The potential of tissue engineering in orthopedics.

This article presents models of human phalanges and small joints developed by tissue engineering. Biodegradable polymer scaffolds support growth of osteoblasts, chondrocytes, and tenocytes after implantation of the models in athymic mice. The cell-polymer constructs are vascularized by the host mice, form new bone, cartilage, and tendon with characteristic gene expression and protein synthesis and secretion, and maintain the shape of human phalanges with joints. The study demonstrates critical progress in the design and fabrication of bone, cartilage, and tendon by tissue engineering and the potential of this field for human clinical orthopedic applications.

Invited Review: Role of mechanophysiology in aging of ECM: effects of changes in mechanochemical transduction.

Mechanical forces play a role in the development and evolution of extracellular matrices (ECMs) found in connective tissue. Gravitational forces acting on mammalian tissues increase the net muscle forces required for movement of vertebrates. As body mass increases during development, musculoskeletal tissues and other ECMs are able to adapt their size to meet the increased mechanical requirements. However, the control mechanisms that allow for rapid growth in tissue size during development are altered during maturation and aging. The purpose of this mini-review is to examine the relationship between mechanical loading and cellular events that are associated with downregulation of mechanochemical transduction, which appears to contribute to aging of connective tissue. These changes result from decreases in growth factor and hormone levels, as well as decreased activation of the phosphorelay system that controls cell division, gene expression, and protein synthesis. Studies pertaining to the interactions among mechanical forces, growth factors, hormones, and their receptors will better define the relationship between mechanochemical transduction processes and cellular behavior in aging tissues.

Mechanosensing and mechanochemical transduction: how is mechanical energy sensed and converted into chemical energy in an extracellular matrix?

Gravity plays a central role in vertebrate development and evolution. Gravitational forces acting on mammalian tissues cause the net muscle forces required for locomotion to be higher on earth than on a body subjected to a microgravitational field. As body mass increases during development, the musculoskeleton must be able to adapt by increasing the size of its functional units. Thus mechanical forces required to do the work (mechanical energy) of locomotion must be sensed by cells and converted into chemical energy (synthesis of new tissue). Extracellular matrices (ECMs) are multicomponent tissues that transduce internal and external mechanical signals into changes in tissue structure and function through a process termed mechanochemical transduction. Under the influence of an external gravitational field, both mineralized and unmineralized vertebrate tissues exhibit internal tensile forces that serve to preserve a synthetic phenotype in the resident cell population. Application of additional external forces alters the balance between the external gravitational force and internal forces acting on resident cells leading to changes in the expression of genes and production of protein that ultimately may alter the exact structure and function of the extracellular matrix. Changes in the equilibrium between internal and external forces acting on ECMs and changes in mechanochemical transduction processes at the cellular level appear to be important mechanisms by which mammals adjust their needs to store, transmit, and dissipate energy that is required during development and for bodily movements. Mechanosensing is postulated to involve many different cellular and extracellular components. Mechanical forces cause direct stretching of protein-cell surface integrin binding sites that occur on all eukaryotic cells. Stress-induced conformational changes in the extracellular matrix may alter integrin structure and lead to activation of several secondary messenger pathways within the cell. Activation of these pathways leads to altered regulation of genes that synthesize and catabolize extracellular matrix proteins as well as to alterations in cell division. Another aspect by which mechanal signals are transduced involves deformation of gap junctions containing calcium-sensitive stretch receptors. Once activated, these channels trigger secondary messenger activation through pathways similar to those involved in integrin-dependent activation and allow cell-to-cell communications between cells with similar and different phenotypes. Another process by which mechanochemical transduction occurs is through the activation of ion channels in the cell membrane. Mechanical forces have been shown to alter cell membrane ion channel permeability associated with Ca(+2) and other ion fluxes. In addition, the application of mechanical forces to cells leads to the activation of growth factor and hormone receptors even in the absence of ligand binding. These are some of the mechanisms that have evolved in vertebrates by which cells respond to changes in external forces that lead to changes in tissue strcture and function.

Colorimetric-solid phase extraction method for trace level determination of arsenite in water.

This paper introduces a method for the determination of inorganic arsenite [As(III)] in water at low µg L(-1) by a sorption-photometric method known as colorimetric-solid phase extraction (C-SPE). The method relies on the selective extraction and concentration of an analyte on a reagent-impregnated SPE membrane, followed by direct detection of the extracted colored complex by a handheld diffuse reflectance spectrophotometer (DRS) operating in the visible spectral region. The well-established chemistry of the classic redox titrimetric method for molecular iodine (I(2)) standardization by arsenious oxide (As(2)O(3)) serves as the basis for this analysis. I(2), which is added to the aqueous sample in an excess with respect to the analyte, serves as a colorimetric indicator. The arsenite-iodine reaction is rapid, allowing an exact volume of analyte solution to be immediately passed through an SPE membrane via a syringe after mixing with the indicator. An SPE membrane that is impregnated with the complexing agent poly(vinyl-pyrrolidone) (PVP) serves to complex and concentrate excess I(2) not consumed by the As(III) analyte. The amount of complexed I(2) is determined by a DRS reading directly on the membrane surface. The spectrophotometric measurement can be made in a few seconds, with a total sample workup and readout time of ∼ 1-2 min. The limit of detection (LOD) for this determination is below 10 µg L(-1). The potential effectiveness of the method for the analysis of spiked tap water and surface water is examined, and results from preliminary interference studies are described. The work herein also shows that by applying the principles of negligible depletion (ND), the analytical procedure could be simplified by eliminating the need to pass an exact volume of a sample through the impregnated membrane as long as it exceeds the predetermined minimum volume.

SERS as a bioassay platform: fundamentals, design, and applications.

Bioanalytical science is experiencing a period of unprecedented growth. Drivers behind this growth include the need to detect markers central to human and veterinary diagnostics at ever-lower levels and greater speeds. A set of parallel arguments applies to pathogens with respect to bioterrorism prevention and food and water safety. This tutorial review outlines our recent explorations on the use of surface enhanced Raman scattering (SERS) for detection of proteins, viruses, and microorganisms in heterogeneous immunoassays. It will detail the design and fabrication of the assay platform, including the capture substrate and nanoparticle-based labels. The latter, which is the cornerstone of our strategy, relies on the construction of gold nanoparticles modified with both an intrinsically strong Raman scatterer and an antibody. This labelling motif, referred to as extrinsic Raman labels (ERLs), takes advantage of the well-established signal enhancement of scatterers when coated on nanometre-sized gold particles, whereas the antibody imparts antigenic specificity. We will also examine the role of plasmon coupling between the ERLs and capture substrate, and challenges related to particle stability, nonspecific adsorption, and assay speed.

Mechanobiology of force transduction in dermal tissue.

BACKGROUND/AIMS: The influence of mechanical forces on skin has been examined since 1861 when Langer first reported the existence of lines of tension in cadaver skin. Internal tension in the dermis is not only passively transferred to the epidermis but also gives rise to active cell-extracellular matrix and cell-cell mechanical interactions that may be an important part of the homeostatic processes that are involved in normal skin metabolism. The purpose of this review is to analyse how internal and external mechanical loads are applied at the macromolecular and cellular levels in the epidermis and dermis. METHODS: A review of the literature suggests that internal and external forces applied to dermal cells appear to be involved in mechanochemical transduction processes involving both cell-cell and cell-extra-cellular matrix (ECM) interactions. Internal forces present in dermis are the result of passive tension that is incorporated into the collagen fiber network during development. Active tension generated by fibroblasts involves specific interactions between cell membrane integrins and macromolecules found in the ECM, especially collagen fibrils. Forces appear to be transduced at the cell-ECM interface via re-arrangement of cytoskeletal elements, activation of stretch-induced changes in ion channels, cell contraction at adherens junctions, activation of cell membrane-associated secondary messenger pathways and through growth factor-like activities that influence cellular proliferation and protein synthesis. CONCLUSIONS: Internal and external mechanical loading appears to affect skin biology through mechanochemical transduction processes. Further studies are needed to understand how mechanical forces, energy storage and conversion of mechanical energy into changes in chemical potential of small and large macromolecules may occur and influence the metabolism of dermal cells.