Effect of type 2 diabetes mellitus on the microstructural, compositional and mechanical properties of cartilages.

BACKGROUND: Osteoarthritis (OA) is a chronic and complicated degenerative disorder of joints, including several phenotypes. Type 2 diabetes mellitus (T2DM) is one of the major causes of OA. However, few studies on the mechanical behavior of diabetic cartilages have been conducted. METHODS: This study evaluated the microstructural, compositional, and mechanical properties of healthy and diabetic rat cartilages using scanning electronic microscopy, X-ray energy spectroscopy, histology staining, and microindentation tests. RESULTS: Our results indicated that the diabetic cartilages had a significantly higher elastic modulus and similar permeability (95%CI: 3.72-8.56 MPa and 3.16×10-6-1.83×10-5 mm4/N·s) compared to the healthy cartilages (95%CI: 0.741-3.58 MPa and 3.15×10-6-1.14×10-5 mm4/N·s). Their stress relaxation behaviors were similar regardless of the loading rate except for the stretching parameter under the fast loading. Furthermore, the stress relaxation behaviors of the diabetic cartilages were significantly affected by the loading rate, especially the equilibrium force ratio and time constant. These mechanical outcomes could be attributed to the increase of fibril diameters and calcium aggregation in the cartilage. CONCLUSIONS: This study deepens our understanding of how T2DM might facilitate OA in cartilages, which could contribute to the development of more scientific diagnosis and therapies for patients with diabetes.

Treatment of skeletal and non-skeletal alterations of Mucopolysaccharidosis type IVA by AAV-mediated gene therapy.

Mucopolysaccharidosis type IVA (MPSIVA) or Morquio A disease, a lysosomal storage disorder, is caused by N-acetylgalactosamine-6-sulfate sulfatase (GALNS) deficiency, resulting in keratan sulfate (KS) and chondroitin-6-sulfate accumulation. Patients develop severe skeletal dysplasia, early cartilage deterioration and life-threatening heart and tracheal complications. There is no cure and enzyme replacement therapy cannot correct skeletal abnormalities. Here, using CRISPR/Cas9 technology, we generate the first MPSIVA rat model recapitulating all skeletal and non-skeletal alterations experienced by patients. Treatment of MPSIVA rats with adeno-associated viral vector serotype 9 encoding Galns (AAV9-Galns) results in widespread transduction of bones, cartilage and peripheral tissues. This led to long-term (1 year) increase of GALNS activity and whole-body correction of KS levels, thus preventing body size reduction and severe alterations of bones, teeth, joints, trachea and heart. This study demonstrates the potential of AAV9-Galns gene therapy to correct the disabling MPSIVA pathology, providing strong rationale for future clinical translation to MPSIVA patients.

Chondrogenesis of human amniotic fluid stem cells in Chitosan-Xanthan scaffold for cartilage tissue engineering.

Articular chondral lesions, caused either by trauma or chronic cartilage diseases such as osteoarthritis, present very low ability to self-regenerate. Thus, their current management is basically symptomatic, progressing very often to invasive procedures or even arthroplasties. The use of amniotic fluid stem cells (AFSCs), due to their multipotentiality and plasticity, associated with scaffolds, is a promising alternative for the reconstruction of articular cartilage. Therefore, this study aimed to investigate the chondrogenic potential of AFSCs in a micromass system (high-density cell culture) under insulin-like growth factor 1 (IGF-1) stimuli, as well as to look at their potential to differentiate directly when cultured in a porous chitosan-xanthan (CX) scaffold. The experiments were performed with a CD117 positive cell population, with expression of markers (CD117, SSEA-4, Oct-4 and NANOG), selected from AFSCs, after immunomagnetic separation. The cells were cultured in both a micromass system and directly in the scaffold, in the presence of IGF-1. Differentiation to chondrocytes was confirmed by histology and by using immunohistochemistry. The construct cell-scaffold was also analyzed by scanning electron microscopy (SEM). The results demonstrated the chondrogenic potential of AFSCs cultivated directly in CX scaffolds and also in the micromass system. Such findings support and stimulate future studies using these constructs in osteoarthritic animal models.

Protein Levels and Microstructural Changes in Localized Regions of Early Cartilage Degeneration Compared with Adjacent Intact Cartilage.

OBJECTIVE: It was hypothesized that the respective protein profiles of bovine cartilage from sites of localized mild to moderate (GI to GII) degeneration versus adjacent sites of intact tissue would vary in accordance with the tissue microstructural changes associated with a pre-osteoarthritic state. METHODS: A total of 15 bovine patellae were obtained for this study. Paired samples of tissue were collected from the lateral region of each patella. If the patella contained a site of degeneration, a paired tissue set involved taking one sample each from the degenerated site and the intact tissue adjacent to it. Sufficient tissue was collected to facilitate 2 arms of investigation: microstructural imaging and proteome analysis. The microstructural analysis used a bespoke tissue preparation technique imaged with differential interference contrast optical microscopy to assess fibrillar scale destructuring and underlying bone spicule formation. An iTRAQ-based proteome analysis was performed using liquid chromatography-tandem mass spectrometry to identify the differential levels of proteins across the intact and degenerated cartilage and further, the results were validated with multiple reaction monitoring assay. RESULTS: In the healthy cartilage pairs, there was no significant variation in protein profiles between 2 adjacent sample sites. In pairs of tissue that contained a sample of GI/GII tissue, there were both significant microstructural changes as well as the difference in abundance levels of 24 proteins. CONCLUSIONS: From the known functions of the 24 proteins, found to be strongly aligned with the specific microstructural changes observed, a unique "proteins ensemble" involved in the initiation and progression of early cartilage degeneration is proposed.

The Matrilin-3 T298M mutation predisposes for post-traumatic osteoarthritis in a knock-in mouse model.

OBJECTIVE: The human matrilin-3 T303M (in mouse T298M) mutation has been proposed to predispose for osteoarthritis, but due to the lack of an appropriate animal model this hypothesis could not be tested. This study was carried out to identify pathogenic mechanisms in a transgenic mouse line by which the mutation might contribute to disease development. METHODS: A mouse line carrying the T298M point mutation in the Matn3 locus was generated and features of skeletal development in ageing animals were characterized by immunohistology, micro computed tomography, transmission electron microscopy and atomic force microscopy. The effect of transgenic matrilin-3 was also studied after surgically induced osteoarthritis. RESULTS: The matrilin-3 T298M mutation influences endochondral ossification and leads to larger cartilage collagen fibril diameters. This in turn leads to an increased compressive stiffness of the articular cartilage, which, upon challenge, aggravates osteoarthritis development. CONCLUSIONS: The mouse matrilin-3 T298M mutation causes a predisposition for post-traumatic osteoarthritis and the corresponding knock-in mouse line therefore represents a valid model for investigating the pathogenic mechanisms involved in osteoarthritis development.

Structure and mechanical properties of high-weight-bearing and low-weight-bearing areas of hip cartilage at the micro- and nano-levels.

BACKGROUND: Articular cartilage has a high-weight-bearing area and a low-weight-bearing area, the macroscopic elastic moduli of the two regions are different. Chondrocytes are affected by the applied force at the microscopic level. Currently, the modulus of the two areas at the micro and nano levels is unknown, and studies on the relationship between macro-, micro- and nano-scale elastic moduli are limited. Such information may be important for further understanding of cartilage mechanics. Moreover, the surface morphology, proteoglycan content, and micro and nano structure of the two areas, which influences the mechanical properties of cartilage should be discussed. METHODS: Safranin-O/Fast Green staining was used to evaluate the surface morphology and semi-quantify proteoglycan content of porcine femoral head cartilage between the two weight-bearing areas. The unconfined compression test was used to determine the macro elastic modulus. Atomic force microscope was used to measure the micro and nano compressive elastic modulus as well as the nano structure. Scanning electron microscope was employed to evaluate the micro structure. RESULTS: No significant differences in the fibrillation index were observed between two areas (P = 0.5512). The Safranin-O index of the high-weight-bearing area was significantly higher than that of the low-weight-bearing area (P = 0.0387). The compressive elastic modulus of the high-weight-bearing area at the macro and micro level was significantly higher than that of the low-weight-bearing area (P = 0.0411 for macro-scale, and P = 0.0001 for micro-scale), while no statistically significant differences were observed in the elastic modulus of collagen fibrils at the nano level (P = 0.8544). The density of the collagen fibers was significantly lower in the high-weight-bearing area (P = 0.0177). No significant differences were observed in the structure and diameter of the collagen fibers between the two areas (P = 0.7361). CONCLUSIONS: A higher proteoglycan content correlated with a higher compressive elastic modulus of the high-weight-bearing area at the micro level than that of the low-weight-bearing area, which was consistent with the trend observed from the macroscopic compressive elastic modulus. The weight-bearing level was not associated with the elastic modulus of individual collagen fibers and the diameter at the nano level. The micro structure of cartilage may influence the macro- and micro-scale elastic modulus.

Ryanodine receptor 1 mediated dexamethasone-induced chondrodysplasia in fetal rats.

BACKGROUND: Osteoarthritis is caused by cartilage dysplasia and has fetal origin. Prenatal dexamethasone exposure (PDE) induced chondrodysplasia in fetal rats by inhibiting transforming growth factor ß (TGFß) signaling. This study aimed to determine the effect of dexamethasone on fetal cartilage development and illustrate the underlying molecular mechanism. METHODS: Dexamethasone (0.2 mg/kg.d) was injected subcutaneously every morning in pregnant rats from gestational day (GD) 9 to GD21. Harvested fetal femurs and tibias at GD21 for immunofluorescence and gene expression analysis. Fetal chondrocytes were treated with dexamethasone (100, 250 and 500 nM), endoplasmic reticulum stress (ERS) inhibitor, and ryanodine receptor 1 (RYR1) antagonist for subsequent analyses. RESULTS: In vivo, prenatal dexamethasone exposure (PDE) decreased the total length of the fetal cartilage, the proportion of the proliferation area and the cell density and matrix content in fetal articular cartilage. Moreover, PDE increased RYR1 expression and intracellular calcium levels and elevated the expression of ERS-related genes, while downregulated the TGFß signaling pathway and extracellular matrix (ECM) synthesis in fetal chondrocytes. In vitro, we verified dexamethasone significantly decreased ECM synthesis through activating RYR 1 mediated-ERS. CONCLUSIONS: PDE inhibited TGFß signaling pathway and matrix synthesis through RYR1 / intracellular calcium mediated ERS, which ultimately led to fetal dysplasia. This study confirmed the molecular mechanism of ERS involved in the developmental toxicity of dexamethasone and suggested that RYR1 may be an early intervention target for fetal-derived adult osteoarthritis.

Metformin pretreatment suppresses alterations to the articular cartilage ultrastructure and knee joint tissue damage secondary to type 2 diabetes mellitus in rats.

Osteoarthritis (OA) secondary to diabetes affects millions of people worldwide and can lead to disability. The protective effect of metformin pretreatment against alterations to the articular cartilage ultrastructure induced by type 2 diabetes mellitus (T2DM) associated with the inhibition of oxidative stress and inflammation has not been investigated before. Therefore, we induced T2DM in rats (the model group) using high carbohydrate and fat diet and a single injection of streptozotocin (50 mg/kg body weight). The protective group of rats started metformin (200 mg/kg body weight) treatment 14 days before diabetic induction and continued on metformin until the end of the experiment at week 12. Harvested tissues obtained from knee joints were prepared for staining with hematoxylin and eosin (H&E), safranin o staining, and electron microscopy. Histology images showed that OA was developed in the T2DM rats as demonstrated by a substantial damage to the articular cartilage and profound chondrocyte and territorial matrix ultrastructural alterations, which were partially protected by metformin. In addition, metformin significantly (p < .05) reduced hyperglycemia, glycated hemoglobin (HbA1 c), malondialdehyde (MDA), high sensitivity C-reactive protein (hs-CRP), and interleukin-6 blood levels induced by diabetes. Furthermore, a significant (p ≤ 0.015) correlation between either OA cartilage grade score or the thickness of the articular cartilage and the blood levels of HbA1 c, hs-CRP, MDA, superoxide dismutase (SOD) were observed. These findings demonstrate effective protection of the articular cartilage by metformin against damage induced secondary to T2DM in rats, possibly due to the inhibition of hyperglycemia and biomarkers of oxidative stress and inflammation.

Three-dimensional architecture of the acetabular labrum in the human hip joint.

The acetabular labrum is frequently damaged with advancing age. As collagen fibers are the main sources of strength, knowledge of their ultrastructure is important to determine the cause of age-induced changes. We aimed to investigate the ultrastructure of collagen fibers constituting the acetabular labrum using scanning electron microscopy (SEM). Acetabular labrum samples obtained during total hip arthroplasty were studied. The samples were specially prepared to observe the steric construction of collagen fibrils constituting the acetabular labrum under light microscopy followed by SEM. The acetabular labrum was mostly composed of cartilage tissue, consisting of chondrocytes and collagen type II, with a layer of collagen type I. In adults, chondrocytes with a rich cytoplasm were surrounded by a dense network of fine type II collagen fibrils, and small bundles of type I collagen fibrils were interposed in the cartilage layer. In elderly individuals, the chondrocytes atrophied and both type I and II collagen fibrils were sparse. We suggest that cartilage has three to five layers, consisting of type I and type II collagen fibrils with a solid cartilage substrate. In elderly individuals, the density of chondrocytes decreases and the cellular shape and architecture of collagen fibrils also changes.

Full-Scale Osteochondral Regeneration by Sole Graft of Tissue-Engineered Hyaline Cartilage without Co-Engraftment of Subchondral Bone Substitute.

In this study, full-scale osteochondral defects are hypothesized, which penetrate the articular cartilage layer and invade into subchondral bones, and can be fixed by sole graft of tissue-engineered hyaline cartilage without co-engraftment of any subchondral bone substitute. It is hypothesized that given a finely regenerated articular cartilage shielding on top, the restoration of subchondral bones can be fulfilled via spontaneous self-remodeling in situ. Hence, the key challenge of osteochondral regeneration lies in restoration of the non-self-regenerative articular cartilage. Here, traumatic osteochondral lesions to be repaired in rabbit knee models are endeavored using novel tissue-engineered hyaline-like cartilage grafts that are produced by 3D cultured porcine chondrocytes in vitro. Comparative trials are conducted in animal models that are implanted with living hyaline cartilage grafts (LhCG) and decellularized LhCG (dLhCG). Sound osteochondral regeneration is gradually revealed from both LhCG and dLhCG-implanted samples 50-100 d after implantation. Quality regeneration in both zones of articular cartilage and subchondral bones are validated by the restored osteochondral composition, structure, phenotype, and mechanical property, which validate the hypothesis of this study.

Propagation phase-contrast micro-computed tomography allows laboratory-based three-dimensional imaging of articular cartilage down to the cellular level.

OBJECTIVE: High-resolution non-invasive three-dimensional (3D) imaging of chondrocytes in articular cartilage remains elusive. The aim of this study was to explore whether laboratory micro-computed tomography (micro-CT) permits imaging cells within articular cartilage. DESIGN: Bovine osteochondral plugs were prepared four ways: in phosphate-buffered saline (PBS) or 70% ethanol (EtOH), both with or without phosphotungstic acid (PTA) staining. Specimens were imaged with micro-CT following two protocols: 1) absorption contrast (AC) imaging 2) propagation phase-contrast (PPC) imaging. All samples were scanned in liquid. The contrast to noise ratio (C/N) of cellular features quantified scan quality and were statistically analysed. Cellular features resolved by micro-CT were validated by standard histology. RESULTS: The highest quality images were obtained using propagation phase-contrast imaging and PTA-staining in 70% EtOH. Cellular features were also visualised when stained in PBS and unstained in EtOH. Under all conditions PPC resulted in greater contrast than AC (p < 0.0001 to p = 0.038). Simultaneous imaging of cartilage and subchondral bone did not impede image quality. Corresponding features were located in both histology and micro-CT and followed the same distribution with similar density and roundness values. CONCLUSIONS: Three-dimensional visualisation and quantification of the chondrocyte population within articular cartilage can be achieved across a field of view of several millimetres using laboratory-based micro-CT. The ability to map chondrocytes in 3D opens possibilities for research in fields from skeletal development through to medical device design and treatment of cartilage degeneration.

Bioinspired Hyaluronic Acid/Phosphorylcholine Polymer with Enhanced Lubrication and Anti-Inflammation.

Under pathological conditions, the joint is not well lubricated, which inevitably leads to osteoarthritis. Currently, in clinics injection of hyaluronic acid (HA) as an intra-articular viscosupplement is one of the main methods for alleviation of osteoarthritis. However, the viscosity of HA reduces dramatically under high shear rate due to the shear-thinning effect. Therefore, it is crucial to enhance the lubrication property of HA in order to treat osteoarthritis effectively. In this study, we successfully grafted 2-methacryloyloxyethyl phosphorylcholine (MPC), which is a zwitterionic biomaterial with excellent hydration lubrication, onto the HA with two different molecular weights (HAMPC) to enhance lubrication. The lubrication test performed using an atomic force microscope showed that, compared with HA, the friction coefficient of HAMPC was greatly reduced under various conditions. The in vitro test demonstrated that HAMPC was biocompatible and could upregulate cartilage anabolic genes while simultaneously downregulating cartilage catabolic proteases and pain-related genes. Importantly, high molecular weight HAMPC exhibited improved the capability to regulate these genes compared with low molecular weight HAMPC. In conclusion, the high molecular weight HAMPC developed herein, with enhanced lubrication and anti-inflammation, may be a promising polymer for the treatment of osteoarthritis.

The interplay between chondrocyte spheroids and mesenchymal stem cells boosts cartilage regeneration within a 3D natural-based hydrogel.

Articular cartilage (AC) lacks the ability to self-repair and cell-based approaches, primarily based on using chondrocytes and mesenchymal stem cells (MSCs), are emerging as effective technology to restore cartilage functionality, because cells synergic functionality may support the maintenance of chondrogenic phenotype and promote extracellular matrix regeneration. This work aims to develop a more physiologically representative co-culture system to investigate the influence of MSCs on the activity of chondrocytes. A thermo-sensitive chitosan-based hydrogel, ionically crosslinked with ß-glycerophosphate, is optimised to obtain sol/gel transition at physiological conditions within 5 minutes, high porosity with pores diameter <30 µm, and in vitro mechanical integrity with compressive and equilibrium Young's moduli of 37 kPa and 17 kPa, respectively. Live/dead staining showed that after 1 and 3 days in culture, the encapsulated MSCs into the hydrogels are viable and characterised by round-like morphology. Furthermore chondrocyte spheroids, seeded on top of gels that contained either MSCs or no cells, show that the encapsulated MSCs stimulate chondrocyte activity within a gel co-culture, both in terms of maintaining the coherence of chondrocyte spheroids, leading to a larger quantity of CD44 (by immunofluorescence) and a higher production of collagen and glycosaminoglycans (by histology) compared with the mono-culture.

Concentric lamellae - novel microanatomical structures in the articular calcified cartilage of mice.

The structure, ultrastructure and function of hyaline articular cartilage (HAC) and subchondral bone (SCB), and their involvement in the pathogenesis of osteoarthritis (OA) have been extensively researched. However, much less attention has been focused on the intervening tissue, articular calcified cartilage (ACC) and its role in the initiation and progression of OA. Using both light microscopy (LM) and transmission electron microscopy (TEM), a study of ACC in wild type (WT) mice, and mice with genetic osteoarthropathies (AKU) was undertaken to further understand the role played by ACC in the early stages of OA.Tibio-femoral joints were obtained from BALB/c WT and BALB/c AKU mice aged between 7 and 69 weeks. One joint was processed for routine histological analysis. The tip of the medial femoral condyle (MFC), which contained HAC, ACC, and SCB, was dissected from the contra-lateral joint and processed for TEM.In WT and AKU mice novel microanatomical structures, designated concentric lamellae, were identified surrounding chondrocytes in the ACC. The lamellae appeared to be laid down in association with advancement of the tidemark indicating they may be formed during calcification of cartilage matrix. The lamellae were associated with hypertrophic chondrocytes throughout the ACC.Novel microanatomical structures, termed concentric lamellae, which were present around hypertrophic chondrocytes in the ACC are described for the first time. Their apparent association with mineralisation, advancement of the tidemark, and greater abundance in a model of osteoarthropathy indicate their formation could be important in the pathogenesis of OA and AKU.

Application of confocal, SHG and atomic force microscopy for characterizing the structure of the most superficial layer of articular cartilage.

The surface of articular cartilage plays a crucial role in attenuating and transmitting mechanical loads in synovial joints to facilitate painless locomotion. Disruption to the surface of articular cartilage causes changes to its frictional properties instigating the deterioration of the tissue. In this study, we physically peeled the most superficial layer, a transparent membrane of 20.0 ± 4.7 µm thick, from the central loading region of femoral condyles of sheep. The ultrastructure of this layer without interference from the underlying cartilage was independently investigated using confocal, second harmonic generation and atomic force microscopy. We found that the most superficial layer contains chondrocytes, densely packed collagen, coarse elastic fibres and a fine elastic network. The elastic fibres are most prevalent at the surface of the layer, where collagen and chondrocyte densities are lowest. At the interface of this most superficial layer with the underlying bulk cartilage, a dense fibrillar network exists, formed mainly by collagen fibrils and elastin microfibrils. By contrast, the interface of the underlying cartilage with the most superficial layer contains collagen fibrils, fine microfibrils and microfibrils distinctively laced on one side. The findings of this study will play an important role in understanding the mechanical function and wear resistance of articular cartilage, and in developing more promising tissue engineering techniques to treat cartilage defects and osteoarthritis. LAY DESCRIPTION: The chronic pain and dysfuction in synovial joints caused by osteoarthritis can have a debilitating impact on daily activities for sufferers. Osteoarthritis is characterised by the deterioration of the articular cartilage. Despite intensive research, the wear mechanism of articular cartilage and the progression of osteoarthritis remain unclear in the literature. Articular cartilage is a resilient tissue that provides a low friction surface to facilitate painless locomotion. The surface of articular cartilage plays a crucial role in attenuating and transmitting mechanical loads. Disruption at the surface of articular cartilage causes changes to its frictional properties, instigating the deterioration of the tissue. Despite this, the definition of the most superficial layer of articular cartilage, as well as its composition and microstructure, have endured a long history of debate, clouding our understanding of the early progression of osteoarthritis. In order to investigate the surface of articular cartilage independently from the underlying cartilage, we physically peeled a transparent membrane of 20.0 ± 4.7 µm thickness, the most superficial layer, from the central loading region of the femoral condyles of sheep. Using confocal, second harmonic generation and atomic force microscopy, we found that the most superficial layer contains cartilage cells (chondrocytes), densely packed collagen, coarse elastic fibres and a fine elastic network. The coarse elastic fibres are most prevalent at the surface of the layer where collagen and chondrocyte densities are lowest. Furthermore, we investigated the surfaces at the interface of the most superficial layer with the underlying articular cartilage. At the interface of this most superficial layer with the underlying bulk cartilage, a dense fibrillar network exists, formed mainly by collagen fibrils and elastin microfibrils. In contrast, the interface of the underlying cartilage with the most superficial layer contains collagen fibrils, fine microfibrils and microfibrils distinctively laced on one side. The findings of this study have confirmed that there is a most superficial layer that is able to be removed using a tangential force. Through the application of advanced imaging technologies, we have shown that this most superficial layer is cellular and have detailed its composition and ultrastructure. Due to the close association between the form and function of tissues, the findings of this study will play an important role in understanding the mechanical function and wear mechanism of articular cartilage. This may lead to the development of more promising tissue engineering techniques to treat cartilage defects and osteoarthritis.

A comparison study of different decellularization treatments on bovine articular cartilage.

Previous researches have emphasized on suitability of decellularized tissues for regenerative applications. The decellularization of cartilage tissue has always been a challenge as the final product must be balanced in both immunogenic residue and mechanical properties. This study was designed to compare and optimize the efficacy of the most common chemical decellularization treatments on articular cartilage. Freeze/thaw cycles, trypsin, ethylenediaminetetraacetic acid (EDTA), sodium dodecyl sulfate (SDS), and Triton-X 100 were used at various concentrations and time durations for decellularization of bovine distal femoral joint cartilage samples. Histological staining, scanning electron microscopy, DNA quantification, compressive strength test, and Fourier-transform infrared spectroscopy were performed for evaluation of the decellularized cartilage samples. Treatment with 0.05% trypsin/EDTA for 1 day followed by 3% SDS for 2 days and 3% Triton X-100 for another 2 days resulted in significant reduction in DNA content and simultaneous maintenance of mechanical properties. Seeding the human adipose-derived stem cells onto the decellularized cartilage confirmed its biocompatibility. According to our findings, an optimized physiochemical decellularization method can yield in a nonimmunogenic biomechanically compatible decellularized tissue for cartilage regeneration application.

Atomic Force Microscopy on Biological Materials Related to Pathological Conditions.

Atomic force microscopy (AFM) is an easy-to-use, powerful, high-resolution microscope that allows the user to image any surface and under any aqueous condition. AFM has been used in the investigation of the structural and mechanical properties of a wide range of biological matters including biomolecules, biomaterials, cells, and tissues. It provides the capacity to acquire high-resolution images of biosamples at the nanoscale and allows at readily carrying out mechanical characterization. The capacity of AFM to image and interact with surfaces, under physiologically relevant conditions, is of great importance for realistic and accurate medical and pharmaceutical applications. The aim of this paper is to review recent trends of the use of AFM on biological materials related to health and sickness. First, we present AFM components and its different imaging modes and we continue with combined imaging and coupled AFM systems. Then, we discuss the use of AFM to nanocharacterize collagen, the major fibrous protein of the human body, which has been correlated with many pathological conditions. In the next section, AFM nanolevel surface characterization as a tool to detect possible pathological conditions such as osteoarthritis and cancer is presented. Finally, we demonstrate the use of AFM for studying other pathological conditions, such as Alzheimer's disease and human immunodeficiency virus (HIV), through the investigation of amyloid fibrils and viruses, respectively. Consequently, AFM stands out as the ideal research instrument for exploring the detection of pathological conditions even at very early stages, making it very attractive in the area of bio- and nanomedicine.

Propagation of microcracks in collagen networks of cartilage under mechanical loads.

OBJECTIVE: We recently demonstrated that low-energy mechanical impact to articular cartilage, usually considered non-injurious, can in fact cause microscale cracks (widths <30µm) in the collagen network of visually pristine human cartilage. While research on macro-scale cracks in cartilage and microcracks in bone abounds, how microcracks within cartilage initiate and propagate remains unknown. We quantified the extent to which microcracks initiate and propagate in the collagen network during mechanical loading representative of normal activities. DESIGN: We tested 76 full-thickness, cylindrical osteochondral plugs. We imaged untreated specimens (pristine phase) via second harmonic generation and assigned specimens to three low-energy impact groups (none, low, high), and thereafter to three cyclic compression groups (none, low, high) which simulate walking. We re-imaged specimens in the post-impact and post-cyclic compression phases to identify and track microcracks. RESULTS: Microcracks in the network of collagen did not present in untreated controls but did initiate and propagate under mechanical treatments. We found that the length and width of microcracks increased from post-impact to post-cyclic compression in tracked microcracks, but neither depth nor angle presented statistically significant differences. CONCLUSIONS: The microcracks we initiated under low-energy impact loading increased in length and width during subsequent cyclic compression that simulated walking. The extent of this propagation depended on the combination of impact and cyclic compression. More broadly, the initiation and propagation of microcracks may characterize pathogenesis of osteoarthritis, and may suggest therapeutic targets for future studies.

Expression of minor cartilage collagens and small leucine rich proteoglycans may be relatively reduced in osteoarthritic cartilage.

BACKGROUND: In osteoarthritis (OA), cartilage matrix is lost despite vigorous chondrocyte anabolism. In this study, we attempted to determine whether altered matrix synthesis is involved in this paradox in disease progression through gene expression analysis and ultrastructural analysis of collagen fibrils within the cartilage matrix. METHODS: Cartilage tissues were obtained from 29 end-stage OA knees and 11 control knees. First, cDNA microarray analysis was performed and the expression of 9 genes involved in collagen fibrillogenesis was compared between OA and control cartilages. Then their expression was investigated in further detail by a quantitative polymerase chain reaction (qPCR) analysis combined with laser capture microdissection. Finally, collagen fibril formation was compared between OA and control cartilage by transmission electron microscopy. RESULTS: The result of the microarray analysis suggested that the expression of type IX and type XI collagens and fibrillogenesis-related small leucine-rich proteoglycans (SLRPs) may be reduced in OA cartilage relative to the type II collagen expression. The qPCR analysis confirmed these results and further indicated that the relative reduction in the minor collagen and SLRP expression may be more obvious in degenerated areas of OA cartilage. An ultrastructural analysis suggested that thicker collagen fibrils may be formed by OA chondrocytes possibly through reduction in the minor collagen and SLRP expression. CONCLUSIONS: This may be the first study to report the possibility of altered collagen fibrillogenesis in OA cartilage. Disturbance in collagen fibril formation may be a previously unidentified mechanism underlying the loss of cartilage matrix in OA.

Effects of low-level laser therapy on the organization of articular cartilage in an experimental microcrystalline arthritis model.

The aim of this study was to evaluate the effects of low-level laser therapy using the gallium arsenide laser (λ = 830 nm) on the articular cartilage (AC) organization from knee joint in an experimental model of microcrystalline arthritis in adult male Wistar rats. Seventy-two animals were divided into three groups: A (control), B (induced arthritis), and C (induced arthritis + laser therapy). The arthritis was induced in the right knee using 2 mg of Na4P2O7 in 0.5 mL of saline solution. The treatments were daily applied in the patellar region of the right knee after 48 h of induction. On the 7th, 14th, and 21st days of treatment, the animals were euthanized and their right knees were removed and processed for structural and biochemical analysis of the AC. The chondrocytes positively labeled for the TUNEL reaction were lower in C than in B on the 14th and 21st days. The content of glycosaminoglycans and hydroxyproline in A and C was higher than B on the 21st day. The amount of tibial TNF-α in B and C was lower than in A. The amount of tibial BMP-7 in B and C was higher than in A. The femoral MMP-13 was lower in B and C than for A. The tibial TGF-ß for C was higher than the others. The femoral ADAMT-S4 content of A and C presented similar and inferior data to B on the 21st day. The AsGa-830 nm therapy preserved the content of glycosaminoglycans, reduced the cellular changes and the inflammatory process compared to the untreated group.