Friction and durability of virgin and damaged skin with and without skin cream treatment using atomic force microscopy

Research on tactile perception by skin friction based on a multimodal method

BACKGROUND

Tactile perception is an essential function of skin. As this research involves many fields, such as skin friction, psychology, and neuroscience, the achievement tactile perception is scattered in various fields with different research methods. Therefore, it is necessary to study the whole tactile loop in a multimodal way, synchronizing all tactile information.

MATERIALS AND METHODS

To measure information from touch to haptics, we developed a specially designed measuring platform connecting to an electroencephalogram (EEG) recording system. Sandpapers with different roughness were used as samples. First, the surface properties were measured in tribological experiments. Second, psychophysical experiments were conducted to assess the volunteers' cognition of samples' roughness. Third, the mechanical parameters and EEG were measured at the same time during fingertip sliding on samples. Then, the data of all four tactile elements were processed and analyzed separately. The characteristic features were extracted from those data in the time-frequency domain. Furthermore, the correlation coefficient was calculated in the pairwise comparison of each element to evaluate the feasibility of the multimodal method in the study of tactile perception.

RESULTS

The 600-mesh sandpaper has the largest Ra, Rz, Rsm, and particle size. The normal load, friction force, spectral centroid, and α- and β-wave energy ratios of EEG at chosen electrodes have significant differences and correlations between 3000- and 600-mesh sandpaper in general.

CONCLUSION

This multimodal method could be used in the study of tactile perception, which is a comprehensive way to observe the whole tactile loop from multiple perspectives.

Tattoo Inks for Optical Biosensing in Interstitial Fluid

The persistence of traditional tattoo inks presents an advantage for continuous and long-term health monitoring in point of care devices. The replacement of tattoo pigments with optical biosensors aims a promising alternative for monitoring blood biomarkers. Tattoo inks functionalization enables the control of interstitial biomarkers with correlated concentrations in plasma, to diagnose diseases, evaluate progression, and prevent complications associated with physio pathological disorders or medication mismatches. The specific biomarkers in interstitial fluid provide a new source of information, especially for skin diseases. The study of tattoo inks displays insufficient regulation in their composition, a lack of reports of the related complications, and a need for further studies on their degradation kinetics. This review focuses on tattoo optical biosensors for monitoring dermal interstitial biomarkers and discusses the clinical advantages and main challenges for in vivo implantation. Tattoo functionalization provides a minimally invasive, reversible, biocompatible, real-time sensing with long-term permanence and multiplexing capabilities for the control, diagnosis, and prevention of illness; it enables self-controlling management by the patient, but also the possibility of sending the records to the doctor.

Bioinspired Non-Immunogenic Multifunctional Sealant for Efficient Blood Clotting and Suture-Free Wound Closure

Engineering bioinspired peptide-based molecular medicine is an emerging paradigm for the management of traumatic coagulopathies and inherent bleeding disorder. A hemostat-based strategy in managing uncontrolled bleeding is limited due to the lack of adequate efficacy and clinical noncompliance. In this study, we report an engineered adhesive peptide-based hybrid regenerative medicine, sealant 5, which is designed integrating the structural and functional features of fibrin and mussel foot-pad protein. AFM studies have revealed that sealant 5 (55.8 ± 6.8 nN adhesive force) has higher adhesive force than fibrin (46.4 ± 7.3 nN adhesive force). SEM data confirms that sealant 5 retains its network-like morphology both at 37 and 60 °C, inferring its thermal stability. Both sealant 5 and fibrin exhibit biodegradability in the presence of trypsin, and sealant 5 also showed biocompatibility in the presence of fibroblast cells. Engineered sealant 5 efficiently promotes hemostasis with enhanced adhesiveness and less blood-loss than fibrin. In vivo data suggests that in heparinized conditions, sealant 5 ceases bleeding at 212.3 ± 15.1 s, whereas fibrin halts bleeding at 294.3 ± 21.4 s and blood-loss is ∼4-fold less in sealant 5 than in fibrin. In a heparinized system, sealant 5 facilitates faster blood-clotting than fibrin (∼82 s faster) and RADA-16, a reported peptide-based sealant (∼113 s faster). Additionally, in the case of sealant 5, the process of clotting mimicry-like fibrin is independent of the body's own coagulation system. Sealant 5 efficiently halts bleeding for both external and internal wounds, even for a heparinized system overcoming the bacterial infection. ELISA data and PMBC cell proliferation data support the non-immunogenic feature of sealant 5. Though fibrin and sealant 5 have exhibited comparable efficacy in suture-free wound closure, in vivo H&E staining images have revealed infiltration of very few immune cells as well as the presence of abundant collagen formation in the case of sealant 5-treated wound. Such nature-inspired non-immunogenic sealants offer exciting possibilities for the treatment of uncontrolled bleeding vis-à-vis wound closure.

Frontiers in nanotribology: Magnetic storage, bio/nanotechnology, cosmetics, and bioinspiration

The word "nanotribology" was introduced for the first time in the title of a paper and a book in 1995. This field encompasses fundamental studies of surface characterization, adhesion, friction, scratching, wear, and lubrication at the atomic scale. At most solid-solid interfaces of technological relevance, contact occurs at numerous asperities. It is of importance to investigate a single asperity contact in the fundamental tribological studies. A nanoprobe sliding on a surface in probe-based microscopies, including atomic force microscopy (AFM) at ultralow loads, simulates one such contact. AFMs and depth-sensing nanoindentation techniques are also used for nanomechanical characterization. The field is referred to as nanomechanics. AFMs can also be used for nanoelectrical characterization which includes electrical resistance, surface potential, and capacitance mapping. Research in the field of nanotribology and nanomechanics was initiated by or for the magnetic storage industry in the late 1980s. Later in the mid-1990s, nanotribology and nanomechanics research became important in bio/nanotechnology devices which involve relative motion, as well as ultrathin films. Adhesion, friction and wear issues in bio/nanotechnology devices led to the development of the field of bio/nanotribology. Research in ultrathin films used in the cosmetic industry, including hair, hair conditioner, skin, and skin cream, led to development of the field of nanotribology in cosmetics. Biologically inspired design, adaptation, or derivation from nature, referred to as biomimetics or bioinspiration, can guide us to initiate and produce nanomaterials, nanodevices, and processes in a sustainable and environmentally friendly manner. So called, green nanotribology research is important in this field. This perspective article presents an overview of fundamental understanding of nanotribology and nanomechanics and their applications in various fields ranging from magnetic storage, bio/nanotechnology, hair and hair conditioner, skin and skin cream, and bioinspiration (green nanotribology).

Probing the frictional properties of soft materials at the nanoscale

The understanding of friction in soft materials is of increasing importance due to the demands of industries such as healthcare, biomedical, food and personal care, the incorporation of soft materials into technology, and in the study of interacting biological interfaces. Many of these processes occur at the nanoscale, but even at micrometer length scales there are fundamental aspects of tribology that remain poorly understood. With the advent of Friction Force Microscopy (FFM), there have been many fundamental insights into tribological phenomena at the atomic scale, such as 'stick-slip' and 'super-lubricity'. This review examines the growing field of soft tribology, the experimental aspects of FFM and its underlying theory. Moving to the nanoscale changes the contact mechanics which govern adhesive forces, which in turn play a pivotal role in friction, along with the deformation of the soft interface and dissipative phenomena. We examine recent progress and future prospects in soft nanotribology.

Microclimate: A critical review in the context of pressure ulcer prevention

Pressure ulcers are caused by sustained mechanical loading and deformation of the skin and subcutaneous layers between internal stiff anatomical structures and external surfaces or devices. In addition, the skin microclimate (temperature, humidity and airflow next to the skin surface) is an indirect pressure ulcer risk factor. Temperature and humidity affect the structure and function of the skin increasing or lowering possible damage thresholds for the skin and underlying soft tissues. From a pressure ulcer prevention research perspective, the effects of humidity and temperature next to the skin surface are inextricably linked to concurrent soft tissue deformation. Direct clinical evidence supporting the association between microclimate and pressure ulceration is sparse and of high risk of bias. Currently, it is recommended to keep the skin dry and cool and/or to allow recovery periods between phases of occlusion. The stratum corneum must be prevented from becoming overhydrated or from drying out but exact ranges of an acceptable microclimate are unknown. Therefore, vague terms like 'microclimate management' should be avoided but product and microclimate characteristics should be explicitly stated to allow an informed decision making. Pressure ulcer prevention interventions like repositioning, the use of special support surfaces, cushions, and prophylactic dressings are effective only if they reduce sustained deformations in soft tissues. This mode of action outweighs possible undesirable microclimate properties. As long as uncertainty exists efforts must be taken to use as less occlusive materials as possible. There seems to be individual intrinsic characteristics making patients more vulnerable to microclimate effects.

The hyperelastic and failure behaviors of skin in relation to the dynamic application of microscopic penetrators in a murine model

In-depth understanding of skin elastic and rupture behavior is fundamental to enable next-generation biomedical devices to directly access areas rich in cells and biomolecules. However, the paucity of skin mechanical characterization and lack of established fracture models limits their rational design. We present an experimental and numerical study of skin mechanics during dynamic interaction with individual and arrays of micro-penetrators. Initially, micro-indentation of individual skin strata revealed hyperelastic moduli were dramatically rate-dependent, enabling extrapolation of stiffness properties at high velocity regimes (>1ms^-1). A layered finite-element model satisfactorily predicted the penetration of micro-penetrators using characteristic fracture energies (∼10pJμm^-2) significantly lower than previously reported (≫100pJμm^-2). Interestingly, with our standard application conditions (∼2ms^-1, 35gpistonmass), ∼95% of the application kinetic energy was transferred to the backing support rather than the skin ∼5% (murine ear model). At higher velocities (∼10ms^-1) strain energy accumulated in the top skin layers, initiating fracture before stress waves transmitted deformation to the backing material, increasing energy transfer efficiency to 55%. Thus, the tools developed provide guidelines to rationally engineer skin penetrators to increase depth targeting consistency and payload delivery across patients whilst minimizing penetration energy to control skin inflammation, tolerability and acceptability.

STATEMENT OF SIGNIFICANCE

The mechanics of skin penetration by dynamically-applied microscopic tips is investigated using a combined experimental-computational approach. A FE model of skin is parameterized using indentation tests and a ductile-failure implementation validated against penetration assays. The simulations shed light on skin elastic and fracture properties, and elucidate the interaction with microprojection arrays for vaccine delivery allowing rational design of next-generation devices.

Effect of friction on vibrotactile sensation of normal and dehydrated skin

BACKGROUND

Vibrotactile sensation mediated is highly dependent on surface mechanical and frictional properties. Dehydration of skin could change these properties.

OBJECTIVES

To investigate the relationship between friction and vibrotactile sensation of normal and dehydrated skin.

METHODS

Vibrations were firstly measured during surface exploration using a biomimetic sensor. Piglet skin was used as human skin model to study frictional properties for both normal and dehydrated skin using an atomic force microscope on nanoscale and a pin-on-disk tribometer on macroscale. Effect of vibrational frequency on friction and vibrotactile perception was also observed on nano and macro scale for normal and dehydrated skin.

RESULTS

The result indicated that dehydrated skin was less sensitive than normal skin. The coefficient of friction of dehydrated skin is smaller than that of normal skin on both nano and macro scale. The coefficient of friction increases as increasing scanning frequencies.

CONCLUSION

There is a positive correlation between coefficient of friction and vibrotactile sensation on nanoscale and macroscale.