Smooth Control Surfaces Research Articles

Contact Guidance of Connective Tissue Fibroblasts on Submicrometer Anisotropic Topographical Cues Is Dependent on Tissue of Origin, β1 Integrins, and Tensin-1 Recruitment.

The substratum topography of both natural and synthetic materials is a prominent regulator of cell behaviors including adhesion, migration, matrix fibrillogenesis, and cell phenotype. Connective tissue fibroblasts are known to respond to repeating groove topographical modifications by aligning and exhibiting directed migration, a phenomenon termed contact guidance. Although both reside in collagen rich connective tissues, dermal and gingival fibroblasts are known to exhibit differences in phenotype during wound healing, with gingival tissue showing a fetal-like scarless response. Differences in adhesion formation and maturation are known to underlie both a scarring phenotype and cell response to topographical features. Utilizing repeating groove substrates with periodicities of 600, 900, and 1200 nm (depth, 100 nm), we investigated the roles of integrins αvβ3 and β1 associated adhesions on contact guidance of human gingival (HGFs) and dermal fibroblasts (HDFs). HGFs showed a higher degree of orientation with the groove long axis than HDFs, with alignment of both vinculin and tensin-1 evident on 600 and 900 nm periodicities in both cell types. Orientation with grooves of any periodicity in HGFs and HDFs did not alter the adhesion number or area compared to smooth control surfaces. Growth of both cell types on all periodicities reduced fibronectin fibrillogenesis compared to control surfaces. Independent inhibition of integrin αvβ3 and β1 in both cell types induced changes in spreading up to 6 h and reduced alignment with the groove long axis. At 24 h post-seeding with blocking antibodies, HGFs recovered orientation, but in HDFs, blocking of β1, but not αvβ3 integrins, inhibited alignment. Blocking of β1 and αvβ3 in HDFs, but not HGFs, inhibited tensin-1-associated fibrillar adhesion formation. Furthermore, inhibition of β1 integrins in HDFs, but not HGFs, resulted in recruitment of tensin-1 to αvβ3 focal adhesions, preventing HDFs from aligning with the groove long axis. Our work demonstrates that tensin-1 localization with specific integrins in adhesion sites is an important determinant of contact guidance. This work emphasizes further the need for tissue-specific biomaterials, when integration into host tissues is required.

Two-phase flow pressure drop in superhydrophobic channels

Superhydrophobic surfaces have been shown to reduce drag in single-phase channel flow; however, little work has been done to characterize their drag-reducing ability found in two-phase flows. Adiabatic, air-water mixtures were used to explore the influence of hydrophobicity on two-phase flows and the hydrodynamics which might be present in flow condensation environments. Pressure drop measurements in a rectangular channel with one superhydrophobic wall (cross-section approximately 0.37×10mm) and three transparent hydrophilic walls were obtained. Data for air/water mixtures with superficial Reynolds numbers ranging from 22–215 and 55–220, respectively, were obtained for superhydrophobic surfaces with three different cavity fractions. Agreement between experimentally obtained two-phase pressure drop data and correlations in the literature for conventional smooth control surfaces was better than 20 percent, which is within the accuracy of the correlations. The data reveal a reduction in the pressure drop for two-phase flow in a channel with a single superhydrophobic wall compared to a control scenario. The observed reduction is approximately 10 percent greater than the reduction that is observed for single-phase flow (relative to a classical channel).

Surface micropattern limits bacterial contamination.

BackgroundBacterial surface contamination contributes to transmission of nosocomial infections. Chemical cleansers used to control surface contamination are often toxic and incorrectly implemented. Additional non-toxic strategies should be combined with regular cleanings to mitigate risks of human error and further decrease rates of nosocomial infections. The Sharklet micropattern (MP), inspired by shark skin, is an effective tool for reducing bacterial load on surfaces without toxic additives. The studies presented here were carried out to investigate the MP surfaces capability to reduce colonization of methicillin-sensitive Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) compared to smooth control surfaces.MethodsThe MP and smooth surfaces produced in acrylic film were compared for remaining bacterial contamination and colonization following inoculation. Direct sampling of surfaces was carried out after inoculation by immersion, spray, and/or touch methods. Ultimately, a combination assay was developed to assess bacterial contamination after touch transfer inoculation combined with drying (persistence) to mimic common environmental contamination scenarios in the clinic or hospital environment. The combination transfer and persistence assay was then used to test antimicrobial copper beside the MP for the ability to reduce MSSA and MRSA challenge.ResultsThe MP reduced bacterial contamination with log reductions ranging from 87-99% (LR = 0.90-2.18; p < 0.05) compared to smooth control surfaces. The MP was more effective than the 99.9% pure copper alloy C11000 at reducing surface contamination of S. aureus (MSSA and MRSA) through transfer and persistence of bacteria. The MP reduced MSSA by as much as 97% (LR = 1.54; p < 0.01) and MRSA by as much as 94% (LR = 1.26; p < 0.005) compared to smooth controls. Antimicrobial copper had no significant effect on MSSA contamination, but reduced MRSA contamination by 80% (LR = 0.70; p < 0.005).ConclusionThe assays developed in this study mimic hospital environmental contamination events to demonstrate the performance of a MP to limit contamination under multiple conditions. Antimicrobial copper has been implemented in hospital room studies to evaluate its impact on nosocomial infections and a decrease in HAI rate was shown. Similar implementation of the MP has potential to reduce the incidence of HAIs although future clinical studies will be necessary to validate the MP’s true impact.

Enhanced protein adsorption and cellular adhesion using transparent titanate nanotube thin films made by a simple and inexpensive room temperature process: Application to optical biochips

A new type of titanate nanotube (TNT) coating is investigated for exploitation in biosensor applications. The TNT layers were prepared from stable but additive-free sols without applying any binding compounds. The simple, fast spin-coating process was carried out at room temperature, and resulted in well-formed films around 10nm thick. The films are highly transparent as expected from their nanostructure and may, therefore, be useful as coatings for surface-sensitive optical biosensors to enhance the specific surface area. In addition, these novel coatings could be applied to medical implant surfaces to control cellular adhesion. Their morphology and structure was characterized by spectroscopic ellipsometry (SE) and atomic force microscopy (AFM), and their chemical state by X-ray photoelectron spectroscopy (XPS). For quantitative surface adhesion studies, the films were prepared on optical waveguides. The coated waveguides were shown to still guide light; thus, their sensing capability remains. Protein adsorption and cell adhesion studies on the titanate nanotube films and on smooth control surfaces revealed that the nanostructured titanate enhanced the adsorption of albumin; furthermore, the coatings considerably enhanced the adhesion of living mammalian cells (human embryonic kidney and preosteoblast).

Advancing and receding contact lines on patterned structured surfaces

An experimental investigation of advancing and receding contact lines on patterned surfaces was performed in a controlled environment. Hydrophobic polymers were used to create patterned surfaces to mimic defects and the working fluid was water. Surfaces were prepared with holes or pillars every 200 μm and depth/height from 1 to 11 μm. An optical technique was used to measure contact angle. On smooth (control) surfaces, an advancing or receding contact angle was observed. On the patterned surfaces, pinning and depinning at the defects (holes or pillars, respectively) was observed, with advancing or receding contact lines occurring between these depinning/pinning events. The observed pinning/depinning phenomenon of the contact line was investigated to demonstrate the dynamics of the contact line motion over rough surfaces for a small range of contact line velocity. The competition between the Young unbalanced force and the anchoring forces of the defects is thought to dominate the pinning/depinning process. Stick–slip behaviour of the contact line is observed for larger structures and the results show a strong pinning of the contact line on surfaces with larger defects. The datum contact angle and its deviation were measured and a new concept of scaled energy barrier was calculated for advancing contact lines. This was strongly dependent on defect size. An estimation of the unbalanced Young force per unit length was also made for comparison, which also depended on defect size. This new approach allows new insights into this wetting phenomenon.

Nanostructure-Mediated Drug Delivery

A new type of titanate nanotube (TNT) coating is investigated for exploitation in biosensor applications. The TNT layers were prepared from stable but additive-free sols without applying any binding compounds. The simple, fast spin-coating process was carried out at room temperature, and resulted in well-formed films around 10 nm thick. The films are highly transparent as expected from their nanostructure and may, therefore, be useful as coatings for surface-sensitive optical biosensors to enhance the specific surface area. In addition, these novel coatings could be applied to medical implant surfaces to control cellular adhesion. Their morphology and structure was characterized by spectroscopic ellipsometry (SE) and atomic force microscopy (AFM), and their chemical state by X-ray photoelectron spectroscopy (XPS). For quantitative surface adhesion studies, the films were prepared on optical waveguides. The coated waveguides were shown to still guide light; thus, their sensing capability remains. Protein adsorption and cell adhesion studies on the titanate nanotube films and on smooth control surfaces revealed that the nanostructured titanate enhanced the adsorption of albumin; furthermore, the coatings considerably enhanced the adhesion of living mammalian cells (human embryonic kidney and preosteoblast).

Growth of connective tissue progenitor cells on microtextured polydimethylsiloxane surfaces.

Growth of human connective tissue progenitor cells (CTPs) was characterized on smooth and microtextured polydimethylsiloxane (PDMS) surfaces. Human bone-marrow-derived cells were cultured for 9 days under conditions promoting osteoblastic differentiation on smooth PDMS surfaces and on PDMS post microtextures that were 6 microm high and 5, 10, 20, and 40 microm in diameter, respectively. Glass tissue-culture dishes were used as controls. The number of viable cells was determined, and an alkaline phosphatase stain was used as a marker for osteoblastic phenotype. CTPs attached, proliferated, and differentiated on all surfaces. Cells on the smooth PDMS and control surfaces spread and proliferated as colonies in proximity to other cells and migrated in random directions, with cell process lengths of up to 80 microm. In contrast, cells on the PDMS post microtextures grew as sparsely distributed networks of cells, with processes, occasionally up to 300 microm, that appeared to interact with the posts. Cell counts revealed that there were fewer (50%) CTPs on the smooth PDMS surface than were on the glass control surfaces. However, there were consistently more (>144%) CTPs on the PDMS post textures than on the controls. In particular, the 10-microm-in-diameter posts (268%) exhibited a significantly (p < 0.05) greater cell number than did the smooth PDMS.

Analysis of connective tissue progenitor cell behavior on polydimethylsiloxane smooth and channel micro-textures.

Growth of human connective tissue progenitor cells (CTPs) was characterized on smooth and microtextured polydimethylsiloxane (PDMS) surfaces. Human bone marrow derived cells were cultured for nine days under conditions promoting osteoblastic differentiation on Smooth PDMS and PDMS Channel microtextures (11 microm high, 45 microm wide channels, and separated by 5 microm wide ridges). Glass tissue culture dish surfaces were used as controls. Cell numbers per colony, cell density within colonies, alignment of cells, area of colonies, and colony shapes were determined as a function of substrate surface topography. An alkaline phosphatase stain was used as a marker for osteoblastic phenotype. CTPs attached, proliferated, and differentiated on all surfaces with cell process lengths of up to 80 microm. Cells on the Smooth PDMS and control surfaces spread and proliferated as colonies in proximity to other cells and migrated in random directions creating colonies that covered significantly larger areas (0.96 and 1.05 mm(2), respectively) than colonies formed on PDMS Channel textures (0.64 mm(2)). In contrast, cells on PDMS Channel textures spread, proliferated, aligned along the channel axis, and created colonies that were more dense, and with lengths of longest colony axes that were significantly longer (3252 microm) than those on the Smooth PDMS (1265 microm) and control surfaces (1319 microm). Cells on PDMS Channel textures were aligned at an angle of 14.44 degrees relative to the channel axis, and the resulting colonies exhibited a significantly higher aspect ratio (13.72) compared to Smooth PDMS (1.57) and control surfaces (1.51).

Subcutaneous microfabricated surfaces inhibit epithelial recession and promote long-term survival of percutaneous implants

The long-term success of percutaneous devices is compromised by problems such as infection, mechanical avulsion and epithelial downgrowth. The objective of this study was to test the effects of microfabricated surfaces on tissue integration and long-term survival of percutaneous implants, using a modified implant design and a two-stage surgical method. Hexagonal titanium-coated epoxy implants were constructed with separate subcutaneous and percutaneous components, so that the effects of surface topography on connective tissue could be separated from the effects on epithelium. Subcutaneous components with 30-μm-deep micromachined grooves, 120-μm-deep tapered pits, or smooth control surfaces were secured to the calvarial bone of rats by a titanium pin. After 8 weeks, a percutaneous smooth-surfaced component was secured to the subcutaneous component. Dental impression materials were used to make models of the components and adjacent tissues at weekly intervals and tissue recession around the implants was measured. Some implants were removed at intervals up to 24 weeks and processed for histology. Connective-tissue ingrowth and mineralized tissue were noticed on the micromachined surfaces, whereas a thick capsule and epithelial downgrowth were observed on smooth control surfaces. On all implants, recession occurred most rapidly in the first 3 weeks, but was significantly reduced relative to the smooth controls only on implants with micromachined grooved subcutaneous surfaces ( p<0.05). In addition, the time before failure was significantly ( p<0.05) longer for implants with grooved subcutaneous surfaces than implants with smooth and pitted subcutaneous surfaces. This study indicated that an impression technique could be used to monitor tissue recession on percutaneous devices, and that micromachined grooved surfaces located subcutaneously improved the performance and longevity of percutaneous devices by promoting tissue integration.

An adaptive fuzzy-synchronous machine stabilizer

Describes an adaptive fuzzy-synchronous machine power system stabilizer (PSS) that behaves like a proportional integral derivative (PID) controller. The implemented adaptive technique predicts tracking-error divergence and makes online adjustments to the controller gain parameters in order to obtain a faster regulation of the error signal. The proposed PSS is less sensitive to the quality of expert knowledge, and thus is more robust than a non-adaptive fuzzy PSS when subjected to large disturbances. Hence, adequate controls are derived for the various error cases, and smooth control surfaces are achieved. Simulations are carried out using the proposed PSS to show that it consistently gives a stable response with acceptable overshoots and settling times on the frequency, angle and voltage errors.

The effects of micromachined surfaces on formation of bonelike tissue on subcutaneous implants as assessed by radiography and computer image processing.

Surface topography varies widely among commercially available orthopedic and dental implants. While it is generally accepted that the surface topography of an implant influences the formation of bone and affects its performance, few systematic studies have dealt with this important feature. Quantification of the mineralized tissue at the implant interface has typically been attempted using histologic methods or conventional radiographic procedures. However, histologic methods are often technically demanding and time consuming, whereas conventional radiographic procedures lack resolution and sensitivity to identify small areas of mineralization. The objective of this study was to study systematically the effects of micromachined surfaces on bone formation by applying digital radiographic techniques to identify and quantify mineralized tissue. Titanium-coated epoxy replicas of 19 different micromachined grooved or pitted surfaces that ranged between 30 and 120 microns deep, as well as smooth control surfaces, were implanted percutaneously and fixed to the parietal bone of rats. After 8 weeks the implants and attached tissue were removed and processed for light and electron microscopy. A total of 316 implant surfaces were processed, radiographed using conventional and digital techniques, and sectioned for histologic observations. The area of the bonelike tissue and its density were calculated using National Institutes of Health Image software. Mineralization was frequently noted at the interface of some types of micromachined surface but rarely on smooth surfaces. The presence of bone in histologic sections and areas identified as bone through digital radiography and image processing correlated strongly. The frequency of bonelike foci formation decreased as the depth of the grooves increased. In contrast, mineralization occurred more frequently as the depth of the pit increased. In addition, bonelike foci were oriented along the long axis of the grooves. It is thus feasible that the bonelike tissue is shaped, directed, or engineered to a predetermined configuration which is dictated by the surface topography. This study indicated that surface topography influences the frequency as well as the amount of bone deposited adjacent to implants, and mineralized product can be guided by the surface topography. Moreover, digital radiography and image processing can be used reliably to identify and quantify mineralized tissue at the implant interface.

Titanium‐coated micromachined grooves of different dimensions affect epithelial and connective‐tissue cells differently in vivo

A desirable feature of an implant surface which penetrates epithelium would be that the surface impedes epithelial downgrowth. Previous experiments have shown that the micromachined, horizontally oriented grooves on the percutaneous implant surface can impede epithelial downgrowth (Chehroudi et al., J. Biomed. Mater. Res., 22, 459 (1988) and 23, 1067 (1989)). However, little is known of the effect of varying groove parameters such as depth, spacing, and orientation on epithelial downgrowth and attachment of epithelial (E)-cells and fibroblasts (F) to percutaneous implants in vivo. Grooves were produced with a 30-micron pitch and depths of 22 microns, 10 microns, or 3 microns. In addition, 10-microns- and 3-microns-deep grooves were made with pitches of 39 microns and 7 microns, respectively. Implants with grooves oriented either horizontally or vertically to the long axis of the implant as well as smooth control surfaces were coated with 50 nm of titanium and placed in the parietal area of rats for a period of 7 days. Close attachment of E-cells was found on the smooth, 10-microns- and 3-microns-deep, horizontally or vertically aligned grooved surfaces; in contrast, E-cells bridged over the 22-microns-deep, horizontally oriented grooves. F formed a capsule on the smooth surface as well as the 10-microns- and 3-microns-deep horizontally oriented grooves, but F inserted obliquely into the 22-microns-deep, horizontally aligned grooved surface. Histomorphometric measurements indicated that the epithelial downgrowth was greatest on the vertically oriented grooved and smooth surfaces and was shortest on the 22-microns-deep and 10-microns-deep horizontally aligned grooved surfaces. These differences indicate that epithelial downgrowth was accelerated on the vertically oriented grooved surfaces and inhibited on the horizontally oriented grooved surfaces. Moreover, the mechanism of inhibition of the epithelial downgrowth may differ among these surfaces. E-cells bridged over the 22-microns-deep grooves and their migration appeared to be inhibited by the F that inserted into the implant surface. In the shallower horizontal grooves, however, epithelial downgrowth was probably inhibited by contact guidance because there was no evidence of F inserting obliquely into the implant surface.