Vascularization of engineered cartilage constructs in a mouse model

Ultrasound visualization of augmentation rhinoplasty using diced cartilage framework: A pictorial study

BACKGROUND

Diced cartilage (DC) plays an integral role in rhinoplasty, and its application is well established in nasal dorsal augmentation rhinoplasty as a diced cartilage framework (DCF).

METHODS

Fifteen patients requiring nasal dorsal augmentation were included. Two different types of DCF were applied: DC wrapped in fascia lata or Lyomesh® and DC embedded in platelet-rich fibrin (PRF). Postoperative ultrasound follow-ups were performed at intervals of one month, three months, and one year after surgery using a high-frequency linear ultrasound transducer. The aim was to depict the viability of the DCF in vivo.

RESULTS

DCF was successfully depicted using ultrasound imaging in all 15 patients. Ultrasound rendered DC as hypoechoic and inhomogeneous areas. Perifocal hypoechoic edema was detected, which significantly decreased by the one-year follow-up. During the one-year postoperative period, very little DC had decreased in diameter and the framework was fully intact, with no signs of migration. On high-frequency ultrasound, DC wrapped in fascia lata or Lyomesh® appeared as a hypoechoic and inhomogeneous area clearly limited by a thin hyperechoic envelope material, whereas DC embedded in PRF presented as a hypoechogenic area that spread laterally along the bone and nasal cartilage on both sides. Using color Doppler imaging, neovascularization of the DCF was identified in 7 of 15 patients at the postoperative examination.

CONCLUSION

High-resolution ultrasound is an accurate, non-invasive imaging method appropriate for visualizing DCF in augmentation rhinoplasty. Additionally, it is possible to detect nascent neovascularization within grafts by using color Doppler imaging.

3D printing of Ceffe-infused scaffolds for tailored nipple-like cartilage development

The reconstruction of a stable, nipple-shaped cartilage graft that precisely matches the natural nipple in shape and size on the contralateral side is a clinical challenge. While 3D printing technology can efficiently and accurately manufacture customized complex structures, it faces limitations due to inadequate blood supply, which hampers the stability of nipple-shaped cartilage grafts produced using this technology. To address this issue, we employed a biodegradable biomaterial, Poly(lactic-co-glycolic acid) (PLGA), loaded with Cell-Free Fat Extract (Ceffe). Ceffe has demonstrated the ability to promote angiogenesis and cell proliferation, making it an ideal bio-ink for bioprinting precise nipple-shaped cartilage grafts. We utilized the Ceffe/PLGA scaffold to create a porous structure with a precise nipple shape. This scaffold exhibited favorable porosity and pore size, ensuring stable shape maintenance and satisfactory biomechanical properties. Importantly, it could release Ceffe in a sustained manner. Our in vitro results confirmed the scaffold's good biocompatibility and its ability to promote angiogenesis, as evidenced by supporting chondrocyte proliferation and endothelial cell migration and tube formation. Furthermore, after 8 weeks of in vivo culture, the Ceffe/PLGA scaffold seeded with chondrocytes regenerated into a cartilage support structure with a precise nipple shape. Compared to the pure PLGA group, the Ceffe/PLGA scaffold showed remarkable vascular formation, highlighting the beneficial effects of Ceffe. These findings suggest that our designed Ceffe/PLGA scaffold with a nipple shape represents a promising strategy for precise nipple-shaped cartilage regeneration, laying a foundation for subsequent nipple reconstruction.

Vascularization of tissue engineered cartilage - Sequential in vivo MRI display functional blood circulation

Establishing functional circulation in bioengineered tissue after implantation is vital for the delivery of oxygen and nutrients to the cells. Native cartilage is avascular and thrives on diffusion, which in turn depends on proximity to circulation. Here, we investigate whether a gridded three-dimensional (3D) bioprinted construct would allow ingrowth of blood vessels and thus prove a functional concept for vascularization of bioengineered tissue. Twenty 10 × 10 × 3-mm 3Dbioprinted nanocellulose constructs containing human nasal chondrocytes or cell-free controls were subcutaneously implanted in 20 nude mice. Over the next 3 months, the mice were sequentially imaged with a 7 T small-animal MRI system, and the diffusion and perfusion parameters were analyzed. The chondrocytes survived and proliferated, and the shape of the constructs was well preserved. The diffusion coefficient was high and well preserved over time. The perfusion and diffusion patterns shown by MRI suggested that blood vessels develop over time in the 3D bioprinted constructs; the vessels were confirmed by histology and immunohistochemistry. We conclude that 3D bioprinted tissue with a gridded structure allows ingrowth of blood vessels and has the potential to be vascularized from the host. This is an essential step to take bioengineered tissue from the bench to clinical practice.

Prevascularized Tracheal Scaffolds Using the Platysma Flap for Enhanced Tracheal Regeneration

OBJECTIVES

One of the greatest hurdles in tracheal tissue engineering is insufficient vascularization, which leads to delayed mucosal regeneration, inflammation, and restenosis. This study investigated whether a prevascularized segmental tracheal substitute using platysma can enhance tracheal mucosal regeneration.

METHODS

Three-dimensional (3D) printed scaffolds with (group M) or without (group S) Matrigel coating were implanted under the feeding vessels of the platysma in New Zealand White rabbits (n = 3) to induce vascularization. After 1 or 2 weeks, tracheal defects were created and vascularized scaffolds with feeders of the platysma were transplanted as rotational flaps. As controls, scaffolds with or without Matrigel coating was transplanted into a tracheal defect without prevascularization. Airway patency and epithelization were examined using a rigid bronchoscope every 2 weeks. Surviving animals were euthanized at 24 weeks, and microcomputed tomography and histological evaluation were performed.

RESULTS

Animals with 2 weeks of prevascularization showed longer survival than animals with 0 or 1 weeks of prevascularization regardless of the Matrigel coating. Wider airway patency was observed in group M than group S. Group M showed migration of epithelium over the scaffold from 4 weeks after transplantation and complete coverage with epithelium at 12 weeks, whereas group S showed migration of the epithelium from 14 weeks and incomplete coverage with epithelium even at 24 weeks.

CONCLUSION

This two-step method, utilizing the platysma as an in vivo bioreactor, may be a promising approach to achieve long-term survival and enhanced luminal patency. Matrigel coating on the scaffold had a synergistic effect on epithelial regeneration.

LEVEL OF EVIDENCE

NA Laryngoscope, 131:1732-1740, 2021.

Tissue engineering applications in otolaryngology-The state of translation

While tissue engineering holds significant potential to address current limitations in reconstructive surgery of the head and neck, few constructs have made their way into routine clinical use. In this review, we aim to appraise the state of head and neck tissue engineering over the past five years, with a specific focus on otologic, nasal, craniofacial bone, and laryngotracheal applications. A comprehensive scoping search of the PubMed database was performed and over 2000 article hits were returned with 290 articles included in the final review. These publications have addressed the hallmark characteristics of tissue engineering (cellular source, scaffold, and growth signaling) for head and neck anatomical sites. While there have been promising reports of effective tissue engineered interventions in small groups of human patients, the majority of research remains constrained to in vitro and in vivo studies aimed at furthering the understanding of the biological processes involved in tissue engineering. Further, differences in functional and cosmetic properties of the ear, nose, airway, and craniofacial bone affect the emphasis of investigation at each site. While otolaryngologists currently play a role in tissue engineering translational research, continued multidisciplinary efforts will likely be required to push the state of translation towards tissue-engineered constructs available for routine clinical use.

LEVEL OF EVIDENCE

NA.

Oxygen and nutrient delivery in tissue engineering: Approaches to graft vascularization

The field of tissue engineering is making great strides in developing replacement tissue grafts for clinical use, marked by the rapid development of novel biomaterials, their improved integration with cells, better-directed growth and differentiation of cells, and improved three-dimensional tissue mass culturing. One major obstacle that remains, however, is the lack of graft vascularization, which in turn renders many grafts to fail upon clinical application. With that, graft vascularization has turned into one of the holy grails of tissue engineering, and for the majority of tissues, it will be imperative to achieve adequate vascularization if tissue graft implantation is to succeed. Many different approaches have been developed to induce or augment graft vascularization, both in vitro and in vivo. In this review, we highlight the importance of vascularization in tissue engineering and outline various approaches inspired by both biology and engineering to achieve and augment graft vascularization.

In vivo analysis of vascularization and biocompatibility of electrospun polycaprolactone fibre mats in the rat femur chamber

In orthopaedic medicine, connective tissues are often affected by traumatic or degenerative injuries, and surgical intervention is required. Rotator cuff tears are a common cause of shoulder pain and disability among adults. The development of graft materials for bridging the gap between tendon and bone after chronic rotator cuff tears is essentially required. The limiting factor for the clinical success of a tissue engineering construct is a fast and complete vascularization of the construct. Otherwise, immigrating cells are not able to survive for a longer period of time, resulting in the failure of the graft material. The femur chamber allows the observation of microhaemodynamic parameters inside implants located in close vicinity to the femur in repeated measurements in vivo. We compared a porous polymer patch (a commercially available porous polyurethane‐based scaffold from Biomerix™) with electrospun polycaprolactone (PCL) fibre mats and chitosan (CS)‐graft‐PCL modified electrospun PCL (CS‐g‐PCL) fibre mats in vivo. By means of intravital fluorescence microscopy, microhaemodynamic parameters were analysed repetitively over 20 days at intervals of 3 to 4 days. CS‐g‐PCL modified fibre mats showed a significantly increased vascularization at Day 10 compared with Day 6 and at Day 14 compared with the porous polymer patch and the unmodified PCL fibre mats at the same day. These results could be verified by histology. In conclusion, a clear improvement in terms of vascularization and biocompatibility is achieved by graft‐copolymer modification compared with the unmodified material.

Uncultivated stromal vascular fraction is equivalent to adipose-derived stem and stromal cells on porous polyurethrane scaffolds forming adipose tissue in vivo

OBJECTIVES/HYPOTHESIS

To find an alternative approach to contemporary techniques in tissue augmentation and reconstruction, tissue engineering strategies aim to involve adipose-derived stem and stromal cells (ASCs) harboring a strong differentiation potential into various tissue types such as bone, cartilage, and fat.

STUDY DESIGN

Animal research.

METHODS

The stromal vascular fraction (SVF) was used directly as a cell source to provide a potential alternative to contemporary ASC-based adipose tissue engineering. Seeded in TissuCol fibrin, we applied ASCs or SVF cells to porous, degradable polyurethane (PU) scaffolds.

RESULTS

We successfully demonstrated the in vivo generation of volume-stable, well-vascularized PU-based constructs containing host-derived mature fat pads. Seeded human stem cells served as modulators of host-cell migration rather than differentiating themselves. We further demonstrated that preliminary culture of SVF cells was not necessary.

CONCLUSIONS

Our results bring adipose tissue engineering, together with automated processing devices, closer to clinical applicability. The time-consuming and cost-intensive culture and induction of the ASCs is not necessary.

LEVEL OF EVIDENCE

NA. Laryngoscope, 128:E206-E213, 2018.

Effect of Compound 21, a Selective Angiotensin II Type 2 Receptor Agonist, in a Murine Xenograft Model of Dupuytren Disease

BACKGROUND

Although surgical excision and intralesional collagenase injection are mainstays in Dupuytren disease treatment, no effective medical therapy exists for recurrent disease. Compound 21, a selective agonist of the angiotensin II type 2 receptor, has been shown to protect against fibrosis in models of myocardial infarction and stroke. The authors investigated the potential use of compound 21 in the treatment of Dupuytren disease.

METHODS

Human dermal fibroblasts were treated in vitro with compound 21 and assessed for viability using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, migration by means of scratch assay, and profibrotic gene transcription by means of quantitative reverse transcription polymerase chain reaction. Compound 21 effects in vivo were assessed using a xenograft model. Dupuytren disease cord specimens from patients undergoing open partial fasciectomy were divided into two segments. Segments were implanted under the dorsal skin of nude mouse pairs. Beginning on day 5, one mouse from each pair received daily intraperitoneal injections of compound 21 (10 μg/kg/day), and the other received vehicle. On day 10, segments were explanted and submitted for immunohistochemistry.

RESULTS

Human dermal fibroblasts treated with compound 21 displayed decreased migration and decreased gene expression of connective tissue growth factor, fibroblast specific protein-1, transforming growth factor-β1, Smad3, and Smad4. Dupuytren disease segments from compound 21-treated mice demonstrated significantly reduced alpha-smooth muscle actin and Ki67 staining, with increased density of CD31 staining vessels.

CONCLUSIONS

Compound 21 significantly decreases expression of profibrotic genes and decreases myofibroblast proliferation as indicated by reduced Ki67 and alpha-smooth muscle actin expression. These findings support compound 21 as a potential novel treatment modality for Dupuytren disease.

A Biomimetic Poly(vinyl alcohol)-Carrageenan Composite Scaffold with Oriented Microarchitecture

In general, the design of a scaffold should imitate certain advantageous properties of native extracellular matrix (ECM) to operate as a temporary ECM for cells. From this perspective, a biomimetic scaffold was prepared using poly(vinyl alcohol) and carrageenan in which axially oriented pore structure can be formed through a facile unidirectional freeze-thaw method. We examined the feasibility of this oriented scaffold, which has better physicochemical properties than a non-oriented scaffold fabricated by the conventional method. The microenvironment of this oriented scaffold could imitate biochemical and physical cues of natural cartilage ECM for guiding spatial organization and proliferation of cells in vitro, indicating its potential in cartilage repair strategy. Furthermore, the biocompatibility of the scaffold in vivo was demonstrated in a subcutaneous rat model, which revealed uniform infiltration and survival of newly formed tissue into the oriented scaffold after 4 weeks with only a minimal inflammatory response being observed over the course of the experiments. These results together indicated that the present biomimetic scaffold with oriented microarchitecture could be a promising candidate for cartilage tissue engineering.

Prevascularization in tissue engineering: Current concepts and future directions

The survival of engineered tissue constructs during the initial phase after their implantation depends on the rapid development of an adequate vascularization. This, in turn, is a major prerequisite for the constructs' long-term function. 'Prevascularization' has emerged as a promising concept in tissue engineering, aiming at the generation of a preformed microvasculature in tissue constructs prior to their implantation. This should shorten the time period during which the constructs are avascular and suffer hypoxic conditions. Herein, we provide an overview of current strategies for the generation of preformed microvascular networks within tissue constructs. In vitro approaches use cell seeding, spheroid formation or cell sheet technologies. In situ approaches use the body as a natural bioreactor to induce vascularization by angiogenic ingrowth or flap and arteriovenous (AV)-loop techniques. In future, these strategies may be supplemented by the transplantation of adipose tissue-derived microvascular fragments or the in vitro generation of highly organized microvascular networks by means of sophisticated microscale technologies and microfluidic systems. The further advancement of these prevascularization concepts and their adaptation to individual therapeutic interventions will markedly contribute to a broad implementation of tissue engineering applications into clinical practice.