The application of atomic force microscopy for the detection of microcrystals in synovial fluid from patients with recurrent synovitis

Pathological calcification in osteoarthritis: an outcome or a disease initiator?

In the progression of osteoarthritis, pathological calcification in the affected joint is an important feature. The role of these crystallites in the pathogenesis and progression of osteoarthritis is controversial; it remains unclear whether they act as a disease initiator or are present as a result of joint damage. Recent studies reported that the molecular mechanisms regulating physiological calcification of skeletal tissues are similar to those regulating pathological or ectopic calcification of soft tissues. Pathological calcification takes place when the equilibrium is disrupted. Calcium phosphate crystallites are identified in most affected joints and the presence of these crystallites is closely correlated with the extent of joint destruction. These observations suggest that pathological calcification is most likely to be a disease initiator instead of an outcome of osteoarthritis progression. Inhibiting pathological crystallite deposition within joint tissues therefore represents a potential therapeutic target in the management of osteoarthritis.

Multidimensional atomic force microscopy: a versatile novel technology for nanopharmacology research

Nanotechnology is giving us a glimpse into a nascent field of nanopharmacology that deals with pharmacological phenomena at molecular scale. This review presents our perspective on the use of scanning probe microscopy techniques with special emphasis to multidimensional atomic force microscopy (m-AFM) to explore this new field with a particular emphasis to define targets, design therapeutics, and track outcomes of molecular-scale pharmacological interactions. The approach will be to first discuss operating principles of m-AFM and provide representative examples of studies to understand human health and disease at the molecular level and then to address different strategies in defining target macromolecules, screening potential drug candidates, developing and characterizing of drug delivery systems, and monitoring target–drug interactions. Finally, we will discuss some future directions including AFM tip-based parallel sensors integrated with other high-throughput technologies which could be a powerful platform for drug discovery.

Detection of calcium phosphate crystals in the joint fluid of patients with osteoarthritis - analytical approaches and challenges

Clinically, osteoarthritis (OA) is characterised by joint pain, stiffness after immobility, limitation of movement and, in many cases, the presence of basic calcium phosphate (BCP) crystals in the joint fluid. The detection of BCP crystals in the synovial fluid of patients with OA is fraught with challenges due to the submicroscopic size of BCP, the complex nature of the matrix in which they are found and the fact that other crystals can co-exist with them in cases of mixed pathology. Routine analysis of joint crystals still relies almost exclusively on the use of optical microscopy, which has limited applicability for BCP crystal identification due to limited resolution and the inherent subjectivity of the technique. The purpose of this Critical Review is to present an overview of some of the main analytical tools employed in the detection of BCP to date and the potential of emerging technologies such as atomic force microscopy (AFM) and Raman microspectroscopy for this purpose.

Multiscale mechanics of hierarchical structure/property relationships in calcified tissues and tissue/material interfaces

This paper presents a review plus new data that describes the role hierarchical nanostructural properties play in developing an understanding of the effect of scale on the material properties (chemical, elastic and electrical) of calcified tissues as well as the interfaces that form between such tissues and biomaterials. Both nanostructural and microstructural properties will be considered starting with the size and shape of the apatitic mineralites in both young and mature bovine bone. Microstructural properties for human dentin and cortical and trabecular bone will be considered. These separate sets of data will be combined mathematically to advance the effects of scale on the modeling of these tissues and the tissue/biomaterial interfaces as hierarchical material/structural composites. Interfacial structure and properties to be considered in greatest detail will be that of the dentin/adhesive (d/a) interface, which presents a clear example of examining all three material properties, (chemical, elastic and electrical). In this case, finite element modeling (FEA) was based on the actual measured values of the structure and elastic properties of the materials comprising the d/a interface; this combination provides insight into factors and mechanisms that contribute to premature failure of dental composite fillings. At present, there are more elastic property data obtained by microstructural measurements, especially high frequency ultrasonic wave propagation (UWP) and scanning acoustic microscopy (SAM) techniques. However, atomic force microscopy (AFM) and nanoindentation (NI) of cortical and trabecular bone and the dentin-enamel junction (DEJ) among others have become available allowing correlation of the nanostructural level measurements with those made on the microstructural level.

Pathogenesis of cartilage calcification: mechanisms of crystal deposition in cartilage

Apatite crystals form in physiologically calcified tissues, including the hyaline cartilage of the epiphyseal growth plate. While apatite crystals appear as unwanted deposits in other cartilage sites, more frequently, crystalline materials other than or in addition to apatite develop in dystrophic cartilage deposits. These crystalline materials include calcium pyrophosphate dihydrate and other calcium phosphate and calcium carbonate phases, monosodium urate, calcium oxalate, cholesterol, and crystallized proteins. This review describes the physical chemistry of crystal deposition and the events that occur in the growth plate as a basis for understanding the pathogenesis of nonphysiologic crystal deposition in cartilage.

Shape and size of isolated bone mineralites measured using atomic force microscopy

The inorganic phase of bone is comprised primarily of very small mineralites. The size and shape of these mineralites play fundamental roles in maintaining ionic homeostasis and in the biomechanical function of bone. Using atomic force microscopy, we have obtained direct three-dimensional visual evidence of the size and shape of native protein-free mineralites isolated from mature bovine bone. Approximately 98% of the mineralites are less than 2 nm thick displaying a plate-like habit. Distributions of both thickness and width show single peaks. The distribution of lengths may be multimodal with distinct peaks separated by approximately 6 nm. Application of our results is expected to be of use in the design of novel orthopaedic biomaterials. In addition, they provide more accurate inputs to molecular-scale models aimed at predicting the physiological and mechanical behavior of bone.

Identification of crystals in synovial fluids and joint tissues

The identification of crystals in synovial fluids and joint tissues is the most rapid and accurate method of diagnosing the common forms of crystal-associated arthritis. Although there are numerous methods available for identifying and characterizing crystals in biologic specimens including x-ray crystallography and Fourier transform infrared spectroscopy, in practice, polarizing light microscopy is used almost exclusively for articular crystals. Unfortunately, problems with reliability and reproducibility undercut the usefulness of this simple procedure. This article highlights recent developments in the field and discusses the importance of identifying synovial fluid crystals, proper handling of specimens, and the appropriate use of available technologies for crystal identification.

Atomic (scanning) force microscopy in cardiovascular research

The promise of atomic (scanning) force microscopy (AFM) for cardiovascular research is enormous. The AFM images by using a sharp cantilever tip to sense the repulsive and attractive forces between the tip and the sample surface. The force of interaction is kept constant while raster scanning, resulting in images of the surface contours with molecular and, on hard inorganic surfaces, even atomic resolution. Movement of the cantilever in the Z plane is detected by a laser beam reflected off the cantilever to a photodiode system, a piezotube allows an X and Y raster, and a three-dimensional image results. Its capabilities include: (1) the three-dimensional imaging of membranes and biomolecules with molecular and submolecular resolution; (2) such imaging not only of dry specimens but of specimens in a physiologic solution, thereby allowing the investigation of dynamic processes in both viable biomolecules and living cells; (3) the sensing of charge and intermolecular interaction forces; (4) the chemical or biochemical modification of the cantilever tip, which allows the identification of specific structures and the measurement of specific interactions (e.g., a ligand-receptor interaction); (5) nanometer control of the position and force of the cantilever, which, in turn, allows the physical manipulation of biomolecules, the dissection of biological structures (e.g., the separation of one gap junctional hemichannel from its neighbor, thereby revealing normally inaccessible surfaces), the delivery of ligands, drugs, or other materials to specific locations, and the precise measurement of interacting forces at specific sites; and (6) the modification of the apparatus by adding complementary methodologies (e.g., magnetic resonance imaging, fluorescence microscopy, confocal microscopy, and perhaps electrophysiology). AFM, however, is only now being applied to biological research, many technical and methodologic problems exist, and a number of them are considered in this review. Little work has been done in cardiovascular research and the purpose of this review is to introduce this new and exciting approach to investigation.