The use of surgical site drains in breast reconstruction: A systematic review.

BACKGROUND: Use of drains has been advocated in order to prevent seroma and hematoma; however, specific recommendations vary widely. The goal is to perform a systematic analysis of published literature on the use of drains for breast reconstruction. METHODS: The literature search was performed according to the PRISMA guidelines. The search included the Cochrane Library, Embase, and Pubmed databases using the terms "breast reconstruction" and "breast flap" combined with "drain", "seroma," and "seroma prevention". The references were appraised in two rounds, by two independent reviewers; studies were included/excluded based on relevance of title and subsequently by the content of their abstracts/manuscripts. Outcomes regarding seroma, infection rate, length of stay (LOS), drainage, reconstruction type and complications were analyzed. RESULTS: Of 2252 studies identified via search, 64 were relevant and 21 met inclusion criteria. Most of the study designs were case series or retrospective cohort studies (Level of Evidence III or IV), with the exception of one prospective randomized-controlled trial. Seroma rate was given in 18 studies, infection rate in 11, and criteria for drain removal in 19. Reoperation rate was available in 7 and LOS in 18 studies. The majority of studies (13) agreed to remove the drain when the output was less than 30 ml/24 h. Drain output was reported in 11, and 20 reported drain type used. CONCLUSION: There is sparse literature available with which to make evidence-based guidelines. A standardized guideline for reporting drain use is crucial to providing a better understanding of complications in breast reconstruction related to surgical drains.

Biomechanical Comparison of Fibrin Sealants for Mesh Fixation.

Adhesive use for fixation in hernia repair allows for complete and immediate mesh surface area adherence. Little is known about the fixation strengths of the products and application methods available. The purpose of this study was to compare the immediate and early strength of fixation of Tisseel™ and Evicel™ using hand and spray application techniques. Sixteen Mongrel swine underwent implantation of large-pore, mid-weight polypropylene mesh fixated with either Tisseel™ or Evicel™, applied by hand or with a spray apparatus. Time points studied were zero and four days. All samples underwent lap shear testing to quantify the strength of the mesh-tissue interface as an indicator of mesh fixation strength. Thirty Day 4 and 16 Day 0 samples were tested. Manually applied Tisseel™ mean fixation strength was 2.05 N/cm at Day 0 and 6.02 N/cm at Day 4. Sprayed Tisseel™ had mean fixation strength of 1.22 N/cm at Day 0 and 7.21 N/cm at Day 4. Manually applied Evicel™ showed mean fixation strength of 0.92 N/cm at Day 0 and 6.73 N/cm at Day 4. Mean fixation strength of sprayed Evicel™ was 0.72 N/cm at Day 0 and 6.70 N/cm at Day 4. Analysis of variance showed no difference between groups at Day 0 or Day 4. Immediate strength of mesh fixation could have significant implications for early recurrence and mesh contraction. This study demonstrates that no difference exists in immediate or early fixation strength between these two brands of sealants or their method of application.

The Problem of Seroma After Ventral Hernia Repair.

Seroma is a common postoperative finding after ventral hernia repair with an incidence of 20%. Often, it can be managed conservatively, but in the case of persistent or chronic seroma, reinterventions may be required. Closed drain suction has been the mainstay of seroma management for the last 40 years. Other alternative technologies have been evaluated to improve outcomes with mixed results. Because seroma is common, it is often an accepted outcome. Patient morbidity and costs to the healthcare system are underestimated, which begs for a re-evaluation of the current state of seroma management that is nearly a half-century old.

Chondron curvature mapping in growth plate cartilage under compressive loading.

The physis, or growth plate, is a layer of cartilage responsible for long bone growth. It is organized into reserve, proliferative and hypertrophic zones. Unlike the reserve zone where chondrocytes are randomly arranged, either singly or in pairs, the proliferative and hypertrophic chondrocytes are arranged within tubular structures called chondrons. In previous studies, the strain patterns within the compressed growth plate have been reported to be nonuniform and inhomogeneous, with an apparent random pattern in compressive strains and a localized appearance of tensile strains. In this study we measured structural deformations along the entire lengths of chondrons when the physis was subjected to physiological (20%) and hyper-physiological (30% and 40%) levels of compression. This provided a means to interpret the apparent random strain patterns seen in texture correlation maps in terms of bending deformations of chondron structures and provided a physical explanation for the inhomogeneous and nonuniform strain patterns reported in previous studies. We observed relatively large bending deformations (kinking) of the chondron structures at the interface of the reserve and proliferative zones during compression. Bending in this region may induce dividing cells to align longitudinally to maintain column formation and drive longitudinal growth.

Biomechanical and Histologic Evaluation of LifeMesh™: A Novel Self-Fixating Mesh Adhesive.

Mesh fixation with the use of adhesives results in an immediate and total surface area adhesion of the mesh, removing the need for penetrating fixation points. The purpose of this study was to evaluate LifeMesh™, a prototype mesh adhesive technology which coats polypropylene mesh. The strength of the interface between mesh and tissue, inflammatory responses, and histology were measured at varying time points in a swine model, and these results were compared with sutures. Twenty Mongrel swine underwent implantation of LifeMesh™ and one piece of bare polypropylene mesh secured with suture (control). One additional piece of either LifeMesh™ or control was used for histopathologic evaluation. The implants were retrieved at 3, 7, and 14 days. Only 3- and 7-day specimens underwent lap shear testing. On Day 3, LifeMesh™ samples showed considerably less contraction than sutured samples. The interfacial strength of Day 3 LifeMesh™ samples was similar to that of sutured samples. At seven days, LifeMesh™ samples continued to show significantly less contraction than sutured samples. The strength of fixation at seven days was greater in the control samples. The histologic findings were similar in LifeMesh™ and control samples. LifeMesh™ showed significantly less contraction than sutured samples at all measured time points. Although fixation strength was similar at three days, the interfacial strength of LifeMesh™ remained unchanged, whereas sutured controls increased by day 7. With histologic equivalence, considerably less contraction, and similar early fixation strength, LifeMesh™ is a viable mesh fixation technology.

Omega-3 Fatty Acids Modulate TRPV4 Function through Plasma Membrane Remodeling.

Dietary consumption of ω-3 polyunsaturated fatty acids (PUFAs), present in fish oils, is known to improve the vascular response, but their molecular targets remain largely unknown. Activation of the TRPV4 channel has been implicated in endothelium-dependent vasorelaxation. Here, we studied the contribution of ω-3 PUFAs to TRPV4 function by precisely manipulating the fatty acid content in Caenorhabditis elegans. By genetically depriving the worms of PUFAs, we determined that the metabolism of ω-3 fatty acids is required for TRPV4 activity. Functional, lipid metabolome, and biophysical analyses demonstrated that ω-3 PUFAs enhance TRPV4 function in human endothelial cells and support the hypothesis that lipid metabolism and membrane remodeling regulate cell reactivity. We propose a model whereby the eicosanoid's epoxide group location increases membrane fluidity and influences the endothelial cell response by increasing TRPV4 channel activity. ω-3 PUFA-like molecules might be viable antihypertensive agents for targeting TRPV4 to reduce systemic blood pressure.

Short-term strength of non-penetrating mesh fixation: LifeMesh™, Tisseel™, and ProGrip™.

BACKGROUND: Non-penetrating mesh fixation is becoming widely accepted even though little is known about the short-term fixation strength of these techniques. Although clinical outcomes are the ultimate measure of effectiveness, ex vivo biomechanical evaluation provides insights about the load-carrying capacity of the mesh-tissue complex in vivo. As such, the purpose of this study was to compare the short-term fixation strength of three unique non-penetrating methods of fixation: LifeMesh™, ProGrip™, and Tisseel™. Among these, LifeMesh™ is a novel technology where large-pore, mid-weight polypropylene mesh is embedded in a dry matrix of porcine gelatin and microbial transglutaminase enzyme, providing self-fixation without the need for a separate adhesive application. METHODS: Seven mongrel swine underwent implantation of two 4 × 7 cm pieces of either LifeMesh™, ProGrip™, or polypropylene mesh fixated with 2 mL of Tisseel™; 10 min after application, the samples were excised with the abdominal wall and stored for immediate biomechanical testing. The samples underwent lap shear testing to determine the short-term fixation strength of these three technologies. RESULTS: ProGrip™ demonstrated mean fixation strength of 1.3 N/cm (±STE 0.2). Mean fixation for mesh fixated with Tisseel™ was 2.6 N/cm (±STE 0.5). LifeMesh™ samples had mean fixation strength of 8.0 N/cm (±STE 2.1). Analysis of variance testing showed that interfacial strength of LifeMesh™ was significantly greater than that of either ProGrip™ or Tisseel™. ProGrip™ and Tisseel™ were not significantly different from each other (p = 0.06). CONCLUSIONS: Short-term strength of mesh fixation is an undescribed factor in hernia repair, but could have significant implications for early recurrence and mesh contraction. While further investigation is needed to define adequate interfacial strength, this comparison of non-penetrating mesh fixation methods shows that the novel LifeMesh™ technology exhibits greater strength than other non-penetrating fixation techniques.

Multiscale modeling of growth plate cartilage mechanobiology.

Growth plate chondrocytes are responsible for bone growth through proliferation and differentiation. However, the way they experience physiological loads and regulate bone formation, especially during the later developmental phase in the mature growth plate, is still under active investigation. In this study, a previously developed multiscale finite element model of the growth plate is utilized to study the stress and strain distributions within the cartilage at the cellular level when rapidly compressed to 20 %. Detailed structures of the chondron are included in the model to examine the hypothesis that the same combination of mechanoregulatory signals shown to maintain cartilage or stimulate osteogenesis or fibrogenesis in the cartilage anlage or fracture callus also performs the same function at the cell level within the chondrons of growth plate cartilage. Our cell-level results are qualitatively and quantitatively in agreement with tissue-level theories when both hydrostatic cellular stress and strain are considered simultaneously in a mechanoregulatory phase diagram similar to that proposed at the tissue level by Claes and Heigele for fracture healing. Chondrocytes near the reserve/proliferative zone border are subjected to combinations of high compressive hydrostatic stresses ([Formula: see text] MPa), and cell height and width strains of [Formula: see text] to [Formula: see text] respectively, that maintain cartilage and keep chondrocytes from differentiating and provide conditions favorable for cell division, whereas chondrocytes closer to the hypertrophic/calcified zone undergo combinations of lower compressive hydrostatic stress ([Formula: see text] MPa) and cell height and width strains as low as [Formula: see text] to +4 %, respectively, that promote cell differentiation toward osteogenesis; cells near the outer periphery of the growth plate structure experience a combination of low compressive hydrostatic stress (0 to [Formula: see text] MPa) and high maximum principal strain (20-29 %) that stimulate cell differentiation toward fibrocartilage or fibrous tissue.

Kymographic Imaging of the Elastic Modulus of Epithelial Cells during the Onset of Migration.

Epithelial cell migration during wound repair involves a complex interplay of intracellular processes that enable motility while preserving contact among the cells. Recent evidence suggests that fluctuations of the intracellular biophysical state of cells generate traction forces at the basal side of the cells that are necessary for the cells to migrate. However, less is known about the biophysical and structural changes throughout the cells that accompany these fluctuations. Here, we utilized, to our knowledge, a novel kymographic nanoindentation method to obtain spatiotemporal measurements of the elastic moduli of living cells during migration after wounding. At the onset of migration, the elastic modulus increased near the migration front. In addition, the intensity of fluctuations in the elastic modulus changed at the migration front, and these changes were dependent upon f-actin, one of the major components of the cytoskeleton. These results demonstrate the unique biophysical changes that occur at the onset of migration as cells transition from a stationary to a migratory state.

Live Cell Imaging during Mechanical Stretch.

There is currently a significant interest in understanding how cells and tissues respond to mechanical stimuli, but current approaches are limited in their capability for measuring responses in real time in live cells or viable tissue. A protocol was developed with the use of a cell actuator to distend live cells grown on or tissues attached to an elastic substrate while imaging with confocal and atomic force microscopy (AFM). Preliminary studies show that tonic stretching of human bronchial epithelial cells caused a significant increase in the production of mitochondrial superoxide. Moreover, using this protocol, alveolar epithelial cells were stretched and imaged, which showed direct damage to the epithelial cells by overdistention simulating one form of lung injury in vitro. A protocol to conduct AFM nano-indentation on stretched cells is also provided.

TREK-1 Regulates Cytokine Secretion from Cultured Human Alveolar Epithelial Cells Independently of Cytoskeletal Rearrangements.

BACKGROUND: TREK-1 deficient alveolar epithelial cells (AECs) secrete less IL-6, more MCP-1, and contain less F-actin. Whether these alterations in cytokine secretion and F-actin content are related remains unknown. We now hypothesized that cytokine secretion from TREK-1-deficient AECs was regulated by cytoskeletal rearrangements. METHODS: We determined F-actin and α-tubulin contents of control, TREK-1-deficient and TREK-1-overexpressing human A549 cells by confocal microscopy and western blotting, and measured IL-6 and MCP-1 levels using real-time PCR and ELISA. RESULTS: Cytochalasin D decreased the F-actin content of control cells. Jasplakinolide increased the F-actin content of TREK-1 deficient cells, similar to the effect of TREK-1 overexpression in control cells. Treatment of control and TREK-1 deficient cells with TNF-α, a strong stimulus for IL-6 and MCP-1 secretion, had no effect on F-actin structures. The combination of TNF-α+cytochalasin D or TNF-α+jasplakinolide had no additional effect on the F-actin content or architecture when compared to cytochalasin D or jasplakinolide alone. Although TREK-1 deficient AECs contained less F-actin at baseline, quantified biochemically, they contained more α-tubulin. Exposure to nocodazole disrupted α-tubulin filaments in control and TREK-1 deficient cells, but left the overall amount of α-tubulin unchanged. Although TNF-α had no effect on the F-actin or α-tubulin contents, it increased IL-6 and MCP-1 production and secretion from control and TREK-1 deficient cells. IL-6 and MCP-1 secretions from control and TREK-1 deficient cells after TNF-α+jasplakinolide or TNF-α+nocodazole treatment was similar to the effect of TNF-α alone. Interestingly, cytochalasin D decreased TNF-α-induced IL-6 but not MCP-1 secretion from control but not TREK-1 deficient cells. CONCLUSION: Although cytochalasin D, jasplakinolide and nocodazole altered the F-actin and α-tubulin structures of control and TREK-1 deficient AEC, the changes in cytokine secretion from TREK-1 deficient cells cannot be explained by cytoskeletal rearrangements in these cells.

Regional variations in growth plate chondrocyte deformation as predicted by three-dimensional multi-scale simulations.

The physis, or growth plate, is a complex disc-shaped cartilage structure that is responsible for longitudinal bone growth. In this study, a multi-scale computational approach was undertaken to better understand how physiological loads are experienced by chondrocytes embedded inside chondrons when subjected to moderate strain under instantaneous compressive loading of the growth plate. Models of representative samples of compressed bone/growth-plate/bone from a 0.67 mm thick 4-month old bovine proximal tibial physis were subjected to a prescribed displacement equal to 20% of the growth plate thickness. At the macroscale level, the applied compressive deformation resulted in an overall compressive strain across the proliferative-hypertrophic zone of 17%. The microscale model predicted that chondrocytes sustained compressive height strains of 12% and 6% in the proliferative and hypertrophic zones, respectively, in the interior regions of the plate. This pattern was reversed within the outer 300 µm region at the free surface where cells were compressed by 10% in the proliferative and 26% in the hypertrophic zones, in agreement with experimental observations. This work provides a new approach to study growth plate behavior under compression and illustrates the need for combining computational and experimental methods to better understand the chondrocyte mechanics in the growth plate cartilage. While the current model is relevant to fast dynamic events, such as heel strike in walking, we believe this approach provides new insight into the mechanical factors that regulate bone growth at the cell level and provides a basis for developing models to help interpret experimental results at varying time scales.

Bone morphology in 46 BXD recombinant inbred strains and femur-tibia correlation.

We examined the bone properties of BXD recombinant inbred (RI) mice by analyzing femur and tibia and compared their phenotypes of different compartments. 46 BXD RI mouse strains were analyzed including progenitor C57BL/6J (n = 16) and DBA/2J (n = 15) and two first filial generations (D2B6F1 and B6D2F1). Strain differences were observed in bone quality and structural properties (P < 0.05) in each bone profile (whole bone, cortical bone, or trabecular bone). It is well known that skeletal phenotypes are largely affected by genetic determinants and genders, such as bone mineral density (BMD). While genetics and gender appear expectedly as the major determinants of bone mass and structure, significant correlations were also observed between femur and tibia. More importantly, positive and negative femur-tibia associations indicated that genetic makeup had an influence on skeletal integrity. We conclude that (a) femur-tibia association in bone morphological properties significantly varies from strain to strain, which may be caused by genetic differences among strains, and (b) strainwise variations were seen in bone mass, bone morphology, and bone microarchitecture along with bone structural property.

The 2-pore domain potassium channel TREK-1 regulates stretch-induced detachment of alveolar epithelial cells.

Acute Respiratory Distress Syndrome remains challenging partially because the underlying mechanisms are poorly understood. While inflammation and loss of barrier function are associated with disease progression, our understanding of the biophysical mechanisms associated with ventilator-associated lung injury is incomplete. In this line of thinking, we recently showed that changes in the F-actin content and deformability of AECs lead to cell detachment with mechanical stretch. Elsewhere, we discovered that cytokine secretion and proliferation were regulated in part by the stretch-activated 2-pore domain K(+) (K2P) channel TREK-1 in alveolar epithelial cells (AECs). As such, the aim of the current study was to determine whether TREK-1 regulated the mechanobiology of AECs through cytoskeletal remodeling and cell detachment. Using a TREK-1-deficient human AEC line (A549), we examined the cytoskeleton by confocal microscopy and quantified differences in the F-actin content. We used nano-indentation with an atomic force microscope to measure the deformability of cells and detachment assays to quantify the level of injury in our monolayers. We found a decrease in F-actin and an increase in deformability in TREK-1 deficient cells compared to control cells. Although total vinculin and focal adhesion kinase (FAK) levels remained unchanged, focal adhesions appeared to be less prominent and phosphorylation of FAK at the Tyr(925) residue was greater in TREK-1 deficient cells. TREK-1 deficient cells have less F-actin and are more deformable making them more resistant to stretch-induced injury.

Hyperoxia increases the elastic modulus of alveolar epithelial cells through Rho kinase.

Patients with acute lung injury are administered high concentrations of oxygen during mechanical ventilation, and while both hyperoxia and mechanical ventilation are necessary, each can independently cause additional injury. However, the precise mechanisms that lead to injury are not well understood. We hypothesized that alveolar epithelial cells may be more susceptible to injury caused by mechanical ventilation because hyperoxia causes cells to be stiffer due to increased filamentous actin (f-actin) formation via the GTPase RhoA and its effecter Rho kinase (ROCK). We examined cytoskeletal structures in cultured murine lung alveolar epithelial cells (MLE-12) under normoxic and hyperoxic (48 h) conditions. We also measured cell elasticity (E) using an atomic force microscope in the indenter mode. Hyperoxia caused increased f-actin stress fibers and bundle formation, an increase in g- and f-actin, an increase in nuclear area and a decrease in nuclear height, and cells became stiffer (higher E). Treatment with an inhibitor (Y-27632) of ROCK significantly decreased E and prevented the cytoskeletal changes, while it did not influence the nuclear height and area. Pre-exposure of cells to hyperoxia promoted detachment when cells were subsequently stretched cyclically, but the ROCK inhibitor prevented this effect. Hyperoxia caused thickening of vinculin focal adhesion plaques, and inhibition of ROCK reduced the formation of distinct focal adhesion plaques. Phosphorylation of focal adhesion kinase was significantly reduced by both hyperoxia and treatment with Y-27632. Hyperoxia caused increased cell stiffness and promoted cell detachment during stretch. These effects were ameliorated by inhibition of ROCK.

Cohesive zone modeling of mode I tearing in thin soft materials.

The use of modeling and simulation is growing rapidly in applications such as surgery simulations, injury mechanics and tissue engineering. The aim of this study is to model and simulate tissue tearing and the resulting failure for use in such applications. In particular, our goal is to characterize the mechanics of mode I tearing in thin soft materials. We use the cohesive zone modeling approach to characterize the propagation of tears in a processed meat product (PMP). The bulk response of the PMP is modeled with a hyperelastic material model and the interface with a cohesive zone model. A multistep parameter estimation approach is developed to determine the bulk and the cohesive model parameters from uniaxial extension and tearing experiments. Results show that the proposed approach is able to capture both material and geometrical nonlinearities inherent to such problems, and accurately model the overall force-displacement response of thin soft materials during tearing at slow rates.

Hyperoxia alters the mechanical properties of alveolar epithelial cells.

Patients with severe acute lung injury are frequently administered high concentrations of oxygen (>50%) during mechanical ventilation. Long-term exposure to high levels of oxygen can cause lung injury in the absence of mechanical ventilation, but the combination of the two accelerates and increases injury. Hyperoxia causes injury to cells through the generation of excessive reactive oxygen species. However, the precise mechanisms that lead to epithelial injury and the reasons for increased injury caused by mechanical ventilation are not well understood. We hypothesized that alveolar epithelial cells (AECs) may be more susceptible to injury caused by mechanical ventilation if hyperoxia alters the mechanical properties of the cells causing them to resist deformation. To test this hypothesis, we used atomic force microscopy in the indentation mode to measure the mechanical properties of cultured AECs. Exposure of AECs to hyperoxia for 24 to 48 h caused a significant increase in the elastic modulus (a measure of resistance to deformation) of both primary rat type II AECs and a cell line of mouse AECs (MLE-12). Hyperoxia also caused remodeling of both actin and microtubules. The increase in elastic modulus was blocked by treatment with cytochalasin D. Using finite element analysis, we showed that the increase in elastic modulus can lead to increased stress near the cell perimeter in the presence of stretch. We then demonstrated that cyclic stretch of hyperoxia-treated cells caused significant cell detachment. Our results suggest that exposure to hyperoxia causes structural remodeling of AECs that leads to decreased cell deformability.

Disruption of Kif3a in osteoblasts results in defective bone formation and osteopenia.

We investigated whether Kif3a in osteoblasts has a direct role in regulating postnatal bone formation. We conditionally deleted Kif3a in osteoblasts by crossing osteocalcin (Oc; also known as Bglap)-Cre with Kif3a(flox/null) mice. Conditional Kif3a-null mice (Kif3a(Oc-cKO)) had a 75% reduction in Kif3a transcripts in bone and osteoblasts. Conditional deletion of Kif3a resulted in the reduction of primary cilia number by 51% and length by 27% in osteoblasts. Kif3a(Oc-cKO) mice developed osteopenia by 6 weeks of age unlike Kif3a(flox/+) control mice, as evidenced by reductions in femoral bone mineral density (22%), trabecular bone volume (42%) and cortical thickness (17%). By contrast, Oc-Cre;Kif3a(flox/+) and Kif3a(flox/null) heterozygous mice exhibited no skeletal abnormalities. Loss of bone mass in Kif3a(Oc-cKO) mice was associated with impaired osteoblast function in vivo, as reflected by a 54% reduction in mineral apposition rate and decreased expression of Runx2, osterix (also known as Sp7 transcription factor 7; Sp7), osteocalcin and Dmp1 compared with controls. Immortalized osteoblasts from Kif3a(Oc-cKO) mice exhibited increased cell proliferation, impaired osteoblastic differentiation, and enhanced adipogenesis in vitro. Osteoblasts derived from Kif3a(Oc-cKO) mice also had lower basal cytosolic calcium levels and impaired intracellular calcium responses to fluid flow shear stress. Sonic hedgehog-mediated Gli2 expression and Wnt3a-mediated ß-catenin and Axin2 expression were also attenuated in Kif3a(Oc-cKO) bone and osteoblast cultures. These data indicate that selective deletion of Kif3a in osteoblasts disrupts primary cilia formation and/or function and impairs osteoblast-mediated bone formation through multiple pathways including intracellular calcium, hedgehog and Wnt signaling.

Mechanobiology in lung epithelial cells: measurements, perturbations, and responses.

Epithelial cells of the lung are located at the interface between the environment and the organism and serve many important functions including barrier protection, fluid balance, clearance of particulate, initiation of immune responses, mucus and surfactant production, and repair following injury. Because of the complex structure of the lung and its cyclic deformation during the respiratory cycle, epithelial cells are exposed to continuously varying levels of mechanical stresses. While normal lung function is maintained under these conditions, changes in mechanical stresses can have profound effects on the function of epithelial cells and therefore the function of the organ. In this review, we will describe the types of stresses and strains in the lungs, how these are transmitted, and how these may vary in human disease or animal models. Many approaches have been developed to better understand how cells sense and respond to mechanical stresses, and we will discuss these approaches and how they have been used to study lung epithelial cells in culture. Understanding how cells sense and respond to changes in mechanical stresses will contribute to our understanding of the role of lung epithelial cells during normal function and development and how their function may change in diseases such as acute lung injury, asthma, emphysema, and fibrosis.