Instability of myelin tubes under dehydration: Deswelling of layered cylindrical structures

Abstract

We report experimental observations of an undulational instability of myelin figures. Motivated by this, we examine theoretically the deformation and possible instability of concentric, cylindrical, multi-lamellar membrane structures. Under conditions of osmotic stress (swelling or dehydration), we find a stable, deformed state in which the layer deformation is given by δR ∝ r √ B A /(hB) , where BA is the area compression modulus, B is the inter-layer compression modulus, and h is the repeat distance of layers. Also, above a finite threshold of dehydration (or osmotic stress), we find that the system becomes unstable to undulations, first with a characteristic wavelength of order √ ξd0, where ξ is the standard smectic penetration depth and d0 is the thickness of dehydrated region.PACS numbers: PACS numbers: 87.22. Bt, 68.15.+e The swelling of bulk phospholipid by water at a temperature higher than the chain melting temperature can lead to the growth of multilayer lipid tubules from the interface of bulk lipid and water [1,2,3,4,5]. These tubules are of mesoscopic dimensions with a diameter about 20-40 µm. They have the symmetry of a smectic-A liquid crystal and a strong optical anisotropy. Both electron microscopy [6] and X-ray diffraction show a concentric multilayer structure of these lipid tubes with a layer spacing about 60Å [7]. Due to the similarity of their structural features to those of nerve myelin sheaths, these tubules are often referred as "myelin tubes" or "myelin figures". The morphological features of myelin tubes have been classified into two steps according to the time of growth [3]. During the first step, simple tubes grow into bulk water with an initial growth rate in length about 1 µm/sec. The diameter and number of layers of tubes appear to remain constant during this process and the growth rate is inversely proportional to the square root of growth time [2,4]. The growth almost stops in the second step which is characterized by the formation of complicated morphologies of myelin tubes, such as helical and coiling forms, apparently in order to maximize their inter-membrane attraction [8].In our experiments, we have observed an instability of myelin tubes under dehydration by isolating a single myelin tube from others (during the first step, as shown in Fig. 1) and allowing the bulk water to evaporate in a controlled open chamber. During this dehydration step, periodic bumps with a wavelength about 1 µm are observed on the surface of myelin tubes as shown in Fig. 2(a). As water further evaporates, these bumps grow into arms, as shown in Figs. 2(b) and 2(c), and a similar instability can occur for these long arms. As far as we know, this is the first reported observation of the instability of myelin tubes under dehydration. After the bulk water dries out, the tubular structure of myelins disappear and a mosaic structure is observed. Although the full structural change of myelin tubes under dehydration is very complicated and highly nonlinear, the initial instability of myelin tubes under...

Coiling instabilities of multilamellar tubes

“…We expect, therefore, that there may be many instabilities of nested cylindrical stacks that lead to similar behavior. The instability resulting from decreasing the layer equilibrium distance bears some resemblence to an instability due to deswelling a myelin figure discovered by Chen, et al [17,18]. They consider myelin figures whose outer layers only have been deswelled.…”

Tension Headaches: An Investigation into Their Causes from a Naturopathic Perspective

“…When the ground substance of fascia becomes dehydrated it compromises the tissue's ability to dissipate compression forces, lubricate surrounding tissues, and transfer nutrients between capillaries and cells (Muscolino, 2011). When muscle tissue becomes dehydrated, its myelin tubes develop an undulating contracted formation, which presents as hypertonicity of the muscles and results in pain (Chen, Schmidt, Olmsted, & MacKintosh, 2001). Ensuring adequate fluid intake for the weight, age, activity level, and environment of the patient is a vital consideration in the setting of tension headache.…”

Liquid Crystals in Aqueous Ionic Surfactant Solutions: Interfacial Instabilities & Optical Applications

“…The positional order (molecular layered structure) in smectic liquid crystals has a striking influence on their interaction with ionic micellar solutions. Smectic liquid crystals in aqueous ionic micellar solutions spontaneously show the formation smectic filaments at the interface which resemble myelin figures observed in lyotropic lamellar systems [39,55,56,[143][144][145][146][147][148][149][150][151][152][153][154][155]. Detailed structural investigation of the smectic filaments is undertaken.…”