Histomorphologic changes of hair follicles in human expanded scalp

Mechanical stretch induces hair regeneration through the alternative activation of macrophages

Tissues and cells in organism are continuously exposed to complex mechanical cues from the environment. Mechanical stimulations affect cell proliferation, differentiation, and migration, as well as determining tissue homeostasis and repair. By using a specially designed skin-stretching device, we discover that hair stem cells proliferate in response to stretch and hair regeneration occurs only when applying proper strain for an appropriate duration. A counterbalance between WNT and BMP-2 and the subsequent two-step mechanism are identified through molecular and genetic analyses. Macrophages are first recruited by chemokines produced by stretch and polarized to M2 phenotype. Growth factors such as HGF and IGF-1, released by M2 macrophages, then activate stem cells and facilitate hair regeneration. A hierarchical control system is revealed, from mechanical and chemical signals to cell behaviors and tissue responses, elucidating avenues of regenerative medicine and disease control by demonstrating the potential to manipulate cellular processes through simple mechanical stimulation.

[The complications of skin expansion in paediatrics: Diagnostic, taking over and prevention]

Skin expansion is a difficult and long process in which can occur more or less serious complications. Overall complications rates describe in the literature vary between 13 and 37%. We can categorize them in major complications, which can lead to a failure maybe even an aggravation of the anterior status, and in minor complications that do not compromise the expansion process but can alter it. The main major complications are infection, skin suffering and necrosis which can lead to prosthesis exposition, leaks and technical problems with equipment dysfunctions that may cause difficulties or a failure of the inflations. The main minor complications are hematomas, seromas, valve or tube exposition, pains with paraesthesias caused by neighbouring organs compression, pathologic and unsightly scares and can lead to an important psychological impact. These complications can be due to a precarious skin's state, a material dysfunction or unpredictable technical problems but also by an inappropriate preoperative indication or planning. The emerging of a complication, however, is not synonymous to a failure of the procedure; a satisfactory reconstruction may still be obtained in 75% of all cases. The purpose of this article is to help to identify the situations at risk of complications in order to prevent, detect and treat them early.

Regeneration of hair and other skin appendages: A microenvironment-centric view

Advances in skin regeneration have resulted in techniques and products that have allowed regeneration of both the dermis and epidermis. Yet complete skin regeneration requires the adnexal skin structures. Thus it is crucial to understand the regenerative potential of hair follicles where genetic, nutritional, and hormonal influences have important effects and are critical for skin regeneration. The follicular stem cell niche serves as an anatomical compartment, a structural unit, a functional integrator, and a dynamic regulator necessary to sustain internal homeostasis and respond to outside stimuli. In particular, mechanics such as pressure, compression, friction, traction, stretch, shear, and mechanical wounding can influence hair loss or growth. Relevant niche signaling pathways such as Wnt, bone morphogenetic protein, fibroblast growth factor, Shh, and Notch may yield potential targets for therapeutic interventions.

A novel approach to soft-tissue repair: reoverexpanded flaps

Postburn sequelae or excisional defect reconstruction after significant burn injury or resection of giant hairy nevus continues to be a significant challenge for the reconstructive surgeon. Unfortunately, the quality and quantity of available tissue for the repair of extensive defects is often limited. The techniques of tissue expansion have been used for many years to expand normal skin adjacent to the defect for the reconstruction of even wider defects in various parts of the body with its numerous advantages.Nine patients in whom reoverexpanded neighboring skin flaps were used to improve the capacity of wider soft-tissue defect coverage for postburn scar revision or excisional defect of giant hairy nevus in the various parts of the body is reported here.

Tissue regeneration during tissue expansion and choosing an expander

This paper reviews the various aspects of tissue regeneration during the process of tissue expansion. “Creep” and mechanical and biological “stretch” are responsible for expansion. During expansion, the epidermis thickens, the dermis thins out, vascularity improves, significant angiogenesis occurs, hair telogen phase becomes shorter and the peripheral nerves, vessels and muscle fibres lengthen. Expansion is associated with molecular changes in the tissue. Almost all these biological changes are reversible after the removal of the expander.This study is also aimed at reviewing the difficulty in deciding the volume and dimension of the expander for a defect. Basic mathematical formulae and the computer programmes for calculating the dimension of tissue expanders, although available in the literature, are not popular. A user-friendly computer programme based on the easily available Microsoft Excel spread sheet has been introduced. When we feed the area of defect and base dimension of the donor area or tissue expander, this programme calculates the volume and height of the expander. The shape of the expander is decided clinically based on the availability of the donor area and the designing of the future tissue movement. Today, tissue expansion is better understood biologically and mechanically. Clinical judgement remains indispensable in choosing the size and shape of the tissue expander.

Upper extremity resurfacing via an expanded latissimus dorsi musculocutaneus flap for large circumferential defects: the "spiral" reconstruction technique

We present an expanded latissimus dorsi musculocutaneus (LDMC) flap to treat circumferential upper extremity defects via resurfacing and “spiral reconstruction” in 5 patients during a 17-year period. Five patients with different indications for tissue expansion from burns to congenital hairy nevi were operated. The expansion was done in a longitudinal direction, and a rectangular tissue expander (TE) was inserted under the LD muscle to expand the flap in a longitudinal direction thereby forming a “long” flap rather than a “wide” one. After excising the circumferential lesion, the expanded “elongated” flap was wrapped spirally around the extremity to cover the defect; the donor site was closed as usual. The 5 patients we treated via LDMC flaps in a spiral fashion were free of complications, and all were satisfied with the outcome. All the flaps survived and the spiral reconstruction allowed for a tension-free donor site closure and near complete recipient coverage. This technique is indicated for large circumferential extremity skin defects and deformities. Application of expanded LDMC flaps in a spiral fashion can be used by the reconstructive surgeon to resurface large circumferential upper extremity lesions when indicated. The idea of a long and thinned expansion flap must be in a longitudinal direction and we need this long expanded and thin flap to “spiral” it around the extremity to cover a large defect. The “spiral” flap coverage introduced here for large circumferential extremity defects enables the surgeon to cover the defect with simultaneous donor site closure and good results.

Cosmetic aspects of cranial reconstruction

Cranial reconstruction has evolved to achieve both functional coverage and esthetic appearance. Hair preservation/reconstruction and free flaps have markedly improved the soft tissue esthetic outcome. Restoration of bony contour has been facilitated by advanced craniofacial techniques and three-dimensional alloplast.

Hair removal by long-pulse alexandrite laser in oriental patients

The laser depilation system, cleared by the Food and Drug Administration since 1995, is evolving rapidly. However, the parameters in the hair removal function of these devices emphasize use for white people with fair skin (Fitzpatrick types I, II, or III). The characteristics of oriental skin and hair are black, coarse hairs in darker skin (Fitzpatrick types IV or V). As seen, the higher the skin melanin content, the more difficult to remove hair by laser. The authors report 146 oriental patients (156 body sites) who underwent treatment with the long-pulse alexandrite laser (wavelength, 755 nm) depilation system since November 1997. Percentage of hair removal (clearance rate) was assessed, and the histological change from laser pulse damage was observed. After two treatments, the clearance rates in the axillae and the leg were 61% and 62% respectively in the 15 to 20-J group (N = 47), and were 66% and 67% respectively in 21 to 25-J group (N = 64). After five treatments, 59 patients (37 axillae and 22 legs, all of which received 21-25 J per square centimeter of laser energy treatment during the course) had an average clearance rate of 91% (axillae) and 86% (leg), and the clearance rates have been maintained near 90% after long-term follow-up (average follow-up, 17 months). Minimal and transient complications are noted. In conclusion, using a combination of longer wavelength (but still in the optimal window of 630-870 nm), long pulse duration (10-40 msec), high fluence (but limited up to 25 J per square centimeter), multiple treatments, and concomitant direct cooling applied to the skin of oriental patients (Fitzpatrick types IV and V) with black, moderately coarse hair shafts achieves satisfying long-term hair removal results.