Lymphatic Vessels in Regenerative Medicine and Tissue Engineering

Progenitor Cell Sources for 3D Bioprinting of Lymphatic Vessels and Potential Clinical Application

The lymphatic system maintains tissue fluid homeostasis and it is involved in the transport of nutrients and immunosurveillance. It also plays a pivotal role in both pathological and regenerative processes. Lymphatic development in the embryo occurs by polarization and proliferation of lymphatic endothelial cells from the lymph sacs, that is, lymphangiogenesis. Alternatively, lymphvasculogenesis further contributes to the formation of lymphatic vessels. In adult tissues, lymphatic formation rarely occurs under physiological conditions, being restricted to pathological processes. In lymphvasculogenesis, progenitor cells seem to be a source of lymphatic vessels. Indeed, mesenchymal stem cells, adipose stem cells, endothelial progenitor cells, and colony-forming endothelial cells are able to promote lymphatic regeneration by different mechanisms, such as direct differentiation and paracrine effects. In this review, we summarize what is known on the diverse stem/progenitor cell niches available for the lymphatic system, emphasizing the potential that these cells hold for lymphatic tissue engineering through 3D bioprinting and their translation to clinical application.

Engineering blood and lymphatic microvascular networks

The human vasculature plays a crucial role in the blood supply of nearly all organs as well as the drainage of the interstitial fluid. Consequently, if these physiological systems go awry, pathological changes might occur. Hence, the regeneration of existing vessels, as well as approaches to engineer artificial blood and lymphatic structures represent current challenges within the field of vascular research. In this review, we provide an overview of both the vascular blood circulation and the long-time neglected but equally important lymphatic system, with regard to their organotypic vasculature. We summarize the current knowledge within the field of vascular tissue engineering focusing on the design of co-culture systems, thereby mainly discussing suitable cell types, scaffold design and disease models. This review will mainly focus on addressing those subjects concerning atherosclerosis. Moreover, current technological approaches such as vascular organ-on-a-chip models and microfluidic devices will be discussed.

Breast Cancer-related Lymphedema: Recent Updates on Clinical Efficacy of Therapies and Bioengineering Approaches for a Personalized Therapy

BACKGROUND

Post-mastectomy lymphedema is a chronic progressive disease characterized by a significant reduction in quality of life and a range of complications.

AIM

To this date, no single treatment method provides pathological correction of the mechanisms associated with tissue reorganization observed in later-stage breast cancer-related lymphedema (BCRL).

METHODS

To define a personalized approach to the management of patients with iatrogenic lymphedema, we performed a systematic review of literature without a comprehensive meta-analysis to outline existing molecular- genetic patterns, overview current treatment methods and their efficacy, and highlight the specific tissue-associated changes in BCRL conditions and other bio-engineering approaches to develop personalized therapy.

RESULTS

Our results show that several tissue-specific and pathological molecular markers may be found, yet current research does not aim to define them.

CONCLUSION

As such, currently, a strong foundation for further research into molecular-genetic changes in lymphedema tissue exists, and further research should focus on finding specific targets for personalized treatment through bio-engineering approaches.

Gelation of Uniform Interfacial Diffusant in Embedded 3D Printing

While the human body has many different examples of perfusable structures with complex geometries, biofabrication methods to replicate this complexity are still lacking. Specifically, the fabrication of self-supporting, branched networks with multiple channel diameters is particularly challenging. Here, we present the Gelation of Uniform Interfacial Diffusant in Embedded 3D Printing (GUIDE-3DP) approach for constructing perfusable networks of interconnected channels with precise control over branching geometries and vessel sizes. To achieve user-specified channel dimensions, this technique leverages the predictable diffusion of crosslinking reaction-initiators released from sacrificial inks printed within a hydrogel precursor. We demonstrate the versatility of GUIDE-3DP to be adapted for use with diverse physicochemical crosslinking mechanisms by designing seven printable material systems. Importantly, GUIDE-3DP allows for the independent tunability of both the inner and outer diameters of the printed channels and the ability to fabricate seamless junctions at branch points. This 3D bioprinting platform is uniquely suited for fabricating lumenized structures with complex shapes characteristic of multiple hollow vessels throughout the body. As an exemplary application, we demonstrate the fabrication of vasculature-like networks lined with endothelial cells. GUIDE-3DP represents an important advance toward the fabrication of self-supporting, physiologically relevant networks with intricate and perfusable geometries.

Gelation of Uniform Interfacial Diffusant in Embedded 3D Printing

While the human body has many different examples of perfusable structures with complex geometries, biofabrication methods to replicate this complexity are still lacking. Specifically, the fabrication of self-supporting, branched networks with multiple channel diameters is particularly challenging. Here, we present the Gelation of Uniform Interfacial Diffusant in Embedded 3D Printing (GUIDE-3DP) approach for constructing perfusable networks of interconnected channels with precise control over branching geometries and vessel sizes. To achieve user-specified channel dimensions, this technique leverages the predictable diffusion of crosslinking reaction-initiators released from sacrificial inks printed within a hydrogel precursor. We demonstrate the versatility of GUIDE-3DP to be adapted for use with diverse physiochemical crosslinking mechanisms by designing seven printable material systems. Importantly, GUIDE-3DP allows for the independent tunability of both the inner and outer diameters of the printed channels and the ability to fabricate seamless junctions at branch points. This 3D bioprinting platform is uniquely suited for fabricating lumenized structures with complex shapes characteristic of multiple hollow vessels throughout the body. As an exemplary application, we demonstrate the fabrication of vasculature-like networks lined with endothelial cells. GUIDE-3DP represents an important advance toward the fabrication of self-supporting, physiologically relevant networks with intricate and perfusable geometries.

A Novel Dressing Composed of Adipose Stem Cells and Decellularized Wharton's Jelly Facilitated Wound Healing and Relieved Lymphedema by Enhancing Angiogenesis and Lymphangiogenesis in a Rat Model

Lymphedema causes tissue swelling due to the accumulation of lymphatic fluid in the tissue, which delays the process of wound-healing. Developing effective treatment options of lymphedema is still an urgent issue. In this study, we aim to fabricate tissue-engineered moist wound dressings with adipose stem cells (ASCs) and decellularized Wharton's jelly (dWJ) from the human umbilical cord in order to ameliorate lymphedema. Rat ASCs were proliferated and an apparent layer was observed on dWJ at day 7 and 14. A rat tail lymphedema model was developed to evaluate the efficacy of the treatment. Approximately 1 cm of skin near the base of the rat tail was circularly excised. The wounds were treated by secondary healing (control) (n = 5), decellularized Wharton's jelly (n = 5) and ASC-seeded dWJ (n = 5). The wound-healing rate and the tail volume were recorded once a week from week one to week five. Angiogenesis and lymphangiogenesis were assessed by immunochemistry staining with anti-CD31 and anti-LYVE1. The results showed that the wound-healing rate was faster and the tail volume was lesser in the ASC-seeded dWJ group than in the control group. More CD31+ and LYVE-1+ cells were observed at the wound-healing area in the ASC-seeded dWJ group than in the control group. This proves that tissue-engineered moist wound dressings can accelerate wound-healing and reduce lymphedema by promoting angiogenesis and lymphangiogenesis.

Lymphatic Tissue and Organ Engineering for In Vitro Modeling and In Vivo Regeneration

The lymphatic system has an important role in maintaining fluid homeostasis and transporting immune cells and biomolecules, such as dietary fat, metabolic products, and antigens in different organs and tissues. Therefore, impaired lymphatic vessel function and/or lymphatic vessel deficiency can lead to numerous human diseases. The discovery of lymphatic endothelial markers and prolymphangiogenic growth factors, along with a growing number of in vitro and in vivo models and technologies has expedited research in lymphatic tissue and organ engineering, advancing therapeutic strategies. In this article, we describe lymphatic tissue and organ engineering in two- and three-dimensional culture systems and recently developed microfluidics and organ-on-a-chip systems in vitro. Next, we discuss advances in lymphatic tissue and organ engineering in vivo, focusing on biomaterial and scaffold engineering and their applications for lymphatic vessels and lymphoid organ regeneration. Last, we provide expert perspective and prospects in the field of lymphatic tissue engineering.

Adipose tissue-derived microvascular fragments promote lymphangiogenesis in a murine lymphedema model

Chronic lymphedema after cancer treatment is common and there is still no cure for this disease. We herein investigated the lymphangiogenic capacity of adipose tissue-derived microvascular fragments (MVF), which contain stem cells and lymphatic vessel fragments. Secondary lymphedema was induced in the hindlimbs of C57BL/6J mice. Green fluorescence protein (GFP)+ MVF were isolated from transgenic C57BL/6Tg (CAG-EGFP)1Osb/J mice, suspended in collagen hydrogel, and injected in the lymphadenectomy defect of wild-type animals. This crossover model allowed the detection of MVF-derived blood and lymphatic vessels after transplantation. The MVF group was compared with animals receiving collagen hydrogel only or a sham intervention. Lymphangiogenic effects were analyzed using volumetry, magnetic resonance (MR) lymphography, histology, and immunohistochemistry. MVF injection resulted in reduced hindlimb volumes when compared to non-treated controls. MR lymphography revealed lymphatic regeneration with reduced dermal backflow after MVF treatment. Finally, MVF transplantation promoted popliteal angiogenesis and lymphangiogenesis associated with a significantly increased microvessel and lymphatic vessel density. These findings indicate that MVF transplantation represents a promising approach to induce therapeutic lymphangiogenesis.

Hot or cold: Bioengineering immune contextures into in vitro patient-derived tumor models

In the past decade, immune checkpoint inhibitors (ICI) have proven to be tremendously effective for a subset of cancer patients. However, it is difficult to predict the response of individual patients and efforts are now directed at understanding the mechanisms of ICI resistance. Current models of patient tumors poorly recapitulate the immune contexture, which describe immune parameters that are associated with patient survival. In this Review, we discuss parameters that influence the induction of different immune contextures found within tumors and how engineering strategies may be leveraged to recapitulate these contextures to develop the next generation of immune-competent patient-derived in vitro models.

Matrix stiffness primes lymphatic tube formation directed by vascular endothelial growth factor-C

Dysfunction of the lymphatic system is associated with a wide range of disease phenotypes. The restoration of dysfunctional lymphatic vessels has been hypothesized as an innovative method to rescue healthy phenotypes in diseased states including neurological conditions, metabolic syndromes, and cardiovascular disease. Compared to the vascular system, little is known about the molecular regulation that controls lymphatic tube morphogenesis. Using synthetic hyaluronic acid (HA) hydrogels as a chemically and mechanically tunable system to preserve lymphatic endothelial cell (LECs) phenotypes, we demonstrate that low matrix elasticity primes lymphatic cord-like structure (CLS) formation directed by a high concentration of vascular endothelial growth factor-C (VEGF-C). Decreasing the substrate stiffness results in the upregulation of key lymphatic markers, including PROX-1, lymphatic vessel endothelial hyaluronan receptor 1 (LYVE-1), and VEGFR-3. Consequently, higher levels of VEGFR-3 enable stimulation of LECs with VEGF-C which is required to both activate matrix metalloproteinases (MMPs) and facilitate LEC migration. Both of these steps are critical in establishing CLS formation in vitro. With decreases in substrate elasticity, we observe increased MMP expression and increased cellular elongation, as well as formation of intracellular vacuoles, which can further merge into coalescent vacuoles. RNAi studies demonstrate that MMP-14 is required to enable CLS formation and that LECs sense matrix stiffness through YAP/TAZ mechanosensors leading to the activation of their downstream target genes. Collectively, we show that by tuning both the matrix stiffness and VEGF-C concentration, the signaling pathways of CLS formation can be regulated in a synthetic matrix, resulting in lymphatic networks which will be useful for the study of lymphatic biology and future approaches in tissue regeneration.

Tissue Engineering Strategies for Cancer-Related Lymphedema

Tissue engineering has witnessed remarkable advancement in various fields of medicine and has the potential of revolutionizing the management of lymphedema. Combining approaches of biotechnology with the evolving understanding of lymphangiogenesis may offer promising treatment modalities for patients suffering from lymphedema. The strategies to lymphatic vessels tissue engineer can be grouped into four main categories: Delivery of chemokines, cytokines, and other growth factors to induce lymphangiogenesis; cell-based approach using lymphatic endothelial cells or stem-cells; scaffold-based tissue engineering; or a combination of these. This review will summarize the current approach to cancer-related lymphedema and advances in lymphatic tissue engineering strategies and the challenges facing the regeneration of lymphatic vasculature, particularly in an oncologic setting.

Construction of a Silk Fibroin/Polyethylene Glycol Double Network Hydrogel with Co-Culture of HUVECs and UCMSCs for a Functional Vascular Network

The success of complex tissue and internal organ reconstruction relies principally on the fabrication of a 3D vascular network, which guarantees the delivery of oxygen and nutrients in addition to the disposal of waste. In this study, a rapidly forming cell-encapsulated double network (DN) hydrogel is constructed by an ultrasonically activated silk fibroin network and bioorthogonal-mediated polyethylene glycol network. This DN hydrogel can be solidified within 10 s, and its mechanical property gradually increases to ∼20 kPa after 30 min. This work also demonstrates that coencapsulation of human umbilical vein endothelial cells (HUVECs) and umbilical cord-derived mesenchymal stem cells (UCMSCs) into the DN hydrogel can facilitate the formation of more mature vessels and complete the capillary network in comparison with the hydrogels encapsulated with a single cell type both in vitro and in vivo. Taking together, the DN hydrogel, combined with coencapsulation of HUVECs and UCMSCs, represents a strategy for the construction of a functional vascular network.

Focused Extracorporeal Shockwave Therapy in Physical Medicine and Rehabilitation

Purpose of Review

Focused extracorporeal shockwave therapy (fESWT) is a physical treatment modality developed over the last 25 years for musculoskeletal indications. It has many indications in the field of physical medicine and rehabilitation (PM&R) and is effective, time-efficient, and cost-efficient. This review focuses on basics and on clinical indications as well as on significant trends in fESWT.

Recent Findings

In PM&R, stimulation of healing processes in tendons, surrounding tissue, and bones via mechanotransduction seems to be a relevant biological effect. The International Society for Medical Shockwave Treatment (ISMST) describes different types of indications (such as approved standard indications—in accordance with most scientific evidence—like calcifying tendinopathy of the shoulder, plantar fasciitis lateral epicondylopathy of the elbow, greater trochanter pain syndrome, patellar tendinopathy, Achilles tendinopathy and bone non-union, common empirically tested clinical uses, exceptional or expert indications, and experimental indications).

Summary

fESWT is a relevant treatment option in PM&R and regenerative medicine. In recent years, historical paradigms (for example, application in cancer patients) have changed and new indications (such as nerve regeneration, myofascial trapezius syndrome, low back pain, dermatosclerosis, and lymphedema) are supported. Future translational research should focus on establishing actual exceptional indications and experimental indications for clinical routine.

Network patterning, morphogenesis and growth in lymphatic vascular development

The lymphatic vasculature is a vital component of the vertebrate vascular system that mediates tissue fluid homeostasis, lipid uptake and immune surveillance. The development of the lymphatic vasculature starts in the early vertebrate embryo, when a subset of blood vascular endothelial cells of the cardinal veins acquires lymphatic endothelial cell fate. These cells sprout from the veins, migrate, proliferate and organize to give rise to a highly structured and unique vascular network. Cellular cross-talk, cell-cell communication and the interpretation of signals from surrounding tissues are all essential for coordinating these processes. In this chapter, we highlight new findings and review research progress with a particular focus on LEC migration and guidance, expansion of the LEC lineage, network remodeling and morphogenesis of the lymphatic vasculature.

Effect of Hypoxia Preconditioned Secretomes on Lymphangiogenic and Angiogenic Sprouting: An in Vitro Analysis

Hypoxia Preconditioned Plasma (HPP) and Serum (HPS) are two blood-derived autologous growth factor compositions that are being clinically employed as tools for promoting tissue regeneration, and have been extensively examined for their angiogenic activity. As yet, their ability to stimulate/support lymphangiogenesis remains unknown, although this is an important but often-neglected process in wound healing and tissue repair. Here we set out to characterize the potential of hypoxia preconditioned secretomes as promoters of angiogenic and lymphangiogenic sprouting in vitro. We first analysed HPP/HPS in terms of pro- (VEGF-C) and anti- (TSP-1, PF-4) angiogenic/lymphangiogenic growth factor concentration, before testing their ability to stimulate microvessel sprouting in the mouse aortic ring assay and lymphatic sprouting in the thoracic duct ring assay. The origin of lymphatic structures was validated with lymph-specific immunohistochemical staining (Anti-LYVE-1) and lymphatic vessel-associated protein (polydom) quantification in culture supernatants. HPP/HPS induced greater angiogenic and lymphatic sprouting compared to non-hypoxia preconditioned samples (normal plasma/serum), a response that was compatible with their higher VEGF-C concentration. These findings demonstrate that hypoxia preconditioned blood-derived secretomes have the ability to not only support sprouting angiogenesis, but also lymphangiogenesis, which underlines their multimodal regenerative potential.

Biomaterial Based Strategies for Engineering New Lymphatic Vasculature

The lymphatic system is essential for tissue regeneration and repair due to its pivotal role in resolving inflammation, immune cell surveillance, lipid transport, and maintaining tissue homeostasis. Loss of functional lymphatic vasculature is directly implicated in a variety of diseases, including lymphedema, obesity, and the progression of cardiovascular diseases. Strategies that stimulate the formation of new lymphatic vessels (lymphangiogenesis) could provide an appealing new approach to reverse the progression of these diseases. However, lymphangiogenesis is relatively understudied and stimulating therapeutic lymphangiogenesis faces challenges in precise control of lymphatic vessel formation. Biomaterial delivery systems could be used to unleash the therapeutic potential of lymphangiogenesis for a variety of tissue regenerative applications due to their ability to achieve precise spatial and temporal control of multiple therapeutics, direct tissue regeneration, and improve the survival of delivered cells. In this review, the authors begin by introducing therapeutic lymphangiogenesis as a target for tissue regeneration, then an overview of lymphatic vasculature will be presented followed by a description of the mechanisms responsible for promoting new lymphatic vessels. Importantly, this work will review and discuss current biomaterial applications for stimulating lymphangiogenesis. Finally, challenges and future directions for utilizing biomaterials for lymphangiogenic based treatments are considered.

Vascularization strategies for skin tissue engineering

Lack of proper vascularization after skin trauma causes delayed wound healing. This has sparked the development of various tissue engineering strategies to improve vascularization.

Extracorporeal shock wave therapy in the supportive care and rehabilitation of cancer patients

Purpose

Cancer patients sometimes show immobilizing musculoskeletal conditions which prohibit active exercise due to severe bodily pain. Therefore, before starting a rehabilitative exercise program, the pain has to be reduced to enable the patient to participate actively in the exercise program. Extracorporeal shock wave therapy (ESWT, the application of radial and/or focused shock waves with low or high energy) has been shown to be effective and efficient in the treatment of musculoskeletal disorders. However, one historical paradigm was the fact that, in the past, cancer was seen as a contraindication for the use of ESWT.

Methods

Clinical note to present indications, benefits, and contraindications of shock wave treatment in cancer patients.

Results

Malignant tumors in the treatment area have to be seen as a contraindication for the use of ESWT treatment. Cancer itself—in the form of the underlying disease—is not a contraindication for the treatment with radial and focused shock wave therapy with low or high energy. Plantar fasciitis and calcaneal spurs, calcified shoulder, tennis elbow or Achilles tendinopathy, and delayed healing and chronic wounds are typical approved standard indications for ESWT, and are allowed when the malignant tumor is not in the treatment area. There are also other musculoskeletal and non-musculoskeletal indications (e.g., myofascial syndrome, erectile dysfunction, polyneuropathy, and lymphedema) that are relevant for cancer survivors. These indications are recommended by the International Society for Medical Shockwave Treatment (ISMST) for “common empirically tested clinical use” and as exceptional indications/expert indications.

Conclusion

ESWT is a safe and relevant modality for the supportive care and rehabilitation of cancer patients.

Influence of Adipose Tissue-Derived Stem Cells on the Burn Wound Healing Process

Burns are lesions in which the thermal energy of the causative agent transfers heat to the surface of the body, causing superficial or deep damage to the skin with protein denaturation in cells and biochemical maladjustments, which delay and disrupt the cicatricial process, increasing the chances of functional and aesthetic sequelae. This study evaluates the influence of adipose tissue-derived stem cells (ADSCs) on burn healing in terms of the size of the cicatricial space and quantified measures of collagen deposition, inflammatory infiltrate, blood vessels, and lymphatic vessels. Initially, intra-abdominal adipose tissue was resected from a single donor Wistar rat that was not part of any of the subsequent groups to obtain ADSCs by isolation and cell culture. Burns were made in the left lateral abdominal region of Wistar rats by contact with a square ceramic paper with a 484 mm² area heated to 100°C for 30 seconds. Intradermal ADSC transplantation was performed in two stages. The first was on the same day of the burn, when 3.2 × 10⁶ ADSCs were transplanted shortly after the burned region cooled, while the second stage occurred four days later with the same number of ADSCs. The progress was evaluated by immunohistochemical methods and H&E, Masson's trichrome, Picrosirius red, and Lyve-1 immunofluorescence staining. Despite the quantitative similarity of blood vessels and the inflammatory infiltrate observed by H&E, there were statistically significant differences between the groups on the fourteenth day of evolution. The group that received ADSCs showed a reduction in the scar tissue area, increased collagen type III deposition, and a quantifiable reduction in lymphatic vessels, so we conclude that ADSCs influence the healing of total thickness burns in rats.

High-resolution acoustophoretic 3D cell patterning to construct functional collateral cylindroids for ischemia therapy

The fabrication of functional tissues is essential for clinical applications such as disease treatment and drug discovery. Recent studies have revealed that the mechanical environments of tissues, determined by geometric cell patterns, material composition, or mechanical properties, play critical roles in ensuring proper tissue function. Here, we propose an acoustophoretic technique using surface acoustic waves to fabricate therapeutic vascular tissue containing a three-dimensional collateral distribution of vessels. Co-aligned human umbilical vein endothelial cells and human adipose stem cells that are arranged in a biodegradable catechol-conjugated hyaluronic acid hydrogel exhibit enhanced cell-cell contacts, gene expression, and secretion of angiogenic and anti-inflammatory paracrine factors. The therapeutic effects of the fabricated vessel constructs are demonstrated in experiments using an ischemia mouse model by exhibiting the remarkable recovery of damaged tissue. Our study can be referenced to fabricate various types of artificial tissues that mimic the original functions as well as structures.

Engineering 3D tissues faces the challenge of adequate vascularisation for nutrient delivery and gas exchange deep inside the construct. Here the authors use surface acoustic waves to create an aligned array of blood vessels in a hyaluronic acid hydrogel and use it to improve function in a mouse hindlimb ischemia model.

Lymphatic Tissue Engineering and Regeneration

The lymphatic system is a major circulatory system within the body, responsible for the transport of interstitial fluid, waste products, immune cells, and proteins. Compared to other physiological systems, the molecular mechanisms and underlying disease pathology largely remain to be understood which has hindered advancements in therapeutic options for lymphatic disorders. Dysfunction of the lymphatic system is associated with a wide range of disease phenotypes and has also been speculated as a route to rescue healthy phenotypes in areas including cardiovascular disease, metabolic syndrome, and neurological conditions. This review will discuss lymphatic system functions and structure, cell sources for regenerating lymphatic vessels, current approaches for engineering lymphatic vessels, and specific therapeutic areas that would benefit from advances in lymphatic tissue engineering and regeneration.

3D bioprinting of tissues and organs for regenerative medicine

3D bioprinting is a pioneering technology that enables fabrication of biomimetic, multiscale, multi-cellular tissues with highly complex tissue microenvironment, intricate cytoarchitecture, structure-function hierarchy, and tissue-specific compositional and mechanical heterogeneity. Given the huge demand for organ transplantation, coupled with limited organ donors, bioprinting is a potential technology that could solve this crisis of organ shortage by fabrication of fully-functional whole organs. Though organ bioprinting is a far-fetched goal, there has been a considerable and commendable progress in the field of bioprinting that could be used as transplantable tissues in regenerative medicine. This paper presents a first-time review of 3D bioprinting in regenerative medicine, where the current status and contemporary issues of 3D bioprinting pertaining to the eleven organ systems of the human body including skeletal, muscular, nervous, lymphatic, endocrine, reproductive, integumentary, respiratory, digestive, urinary, and circulatory systems were critically reviewed. The implications of 3D bioprinting in drug discovery, development, and delivery systems are also briefly discussed, in terms of in vitro drug testing models, and personalized medicine. While there is a substantial progress in the field of bioprinting in the recent past, there is still a long way to go to fully realize the translational potential of this technology. Computational studies for study of tissue growth or tissue fusion post-printing, improving the scalability of this technology to fabricate human-scale tissues, development of hybrid systems with integration of different bioprinting modalities, formulation of new bioinks with tuneable mechanical and rheological properties, mechanobiological studies on cell-bioink interaction, 4D bioprinting with smart (stimuli-responsive) hydrogels, and addressing the ethical, social, and regulatory issues concerning bioprinting are potential futuristic focus areas that would aid in successful clinical translation of this technology.

Designing natural and synthetic immune tissues

Vaccines and immunotherapies have provided enormous improvements for public health, but there are fundamental disconnects between where most studies are performed-in cell culture and animal models-and the ultimate application in humans. Engineering immune tissues and organs, such as bone marrow, thymus, lymph nodes and spleen, could be instrumental in overcoming these hurdles. Fundamentally, designed immune tissues could serve as in vitro tools to more accurately study human immune function and disease, while immune tissues engineered for implantation as next-generation vaccines or immunotherapies could enable direct, on-demand control over generation and regulation of immune function. In this Review, we discuss recent interdisciplinary strategies that are merging materials science and immunology to create engineered immune tissues in vitro and in vivo. We also highlight the hurdles facing these approaches and the need for comparison to existing clinical options, relevant animal models, and other emerging technologies.

Key molecules in lymphatic development, function, and identification

While both blood and lymphatic vessels transport fluids and thus share many similarities, they also show functional and structural differences, which can be used to differentiate them. Specific visualization of lymphatic vessels has historically been and still is a pivot point in lymphatic research. Many of the proteins that are investigated by molecular biologists in lymphatic research have been defined as marker molecules, i.e. to visualize and distinguish lymphatic endothelial cells (LECs) from other cell types, most notably from blood vascular endothelial cells (BECs) and cells of the hematopoietic lineage. Among the factors that drive the developmental differentiation of lymphatic structures from venous endothelium, Prospero homeobox protein 1 (PROX1) is the master transcriptional regulator. PROX1 maintains lymphatic identity also in the adult organism and thus is a universal LEC marker. Vascular endothelial growth factor receptor-3 (VEGFR-3) is the major tyrosine kinase receptor that drives LEC proliferation and migration. The major activator for VEGFR-3 is vascular endothelial growth factor-C (VEGF-C). However, before VEGF-C can signal, it needs to be proteolytically activated by an extracellular protein complex comprised of Collagen and calcium binding EGF domains 1 (CCBE1) protein and the protease A disintegrin and metallopeptidase with thrombospondin type 1 motif 3 (ADAMTS3). This minireview attempts to give an overview of these and a few other central proteins that scientific inquiry has linked specifically to the lymphatic vasculature. It is limited in scope to a brief description of their main functions, properties and developmental roles.

Clinical evaluation of simultaneously applied monopolar radiofrequency and targeted pressure energy as a new method for noninvasive treatment of cellulite in postpubertal women

INTRODUCTION

This study investigates noninvasive cellulite treatments based on simultaneous application of monopolar radiofrequency (RF) and targeted pressure energy to evaluate efficacy and safety and to see whether simultaneous application has any benefits in noninvasive cellulite treatments.

METHODS

Thirty women with cellulite (fibrous/adipose/aqueous types) received 4 gluteofemoral treatments (~24 minutes; ~1000 cm² ) using a simultaneous application of RF and targeted pressure energy. Clinical improvement was assessed using a pentile grading scale and satisfaction questionnaires. Hip/thigh circumference was measured. Ultrasonography and thermography observed changes in dermal/subcutaneous tissue composition and in gluteofemoral thermal profile. Evaluation at 3 months posttreatment was compared against the baseline.

RESULTS

The clinical improvement averaged 2.17 ± 0.95 (54% improvement). Cellulite was reduced in 93% of cases, while 73% of patients showed good/very good/excellent improvement, with most significant improvement seen in patients with moderately severe cellulite. Hips and thigh circumference decreased on average by 2.31 cm and 2.13 cm, respectively (P < .001). Patient satisfaction was very high, averaging 4.47 ± 0.57 points (1-5 scale). Ultrasonography revealed smoothing and thickening (+0.28 ± 0.15 mm) of the dermis and an average reduction of 1.96 ± 1.60 mm in fat thickness (P < .05). Subjects with significant cellulite reduction had a more homogenous thermal profile at follow-up as a result of therapy-induced diminution of topographic skin defects. No adverse events were recorded.

CONCLUSION

The application is effective and safe for treating cellulite. The level of clinical improvement after 4 sessions is comparable to results reported after 6-20 sessions in studies on stand-alone RF/laser/targeted pressure energy devices. The technology is promising and deserves further attention and research.

Biology of Vascular Endothelial Growth Factor C in the Morphogenesis of Lymphatic Vessels

Because virtually all tissues contain blood vessels, the importance of hemevascularization has been long recognized in regenerative medicine and tissue engineering. However, the lymphatic vasculature has only recently become a subject of interest. Central to the task of growing a lymphatic network are lymphatic endothelial cells (LECs), which constitute the innermost layer of all lymphatic vessels. The central molecule that directs proliferation and migration of LECs during embryogenesis is vascular endothelial growth factor C (VEGF-C). VEGF-C is therefore an important ingredient for LEC culture and attempts to (re)generate lymphatic vessels and networks. During its biosynthesis VEGF-C undergoes a stepwise proteolytic processing, during which its properties and affinities for its interaction partners change. Many of these fundamental aspects of VEGF-C biosynthesis have only recently been uncovered. So far, most—if not all—applications of VEGF-C do not discriminate between different forms of VEGF-C. However, for lymphatic regeneration and engineering purposes, it appears mandatory to understand these differences, since they relate, e.g., to important aspects such as biodistribution and receptor activation potential. In this review, we discuss the molecular biology of VEGF-C as it relates to the growth of LECs and lymphatic vessels. However, the properties of VEGF-C are similarly relevant for the cardiovascular system, since both old and recent data show that VEGF-C can have a profound effect on the blood vasculature.

Engineering Blood and Lymphatic Microvascular Networks in Fibrin Matrices

Vascular network engineering is essential for nutrient delivery to tissue-engineered constructs and, consequently, their survival. In addition, the functionality of tissues also depends on tissue drainage and immune cell accessibility, which are the main functions of the lymphatic system. Engineering both the blood and lymphatic microvasculature would advance the survival and functionality of tissue-engineered constructs. The aim of this study was to isolate pure populations of lymphatic endothelial cells (LEC) and blood vascular endothelial cells (BEC) from human dermal microvascular endothelial cells and to study their network formation in our previously described coculture model with adipose-derived stromal cells (ASC) in fibrin scaffolds. We could follow the network development over a period of 4 weeks by fluorescently labeling the cells. We show that LEC and BEC form separate networks, which are morphologically distinguishable and sustainable over several weeks. In addition, lymphatic network development was dependent on vascular endothelial growth factor (VEGF)-C, resulting in denser networks with increasing VEGF-C concentration. Finally, we confirm the necessity of cell–cell contact between endothelial cells and ASC for the formation of both blood and lymphatic microvascular networks. This model represents a valuable platform for in vitro drug testing and for the future in vivo studies on lymphatic and blood microvascularization.