Fewer polymer chains but higher adhesion: How gradient-stiffness hydrogel layers mediate adhesion through network stretch

The presence of gradient softer outer layers, commonly observed in biological systems (such as cartilage and ocular tissues), as well as synthetic crosslinked hydrogels, profoundly influences their interactions with opposing surfaces. Our prior research demonstrated that gradient-stiffness hydrogel layers, characterized by increasing elasticity with depth, control contact mechanics, particularly in proximity to the layer thickness. We postulate that the distribution of polymers within these gradient layers imparts extraordinary stretch and adhesion characteristics due to network adaptability and stress-induced reorganization. To investigate this phenomenon, we utilized Atomic Force Microscopy nanoindentation to assess the depth-dependent adhesion behavior of polyacrylamide hydrogels with varying gradient layer thicknesses. Two gradient layer thicknesses were achieved by employing different molding materials: glass and polyoxymethylene (POM). Glass-molded hydrogels exhibited a thinner gradient layer alongside a stiffer bulk layer compared to their POM-molded counterparts. In indentation experiments, the POM-molded hydrogel had larger adhesion compared to glass-molded hydrogel. We find that indenting within the gradient layer engenders increased load-unload hysteresis due to heightened fluid transport in the sparse outer polymer network. Consequently, this led to augmented adhesion and work of separation at shallow depths. We suggest that the prominent stretching capability of the sparse outer polymer network during probe retraction contributes to enhanced adhesion. The Maugis-Dugdale adhesive model only fits well to indentations on the thin layer or indentations which engage significantly with the bulk. These results facilitate a comprehensive characterization of adhesion mechanics in gradient-stiffness hydrogels, which could foster their application across emerging contexts in health science and environmental domains.

Soft Contact Mechanics with Gradient-Stiffness Surfaces

The stiffness in the top surface of many biological entities like cornea or articular cartilage, as well as chemically cross-linked synthetic hydrogels, can be significantly lower or more compliant than the bulk. When such a heterogeneous surface comes into contact, the contacting load is distributed differently from typical contact models. The mechanical response under indentation loading of a surface with a gradient of stiffness is a complex, integrated response that necessarily includes the heterogeneity. In this work, we identify empirical contact models between a rigid indenter and gradient elastic surfaces by numerically simulating quasi-static indentation. Three key case studies revealed the specific ways in which (I) continuous gradients, (II) laminate-layer gradients, and (III) alternating gradients generate new contact mechanics at the shallow-depth limit. Validation of the simulation-generated models was done by micro- and nanoindentation experiments on polyacrylamide samples synthesized to have a softer gradient surface layer. The field of stress and stretch in the subsurface as visualized from the simulations also reveals that the gradient layers become confined, which pushes the stretch fields closer to the surface and radially outward. Thus, contact areas are larger than expected, and average contact pressures are lower than predicted by the Hertz model. The overall findings of this work are new contact models and the mechanisms by which they change. These models allow a more accurate interpretation of the plethora of indentation data on surface gradient soft matter (biological and synthetic) as well as a better prediction of the force response to gradient soft surfaces. This work provides examples of how gradient hydrogel surfaces control the subsurface stress distribution and loading response.

Cartilage-like tribological performance of charged double network hydrogels

A synthetic hydrogel material may offer utility as a cartilage replacement if it is able to maintain low friction in different sliding environments and achieve bulk mechanical properties to withstand the severe environment of the joint. In this work, we compared the tribological behavior of four double network (DN) hydrogels to that of fresh porcine cartilage in both water and fetal bovine serum (FBS). The DN hydrogels were comprised of a negatively charged 1st network and a 2nd network wherein comonomers of varying charge (i.e. neutral, positive, negative, and zwitterionic) were introduced at 10 wt% to an otherwise neutral network. A steel ball probe was used to perform microindentation tests to determine the surface elastic modulus of the samples and estimate their contact areas during sliding. Friction tests using a stationary probe with a stage that reciprocated at a range of speeds were performed to develop lubrication curves in both water and FBS. We found that the DN hydrogels with a neutral or zwitterionic 2nd network had the lowest friction and shear stresses, notably below that of cartilage. The differences in charge and structure of the samples were more evident in water than in FBS, as the lubrication responses for all the hydrogels spanned a wider range of values. In FBS, the lubrication responses were pushed towards elasto-hydrodynamics with nearly all friction coefficient values falling below 0.3. This indicates that the FBS interacts with the hydrogels and cartilage samples in a similar manner as that of cartilage by maintaining a robust layer of solution at the interface during sliding. These DN hydrogels prove to fulfill, and in some cases surpass, the lubrication demands for cartilage replacement in load bearing joints.

Self-regenerating compliance and lubrication of polyacrylamide hydrogels

Pristine hydrogel surfaces typically have low friction, which is controlled by composition, slip speeds, and immediate slip history. The stiffness of such samples is typically measured with bulk techniques, and is assumed to be homogeneous at the surface. While the surface properties of homogeneous hydrogel samples are generally controlled by composition, the surface also interfaces with the open bath, which distinguishes it from the bulk. In this work, we disrupt as-molded polyacrylamide surfaces with abrasive wear and connect the effects on the surface stiffness and lubrication to the wear events. At both the nanoscale and the microscale, quasistatic indentations reveal a stiffer surface by up to two times following wear events, even considering roughness. Longitudinal experiments with a series of wear episodes interposed with periods of re-equilibration show that increased stiffness is reversible: more compliant surfaces regenerate within 24 hours. The timescale suggests an osmotic swelling mechanism, and we postulate that abrasive wear removes a swollen surface layer, revealing the stiffer bulk. The newly-revealed bulk becomes the surface, which re-swells over time. We quantify the effects on the self-lubricating ability of these surfaces following abrasive wear using micro-tribometry. The lubrication curve shows that robust low friction is maintained, and that the friction becomes less dependent upon the sliding speed. The unique ability of these materials to regenerate swollen surfaces and maintain robust low friction following abrasive wear is promising for designing their slip behavior into aqueous soft robotics components or biomedicine applications.

An indentation-based approach to determine the elastic constants of soft anisotropic tissues

Characterization of the mechanical properties of tissue can help to understand tissue mechanobiology, including disease diagnosis and progression. Indentation is increasingly used to measure the local mechanical properties of tissue, but it has not been fully adapted to capture anisotropic properties. This paper presents an indentation-based method to measure elastic constants of soft anisotropic tissues without additional mechanical tests. The approach uses measurement of the indentation modulus and the aspect ratio of the elliptical contact introduced by anisotropic mechanical properties of tissue to determine the elastic constants from finite element analysis. The imprinted area imparted by a fluorescent bead-coated spherical indenter showed the aspect ratio of the contact area, giving a generalized sense of the level of anisotropy, and instrumented indentation determined the indentation modulus. A parametric study using finite element simulation of the indentation tests established the relationship between the aspect ratio of contact and the non-dimensional ratios, E_x/E_y and G_xy/E_y; here, E_x and E_y are the Young's moduli (E_x > E_y) and G_xy is the shear modulus in the xy plane. For strongly anisotropic materials (E_x/E_y > 150), aspect ratio and indentation modulus are sufficient to determine G_xy and E_y. For weakly anisotropic materials, indentation modulus in the transverse direction, E_y, and the aspect ratio of contact in the anisotropic plane can be used to determine the elastic constants. The proposed approach improves the elastic characterization of soft, anisotropic biological materials from indentation and helps to elucidate the complex mechanical behavior of soft anisotropic tissues.

Latching of the click beetle (Coleoptera: Elateridae) thoracic hinge enabled by the morphology and mechanics of conformal structures

Elaterid beetles have evolved to 'click' their bodies in a unique maneuver. When this maneuver is initiated from a stationary position on a solid substrate, it results in a jump not carried out by the traditional means of jointed appendages (i.e. legs). Elaterid beetles belong to a group of organisms that amplify muscle power through morphology to produce extremely fast movements. Elaterids achieve power amplifications through a hinge situated in the thoracic region. The actuating components of the hinge are a peg and mesosternal lip, two conformal parts that latch to keep the body in a brace position until their release, the 'click', that is the fast launch maneuver. Although prior studies have identified this mechanism, they were focused on the ballistics of the launched body or limited to a single species. In this work, we identify specific morphological details of the hinges of four click beetle species - Alaus oculatus, Parallelostethus attenuatus, Lacon discoideus and Melanotus spp. - which vary in overall length from 11.3 to 38.8 mm. Measurements from environmental scanning electron microscopy (ESEM) and computerized tomography (CT) were combined to provide comparative structural information on both exterior and interior features of the peg and mesosternal lip. Specifically, ESEM and CT reveal the morphology of the peg, which is modeled as an Euler-Bernoulli beam. In the model, the externally applied force is estimated using a micromechanical experiment. The equivalent stiffness, defined as the ratio between the applied force and the peg tip deflection, is estimated for all four species. The estimated peg tip deformation indicates that, under the applied forces, the peg is able to maintain the braced position of the hinge. This work comprehensively describes the critical function of the hinge anatomy through an integration of specific anatomical architecture and engineering mechanics for the first time.

Compliant and stretchable thermoelectric coils for energy harvesting in miniature flexible devices

With accelerating trends in miniaturization of semiconductor devices, techniques for energy harvesting become increasingly important, especially in wearable technologies and sensors for the internet of things. Although thermoelectric systems have many attractive attributes in this context, maintaining large temperature differences across the device terminals and achieving low-thermal impedance interfaces to the surrounding environment become increasingly difficult to achieve as the characteristic dimensions decrease. Here, we propose and demonstrate an architectural solution to this problem, where thin-film active materials integrate into compliant, open three-dimensional (3D) forms. This approach not only enables efficient thermal impedance matching but also multiplies the heat flow through the harvester, thereby increasing the efficiencies for power conversion. Interconnected arrays of 3D thermoelectric coils built using microscale ribbons of monocrystalline silicon as the active material demonstrate these concepts. Quantitative measurements and simulations establish the basic operating principles and the key design features. The results suggest a scalable strategy for deploying hard thermoelectric thin-film materials in harvesters that can integrate effectively with soft materials systems, including those of the human body.

Mechanically-Guided Deterministic Assembly of 3D Mesostructures Assisted by Residual Stresses

Formation of 3D mesostructures in advanced functional materials is of growing interest due to the widespread envisioned applications of devices that exploit 3D architectures. Mechanically guided assembly based on compressive buckling of 2D precursors represents a promising method, with applicability to a diverse set of geometries and materials, including inorganic semiconductors, metals, polymers, and their heterogeneous combinations. This paper introduces ideas that extend the levels of control and the range of 3D layouts that are achievable in this manner. Here, thin, patterned layers with well-defined residual stresses influence the process of 2D to 3D geometric transformation. Systematic studies through combined analytical modeling, numerical simulations, and experimental observations demonstrate the effectiveness of the proposed strategy through ≈20 example cases with a broad range of complex 3D topologies. The results elucidate the ability of these stressed layers to alter the energy landscape associated with the transformation process and, specifically, the energy barriers that separate different stable modes in the final 3D configurations. A demonstration in a mechanically tunable microbalance illustrates the utility of these ideas in a simple structure designed for mass measurement.

Poroelasticity-driven lubrication in hydrogel interfaces

It is widely accepted that hydrogel surfaces are slippery, and have low friction, but dynamic applied stresses alter the hydrogel composition at the interface as water is displaced. The induced osmotic imbalance of compressed hydrogel which cannot swell to equilibrium should drive the resistance to slip against it. This paper demonstrates the driving role of poroelasticity in the friction of hydrogel-glass interfaces, specifically how poroelastic relaxation of hydrogels increases adhesion. We translate the work of adhesion into an effective surface energy density that increases with the duration of applied pressure from 10 to 50 mJ m^-2, as measured by micro-indentation. A model of static friction coefficient is derived from an area-based rules of mixture for the surface energies, and predicts the friction coefficient changes upon initiation of slip. For kinetic friction, the competition between duration of contact and relaxation time is quantified by a contacting Péclet number, Pe_C. A single length parameter on the scale of micrometers fits these two models to experimental micro-friction data. These models predict how short durations of applied pressure and faster sliding speeds, do not disrupt interfacial hydration; this prevailing water maintains low friction. At low speeds where interface drainage dominates, the osmotic suction works against slip for higher friction. The prediction of friction coefficients after adhesion characterization by micro-indentation makes use of the interplay between poroelasticity, adhesion, and friction. This approach provides a starting point for prediction of, and design for, hydrogel interfacial friction.

Soft hydrated sliding interfaces as complex fluids

Hydrogel surfaces are biomimics for sensing and mobility systems in the body such as the eyes and large joints due to their important characteristics of flexibility, permeability, and integrated aqueous component. Recent studies have shown polymer concentration gradients resulting in a less dense region in the top micrometers of the surface. Under shear, this gradient is hypothesized to drive lubrication behavior due to its rheological similarity to a semi-dilute polymer solution. In this work we map 3 distinct lubricating regimes between a polyacrylamide surface and an aluminum annulus using stepped-velocity tribo-rheometry over 5 decades of sliding speed in increasing and decreasing steps. These regimes, characterized by weakly or strongly time-dependent response and thixotropy-like hysteresis, provide the skeleton of a lubrication curve for hydrogel-against-hard material interfaces and support hypotheses of polymer mechanics-driven lubrication. Tribo-rheometry is particularly suited to uncover the lubrication mechanisms of complex interfaces such as are formed with hydrated hydrogel surfaces and biological surfaces.

Publisher's Note: Multicellular density fluctuations in epithelial monolayers [Phys. Rev. E 92, 032729 (2015)]

This corrects the article DOI: 10.1103/PhysRevE.92.032729.

Kinetics of aqueous lubrication in the hydrophilic hydrogel Gemini interface

The exquisite sliding interfaces in the human body share the common feature of hydrated dilute polymer mesh networks. These networks, especially when they constitute a sliding interface such as the pre-corneal tear film on the ocular interface, are described by the molecular weight of the polymer chains and a characteristic size of a minimum structural unit, the mesh size, ξ. In a Gemini interface where hydrophilic hydrogels are slid against each other, the aqueous lubrication behavior has been shown to be a function of sliding velocity, introducing a sliding timescale competing against the time scales of polymer fluctuation and relaxation at the surface. In this work, we examine two recent studies and postulate that when the Gemini interface slips faster than the single-chain relaxation time, chains must relax, suppressing the amplitude of the polymer chain thermal fluctuations.

Multicellular density fluctuations in epithelial monolayers

Changes in cell size often accompany multicellular motion in tissue, and cell number density is known to strongly influence collective migration in monolayers. Density fluctuations in other forms of active matter have been explored extensively, but not the potential role of density fluctuations in collective cell migration. Here we investigate collective motion in cell monolayers, focusing on the divergent component of the migration velocity field to probe density fluctuations. We find spatial patterns of diverging and converging cell groups throughout the monolayers, which oscillate in time with a period of approximately 3-4 h. Simultaneous fluorescence measurements of a cytosol dye within the cells show that fluid passes between groups of cells, facilitating these oscillations in cell density. Our findings reveal that cell-cell interactions in monolayers may be mediated by intercellular fluid flow.

Polymer fluctuation lubrication in hydrogel gemini interfaces

Interfacial sliding speed and contact pressure between the sub-units of particulate soft matter assemblies can vary dramatically across systems and with dynamic conditions. By extension, frictional interactions between particles may play a key role in their assembly, global configuration, collective motion, and bulk material properties. For example, in tightly packed assemblies of microgels - colloidal microspheres made of hydrogel - particle stiffness controls the fragility of the glassy state formed by the particles. The interplay between particle stiffness and shear stress is likely mediated by particle-particle normal forces, highlighting the potential role of hydrogel-hydrogel friction. Here we study friction at a twinned "Gemini" interface between hydrogels. We construct a lubrication curve that spans four orders of magnitude in sliding speed, and find qualitatively different behaviour from traditional lubrication of engineering material surfaces; fundamentally different types of lubrication occur at the hydrogel Gemini interface. We also explore the role played by polymer solubility and hydrogel-hydrogel adhesion in hydrogel friction. We find that polymer network elasticity, mesh size, and single-chain relaxation times can describe friction at the gel-gel interface, including a transition between lubrication regimes with varying sliding speed.

Cell friction

Cells sense and respond to their environment. Mechanotransduction is the process by which mechanical forces, stress, and strains are converted into biochemical signals that control cell behavior. In recent decades it has been shown that appropriate mechanical signals are essential to tissue health, but the role of friction and direct contact shearing across cell surfaces has been essentially unexplored. This, despite the obvious existence of numerous biological tissues whose express function depends on sliding contacts. In our studies on frictional interactions of corneal cells we find that the friction coefficients are on the order of mu = 0.03-0.06 for in vitro and in vivo experiments. Additionally, we observe cell death after single cycles of sliding at contact pressures estimated to be approximately 12 kPa. These experimental results suggest that frictional contact forces produce mechanical stresses and strains that are in the cellular mechanosensing ranges.

A Biphasic Model for Micro-Indentation of a Hydrogel-Based Contact Lens

The stiffness and hydraulic permeability of soft contact lenses may influence its clinical performance, e.g., on-eye movement, fitting, and wettability, and may be related to the occurrence of complications; e.g., lesions. It is therefore important to determine these properties in the design of comfortable contact lenses. Micro-indentation provides a nondestructive means of measuring mechanical properties of soft, hydrated contact lenses. However, certain geometrical and material considerations must be taken into account when analyzing output force-displacement (F-D) data. Rather than solely having a solid response, mechanical behavior of hydrogel contact lenses can be described as the coupled interaction between fluid transport through pores and solid matrix deformation. In addition, indentation of thin membranes (∼100μm) requires special consideration of boundary conditions at lens surfaces and at the indenter contact region. In this study, a biphasic finite element model was developed to simulate the micro-indentation of a hydrogel contact lens. The model accounts for a curved, thin hydrogel membrane supported on an impermeable mold. A time-varying boundary condition was implemented to model the contact interface between the impermeable spherical indenter and the lens. Parametric studies varying the indentation velocities and hydraulic permeability show F-D curves have a sensitive region outside of which the force response reaches asymptotic limits governed by either the solid matrix (slow indentation velocity, large permeability) or the fluid transport (high indentation velocity, low permeability). Using these results, biphasic properties (Young’s modulus and hydraulic permeability) were estimated by fitting model results to F-D curves obtained at multiple indentation velocities (1.2 and 20μm∕s). Fitting to micro-indentation tests of Etafilcon A resulted in an estimated permeability range of 1.0×10−15 to 5.0×10−15m4∕Ns and Young’s modulus range of 130to170kPa.

The use of rhodamine 6G and fluorescence microscopy in the evaluation of phospholipid-based polymeric biomaterials

A technique is described that allows the staining and subsequent visualization of polymers that contain the phosphorylcholine (PC) group. These materials are useful as bulk materials or coatings for the fabrication of medical devices. The staining method employs rhodamine 6G, which can be simply and rapidly applied to the polymer coating and imaged using fluorescence microscopy. The specificity of the staining for the PC polymers makes this technique suitable for the evaluation of a wide range of substrates and provides qualitative information on coating uniformity, coverage and morphology. It can be used to examine the durability of, and defects in, the coating. Statistical analysis of the fluorescent intensity by measuring the pixel value during imaging can allow for the method to be used as a quality control tool.

Anti-neutrophil cytoplasmic antibodies (ANCA) against bactericidal/permeability-increasing protein (BPI) and cystic fibrosis lung disease

Persistent infection with Pseudomonas aeruginosa and inflammatory mechanisms play an important role in cystic fibrosis (CF) lung disease. ANCA against BPI, a potent host defence protein with anti-bacterial and anti-endotoxin properties, have been described in CF. We have assessed the relationship of anti-BPI antibodies to pulmonary disease severity in 148 CF subjects. IgA and IgG anti-BPI antibodies were found in 55.4% and 70.3% of CF patients, respectively, and higher levels were strongly associated with colonization with P. aeruginosa (P = 0.001 and 0.039 for IgA and IgG antibodies, respectively). IgA and IgG anti-BPI antibodies were independently associated with more severe lung disease as assessed by chest radiograph score (P = 0.023) and a significantly lower forced expiratory volume in 1 s (FEV1)% (P = 0.01). The pathophysiological relevance of the autoantibodies was investigated further by determining their epitope specificity and their effect on bacterial phagocytosis in vitro. Both isotypes of anti-BPI antibodies were specific for the C-terminus of BPI shown recently to be important for BPI-mediated opsonization, and in vitro affinity-purified anti-BPI antibodies significantly reduced BPI-induced phagocytosis of Escherichia coli compared with controls. These data indicate that anti-BPI autoantibodies are associated with colonization with P. aeruginosa and worse lung disease in CF. The inhibition of bacterial phagocytosis suggests that these autoantibodies may contribute to the persistence of P. aeruginosa in the CF lung and so play a role in perpetuating CF lung damage.

Anti-neutrophil cytoplasmic autoantibodies (ANCA) to bactericidal/permeability-increasing (BPI) protein recognize the carboxyl terminal domain

OBJECTIVES

to identify the region of bactericidal/permeability-increasing protein (BPI) recognized by anti-BPI ANCA.

METHODS

sera from 140 patients with a variety of clinical diagnoses (20 systemic vasculitis, 12 cystic fibrosis, 22 bronchiectasis/chronic obstructive airways disease, three diabetes mellitus, 13 chronic renal failure, 12 primary sclerosing cholangitis, eight ulcerative colitis, three Crohn's disease, seven cancer, and 40 other or unknown diagnoses) known to be reactive against native (nBPI), were screened by solid phase enzyme linked immunosorbent assay (ELISA) against a panel of recombinant fusion proteins; holo BPI (rBPI), recombinant lipopolysaccharide binding protein (rLBP), an N-terminal fragment of rBPI (rBPI21 ) and 'fusion' proteins containing the C- or N-terminal ends of BPI spliced with N-or C-ends of LBP, respectively.

RESULTS

a strong correlation was seen between the degree of reactivity to rBPI and the BPI C-terminal fusion protein, r=0.69, P < 0.001, as well as between nBPI and rBPI protein, r=0.55, P < 0.001, but not between nBPI and the N-terminal region of BPI (rBPI21), or proteins containing only the N-terminal fragment. Binding to proteins containing the BPI C-terminus was confirmed to be specific by fluid phase inhibition ELISA and Western blot analyses.

CONCLUSIONS

together these data suggest that circulating autoantibodies to BPI from patients with different diseases recognize the C-terminal region of BPI.

Antineutrophil cytoplasmic autoantibodies (ANCA) in children with cystic fibrosis

Anti-neutrophil cytoplasmic antibodies (ANCA) represent a useful diagnostic tool in patients with small vessel vasculitis. Circulating ANCA specific for bactericidal/permeability increasing protein (BPI) have been recently reported in adult patients with cystic fibrosis (CF), an autosomal recessive disorder caused by mutations in the cystic fibrosis transmembrane regulator (CFTR) gene with consequent impaired function of a transmembrane chloride channel. To contribute to the better understanding of the significance of ANCA in this disease, we investigated ANCA presence and antigenic specificity in children with CF. Results were correlated with clinical status, immunological data, age and genotype. The indirect immunofluorescence pattern of a total of 71 children with CF indicated that 31 were c-ANCA positive, while seven were p-ANCA positive. In further ELISA studies of ANCA antigenic specificity, 51 out of 66 investigated samples were positive for BPI, and 14 out of 28 were positive for proteinase 3 (PR3). We found an association between levels of antibodies against PR3 with age and Pseudomonas infection. We did not, however, find any correlation between CFTR genotypes, Pseudomonas infection or paediatric parameters and the level of anti-BPI antibodies. High positivity of anti-BPI antibodies were seen even among the youngest CF patients, before the development of clinical signs of CF, indicating that formation of ANCA might be a very early event in the disease. Both anti-BPI and anti-PR3 antibodies may play a significant, although variable role, in the pathogenesis of CF.

The incidence, cost and factors associated with foot lameness in dairy cattle in south-western Victoria

A survey of 73 dairy farms in south-western Victoria was conducted to assess the cost and mean herd incidence of foot lameness for the period from calving to the end of November, 1985, and to identify the herd, management and environmental factors associated with foot lameness. The mean herd size was 125 cows (range 82 to 220). Lameness occurred in 64 (88%) herds, and the mean herd incidence was 7.0% (range 0.0 to 30.9%). The main clinical signs associated with lameness were the presence of overworn and/or bruised soles, or stones lodged in the interdigital cleft. Factors associated with lameness were: property and herd size, age of cow, bail feeding, voluntary entry into the bails, and features of the farm track including its length, the presence of steep slopes, the type of surface material, presence and treatment of broken sections and maintenance including rolling history. The association of these factors with specific clinical signs was examined. The mean cost was estimated to be $42.90 per lame cow due to loss of production, treatment, the culling or death of lame cows, and extra man hours spent managing lame cows. It was concluded that the site, construction, maintenance and use of the farm track were of major importance to the incidence of lameness in herds in this area and recommendations for reducing lameness are made.