Differential Behavior of Normal and Fibrotic Fibroblasts under the Synergistic Influence of Micropillar Topography and the Rigidity of Honey/Silk-Fibroin Substrates

Modulation of Biophysical Cues in Nature Inspired Patterning of Porous Silk Fibroin Scaffold for Replenishable Controlled Drug Delivery

While a sticking plasteris enough for healing of most of the minor cuts they may get routinely, critical situations like surgical, gunshot, accidental or diabetic wounds;lacarations and other cutaneous deep cuts may require implants and simultaneous medications for healing. From the biophysical standpoint, an internal force-based physical surface stimulusis crucial for cellular sensing during wound repair. In this paper, the authors report the fabrication of a porous, biomimmetically patterned silk fibroin scaffold loaded with ampicillin, which exhibits controlled release of the drug along with possible replenishment of the same. In vitro swelling study reveals that the scaffolds with hierarchical surface patterns exhibit lower swelling and degradation than other types of scaffolds. The scaffolds, that show remarkable broad-spectrum antibacterial efficacy, exhibit Korsemeyer-Peppas model for the ampicillin release patterns due to the structural hydrophobicity imparted by the patterns. Four distinct cell-matrix adhesion regimes are investigated for the fibroblasts to eventually form cell sheets all over the hierarchical surface structures. 4',6-diamidino-2-phenylindole (DAPI) and Fluorescein Diacetate (FDA) fluorescent staining clearly demonstrate the superiority of patterned surface over its other variants. A comparative immunofluorescence study among collagen I, vinculin, and vimentin expressions substantiated the patterned surface to be superior to others.

A critical review on robust self-cleaning properties of lotus leaf

The robust self-cleaning of a lotus leaf is the most classic and powerful phenomenon in nature, whose hybrid papillae and biological wax guarantee its functions. The stability of the lotus leaf surface function is determined by its overall structural design, and is also the fundamental reason for its long-term survival in the natural environment. In fact, the durability of lotus leaf surface function is facilitated by the coordination of many factors which is why it is challenging to be investigated using bionic technology. In this review, we comprehensively examined the synergistic effects of flexible characteristics, surface topography, hollow interlayers, leaf shape, and bent petioles on the structural stability of the lotus leaf surface. The key significance of these factors is in transferring the stress and strain on the surface downwards, reducing the load on the surface, improving the durability of the self-cleaning function, and ultimately ensuring respiration and photosynthesis of leaves in the natural environment. This comprehensive scrutiny offers a novel classical bionic scheme for enhancing the structural stability of a surface, which has potential for applications in deepwater self-cleaning, anti-drag, anti-icing, thermal insulation, and mechanical enhancement of membranes and buildings.

Secretory Fluid-Aggregated Janus Electrospun Short Fiber Scaffold for Wound Healing

Exudate management is critical to improve chronic wound healing. Herein, inspired by a Janus-structured lotus leaf with asymmetric wettability, a Janus electrospun short fiber scaffold is fabricated via electrospinning technologies and short fiber modeling. This scaffold is composed of hydrophilic 2D curcumin-loaded electrospun fiber and hydrophobic 3D short fiber via layer-by-layer assembly and electrostatic interactions which can aggregate the wound exudate by pumping from the hydrophobic layer to the hydrophilic via multiple contact points between hydrophilic and hydrophobic fibers, and simultaneously trigger the cascade release of curcumin in the upper 2D electrospun fiber. The 3D short fiber with high porosity and hydrophobicity can quickly aggregate exudate within 30 s after compounding with hydrophilic 2D electrospun fiber via a spontaneous pump. In vitro experiments show that Janus electrospun short fiber has good biocompatibility, and the cascade release of curcumin can significantly promote the proliferation and migration of fibroblasts. In vivo experiments show that it can trigger cascade release of curcumin by aggregating wound exudate, so as to accelerate wound healing process and promote collagen deposition and vascularization. Hence, this unique biometric Janus scaffold provides an alternative for chronic wound healing.

Bioinspired silk fibroin materials: From silk building blocks extraction and reconstruction to advanced biomedical applications

Silk fibroin has become a promising biomaterial owing to its remarkable mechanical property, biocompatibility, biodegradability, and sufficient supply. However, it is difficult to directly construct materials with other formats except for yarn, fabric and nonwoven based on natural silk. A promising bioinspired strategy is firstly extracting desired building blocks of silk, then reconstructing them into functional regenerated silk fibroin (RSF) materials with controllable formats and structures. This strategy could give it excellent processability and modifiability, thus well meet the diversified needs in biomedical applications. Recently, to engineer RSF materials with properties similar to or beyond the hierarchical structured natural silk, novel extraction and reconstruction strategies have been developed. In this review, we seek to describe varied building blocks of silk at different levels used in biomedical field and their effective extraction and reconstruction strategies. This review also present recent discoveries and research progresses on how these functional RSF biomaterials used in advanced biomedical applications, especially in the fields of cell-material interactions, soft tissue regeneration, and flexible bioelectronic devices. Finally, potential study and application for future opportunities, and current challenges for these bioinspired strategies and corresponding usage were also comprehensively discussed. In this way, it aims to provide valuable references for the design and modification of novel silk biomaterials, and further promote the high-quality-utilization of silk or other biopolymers.

One-step laser etching of a bionic hierarchical structure on a silicone rubber surface with thermal and acid/alkali resistance and tunable wettability

Superhydrophobic silicone rubbers with robust physical and chemical stability have promising application potential in the field of flexible electronics. A one-step laser etching strategy is proposed for successfully fabricating superhydrophobic silicone rubbers with bioinspired hierarchical micro/nanostructures. Regular and dense micro/nano spheres gradually accumulate on the modified silicone rubber surface with the increase of laser etching cycles. Owing to the bioinspired hierarchical micro/nano spheres, a 5 μL water droplet on the modified silicone rubber surface exhibits a contact angle of 158 ± 3° and a sliding angle of 5 ± 1°. Moreover, the modified silicone rubber can maintain a stable superhydrophobic state in acid/alkali (pH = 2, 4, 6, 8, and 10) and thermal environments (50-90 °C). Importantly, the contact angle and sliding angle are adjustable depending on the number of laser etching cycles, which is beneficial for the different application requirements. The proposed method for the fast fabrication of superhydrophobic silicone rubbers with tunable wettability can provide an excellent candidate for the protection of flexible electronics in rainy and acid/alkali environments.

Improved Mesenchymal Stem Cell Proliferation, Differentiation, Epithelial Transition, and Restrained Senescence on Hierarchically Patterned Porous Honey Silk Fibroin Scaffolds

We report a significant improvement of adipose-derived mesenchymal stem cells' (ADMSCs) biocompatibility and proliferation on hierarchically patterned porous honey-incorporated silk fibroin scaffolds fabricated using a combination of soft lithography and freeze-drying techniques. Parametric variations show enhanced surface roughness, swelling, and degradation rate with good pore interconnectivity, porosity, and mechanical strength for soft-lithographically fabricated biomimetic microdome arrays on the 2% honey silk fibroin scaffold (PHSF2) as compared to its other variants, which eventually made PHSF2 more comparable to the native environment required for stem cell adhesion and proliferation. PHSF2 also exhibits sustained honey release with remarkable antibacterial efficacy against methicillin-resistant Staphylococcus aureus (MRSA). Honey incorporation (biochemical cue) influences microdome structural features, that is, biophysical cues (height, width, and periodicity), which further allows ADMSCs pseudopods (filopodia) to grasp the microdomes for efficient cell-cell communication and cell-matrix interaction and regulates ADMSCs behavior by altering their cytoskeletal rearrangement and thereby increases the cellular spreading area and cell sheet formation. The synergistic effect of biochemical (honey) and biophysical (patterns) cues on ADMSCs studied by the nitro blue tetrazolium assay and DCFDA fluorescence spectroscopy reveals limited free radical generation within cells. Molecular expression studies show a decrease in p53 and p21 expressions validating ADMSCs senescence inhibition, which is further correlated with a decrease in cellular senescence-associated β galactosidase activity. We also show that an increase in CDH1 and CK19 molecular expressions along with an increase in SOX9, RUNX2, and PPARγ molecular expressions supported by PHSF2 justify the substrate's efficacy of underpinning mesenchymal to epithelial transition and multilineage trans-differentiation. This work highlights the fabrication of a naturally healing nutraceutical (honey)-embedded patterned porous stand-alone tool with the potential to be used as smart stem cells delivering regenerative healing implant.

Flow and deformation characteristics of a flexible microfluidic channel with axial gradients in wall elasticity

Axial gradients in wall elasticity may have significant implications in the deformation and flow characteristics of a narrow fluidic conduit, bearing far-reaching consequences in physiology and bio-engineering. Here, we present a theoretical and experimental framework for fluid-structure interactions in microfluidic channels with axial gradients in wall elasticity, in an effort to arrive at a potential conceptual foundation for in vitro study of mirovascular physiology. Towards this, we bring out the static deformation and steady flow characteristics of a circular microchannel made of polydimethylsiloxane (PDMS) bulk, considering imposed gradients in the substrate elasticity. In particular, we study two kinds of elasticity variations - a uniformly soft (or hard) channel with a central strip that is hard (or soft), and, increasing elasticity along the length of the channel. The former kind yields a centrally constricted (or expanded) deformed profile in response to the flow. The latter kind leads to increasingly bulged channel radius from inlet to outlet in response to flow. We also formulate an analytical model capturing the essential physics of the underlying elastohydrodynamic interactions. The theoretical predictions match favourably with the experimental observations and are also in line with reported results on stenosis in mice. The present framework, thus, holds the potential for acting as a fundamental design basis towards developing in vitro models for micro-circulation, capable of capturing exclusive artefacts of healthy and diseased conditions.

Dual cross-linked honey coupled 3D antimicrobial alginate hydrogels for cutaneous wound healing

We report potentiation of healing efficacy of alginate by value addition at its structural level. Dual crosslinked (ionically and covalently) sodium alginate hydrogel coupled with honey (HSAG) brings about an intermediate stiffness in the fabric, confers consistent swelling property and limits erratic degradation of the polymer which ultimately provides conducive milieu to cellular growth and proliferation. In this work honey concentrations in HSAGs are varied from 2% to 10%. FTIR, XRD and nanoindentation studies on the HSAGs exhibited physicochemical integrity. In vitro degradation study provided the crucial finding on 4% HSAG having controlled degradation rate up to 12 days with a weight loss of 87.36 ± 1.14%. This particular substrate also has an ordered crystalline surface morphology with decent cellular viability (HaCaT and 3T3) and antimicrobial potential against Methicillin Resistant Staphylococcus aureus (MRSA) and Escherichia coli. The in vivo wound contraction kinetics on murine models (4% HSAG treated wound contraction: 94.56 ± 0.1%) has been monitored by both invasive (histopathology) and noninvasive (Swept Source Optical Coherence Tomography) imaging and upon corroborating them it evidenced that 4% HSAG treated wound closure achieved epithelial thickness resembling to that of unwounded skin. Thus, the work highlights structurally modified alginate hydrogel embedded with honey as a potential antimicrobial healing agent.

Durability of submerged hydrophobic surfaces

Hydrophobic and superhydrophobic surfaces have gained wide popularity due to their potential in various areas such as in self-cleaning and anti-fouling materials, drag reduction and microfluidics. However, for all practical applications, the long term durability of these surfaces is extremely important, yet not often investigated. Of particular interest is the long term durability of soft hydrophobic surfaces that remain submerged underwater for a prolonged duration. In this article, we explore how the chemical durability of flat and patterned crosslinked PDMS surfaces (polydimethylsiloxane, a preferred material for microfabrication) change as a function of time when submerged in acidic, basic and neutral media for different durations over a prolonged period of time. Based on contact angle measurements, atomic force microscopy, confocal microscopy and SEM analysis of the surfaces, we checked if there is any change in the morphology of the surface due to deposition or etching. We created a biomimetic positive replica of a lotus leaf that exhibited super-hydrophobicity and Cassie state of wetting with a static water contact angle (θ) > 150°, and compared the degradation with a negative replica of lotus leaf (θ ∼ 127°), a grating patterned surface that exhibited Wenzel state of wetting (θ ∼ 110°) and a flat crosslinked PDMS surface (θ ∼ 105°). The positive replica maintained reasonable hydrophobicity (θ > 90°) for up to a month, but lost its super-hydrophobic property. The surface hydrophobicity degraded the most in the case of basic solution due to deposition.

Tunable adhesion and slip on a bio-mimetic sticky soft surface

Simultaneous tuning of wettability and adhesion of a surface requires intricate procedures for altering the interfacial structures. Here, we present a simple method for preparing a stable slippery surface, with an intrinsic capability of varying its adhesion characteristics. Cross-linked PDMS, an inherent hydrophobic material commonly used for microfluidic applications, is used to replicate the structures on the surface of a rose petal which acts as a high adhesion solid base and is subsequently oleoplaned with silicone oil. Our results demonstrate that the complex hierarchical rose petal structures can arrest dewetting of the silicone oil on the cross linked PDMS base by anchoring the oil film strongly even under flow. Further, by tuning the extent of submergence of the rose petal structures with silicone oil, we could alter the adhesion characteristics of the surface on demand, while retaining its slippery characteristics for a wide range of the pertinent parameters. We have also demonstrated the possible fabrication of gradient adhesion surfaces. This, in turn, may find a wide variety of applications in water harvesting, droplet maneuverability and no-loss transportation in resource-limited settings.

Capillary Force Lithography Pattern-Directed Self-Assembly (CFL-PDSA) of Phase-Separating Polymer Blend Thin Films

We report capillary force lithography pattern-directed self-assembly (CFL-PDSA), a facile technique for patterning immiscible polymer blend films of polystyrene (PS)/poly(methyl methacrylate) (PMMA), resulting in a highly ordered phase-separated morphology. The pattern replication is achieved by capillary force lithography (CFL), by annealing the film beyond the glass transition temperature of both the constituent polymers, while confining it between a patterned cross-linked poly(dimethyl siloxane) (PDMS) stamp and the silicon substrate. As the pattern replication takes place because of rise of the polymer meniscus along the confining stamp walls, higher affinity of PMMA toward the oxide-coated silicon substrate and of PS toward cross-linked PDMS leads to well-controlled vertically patterned phase separation of the two constituent polymers during thermal annealing. Although a perfect negative replica of the stamp pattern is obtained in all cases, the phase-separated morphology of the films under pattern confinement is strongly influenced by the blend composition and annealing time. The phase-separated domains coarsen with time because of migration of the two components into specific areas, PS into an elevated mesa region and PMMA toward the substrate, because of preferential wetting. We show that a well-controlled, phase-separated morphology is achieved when the blend ratio matches the volume ratio of the elevated region to the base region in the patterned films. The proposed top-down imprint patterning of blends can be easily made roll-to-roll-compatible for industrial adoption.

Programmable Nanopatterns by Controlled Debonding of Soft Elastic Films

We report a facile patterning technique capable of creating nanostructures with different feature heights (h_S), periodicities (λ_S), aspect ratios (A_R), and duty ratios (D_R), using a single grating stamp with fixed feature height h_P and periodicity λ_P. The proposed method relies on controlling the extent of debonding and morphology of the contact instability features, when a rigid patterned stamp is gradually debonded from a soft elastic film to which it was in initial conformal contact. Depending on whether the instability wavelength (λ_F scales with the film thickness h_F as λ_F ≈ 3h_F) and the periodicity of the stamp feature (λ_P) are commensurate or not, it is possible to obtain features along each stamp protrusion when λ_F ≈ λ_P or patterns that span several stripes of the stamp when λ_F > λ_P. In both cases, the patterns fabricated during debonding are taller than the original stamp features (h_S > h_P). We show that h_S can be modulated by controlling the extent of debonding as well as the shear modulus of the film (μ). Additionally, when λ_F > λ_P, progressive debonding leads to the gradual peeling of replicated features, which, in turn, allows possible tuning of the duty ratio (D_R) of the patterns. Finally we show that by the simultaneous modulation of A_R, D_R, and h_S, it becomes possible to create surfaces with controlled wettability.