The Role of the Inflammatory Response in Mediating Functional Recovery Following Composite Tissue Injuries

Composite tissue injuries (CTI) are common among US Military Service members during combat operations, and carry a high potential of morbidity. Furthermore, CTI are often complicated due to an altered wound healing response, resulting in part from a dysregulation of the innate and adaptive immune responses. Unlike normal wound healing, in CTI, disruptions occur in innate immune responses, altering neutrophil functions, macrophage activation and polarization, further impacting the functions of T regulatory cells. Additionally, the biological underpinnings of these unfavorable wound healing conditions are multifactorial, including various processes, such as: ischemia, hypoxia, low nutrient levels, and altered cell metabolic pathways, among others, all of which are thought to trigger anergy in immune cells and destabilize adaptive immune responses. As a result, impaired wound healing is common in CTI. Herein, we review the altered innate and adaptive immune cells and their metabolic status and responses following CTI, and discuss the role a multi-pronged immunomodulatory approach may play in facilitating improved outcomes for afflicted patients.

Plastic surgery

This chapter evaluates plastic surgery, which is a constantly evolving surgical discipline based upon technical exactitude, detailed anatomical knowledge, and innovation. Plastic surgeons have strong aesthetic awareness, but the true scope of their practice is very much broader. The ethos of this work is to restore form and function. In pursuit of this goal, techniques have been refined that enable the transfer of tissues around the body as non-vascularised ‘grafts’, or vascularised ‘flaps’ that may be ‘pedicled’ on their anatomical blood supply, or revascularised after autologous transplantation by microvascular anastomosis. Globally, plastic surgeons collaborate with many specialties to enable oncological treatments and manage congenital abnormalities and trauma and severe soft tissue infections (SSTIs) across a broad range of conditions. In addition to this work, plastic surgeons have been involved in the development of composite tissue allotransplantation techniques that include facial, abdominal wall, and hand transplantation. The chapter then highlights some of the common reasons for referral to plastic surgery and describes some of the common plastic surgery techniques available to address these.

Manipulating Stress Receptor Signaling to Enhance Immunosuppression and Prolong Survival of Vascularized Composite Tissue

Vascularized composite tissue allotransplantation (VCA) can replace severely damaged body parts but the unavoidable toxicity of high doses of immunosuppressive drugs, such as tacrolimus, required results in significant morbidity. Here we tested whether we could suppress immune activity in a mouse model of VCA by mimicking the natural immune suppression generated by nervous system-induced signaling of adrenergic receptors (AR) by using a safe and well-studied β-AR agonist (terbutaline). Using wild-type and β2-AR-knockout (KO) mice, we found that increased β2-AR signaling results in delayed rejection in VCA recipients, even with subtherapeutic doses of tacrolimus, and this was associated with changes in immune contexture, expression of pro-inflammatory cytokines and chemokines, and function of endothelial adhesion molecules. We propose that β-AR agonists can be used safely to mimic the natural suppression of immune responses generated by adrenergic stress signaling and thereby reduce the dose needed of other more toxic immunosuppressive drugs.

Rectus Abdominis Flap Replantation after 18 h Hypothermic Extracorporeal Perfusion—A Porcine Model

Cold storage remains the clinical standard for composite tissue preservation but is time-limited. A long ischemia time during surgery will adversely affect postoperative outcomes due to ischemia-reperfusion injury. Extracorporeal perfusion (ECP) seems to be a promising alternative for prolonged preservation, but more evidence is needed to support its use and to identify optimal perfusion fluids. This article assessed musculocutaneous flap vitality after prolonged ECP and compared outcomes after replantation to short static cold storage (SCS). Unilateral musculocutaneous rectus abdominis flaps were raised from 15 pigs and preserved by 4 h SCS (n = 5), 18 h mid-thermic ECP with Histidine–Tryptophan–Ketoglutarate (HTK, n = 5) or University of Wisconsin solution (UW, n = 5). Flaps were replanted and observed for 12 h. Skeletal muscle histology was assessed (score 0–12; high scores equal more damage), blood and perfusate samples were collected and weight was recorded as a marker for oedema. Mean histological scores were 4.0 after HTK preservation, 5.6 after UW perfusion and 5.0 after SCS (p = 0.366). Creatinine kinase (CK) was higher after ECP compared to SCS (p < 0.001). No weight increase was observed during UW perfusion, but increased 56% during HTK perfusion. Following 12 h reperfusion, mean weight gain reduced 39% in the HTK group and increased 24% in the UW group and 17% in the SCS group. To conclude, skeletal muscle seemed well preserved after 18 h ECP with HTK or UW perfusion, with comparable histological results to 4 h SCS upon short reperfusion. The high oedema rate during HTK perfusion remains a challenge that needs to be further addressed.

Autofluorescence of stingray skeletal cartilage: hyperspectral imaging as a tool for histological characterization

Tessellated cartilage is a distinctive composite tissue forming the bulk of the skeleton of cartilaginous fishes (e.g. sharks and rays), built from unmineralized cartilage covered at the surface by a thin layer of mineralized tiles called tesserae. The finescale structure and composition of elasmobranch tessellated cartilage has largely been investigated with electron microscopy, micro-computed tomography and histology, but many aspects of tissue structure and composition remain uncharacterized. In our study, we demonstrate that the tessellated cartilage of a stingray exhibits a strong and diverse autofluorescence, a native property of the tissue which can be harnessed as an effective label-free imaging technique. The autofluorescence signal was excited using a broad range of wavelengths in confocal and light sheet microscopy, comparing several sample preparations (fresh; demineralized and paraffin-embedded; non-demineralized and plastic-embedded) and imaging the tissue at different scales. Autofluorescence varied with sample preparation with the signal in both plastic- and paraffin-embedded samples strong enough to allow visualization of finescale (≥ 1 μm) cellular and matrix structures, such as cell nuclei and current and former mineralization fronts, identifiable by globular mineralized tissue. A defined pericellular matrix (PCM) surrounding chondrocytes was also discernible, described here for the first time in elasmobranchs. The presence of a PCM suggests similarities with mammalian cartilage regarding how chondrocytes interact with their environment, the PCM in mammals acting as a transducer for biomechanical and biochemical signals. A posterior analysis of hyperspectral images by an MCR-ALS unmixing algorithm allowed identification of several distinct fluorescence signatures associated to specific regions in the tissue. Some fluorescence signatures identified could be correlated with collagen type II, the most abundant structural molecule of cartilage. Other fluorescence signatures, however, remained unidentified, spotlighting tissue regions that deserve deeper characterization and suggesting the presence of molecules still unidentified in elasmobranch skeletal cartilage. Our results show that autofluorescence can be a powerful exploratory imaging tool for characterizing less-studied skeletal tissues, such as tessellated cartilage. The images obtained are largely comparable with more commonly used techniques, but without the need for complicated sample preparations or external staining reagents standard in histology and electron microscopy (TEM, SEM).

Vascularized composite allotransplantation

Vascularized composite allotransplants contain the products of multiple cell lineages to reconstruct the form and function of complex, composite tissue defects. This chapter discusses the ethical principles and the immunology behind composite transplantation, including the selection of immunomodulatory agents and the immune basis and treatment of rejection. The principles of organ allocation and candidate preparation are presented prior to discussion of the clinical applications and outcomes of hand, face, abdominal wall, uterus, penis, and lower limb transplantation.