BACKGROUND/PURPOSE: Friction blisters, a common injury in sports and military operations, can adversely effect or even halt performance. Given its frequency and hazardous nature, recent research efforts appear limited. Blistering can be treated as a delamination phenomenon; similar issues in materials science have been extensively investigated in theory and experiment. An obstacle in studying blistering is the difficulty of conducting experiment on humans and animals. Computer modeling thus becomes a preferred tool. METHOD: This paper used a dynamic non-linear finite-element model with a blister-characterized structure and contact algorithm for outer materials and blister roof to investigate the effects on deformation and stress of an existing blister by changing the friction coefficient and elastic modulus of the material in contact with the blister. RESULTS: Through the dynamics mode and harmonic frequency approach, we demonstrated that the loading frequency leads to dramatic changes of displacement and stress in spite of otherwise similar loading. Our simulations show that an increased friction coefficient does not necessarily result in an increase in either the stress on the hot spot or blister deformation; local maximum friction stress and Von Mises stress exist for some friction coefficients over the wide range examined here. In addition, the stiffness of contact material on blistering is also investigated, and no significant effects on deformation and Von Mises stress are found, again at the range used. The model and method provided here may be useful for evaluating loading environments and contact materials in reducing blistering incidents. CONCLUSION: The coupling finite-element model can predict the effects of friction coefficient and contacting materials' stiffness on blister deformation and hot spot stress.

BACKGROUND/PURPOSE: Friction blisters, a common injury in sports and military operations, can adversely effect or even halt performance. Given its frequency and hazardous nature, recent research efforts appear limited. Blistering can be treated as a delamination phenomenon; similar issues in materials science have been extensively investigated in theory and experiment. An obstacle in studying blistering is the difficulty of conducting experiment on humans and animals. Computer modeling thus becomes a preferred tool.

METHOD: This paper used a dynamic non-linear finite-element model with a blister-characterized structure and contact algorithm for outer materials and blister roof to investigate the effects on deformation and stress of an existing blister by changing the friction coefficient and elastic modulus of the material in contact with the blister.

RESULTS: Through the dynamics mode and harmonic frequency approach, we demonstrated that the loading frequency leads to dramatic changes of displacement and stress in spite of otherwise similar loading. Our simulations show that an increased friction coefficient does not necessarily result in an increase in either the stress on the hot spot or blister deformation; local maximum friction stress and Von Mises stress exist for some friction coefficients over the wide range examined here. In addition, the stiffness of contact material on blistering is also investigated, and no significant effects on deformation and Von Mises stress are found, again at the range used. The model and method provided here may be useful for evaluating loading environments and contact materials in reducing blistering incidents.

CONCLUSION: The coupling finite-element model can predict the effects of friction coefficient and contacting materials' stiffness on blister deformation and hot spot stress.

BACKGROUND/PURPOSE: Friction blisters, a common injury in sports and military operations, can adversely effect or even halt performance. Given its frequency and hazardous nature, recent research efforts appear limited. Blistering can be treated as a delamination phenomenon; similar issues in materials science have been extensively investigated in theory and experiment. An obstacle in studying blistering is the difficulty of conducting experiment on humans and animals. Computer modeling thus becomes a preferred tool. METHOD: This paper used a dynamic non-linear finite-element model with a blister-characterized structure and contact algorithm for outer materials and blister roof to investigate the effects on deformation and stress of an existing blister by changing the friction coefficient and elastic modulus of the material in contact with the blister. RESULTS: Through the dynamics mode and harmonic frequency approach, we demonstrated that the loading frequency leads to dramatic changes of displacement and stress in spite of otherwise similar loading. Our simulations show that an increased friction coefficient does not necessarily result in an increase in either the stress on the hot spot or blister deformation; local maximum friction stress and Von Mises stress exist for some friction coefficients over the wide range examined here. In addition, the stiffness of contact material on blistering is also investigated, and no significant effects on deformation and Von Mises stress are found, again at the range used. The model and method provided here may be useful for evaluating loading environments and contact materials in reducing blistering incidents. CONCLUSION: The coupling finite-element model can predict the effects of friction coefficient and contacting materials' stiffness on blister deformation and hot spot stress.

BACKGROUND/PURPOSE: Percutaneous permeation is a frequently used approach in drug delivery, but the detailed physics process in the patch--stratum corneum (SC)--viable epidermis system remains unclear: the influence of the interphases in the multilayered structure has been little studied.

METHODS: This paper applied the finite-element method to develop a contact algorithm with an interphase element to account for the interphase barrier on drug diffusion and chemical absorption during a transdermal drug delivery process. A more realistic multilayer structure, including the patch, SC and viable epidermis, are incorporated into the algorithm. Both interphases between the patch and SC, and between SC and viable epidermis are considered.

RESULTS: Our study confirms that the interphase transfer coefficients have a direct connection with drug concentration and flux distribution along the diffusion paths. The simulation results suggested a potential for the optimal control of drug diffusion. The partition coefficients and other interphase barrier factors can be incorporated into the model.

CONCLUSIONS: The algorithm can deal with complicated geometrical conditions, which is difficult using classical analytical approaches. Furthermore, calibrated against experiments, the model may predict more realistically the drug delivery process and drug distribution profiles so as to assist in the patch and even drug design.

BACKGROUND/PURPOSE: Percutaneous permeation is a frequently used approach in drug delivery, but the detailed physics process in the patch--stratum corneum (SC)--viable epidermis system remains unclear: the influence of the interphases in the multilayered structure has been little studied. METHODS: This paper applied the finite-element method to develop a contact algorithm with an interphase element to account for the interphase barrier on drug diffusion and chemical absorption during a transdermal drug delivery process. A more realistic multilayer structure, including the patch, SC and viable epidermis, are incorporated into the algorithm. Both interphases between the patch and SC, and between SC and viable epidermis are considered. RESULTS: Our study confirms that the interphase transfer coefficients have a direct connection with drug concentration and flux distribution along the diffusion paths. The simulation results suggested a potential for the optimal control of drug diffusion. The partition coefficients and other interphase barrier factors can be incorporated into the model. CONCLUSIONS: The algorithm can deal with complicated geometrical conditions, which is difficult using classical analytical approaches. Furthermore, calibrated against experiments, the model may predict more realistically the drug delivery process and drug distribution profiles so as to assist in the patch and even drug design.

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.

This article overviews research in the interdisciplinary area of textile/skin interaction and related cutaneous intolerance. Microclimate in the skin/clothing system and especially the skin responses relates to the moisture and heat transfer within this system and plays a critical role in skin irritation from textiles. A discussion is then given on skin irritation reactions to textiles, including intolerance caused by chemicals (dyes and finishes) and physical contact/friction. Finally, two skin injuries, blisters and pressure ulcers, which are caused by physical contact, pressure, and friction, are documented. Despite the prevalent problems caused by ill textile/skin interactions, minimal efforts have been devoted to this field. In addition, the in vivo experimental studies infrequently lead to a solid conclusion. The cause may lie in the dramatic variation of skin conditions among individuals as well as among different anatomic sites of the same person. Another reason might be the lack of communications between researchers in the areas of textiles and dermatology.

Use of the percutaneous route may avoid some of the undesirable side effects that occur following oral administration in estrogen replacement therapy. At present, knowledge of estradiol transdermal properties relating to delivery of drugs in the skin is lacking. One reason is that in the existing transport models of estradiol, the skin is regarded as a single layer. This study revealed a significant difference of effects on estradiol delivery in the 3 sublayers of the skin and has caused us to believe that if we can obtain information about the transfer properties of estradiol in human skin (3 sublayers), we will not only increase our understanding of the estradiol biotransport mechanism, but also benefit clinical application. Accordingly, radioactive 17beta-estradiol was used to clarify the percutaneous absorption of estradiol into the 3 sublayers of the skin (stratum corneum, epidermis, and dermis) and to evaluate the effect of drugs delivered in each sublayer. Based on data thereby obtained, mathematical models were built to further obtain transport parameters (diffusivity, permeability, lag time, and partition coefficients) for the 3 layers of the skin.

BACKGROUND/PURPOSE: Percutaneous permeation is a frequently used approach in drug delivery, but the detailed physics process in the patch--stratum corneum (SC)--viable epidermis system remains unclear: the influence of the interphases in the multilayered structure has been little studied. METHODS: This paper applied the finite-element method to develop a contact algorithm with an interphase element to account for the interphase barrier on drug diffusion and chemical absorption during a transdermal drug delivery process. A more realistic multilayer structure, including the patch, SC and viable epidermis, are incorporated into the algorithm. Both interphases between the patch and SC, and between SC and viable epidermis are considered. RESULTS: Our study confirms that the interphase transfer coefficients have a direct connection with drug concentration and flux distribution along the diffusion paths. The simulation results suggested a potential for the optimal control of drug diffusion. The partition coefficients and other interphase barrier factors can be incorporated into the model. CONCLUSIONS: The algorithm can deal with complicated geometrical conditions, which is difficult using classical analytical approaches. Furthermore, calibrated against experiments, the model may predict more realistically the drug delivery process and drug distribution profiles so as to assist in the patch and even drug design.

This article overviews research in the interdisciplinary area of textile/skin interaction and related cutaneous intolerance. Microclimate in the skin/clothing system and especially the skin responses relates to the moisture and heat transfer within this system and plays a critical role in skin irritation from textiles. A discussion is then given on skin irritation reactions to textiles, including intolerance caused by chemicals (dyes and finishes) and physical contact/friction. Finally, two skin injuries, blisters and pressure ulcers, which are caused by physical contact, pressure, and friction, are documented. Despite the prevalent problems caused by ill textile/skin interactions, minimal efforts have been devoted to this field. In addition, the in vivo experimental studies infrequently lead to a solid conclusion. The cause may lie in the dramatic variation of skin conditions among individuals as well as among different anatomic sites of the same person. Another reason might be the lack of communications between researchers in the areas of textiles and dermatology.