Intrinsic Vascularization of Recombinant eADF4(C16) Spider Silk Matrices in the Arteriovenous Loop Model

Schwann Cells Do Not Promote Myogenic Differentiation in the EPI Loop Model

In skeletal muscle tissue engineering, innervation and vascularization play an essential role in the establishment of functional skeletal muscle. For adequate three-dimensional assembly, biocompatible aligned nanofibers are beneficial as matrices for cell seeding. The aim of this study was to analyze the impact of Schwann cells (SC) on myoblast (Mb) and adipogenic mesenchymal stromal cell (ADSC) cocultures on poly-ɛ-caprolactone (PCL)-collagen I-nanofibers in vivo. Human Mb/ADSC cocultures, as well as Mb/ADSC/SC cocultures, were seeded onto PCL-collagen I-nanofiber scaffolds and implanted into the innervated arteriovenous loop model (EPI loop model) of immunodeficient rats for 4 weeks. Histological staining and gene expression were used to compare their capacity for vascularization, immunological response, myogenic differentiation, and innervation. After 4 weeks, both Mb/ADSC and Mb/ADSC/SC coculture systems showed similar amounts and distribution of vascularization, as well as immunological activity. Myogenic differentiation could be observed in both groups through histological staining (desmin, myosin heavy chain) and gene expression (MYOD, MYH3, ACTA1) without significant difference between groups. Expression of CHRNB and LAMB2 also implied neuromuscular junction formation. Our study suggests that the addition of SC did not significantly impact myogenesis and innervation in this model. The implanted motor nerve branch may have played a more significant role than the presence of SC.

Only kosmotrope anions trigger fibrillization of the recombinant core spidroin eADF4(C16) from Araneus diadematus

Recombinant core spidroin eADF4(C16) has received increasing attention due to its ability to form micro- and nano-structured scaffolds, which are based on nanofibrils with great potential for biomedical and biotechnological applications. Phosphate anions have been demonstrated to trigger the eADF4(C16) self-assembly into cross-beta fibrils. In the present work, we systematically addressed the effect of nine sodium anions, namely SO4 2- , HPO4 2- (Pi), F- , Cl- , Br- , NO3 - , I- , SCN- , and ClO4 - from the Hofmeister series on the in vitro self-assembly kinetics of eADF4(C16). We show that besides the phosphate anions, only kosmotropic anions such as sulfate and fluoride can initiate the eADF4(C16) fibril formation. Global analysis of the self-assembly kinetics, utilizing the platform AmyloFit, showed the nucleation-based mechanism with a major role of secondary nucleation, surprisingly independent of the type of the kosmotropic anion. The rate constant of the fibril elongation in mixtures of phosphate anions with other studied anions correlated with their kosmotropic or chaotropic position in the Hofmeister series. Our findings suggest an important role of anion hydration in the eADF4(C16) fibrillization process.

A Novel Window into Angiogenesis-Intravital Microscopy in the AV-Loop-Model

Due to the limitations of current in vivo experimental designs, our comprehensive knowledge of vascular development and its implications for the development of large-scale engineered tissue constructs is very limited. Therefore, the purpose of this study was to develop unique in vivo imaging chambers that allow the live visualization of cellular processes in the arteriovenous (AV) loop model in rats. We have developed two different types of chambers. Chamber A is installed in the skin using the purse sting fixing method, while chamber B is installed subcutaneously under the skin. Both chambers are filled with modified gelatin hydrogel as a matrix. Intravital microscopy (IVM) was performed after the injection of fluorescein isothiocyanate (FITC)-labeled dextran and rhodamine 6G dye. The AV loop was functional for two weeks in chamber A and allowed visualization of the leukocyte trafficking. In chamber B, microvascular development in the AV loop could be examined for 21 days. Quantification of the microvascular outgrowth was performed using Fiji-ImageJ. Overall, by combining these two IVM chambers, we can comprehensively understand vascular development in the AV loop tissue engineering model¯.

Sequence Context and Complex Hofmeister Salt Interactions Dictate Phase Separation Propensity of Resilin-like Polypeptides

Resilin is an elastic material found in insects with exceptional durability, resilience, and extensibility, making it a promising biomaterial for tissue engineering. The monomeric precursor, pro-resilin, undergoes thermo-responsive self-assembly through liquid-liquid phase separation (LLPS). Understanding the molecular details of this assembly process is critical to developing complex biomaterials. The present study investigates the interplay between the solvent, sequence syntax, structure, and dynamics in promoting LLPS of resilin-like-polypeptides (RLPs) derived from domains 1 and 3 of Drosophila melanogaster pro-resilin. NMR, UV-vis, and microscopy data demonstrate that while kosmotropic salts and low pH promote LLPS, the effects of chaotropic salts with increasing pH are more complex. Subtle variations between the repeating amino acid motifs of resilin domain 1 and domain 3 lead to significantly different salt and pH dependence of LLPS, with domain 3 sequence motifs more strongly favoring phase separation under most conditions. These findings provide new insight into the molecular drivers of RLP phase separation and the complex roles of both RLP sequence and solution composition in fine-tuning assembly conditions.

Recombinant Spider Silk Bioinks for Continuous Protein Release by Encapsulated Producer Cells

Targeted therapies using biopharmaceuticals are of growing clinical importance in disease treatment. Currently, there are several limitations of protein-based therapeutics (biologicals), including suboptimal biodistribution, lack of stability, and systemic side effects. A promising approach to overcoming these limitations could be a therapeutic cell-loaded 3D construct consisting of a suitable matrix component that harbors producer cells continuously secreting the biological of interest. Here, the recombinant spider silk proteins eADF4(C16), eADF4(C16)-RGD, and eADF4(C16)-RGE have been processed together with HEK293 producer cells stably secreting the highly traceable reporter biological TNFR2-Fc-GpL, a fusion protein consisting of the extracellular domain of TNFR2, the Fc domain of human IgG1, and the luciferase of Gaussia princeps as a reporter domain. eADF4(C16) and eADF4(C16)-RGD hydrogels provide structural and mechanical support, promote HEK293 cell growth, and allow fusion protein production by the latter. Bioink-captured HEK293 producer cells continuously release functional TNFR2-Fc-GpL over 14 days. Thus, the combination of biocompatible, printable spider silk bioinks with drug-producing cells is promising for generating implantable 3D constructs for continuous targeted therapy.

Microvascular development in the rat arteriovenous loop model in vivo-A step by step intravital microscopy analysis

The arteriovenous (AV) loop model is a key technique to solve one of the major problems of tissue engineering-providing adequate vascular support for a tissue construct of significant size. However, the molecular and cellular mechanisms of vascularization and factors influencing the generation of new tissue in the AV loop are still poorly understood. We previously established a novel intravital microscopy approach to study these events. In this study, we implanted our observation chamber filled with two types of hydrogels such as fibrin and methacrylate gelatin (GelMA) and performed intravital microscopy (IVM) on days 7, 14, and 21. Initial microvessel formation was observed in GelMA on day 14, while the vessel network showed clear indicators of network rearrangement and maturation on day 21. No visible microvessels were observed in fibrin. The chambers were explanted on day 21. Histological examination revealed higher numbers of microvessels in GelMA compared to fibrin, while the AV loop was thrombosed in all fibrin constructs, possibly due to matrix degradation. GelMA proved to be an ideal matrix for IVM studies in the AV loop model due to its slow degradation and transparency. This IVM model can be employed as a novel tool for live and thus faster comprehension of crucial events in the tissue regeneration process, which can improve tissue engineering application.

Impact of Endothelial Progenitor Cells in the Vascularization of Osteogenic Scaffolds

The microvascular endothelial network plays an important role in osteogenesis, bone regeneration and bone tissue engineering. Endothelial progenitor cells (EPCs) display a high angiogenic and vasculogenic potential. The endothelialization of scaffolds with endothelial progenitor cells supports vascularization and tissue formation. In addition, EPCs enhance the osteogenic differentiation and bone formation of mesenchymal stem cells (MSCs). This study aimed to investigate the impact of EPCs on vascularization and bone formation of a hydroxyapatite (HA) and beta-tricalcium phosphate (ß-TCP)–fibrin scaffold. Three groups were designed: a scaffold-only group (A), a scaffold and EPC group (B), and a scaffold and EPC/MSC group (C). The HA/ß–TCP–fibrin scaffolds were placed in a porous titanium chamber permitting extrinsic vascularization from the surrounding tissue. Additionally, intrinsic vascularization was achieved by means of an arteriovenous loop (AV loop). After 12 weeks, the specimens were explanted and investigated by histology and CT. We were able to prove a strong scaffold vascularization in all groups. No differences regarding the vessel number and density were detected between the groups. Moreover, we were able to prove bone formation in the coimplantation group. Taken together, the AV loop is a powerful tool for vascularization which is independent from scaffold cellularization with endothelial progenitor cells’ prior implantation.

Site-Specific Functionalization of Recombinant Spider Silk Janus Fibers

Biotechnological production is a powerful tool to design materials with customized properties. The aim of this work was to apply designed spider silk proteins to produce Janus fibers with two different functional sides. First, functionalization was established through a cysteine-modified silk protein, ntagCys eADF4(κ16). After fiber spinning, gold nanoparticles (AuNPs) were coupled via thiol-ene click chemistry. Significantly reduced electrical resistivity indicated sufficient loading density of AuNPs on such fiber surfaces. Then, Janus fibers were electrospun in a side-by-side arrangement, with "non-functional" eADF4(C16) on the one and "functional" ntagCys eADF4(κ16) on the other side. Post-treatment was established to render silk fibers insoluble in water. Subsequent AuNP binding was highly selective on the ntagCys eADF4(κ16) side demonstrating the potential of such silk-based systems to realize complex bifunctional structures with spatial resolutions in the nano scale.

New Forms of Electrospun Nanofibers Applied in Cardiovascular Field

Cardiovascular disease (CVD) is one of the leading causes of death worldwide. In recent years, regenerative medicine, tissue engineering and the development of new materials have become the focus of attention this field, and electrospinning technology to prepare nanofibrous materials for the treatment of cardiovascular diseases has attracted people's attention. Unlike previous reviews, this research enumerates the experimental methods and applications of electrospinning technology combined with nanofibrous materials in the directions of myocardial infarction repair, artificial heart valves, artificial blood vessels and cardiovascular patches from the perspective of cardiovascular surgery. In the end, this review also summarizes the limitations, unresolved technical challenges, and possible future directions of this technology for cardiovascular disease applications.

Impact of Cell Loading of Recombinant Spider Silk Based Bioinks on Gelation and Printability

Printability of bioinks encompasses considerations concerning rheology and extrudability, characterization of filament formation, shape fidelity, cell viability, and post-printing cellular development. Recombinant spider silk based hydrogels might be a suitable material to be used in bioinks, that is, a formulation of cells and materials to be used for bioprinting. Here, the high shape fidelity of spider silk ink is shown by bioprinting the shape and size of a human aortic valve. Further the influence of the encapsulation of cells has been evaluated on spider silk hydrogel formation, hydrogel mechanics, and shape fidelity upon extrusion based bioprinting. It is shown that the presence of cells impacts the gelation of spider silk proteins differently, depending on the used silk variant. RGD-modified spider silk hydrogels are physically crosslinked by the cells, while there is no active interaction between cells and un-tagged spider silk proteins. Strikingly, even at cell densities up to ten million cells per milliliter, cell viability is high after extrusion-based printing, which is a significant prerequisite for future applications. Shape fidelity of the printed constructs is demonstrated using a filament collapse test in the absence and presence of human cells.

Gelatin methacryloyl is a slow degrading material allowing vascularization and long-term usein vivo

In situtissue engineering is an emerging field aiming at the generation of ready-to-use three-dimensional tissues. One solution to supply a proper vascularization of larger tissues to provide oxygen and nutrients is the arteriovenous loop (AVL) model. However, for this model, suitable scaffold materials are needed that are biocompatible/non-immunogenic, slowly degradable, and allow vascularization. Here, we investigate the suitability of the known gelatin methacryloyl (GelMA)-based hydrogel forin-situtissue engineering utilizing the AVL model. Rat AVLs are embedded by two layers of GelMA hydrogel in an inert PTFE chamber and implanted in the groin. Constructs were explanted after 2 or 4 weeks and analyzed. For this purpose, gross morphological, histological, and multiphoton microscopic analysis were performed. Immune response was analyzed based on anti-CD68 and anti-CD163 staining of immune cells. The occurrence of matrix degradation was assayed by anti-MMP3 staining. Vascularization was analyzed by anti-α-smooth muscle actin staining, multiphoton microscopy, as well as expression analysis of 53 angiogenesis-related proteins utilizing a proteome profiler angiogenesis array kit. Here we show that GelMA hydrogels are stable for at least 4 weeks in the rat AVL model. Furthermore, our data indicate that GelMA hydrogels are biocompatible. Finally, we provide evidence that GelMA hydrogels in the AVL model allow connective tissue formation, as well as vascularization, introducing multiphoton microscopy as a new methodology to visualize neovessel formation originating from the AVL. GelMA is a suitable material forin situandin vivoTE in the AVL model.

Enhanced vascularization andde novotissue formation in hydrogels made of engineered RGD-tagged spider silk proteins in the arteriovenous loop model

Due to its low immunogenic potential and the possibility to fine-tune their properties, materials made of recombinant engineered spider silks are promising candidates for tissue engineering applications. However, vascularization of silk-based scaffolds is one critical step for the generation of bioartificial tissues and consequently for clinical application. To circumvent insufficient vascularization, the surgically induced angiogenesis by means of arteriovenous loops (AVL) represents a highly effective methodology. Here, previously established hydrogels consisting of nano-fibrillary recombinant eADF4(C16) were transferred into Teflon isolation chambers and vascularized in the rat AVL model over 4 weeks. To improve vascularization, also RGD-tagged eADF4(C16) hydrogels were implanted in the AVL model over 2 and 4 weeks. Thereafter, the specimen were explanted and analyzed using histology and microcomputed tomography. We were able to confirm biocompatibility and tissue formation over time. Functionalizing eADF4(C16) with RGD-motifs improved hydrogel stability and enhanced vascularization even outperforming other hydrogels, such as fibrin. This study demonstrates that the scaffold ultrastructure as well as biofunctionalization with RGD-motifs are powerful tools to optimize silk-based biomaterials for tissue engineering applications.

Watching the Vessels Grow: Establishment of Intravital Microscopy in the Arteriovenous Loop Rat Model

Tissue engineering in reconstructive surgery seeks to generate bioartificial tissue substitutes. The arteriovenous (AV) loop allows the generation of axially vascularized tissue constructs. Cellular mechanisms of this vascularization process are largely unclear. In this study, we developed two different chamber models for intravital microscopy and imaging of the AV loop in the rat. Multiple design variations were implanted and the stability of the chamber and AV loop patency was tested in vivo. Our novel chamber facilitates repetitive observation of the AV loop using fluorescence-enhanced intravital microscopy. This technique can be used for daily evaluation of leukocyte-endothelial cell interactions, vascularization, and tissue formation in the AV loop model on 14 consecutive days. Therefore, our newly developed model for intravital microscopy will provide better understanding of cellular and molecular processes in tissue engineering in the AV loop. Moreover, it supports initiation of the novel approaches for therapeutic applications. Impact statement In the Arteriovenous (AV) loop, axially vascularized tissue can be generated and modified using different tissue engineering approaches. Cellular mechanisms of this vascularization process are largely unclear. We managed to develop an intravital microscopy model for long-term observation of intravascular and perivascular events in the AV loop. Leukocyte-endothelial cell interactions, vascularization, and tissue formation in the AV loop can now be evaluated on a day-to-day basis. This will provide better understanding of cellular and molecular processes happening during tissue engineering within the AV loop.

Silk-Reinforced Collagen Hydrogels with Raised Multiscale Stiffness for Mesenchymal Cells 3D Culture

Type I collagen hydrogels are of high interest in tissue engineering. With the evolution of 3D bioprinting technologies, a high number of collagen-based scaffolds have been reported for the development of 3D cell cultures. A recent proposal was to mix collagen with silk fibroin derived from Bombyx mori silkworm. Nevertheless, due to the difficulties in the preparation and the characteristics of the protein, several problems such as phase separation and collagen denaturation appear during the procedure. Therefore, the common solution is to diminish the concentration of collagen although in that way the most biologically relevant component is reduced. In this study, we present a new, simple, and effective method to develop a collagen-silk hybrid hydrogel with high collagen concentration and with increased stiffness approaching that of natural tissues, which could be of high interest for the development of cardiac patches for myocardial regeneration and for preconditioning of mesenchymal stem cells (MSCs) to improve their therapeutic potential. Sericin in the silk was preserved by using a physical solubilizing procedure that results in a preserved fibrous structure of type I collagen, as shown by ultrastructural imaging. The macro- and micromechanical properties of the hybrid hydrogels measured by tensile stretch and atomic force microscopy, respectively, showed a more than twofold stiffening than the collagen-only hydrogels. Rheological measurements showed improved printability properties for the developed biomaterial. The suitability of the hydrogels for 3D cell culture was assessed by 3D bioprinting bone marrow-derived MSCs cultured within the scaffolds. The result was a biomaterial with improved printability characteristics that better resembled the mechanical properties of natural soft tissues while preserving biocompatibility owing to the high concentration of collagen. Impact statement In this study, we report the development of silk microfiber-reinforced type I collagen hydrogels for 3D bioprinting and cell culture. In contrast with previously reported studies, a novel physical method allowed the preservation of the silk sericin protein. Hydrogels were stable, showed no phase separation between the biomaterials, and they presented improved printability. An increase between two- and threefold of the multiscale stiffness of the scaffolds was achieved with no need of using additional crosslinkers or complex methods, which could be of high relevance for cardiac patches development and for preconditioning mesenchymal stem cells (MSCs) for therapeutic applications. We demonstrate that bone marrow-derived MSCs can be effectively bioprinted and 3D cultured within the stiffened structures.

Designing of spider silk proteins for human induced pluripotent stem cell-based cardiac tissue engineering

Materials made of recombinant spider silk proteins are promising candidates for cardiac tissue engineering, and their suitability has so far been investigated utilizing primary rat cardiomyocytes. Herein, we expanded the tool box of available spider silk variants and demonstrated for the first time that human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes attach, contract, and respond to pharmacological treatment using phenylephrine and verapamil on explicit spider silk films. The hiPSC-cardiomyocytes contracted for at least 14 days on films made of positively charged engineered Araneus diadematus fibroin 4 (eADF4(κ16)) and three different arginyl-glycyl-aspartic acid (RGD)-tagged spider silk variants (positively or negatively charged and uncharged). Notably, hiPSC-cardiomyocytes exhibited different morphologies depending on the spider silk variant used, with less spreading and being smaller on films made of eADF4(κ16) than on RGD-tagged spider silk films. These results indicate that spider silk engineering is a powerful tool to provide new materials suitable for hiPSC-based cardiac tissue engineering.

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hiPSC-cardiomyocytes attach and contract on positively charged and/or RGD-tagged spider silk variants.

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hiPSC-cardiomyocytes exhibit spider silk variant-dependent morphology upon adhesion.

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Explicit spider silk variants promote long-term contractility of hiPSC-cardiomyocytes.

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hiPSC-cardiomyocytes grown on spider silk materials respond to pharmacological treatment.

Actually Seeing What Is Going on - Intravital Microscopy in Tissue Engineering

Intravital microscopy (IVM) study approach offers several advantages over in vitro, ex vivo, and 3D models. IVM provides real-time imaging of cellular events, which provides us a comprehensive picture of dynamic processes. Rapid improvement in microscopy techniques has permitted deep tissue imaging at a higher resolution. Advances in fluorescence tagging methods enable tracking of specific cell types. Moreover, IVM can serve as an important tool to study different stages of tissue regeneration processes. Furthermore, the compatibility of different tissue engineered constructs can be analyzed. IVM is also a promising approach to investigate host reactions on implanted biomaterials. IVM can provide instant feedback for improvising tissue engineering strategies. In this review, we aim to provide an overview of the requirements and applications of different IVM approaches. First, we will discuss the history of IVM development, and then we will provide an overview of available optical modalities including the pros and cons. Later, we will summarize different fluorescence labeling methods. In the final section, we will discuss well-established chronic and acute IVM models for different organs.

Silkworm and spider silk electrospinning: a review

Issues of fossil fuel and plastic pollution are shifting public demand toward biopolymer-based textiles. For instance, silk, which has been traditionally used during at least 5 milleniums in China, is re-emerging in research and industry with the development of high-tech spinning methods. Various arthropods, e.g. insects and arachnids, produce silky proteinic fiber of unique properties such as resistance, elasticity, stickiness and toughness, that show huge potential for biomaterial applications. Compared to synthetic analogs, silk presents advantages of low density, degradability and versatility. Electrospinning allows the creation of nonwoven mats whose pore size and structure show unprecedented characteristics at the nanometric scale, versus classical weaving methods or modern techniques such as melt blowing. Electrospinning has recently allowed to produce silk scaffolds, with applications in regenerative medicine, drug delivery, depollution and filtration. Here we review silk production by the spinning apparatus of the silkworm Bombyx mori and the spiders Aranea diadematus and Nephila Clavipes. We present the biotechnological procedures to get silk proteins, and the preparation of a spinning dope for electrospinning. We discuss silk's mechanical properties in mats obtained from pure polymer dope and multi-composites. This review highlights the similarity between two very different yarn spinning techniques: biological and electrospinning processes.

Tissue Engineering of Lymphatic Vasculature in the Arteriovenous Loop Model of the Rat

Various therapeutic approaches, for example, in case of trauma or cancer require the transplantation of autologous tissue. Depending on the size and the origin of the harvested tissue, these therapies can lead to iatrogenic complications and donor-site morbidities. In future, these side effects could be avoided by transplanting artificially generated tissue consisting of different cell types and matrix components derived from the host body. Tissue that is grown in the patient could be advantageous compared with the more simply structured in vitro-grown alternatives. To overcome the limitations of graft vascularization, the arteriovenous (AV) loop technique has been established for different tissues in the last years and was adapted for lymphatic tissue engineering in the present study. We utilized the AV loop technique to grow human lymphatic vasculature in vivo in the Rowett nude (RNU) rat. A combination of human lymphatic endothelial cells (LECs) and bone marrow-derived mesenchymal stem cells was implanted in a fibrin matrix surrounding the AV loop. After 2 or 4 weeks of implantation, the animals were perfused and the tissue was harvested. It could be demonstrated by immunohistochemistry for human LYVE1, human CD31, and murine podoplanin that the implanted cells formed human lymphatic vasculature in the AV loop chamber. Beside development of murine podoplanin-positive vasculature in the AV loop tissue, vasculature positive for human marker proteins developed in comparable numbers. This suggests that implanted LECs are able to improve the lymphatic vascularization of the newly engineered tissue. Thus, we were able to establish an in vivo tissue engineering method to generate lymphatic vascularized soft tissue. An axially vascularized transplantable lymphatic vessel network was engineered without requiring advanced cell culture equipment, rendering the lymphatic AV loop highly suitable for applied regenerative medicine. Impact statement Various surgical procedures require the transplantation of autologous harvested tissue, for example, the vascularized lymph node transfer for the treatment of lymphedema. Tissue-engineered transplants could be used instead of autologous transplants and thereby help to reduce the side effects of those therapies. However, in vitro tissue engineering of large constructs requires a lot of know-how as well as advanced cell culture equipment, which might not be accessible in every hospital. In vivo tissue engineering approaches like the presented technique for the generation of transplantable networks of lymphatic vasculature could serve as an alternative for in vitro tissue engineering approaches in clinical settings.

Human Umbilical Vein Endothelial Cell Support Bone Formation of Adipose-Derived Stem Cell-Loaded and 3D-Printed Osteogenic Matrices in the Arteriovenous Loop Model

Introduction: For the regeneration of large volume tissue defects, the interaction between angiogenesis and osteogenesis is a crucial prerequisite. The surgically induced angiogenesis by means of an arteriovenous loop (AVL), is a powerful methodology to enhance vascularization of osteogenic matrices. Moreover, the AVL increases oxygen and nutrition supply, thereby supporting cell survival as well as tissue formation. Adipose-derived stem cells (ADSCs) are interesting cell sources because of their simple isolation, expansion, and their osteogenic potential. This study targets to investigate the coimplantation of human ADSCs after osteogenic differentiation and human umbilical vein endothelial cells (HUVECs), embedded in a vascularized osteogenic matrix of hydroxyapatite (HAp) ceramic for bone tissue engineering. Materials and Methods: An osteogenic matrix consisting of HAp granules and fibrin has been vascularized by means of an AVL. Trials in experimental groups of four settings were performed. Control experiments without any cells (A) and three cell-loaded groups using HUVECs (B), ADSCs (C), as well as the combination of ADSCs and HUVECs (D) were performed. The scaffolds were implanted in a porous titanium chamber, fixed subcutaneously in the hind leg of immunodeficient Rowett Nude rats and explanted after 6 weeks. Results: In all groups, the osteogenic matrix was strongly vascularized. Moreover, remodeling processes and bone formation in the cell-containing groups with more bone in the coimplantation group were proved successful. Conclusion: Vascularization and bone formation of osteogenic matrices consisting of ADSCs and HUVECs in the rat AVL model could be demonstrated successfully for the first time. Hence, the coimplantation of differentiated ADSCs with HUVECs may therefore be considered as a promising approach for bone tissue engineering.

Interdisciplinary Treatment of Breast Cancer After Mastectomy With Autologous Breast Reconstruction Using Abdominal Free Flaps in a University Teaching Hospital-A Standardized and Safe Procedure

Background: Breast cancer is the most common malignancy in women. The interdisciplinary treatment is based on the histological tumor type, the TNM classification, and the patient's wishes. Following tumor resection and (neo-) adjuvant therapy strategies, breast reconstruction represents the final step in the individual interdisciplinary treatment plan. Although manifold flaps have been described, abdominal free flaps, such as the deep inferior epigastric artery perforator (DIEP) or the muscle-sparing transverse rectus abdominis myocutaneous (ms-TRAM) flap, are the current gold standard for autologous breast reconstruction. This retrospective study focuses on the safety of autologous breast reconstruction upon mastectomy using abdominal free flaps. Methods: From April 2012 until December 2018, 193 women received 217 abdominal free flaps for autologous breast reconstruction at the University Hospital of Erlangen. For perforator mapping, we performed computed tomography angiography (CTA). Venous anastomosis was standardized using a ring pin coupler system, and flap perfusion was assessed with fluorescence angiography. A retrospective analysis was performed based on medical records, the surgery report, and follow-up of outpatient course. Results: In most cases, autologous breast reconstruction was performed as a secondary reconstructive procedure after mastectomy and radiotherapy. In total, 132 ms1-TRAM, 23 ms2-TRAM, and 62 DIEP flaps were performed with 21 major complications (10%) during hospital stay including five free flap losses (2.3%). In all cases of free flap loss, we found an arterial thrombosis as the main cause. In 24 patients a bilateral breast reconstruction was performed without free flap loss. The majority of free flaps (96.7%) did not need additional supercharging or turbocharging to improve venous outflow. Median venous coupler size was 2.5 mm (range, 1.5-3.5 mm). Conclusion: Using CTA, intraoperative fluorescence angiography, titanized hernia meshes for rectus sheath reconstruction, and venous coupler systems, autologous breast reconstruction with DIEP or ms-TRAM free flaps is a safe and standardized procedure in high-volume microsurgery centers.

Spider Silk for Tissue Engineering Applications

Due to its properties, such as biodegradability, low density, excellent biocompatibility and unique mechanics, spider silk has been used as a natural biomaterial for a myriad of applications. First clinical applications of spider silk as suture material go back to the 18th century. Nowadays, since natural production using spiders is limited due to problems with farming spiders, recombinant production of spider silk proteins seems to be the best way to produce material in sufficient quantities. The availability of recombinantly produced spider silk proteins, as well as their good processability has opened the path towards modern biomedical applications. Here, we highlight the research on spider silk-based materials in the field of tissue engineering and summarize various two-dimensional (2D) and three-dimensional (3D) scaffolds made of spider silk. Finally, different applications of spider silk-based materials are reviewed in the field of tissue engineering in vitro and in vivo.

Size matters-in vitro behaviour of human fibroblasts on textured silicone surfaces with different pore sizes

Capsular contracture remains a challenge in plastic surgery and represents one of the most common postoperative complications following alloplastic breast reconstruction. The impact of the surface structure of silicone implants on the foreign body reaction and the behaviour of connective tissue-producing cells has already been discussed. The aim of this study was to investigate different pore sizes of silicone surfaces and their influence on human fibroblasts in an in vitro model. Four different textures (no, fine, medium and coarse texture) produced with the salt-loss technique, have been assessed in an in vitro model. Human fibroblasts were seeded onto silicone sheets and evaluated after 1, 4 and 7 days microscopically, with viability assay and gene expression analysis. Comparing the growth behaviour and adhesion of the fibroblasts on the four different textures, a dense cell layer, good adhesion and bridge-building ability of the cells could be observed for the fine and medium texture. Cell number and viability of the cells were increasing during the time course of experiments on every texture. TGFß1 was lowest expressed on the fine and medium texture indicating a trend for decreased fibrotic activity. For silicone surfaces produced with the salt-loss technique, we were able to show an antifibrotic effect of smaller sized pores. These findings underline the hypothesis of a key role of the implant surface and the pore size and pore structure in preventing capsular contracture.

Nerve guidance conduit design based on self-rolling tubes

The current gold standard in peripheral nerve repair is nerve autografts for bridging gaps larger than a centimeter. However, autografts are associated with a low availability and the loss of function at the donor site. Nerve guidance conduits (NGCs) made of biocompatible and biodegradable materials reflect suitable alternatives. Clinically approved NGCs comprise either wraps that are rolled around the loose ends of the nerve or steady-state tubes; however, both lack internal guidance structures. Here, we established self-rolling NGCs to allow for gentle encapsulation of nerve cells together with supportive microenvironments, such as (1) an inner tube wall coating with a bioactive spider silk film, (2) an inner tube wall lining using an anisotropic spider silk non-woven mat, or (3) a luminal filler using an anisotropic collagen cryogel. Neuronal cells adhered and differentiated inside the modified tubes and formed neurites, which were oriented along the guidance structures provided by the spider silk non-woven mat or by the fibrillary structure of the collagen cryogel. Thus, our size-adaptable NGCs provide several features useful for peripheral nerve repair, and distinct combinations of the used elements might support and enhance the clinical outcome.