Within days after birth, rapid surface colonization of infant skin coincides with significant functional changes. Gradual maturation of skin function, structure, and composition continues throughout the first years of life. Recent reports have revealed topographical and temporal variations in the adult skin microbiome. Here we address the question of how the human skin microbiome develops early in life. We show that the composition of cutaneous microbial communities evolves over the first year of life, showing increasing diversity with age. Although early colonization is dominated by Staphylococci, their significant decline contributes to increased population evenness by the end of the first year. Similar to what has been shown in adults, the composition of infant skin microflora appears to be site specific. In contrast to adults, we find that Firmicutes predominate on infant skin. Timely and proper establishment of healthy skin microbiome during this early period might have a pivotal role in denying access to potentially infectious microbes and could affect microbiome composition and stability extending into adulthood. Bacterial communities contribute to the establishment of cutaneous homeostasis and modulate inflammatory responses. Early microbial colonization is therefore expected to critically affect the development of the skin immune function.

Skin water barrier development begins in utero and is believed to be complete by week 34 of gestational age. The goal of this investigation was to assess the dynamic transport and distribution of water of the stratum corneum of infants and compare it to those of adults. The interaction of water with the stratum corneum was assessed by measuring capacitance, transepidermal water loss (TEWL), rates of absorption-desorption as well as Raman spectra as a function of depth (a total of 124 infants (3-12 months) and 104 adults (14-73 years)). The results show that capacitance, TEWL, and absorption-desorption rates had larger values consistently for infant stratum corneum throughout the first year of life and showed greater variation than those of adults. The Raman spectra analyzed for water and for the components of natural moisturizing factor (NMF) showed the distribution of water to be higher and have a steeper gradient in infants than in adults; the concentration of NMF was significantly lower in infants. The results suggest that although the stratum corneum of infants may appear intact shortly after birth (<1 month), the way it stores and transports water becomes adult-like only after the first year of life.

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We show that the appropriate combinations of mechanical stimuli and polymeric scaffolds can enhance the mechanical properties of engineered tissues. The mechanical properties of tissues engineered from cells and polymer scaffolds are significantly lower than the native tissues they replace. We hypothesized that application of mechanical stimuli to engineered tissues would alter their mechanical properties. Smooth muscle tissue was engineered on two different polymeric scaffolds and subjected to cyclic mechanical strain. Short-term application of strain increased proliferation of smooth muscle cells (SMCs) and expression of collagen and elastin, but only when SMCs were adherent to specific scaffolds. Long-term application of cyclic strain upregulated elastin and collagen gene expression and led to increased organization in tissues. This resulted in more than an order of magnitude increase in the mechanical properties of the tissues.

Functional differences between infant and adult skin may be attributed to putative differences in skin microstructure. The purpose of this study was to examine infant skin microstructure in vivo and to compare it with that of adult skin. The lower thigh area of 20 healthy mothers (ages 25-43) and their biological children (ages 3-24 months) was examined using in vivo noninvasive methods including fluorescence spectroscopy, video microscopy, and confocal laser scanning microscopy. Stratum corneum and supra-papillary epidermal thickness as well as cell size in the granular layer were assessed from the confocal images. Adhesive tapes were used to remove corneocytes from the outer-most layer of stratum corneum and their size was computed using image analysis. Surface features showed differences in glyph density and surface area. Infant stratum corneum was found to be 30% and infant epidermis 20% thinner than in adults. Infant corneocytes were found to be 20% and granular cells 10% smaller than adult corneocytes indicating a more rapid cell turnover in infants. This observation was confirmed by fluorescence spectroscopy. Dermal papillae density and size distribution also differed. Surprisingly, a distinct direct structural relationship between the stratum corneum morphology and the dermal papillae was observed exclusively in infant skin. A change in reflected signal intensity at approximately 100 mum indicating the transition between papillary and reticular dermis was evident only in adult skin. We demonstrate in vivo qualitative and quantitative differences in morphology between infant and adult skin. These differences in skin microstructure may help explain some of the reported functional differences.