Autonomously vascularized cellular constructs in tissue engineering: opening a new perspective for biomedical science

Hypoxia as a stimulus for tissue formation: The concept of organogenesis in microsurgically vascularized tissue engineering constructs

Axial vascularization of tissue constructs is essential to maintain an adequate blood supply for a stable regeneration of a clinically relevant tissue size. The versatility of the arterio-venous loop (AVL) has been previously shown in various small and large animal models as well as in clinical reports for bone regeneration. We have previously demonstrated the capability of the AVL to induce axial vascularization and to support the nourishment of tissue constructs in small animal models after applying high doses of ionizing radiation comparable to those applied for adjuvant radiotherapy after head and neck cancer. We hypothesize that this robust ability to induce regeneration after irradiation could be related to a state of hypoxia inside the constructs that triggers the HIF1 (hypoxia induced factor 1) - SDF1 (stromal derived factor 1) axis leading to chemotaxis of progenitor cells and induction of tissue regeneration and vascularization. We analyzed the expression of HIF1 and SDF1 via immunofluorescence in axially vascularized bone tissue engineering constructs in Lewis rats 2 and 5 weeks after local irradiation with 9Gy or 15Gy. We also analyzed the expression of various genes for osteogenic differentiation (collagen 1, RUNX, alkaline phosphatase and osteonectin) via real time PCR analysis. The expression of HIF1 and SDF1 was enhanced two weeks after irradiation with 15Gy in comparison to non-irradiated constructs. The expression of osteogenic markers was enhanced at the 5-weeks time point with significant results regarding collagen, alkaline phosphatase and osteonectin. These results indicate that the hypoxia within the AVL constructs together with an enhanced SDF1 expression probably play a role in promoting tissue differentiation. The process of tissue generation triggered by hypoxia in the vicinity of a definite vascular axis with enhanced tissue differentiation over time resembles hereby the well-known concept of organogenesis in fetal life.

Dual siRNA-Loaded Cell Membrane Functionalized Matrix Facilitates Bone Regeneration with Angiogenesis and Neurogenesis

Vascularization and innervation play irreplaceable roles in bone regeneration and bone defect repair. However, the reconstruction of blood vessels and neural networks is often neglected in material design. This study aims to design a genetically functionalized matrix (GFM) and enable it to regulate angiogenesis and neurogenesis to accelerate the process of bone defect repair. The dual small interfering RNA (siRNA)-polyvinylimide (PEI) (siRP) complexes that locally knocked down soluble vascular endothelial growth factor receptor 1 (sFlt-1) and p75 neurotrophic factor receptor (p75NTR ) are prepared. The hybrid cell membrane (MM) loaded siRP is synthesized as siRNA@MMs to coat on polylactone (PCL) electrospun fibers for mimicking the natural bone matrix. The results indicates that siRNA@MMs could regulate the expression of vascular-related and neuro-related cytokines secreted by mesenchymal stem cells (MSCs). GFMs promote the expression of osteogenic differentiation through paracrine function in vitro. GFMs attenuates inflammation and promotes osseointegration by regulating the coupling of vascularization and innervation in vivo. This study uses the natural hybrid cell membrane to carry genetic material and assist in the vascularization and innervation function of two siRNA. The results present the significance of neuro-vascularized organoid bone and may provide a promising choice for the design of bone tissue engineering scaffold.

In situ production of pre-vascularized synthetic bone grafts for regenerating critical-sized defects in rabbits

Reconstructing large bone defects caused by severe trauma or resection of tumors remains a challenge for surgeons. A fibula free flap and its vascularized bed can be transplanted to the reconstruction site to achieve healing. However, this technique adds morbidity, and requires microsurgery and sculpting of the bone tissue to adapt the graft to both the vasculature and the anatomy of the defect. The aim of the current study was to evaluate an alternative approach consisting of the in situ production of a pre-vascularized synthetic bone graft and its subsequent transplantation to a critical-sized bone defect. 3D printed chambers containing biphasic calcium phosphate (BCP) granules, perfused by a local vascular pedicle, with or without the addition of stromal vascular fraction (SVF), were subcutaneously implanted into New Zealand White female rabbits. SVF was prepared extemporaneously from autologous adipose tissue, the vascular pedicle was isolated from the inguinal site, while BCP granules alone served as a control group. After 8 weeks, the constructs containing a vascular pedicle exhibited abundant neovascularization with blood vessels sprouting from the pedicle, leading to significantly increased vascularization compared to BCP controls. Pre-vascularized synthetic bone grafts were then transplanted into 15 mm critical-sized segmental ulnar defects for a further 8 weeks. Micro-CT and decalcified histology revealed that pre-vascularization of synthetic bone grafts led to enhanced bone regeneration. This pre-clinical study demonstrates the feasibility and efficacy of the in situ production of pre-vascularized synthetic bone grafts for regenerating large bone defects, thereby addressing an important clinical need. STATEMENT OF SIGNIFICANCE: The current gold standard in large bone defect regeneration is vascularized fibula grafting. An alternative approach consisting of in situ production of a pre-vascularized synthetic bone graft and its subsequent transplantation to a bone defect is presented here. 3D printed chambers were filled with biphasic calcium phosphate granules, supplemented with autologous stromal vascular fraction and an axial vascular pedicle and subcutaneously implanted in inguinal sites. These pre-vascularized synthetic grafts were then transplanted into critical-sized segmental ulnar defects. Micro-CT and decalcified histology revealed that the pre-vascularized synthetic bone grafts led to higher bone regeneration than non-vascularized constructs. An alternative to vascularized fibula grafting is provided and may address an important clinical need for large bone defect reconstruction.

Engineering vascularized and innervated bone biomaterials for improved skeletal tissue regeneration

Blood vessels and nerve fibers are distributed throughout the entirety of skeletal tissue, and play important roles during bone development and fracture healing by supplying oxygen, nutrients, and cells. However, despite the successful development of bone mimetic materials that can replace damaged bone from a structural point of view, most of the available bone biomaterials often do not induce sufficient formation of blood vessels and nerves. In part, this is due to the difficulty of integrating and regulating multiple tissue types within artificial materials, which causes a gap between native skeletal tissue. Therefore, understanding the anatomy and underlying interaction mechanisms of blood vessels and nerve fibers in skeletal tissue is important to develop biomaterials that can recapitulate its complex microenvironment. In this perspective, we highlight the structure and osteogenic functions of the vascular and nervous system in bone, in a coupled manner. In addition, we discuss important design criteria for engineering vascularized, innervated, and neurovascularized bone implant materials, as well as recent advances in the development of such biomaterials. We expect that bone implant materials with neurovascularized networks can more accurately mimic native skeletal tissue and improve the regeneration of bone tissue.

Collagen-Elastin and Collagen-Glycosaminoglycan Scaffolds Promote Distinct Patterns of Matrix Maturation and Axial Vascularization in Arteriovenous Loop-Based Soft Tissue Flaps

INTRODUCTION

Autologous free flaps are the criterion standard for reconstructions of complex soft tissue defects; however, they are limited by donor-site morbidities. The arteriovenous (AV) loop model enables the generation of soft tissue constructs based on acellular dermal matrices with a functional microvasculature and minimal donor site morbidity. The ideal scaffold for AV loop-based tissue engineering has not been determined.

METHODS

AV loops were placed into subcutaneous isolation chambers filled with either a collagen-elastin scaffold or a collagen-glycosaminoglycan scaffold in the thighs of rats. Matrix elasticity, neoangiogenesis, cell migration, and proliferation were compared after 14 and 28 days.

RESULTS

Mean vessel count and area had increased in both matrices at 28 compared with 14 days. Collagen-elastin matrices showed a higher mean vessel count and area compared with collagen-glycosaminoglycan matrices at 14 days. At 28 days, a more homogeneous vascular network and higher cell counts were observed in collagen-elastin matrices. Collagen-glycosaminoglycan matrices, however, exhibited less volume loss at day 28.

CONCLUSIONS

Collagen-based scaffolds are suitable for soft tissue engineering in conjunction with the AV loop technique. These scaffolds exhibit distinct patterns of angiogenesis, cell migration, and proliferation and may in the future serve as the basis of tissue-engineered free flaps as an individualized treatment concept for critical wounds.

Haemodynamically stimulated and in vivo generated axially vascularized soft-tissue free flaps for closure of complex defects: Evaluation in a small animal model

The arteriovenous (AV) loop model permits the creation of significant volumes of axially vascularized tissue that represents an alternative to conventional free flaps, circumventing their common limitations. However, such AV loop-based flaps have never before been examined in standardized animal models with respect to their suitability for reconstruction of critical bone-exposing defects. In the course of our preliminary studies, we implemented a novel defect model in rats that provides standardized and critical wound conditions and evaluated whether AV loop-generated flaps are suitable for free microsurgical transfer and closure of composite defects. We compared three groups of rodents with similar scapular defects: one received the AV flap, whereas controls were left to heal by secondary intention or with supplementary acellular matrix alone. To create the flaps, AV loops were placed into subcutaneous Teflon chambers filled with acellular matrix and transferred to the thigh region. Flap maturation was evaluated by histological analysis of angiogenesis and cell migration at days 14 and 28 after loop creation. Flap transfer to the scapular region and microsurgical anastomoses were performed after 14 days. Postoperative defect closure and perfusion were continually compared between groups. Within the AV flap chamber, the mean vessel number, cell count and the proportion of proliferating cells increased significantly over time. The novel defect model revealed that stable wound coverage with homogeneous vascular integration was achieved by AV loop-vascularized soft-tissue free flaps compared with controls. In summary, our study indicates for the first time that complex composite defects in rats can successfully be treated with AV loop-based free flaps.

The differentiation potential of gingival mesenchymal stem cells induced by apical tooth germ cell‑conditioned medium

Gingival-derived mesenchymal stem cells (GMSCs) have recently been harvested; however, the use of GMSCs in periodontal tissue engineering requires further study. The present study established an indirect co‑culture system between rat apical tooth germ‑conditioned medium (APTG‑CM) and GMSCs, in order to determine the effects on periodontal tissue differentiation in vitro and in vivo. Using the limiting dilution technique, single‑colony derived human GMSCs and periodontal ligament stem cells (PDLSCs) were isolated and expanded to obtain homogeneous populations. PDLSCs were used as a positive control group. Cell cycle distribution, alkaline phosphatase (ALP) activity, mineralization behavior, expression of genes associated with a cementoblast phenotype (osteocalcin, bone sialoprotein, ALP, type I collagen, cementum‑derived protein 23), and in vivo differentiation capacities of GMSCs/PDLSCs co‑cultured with APTG‑CM were evaluated. Flow cytometry indicated that GMSCs and PDLSCs were positive for STRO‑1 and CD105, whereas CD45 expression was negative. The cell types were capable of forming colonies, and of osteogenic and adipogenic differentiation in response to appropriate stimuli. The induced GMSCs and PDLSCs exhibited numerous characteristics associated with cementoblast lineages, as indicated by increased proliferation and ALP activity, and upregulated expression of cementum‑associated genes in vitro. In vivo, cementum/periodontal ligament‑like structures were shown to form along the dentin surface and ceramic bovine bone in GMSCs and PDLSCs induced by APTG‑CM group. Conversely, vertical fibers could not insert in the control group, which was not co‑cultured with APTG‑CM. In conclusion, GMSCs are likely to have a role in periodontal tissue regeneration. In addition, APTG‑CM was able to provide a cementogenic microenvironment and promote differentiation of GMSCs along the cementoblastic lineage.

AAV vector encoding human VEGF165-transduced pectineus muscular flaps increase the formation of new tissue through induction of angiogenesis in an in vivo chamber for tissue engineering: A technique to enhance tissue and vessels in microsurgically engineered tissue

In regenerative medicine, new approaches are required for the creation of tissue substitutes, and the interplay between different research areas, such as tissue engineering, microsurgery and gene therapy, is mandatory. In this article, we report a modification of a published model of tissue engineering, based on an arterio-venous loop enveloped in a cross-linked collagen–glycosaminoglycan template, which acts as an isolated chamber for angiogenesis and new tissue formation. In order to foster tissue formation within the chamber, which entails on the development of new vessels, we wondered whether we might combine tissue engineering with a gene therapy approach. Based on the well-described tropism of adeno-associated viral vectors for post-mitotic tissues, a muscular flap was harvested from the pectineus muscle, inserted into the chamber and transduced by either AAV vector encoding human VEGF₁₆₅ or AAV vector expressing the reporter gene β-galactosidase, as a control. Histological analysis of the specimens showed that muscle transduction by AAV vector encoding human VEGF₁₆₅ resulted in enhanced tissue formation, with a significant increase in the number of arterioles within the chamber in comparison with the previously published model. Pectineus muscular flap, transduced by adeno-associated viral vectors, acted as a source of the proangiogenic factor vascular endothelial growth factor, thus inducing a consistent enhancement of vessel growth into the newly formed tissue within the chamber. In conclusion, our present findings combine three different research fields such as microsurgery, tissue engineering and gene therapy, suggesting and showing the feasibility of a mixed approach for regenerative medicine.

Axially vascularised mandibular constructs: Is it time for a clinical trial?

Applying regenerative therapies in the field of cranio-maxillofacial reconstruction has now become a daily practice. However, regeneration of challenging or irradiated bone defects following head and neck cancer is still far beyond clinical application. As the key factor for sound regeneration is the development of an adequate vascular supply for the construct, the current modalities using extrinsic vascularization are incapable of regenerating such complex defects. Our group has recently introduced the intrinsic axial vascularization technique to regenerate mandibular defects using the arteriovenous loop (AVL). The technique has shown promising results in terms of efficient vascularization and bone regeneration at the preclinical level. In this article, we have conducted a narrative literature review about using the AVL to vascularize tissue-engineering constructs at the preclinical level. We have also conducted a systematic literature review about applying the technique of axial vascularization in the field of craniofacial regeneration. The versatility of the technique and the possible challenges are discussed, and a suggested protocol for the first clinical trial applying the AVL technique for mandibular reconstruction is also presented.

Automatic quantification of angiogenesis in 2D sections: a precise and timesaving approach

INTRODUCTION

The standardized characterization of angiogenesis is crucial in the field of tissue engineering as sufficient blood supply is the limiting factor of mass transfer. However, reliable algorithms that provide a straight forward and observer-independent assessment of new vessel formation are still lacking. We propose an automatic observer-independent quantitative method (including downloadable source code) to analyze vascularization using two-dimensional microscopic images of histological cross-sections and advanced postprocessing, based on a 'positive- and negative-experts' model and a (corrected) nearest neighbour classification, in a vascularized tissue engineering model.

MATERIALS AND METHODS

An established angioinductive rat arteriovenous loop model was used to compare the new automatic analysis with a common 2D method and a μCT algorithm. Angiogenesis was observed at three different time points (5, 10 and 15 days).

RESULTS

In line with previous results, formation of functional new vessels that arose from the venous graft was evident within the three-dimensional construct and a significant (p < 0.05) increase in vessel count and area was observed over time. The proposed automatic analysis obtained precise values for vessel count and vessel area that were similar to the manually gained data. The algorithm further provided vectorized parameterization of the newly formed vessels for advanced statistical analysis. Compared to the μCT-based three-dimensional analyses, the presented two-dimensional algorithm was superior in terms of small vessel detection as well as cost and time efficiency.

CONCLUSIONS

The quantitative evaluation method, using microscopic images of stained histological sections, 'positive- and negative-experts'-based vessel segmentation, and nearest neighbour classification, provides a user-independent and precise but also time- and cost-effective tool for the analysis of vascularized constructs. Our algorithm, which is freely available to the public, outperforms previous approaches especially in terms of unambiguous vessel classification and statistical analyses.

A method for constructing vascularized muscle flap

Abdominal wall reconstruction following extensive tissue loss is essential and can be achieved using autologous flaps. However, their use is limited due to their inadequate availability and due to post-operative donor site scarification. This work presents a step-by-step technique for fabrication of a vascularized muscle flap, to be applied in full-thickness abdominal wall defect reconstruction. Poly L-lactic acid/poly lactic-co-glycolic acid scaffolds, prepared using a salt leaching technique, were used as the supporting matrix in vitro for simultaneously seeded endothelial cells, fibroblasts and myoblasts. The cell-embedded graft was then implanted around femoral artery and vein vessels, which provided a central blood supply. Vascularization and perfusion were achieved by capillary sprouting from the main host vessel into the graft. A thick and vascularized tissue was formed within one week, and was then transferred as an autologous flap together with its main vessels, to a full-thickness abdominal wall defect. The flap remained viable after transfer and featured sufficient mechanical strength to support the abdominal viscera. Thus, this engineered muscle flap can be used as an alternative source for autologous flaps to reconstruct full-thickness abdominal wall defects.

PHDs inhibitor DMOG promotes the vascularization process in the AV loop by HIF-1a up-regulation and the preliminary discussion on its kinetics in rat

BACKGROUND

The Arterovenous Loop (AV Loop) model is a vascularization model in tissue engineering research, which is capable of generating a three dimensional in vivo unit with cells as well as the supporting vessels within an isolation chmaber. In our previous studies the AV loop in the isolation chamber was discovered to undergo hypoxia, characterized by Hypoxia Inducible Factor (HIF) up-regulation. The vascularization followed the increase of HIF-α temporally, while it was spatially positively correlated with the HIF-α level, as well. This study aims to prove that HIF-1a up-regulation is the stimulus for vascularization in the AV loop model.

METHOD

The AV loop model in rats was created by interposing a femoral vein graft into the distal ends of the contralateral femoral artery and vein, and the loop was embeded in fibrin matrix and fixed in isolation chamber. PHD (prolyl hydroxylases) inhibitor DMOG (Dimethyloxallyl Glycine) was applied systemically in the rats in 40 mg/KG at day 0 and day 3 (DMOG-1), or in 15 mg/KG at day 8, day10 and day12 (DMOG-2). Two weeks later the specimens were explanted and underwent morphological and molecular evaluations.

RESULTS

Compared to the control group, in the DMOG-2 group the HIF-1α positive rate was siginicantly raised as shown in immunohistochemistry staining, accompanied with a smaller cross section area and greater vessel density, and a HIF-1α accumulation in the kidney. The mRNA of HIF-1α and its angiogenic target gene all increased in different extends. Ki67 IHC demostrate more positive cells. There were no significant change in the DMOG-1 group.

CONCLUSION

By applying DMOG systemically, HIF-1α was up-regulated at the protein level and at the mRNA level, acompanied with angiogenic target gene up-regulateion, and the vascularization was promoted correspondingly. DMOG given at lower dosage constantly after one week tends to have better effect than the group given at larger dosage in the early stage in this model, and promotes cell proliferation, as evidenced by Ki67 IHC. Thus, this study proves that HIF-1a up-regulation is the stimulus for vascularization in the AV loop model and that the process of the vessel outgrowth can be controlled in the AV Loop model utilizing this mechanism.

Different effects of implanting sensory nerve or blood vessel on the vascularization, neurotization, and osteogenesis of tissue-engineered bone in vivo

To compare the different effects of implanting sensory nerve tracts or blood vessel on the osteogenesis, vascularization, and neurotization of the tissue-engineered bone in vivo, we constructed the tissue engineered bone and implanted the sensory nerve tracts (group SN), blood vessel (group VB), or nothing (group Blank) to the side channel of the bone graft to repair the femur defect in the rabbit. Better osteogenesis was observed in groups SN and VB than in group Blank, and no significant difference was found between groups SN and VB at 4, 8, and 12 weeks postoperatively. The neuropeptides expression and the number of new blood vessels in the bone tissues were increased at 8 weeks and then decreased at 12 weeks in all groups and were highest in group VB and lowest in group Blank at all three time points. We conclude that implanting either blood vessel or sensory nerve tract into the tissue-engineered bone can significantly enhance both the vascularization and neurotization simultaneously to get a better osteogenesis effect than TEB alone, and the method of implanting blood vessel has a little better effect of vascularization and neurotization but almost the same osteogenesis effect as implanting sensory nerve.

Microsurgical techniques used to construct the vascularized and neurotized tissue engineered bone

The lack of vascularization in the tissue engineered bone results in poor survival and ossification. Tissue engineered bone can be wrapped in the soft tissue flaps which are rich in blood supply to complete the vascularization in vivo by microsurgical technique, and the surface of the bone graft can be invaded with new vascular network. The intrinsic vascularization can be induced via a blood vessel or an arteriovenous loop located centrally in the bone graft by microsurgical technique. The peripheral nerve especially peptidergic nerve has effect on the bone regeneration. The peptidergic nerve can be used to construct the neurotized tissue engineered bone by implanting the nerve fiber into the center of bone graft. Thus, constructing a highly vascularized and neurotized tissue engineered bone according with the theory of biomimetics has become a useful method for repairing the large bone defect. Many researchers have used the microsurgical techniques to enhance the vascularization and neurotization of tissue engineered bone and to get a better osteogenesis effect. This review aims to summarize the microsurgical techniques mostly used to construct the vascularized and neurotized tissue engineered bone.

An engineered muscle flap for reconstruction of large soft tissue defects

Large soft tissue defects involve significant tissue loss, requiring surgical reconstruction. Autologous flaps are occasionally scant, demand prolonged transfer surgery, and induce donor site morbidity. The present work set out to fabricate an engineered muscle flap bearing its own functional vascular pedicle for repair of a large soft tissue defect in mice. Full-thickness abdominal wall defect was reconstructed using this engineered vascular muscle flap. A 3D engineered tissue constructed of a porous, biodegradable polymer scaffold embedded with endothelial cells, fibroblasts, and/or myoblasts was cultured in vitro and then implanted around the femoral artery and veins before being transferred, as an axial flap, with its vascular pedicle to reconstruct a full-thickness abdominal wall defect in the same mouse. Within 1 wk of implantation, scaffolds showed extensive functional vascular density and perfusion and anastomosis with host vessels. At 1 wk posttransfer, the engineered muscle flaps were highly vascularized, were well-integrated within the surrounding tissue, and featured sufficient mechanical strength to support the abdominal viscera. Thus, the described engineered muscle flap, equipped with an autologous vascular pedicle, constitutes an effective tool for reconstruction of large defects, thereby circumventing the need for both harvesting autologous flaps and postoperative scarification.

Tissue engineering and regenerative medicine -where do we stand?

Tissue Engineering (TE) in the context of Regenerative Medicine (RM) has been hailed for many years as one of the most important topics in medicine in the twenty-first century. While the first clinically relevant TE efforts were mainly concerned with the generation of bioengineered skin substitutes, subsequently TE applications have been continuously extended to a wide variety of tissues and organs. The advent of either embryonic or mesenchymal adult stem-cell technology has fostered many of the efforts to combine this promising tool with TE approaches and has merged the field into the term Regenerative Medicine. As a typical example in translational medicine, the discovery of a new type of cells called Telocytes that have been described in many organs and have been detected by electron microscopy opens another gate to RM. Besides cell-therapy strategies, the application of gene therapy combined with TE has been investigated to generate tissues and organs. The vascularization of constructs plays a crucial role besides the matrix and cell substitutes. Therefore, novel in vivo models of vascularization have evolved allowing axial vascularization with subsequent transplantation of constructs. This article is intended to give an overview over some of the most recent developments and possible applications in RM through the perspective of TE achievements and cellular research. The synthesis of TE with innovative methods of molecular biology and stem-cell technology appears to be very promising.

Axially vascularized bone substitutes: a systematic review of literature and presentation of a novel model

INTRODUCTION

The creation of axially vascularized bone substitutes (AVBS) has been successfully demonstrated in several animal models. One prototypical indication is bone replacement in patients with previously irradiated defect sites, such as in the mandibular region. The downside of current clinical practice, when free fibular or scapular grafts are used, is the creation of significant donor site morbidity.

METHODS

Based on our previous experiments, we extended the creation of an arterio-venous loop to generate vascularized bone substitutes to a new defect model in the goat mandibula. In this report, we review the literature regarding different models for axially vascularized bone substitutes and present a novel model demonstrating the feasibility of combining this model with synthetic porous scaffold materials and biological tissue adhesives to grow cells and tissue.

RESULTS

We were able to show the principal possibility to generate axially vascularized bony substitutes in vivo in goat mandibular defects harnessing the regenerative capacity of the living organism and completely avoiding donor site morbidity.

CONCLUSION

From our findings, we conclude that this novel model may well offer new perspectives for orthopedic and traumatic bone defects that might benefit from the reduction of donor site morbidity.

A new approach of in vivo musculoskeletal tissue engineering using the epigastric artery as central core vessel of a 3-dimensional construct

The creation of musculoskeletal tissue represents an alternative for the replacement of soft tissue in reconstructive surgery. However, most of the approaches of creating artificial tissue have their limitations in the size as the maximally obtainable dimension of bioartificial tissue (BAT) is limited due to the lack of supporting vessels within the 3-dimensional construct. The seeded myoblasts require high amounts of perfusion, oxygen, and nutrients to survive. To achieve this, we developed a 3-dimensional scaffold which features the epigastric artery as macroscopic core vessel inside the BAT in a rat model (perfused group, n = 4) and a control group (n = 3) without the epigastric vessels and, therefore, without perfusion. The in vivo monitoring of the transplanted myoblasts was assessed by bioluminescence imaging and showed both the viability of the epigastric artery within the 3-dimensional construct and again that cell survival in vivo is highly depending on the blood supply with the beginning of capillarization within the BAT seven days after transplantation in the perfused group. However, further studies focussing on the matrix improvement will be necessary to create a transplantable BAT with the epigastric artery as anastomosable vessel.

Prefabrication of axial vascularized tissue engineering coral bone by an arteriovenous loop: a better model

The most important problem for the survival of thick 3-dimensional tissues is the lack of vascularization in the context of bone tissue engineering. In this study, a modified arteriovenous loop (AVL) was developed to prefabricate an axial vascularized tissue engineering coral bone in rabbit, with comparison of the arteriovenous bundle (AVB) model. An arteriovenous fistula between rabbit femoral artery and vein was anastomosed to form an AVL. It was placed in a circular side groove of the coral block. The complex was wrapped with an expanded-polytetrafluoroethylene membrane and implanted beneath inguinal skin. After 2, 4, 6 and 8 weeks, the degree of vascularization was evaluated by India ink perfusion, histological examination, vascular casts, and scanning electron microscopy images of vascular endangium. Newly formed fibrous tissues and vasculature extended over the surfaces and invaded the interspaces of entire coral block. The new blood vessels robustly sprouted from the AVL. Those invaginated cavities in the vascular endangium from scanning electron microscopy indicated vessel's sprouted pores. Above indexes in AVL model are all superior to that in AVB model, indicating that the modified AVL model could more effectively develop vascularization in larger tissue engineering bone.

A novel mixed-type stem cell pellet for cementum/periodontal ligament-like complex

BACKGROUND

Functional tissue regeneration underscores the construction of favorable extracellular matrix environment and neovascularization. In this study, we propose a mixed-type stem cell-pellet cultivation system for human periodontal ligament stem cells (hPDLSCs) to recreate a favorable regeneration microenvironment.

METHODS

The hPDLSCs were cocultured with human bone marrow mesenchymal stem cells (hBMMSCs) and mixed by osteoinduced ceramic bovine bone (CBB) powder as a mixed-type stem cell sheet. The influence of osteoinduced CBB on hPDLSCs was analyzed by alkaline phosphatase (ALP) and osteogenic differentiation assays. The effects of hBMMSCs on hPDLSCs were estimated by proliferating cell nuclear antigen, ALP, real-time reverse transcription polymerase chain reaction, and Western blot assays. The mixed-cell sheet was the preliminary observations in vitro that laid the foundation for additional implantation. After the cells were detached, the mixed-type sheet spontaneously contracted to produce a mixed-type stem cell pellet, which was transplanted into immunocompromised mice.

RESULTS

In vitro, the results showed that osteoinduced CBB could upregulate ALP activity and accelerate mineralization of hPDLSCs. When the hPDLSCs were cocultured with hBMMSCs, the ALP activity and proliferation kinetics were upregulated and also indicated in the expression of collagen I, osteocalcin, and vascular endothelial growth factor. It was found that, in vivo, the mixed-type hPDLSC pellets support cementum/periodontal ligament (PDL)-like tissue regeneration with neovascularization.

CONCLUSIONS

These results suggest that the mixed-type hPDLSC pellet could mimic the microenvironment of PDL and enhance the reconstruction of physiologic architecture of a dental cementum/PDL-like complex. This tissue mimicking may also be a promising alternative to promote periodontal defect repair for additional clinical applications.

[Upper and lower eyelid blepharoplasty : development of aesthetic periocular plastic surgery]

The article describes the indications and techniques for blepharoplasty of the upper and lower eyelids as well as combinations with other eyelid correction techniques. Upper eyelid blepharoplasty may include skin excision with orbital fat modulation as well as ptosis correction and definition of the superior sulcus palpebralis. The main goal of lower lid blepharoplasty is modulation of intraseptal fat and also often the treatment of a lower lid laxity by canthopexy. It is recommended to avoid excessive skin resection in the lower lid. Furthermore techniques to address an ectropium are reviewed and possible complications of blepharoplasty are presented.

Improved vascular organization enhances functional integration of engineered skeletal muscle grafts

Severe traumatic events such as burns, and cancer therapy, often involve a significant loss of tissue, requiring surgical reconstruction by means of autologous muscle flaps. The scant availability of quality vascularized flaps and donor site morbidity often limit their use. Engineered vascularized grafts provide an alternative for this need. This work describes a first-time analysis, of the degree of in vitro vascularization and tissue organization, required to enhance the pace and efficacy of vascularized muscle graft integration in vivo. While one-day in vitro was sufficient for graft integration, a three-week culturing period, yielding semiorganized vessel structures and muscle fibers, significantly improved grafting efficacy. Implanted vessel networks were gradually replaced by host vessels, coupled with enhanced perfusion and capillary density. Upregulation of key graft angiogenic factors suggest its active role in promoting the angiogenic response. Transition from satellite cells to mature fibers was indicated by increased gene expression, increased capillary to fiber ratio, and similar morphology to normal muscle. We suggest a "relay" approach in which extended in vitro incubation, enabling the formation of a more structured vascular bed, allows for graft-host angiogenic collaboration that promotes anastomosis and vascular integration. The enhanced angiogenic response supports enhanced muscle regeneration, maturation, and integration.

Mandibular reconstruction using an axially vascularized tissue-engineered construct

Background

Current reconstructive techniques for continuity defects of the mandible include the use of free flaps, bone grafts, and alloplastic materials. New methods of regenerative medicine designed to restore tissues depend mainly on the so-called extrinsic neovascularization, where the neovascular bed originates from the periphery of the construct. This method is not applicable for large defects in irradiated fields.

Methods

We are introducing a new animal model for mandibular reconstruction using intrinsic axial vascularization by the Arterio-Venous (AV) loop. In order to test this model, we made cadaveric, mechanical loading, and surgical pilot studies on adult male goats. The cadaveric study aimed at defining the best vascular axis to be used in creating the AV loop in the mandibular region. Mechanical loading studies (3 points bending test) were done to ensure that the mechanical properties of the mandible were significantly affected by the designed defect, and to put a base line for further mechanical testing after bone regeneration. A pilot surgical study was done to ensure smooth operative and post operative procedures.

Results

The best vascular axis to reconstruct defects in the posterior half of the mandible is the facial artery (average length 32.5 ± 1.9 mm, caliber 2.5 mm), and facial vein (average length 33.3 ± 1.8 mm, caliber 2.6 mm). Defects in the anterior half require an additional venous graft. The defect was shown to be significantly affecting the mechanical properties of the mandible (P value 0.0204). The animal was able to feed on soft diet from the 3^rd postoperative day and returned to normal diet within a week. The mandible did not break during the period of follow up (2 months).

Conclusions

Our model introduces the concept of axial vascularization of mandibular constructs. This model can be used to assess bone regeneration for large bony defects in irradiated fields. This is the first study to introduce the concept of axial vascularization using the AV loop for angiogenesis in the mandibular region. Moreover, this is the first study aiming at axial vascularization of synthetic tissue engineering constructs at the site of the defect without any need for tissue transfer (in contrast to what was done previously in prefabricated flaps).

Regenerative medicine: then and now--an update of recent history into future possibilities

The fields of tissue engineering (TE) and regenerative medicine (RegMed) are yet to bring about the anticipated therapeutic revolution. After two decades of extremely high expectations and often disappointing returns both in the medical as well as in the financial arena, this scientific field reflects the sense of a new era and suggests the feeling of making a fresh start although many scientists are probably seeking reorientation. Much of research was industry driven, so that especially in the aftermath of the recent financial meltdown in the last 2 years we have witnessed a biotech asset yard sale. Despite any monetary shortcomings, from a technological point of view there have been great leaps that are yet to find their way to the patient. RegMed is definitely bound to play a major role in our life because it embodies one of the primordial dreams of mankind, such as: everlasting youth, flying, remote communication and setting foot on the moon. The Journal of Cellular and Molecular Medicine has been at the frontier of these developments in TE and RegMed from its beginning and reflects recent scientific advances in both fields. Therefore this review tries to look at RegMed through the keyhole of history which might just be like looking ‘back to the future’.

In vitro models for the evaluation of angiogenic potential in bone engineering

Blood vessels have a fundamental role both in skeletal homeostasis and in bone repair. Angiogenesis is also important for a successful bone engineering. Therefore, scaffolds should be tested for their ability to favour endothelial cell adhesion, proliferation and functions. The type of endothelial cell to use for in vitro assays should be carefully considered, because the properties of these cells may depend on their source. Morphological and functional relationships between endothelial cells and osteoblasts are evaluated with co-cultures, but this model should still be standardized, particularly for distinguishing the two cell types. Platelet-rich plasma and recombinant growth factors may be useful for stimulating angiogenesis.

Smooth and textured silicone surfaces of modified gel mammary prostheses cause a different impact on fibroproliferative properties of dermal fibroblasts

Our study addressed the question of whether surface properties of modern standard gel prostheses may have a measurable impact on the fibrogenic properties of cultured human dermal fibroblasts. Fibroblasts were isolated from breast implants by using the explant culture technique and incubated either on smooth or on textured silicone elastomere surfaces. Fibroblast growth was observed 4 weeks following incubation. Expression of transforming growth factor (TGF)-β1 was measured after cell culture. Incubated fibroblasts on textured surfaces showed a fivefold lower growth rate during all experiments. TGF-β1 expression was lowered in smooth surface fibroblasts compared with textured surface cultures. Our results show that smooth and textured silicone surfaces of modified gel breast implants have a different impact on the fibroproliferative properties of dermal fibroblasts. These preliminary results seem promising and we aim to further perform qualitative and quantitative analyses of the inflammatory processes in the environment of the implant and their link to the TGF-β pathway.

Cartilage cell proliferation in degenerative TFCC wrist lesions

INTRODUCTION

The central zone of the triangular fibrocartilage complex (TFCC) of the wrist is thought to be avascular and is generally considered to lack any healing potential.

AIM

The purpose of this study was to investigate, if cartilage cells of degenerative disc lesions possess any healing or proliferation potential and whether ulna length plays a significant role in the proliferation process.

RESULTS

Cells positive for proliferating cell nuclear antigen (PCNA) were found in all specimens. Specimens of patients with ulna positive variance showed a decreased number of PCNA positive cells than specimens of patients with either negative or neutral ulna variance.

CONCLUSION

We found that cartilage cells of Palmer type 2C lesions undergo mitotic cell division, thus exhibiting proliferation capability. It could not be shown that ulnar length is significantly correlated with the number of PCNA positive cells.

Directionally Solidified Biopolymer Scaffolds: Mechanical Properties and Endothelial Cell Responses

Vascularization is a primary challenge in tissue engineering. To achieve it in a tissue scaffold, an environment with the appropriate structural, mechanical, and biochemical cues must be provided enabling endothelial cells to direct blood vessel growth. While biochemical stimuli such as growth factors can be added through the scaffold material, the culture medium, or both, a well-designed tissue engineering scaffold is required to provide the necessary local structural and mechanical cues. As chitosan is a well-known carrier for biochemical stimuli, the focus of this study was on structure-property correlations, to evaluate the effects of composition and processing conditions on the three-dimensional architecture and properties of freeze-cast scaffolds; to establish whether freeze-cast scaffolds are promising candidates as constructs promoting vascularization; and to conduct initial tissue culture studies with endothelial cells on flat substrates of identical compositions as those of the scaffolds to test whether these are biocompatible and promote cell attachment and proliferation.

[The development of plastic surgery: retrospective view of 80 years of "Der Chirurg" (The Surgeon)]

The often groundbreaking developments of new methods in Plastic Surgery have been published in the journal "Der Chirurg" (The Surgeon) ever since its foundation in 1928, when it was established as a journal dealing with all aspects of surgery and containing many innovations and developments. Historically this is also reflected in the establishment of Plastic Surgery initially as a subspecialty and later on as a specialty within the German Society for Surgery. The interdisciplinary character of modern reconstructive and oncological concepts, not only with other specialties but also within various surgical specialties, raises further challenges and leads to new developments in reconstruction, which will definitely induce an increasing amount of knowledge to the advantage of our patients. Scientific and clinical advances over the last 80 years give rise to the hope that similar success will be attained for reconstruction of traumatic and oncological defects and malformations or disfigurations in the future. Consolidated findings from regenerative medicine and tissue engineering will enrich the daily practice of surgical reconstruction.

Vascularization in bone tissue engineering: physiology, current strategies, major hurdles and future challenges

The lack of a functional vascular supply has, to a large extent, hampered the whole range of clinical applications of 'successful' laboratory-based bone tissue engineering strategies. To the present, grafts have been dependent on post-implant vascularization, which jeopardizes graft integration and often leads to its failure. For this reason, the development of strategies that could effectively induce the establishment of a microcirculation in the engineered constructs has become a major goal for the tissue engineering research community. This review addresses the role and importance of the development of a vascular network in bone tissue engineering and provides an overview of the most up to date research efforts to develop such a network.

Reconstruction of a child's forefoot defect using a distally based pedicled medial plantar flap

This report describes a case of a 10-year-old boy who received a distally based, pedicled medial plantar artery flap to cover a defect on the distal lateral side of his right foot. The defect resulted from amniotic constriction. The flap served as defect coverage and was kept viable solely by the distal medial plantar vessels. Use of this particular kind of flap proves advantageous in that it provides good protection in the weight-bearing area of the foot, while causing only a minor donor site defect.

Foetal hepatocyte transplantation in a vascularized AV-Loop transplantation model in the rat

The use of foetal liver cells (FLC) in the context of hepatic tissue engineering might permit efficient in vitro expansion and cryopreservation in a cell bank. A prerequisite for successful application of bioartificial liver tissue is sufficient initial vascularization. In this study, we evaluated the transplantation of fibrin gel-immobilized FLC in a vascularized arterio-veno-venous (AV)-loop model. FLC were isolated from embryonic/foetal (ED 16) rat livers and were enriched by using magnetic cell sorting (MACS). After cryopreservation, FLC were labelled by pkh-26. Cells were transplanted in a fibrin matrix into a subcutaneous chamber containing a microsurgically created AV-loop in the femoral region of the recipient rat. The chambers were explanted after 14 days. Subcutaneous implants without an AV-loop and cell-free implants served as controls. Fluorescence microscopy of the constructs was used to identify pkh-26(+)- donor cells. Characterization was performed by RT-PCR and immunhistology (IH) for CK-18 and CD31. Transplantation of FLC using the AV-loop permitted a neo-tissue formation in the fibrin matrix. A high-density vascularization was observed in the AV-loop constructs as shown by CD31 IH. Viable foetal donor cells were detected which expressed CK-18. FLC can be successfully used for heterotopic transplantation. Fibrin matrix permits rapid blood vessel ingrowth from the AV-loop and supports engraftment of FLC. It is therefore an appropriate environment for hepatocyte transplantation in combination with microsurgical vascularization strategies. Transplantation of fibrin gel-immobilized FLC may be a promising approach for the development of highly vascularized in vivo tissue-engineering-based liver support systems.

Dose-finding study of fibrin gel-immobilized vascular endothelial growth factor 165 and basic fibroblast growth factor in the arteriovenous loop rat model

The angiogenic effects of different concentrations of vascular endothelial growth factor (VEGF) 165 and basic fibroblast growth factor (bFGF) immobilized in a fibrin-based drug-delivery system were quantitatively assessed in the arteriovenous (AV) loop model. An AV loop was created in the medial thigh of 60 rats. The loop was placed in a Teflon isolation chamber and embedded in 500 microL of fibrin gel loaded with VEGF and bFGF in four different concentrations (no growth factor, 100 ng/mL of VEGF, 25 ng/mL of VEGF and bFGF, 100 ng/mL pf VEGF and bFGF). The explantation intervals were 1, 2, and 4 weeks after the initial operation for all groups. Specimens were investigated using (micro-CT) and histological and morphometrical techniques. After 2 weeks, the cross-section area and construct weight were significantly lower with the use of 100 ng/mL of VEGF and bFGF. Micro-CT and histology showed significantly greater vascular density and number of vessels of the constructs at 2 and 4 weeks when 100 ng/mL of VEGF165 and bFGF were applied than in the growth factor-free specimens. The angioinductive effects were dose-dependent, with best results when using 100 ng/mL of VEGF165 and bFGF. The greater tissue formation was accompanied by faster resorption of the fibrin matrix.

T17b murine embryonal endothelial progenitor cells can be induced towards both proliferation and differentiation in a fibrin matrix

Endothelial progenitor cells (EPC) may enhance blood vessel formation in a variety of clinical settings such as ischaemia and tumour angiogenesis as well as in tissue-engineered matrices. In the present study, we cultured a murine endothelial progenitor cell line, T17b, in vitro in cell culture as well as in an FDA-approved fibrin matrix and investigated cell proliferation, differentiation and secretion patterns of the angiogenic growth factor VEGF under hypoxia and differentiation. We show that T17b EPC remain viable for at least 8 days in the fibrin matrix where they proliferate and form clusters including lumen-like structures. Proliferation in fibrin clots overlayed with basal medium (BM) was confirmed morphologically and immunohistochemically by positive Ki67 staining, indicating mitotic activity. Significant cell proliferation and Ki-67 expression were absent when cells were incubated with dibutyryl-cAMP and retinoic acid (RA). Incubation with dibutyryl-cAMP and RA stimulated the expression of the EPC differentiation markers von Willebrand Factor (vWF) and VEGF receptor 2 (VEGFR-2), indicating successful differentiation in the fibrin clot. EPC differentiation induced by dibutyryl-cAMP and RA was confirmed in 2-D chamber slide cultures by positive vWF immunostaining, which was absent in BM controls. EPC chamber slides also displayed positive vWF staining when exposed to hypoxia under BM conditions, indicating EPC activation and differentiation could also be induced by hypoxia. Taken together, T17b EPC secrete increased levels of VEGF when submitted to either hypoxia or differentiation and can be differentiated into mature endothelial cells not only in cell and matrigel cultures but also in a fibrin matrix that is FDA approved for clinical application.

[Intraarticular fractures of the proximal interphalangeal joint: dynamic early functional therapy with an external fixation system]

The results of treating fracture dislocations of the proximal interphalangeal joint are often unsatisfactory for the patient because conservative methods cannot prevent stiffness of the joint. Thus, early functional treatment with external fixation systems is increasingly favoured. This therapy combines the principles of ligamentotaxis and the possibility of early movement of the injured joint. The frequently modified pins and rubbers traction system is especially effective. It is cheap, easy to apply, and well accepted by patients due to its light weight and small size. This paper gives an overview of the therapeutic options and the clinical results of treating fractures of the proximal interphalangeal joint.

Tissue engineered bone grafts: biological requirements, tissue culture and clinical relevance

The tremendous need for bone tissue in numerous clinical situations and the limited availability of suitable bone grafts are driving the development of tissue engineering approaches to bone repair. In order to engineer viable bone grafts, one needs to understand the mechanisms of native bone development and fracture healing, as these processes should ideally guide the selection of optimal conditions for tissue culture and implantation. Engineered bone grafts have been shown to have capacity for osteogenesis, osteoconduction, osteoinduction and osteointegration - functional connection between the host bone and the graft. Cells from various anatomical sources in conjunction with scaffolds and osteogenic factors have been shown to form bone tissue in vitro. The use of bioreactor systems to culture cells on scaffolds before implantation further improved the quality of the resulting bone grafts. Animal studies confirmed the capability of engineered grafts to form bone and integrate with the host tissues. However, the vascularization of bone remains one of the hurdles that need to be overcome if clinically sized, fully viable bone grafts are to be engineered and implanted. We discuss here the biological guidelines for tissue engineering of bone, the bioreactor cultivation of human mesenchymal stem cells on three-dimensional scaffolds, and the need for vascularization and functional integration of bone grafts following implantation.

Translating tissue engineering technology platforms into cancer research

Technology platforms originally developed for tissue engineering applications produce valuable models that mimic three-dimensional (3D) tissue organization and function to enhance the understanding of cell/tissue function under normal and pathological situations. These models show that when replicating physiological and pathological conditions as closely as possible investigators are allowed to probe the basic mechanisms of morphogenesis, differentiation and cancer. Significant efforts investigating angiogenetic processes and factors in tumorigenesis are currently undertaken to establish ways of targeting angiogenesis in tumours. Anti-angiogenic agents have been accepted for clinical application as attractive targeted therapeutics for the treatment of cancer. Combining the areas of tumour angiogenesis, combination therapies and drug delivery systems is therefore closely related to the understanding of the basic principles that are applied in tissue engineering models. Studies with 3D model systems have repeatedly identified complex interacting roles of matrix stiffness and composition, integrins, growth factor receptors and signalling in development and cancer. These insights suggest that plasticity, regulation and suppression of these processes can provide strategies and therapeutic targets for future cancer therapies. The historical perspective of the fields of tissue engineering and controlled release of therapeutics, including inhibitors of angiogenesis in tumours is becoming clearly evident as a major future advance in merging these fields. New delivery systems are expected to greatly enhance the ability to deliver drugs locally and in therapeutic concentrations to relevant sites in living organisms. Investigating the phenomena of angiogenesis and anti-angiogenesis in 3D in vivo models such as the Arterio-Venous (AV) loop mode in a separated and isolated chamber within a living organism adds another significant horizon to this perspective and opens new modalities for translational research in this field.

Regression and persistence: remodelling in a tissue engineered axial vascular assembly

In later stages of vasculoangiogenesis a vascular network is going through a metamorphosis for optimal perfusion and economy of energy. In this study we make a quantitative approach to phenomena of remodelling in a bioartificial neovascular network and suggest variance of calibre as a parameter of neovascular maturation. For this study, 18 male Lewis rats were subjected to the AV loop operation in combination with a hard porous biogenic matrix and an isolation chamber. The animals were allocated into three groups for different explantation intervals set to 2, 4 and 8 weeks, respectively. Collective attributes like vascular density, percent fractional area and variance of calibre were evaluated for a predefined region of interest (ROI). Late morphogenesis was evaluated by means of scanning electron microscopy. After the fourth week the absolute number of vessels within the ROI decreased (P < 0.03) whereas, on the contrary, the fractional area of all segments increased (P < 0.02). The variance in calibre was significantly increased in the 8-week group (P < 0.05). Lymphatic growth after week 4, early pericyte migration as well as intussusceptive angiogenesis were identified immunohistologically. Phenomena of remodelling were evaluated quantitatively in a neovascular network and variance could be proposed as a parameter of net vascular maturation.