Design of a Biomimetic Skin for an Octopus-Inspired Robot - Part Ⅰ: Characterising Octopus Skin

Octopus skin samples were tested under quasi-static and scissor cutting conditions to measure the in-plane material properties and fracture toughness. Samples from all eight arms of one octopus were tested statically to investigate how properties vary from arm to arm. Another nine octopus skins were measured to study the influence of body mass on skin properties. Influence of specimen location on skin mechanical properties was also studied. Material properties of skin, i.e. the Young's modulus, ultimate stress, failure strain and fracture toughness have been plotted against the position of skin along the length of arm or body. Statistical studies were carried out to help analyzing experimental data obtained. Results of this work will be used as guidelines for the design and development of artificial skins for an octopus-inspired robot.     

Developing Skin Analogues for a Robotic Octopus

In order to fabricate a biomimetic skin for an octopus inspired robot,a new process was developed based on mechanical properties measured from real octopus skin.Various knitted nylon textiles were tested and the one of 10-denier nylon was chosen as reinforcement.A combination of Ecoflex 0030 and 0010 silicone rubbers was used as matrix of the composite to obtain the right stiffness for the skin-analogue system.The open mould fabrication process developed allows air bubble to escape easily and the artificial skin produced was thin and waterproof.Material properties of the biomimetic skin were characterised using static tensile and instrumented scissors cutting tests.The Young's moduli of the artificial skin are 0.08 MPa and 0.13 MPa in the longitudinal and transverse directions,which are much lower than those of the octopus skin.The strength and fracture toughness of the artificial skin,on the other hand are higher than those of real octopus skins.Conically-shaped skin prototypes to be used to cover the robotic arm unit were manufactured and tested.The biomimetic skin prototype was stiff enough to maintain it conical shape when filled with water.The driving force for elongation was reduced significantly compared with previous prototypes.     

Development of Biomimetic Squid-Inspired Suckers

Biomechanical properties of squid suckers were studied to provide inspiration for the development of sucker artefacts for a robotic octopus.Mechanical support of the rings found inside squid suckers was studied by bending tests.Tensile tests were carried out to study the maximum possible sucking force produced by squid suckers based on the strength of sucker stalks,normalized by the sucking areas.The squid suckers were also directly tested to obtain sucking forces by a special testing arrangement.Inspired by the squid suckers,three types of sucker artefacts were developed for the arm skin of an octopus inspired robot.The first sucker artefact made of knitted nylon sheet reinforced silicone rubber has the same shape as the squid suckers.Like real squid suckers,this type of artefact also has a stalk that is connected to the arm skin and a ring to give radial support.The second design is a straight cylindrical structure with uniform wall thickness made of silicone rubber.One end of the cylinder is directly connected to the arm skin and the other end is open.The final design of the sucker has a cylindrical base and a concave meniscus top.The meniscus was formed naturally using the surface tension of silicone gel,which leads to a higher level of the liquid around the edge of a container.The wall thickness decreases towards the tip of the sucker opening.Sucking forces of all three types of sucker artefacts were measured.Advantages and disadvantages of each sucker type were discussed.The final design of suckers has been implemented to the arm skin prototypes.     

The Expression and Activation of Protease‐Activated Receptor‐2 Correlate with Skin Color

Skin color results from the production and distribution of melanin in the epidermis. The protease‐activated receptor‐2 (PAR‐2), expressed on keratinocytes but not on melanocytes, is involved in melanosome uptake via phagocytosis, and modulation of PAR‐2 activation affects skin color. The pattern of melanosome distribution within the epidermis is skin color‐dependent. In vitro, this distribution pattern is regulated by the ethnic origin of the keratinocytes, not the melanocytes. Therefore, we hypothesized that PAR‐2 may play a role in the modulation of pigmentation in a skin type‐dependent manner. We examined the expression of PAR‐2 and its activator, trypsin, in human skins with different pigmentary levels. Here we show that PAR‐2 and trypsin are expressed in higher levels, and are differentially localized in highly pigmented, relative to lightly pigmented skins. Moreover, highly pigmented skins exhibit an increase in PAR‐2‐specific protease cleavage ability. Microsphere phagocytosis was more efficient in keratinocytes from highly pigmented skins, and PAR‐2 induced phagocytosis resulted in more efficient microsphere ingestion and more compacted microsphere organization in dark skin‐derived keratinocytes. These results demonstrate that PAR‐2 expression and activity correlate with skin color, suggesting the involvement of PAR‐2 in ethnic skin color phenotypes.     

The Nature of Water Transport across Frog Skin

A method has been developed for determining simultaneously shortcircuit currents and net water fluxes across frog skin. The basis of the water flux measurement is the determination of changes in weight of a plastic chamber containing the skin and external solution. The accuracy of this method permits net water flows larger than 0.5 mg cm^-2hr.^-1 to be detected, and the apparatus has been used to investigate the relationship between active Na transport and non-osmotic water flow across the skin. Measurement of Na transport and net water influx across completely short-circuited skins provides no good correlation between the two flows. However, skins exhibiting no net water movement in sulfate Ringer displayed an apparent electroosmotic flow of about 40 water molecules per Na ion when depolarizing current densities of 50 and 100 μA cm^-2 are used. It is concluded from this and other evidence that the net water influx across frog skin may be partially electroosmotic in character and that there remains another component of water flow unrelated to active Na transport. A theoretical model, based on irreversible thermodynamics, has been developed to explain the non-osmotic water flow across frog skin.     

Effects of intracortical porosity on fracture toughness in aging human bone: a microCT-based cohesive finite element study

The extent to which increased intracortical porosity affects the fracture properties of aging and osteoporotic bone is unknown. Here, we report the development and application of a microcomputed tomography based finite element approach that allows determining the effects of intracortical porosity on bone fracture by blocking all other age-related changes in bone. Previously tested compact tension specimens from human tibiae were scanned using microcomputed tomography and converted to finite element meshes containing three-dimensional cohesive finite elements in the direction of the crack growth. Simulations were run incorporating age-related increase in intracortical porosity but keeping cohesive parameters representing other age-related effects constant. Additional simulations were performed with reduced cohesive parameters. The results showed a 6% decrease in initiation toughness and a 62% decrease in propagation toughness with a 4% increase in porosity. The reduction in toughnesses became even more pronounced when other age-related effects in addition to porosity were introduced. The initiation and propagation toughness decreased by 51% and 83%, respectively, with the combined effect of 4% increase in porosity and decrease in the cohesive properties reflecting other age-related changes in bone. These results show that intracortical porosity is a significant contributor to the fracture toughness of the cortical bone and that the combination of computational modeling with advanced imaging improves the prediction of the fracture properties of the aged and the osteoporotic cortical bone.     

Effect of autoclave postpolymerization treatments on the fracture toughness of autopolymerizing dental acrylic resins

Introduction: Microwave and water bath postpolymerization have been suggested as methods to improve the mechanical properties of heat and autopolymerizing acrylic resins. However, the effects of autoclave heating on the fracture properties of autopolymerizing acrylic resins have not been investigated. Purpose: The aim of this study was to assess the effectiveness of various autoclave postpolymerization methods on the fracture properties of 3 different autopolymerizing acrylic resins. Methods: Forty-two specimens of 3 different autopolymerizing acrylic resins (Orthocryl, Paladent RR and Futurajet) were fabricated (40x8x4mm), and each group was further divided into 6 subgroups (n=7). Control group specimens remained as processed (Group 1). The first test group was postpolymerized in a cassette autoclave at 135°C for 6 minutes and the other groups were postpolymerized in a conventional autoclave at 130°C using different time settings (5, 10, 20 or 30 minutes). Fracture toughness was then measured with a three-point bending test. Data were analyzed by ANOVA followed by the Duncan test (α=0.05). Results: The fracture toughness of Orthocryl and Paladent-RR acrylic resins significantly increased following conventional autoclave postpolymerization at 130°C for 10 minutes (P<.05). However, the fracture toughness of autoclave postpolymerized Futurajet was not significantly different than its control specimens (P<.05). The fracture toughness of Futurajet was significantly less than Paladent RR and Orthocryl specimens when autoclaved at 130°C for 10 minutes. Conclusions: Within the limitations of this study, it can be suggested that autoclave postpolymerization is an effective method for increasing the fracture toughness of tested autoploymerized acrylic resins.     

皮肤模型与微针穿刺性能评价的研究

微针阵列作为新型透皮给药技术,受到广泛关注。通常以刺入力、刺入率和刺入深度来评价微针刺入皮肤的程度和效率。皮肤是其性能评价的基础。皮肤的物理特性主要由角蛋白丝、胶原纤维、弹性纤维和皮下组织综合决定,并且从厚度、弹性、硬度和韧性等维度反映其对微针刺入的影响。机械的、渗透的、组织的和屏障的等皮肤模型被用于解读和模拟真实皮肤的该方面功能。同样,通过皮肤力学分析后建立的包括本构模型在内的各种皮肤力学模型也从物理维度解析皮肤的力学特征。真实皮肤具有复杂性,存在差异性大、不易获取和储存,以及伦理等问题,而皮肤模型可在一定程度上代替真实皮肤辅助微针递送系统设计、开发和性能评价。本文系统回顾分析了皮肤组织的物理特性、各种皮肤模型的制备及特点、真实皮肤和模拟皮肤在评价微针穿刺性能方面的应用,为开发及建立合适的皮肤模型提供借鉴。     

Body Site Is a More Determinant Factor than Human Population Diversity in the Healthy Skin Microbiome

We studied skin microbiota present in three skin sites (forearm, axilla, scalp) in men from six ethnic groups living in New York City. Methods. Samples were obtained at baseline and after four days following use of neutral soap and stopping regular hygiene products, including shampoos and deodorants. DNA was extracted using the MoBio Power Lyzer kit and 16S rRNA gene sequences determined on the IIlumina MiSeq platform, using QIIME for analysis. Results. Our analysis confirmed skin swabbing as a useful method for sampling different areas of the skin because DNA concentrations and number of sequences obtained across subject libraries were similar. We confirmed that skin location was the main factor determining the composition of bacterial communities. Alpha diversity, expressed as number of species observed, was greater in arm than on scalp or axilla in all studied groups. We observed an unexpected increase in α-diversity on arm, with similar tendency on scalp, in the South Asian group after subjects stopped using their regular shampoos and deodorants. Significant differences at phylum and genus levels were observed between subjects of the different ethnic origins at all skin sites. Conclusions. We conclude that ethnicity and particular soap and shampoo practices are secondary factors compared to the ecological zone of the human body in determining cutaneous microbiota composition.     

Skin color variation in eastern Nepal

The purpose of this paper is to provide skin color data on several endogamous groups of eastern Nepal and to demonstrate genetic microdifferentiation in skin color. Skin reflectance measures were taken at the upper inner arm and forehead sites, using the British DSL Model 99 Reflectance Spectrophotometer fitted with blue, green, and red filters. Measurements on 484 males representing six endogamous groups (Jirel, Sunwar, Sherpa, Tamang, Brahman, Chetri) were utilized. After adjusting for group-specific age effects, multivariate likelihood ratio permutation tests were used to assess ethnic differences in skin reflectance means and covariance matrices. Ethnic group membership had a highly significant effect on skin color at the upper inner arm site and at the forehead site. Differential tanning responses among groups were also detected and may represent the influence of genotype-environment interaction on reflectance traits. Mahalanobis distance analysis revealed patterns of microdifferentiation that are inconsistent with oral historical accounts. Little support was found for the ethnohistorical belief that Jirels are a hybrid group descended from Sunwars and Sherpas, even though this scenario is supported by linguistic, anthropometric, and dermatoglyphic data. We suggest that while reflectometric studies of skin pigmentation may be useful in assessing the macrodifferentiation of human populations, the use of skin color in differentiation studies at the local population level needs to be carefully evaluated.     

组织透明化三维显示全包埋耳皮肤神经血管网（英文）

目的 结合组织学染色技术和组织透明化策略研究耳部皮肤中神经纤维和血管的空间对应关系。方法 将耳廓前面和后面的皮肤从其中间软骨仔细剥离，然后直接分别用蛋白基因产物9.5 (PGP 9.5)和鬼笔环肽对耳部皮肤的神经纤维和血管进行免疫荧光染色并进行组织透明化处理。随后，以全包埋方式将耳皮肤组织裱贴在载玻片上用于荧光显微镜和共聚焦显微镜观察。结果 本研究显示PGP 9.5阳性神经纤维伴随鬼笔环肽标记的血管一道从耳廓的基部走行到其外围区域形成耳廓的神经血管网。在传统的免疫荧光染色技术基础上，后续的组织透明化技术可以更好地展示耳部皮肤中神经纤维和血管的形态学细节。结论 从方法学的角度来看，组织透明化技术增进了耳部皮肤中免疫荧光标记的可视性，它可能成为有效的技术手段用于解析正常和病理状态下耳部神经血管网的空间结构。     

Ongoing Growth Challenges Fruit Skin Integrity

As a result of continuing volume and hence surface-area growth, the skins of most fruit species suffer ongoing strain throughout development. Maintenance of surface integrity is essential to protect the underlying tissues from desiccation and pathogen attack. Fruit skins are commonly “primary” in structure. They comprise a polymeric cuticle overlying an epidermis and a hypodermis. The cuticle is responsible for the skin's barrier function and the cellular layers for the skin's load-bearing functions. Skin failure can be just of the cuticle layer (microcracking) resulting in barrier impairment or it can involve cuticle and cellular layers (macrocracking) resulting in both barrier and structural impairment. Fruit skin failure is associated with a number of disorders including shriveling, cracking, russeting, and skin spots. All result in reduced market value. Our objective is to review the literature on the strategies adopted by fruit to cope with the challenge of continuing skin expansion. We uncover a multistep strategy to prevent or minimize the risk of fruit skin failure. This comprises: (1) area expansion of the load-bearing skin-cell layer(s) by ongoing cell division and (2) the avoidance of skin stress or strain concentrations by matching patterns of skin-cell division to those of area expansion. Also involved, (3) are the partitioning of cuticle strain into plastic and viscoelastic components at the expense of the elastic one. For this, wax and cutin are deposited in the cuticle during growth. Wax and cutin deposition “fix” the strain in the cuticle. Cutin is preferentially deposited on the inner surface of the cuticle, which fixes the strain, but it leaves the outer cuticle surface more strained. Last, (4) if the primary skin is damaged, the barrier functions are restored by the formation of a “secondary” fruit surface (periderm). Lignin can also be used to strengthen the underlying cells following structural failure.     

STX17在不同毛色小鼠皮肤中差异表达与在毛囊中的定位

突触融合蛋白17 (STX17)是一种囊泡蛋白,参与细胞中物质的运输.为研究Stx17在不同毛色皮肤中是否存在差异表达及明确它在毛囊中的定位,进行了普通PCR、real-time PCR、免疫组化和蛋白免疫印迹实验对小鼠皮肤组织和体外培养黑素细胞的Stx17基因及蛋白的检测.普通PCR检测得出小鼠皮肤和黑色素细胞总RNA有Stx17 CDS区序列的表达;荧光定量检测显示,在白、灰、黑3种组织中Stx17均有表达,在灰色腹部表达量最高,是黑色皮肤的1.682倍,昆明鼠白色皮肤中表达量最低,是黑色皮肤的0.115倍;皮肤组织免疫组化结果显示,STX17表达于毛囊的上皮根鞘,且毛囊上段和中段表达量高于下段,黑色素细胞的免疫组化分析得出,STX17在黑色素细胞的细胞质和细胞膜上均有表达;蛋白免疫印迹结果显示,在白色、灰色和黑色皮肤均有STX17蛋白阳性条带且灰色皮肤中表达量最高,黑色皮肤次之,白色皮肤中表达量是最低的,这与荧光定量检测结果一致,体外培养的小鼠黑色素细胞中也有STX17蛋白阳性条带.实验结果表明,小鼠Stx17基因在皮肤组织、毛囊角化细胞以及黑色素细胞中均有表达,Stx17可能参与毛色的形成,且在小鼠腹部毛色变浅中起到了一定的作用.     

Material properties of manatee rib bone

Watercraft-related mortality of the Florida manatee Trichechus manatus latirostris accounts for 24% of all deaths from 1974 to 2006. Of these, the proportion of deaths due to impact accounts for 66% of all watercraft fatalities. To establish safe boat speeds for manatee protection, an estimate of the material properties of their bone is needed to quantify the biomechanical effects of boat strikes on manatees. Manatee ribs are unique in that they are pachyostotic. Machined specimens from ribs were tested in three point flexure. Strength, modulus, work of fracture and fracture toughness were determined for three size classes, by sex. The mean flexural strength ranged from 62 to 160 MPa, elastic modulus from 4 to 18 GPa and work of fracture from 3 to 6 MJ m⁻³. Fractographic analysis was used to calculate toughness, which averaged 1.4–2.9 MPa m^1/2. The results show that manatee bone material is less strong and tough than other mammalian bone. Although the bone increases in static strength as the animals grow, it is not able to absorb more energy. In fact, the ability to absorb impact energy appears to decline with increasing size in animals over 265 cm body length. This decline is due in part to the bone's high density and mineral content. There was little change in mineral content with size, suggesting that material properties are likely correlated with bone quantity. There were no differences in mechanical variables between the sexes. The pachyostotic nature of the bone, which makes the manatee well adapted to its environment, also leaves it highly susceptible to fatal injuries from boats.     

Hyperelastic Material Properties of Mouse Skin under Compression

The skin is a dynamic organ whose complex material properties are capable of withstanding continuous mechanical stress while accommodating insults and organism growth. Moreover, synchronized hair cycles, comprising waves of hair growth, regression and rest, are accompanied by dramatic fluctuations in skin thickness in mice. Whether such structural changes alter skin mechanics is unknown. Mouse models are extensively used to study skin biology and pathophysiology, including aging, UV-induced skin damage and somatosensory signaling. As the skin serves a pivotal role in the transfer function from sensory stimuli to neuronal signaling, we sought to define the mechanical properties of mouse skin over a range of normal physiological states. Skin thickness, stiffness and modulus were quantitatively surveyed in adult, female mice (Mus musculus). These measures were analyzed under uniaxial compression, which is relevant for touch reception and compression injuries, rather than tension, which is typically used to analyze skin mechanics. Compression tests were performed with 105 full-thickness, freshly isolated specimens from the hairy skin of the hind limb. Physiological variables included body weight, hair-cycle stage, maturity level, skin site and individual animal differences. Skin thickness and stiffness were dominated by hair-cycle stage at young (6–10 weeks) and intermediate (13–19 weeks) adult ages but by body weight in mature mice (26–34 weeks). Interestingly, stiffness varied inversely with thickness so that hyperelastic modulus was consistent across hair-cycle stages and body weights. By contrast, the mechanics of hairy skin differs markedly with anatomical location. In particular, skin containing fascial structures such as nerves and blood vessels showed significantly greater modulus than adjacent sites. Collectively, this systematic survey indicates that, although its structure changes dramatically throughout adult life, mouse skin at a given location maintains a constant elastic modulus to compression throughout normal physiological stages.     

Movement, injuries and growth of members of a natural population of the Pacific pygmy octopus, Octopus digueti

Sampling inadequacies and an inability to distinguish age classes have limited our knowledge of octopus biology in nature. Using an artificial shelter sampling technique (Voight, 1988 a ), and defining mature males by the presence of enlarged suckers (Voight, In press), an intertidal population of Octopus digueti was monitored for one year.
In total, 803 octopuses were narcotized; the mass, sex, arm injuries and reproductive condition of each octopus were recorded. Captures were more frequent in lower intertidal areas offering higher shelter availability and a more moderate environment. Capture rates, assumed to indicate octopus movement, correlated with sea temperature except during full moon periods when they were reduced. Over 26%, of the octopuses handled had damaged arms or arm tips, with dorsal arm pairs more often injured. The overall sex ratio was significantly male biased, probably due to maturity-linked mobility differences between the sexes.
Reproduction occurred throughout the year; reproductively competent adults, brooding females and juveniles were present every month. However, annual temperature oscillations synchronize spring hatching of eggs spawned from winter to early spring, creating a clear spring cohort. Growth and age at maturity of males in the spring and autumn cohorts were estimated. Variance was too high for these parameters to be estimated in the winter cohort. Growth rates of males over 12 weeks of age did not differ from those reported in laboratory rearing studies. Estimated average age at maturity ranged from 20 to 32 weeks, depending on temperature.     

Skin color comparisons among ethnic groups of college men

Reflectance readings of skin color were taken on the medial aspect of the left upper arm. The subjects were United States college men between ages 18 and 27 years attending the University of South Carolina. Using the DSL 99 Reflectance Spectrophotometer, readings were obtained under controlled conditions at five settings (601, 603, 605, 607, 609). Ethnic groups studied included young men of 1) Northwest European White ancestry, 2) West African Black ancestry, and 3) Afro-Black/Amerind ancestry. Means and variability statistics serve to describe the skin color distributions. Means were near 12 and 32 for filters 601 and 609 on men of West African Black ancestry, with corresponding means near 36 and 64 on men of Northwest European White ancestry. There was no overlapping of comparable frequency distributions from these two ethnic groups. Significance tests at P = .01 allowed acceptance of the hypothesis that skin color on the medial arm surface was darker for young men of Afro-Black ancestry than for those of 75% Afro-Black ancestry and 25% Amerind ancestry. Means from original data were compared with means from earlier studies on black and white males in Africa, America, and Europe.     

An EFE model on skin-sleeve interactions during arm rotation

Skin and garment constitute a dynamic contact system for human body comfort and protection. Although dermatological injuries due to fabric actions during human body movement are common, there is still no general guidance or standard for measuring or evaluating skin/garment contact interactions, especially, during intense sports. A three-dimensional explicit finite element (EFE) model combined with Augmented Lagrange algorithm (ALA) is developed to simulate interactions between skin and fabric during rotation of the arm. Normalized effective shear stresses at the interface between skin and the sleeve during the arm rotation are provided to reflect the severity of the interactions. The effects due to changes in fabric properties, fabric-skin gap, and arm rotation rate are also illustrated. It has been demonstrated from our predictions that factors such as elastic modulus, friction coefficients, density of fabric, and the initial gap between skin and fabric influence significantly the shear stress and thus the discomfort and even injury potential to skin during intensive body movement such as sports and military. Thus this study for the first time confirms quantitatively that poorly chosen fabric with inappropriate garment design renders adverse actions on human skin.     

Patterns of motor activity in the isolated nerve cord of the octopus arm

The extremely flexible octopus arm provides a unique opportunity for studying movement control in a highly redundant motor system. We describe a novel preparation that allows analysis of the peripheral nervous system of the octopus arm and its interaction with the muscular and mechanosensory elements of the arm's intrinsic muscular system. First we examined the synaptic responses in muscle fibers to identify the motor pathways from the axial nerve cord of the arm to the surrounding musculature. We show that the motor axons project to the muscles via nerve roots originating laterally from the arm nerve cord. The motor field of each nerve is limited to the region where the nerve enters the arm musculature. The same roots also carry afferent mechanosensory information from the intrinsic muscle to the axial nerve cord. Next, we characterized the pattern of activity generated in the dorsal roots by electrically stimulating the axial nerve cord. The evoked activity, although far reaching and long lasting, cannot alone account for the arm extension movements generated by similar electrical stimulation. The mismatch between patterns of activity in the isolated cord and in an intact arm may stem from the involvement of mechanosensory feedback in natural arm extension.