Pedicled Transplantation of Axially Vascularized Bone Constructs in a Critical Size Femoral Defect

Clinical challenges in bone tissue engineering - A narrative review

Bone tissue engineering (BTE) has emerged as a promising approach to address large bone defects caused by trauma, infections, congenital malformations, and tumors. This review focuses on scaffold design, cell sources, growth factors, and vascularization strategies, highlighting their roles in developing effective treatments. We explore the complexities of balancing mechanical properties, porosity, and biocompatibility in scaffold materials, alongside optimizing mesenchymal stem cell delivery methods. The critical role of growth factors in bone regeneration and the need for controlled release systems are discussed. Vascularization remains a significant hurdle, with strategies such as angiogenic factors, co-culture systems, and bioprinting under investigation. Mechanical challenges, tissue responses, and inflammation management are examined, alongside gene therapy's potential for enhancing osteogenesis and angiogenesis via both viral and non-viral delivery methods. The review emphasizes the impact of patient-specific factors on bone healing outcomes and the importance of personalized approaches. Future directions are described, emphasizing the necessity of interdisciplinary cooperation to advance the field of BTE and convert laboratory results into clinically feasible solutions.

Multifunctional Prosthesis Surface: Modification of Titanium with Cinnamaldehyde-Loaded Hierarchical Titanium Dioxide Nanotubes

Orthopedic prostheses are the ultimate therapeutic solution for various end-stage orthopedic conditions. However, aseptic loosening and pyogenic infections remain as primary complications associated with these devices. In this study, a hierarchical titanium dioxide (TiO2) nanotube drug delivery system loaded with cinnamaldehyde for the surface modification of titanium implants, is constructed. These specially designed dual-layer TiO2 nanotubes enhance material reactivity and provide an extensive drug-loading platform within a short time. The introduction of cinnamaldehyde enhances the bone integration performance of the scaffold (simultaneously promoting bone formation and inhibiting bone resorption), anti-inflammatory capacity, and antibacterial properties. In vitro experiments have demonstrated that this system promoted osteogenesis by upregulating both Wnt/β-catenin and MAPK signaling pathways. Furthermore, it inhibits osteoclast formation, suppresses macrophage-mediated inflammatory responses, and impedes the proliferation of Staphylococcus aureus and Escherichia coli. In vivo experiments shows that this material enhances bone integration in a rat model of femoral defects. In addition, it effectively enhances the antibacterial and anti-inflammatory properties in a subcutaneous implant in a rat model. This study provides a straightforward and highly effective surface modification strategy for orthopedic Ti implants.

A novel device for treatment of osteonecrosis of femoral head: Feasibility and preliminary efficacy of animal study

Background

Interruption of blood supply will lead to necrosis of body tissues, such as osteonecrosis of femoral head (ONFH). Vascularization has always been regarded as one of the biggest challenges in tissue engineering. In the current study, a novel device was proposed to reconstruct blood supply of necrotic femoral head.

Methods

Cryo-insult with liquid nitrogen method was adopted to establish the ONFH model. In experimental group, a novel scaffold carrying vascular bundle was implanted into the necrotic femoral head after decompression and the transplanted vascular bundles were anastomosed with the existing blood vessels around the hip. In control group, a traditional porous scaffold was inserted alone without vessels. Feasibility of this strategy was verified by animal experiments. Micro-CT analysis and histological evaluation were performed to investigate its preliminary efficacy.

Results

Feasibility of this innovative treatment strategy had been successfully verified in animal experiments. In the area of necrosis repair, more bone tissue grew into the scaffold in experimental group than the control group evaluated by Micro-CT (three months: 29.66% VS 20.35%, P＜0.05; six months: 30.47% VS 25.10%, P＜0.05) and histological analysis (24.71% VS 16.45%, P＜0.05 ​at three months; 31.01% VS 20.60%, P＜0.05 ​at six months). Implanted vascular bundles had the potential to branch out many branches in the osteonecrosis repair area to facilitate blood supply reconstruction and bone repair.

Conclusions

This study proposed a novel device with clinical application prospects in the treatment of ONFH. It has the potential to provide new possibilities for rebuilding the blood supply of femoral head and repairing osteonecrosis.

Translational potential statement

The novel device proposed in this study has the potential to be applied to the treatment of early femoral head necrosis.

Free Transplantation of a Tissue Engineered Bone Graft into an Irradiated, Critical-Size Femoral Defect in Rats

Healing of large bone defects remains a challenge in reconstructive surgery, especially with impaired healing potential due to severe trauma, infection or irradiation. In vivo studies are often performed in healthy animals, which might not accurately reflect the situation in clinical cases. In the present study, we successfully combined a critical-sized femoral defect model with an ionizing radiation protocol in rats. To support bone healing, tissue-engineered constructs were transferred into the defect after ectopic preossification and prevascularization. The combination of SiHA, MSCs and BMP-2 resulted in the significant ectopic formation of bone tissue, which can easily be transferred by means of our custom-made titanium chamber. Implanted osteogenic MSCs survived in vivo for a total of 18 weeks. The use of SiHA alone did not lead to bone formation after ectopic implantation. Analysis of gene expression showed early osteoblast differentiation and a hypoxic and inflammatory environment in implanted constructs. Irradiation led to impaired bone healing, decreased vascularization and lower short-term survival of implanted cells. We conclude that our model is highly valuable for the investigation of bone healing and tissue engineering in pre-damaged tissue and that healing of bone defects can be substantially supported by combining SiHA, MSCs and BMP-2.

The simpler, the better: tissue vascularization using the body's own resources

Tissue regeneration is crucially dependent on sufficient vascularization. In regenerative medicine, this can be effectively achieved by autologous vascularization strategies using the body's own resources. These strategies include the administration of blood-derived factor preparations, adipose tissue-based vascularization, and the in situ engineering of vascularized tissue. Due to their simplicity, the translation of these strategies into clinical practice is easier in terms of feasibility, safety requirements, and regulatory hurdles compared with complex and time-consuming procedures involving intensive cell manipulation. Hence, they are close to clinical application or are already being used to successfully treat patients by distinct personalized medicine concepts.

Vascularization Strategies in Bone Tissue Engineering

Bone is a highly vascularized tissue, and its development, maturation, remodeling, and regeneration are dependent on a tight regulation of blood vessel supply. This condition also has to be taken into consideration in the context of the development of artificial tissue substitutes. In classic tissue engineering, bone-forming cells such as primary osteoblasts or mesenchymal stem cells are introduced into suitable scaffolds and implanted in order to treat critical-size bone defects. However, such tissue substitutes are initially avascular. Because of the occurrence of hypoxic conditions, especially in larger tissue substitutes, this leads to the death of the implanted cells. Therefore, it is necessary to devise vascularization strategies aiming at fast and efficient vascularization of implanted artificial tissues. In this review article, we present and discuss the current vascularization strategies in bone tissue engineering. These are based on the use of angiogenic growth factors, the co-implantation of blood vessel forming cells, the ex vivo microfabrication of blood vessels by means of bioprinting, and surgical methods for creating surgically transferable composite tissues.

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.

[Research progress of in vivo bioreactor for bone tissue engineering]

Objective

To review the research progress of in vivo bioreactor (IVB) for bone tissue engineering in order to provide reference for its future research direction.

Methods

The literature related to IVB used in bone tissue engineering in recent years was reviewed, and the principles of IVB construction, tissue types, sites, and methods of IVB construction, as well as the advantages of IVB used in bone tissue engineering were summarized.

Results

IVB takes advantage of the body's ability to regenerate itself, using the body as a bioreactor to regenerate new tissues or organs at injured sites or at ectopic sites that can support the regeneration of new tissues. IVB can be constructed by tissue flap (subcutaneous pocket, muscle flap/pocket, fascia flap, periosteum flap, omentum flap/abdominal cavity) and axial vascular pedicle (axial vascular bundle, arteriovenous loop) alone or jointly. IVB is used to prefabricate vascularized tissue engineered bone that matched the shape and size of the defect. The prefabricated vascularized tissue engineered bone can be used as bone graft, pedicled bone flap, or free bone flap to repair bone defect. IVB solves the problem of insufficient vascularization in traditional bone tissue engineering to a certain extent.

Conclusion

IVB is a promising method for vascularized tissue engineered bone prefabrication and subsequent bone defect reconstruction, with unique advantages in the repair of large complex bone defects. However, the complexity of IVB construction and surgical complications hinder the clinical application of IVB. Researchers should aim to develop a simple, safe, and efficient IVB.

In vitro and in vivo osteogenesis up-regulated by two-dimensional nanosheets through a macrophage-mediated pathway

Two-dimensional (2D) nanomaterials are attracting more and more interest in regenerative medicine due to their unique properties; however 2D biomimetic calcium mineral has not yet been developed and demonstrated application for bone tissue engineering. Here we described a novel calcium phosphate material with a 2D nanostructure that was synthesized using collagen and sodium alginate as the template. In vitro performance of the nanocrystalline material was evaluated, and we found that 2D CaP nanoparticles (NPs) enhanced the in vitro osteogenic differentiation of rat mesenchymal stem cells (rMSCs) through a macrophage-mediated signal pathway, when co-cultured with RAW 264.7 cells, rather than direct NP/stem cell interaction. A 2D topology structured surface was constructed by encapsulating the CaP nanomaterials in a gelatin hydrogel, which was demonstrated to be able to mediate in vivo ossification through a macrophage polarization related pathway in a femur defect rat model, and allowed the optimal therapeutic outcome compared to normal CaP counterparts. Our current work may have enlightened a new mechanism regarding NP-induced stem cell differentiation through immunoregulation, and the 2D CaP encapsulated hydrogel scaffold may serve as a potential alternative to autograft bone for orthopedic applications.

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.

Rationale for the design of 3D-printable bioresorbable tissue-engineering chambers to promote the growth of adipose tissue

Tissue engineering chambers (TECs) bring great hope in regenerative medicine as they allow the growth of adipose tissue for soft tissue reconstruction. To date, a wide range of TEC prototypes are available with different conceptions and volumes. Here, we addressed the influence of TEC design on fat flap growth in vivo as well as the possibility of using bioresorbable polymers for optimum TEC conception. In rats, adipose tissue growth is quicker under perforated TEC printed in polylactic acid than non-perforated ones (growth difference 3 to 5 times greater within 90 days). Histological analysis reveals the presence of viable adipocytes under a moderate (less than 15% of the flap volume) fibrous capsule infiltrated with CD68⁺ inflammatory cells. CD31-positive vascular cells are more abundant at the peripheral zone than in the central part of the fat flap. Cells in the TEC exhibit a specific metabolic profile of functional adipocytes identified by ¹H-NMR. Regardless of the percentage of TEC porosity, the presence of a flat base allowed the growth of a larger fat volume (p < 0.05) as evidenced by MRI images. In pigs, bioresorbable TEC in poly[1,4-dioxane-2,5-dione] (polyglycolic acid) PURASORB PGS allows fat flap growth up to 75 000 mm³ at day 90, (corresponding to more than a 140% volume increase) while at the same time the TEC is largely resorbed. No systemic inflammatory response was observed. Histologically, the expansion of adipose tissue resulted mainly from an increase in the number of adipocytes rather than cell hypertrophy. Adipose tissue is surrounded by perfused blood vessels and encased in a thin fibrous connective tissue containing patches of CD163⁺ inflammatory cells. Our large preclinical evaluation defined the appropriate design for 3D-printable bioresorbable TECs and thus opens perspectives for further clinical applications.

Vascularization Strategies in the Prevention of Nonunion Formation

Delayed healing and nonunion formation are major challenges in orthopedic surgery, which require the development of novel treatment strategies. Vascularization is considered one of the major prerequisites for successful bone healing, providing an adequate nutrient supply and allowing the infiltration of progenitor cells to the fracture site. Hence, during the last decade, a considerable number of studies have focused on the evaluation of vascularization strategies to prevent or to treat nonunion formation. These involve (1) biophysical applications, (2) systemic pharmacological interventions, and (3) tissue engineering, including sophisticated scaffold materials, local growth factor delivery systems, cell-based techniques, and surgical vascularization approaches. Accumulating evidence indicates that in nonunions, these strategies are indeed capable of improving the process of bone healing. The major challenge for the future will now be the translation of these strategies into clinical practice to make them accessible for the majority of patients. If this succeeds, these vascularization strategies may markedly reduce the incidence of nonunion formation. Impact statement Delayed healing and nonunion formation are a major clinical problem in orthopedic surgery. This review provides an overview of vascularization strategies for the prevention and treatment of nonunions. The successful translation of these strategies in clinical practice is of major importance to achieve adequate bone healing.

Key components of engineering vascularized 3-dimensional bioprinted bone constructs

Vascularization has a pivotal role in engineering successful tissue constructs. However, it remains a major hurdle of bone tissue engineering, especially in clinical applications for the treatment of large bone defects. Development of vascularized and clinically-relevant engineered bone substitutes with sufficient blood supply capable of maintaining implant viability and supporting subsequent host tissue integration remains a major challenge. Since only cells that are 100-200 µm from blood vessels can receive oxygen through diffusion, engineered constructs that are thicker than 400 µm face a challenging oxygenation problem. Following implantation in vivo, spontaneous ingrowth of capillaries in thick engineered constructs is too slow. Thus, it is critical to provide optimal conditions to support vascularization in engineered bone constructs. To achieve this, an in-depth understanding of the mechanisms of angiogenesis and bone development is required. In addition, it is also important to mimic the physiological milieu of native bone to fabricate more successful vascularized bone constructs. Numerous applications of engineered vascularization with cell-and/or microfabrication-based approaches seek to meet these aims. Three-dimensional (3D) printing promises to create patient-specific bone constructs in the future. In this review, we discuss the major components of fabricating vascularized 3D bioprinted bone constructs, analyze their related challenges, and highlight promising future trends.

Tissue Engineering of the Microvasculature

The ability to generate new microvessels in desired numbers and at desired locations has been a long-sought goal in vascular medicine, engineering, and biology. Historically, the need to revascularize ischemic tissues nonsurgically (so-called therapeutic vascularization) served as the main driving force for the development of new methods of vascular growth. More recently, vascularization of engineered tissues and the generation of vascularized microphysiological systems have provided additional targets for these methods, and have required adaptation of therapeutic vascularization to biomaterial scaffolds and to microscale devices. Three complementary strategies have been investigated to engineer microvasculature: angiogenesis (the sprouting of existing vessels), vasculogenesis (the coalescence of adult or progenitor cells into vessels), and microfluidics (the vascularization of scaffolds that possess the open geometry of microvascular networks). Over the past several decades, vascularization techniques have grown tremendously in sophistication, from the crude implantation of arteries into myocardial tunnels by Vineberg in the 1940s, to the current use of micropatterning techniques to control the exact shape and placement of vessels within a scaffold. This review provides a broad historical view of methods to engineer the microvasculature, and offers a common framework for organizing and analyzing the numerous studies in this area of tissue engineering and regenerative medicine. © 2019 American Physiological Society. Compr Physiol 9:1155-1212, 2019.

Reconstruction of composite defects of the scalp and neurocranium-a treatment algorithm from local flaps to combined AV loop free flap reconstruction

Background

Reconstruction of cranial composite defects, including all layers of the scalp and the neurocranium, poses an interdisciplinary challenge. Especially after multiple previous operations and/or radiation therapy, sufficient reconstruction is often only possible using microsurgical free flap transplantation. The aim of this study was to analyze the therapy of interdisciplinary cases with composite defects including the scalp and neurocranium.

Methods

From 2009 to 2017, 23 patients with 18 free flaps and 10 pedicled/local flaps were analyzed. First choices for free flaps were muscle flaps followed by fasciocutaneous flaps.

Results

Except for four patients, a stable coverage could be reached in the first operation. Three of these patients received a local scalp rotation flap in the first operation and needed an additional free flap because the local flap was no longer sufficient for coverage after wound healing deficiency or tumor relapse. The superficial temporal artery or external carotid artery served as recipient vessels. In special cases, venous grafts or an arteriovenous loop (AV loop) were used as extensions for the recipient vessels.

Conclusions

In summary, an interdisciplinary approach with radical debridement of infected or necrotic tissue and the reconstruction of the dura mater are essential to reach a stable, long-lasting reconstructive result. Based on our experience, free flaps seem to be the first choice for patients after multiple previous operations and/or radiation therapy.

Advances in Regenerative Medicine and Tissue Engineering: Innovation and Transformation of Medicine

Humans and animals lose tissues and organs due to congenital defects, trauma, and diseases. The human body has a low regenerative potential as opposed to the urodele amphibians commonly referred to as salamanders. Globally, millions of people would benefit immensely if tissues and organs can be replaced on demand. Traditionally, transplantation of intact tissues and organs has been the bedrock to replace damaged and diseased parts of the body. The sole reliance on transplantation has created a waiting list of people requiring donated tissues and organs, and generally, supply cannot meet the demand. The total cost to society in terms of caring for patients with failing organs and debilitating diseases is enormous. Scientists and clinicians, motivated by the need to develop safe and reliable sources of tissues and organs, have been improving therapies and technologies that can regenerate tissues and in some cases create new tissues altogether. Tissue engineering and/or regenerative medicine are fields of life science employing both engineering and biological principles to create new tissues and organs and to promote the regeneration of damaged or diseased tissues and organs. Major advances and innovations are being made in the fields of tissue engineering and regenerative medicine and have a huge impact on three-dimensional bioprinting (3D bioprinting) of tissues and organs. 3D bioprinting holds great promise for artificial tissue and organ bioprinting, thereby revolutionizing the field of regenerative medicine. This review discusses how recent advances in the field of regenerative medicine and tissue engineering can improve 3D bioprinting and vice versa. Several challenges must be overcome in the application of 3D bioprinting before this disruptive technology is widely used to create organotypic constructs for regenerative medicine.