Experimental time series for trajectories of motile cells may contain so much information that a systematic analysis will yield cell-type-specific motility models. Here we demonstrate how, using human keratinocytes and fibroblasts as examples. The two resulting models reflect the cells' different roles in the organism, it seems, and show that a cell has a memory of past velocities. They also suggest how to distinguish quantitatively between various surfaces' compatibility with the two cell types.
Abstract. The historical co-evolution of biological motility models with models of Brownian motion is outlined. Recent results for how to derive cell-type-specific motility models from experimental cell trajectories are reviewed. Experimental work in progress, which tests the generality of this phenomenological model building is reported. So is theoretical work in progress, which explains the characteristic time scales and correlations of phenomenological models in terms of the dynamics of cytoskeleton, lamellipodia, and pseudopodia.1 The co-evolution of theories for Brownian and biological random motion Robert Brown did not discover Brownian motion.
The nanometer scale topography of self‐assembling structural protein complexes in animals is believed to induce favorable cell responses. An important example of such nanostructured biological complexes is fibrillar collagen that possesses a cross‐striation structure with a periodicity of 69 nm and a peak‐to‐valley distance of 4–6 nm. Bovine collagen type I was assembled into fibrillar structures in vitro and sedimented onto solid supports. Their structural motif was transferred into a nickel replica by physical vapor deposition of a small‐grained metal layer followed by galvanic plating. The resulting inverted nickel structure was found to faithfully present most of the micrometer and nanometer scale topography of the biological original. This nickel replica was used as a die for the injection molding of a range of different thermoplastic polymers. Total injection molding cycle times were in the range of 30–45 seconds. One of the polymer materials investigated, polyethylene, displayed poor replication of the biological nanotopographical motif. However, the majority of the polymers showed very high replication fidelity as witnessed by their ability to replicate the cross‐striation features of less than 5 nm height difference. The latter group of materials includes poly(propylene), poly(methyl methacrylate), poly(L‐lactic acid), polycaprolactone, and a copolymer of cyclic and linear olefins (COC). This work suggests that the current limiting factor for the injection molding of nanometer scale topography in thermoplastic polymers lies with the grain size of the initial metal coating of the mold rather than the polymers themselves. magnified image
Collagen I1 was isolated and characterized from hyaline cartilage (articular cartilage) and fibrocartilage (annulus fibrosus). Collagen I1 from the latter tissue has a substantially higher degree of hydroxylation and glycosylation than that isolated from articular cartilage. The higher degree of posttranslational modification was associated with a slower electrophoretic mobility, a greater resistance to mammalian collagenase digestion and a higher thermal stability. An increase of glycosylation accelerates the initial steps in fibril formation of collagen molecules but slows down the following lateral growth. The newly formed aggregates of collagen I1 from annulus fibrosus consisted of fibrils with a smaller diameter.Based on its histological appearance, cartilage is classified into three tissue entities, i. e. hyaline, elastic and fibrocartilage. Hyaline cartilage covers the articular surface of bone and supports the tracheal tubes, larynx and ventral ends of the ribs. Fibrocartilage is a transitional form between hyaline cartilage and fibrous connective tissue. It occurs in the menisci of joints, in the annulus fibrosus of intervertebral discs and in the attachment sites of tendons onto the bones [l]. Collagen, the main structural protein in both tissues, exhibits a high degree of organization based on fibrillar aggregates.Several factors have been suggested to play a role in the control of fibrillogenesis, such as the presence of proteoglycans [2], the mode of procollagen processing [3], the interaction of different collagen types [4] and non-collagenous proteins including integrins p]. Furthermore, experimental evidence showed that the posttranslational modification of collagen molecules plays a crucial role in the stability of individual molecules as well as the stabilization of collagen fibrils. Specifically, hydroxylation of prolyl residues determines the thermal stability of the triple helix of collagen molecules. Hydroxylation of lysyl residues contributes to the crosslinking of collagen molecules which, in turn, contributes to the biomechanical strength of collagen fibrils [6]. Recent circumstantial evidence provides further support that glycosylation of hydroxylysyl residues may regulate the diameter of collagen fibrils [7, 81. In this study, an approach was made to compare collagen I1 from hyaline cartilage (articular cartilage) and fibrocartilage (annulus fibrosus). The analysis showed that the collagen I1 from annulus fibrosus (AFII) has a substantially higher level of hydroxylation and glycosylation than the collagen I1 from articular cartilage (ACII). In order to clarify the influ- ence of different levels of posttranslational modification on the nature of collagen I1 molecules, their electrophoretic migration, thermal stability and susceptibility to mammalian collagenase were investigated. Additionally, we studied the impact of the varying pattern of collagen I1 modifications on the dynamics of the self-assembly and the structure of the fibrils formed in vitro. MATERIALS AND METHODS Extractio...
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