocyte network on the lamellar structure of osteoporotic trabecular bone. Comparison with normal trabecular bone is included. This paper summarizes partial results of a larger study, which addressed the characterization of the hierarchical structure of normal versus osteoporotic human trabecular bone [Rubin, M.A., 2001. Multiscale characterization of the ultrastructure of trabecular bone in osteoporotic and normal humans and in two inbred strains of mice. MS Thesis, Georgia Institute of Technology.] at several structural scales.

Analysis of fibrous proteins from electron microscopy images

This paper considers an approach for analyzing fibrillar collagen structures from electron microscopy images. It enables the quantitative comparison between collagen structural data (electron-optical data) and chemical data. The particular objectives of the paper are to model the electron microscopy images according to the periodic structure of collagen, provide methods for extracting periodic features directly from the experimental data and propose schemes for comparing these features with the theoretical amino-acid distributions of the examined collagen tissue. Theoretical models in the form of sequence-generated histograms are used as reference for extracting and analyzing the structural unit in images from collagen fibrils. In this respect, collagen provides a valuable model system for studying the chemical basis of ultra-structure and the mechanisms of various treatments on a protein, as well as detecting the alterations in collagen fibril structure produced by a disorder. The algorithms developed in this study can be applied to any fibrous protein, provided that its amino acid sequences and structural properties are known. Several application examples are presented. The algorithmic results are compared with clinical studies as to verify the applicability and potential of the proposed methodology.

Atomic force microscopy on human trabecular bone from an old woman with osteoporotic fractures

AFM images were taken of the exterior surface of a single trabecula, extracted from a human femoral head removed during surgery for a hip fracture in an old women with former fractures. The images showed a dense structure of bundled collagen fibrils banded with 67 nm periodicity. Bundles were seen to run in parallel in layers confirming the collagen structure seen by other techniques. Single collagen fibrils were seen to cross the bundles, thus forming cross-links between neighboring bundles of collagen fibrils. Some of these crossing fibrils did not have the 67 nm band pattern and their dimensions were about half compared to the neighboring collagen fibrils. Very little mineral was found on the surface of the trabecula. An AFM image of a fracture plane was also displayed. The trabecula was extracted from a region close to the hip fracture. However, there were in this case no obvious features in the images that could be linked directly to osteoporosis, but altered collagen banding and collagen protrusions may alter mechanical competence. A path to extensive studies of the nanometer scale structure of bone was demonstrated.