Strain-Stiffening Ionogel with High-Temperature Tolerance via the Synergy of Ionic Clusters and Hydrogen Bonds.

Highly stretchable and conductive ionogels have great potential in flexible electronics and soft robotic skins. However, current ionogels are still far from being able to accurately duplicate the mechanically responsive behavior of real human skin. Furthermore, durable robotic skins that are applicable under harsh conditions are still lacking. Herein, a strong noncovalent interaction, ionic clusters, is combined with hydrogen bonds to obtain a physically cross-linked ionogel (PCI). Benefiting from the strong ionic bonding of the ionic cluster, the PCI shows strain-stiffening behavior similar to that of human skin, thus enabling it to have a perception-strengthening ability. Additionally, the strong ionic clusters can also ensure the PCI remains stable at high temperatures. Even when the temperature is raised to 200 °C, the PCI can maintain the gel state. Moreover, the PCI exhibits high transparency, recyclability, good adhesion, and high conductivity. Such excellent features distinguish the PCI from ordinary ionogels, providing a new way to realize skin-like sensing in harsh environments for future bionic machines.

Adjusting the stiffness of a cell-free hydrogel system based on tissue-specific extracellular matrix to optimize adipose tissue regeneration.

Background: Large-area soft tissue defects are challenging to reconstruct. Clinical treatment methods are hampered by problems associated with injury to the donor site and the requirement for multiple surgical procedures. Although the advent of decellularized adipose tissue (DAT) offers a new solution to these problems, optimal tissue regeneration efficiency cannot be achieved because the stiffness of DAT cannot be altered in vivo by adjusting its concentration. This study aimed to improve the efficiency of adipose regeneration by physically altering the stiffness of DAT to better repair large-volume soft tissue defects. Methods: In this study, we formed three different cell-free hydrogel systems by physically cross-linking DAT with different concentrations of methyl cellulose (MC; 0.05, 0.075 and 0.10 g/ml). The stiffness of the cell-free hydrogel system could be regulated by altering the concentration of MC, and all three cell-free hydrogel systems were injectable and moldable. Subsequently, the cell-free hydrogel systems were grafted on the backs of nude mice. Histological, immunofluorescence and gene expression analyses of adipogenesis of the grafts were performed on days 3, 7, 10, 14, 21 and 30. Results: The migration of adipose-derived stem cells (ASCs) and vascularization were higher in the 0.10 g/ml group than in the 0.05 and 0.075 g/ml groups on days 7, 14 and 30. Notably, on days 7, 14 and 30, the adipogenesis of ASCs and adipose regeneration were significantly higher in the 0.075 g/ml group than in the 0.05 g/ml group (p < 0.01 or p < 0.001) and 0.10 g/ml group (p < 0.05 or p < 0.001). Conclusion: Adjusting the stiffness of DAT via physical cross-linking with MC can effectively promote adipose regeneration, which is of great significance to the development of methods for the effective repair and reconstruction of large-volume soft tissue defects.

Melatonin promotes survival of nonvascularized fat grafts and enhances the viability and migration of human adipose-derived stem cells via down-regulation of acute inflammatory cytokines.

Nonvascularized fat grafting is a valuable technique for soft tissue reconstruction but poor survival of fat in the host environment remains a problem. A process known as cell-assisted transfer is used to enhance fat graft retention by adding stromal vascular fraction, an adipose-derived stem cell (ASC) rich content to lipoaspirate. We have recently shown that the use of melatonin, a reactive oxygen species scavenger, protects human ASCs from hydrogen peroxide-induced oxidative stress and cell death in vitro but its role as a pharmacological adjunct in clinical fat grafting has not been studied. Herein, the effect of melatonin was examined on human ASCs in vitro using survival and functional assays including the MTT assay, CellTox Green assay, monolayer scratch assay as well as a human cytokine chemoluminescence, and tumour necrosis factor-α assay. Further, the effect of melatonin-treated fat grafts was tested in vivo with a murine model. Haematoxylin and eosin staining, perilipin and CD31 immunostaining were performed with morphometric analysis of adipose tissue. The results demonstrate that, in vitro, the addition of melatonin to ASCs significantly improved their cell-viability, promoted cell migration and preserved membrane integrity as compared to controls. In addition, it induced a potent anti-inflammatory response by downregulating acute inflammatory cytokines particularly tumour necrosis factor-α. For the first time, it is demonstrated in vivo that melatonin enhances fat graft volume retention by reducing inflammation and increasing the percentage of adipose volume within fat grafts with comparable volumes to that of cell-assisted lipotransfer. Based on these novel findings, melatonin may be a useful pharmacological adjunct in clinical fat grafting.

Indomethacin Enhances Fat Graft Retention by Up-Regulating Adipogenic Genes and Reducing Inflammation.

BACKGROUND: Cell-assisted lipotransfer has been promisingly applied to restore soft-tissue defects in plastic surgery; however, the harvesting of stromal vascular fraction increases morbidity and poses potential safety hazards. The authors investigated whether adding indomethacin, an antiinflammatory proadipogenic drug, to the fat graft at the time of transplantation would enhance the final graft volume compared with cell-assisted lipotransfer. METHODS: In vitro, human adipose-derived stem cells were cultured in conditioned growth media supplemented with various doses of indomethacin to investigate adipogenesis and the expression of the adipogenic genes. In vivo, lipoaspirate mixed with stromal vascular fractions or indomethacin was injected into the dorsum of mice. Tissues were harvested at weeks 2, 4, and 12 to evaluate histologic changes. RESULTS: In vitro, polymerase chain reaction analysis revealed that increased up-regulation of adipogenic genes and activation of the peroxisome proliferator-activated receptor-γ pathway. In vivo, the percentage volume of adipocytes in the indomethacin-assisted groups was higher than that in the lipoaspirate-alone (control) group at 12 weeks (p = 0.016), and was equivalent to the volume in the cell-assisted groups (p = 1.000). Indomethacin improved adipose volumes but had no effect on vascularity. A larger number of small adipocytes appeared in the treatment samples than in the controls at 2 weeks (p = 0.044) and 4 weeks (p = 0.021). CONCLUSIONS: Pretreating lipoaspirate with indomethacin enhances the final volume retention of engrafted fat. This result is explained in part by increased adipogenesis and possibly by the inhibition of inflammatory responses.

Activated macrophages as key mediators of capsule formation on adipose constructs in tissue engineering chamber models.

In plastic and reconstructive field, it would be much beneficial to fabricate an engineered adipose tissue substitute allowing reliable and complete fat tissue regeneration. Tissue engineering chamber (TEC) holds the promise to optimize an adipogenic configuration that is efficacious as well as reproducible. A frequently occurring complication involves the adipose tissue flap encapsulation and, effectively, its shielding, by a thick fibrous membrane, which hinders development into the proliferative stage. The reason for the deposition of the collagen capsule remains unclear. Numerous studies have highlighted that macrophages play a key role in adipogenesis in a TEC model using a silicone chamber enclosing the fat flap with a superficial epigastric pedicle. As a verification of the role of macrophages in capsule formation, we propose the inhibition of transforming growth factor ß1 (TGF-ß1) synthesis by macrophage populations in the local microenvironment by administrating tranilast into the TEC. We hypothesize that upon reduction of TGF-ß1 levels, capsule formation and inhibition of new adipose tissue development will decrease. Furthermore, we propose that a tissue engineering chamber model in which macrophages are closely related to both neo-adipogenesis and capsule formation.

Polycaprolactone nanofibrous mesh reduces foreign body reaction and induces adipose flap expansion in tissue engineering chamber.

Tissue engineering chamber technique can be used to generate engineered adipose tissue, showing the potential for the reconstruction of soft tissue defects. However, the consequent foreign body reaction induced by the exogenous chamber implantation causes thick capsule formation on the surface of the adipose flap following capsule contracture, which may limit the internal tissue expansion. The nanotopographical property and architecture of nanofibrous scaffold may serve as a promising method for minimizing the foreign body reaction. Accordingly, electrospinning porous polycaprolactone (PCL) nanofibrous mesh, a biocompatible synthetic polymer, was attached to the internal surface of the chamber for the reducing local foreign body reaction. Adipose flap volume, level of inflammation, collagen quantification, capsule thickness, and adipose tissue-specific gene expression in chamber after implantation were evaluated at different time points. The in vivo study revealed that the engineered adipose flaps in the PCL group had a structure similar to that in the controls and normal adipose tissue structure but with a larger flap volume. Interleukin (IL)-1ß, IL-6, and transforming growth factor-ß expression decreased significantly in the PCL group compared with the control. Moreover, the control group had much more collagen deposition and thicker capsule than that observed in the PCL group. These results indicate that the unique nanotopographical effect of electrospinning PCL nanofiber can reduce foreign body reaction in a tissue engineering chamber, which maybe a promising new method for generating a larger volume of mature, vascularized, and stable adipose tissue.

Role of Adipose-derived Stem Cells in Fat Grafting and Reconstructive Surgery.

Autologous fat grafting is commonly utilised to reconstruct soft tissue defects caused by ageing, trauma, chronic wounds and cancer resection. The benefits of fat grafting are minimal donor site morbidity and ease of availability through liposuction or lipectomy. Nonetheless, survival and longevity of fat grafts remain poor post-engraftment. Various methods to enhance fat graft survival are currently under investigation and its stem cell constituents are of particular interest. Cell-assisted lipotransfer refers to the addition of adipose-derived stem cell (ASC) rich component of stromal vascular fraction to lipoaspirate, the results of which have proven promising. This article aims to review the role of ASCs in fat grafting and reconstructive surgery.

Tissue Engineering by Intrinsic Vascularization in an In Vivo Tissue Engineering Chamber.

In reconstructive surgery, there is a clinical need for an alternative to the current methods of autologous reconstruction which are complex, costly and trade one defect for another. Tissue engineering holds the promise to address this increasing demand. However, most tissue engineering strategies fail to generate stable and functional tissue substitutes because of poor vascularization. This paper focuses on an in vivo tissue engineering chamber model of intrinsic vascularization where a perfused artery and a vein either as an arteriovenous loop or a flow-through pedicle configuration is directed inside a protected hollow chamber. In this chamber-based system angiogenic sprouting occurs from the arteriovenous vessels and this system attracts ischemic and inflammatory driven endogenous cell migration which gradually fills the chamber space with fibro-vascular tissue. Exogenous cell/matrix implantation at the time of chamber construction enhances cell survival and determines specificity of the engineered tissues which develop. Our studies have shown that this chamber model can successfully generate different tissues such as fat, cardiac muscle, liver and others. However, modifications and refinements are required to ensure target tissue formation is consistent and reproducible. This article describes a standardized protocol for the fabrication of two different vascularized tissue engineering chamber models in vivo.

Adipose-Derived Stem Cell Delivery for Adipose Tissue Engineering: Current Status and Potential Applications in a Tissue Engineering Chamber Model.

In reconstructive surgery, there is a clinical need for adequate implants to repair soft tissue defects caused by traumatic injury, tumor resection, or congenital abnormalities. Adipose tissue engineering may provide answers to this increasing demand. This study comprehensively reviews current approaches to adipose tissue engineering, detailing different cell carriers under investigation, with a special focus on the application of adipose-derived stem cells (ASCs). ASCs act as building blocks for new tissue growth and as modulators of the host response. Recent studies have also demonstrated that the implantation of a hollow protected chamber, combined with a vascular pedicle within the fat flaps provides blood supply and enables the growth of large-volume of engineered soft tissue. Conceptually, it would be of value to co-regulate this unique chamber model with adipose-derived stem cells to obtain a greater volume of soft tissue constructs for clinical use. Our review provides a cogent update on these advances and details the generation of possible fat substitutes.

Self-synthesized extracellular matrix contributes to mature adipose tissue regeneration in a tissue engineering chamber.

The development of an engineered adipose tissue substitute capable of supporting reliable, predictable, and complete fat tissue regeneration would be of value in plastic and reconstructive surgery. For adipogenesis, a tissue engineering chamber provides an optimized microenvironment that is both efficacious and reproducible; however, for reasons that remain unclear, tissues regenerated in a tissue engineering chamber consist mostly of connective rather than adipose tissue. Here, we describe a chamber-based system for improving the yield of mature adipose tissue and discuss the potential mechanism of adipogenesis in tissue-chamber models. Adipose tissue flaps with independent vascular pedicles placed in chambers were implanted into rabbits. Adipose volume increased significantly during the observation period (week 1, 2, 3, 4, 16). Histomorphometry revealed mature adipose tissue with signs of adipose tissue remolding. The induced engineered constructs showed high-level expression of adipogenic (peroxisome proliferator-activated receptor γ), chemotactic (stromal cell-derived factor 1a), and inflammatory (interleukin 1 and 6) genes. In our system, the extracellular matrix may have served as a scaffold for cell migration and proliferation, allowing mature adipose tissue to be obtained in a chamber microenvironment without the need for an exogenous scaffold. Our results provide new insights into key elements involved in the early development of adipose tissue regeneration.

The angiogenic and adipogenic modes of adipose tissue after free fat grafting.

BACKGROUND: The major drawback of adipose grafting is its clinical unpredictability, which leads to surgeon and patient dissatisfaction. The mechanisms underlying angiogenesis and regeneration of the graft tissue are still unclear. METHODS: Mouse adipose tissue was processed using two different methods (fragmental and integral) and was used to identify the mode of angiogenesis of the graft. Cross-grafting of tissue from normal mice and transgenic mice expressing green fluorescent protein was used to observe the origin of cells during the adipose regeneration. RESULTS: Almost all the CD31 endothelial cells of the new vessels were derived from the recipient. The new vessels in the graft were mainly formed through recipient vessels growing into the graft rather than the reassembly of donor endothelial cells or the reconnection of recipient and donor vessels. Angiogenesis depends largely on recipient-site environment. The retention of donor-derived tissue dropped to only 10 percent 8 weeks after grafting, and the majority of the key regeneration cells, the CD34 cells, came from the recipient during adipogenesis (p < 0.05). In total, the retention of the recipient-derived tissue was up to 73 percent in the fragmental group and 47.5 percent in the integral group. CONCLUSIONS: The angiogenesis of the graft occurs by the classic "vessel branching" mode, in which the recipient plays a dominant role. The mode of graft tissue retention primarily involves CD34 adipose precursor cells derived from the recipient.

[Preliminary study on stromal vascular fraction promoting angiogenesis and tissue regeneration in tissue engineering chamber].

OBJECTIVE: To evaluate the mechanism of stromal vascular fraction (SVF) promoting angiogenesis and tissue regeneration in tissue engineering chamber. METHODS: Twenty-four 6-month-old New Zealand white rabbits, male or female, weighing 2.5-2.8 kg, were selected. Thoracic dorsal arteriovenous bundle combined with collagen type I scaffold was transplanted to dorsal side, and wrapped by cylindrical hollow silicone chamber; all animals were randomly divided into the experimental group (n = 12) and the control group (n = 12). SVF was isolated from the back fat pads of rabbits in experimental group and labelled with DiI at 2 weeks after operation. The 1 mL cell suspension (1 x 10(6) cells/mL) and equal saline were injected into the chamber in experimental group and control group, respectively. The regenerative tissues were harvested for general observation and HE staining at 2 and 4 weeks after injection: and immunofluorescent staining was carried out in experimental group at 4 weeks. RESULTS: At 2 weeks after injection, the regenerative tissue was cylindrical; obvious vessel network and incompletely degradable collagen scaffold could be seen on the surface of the new tissue in 2 groups. The volume of new tissue was (0.87 +/- 0.11) mL in experimental group, and (0.72 +/- 0.08) mL in control group at 2 weeks, showing significant difference (t = 2.701, P = 0.011). At 4 weeks, little collagen scaffold could be seen on the surface in control group, but no collagen scaffold in experimental group; the volume of new tissue was (0.74 +/- 0.14) mL in experimental group, and (0.64 +/- 0.10) mL in control group, showing no significant difference (t = 1.424, P = 0.093). HE staining showed new mature vessels at 4 weeks, but no adipose tissue or fat lobulus formed in both groups; the capillary density was significantly higher in experimental group than in control group at 2 weeks (t = 6.291, P = 0.000) and at 4 weeks (t = 5.445, P = 0.000). The immunofluorescent staining found that SVF survived and located at the edge area after 4 weeks; the expressions of CD31 and DiI were positive in some endothelial cells. CONCLUSION: SVF can promote the angiogenesis and tissue regeneration in tissue engineering chamber, but it can not differentiate into adipocyte spontaneously without adipogenic microenvironment.

Tissue engineering chamber promotes adipose tissue regeneration in adipose tissue engineering models through induced aseptic inflammation.

Tissue engineering chamber (TEC) makes it possible to generate significant amounts of mature, vascularized, stable, and transferable adipose tissue. However, little is known about the role of the chamber in tissue engineering. Therefore, to investigate the role of inflammatory response and the change in mechanotransduction started by TEC after implantation, we placed a unique TEC model on the surface of the groin fat pads in rats to study the expression of cytokines and tissue development in the TEC. The number of infiltrating cells was counted, and vascular endothelial growth factor (VEGF) and monocyte chemotactic protein-1 (MCP-1) expression levels in the chamber at multiple time points postimplantation were analyzed by enzyme-linked immunosorbent assay. Tissue samples were collected at various time points and labeled for specific cell populations. The result showed that new adipose tissue formed in the chamber at day 60. Also, the expression of MCP-1 and VEGF in the chamber decreased slightly from an early stage as well as the number of the infiltrating cells. A large number of CD34+/perilipin- perivascular cells could be detected at day 30. Also, the CD34+/perilipin+ adipose precursor cell numbers increased sharply by day 45 and then decreased by day 60. CD34-/perilipin+ mature adipocytes were hard to detect in the chamber content at day 30, but their number increased and then peaked at day 60. Ki67-positive cells could be found near blood vessels and their number decreased sharply over time. Masson's trichrome showed that collagen was the dominant component of the chamber content at early stage and was replaced by newly formed small adipocytes over time. Our findings suggested that the TEC implantation could promote the proliferation of adipose precursor cells derived from local adipose tissue, increase angiogenesis, and finally lead to spontaneous adipogenesis by inducing aseptic inflammation and changing local mechanotransduction.

[The impact of angiogenic and adipogenic microenvironment on adipose tissue regeneration in tissue engineering chamber].

OBJECTIVE: By observing the adipogenic and angiogenic microenvironment impact on the morphology of newly generated tissue for exploring the key factors which inducing mature adipose tissue regeneration in tissue engineering model. METHODS: 24 healthy 6 months' New Zealand rabbits were picked and put into four groups according to different microenvironment. Every group has 6 rabbits and divided as follows: no axial-blood supply fat flap(0 ml), granular fat only(0.6 ml), axial blood vessel only (0.05 ml), axial vascularized fat flap ((0.6 ml). We separated or combined adipogenic and angiogenic environment within these groups. After 8 weeks, samples were harvested for histologic observation including macroscopic observation, volume analysis and HE testing. RESULTS: In granular fat group, its volume decreased by (0.25 ± 0.10) ml after 8 weeks as the shortage of blood supply and finally it could be enveloped. In axial blood vessel group, its volume increased by (0. 37 ± 0. 04) ml after 8 weeks with fibrous tissue formation as shortage of adipogenic microenvironment. The no axial-blood supply fat flap group grew into(0.12 ± 0.03) ml, which can' t support large volume adipose tissue formation because of lacking independent blood supply. Only axial vascularized fat flap model could generate mature adipose tissue in large volume(3.45 ± 0.48) ml. The number of new capillary in every group was different after 8 weeks. By counting the numbers in every single view, no axial-blood supply fat flap group 15 ± 3.5)and granular fat only group(5 ± 2.5)had a significant difference with axial vascularized fat flap group 22 ± 5) respectively. CONCLUSION: Only both adipogenic or angiogenic microenvironment exist could induce mature adipose tissue in large volume in tissue engineering chamber model.