Ontogeny of water sorption-desorption in the perinatal rat

The dual nature of mouse periderm structure, function, and fate

The periderm is the outer layer of embryonic skin which is essential for the development of the epidermis and the establishment of its barrier function. In humans, the periderm is a monolayer and is shed prenatally. The structure and fate of the mouse periderm remains puzzling. Using electron microscopy of mouse skin between the embryonic day 14.5 and the postnatal day 2, we have assessed the periderm structure and its shedding patterns. In contrast to human periderm, the mouse periderm appears to be bilayered, comprising a presumably absorptive outer periderm with numerous microvilli and an inner periderm packed with specific (glycogen-containing?) granules. The desmosomes between the inner periderm and the underlying epidermis are scarce, and they are totally absent between the inner and the outer periderm. The inner and outer periderms in mice are shed at different stages of development: the outer periderm is shed in utero in conjunction with barrier acquisition (E16-18), while the inner periderm is retained postnatally. We assume that the bilayered structure of the mouse periderm and the postnatal retention of its inner layer represent the evolutionary adaptations in ancestral rodents which helps altricial newborns of their extant descendants to cope with acute dehydration right after birth and/or provides a substrate for proper bacterial colonization of newborn skin.

Biology of the vernix caseosa: A review

The vernix caseosa is a complex membranous structure comprising 80% water, 10% protein, and 10% lipids including barrier lipids such as ceramides, free fatty acids, phospholipids and cholesterol, synthesized partly by fetal sebaceous glands during the last trimester of pregnancy in an antero-posterior and dorsoventral manner. Because of its lipid content, vernix is hydrophobic and protects the skin from excessive water exposure during the development of the stratum corneum. The vernix caseosa has various functions during fetal transition from an intrauterine to an extrauterine environment, including lubrication of the birth canal during parturition, barrier function to prevent water loss, temperature regulation, for innate immunity and for intestinal development. This review discusses the evidence supporting the prenatal and postnatal functions of vernix caseosa, along with its structure, composition, and physical and biological characteristics. Understanding the biology of the vernix may facilitate improved care of preterm infants immediately post-partum.

EEMCO guidance for the assessment of stratum corneum hydration: electrical methods

BACKGROUND/AIMS

The improvement of stratum corneum hydration is one of the most important claims in the cosmetic industry.

METHODS

Objective assessment of moisturization can be done with devices based on electrical methods provided these instruments are used in an appropriate manner.

RESULTS

This paper deals with the biophysical basis behind these techniques and describes the most important variables, pitfalls and drawbacks related to measurements and current instrumentation. Individual-related and environment-related variables are also analyzed as well as study designs for predictive or use tests.

CONCLUSIONS

Practical suggestions for standardization of measurements are given.

Characterization of vernix caseosa: water content, morphology, and elemental analysis

Recent studies have prompted interest in the use of epidermal barrier creams as protective biofilms for very low birthweight preterm infants. The key to understanding the role of epidermal barrier films is an elucidation of their interaction with water and a basic knowledge of their composition. In this study, we investigated the morphologic properties and elemental composition of the naturally occurring biofilm, vernix caseosa. This biofilm is typically lacking in preterm infants and its production coincides in utero with terminal differentiation of the epidermis and formation of the stratum corneum. Significantly, vernix (80.5+/-1.0% H2O) had a much higher water content than other barrier creams (Eucerin: 17.1+/-0.6%, Aquaphor: 0.33+/-0.03%, Ilex: 0.19+/-0.02%, petrolatum: 0.03+/-0.01%; all p<0.05). Phase contrast microscopy of vernix showed multiple cellular elements with nucleic "ghosts" embedded in a putative lipid matrix. Transmission electron microscopy revealed flattened structures approximately 1-2 microm in thickness with distinct cellular envelopes indicative of differentiated corneocytes. Compared with mature corneocytes in adult stratum corneum, vernix corneocytes appeared swollen, the density of the keratin filaments was less, and there was a relative lack of tonofilament orientation. Cryofractured specimens were examined by cryoscanning electron microscopy with subsequent elemental localization by X-ray beam analysis. The findings indicate the high water content of vernix is largely compartmentalized within fetal corneocytes. These results are consistent with the novel view of vernix as a "fluid phase" stratum corneum consisting of a hydrophobic lipid matrix with embedded fetal corneocytes possessing unique biomechanical and water-binding properties.

Adhesives and emollients in the preterm infant

This chapter focuses on recent advances in preterm infant skin care related to skin adhesion and skin emolliency. Different types of adhesives and hydrating agents are reviewed. Clinical applications are best guided by understanding the biology of epidermal barrier development. The role of xeric stress in accelerating formation of the stratum corneum is discussed along with the effects of occlusive agents and emollients on wound healing and epidermal barrier repair. The principles of skin moisturization are introduced. The concept is advanced that programmatic changes in skin adhesion and water handling occur during the normal ontogeny of superficial biofilms (sebum, sweat, acid mantle).

Characterization of vernix caseosa as a natural biofilm: comparison to standard oil-based ointments

The application of occlusive films and oil-in-oil ointments has been reported to improve epidermal barrier function in very low birthweight, preterm infants. Such infants have a structurally immature stratum corneum and lack a surface coating of vernix caseosa. In this study we examined the short-term effects of topical application of vernix caseosa to human skin and contrasted these effects with commonly used ointments and water-in-oil emulsions. Specifically, vernix, Eucerin(R), Aquaphor(R), and petrolatum were applied to the volar skin surface of adult volunteers. Surface electrical capacitance (SEC) and transepidermal water loss (TEWL) were measured as indices of surface hydration. Sorption-desorption profiles were performed to determine skin surface hydrophobicity. Particular attention was given to monitoring the acute (0-120 minutes) changes following vernix treatment in order to compare these effects with earlier reports on the rate of skin surface drying in newborn infants following birth. Immediately after vernix application there was an increase in the rate of water loss from the skin surface. Relative to control skin and skin treated with the ointments and water-in-oil emulsions, the application of vernix to freshly bathed human skin resulted in a unique profile of temporal change in baseline surface hydration, moisture accumulation, and water-holding capacity. These results demonstrate major differences between human vernix and standard oil-based topical ointments. The results provide a framework for discussing the various properties of topical barriers applied to the very low birthweight infant.

Development of diaper rash in the newborn

Diaper rash is a common infant malady. This study documents the earliest stages of rash in a cohort of 31 healthy term newborns over the first 28 days of life. The diaper area was evaluated using a standardized diaper rash grading scale. The anal, buttock, genital, intertriginous, waistband, and leg areas were assessed separately. At birth the average grade was 0.1 and none of the infants had specific features of advanced rash. Nineteen percent had dryness and/or slight redness. By day 7, 71% of infants had some features of skin compromise, giving rise to an overall grade of 0.6. Both the frequency and overall grade increased during postnatal weeks 2 and 3. Overall scores for days 21 and 28 were the same (1.1). The perianal area had the highest overall regional rash grade. Gender differences were present for the genital area only. These findings indicate that epidermal barrier breakdown is an uncommon finding at birth. Clinical signs of irritated skin in the diaper area develop progressively over the first postnatal month. A better understanding of the mechanisms conferring epidermal barrier protection at birth may be important for developing skin care products and practices to extend this protection later into life.

Changes in diapered and nondiapered infant skin over the first month of life

Time- and site-dependent differences in epidermal barrier properties were investigated over the first 28 days of life in healthy term newborn infants. Diapered and nondiapered skin sites were contrasted to the volar forearm of adults (mothers). Thirty-one term infants were evaluated in the hospital on postnatal day 1 and at home on days 4, 7, 14, 21, and 28 for a total of six visits. Measurements included baseline skin hydration, continuous capacitive reactance, peak water sorption, rate of water desorption, skin pH, skin temperature, and environmental conditions. Changes in epidermal barrier properties over the first 4 weeks of life included an increase in surface hydration, a decrease in transepidermal water movement under occlusion, a decrease in surface water desorption rate, and a decrease in surface pH. Diapered and nondiapered regions were indistinguishable at birth but exhibited differential behavior over the first 14 days, with the diapered region showing a higher pH and increased hydration. Maternal measurements remained constant throughout the period. We conclude that healthy newborn skin undergoes progressive changes in epidermal barrier properties over the first 28 days. Adult skin testing does not replicate newborn skin during the first month of life.

Barrier formation in the human fetus is patterned

We recently demonstrated patterned stratum corneum maturation and skin barrier formation during fetal development in rodents and rabbit. The presence of skin patterning in these mammals led us to predict patterned barrier formation during human infant development. Here we extend our mammalian study and demonstrate patterned stratum corneum development and skin barrier formation in the pre-term human infant. Surprisingly, we show initiation of human barrier regionally as early as 20-24 wk gestational age (22-26 wk menstrual age), bringing barrier formation close to the time of periderm disaggregation. We use the mouse model to show that patterns of periderm disaggregation mirrors barrier formation. Periderm disaggregation follows and recapitulates barrier pattern, suggesting a relationship between the processes. This work reveals regional patterning in skin maturation and barrier formation in the human infant and demonstrates that initiation of human skin barrier formation in utero coincides with the current lower limit of viability of the pre-term infant.

Surgical wound healing monitored repeatedly in vivo using electrical resistance of the epidermis

We describe a new transcutaneous electrical resistance method for measuring surgical wound healing which permits repeated measurements in vivo throughout the healing period. A saline-filled silver electrode was used to monitor the increasing ohmic resistance which accompanied the healing. Two validation studies were carried out. In the first study, histology on 16 rats showed that an intact stratum corneum was responsible for the high electrical resistance of skin, since lesions of the corneum markedly lowered the resistance. In the second study, electrical resistance readings of incisional wounds were taken repeatedly over 20 days in 13 rats: regression analysis showed that the healing slope for each incisional wound had a correlation coefficient r-value greater than 0.85. Moreover, all slopes were positive (p < 0.001) demonstrating that resistance increases as wound healing progresses and hence is a valid measure of healing. Test-retest resistance readings showed high reliability when measurements were repeated on the same wound (Pearson r = 0.94, n = 110). Hence we have shown that this new method is both valid and reliable. The device only monitors epidermal repair and gives no indication of wound strength. A modified device recently developed for humans has been used successfully on post-surgical wounds in numerous patients.

Effect of insulated skin probes to increase skin-to-environmental temperature gradients of preterm infants cared for in convective incubators

Thermal support systems for premature infants that are based on skin servocontrol depend on accurate measurement of skin surface temperature. We examined prospectively the effect of probe insulation to alter measured skin temperature in 10 preterm infants. The use of insulated probes resulted in significant alteration in incubator servocontrol, with lower incubator air temperatures and higher skin-to-environment temperature gradients.