Dexamethasone loaded bilayered 3D tubular scaffold reduces restenosis at the anastomotic site of tracheal replacement: in vitro and in vivo assessments

Electrospun composite-coated endotracheal tubes with controlled siRNA and drug delivery to lubricate and minimize upper airway injury

Endotracheal Tubes (ETTs) maintain and secure a patent airway; however, prolonged intubation often results in unintended injury to the mucosal epithelium and inflammatory sequelae which complicate recovery. ETT design and materials used have yet to adapt to address intubation associated complications. In this study, a composite coating of electrospun polycaprolactone (PCL) fibers embedded in a four-arm polyethylene glycol acrylate matrix (4APEGA) is developed to transform the ETT from a mechanical device to a dual-purpose device capable of delivering multiple therapeutics while preserving coating integrity. Further, the composite coating system (PCL-4APEGA) is capable of sustained delivery of dexamethasone from the PCL phase and small interfering RNA (siRNA) containing polyplexes from the 4APEGA phase. The siRNA is released rapidly and targets smad3 for immediate reduction in pro-fibrotic transforming growth factor-beta 1 (TGFϐ1) signaling in the upper airway mucosa as well as suppressing long-term sequelae in inflammation from prolonged intubation. A bioreactor was used to study mucosal adhesion to the composite PCL-4APEGA coated ETTs and investigate continued mucus secretory function in ex vivo epithelial samples. The addition of the 4APEGA coating and siRNA delivery to the dexamethasone delivery was then evaluated in a swine model of intubation injury and observed to restore mechanical function of the vocal folds and maintain epithelial thickness when observed over 14 days of intubation. This study demonstrated that increase in surface lubrication paired with surface stiffness reduction significantly decreased fibrotic behavior while reducing epithelial adhesion and abrasion.

Degradable biomedical elastomers: paving the future of tissue repair and regenerative medicine

Degradable biomedical elastomers (DBE), characterized by controlled biodegradability, excellent biocompatibility, tailored elasticity, and favorable network design and processability, have become indispensable in tissue repair. This review critically examines the recent advances of biodegradable elastomers for tissue repair, focusing mainly on degradation mechanisms and evaluation, synthesis and crosslinking methods, microstructure design, processing techniques, and tissue repair applications. The review explores the material composition and cross-linking methods of elastomers used in tissue repair, addressing chemistry-related challenges and structural design considerations. In addition, this review focuses on the processing methods of two- and three-dimensional structures of elastomers, and systematically discusses the contribution of processing methods such as solvent casting, electrostatic spinning, and three-/four-dimensional printing of DBE. Furthermore, we describe recent advances in tissue repair using DBE, and include advances achieved in regenerating different tissues, including nerves, tendons, muscle, cardiac, and bone, highlighting their efficacy and versatility. The review concludes by discussing the current challenges in material selection, biodegradation, bioactivation, and manufacturing in tissue repair, and suggests future research directions. This concise yet comprehensive analysis aims to provide valuable insights and technical guidance for advances in DBE for tissue engineering.

Endotracheal tubes with dexamethasone eluting electrospun coating improve tissue mechanical function after upper airway injury

Corticosteroid-eluting endotracheal tubes (ETTs) were developed and employed in a swine laryngotracheal injury model to maintain airway patency and provide localized drug delivery to inhibit fibrotic scarring. Polycaprolactone (PCL) fibers with or without dexamethasone were electrospun onto the ETT surface PCL-only coated ETTs and placed in native airways of 18 Yorkshire swine. Regular and dexamethasone-PCL coated ETTs were placed in airways of another 18 swine injured by inner laryngeal mucosal abrasion. All groups were evaluated after 3, 7 and 14 days (n = 3/treatment/time). Larynges were bisected and localized stiffness determined by normal indentation, then sequentially matched with histological assessment. In the native airway, tissue stiffness with PCL-only ETT placement increased significantly from 3 to 7 days (p = 0.0016) and 3 to 14 days (p < 0.0001) while dexamethasone-PCL ETT placement resulted in stiffness decreasing from 7 to 14 days (p = 0.031). In the injured airway, localized stiffness at 14 days was significantly greater after regular ETT placement (23.1 ± 0.725 N/m) versus dexamethasone-PCL ETTs (17.10 ± 0.930 N/m, p < 0.0001). Dexamethasone-loaded ETTs were found to reduce laryngotracheal tissue stiffening after simulated intubation injury compared to regular ETTs, supported by a trend of reduced collagen in the basement membrane in injured swine over time. Findings suggest localized corticosteroid delivery allows for tissue stiffness control and potential use as an approach for prevention and treatment of scarring caused by intubation injury.

Manufacturing 3D Biomimetic Tissue: A Strategy Involving the Integration of Electrospun Nanofibers with a 3D-Printed Framework for Enhanced Tissue Regeneration

3D printing and electrospinning are versatile techniques employed to produce 3D structures, such as scaffolds and ultrathin fibers, facilitating the creation of a cellular microenvironment in vitro. These two approaches operate on distinct working principles and utilize different polymeric materials to generate the desired structure. This review provides an extensive overview of these techniques and their potential roles in biomedical applications. Despite their potential role in fabricating complex structures, each technique has its own limitations. Electrospun fibers may have ambiguous geometry, while 3D-printed constructs may exhibit poor resolution with limited mechanical complexity. Consequently, the integration of electrospinning and 3D-printing methods may be explored to maximize the benefits and overcome the individual limitations of these techniques. This review highlights recent advancements in combined techniques for generating structures with controlled porosities on the micro-nano scale, leading to improved mechanical structural integrity. Collectively, these techniques also allow the fabrication of nature-inspired structures, contributing to a paradigm shift in research and technology. Finally, the review concludes by examining the advantages, disadvantages, and future outlooks of existing technologies in addressing challenges and exploring potential opportunities.

Drug Loaded 3D-Printed Poly(ε-Caprolactone) Scaffolds for Local Antibacterial or Anti-Inflammatory Treatment in Bone Regeneration

Annual bone grafting surgeries due to bone fractures, resections of affected bones, skeletal anomalies, osteoporosis, etc. exceed two million worldwide. In this regard, the creation of new materials for bone tissue repair is one of the urgent tasks of modern medicine. Additive manufacturing, or 3D printing, offers great opportunities for the development of materials with diverse properties and designs. In this study, the one-pot technique for the production of 3D scaffolds based on poly(ε-caprolactone) (PCL) loaded with an antibiotic or anti-inflammatory drug was proposed. In contrast to previously described methods to prepare drug-containing scaffolds, drug-loaded PCL scaffolds were prepared by direct 3D printing from a polymer/drug blend. An investigation of the mechanical properties of 3D-printed scaffolds containing 0.5-5 wt% ciprofloxacin (CIP) or dexamethasone (DEX) showed almost no effect of the drug (compression modulus ~70-90 MPa) compared to unfilled PCL (74 MPa). At the same time, introducing the drug and increasing its content in the PCL matrix contributed to a 1.8-6.8-fold decrease in the specific surface area of the scaffold, depending on composition. The release of CIP and DEX in phosphate buffer solution and in the same buffer containing lipase revealed a faster release in enzyme-containing medium within 45 days. Furthermore, drug release was more intensive from scaffolds with a low drug load. Analysis of the release profiles using a number of mathematical dissolution models led to the conclusion that diffusion dominates over other probable factors. In vitro biological evaluation of the scaffolds containing DEX showed moderate toxicity against osteoblast-like and leukemia monocytic cells. Being 3D-printed together with PCL both drugs retain their biological activity. PCL/CIP and PCL/DEX scaffolds demonstrated antibacterial properties against Pseudomonas aeruginosa (a total inhibition after 48 h) and anti-inflammatory activity in experiments on TNFα-activated monocyte cells (a 4-time reduction in CD-54 expression relative to control), respectively.

A cell-free tissue-engineered tracheal substitute with sequential cytokine release maintained airway opening in a rabbit tracheal full circumferential defect model

In this study, a cell-free tissue-engineered tracheal substitute was developed, which is based on a 3D-printed polycaprolactone scaffold coated with a gelatin-methacryloyl (GelMA) hydrogel, with transforming growth factor-β1 (TGF-β) and stromal cell-derived factor-1α (SDF-1) sequentially embedded, to facilitate cell recruitment and differentiation toward chondrocyte-phenotype. TGF-β was loaded onto polydopamine particles, and then encapsulated into the GelMA together with SDF-1, and called G/S/P@T, which was used to coat 3D-printed PCL scaffold to form the tracheal substitute. A rapid release of SDF-1 was observed during the first week, followed by a slow and sustained release of TGF-β for approximately four weeks. The tracheal substitute significantly promoted the recruitment of mesenchymal stromal cells (MSCs) or human bronchial epithelial cells in vitro, and enhanced the ability of MSCs to differentiate towards chondrocyte phenotype. Implantation of the tissue-engineered tracheal substitute with a rabbit tracheal anterior defect model improved regeneration of airway epithelium, recruitment of endogenous MSCs and expression of markers of chondrocytes at the tracheal defect site. Moreover, the tracheal substitute maintained airway opening for 4 weeks in a tracheal full circumferential defect model with airway epithelium coverage at the defect sites without granulation tissue accumulation in the tracheal lumen or underneath. The promising results suggest that this simple, cell-free tissue-engineered tracheal substitute can be used directly after tracheal defect removal and should be further developed towards clinical application.

Review on Additives in Hydrogels for 3D Bioprinting of Regenerative Medicine: From Mechanism to Methodology

The regeneration of biological tissues in medicine is challenging, and 3D bioprinting offers an innovative way to create functional multicellular tissues. One common way in bioprinting is bioink, which is one type of the cell-loaded hydrogel. For clinical application, however, the bioprinting still suffers from satisfactory performance, e.g., in vascularization, effective antibacterial, immunomodulation, and regulation of collagen deposition. Many studies incorporated different bioactive materials into the 3D-printed scaffolds to optimize the bioprinting. Here, we reviewed a variety of additives added to the 3D bioprinting hydrogel. The underlying mechanisms and methodology for biological regeneration are important and will provide a useful basis for future research.

Development of tissue-engineered tracheal scaffold with refined mechanical properties and vascularisation for tracheal regeneration

Introduction: Attempted tracheal replacement efforts thus far have had very little success. Major limiting factors have been the inability to efficiently re-vascularise and mimic the mechanical properties of native tissue. The major objective of this study was to optimise a previously developed collagen-hyaluronic acid scaffold (CHyA-B), which has shown to facilitate the growth of respiratory cells in distinct regions, as a potential tracheal replacement device. Methods: A biodegradable thermoplastic polymer was 3D-printed into different designs and underwent multi-modal mechanical assessment. The 3D-printed constructs were incorporated into the CHyA-B scaffolds and subjected to in vitro and ex vivo vascularisation. Results: The polymeric backbone provided sufficient strength to the CHyA-B scaffold, with yield loads of 1.31-5.17 N/mm and flexural moduli of 0.13-0.26 MPa. Angiogenic growth factor release (VEGF and bFGF) and angiogenic gene upregulation (KDR, TEK-2 and ANG-1) was detected in composite scaffolds and remained sustainable up to 14 days. Confocal microscopy and histological sectioning confirmed the presence of infiltrating blood vessel throughout composite scaffolds both in vitro and ex vivo. Discussion: By addressing both the mechanical and physiological requirements of tracheal scaffolds, this work has begun to pave the way for a new therapeutic option for large tracheal defects.

3D bioprinting in airway reconstructive surgery: A pilot study

OBJECTIVES

Open surgery is a reliable choice for congenital subglottic stenosis, that represents the third most common congenital anomaly of the larynx. One of the procedures performed is anterior laryngotracheal reconstruction (LTR) with anterior rib graft. The objective of this preliminary study was to evaluate the potential of 3D printing technology for the realization of laryngo-tracheal scaffold in Polycaprolactone (PCL) implanted in vivo in ovine animal model.

METHODS

A 3D computer model of a laryngeal graft and a tracheal graft was designed and printed with PCL through 3D additive manufacturing technology. The scaffolds were seeded with autologous mesenchymal stem cells and cultured in vitro for up to 14 days. Anterior graft LTR with 3D printed scaffolds was performed on 5 sheep. The animals underwent endoscopic examinations at the first, 3rd, 6th, and 12th weeks after surgery and before sacrifice. The integration of the material was evaluated by the pathologist.

RESULTS

Two animals showed a favourable postoperative course and were sacrificed at 6 months postoperatively. In these cases, we observed endoscopically a complete integration of the cellularized PCL scaffold into the peri-implant tissues, and the pathologist found the growth of respiratory epithelium on the scaffold's inner surface. Other two animals showed a difficult post-operative recovery characterized by respiratory distress resulting in early sacrifice on postoperative days 31 and 33. In these animals we found a poor integration of the grafts into the tracheal structure, and a better integration of the laryngeal scaffold. The last animal developed a wound abscess and was sacrificed 80 days after surgery. We observed, in this case, a poor scaffold integration and an acute inflammatory reaction.

CONCLUSIONS

From the preliminary data obtained we found that the excessive stiffness of the material, along with the anatomical features of the sheep, is a major limitation of this study. It will be necessary in the future to create a new biocompatible, more flexible and elastic graft, to achieve greater integration into surrounding tissues. Bioconstructed grafts could simplify surgery for the treatment of laryngo-tracheal stenosis, particularly in the treatment of long tracheal stenoses, which have, at the moment, very complex surgical options.

LEVEL OF EVIDENCE

NA.

A Review of Woven Tracheal Stents: Materials, Structures, and Application

The repair and reconstruction of tracheal defects is a challenging clinical problem. Due to the wide choice of materials and structures, weaving technology has shown unique advantages in simulating the multilayer structure of the trachea and providing reliable performance. Currently, most woven stent-based stents focus only on the effect of materials on stent performance while ignoring the direct effect of woven process parameters on stent performance, and the advantages of weaving technology in tissue regeneration have not been fully exploited. Therefore, this review will introduce the effects of stent materials and fabric construction on the performance of tracheal stents, focusing on the effects of weaving process parameters on stent performance. We will summarize the problems faced by woven stents and possible directions of development in the hope of broadening the technical field of artificial trachea preparation.

Dexamethasone: Insights into Pharmacological Aspects, Therapeutic Mechanisms, and Delivery Systems

Dexamethasone (DEX) has been widely used to treat a variety of diseases, including autoimmune diseases, allergies, ocular disorders, cancer, and, more recently, COVID-19. However, DEX usage is often restricted in the clinic due to its poor water solubility. When administered through a systemic route, it can elicit severe side effects, such as hypertension, peptic ulcers, hyperglycemia, and hydro-electrolytic disorders. There is currently much interest in developing efficient DEX-loaded nanoformulations that ameliorate adverse disease effects inhibiting advancements in scientific research. Various nanoparticles have been developed to selectively deliver drugs without destroying healthy cells or organs in recent years. In the present review, we have summarized some of the most attractive applications of DEX-loaded delivery systems, including liposomes, polymers, hydrogels, nanofibers, silica, calcium phosphate, and hydroxyapatite. This review provides our readers with a broad spectrum of nanomedicine approaches to deliver DEX safely.

Development and clinical translation of tubular constructs for tracheal tissue engineering: a review

Effective restoration of extensive tracheal damage arising from cancer, stenosis, infection or congenital abnormalities remains an unmet clinical need in respiratory medicine. The trachea is a 10-11 cm long fibrocartilaginous tube of the lower respiratory tract, with 16-20 tracheal cartilages anterolaterally and a dynamic trachealis muscle posteriorly. Tracheal resection is commonly offered to patients suffering from short-length tracheal defects, but replacement is required when the trauma exceeds 50% of total length of the trachea in adults and 30% in children. Recently, tissue engineering (TE) has shown promise to fabricate biocompatible tissue-engineered tracheal implants for tracheal replacement and regeneration. However, its widespread use is hampered by inadequate re-epithelialisation, poor mechanical properties, insufficient revascularisation and unsatisfactory durability, leading to little success in the clinical use of tissue-engineered tracheal implants to date. Here, we describe in detail the historical attempts and the lessons learned for tracheal TE approaches by contextualising the clinical needs and essential requirements for a functional tracheal graft. TE manufacturing approaches explored to date and the clinical translation of both TE and non-TE strategies for tracheal regeneration are summarised to fully understand the big picture of tracheal TE and its impact on clinical treatment of extensive tracheal defects.

Tracheal reconstruction with nail grafts: A novel approach

Background

Methods

Results

Conclusions

Converging 3D Printing and Electrospinning: Effect of Poly(l-lactide)/Gelatin Based Short Nanofibers Aerogels on Tracheal Regeneration

Recently, various tissue engineering based strategies have been pursued for the regeneration of tracheal tissues. However, previously developed tracheal scaffolds do not accurately mimic the microstructure and mechanical behavior of the native trachea, which restrict their clinical translation. Here, tracheal scaffolds are fabricated by using 3D printing and short nanofibers (SF) dispersion of poly(l-lactide)/gelatin (0.5-1.5 wt%) to afford tracheal constructs. The results display that the scaffolds containing 1.0 wt % of SF exhibit low density, good water absorption capacity, reasonable degradation rate, and stable mechanical properties, which were comparable to the native trachea. Moreover, the designed scaffolds possess good biocompatibility and promote the growth and infiltration of chondrocytes in vitro. The biocompatibility of tracheal scaffolds is further assessed after subcutaneous implantation in mice for up to 4 and 8 weeks. Histological assessment of tracheal constructs explanted at week 4 shows that scaffolds can maintain their structural integrity and support the formation of neo-vessels. Furthermore, cell-scaffold constructs gradually form cartilage-like tissues, which mature with time. Collectively, these engineered tracheal scaffolds not only possess appropriate mechanical properties to afford a stabilized structure but also a biomimetic extracellular matrix-like structure to accomplish tissue regeneration, which may have broad implications for tracheal regeneration.

Facile Preparation of β-Cyclodextrin-grafted Chitosan Electrospun Nanofibrous Scaffolds as a Hydrophobic Drug Delivery Vehicle for Tissue Engineering Applications

Despite advances in the bio-tissue engineering area, the technical basis to directly load hydrophobic drugs on chitosan (CTS) electrospun nanofibers (ENs) has not yet been fully established. In this study, we fabricated CTS ENs by using an electrospinning (ELSP) system, followed by surface modification using succinyl-beta-cyclodextrin (β-CD) under mild conditions. The β-CD-modified CTS (βCTS) ENs had slightly increased hydrophobicity compared to pristine CTS ENs as well as decreased residual amine content on the surface. Through FTIR spectroscopy and thermogravimetric analysis (TGA), we characterized the surface treatment physiochemically. In the drug release test, we demonstrated the stable and sustained release of a hydrophobic drug (e.g., dexamethasone) loaded on β-CD ENs. During in vitro biocompatibility assessments, the grafting of β-CD was shown to not reduce cell viability compared to pristine CTS ENs. Additionally, cells proliferated well on β-CD ENs, and this was confirmed by F-actin fluorescence staining. Overall, the material and strategies developed in this study have the potential to load a wide array of hydrophobic drugs. This could be applied as a drug carrier for a broad range of tissue engineering applications.

Hyaluronic Acid Coating on Hydrophobic Tracheal Scaffold Enhances Mesenchymal Stem Cell Adhesion and Tracheal Regeneration

BACKGROUND

Long segmental tracheal repair is challenging in regenerative medicine due to low adhesion of stem cells to tracheal scaffolds. Optimal transplantation of stem cells for tracheal defects has not been established. We evaluated the role of hyaluronic acid (HA) coating of tracheal scaffolds in mesenchymal stem cell (MSC) adhesion and tracheal regeneration in a rabbit model.

METHODS

A three-dimensionally printed tubular tracheal prosthesis was incubated with dopa-HA-fluorescein isothiocyanate in phosphate-buffered saline for 2 days. MSCs were incubated with an HA-coated scaffold, and their adhesion was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. HA coated scaffolds with or without MSC seeding were transplanted at the circumferential tracheal defect in rabbits, and survival, rigid bronchoscopy, radiologic findings, and histologic findings were compared between the two groups.

RESULTS

HA-coated scaffolds showed better MSC adhesion than non-coated scaffolds. The HA-coated scaffolds with MSC group showed a wider airway and greater mucosal regeneration compared to the HA-coated scaffolds without MSC group.

CONCLUSION

HA coating of scaffolds can promote MSC adhesion and tracheal regeneration.

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.

Transplantation of a 3D-printed tracheal graft combined with iPS cell-derived MSCs and chondrocytes

For successful tracheal reconstruction, tissue-engineered artificial trachea should meet several requirements, such as biocompatible constructs comparable to natural trachea, coverage with ciliated respiratory mucosa, and adequate cartilage remodeling to support a cylindrical structure. Here, we designed an artificial trachea with mechanical properties similar to the native trachea that can enhance the regeneration of tracheal mucosa and cartilage through the optimal combination of a two-layered tubular scaffold and human induced pluripotent stem cell (iPSC)-derived cells. The framework of the artificial trachea was fabricated with electrospun polycaprolactone (PCL) nanofibers (inner) and 3D-printed PCL microfibers (outer). Also, human bronchial epithelial cells (hBECs), iPSC-derived mesenchymal stem cells (iPSC-MSCs), and iPSC-derived chondrocytes (iPSC-Chds) were used to maximize the regeneration of tracheal mucosa and cartilage in vivo. After 2 days of cultivation using a bioreactor system, tissue-engineered artificial tracheas were transplanted into a segmental trachea defect (1.5-cm length) rabbit model. Endoscopy did not reveal granulation ingrowth into tracheal lumen. Alcian blue staining clearly showed the formation of ciliated columnar epithelium in iPSC-MSC groups. In addition, micro-CT analysis showed that iPSC-Chd groups were effective in forming neocartilage at defect sites. Therefore, this study describes a promising approach for long-term functional reconstruction of a segmental tracheal defect.