Paul A. J. Ackermans

In vitro indentation to determine the mechanical properties of epidermis

The lack of understanding of the mechanical behavior of the human skin layers makes the development of drug delivery using microneedles or microjets a challenging task. In particular, the key mechanical properties of the epidermis composed of stratum corneum and viable epidermis should be better understood. Micro-indentation experiments were applied, using a spherical tip with a large diameter to the sample thickness ratio. The Youngs moduli were derived via an analytical and a numerical method. The tests showed that the analytical method was not appropriate to assess the Youngs moduli. That is why a numerical model was used to obtain the correct stiffness. When loaded perpendicularly, the stiffness of both the epidermis and stratum corneum vary between 1 and 2MPa. No significant differences in stiffness between the stratum corneum and viable epidermis were observed.

A user-friendly integrated monitor-adhesive patch for long-term ambulatory electrocardiogram monitoring.

BACKGROUND Compliance to long-term ambulatory electrocardiogram monitoring is important for diagnosis in patients with cardiac arrhythmia. This requires a system with a minimal impact on daily activities. OBJECTIVE The aim of this study was to investigate if a lightweight integrated adhesive monitor for long-term use without unacceptable adverse effects is feasible. METHODS The participants wore either a prototype lightweight monitor or a control system for a total of up to 30 days, changing patches once (investigational device) or twice (control) weekly. Comfort, skin irritation, and impact on quality of life were recorded. RESULTS The new monitor can be worn by most participants for periods of at least 6 days. Skin irritation and comfort rating were comparable, and impact on the quality of life was low compared with the control. Patients considered the device comfortable. CONCLUSION An integrated adhesive monitor that can be worn on the skin up to 7 days with minimal side effects is feasible.

Generating, Refining and Using Sentiment Lexicons

In order to use a sentiment extraction system for a media analysis problem, a system would have to be able to determine which of the extracted sentiments are relevant, i.e., it would not only have to identify targets of extracted sentiments, but also decide which targets are relevant for the topic at hand.

Linear Viscoelastic Behavior of Adipose Tissue

Adipose tissue plays an important role in the load transfer between different tissue structures like skin and muscle. Though a plethora of papers can be found on properties of these surrounding tissue layers, only few papers addressed the properties of the adipose layer with its specific morphology. As a result, a thorough constitutive model describing the mechanical behavior of adipose tissue is lacking. This seems odd, because numerical models including the subcutaneous adipose tissue are needed in a wide field of applications such as skin device contact, needle insertion procedures, and understanding deep tissue injuries.© 2008 ASME

Mechanical properties of the epidermis and stratum corneum determined by submicron indentation in vitro

The outer skin layers are important drug and vaccine delivery targets in the treatment of diseases. These skin layers possess some important characteristics making them favorable sites for pain-free delivery with minimal damage: a rich population of immunologically sensitive cells as well as the lack of blood vessels and sensory nerve endings [1]. Until today, however, the development of effective cell targeting methods is acquainted with many challenges. A collective shortcoming is a poor understanding of the key mechanical properties of the outer skin layers, e.g. the stratum corneum and epidermis. The anisotropic, dynamic and very complex nature of skin makes it difficult to perform proper mechanical testing as well as to obtain reliable, reproducible data. The stratum corneum is an effective physical barrier of dead cells with a “brick-and-mortar” structure, while the viable epidermis mainly consists of actively migrating keratinocytes constantly undergoing massive morphological and compositional changes. As a consequence, the structure differences among the skin layers lead to significant variations in mechanical properties. Since there is no method available to determine the mechanical behavior of isolated viable epidermis in vivo or in vitro, the mechanical behavior of epidermis and stratum corneum only are investigated here. A commercially available indentation system has been adapted to enable the measurement of these thin soft tissues in an in vitro set up. Combining the outcomes of the two skin layer types leads to an assessment of the contribution of the viable epidermis to the mechanical behavior of skin. To our knowledge, no data have been published yet regarding mechanical bulk properties of (viable) epidermis, while no consistency exists with respect to those of the stratum corneum.Copyright

Mechanical Behaviour of the Subcutaneous Fat Layer

A very important function of the human subcutaneous fat layer is to act as a mechanical cushion. However, prolonged loading may result in damage such as pressure ulcers. Depending on the severity and origin of the ulcer, skin, subcutaneous fat and muscle can be affected. The aetiology of pressure ulcers is still poorly understood; it is not even clear whether wounds start to develop in skin, in the fat layer or even in deeper layers [1]. One of the tools used to better understand the way mechanical loading affects tissues is mechanical modeling. The success of a mechanical model strongly depends on the constitutive equations that are used to describe the mechanical properties obtained with experimental work. For skin and muscle much is already known, but a tremendous lack of data is found regarding the properties of adipose tissue. In the case of the subcutaneous fat tissue, very few of the mechanical properties have been determined experimentally.Copyright