Contractile Nature Research Articles

Real‐Time Force Monitoring of Electrically Stimulated 3D‐Bioengineered Muscle Bioactuators Using Organic Sensors with Tunable Sensitivity

The contractile nature of skeletal muscle tissue makes it especially attractive for powering biohybrid actuators. Significant efforts have been dedicated to the improvement and control of contraction force, going one step forward toward the automation of these biohybrid platforms. Herein, 3D‐bioengineered skeletal muscle tissues are integrated with organic transistor‐based sensors to define a soft bioactuator with real‐time force monitoring capabilities. The muscle tissue is electrically stimulated while the organic sensor ensures transduction of the exerted force into an electrical signal that allows direct monitoring of the bioactuator performance. Sensor calibration is carried out to define its sensitivity at different biasing conditions: as opposed to standard, two‐terminal piezoresistive devices, transistor‐based strain sensors show tunable sensitivity by acting on the voltage applied to a third terminal—the gate. A complete evaluation of sensing performances is provided, demonstrating that real‐time monitoring is effective under different conditions, including stimulation signal frequency and chemical modulation of the bioactuator contraction, demonstrating its potential use as a drug testing platform. In the reported results, the way is paved for a complete exploitation of organic devices in soft robotic applications and to the development of novel biohybrid machines in bioengineering and biomedicine.

Remodeling of murine vaginal smooth muscle function with reproductive age and elastic fiber disruption

Advanced maternal age during pregnancy is associated with increased risk of vaginal tearing during delivery and maladaptive postpartum healing. Although the underlying mechanisms of age-related vaginal injuries are not fully elucidated, changes in vaginal microstructure may contribute. Smooth muscle cells promote the contractile nature of the vagina and contribute to pelvic floor stability. While menopause is associated with decreased vaginal smooth muscle content, whether contractile changes occur before the onset of menopause remains unknown. Therefore, the first objective of this study was to quantify the active mechanical behavior of the murine vagina with age. Further, aging is associated with decreased vaginal elastin content. As such, the second objective was to determine if elastic fiber disruption alters vaginal contractility. Vaginal samples from mice aged 2-14 months were used in maximum contractility experiments and biaxial extension-inflation protocols. To evaluate the role of elastic fibers with age, half of the vaginal samples were randomly allocated to enzymatic elastic fiber disruption. Contractile potential decreased and vaginal material stiffness increased with age. These age-related changes in smooth muscle function may be due, in part, to changes in microstructural composition or contractile gene expression. Furthermore, elastic fiber disruption had a diminished effect on smooth muscle contractility in older mice. This suggests a decreased functional role of elastic fibers with age. Quantifying the age-dependent mechanical contribution of smooth muscle cells and elastic fibers to vaginal properties provides a first step towards better understanding how age-related changes in vaginal structure may contribute to tissue integrity and healing. STATEMENT OF SIGNIFICANCE: Advanced maternal age at the time of pregnancy is linked to increased risks of vaginal tearing during delivery, postpartum hemorrhaging, and the development of pelvic floor disorders. While the underlying causes of increased vaginal injuries with age and associated pathologies remain unclear, changes in vaginal microstructure, such as elastic fibers and smooth muscle cells, may contribute. Menopause is associated with fragmented elastic fibers and decreased smooth muscle content; however, how reproductive aging affects changes in the vaginal composition and the mechanical properties remains unknown. Quantifying the mechanical contribution of smooth muscle cells and elastic fibers to vaginal properties with age will advance understanding of the potential structural causes of age-related changes to tissue integrity and healing.

Targeting Myofibroblasts as a Treatment Modality for Dupuytren Disease

Currently, no treatment corrects the contractile nature of Dupuytren myofibroblasts (DMFs) or prevents recurrence following surgery. Antifibrotic and proadipogenic growth factors are released when adipose-derived stem cells (ASCs) are cultured with platelet-rich plasma (PRP), a platelet concentration from whole blood. Reprograming myofibroblasts into adipocytes via growth factors is proposed as a powerful potential tool to target fibrosis. We aimed to assess whether the combination of ASCs and PRP reprograms DMFs into adipocytes invitro and alters their contractile nature invivo. Normal human dermal fibroblasts (NHDFs) and DMFs from Dupuytren patients were isolated and cocultured with ASCs and PRP either alone or together. Adipocytes were detected by Oil Red O and perilipin staining. DMFs and NHDFs were transplanted into the forepaws of rats (Rowett Nude [rnu/rnu]) and treated with saline, PRP+ASCs, or collagenase Clostridium histolyticum (clinical comparison) 2 months later. After 2 weeks, the tissue was harvested and subjected to Masson trichrome staining, and collagen I and III and alpha-smooth muscle actin detection by immunohistochemistry. Myofibroblasts transform into adipocytes upon coculture with PRP+ASCs. DMFs show increased alpha-smooth muscle actin expression invivo compared with NHDFs, which is significantly decreased after PRP+ASCs and collagenase Clostridium histolyticum treatments. DMFs induce collagen I and III expressions in rat paws compared with NHDFs, with a type III to I ratio increase. Treatment with PRP+ASC reduced the ratio, but collagenase Clostridium histolyticum did not. Treating DMFs with PRP+ASCs provides factors that induce myofibroblast to adipocyte transformation. This treatment reduces the contractile phenotype and fibrosis markers invivo. Future studies should detail the mechanism of this conversion. The combination of PRP and ASCs to induce the differentiation of DMFs into adipocytes may serve to limit surgery to a percutaneous contracture release and biological injection, rather than a moderate or radical fasciectomy, and reduce the recurrence of Dupuytren contracture.

Spontaneous synaptic drive in detrusor smooth muscle: computational investigation and implications for urinary bladder function.

The detrusor, a key component of the urinary bladder wall, is a densely innervated syncytial smooth muscle tissue. Random spontaneous release of neurotransmitter at neuromuscular junctions (NMJs) in the detrusor gives rise to spontaneous excitatory junction potentials (SEJPs). These sub-threshold passive signals not only offer insights into the syncytial nature of the tissue, their spatio-temporal integration is critical to the generation of spontaneous neurogenic action potentials which lead to focal contractions during the filling phase of the bladder. Given the structural complexity and the contractile nature of the tissue, electrophysiological investigations on spatio-temporal integration of SEJPs in the detrusor are technically challenging. Here we report a biophysically constrained computational model of a detrusor syncytium overlaid with spatially distributed innervation, using which we explored salient features of the integration of SEJPs in the tissue and the key factors that contribute to this integration. We validated our model against experimental data, ascertaining that observations were congruent with theoretical predictions. With the help of comparative studies, we propose that the amplitude of the spatio-temporally integrated SEJP is most sensitive to the inter-cellular coupling strength in the detrusor, while frequency of observed events depends more strongly on innervation density. An experimentally testable prediction arising from our study is that spontaneous release frequency of neurotransmitter may be implicated in the generation of detrusor overactivity. Set against histological observations, we also conjecture possible changes in the electrical activity of the detrusor during pathology involving patchy denervation. Our model thus provides a physiologically realistic, heuristic framework to investigate the spread and integration of passive potentials in an innervated syncytial tissue under normal conditions and in pathophysiology.

Retinal ischemia induces \u03b1-SMA-mediated capillary pericyte contraction coincident with perivascular glycogen depletion

Increasing evidence indicates that pericytes are vulnerable cells, playing pathophysiological roles in various neurodegenerative processes. Microvascular pericytes contract during cerebral and coronary ischemia and do not relax after re-opening of the occluded artery, causing incomplete reperfusion. However, the cellular mechanisms underlying ischemia-induced pericyte contraction, its delayed emergence, and whether it is pharmacologically reversible are unclear. Here, we investigate i) whether ischemia-induced pericyte contractions are mediated by alpha-smooth muscle actin (α-SMA), ii) the sources of calcium rise in ischemic pericytes, and iii) if peri-microvascular glycogen can support pericyte metabolism during ischemia. Thus, we examined pericyte contractility in response to retinal ischemia both in vivo, using adaptive optics scanning light ophthalmoscopy and, ex vivo, using an unbiased stereological approach. We found that microvascular constrictions were associated with increased calcium in pericytes as detected by a genetically encoded calcium indicator (NG2-GCaMP6) or a fluoroprobe (Fluo-4). Knocking down α-SMA expression with RNA interference or fixing F-actin with phalloidin or calcium antagonist amlodipine prevented constrictions, suggesting that constrictions resulted from calcium- and α-SMA-mediated pericyte contractions. Carbenoxolone or a Cx43-selective peptide blocker also reduced calcium rise, consistent with involvement of gap junction-mediated mechanisms in addition to voltage-gated calcium channels. Pericyte calcium increase and capillary constrictions became significant after 1 h of ischemia and were coincident with depletion of peri-microvascular glycogen, suggesting that glucose derived from glycogen granules could support pericyte metabolism and delay ischemia-induced microvascular dysfunction. Indeed, capillary constrictions emerged earlier when glycogen breakdown was pharmacologically inhibited. Constrictions persisted despite recanalization but were reversible with pericyte-relaxant adenosine administered during recanalization. Our study demonstrates that retinal ischemia, a common cause of blindness, induces α-SMA- and calcium-mediated persistent pericyte contraction, which can be delayed by glucose driven from peri-microvascular glycogen. These findings clarify the contractile nature of capillary pericytes and identify a novel metabolic collaboration between peri-microvascular end-feet and pericytes.

A Mathematical Model of Plasma Membrane Electrophysiology of a Brain Capillary Pericyte: Investigating Pericyte Contribution to the Electrical Properties of the Capillary Network

IntroductionPericyte cells (PCs) are specialized cells found primarily on the abluminal surface of capillary blood vessels alongside endothelial cells (ECs). They play a role in angiogenesis, formation of the blood‐brain barrier, as well as in the regulation of blood flow. Due to their contractile nature, PCs can modulate capillary diameter and perfusion, however, little is known regarding their contribution to the electrical properties of the capillary network. Furthermore, recent studies show that capillaries can sense neural activity in the brain and transmit electrical signals to upstream feeding arterioles and arteries to match blood supply to local demand. Although passive electrotonic spread underlies signal propagation along the endothelium in larger vessels, evidence for amplification of transmitted signals and preferential upstream propagation have been presented in vessels as branching order increases. We use mathematical modeling to test under what conditions a PC can affect the electrical properties of the capillary network and whether it can act as a sink or an amplifier of conducted hyperpolarization.MethodsA PC and an EC model incorporate the dynamic behavior of known plasma membrane currents, release and uptake of Ca2+ by intracellular stores and dynamic tracking of ionic (Ca2+, K+, Na+, and Cl−) concentrations in the cytosol (Fig. 1). The PC is electrically coupled to capillary ECs through gap junctions and a multicellular model of a capillary network is created. Electrical signal attenuation is examined following hyperpolarizing stimuli at capillary ends in the presence as well as absence of PCs at network bifurcations.ResultsCell models predict physiological resting membrane potential and ionic concentrations. Model predictions were compared against experimental responses to agonist stimulation and K+ challenge for validation. Simulations show that a sufficient inwardly rectifying K+, Kir, channel current density may allow PCs to amplify conducted hyperpolarization. Increased coupling between a PC with the parent relative to the daughter capillaries at a bifurcation may allow preferential conduction of an electrical signal upstream the vascular network.ConclusionA detailed model of a brain capillary pericyte was developed and validated against experimental data. Model simulations suggest that with sufficient Kir density, pericytes can amplify conducted hyperpolarization and regulate the distance and direction of propagating vasodilation and thus blood flow distribution in the vascular network.Support or Funding InformationThis work was supported by the Ronald E. McNair Post‐Baccalaureate Achievement Program.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Vortex formation and dynamics of defects in active nematic shells

We present a hydrodynamic model for a thin spherical shell of active nematic liquid crystal with an arbitrary configuration of defects. The active flows generated by defects in the director lead to the formation of stable vortices, analogous to those seen in confined systems in flat geometries, which generate effective dynamics for four +1/2 defects that reproduces the tetrahedral to planar oscillations observed in experiments. As the activity is increased and two counterrotating vortices dominate the flow, the defects are drawn more tightly into pairs, rotating about antipodal points. We extend this situation to also describe the dynamics of other configurations of defects. For example, two +1 defects are found to attract or repel according to the local geometric character of the director field around them and the extensile or contractile nature of the material, while additional pairs of opposite charge defects can give rise to flow states containing more than two vortices. Finally, we describe the generic relationship between defects in the orientation and singular points of the flow, and suggest implications for the three-dimensional nature of the flow and deformation in the shape of the shell.

Cell culture in three-dimensional lattices of hydrated collagen fibrils – its progress and perspectives

Cell culture methodology has been utilized as a powerful tool to characterize cells with a presupposition that the cells in culture faithfully reproduce their in vivo phenotypes. However, it is generally recognized that the cells cultured currently by the most commonly utilized two-dimensional (2D) monolayer technology exhibit different phenotypes from those in living tissues. Cultivation of cells in three-dimensional (3D) lattices of collagen fibrils (collagen gel culture) has been thought to overcome the shortages of 2D cell culture such that the cells behave as in vivo by interacting with not only nearby other cells but also by surrounding extracellular matrices. A remarkable outcome of studies on collagen gel culture was a demonstration of contractile nature of the cells. One of the not-fully appreciated issues about the 3D cell culture is the effect of fluid flow through the collagen gels on cells’ phenotypes. In this review, we make a short overview of historical and current studies of the collagen gel culture from a viewpoint of ‘how we can more correctly extract the cell-related phenomena in living tissues/organs by in vitro culture technology, placing an emphasis on the importance of stimuli caused by flow of cell culture medium.’

Transcriptomic dissection of myogenic differentiation signature in caprine by RNA-Seq

Muscle growth and development from the embryonic to the adult stage of an organism consists of a series of exquisitely regulated and orchestrated changes in expression of genes leading to muscle maturation. In this study, we performed whole transcriptome profiling of adult caprine skeletal muscle derived myoblast and fused myotubes. Using Ion Torrent PGM sequencing platform, a total of 948,776 and 799,976 reads were generated in myoblasts and fused myotubes, respectively. The sequence reads were analyzed on CLC Genomics Workbench using Bos taurus RNA database to study the gene expression in both stages to study different genes responsible for muscle development and regeneration. The up and down-regulated genes were analyzed for gene ontology (GO) and KEGG pathways by Database for Annotation, Visualization and Integrated Discovery (DAVID) database. We found many genes exclusive to multinuclear fused myotubes and contractile nature of skeletal muscle, whereas up-regulated genes in myoblast stage were related to cell division and transcriptional regulation. Out of 27 genes selected for expression validation by RT-qPCR (reverse transcriptase-quantitative polymerase chain reaction), 19 genes showed the expression pattern comparable with CLC Genomics Workbench findings. Further, mRNA originated muscle specific microRNAs (miRNA-1 and miRNA-133b) were also observed in the fused myotubes along with other miRNAs with possible importance in muscle development. This study highlights important genes responsible for muscle development and differentiation in adult skeletal muscle system.

Drosophila melanogaster muscle LIM protein and alpha-actinin function together to stabilize muscle cytoarchitecture: a potential role for Mlp84B in actin-crosslinking.

Stabilization of tissue architecture during development and growth is essential to maintain structural integrity. Because of its contractile nature, muscle is especially susceptible to physiological stresses, and has multiple mechanisms to maintain structural integrity. The Drosophila melanogaster Muscle LIM Protein (MLP), Mlp84B, participates in muscle maintenance, yet its precise mechanism of action is still controversial. Through a candidate approach, we identified α-actinin as a protein that functions with Mlp84B to ensure muscle integrity. α-actinin RNAi animals die primarily as pupae, and Mlp84B RNAi animals are adult viable. RNAi knockdown of Mlp84B and α-actinin together produces synergistic early larval lethality and destabilization of Z-line structures. We recapitulated these phenotypes using combinations of traditional loss-of-function alleles and single-gene RNAi. We observe that Mlp84B induces the formation of actin loops in muscle cell nuclei in the absence of nuclear α-actinin, suggesting Mlp84B has intrinsic actin cross-linking activity, which may complement α-actinin cross-linking activity at sites of actin filament anchorage. These results reveal a molecular mechanism for MLP stabilization of muscle and implicate reduced actin crosslinking as the primary destabilizing defect in MLP-associated cardiomyopathies. Our data support a model in which α-actinin and Mlp84B have important and overlapping functions at sites of actin filament anchorage to preserve muscle structure and function.

Macular hole overlying pigment epithelial detachment after intravitreal injection with ranibizumab.

To describe a previously unrecognized complication of intravitreal injection in a patient with exudative macular degeneration and vitreomacular adhesion. Case report of a 69-year-old woman. One month after intravitreal injection with ranibizumab for exudative macular degeneration, our patient developed a full-thickness macular hole with visual acuity of 20/100. After pars plana vitrectomy with membrane peeling and fluid-gas exchange, the macular hole was closed and the visual acuity improved to 20/60. Macular hole formation after intravitreal injection with ranibizumab is a potential complication that should be considered before treatment, especially in those patients with large subfoveal pigment epithelial detachments and vitreomacular adhesion. Although successful closure may be attained after pars plana vitrectomy, this potential morbidity should be considered when treating these patients. In addition to the already well-described tractional forces of the vitreous overlying the fovea, and the potential contractile nature of a choroidal neovascular complex in response to ranibizumab, a posterior pushing or stretching mechanism of a large pigment epithelial detachment may also contribute to macular hole formation.

Permeability and stiffness of sands at very low effective stresses

Loose saturated sandy soils may undergo liquefaction under cyclic loading, generating positive excess pore pressures due to their contractile nature and inability to dissipate pore pressures rapidly during earthquake loading. These liquefied soils have a near-zero effective stress state, and hence have very low strength and stiffness, causing severe damage to structures founded upon them. The duration for which this near-zero effective stress state persists is a function of the rate of reconsolidation of the liquefied soil, which in turn is a function of the permeability and stiffness of the soil at this very low effective stress. Existing literature based on observation of physical model tests suggests that the consolidation coefficient Cvassociated with this reconsolidation of liquefied sand is significantly lower than that of the same soil at moderate stress levels. In this paper, the results of a series of novel fluidisation tests in which permeability k and coefficient of consolidation Cvwere independently measured will be presented. These results allow calculation of the variation of stiffness E0and permeability k with effective stress. It is shown that while permeability increases markedly at very low effective stresses, the simultaneous drop in stiffness measured results in a decrease in consolidation coefficient and hence an increase in the duration for which the soil remains liquefied.

Toward a Concept of Stretch Coupling in Smooth Muscle: A Thesis by Lars Thuneberg on Contractile Activity in Neonatal Interstitial Cells of Cajal

The hypothesis was put forward by Thuneberg that rhythmically contracting interstitial cells of Cajal (ICC) were sensing stretch of the musculature and that this information was transmitted to smooth muscle cells via peg and socket contacts. The present study provides the evidence for the contractile nature of ICC as perceived by Thuneberg. The contractile activity is shown by video frame subtraction and by tracking areas of interest in sequential video frames. Thuneberg used neonatal ICC in culture maintained between two coverslips thereby allowing growth factors to quickly reach optimal concentrations. Contractions of ICC were seen to precede smooth muscle contractions. In addition, strong contractions were observed solely in branches of ICC. It is hoped that this communication will stimulate discussion about the contractile nature of ICC and that this phenomenon will eventually find its place amongst the physiological properties of the ICC networks of the gut musculature.

Tropomyosin isoform modulation of focal adhesion structure and cell migration

Orderly cell migration is essential for embryonic development, efficient wound healing and a functioning immune system and the dysregulation of this process leads to a number of pathologies. The speed and direction of cell migration is critically dependent on the structural organization of focal adhesions in the cell. While it is well established that contractile forces derived from the acto-myosin filaments control the structure and growth of focal adhesions, how this may be modulated to give different outcomes for speed and persistence is not well understood. The tropomyosin family of actin-associating proteins are emerging as important modulators of the contractile nature of associated actin filaments. The multiple non-muscle tropomyosin isoforms are differentially expressed between tissues and across development and are thought to be major regulators of actin filament functional specialization. In the present study we have investigated the effects of two splice variant isoforms from the same α-tropomyosin gene, TmBr1 and TmBr3, on focal adhesion structure and parameters of cell migration. These isoforms are normally switched on in neuronal cells during differentiation and we find that exogenous expression of the two isoforms in undifferentiated neuronal cells has discrete effects on cell migration parameters. While both isoforms cause reduced focal adhesion size and cell migration speed, they differentially effect actin filament phenotypes and migration persistence. Our data suggests that differential expression of tropomyosin isoforms may coordinate acto-myosin contractility and focal adhesion structure to modulate cell speed and persistence.

Uterine Magnetomyography

Event Abstract Back to Event Uterine Magnetomyography Hari Eswaran1* 1 University of Arkansas for Medical Sciences, Department of Obstetrics and Gynaecology, United States The SARA System can record the magnetic field corresponding to the electrical activity of uterine contraction and provide requisite spatial-temporal information. The spatial-temporal information provided by the 151 channels will provide much more information about the contractile nature of the uterus than has previously been possible to obtain. Our preliminary studies show that by recording uterine magnetomyographic (MMG) signals we can localize the area of activation over the uterus during a contraction. This allows us explore the origin and propagation of uterine contraction despite the shifting of the pacemaker site from one contraction to another. We can localize the pacemaker by mapping the magnetic field distribution and quantify the spread by obtaining the percent of sensors active during each contraction with sensors spread over the entire maternal abdomen. Using this information, it will be possible to test the hypothesis that during most of pregnancy uterus is spontaneously active but because of limited propagation of the action potentials only small areas of myometrium is activated. Whereas closer to active labor, gap junction appear and increased number of myometrial cells are activated resulting increase in the spread of electrical activity over the uterus. This confirms that the uterus goes through a preparatory phase before labor starts. Conference: Biomag 2010 - 17th International Conference on Biomagnetism , Dubrovnik, Croatia, 28 Mar - 1 Apr, 2010. Presentation Type: Oral Presentation Topic: Fetal and neonatal biomagnetism Citation: Eswaran H (2010). Uterine Magnetomyography. Front. Neurosci. Conference Abstract: Biomag 2010 - 17th International Conference on Biomagnetism . doi: 10.3389/conf.fnins.2010.06.00094 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 23 Mar 2010; Published Online: 23 Mar 2010. * Correspondence: Hari Eswaran, University of Arkansas for Medical Sciences, Department of Obstetrics and Gynaecology, Little Rock, United States, eswaranhari@uams.edu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Hari Eswaran Google Hari Eswaran Google Scholar Hari Eswaran PubMed Hari Eswaran Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Growth Factors and Ocular Scarring

Growth factors play a part in every stage of the wound healing process that leads to scar tissue formation. Ocular scarring can cause decreased vision or blindness by virtue of the opaque nature of the new matrix that is deposited as scar tissue (as in the lens or cornea). In addition, the contractile nature of the ocular scar tissue is the most common cause of failed retinal attachment. Scar formation after glaucoma surgery can lead to surgery failure. Growth factors, particularly the transforming growth factor (TGF-βs), play a major role in scar tissue formation in the eye and induce the synthesis of growth factors that control cell migration, proliferation, enzyme production and matrix deposition. Neurotrophins are also neuroprotective and can delay ganglion cell death, thus delaying scar formation in the retina if retinal attachment is restored promptly. Growth factors can be seen as a major target for preventing ocular scarring in the future.

Living microlens arrays

Both individual cells and sheets of cells exert traction forces on the substrate and these forces have been investigated using a wide range of methods. Here we compare the mechanical properties of fibroblasts and epithelial cells using a novel surface geometry. Living cells are added to a thin film of polystyrene [PS] attached to a substrate of crosslinked poly(dimethyl siloxane) [PDMS] microwells. The contractile nature of the cells attached to the surface and the compliance of the PDMS surface geometry allows the PS thin film to buckle, forming arrays of convex microlenses. The resulting curvature of the microlenses allows us to determine the applied strain of growing cell sheets. We report that a monolayer of epithelial cells exerts more stress on the substrate than fibroblasts and attribute this to the collective behavior of the epithelium. By subsequently adding different chemical triggers to the system, the contractile nature of the cells changes, thus modifying the focal length of the microlenses. Together, these findings demonstrate the importance of studying the mechanics of cell sheets and also introduce a new design paradigm for advanced materials, offering great promise for a range of applications.

Release of Anterior Neck Burn Contracture Using Artificial Dermis and Vacuum-Assisted Closure

Sir: Anatomically, the head and neck, along with upper limbs, are the most frequently burned areas.1 Contractures inherently arise due to the extensive, contractile nature of the scar tissue resulting from the burn. Vascularity and hypertrophy gradually increase over time, while pliability of the dermis decreases. Burn contractures are functionally debilitating and often lead to a poor cosmetic appearance. We report the successful use of artificial dermis and vacuum-assisted closure in the release of an anterior neck contracture in a 14-year-old boy. He was admitted with burns over 70 percent of his body, involving the face, neck, thorax, both arms, abdomen, back, buttocks, and thighs. All of the burns were full thickness, including the circumferential neck burn. Four months after the initial injury, severe anterior neck contracture necessitated fiberoptic intubations and day-to-day activities proved very difficult. His contracture was released through a standard anterior fishmouth incision under general anesthesia, which left a 25 × 8-cm defect. Integra (Integra Life Sciences, Plainsboro, N.J.) was used (Fig. 1) and held in place using vacuum-assisted closure at continuous suction (KCI, San Antonio, Texas) for 2 weeks.Fig. 1.: Contracture released with Integra in situ.The contracture was successfully released, which improved the neck range of movement. Cosmetically, this was also more acceptable for the patient. At 6-month follow-up, there was no recurrence of the neck contracture (Fig. 2).Fig. 2.: View of the patient 6 months after contracture release.The objective in releasing a contracture of the anterior neck is to improve both function and appearance by restoring the anatomic profile and contour of the neck.1 A number of methods have been reported in the literature for the treatment of anterior neck contractures,1,2 including split-thickness skin grafts, full-thickness grafts, local flaps, Z-plasty, and free flaps. Tissue expansion is also an optional adjunct to reconstruction. Integra has a role to play in contracture release.3 It consists of a biosynthetic dermis of porous collagen and glycosaminoglycan, with a thin silicone epidermal substitute. The silicone layer retains moisture and essentially closes the wound. The superficial silicone layer is removed after 2 weeks and replaced by a thin split-thickness skin graft. Histologically, the Integra is incorporated by fibroblast migration, revascularization, and remodeling. The dermal template is eventually replaced by normal dermal collagen. Integra is supple and has a thick dermal layer. It is an effective method for release of the anterior neck contracture in this case, as graft contraction and dermal thickness are inversely related. Vacuum-assisted closure therapy was first described in 1997 by Argenta and Morykwas.4 This simple device facilitates graft take by preventing movement of the graft and protecting it from shearing forces.5 When securing a skin graft, continuous vacuum-assisted closure therapy is applied for 4 days at a low pressure of 50 mmHg. In this case, the therapy was used to secure the Integra in place at a higher pressure of 75 mmHg, which was well tolerated by the patient. This case reports the use of a novel technique to release an anterior neck contracture using Integra and vacuum-assisted closure. Jenny B. Lynch, M.D. Thamir S. Ismael, M.D. Jack L. Kelly, M.D. Department of Plastic, Reconstructive, and Hand Surgery University College Hospital Galway, Ireland

Characterization of the Column and Autocellular Junctions That Define the Vasculature of Gill Lamellae

Novel adhesion junctions have been characterized that are formed at the interface between pillar cells and collagen columns, both of which are essential constituents of the gill lamellae in fish. We termed these junctions the "column junction" and "autocellular junction" and determined their molecular compositions by immunofluorescence microscopy using pufferfish. We visualized collagen columns by concanavalin A staining and found that the components of integrin-mediated cell-matrix adhesion, such as talin, vinculin, paxillin, and fibronectin, were concentrated on plasma membranes surrounding collagen columns (column membranes). This connection is analogous to the focal adhesion of cultured mammalian cells, dense plaque of smooth muscle cells, and myotendinous junction of skeletal muscle cells. We named this connection the "column junction." In the cytoplasm near the column, actin fibers, actinin, and a phosphorylated myosin light chain of 20 kDa are densely located, suggesting the contractile nature of pillar cells. The membrane infoldings surrounding the collagen columns were found to be connected by the autocellular junction, whose components are highly tyrosine-phosphorylated and contain the tight junction protein ZO-1. This study represents the first molecular characterization and fluorescence visualization of the column and autocellular junctions involved in both maintaining structural integrity and the hemodynamics of the branchial lamellae.

Sinusoidal remodeling and angiogenesis: A new function for the liver-specific pericyte?

Sinusoidal remodeling and angiogenesis: A new function for the liver-specific pericyte?