Tissue-engineered tracheal reconstruction using mesenchymal stem cells seeded on a porcine cartilage powder scaffold

Airway stenosis: classification, pathogenesis, and clinical management

Airway stenosis (AS) is a fibroinflammatory disease characterized by abnormal activation of fibroblasts and excessive synthesis of extracellular matrix, which has puzzled many doctors despite its relatively low prevalence. Traditional treatment such as endoscopic surgery, open surgery, and adjuvant therapy have many disadvantages and are limited in the treatment of patients with recurrent AS. Therefore, it is urgent to reveal the pathogenesis of AS and accelerate its clinical transformation. Based on the discovered pathogenesis, including fibrosis, inflammation, epithelial-mesenchymal transition, metabolic reprogramming, microbiome, genetic susceptibility, and other mechanisms, researchers have developed a series of treatments, such as drug therapy, gene therapy, stem cell therapy, growth factor therapy, protein therapy, and photodynamic therapy. This review introduces the classification of AS, explores the existing pathogenesis and preclinical treatments developed based on the pathogenesis, and finally summarizes the current clinical management. In addition, the prospect of exploring the interaction between different types of cells and between microorganisms and cells to identify the intersection of multiple mechanisms based on single-cell RNA sequencing, 16S rRNA gene sequencing and shotgun metagenomic sequencing is worth looking forward to.

3D bioprinted ferret mesenchymal stem cell-laden cartilage grafts for laryngotracheal reconstruction in a ferret surgical model

Chondrogenic differentiation of mesenchymal stem cells (MSCs) within a three-dimensional (3D) environment can be guided to form cartilage-like tissue in vitro to generate cartilage grafts for implantation. 3D bioprinted, MSC-populated cartilage grafts have the potential to replace autologous cartilage in reconstructive airway surgery. Here, bone marrow-derived ferret MSCs (fMSCs) capable of directed musculoskeletal differentiation were generated for the first time. A multi-material, 3D bioprinted fMSC-laden scaffold was then engineered that was capable of in vitro cartilage regeneration, as evidenced by glycosaminoglycan (GAG) production and collagen II immunohistochemical staining. In vivo implantation of these 3D bioprinted scaffolds in a ferret model of laryngotracheal reconstruction (LTR) demonstrated healing of the defect site, epithelial mucosalization of the inner lumen, and expansion of the airway volume. While the implanted scaffold allowed for reconstruction of the created airway defect, minimal chondrocytes were identified at the implant site. Nevertheless, we have established the ferret as a biomedical research model for airway reconstruction and, although further evaluation is warranted, the generation of fMSCs provides an opportunity for realizing the potential for 3D bioprinted regenerative stem cell platforms in the ferret.

Challenges and Opportunities in Developing Tracheal Substitutes for the Recovery of Long-Segment Defects

Tracheal resection and reconstruction procedures are necessary when stenosis, tracheomalacia, tumors, vascular lesions, or tracheal injury cause a tracheal blockage. Replacement with a tracheal substitute is often recommended when the trauma exceeds 50% of the total length of the trachea in adults and 30% in children. Recently, tissue engineering and other advanced techniques have shown promise in fabricating biocompatible tracheal substitutes with physical, morphological, biomechanical, and biological characteristics similar to native trachea. Different polymers and biometals are explored. Even with limited success with tissue-engineered grafts in clinical settings, complete healing of tracheal defects remains a substantial challenge due to low mechanical strength and durability of the graft materials, inadequate re-epithelialization and vascularization, and restenosis. This review has covered a range of reconstructive and regenerative techniques, design criteria, the use of bioprostheses and synthetic grafts for the recovery of tracheal defects, as well as the traditional and cutting-edge methods of their fabrication, surface modification for increased immuno- or biocompatibility, and associated challenges.

Preparation of Decellularized Tissue as Dual Cell Carrier Systems: A Step Towards Facilitating Re-epithelization and Cell Encapsulation for Tracheal Reconstruction

Surgical treatment of tracheal diseases, trauma, and congenital stenosis has shown success through tracheal reconstruction coupled with palliative care. However, challenges in surgical-based tracheal repairs have prompted the exploration of alternative approaches for tracheal replacement. Tissue-based treatments, involving the cultivation of patient cells on a network of extracellular matrix (ECM) from donor tissue, hold promise for restoring tracheal structure and function without eliciting an immune reaction. In this study, we utilized decellularized canine tracheas as tissue models to develop two types of cell carriers: a decellularized scaffold and a hydrogel. Our hypothesis posits that both carriers, containing essential biochemical niches provided by ECM components, facilitate cell attachment without inducing cytotoxicity. Canine tracheas underwent vacuum-assisted decellularization (VAD), and the ECM-rich hydrogel was prepared through peptic digestion of the decellularized trachea. The decellularized canine trachea exhibited a significant reduction in DNA content and major histocompatibility complex class II, while preserving crucial ECM components such as collagen, glycosaminoglycan, laminin, and fibronectin. Scanning electron microscope and fluorescent microscope images revealed a fibrous ECM network on the luminal side of the cell-free trachea, supporting epithelial cell attachment. Moreover, the ECM-rich hydrogel exhibited excellent viability for human mesenchymal stem cells encapsulated for 3 days, indicating the potential of cell-laden hydrogel in promoting the development of cartilage rings of the trachea. This study underscores the versatility of the trachea in producing two distinct cell carriers-decellularized scaffold and hydrogel-both containing the native biochemical niche essential for tracheal tissue engineering applications.

A Pilot Study of Decellularized Cartilage for Laryngotracheal Reconstruction in a Neonatal Pig Model

OBJECTIVE

Severe subglottic stenosis develops as a response to intubation in 1% of the >200,000 neonatal intensive care unit infants per year and may require laryngotracheal reconstruction (LTR) with autologous hyaline cartilage. Although effective, LTR is limited by comorbidities, severity of stenosis, and graft integration. In children, there is a significant incidence of restenosis requiring revision surgery. Tissue engineering has been proposed to develop alterative grafting options to improve outcomes and eliminate donor-site morbidity. Our objective is to engineer a decellularized, channel-laden xenogeneic cartilage graft, that we deployed in a proof-of-concept, neonatal porcine LTR model.

METHODS

Meniscal porcine cartilage was freeze-thawed and washed with pepsin/elastase to decellularize and create microchannels. A 6 × 10-mm decellularized cartilage graft was then implanted in 4 infant pigs in an anterior cricoid split. Airway patency and host response were monitored endoscopically until sacrifice at 12 weeks, when the construct phenotype, cricoid expansion, mechanics, and histomorphometry were evaluated.

RESULTS

The selective digestion of meniscal components yielded decellularized cartilage with cell-size channels. After LTR with decellularized meniscus, neonatal pigs were monitored via periodic endoscopy observing re-epithelization, integration, and neocartilage formation. At 12 weeks, the graft appeared integrated and exhibited airway expansion of 4 mm in micro-CT and endoscopy. Micro-CT revealed a larger lumen compared with age-matched controls. Finally, histology showed significant neocartilage formation.

CONCLUSION

Our neonatal porcine LTR model with a decellularized cartilage graft is a novel approach to tissue engineered pediatric LTR. This pilot study sets the stage for "off-the-shelf" graft procurement and future optimization of MEND for LTR.

LEVEL OF EVIDENCE

NA Laryngoscope, 134:807-814, 2024.

Surgical Innovations in Tracheal Reconstruction: A Review on Synthetic Material Fabrication

Background and Objectives: The aim of this review is to explore the recent surgical innovations in tracheal reconstruction by evaluating the uses of synthetic material fabrication when dealing with tracheomalacia or stenotic pathologies, then discussing the challenges holding back these innovations. Materials and Methods: A targeted non-systematic review of published literature relating to tracheal reconstruction was performed within the PubMed database to help identify how synthetic materials are utilised to innovate tracheal reconstruction. Results: The advancements in 3D printing to aid synthetic material fabrication have unveiled promising alternatives to conventional approaches. Achieving successful tracheal reconstruction through this technology demands that the 3D models exhibit biocompatibility with neighbouring tracheal elements by encompassing vasculature, chondral foundation, and immunocompatibility. Tracheal reconstruction has employed grafts and scaffolds, showing a promising beginning in vivo. Concurrently, the integration of resorbable models and stem cell therapy serves to underscore their viability and application in the context of tracheal pathologies. Despite this, certain barriers hinder its advancement in surgery. The intricate tracheal structure has posed a challenge for researchers seeking novel approaches to support its growth and regeneration. Conclusions: The potential of synthetic material fabrication has shown promising outcomes in initial studies involving smaller animals. Yet, to fully realise the applicability of these innovative developments, research must progress toward clinical trials. These trials would ascertain the anatomical and physiological effects on the human body, enabling a thorough evaluation of post-operative outcomes and any potential complications linked to the materials or cells implanted in the trachea.

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.

Current status and future trends of reconstructing a vascularized tissue-engineered trachea

Alternative treatment of long tracheal defects remains one of the challenges faced by thoracic surgeons. Tissue engineering has shown great potential in addressing this regenerative medicine conundrum and the technology to make tracheal grafts using this technique is rapidly maturing, leading to unique therapeutic approaches. However, the clinical application of tissue-engineered tracheal implants is limited by insufficient revascularization. Among them, realizing the vascularization of a tissue-engineered trachea is the most challenging problem to overcome. To achieve long-term survival after tracheal transplantation, an effective blood supply must be formed to support the metabolism of seeded cells and promote tissue healing and regeneration. Otherwise, repeated infection, tissue necrosis, lumen stenosis lack of effective epithelialization, need for repeated bronchoscopy after surgery, and other complications will be inevitable and lead to graft failure and a poor outcome. Here we review and analyze various tissue engineering studies promoting angiogenesis in recent years. The general situation of reconstructing a vascularized tissue-engineered trachea, including current problems and future development trends, is elaborated from the perspectives of seed cells, scaffold materials, growth factors and signaling pathways, surgical interventions in animal models and clinical applications. This review also provides ideas and methods for the further development of better biocompatible tracheal substitutes in the future.

Application of aortic allograft in trachea transplantation

BACKGROUND

The use of tracheal implants for tracheal reconstruction remains a challenge in thoracic medicine due to the complex structure of the trachea in mammalian organisms, including smooth muscles, cartilage, mucosa, blood vessels, cilia, and other tissues, and the difficulty in achieving tracheal regeneration using implants from either allografts or synthetic biomaterials.

METHODS

This project used the Lee-Sung strain pig, a swine breed local to Taiwan, as the experimental subject. The aorta of the pig was harvested, decellularized to form the scaffold, and transplanted into the trachea of allogeneic pigs together with growth factors. Postoperative physiological function and tissue changes were observed. The postoperative physiological parameters of the LSP were monitored, and they were sacrificed after a certain period to observe the pathological changes in the tracheal epithelial cells and cartilages.

RESULTS

Overall, six LSP tracheal transplantations were performed between March 4, 2020, and March 10, 2021. These included aortic patch anastomosis for pig 1 and aortic segmental anastomosis for pigs 2-6. The shortest and longest survival periods were 1 day and 147 days, respectively. Excluding the pig that survived for only 1 day due to a ruptured graft anastomosis, all other subjects survived for over 1 month on average.

CONCLUSION

In this study, we grafted a decellularized porcine aorta into a recipient pig with a tracheal defect. We found cryopreservation of the allogeneic aorta transplantation was a feasible and safe method for the management of airway disease, and immunosuppressants were unnecessary during the treatment course.

Comparison of the biological properties between 3D-printed and decellularized tracheal grafts

This study sought to characterize the differences between the 3D-printed and decellularized tracheal grafts, providing the basis for the synthesis of the more reasonable and effective tissue-engineered trachea. We compared the biomechanical properties and biocompatibility of the 3D-printed tracheal graft and decellularized tracheal graft in vitro and evaluated the biocompatibility, immune rejection and inflammation of the two materials through in vivo implantation experiments. Compared with the decellularized tracheal graft, the 3D-printed tracheal graft was associated with obviously higher biomechanical properties. The results demonstrated enhanced growth of BMSCs in the decellularized tracheal graft compared to the 3D-printed one when co-culture with two tracheal graft groups. Moreover, the CCK-8 assay demonstrated significant cell proliferation on the decellularized tracheal graft. Serum IgG and IgM measured in vivo by implantation testing indicated that the 3D-Printed tracheal graft exhibited the most significant inflammatory response. HE staining indicated that the inflammatory response in the 3D-printed tracheal graft consisted mainly of eosinophils, while little inflammatory cell infiltrates were observed in the decellularized tracheal graft. CD68 immunohistochemical analysis indicated that the infiltration of macrophages was not significant in both tracheal grafts. Our findings suggest that the biomechanical properties of the 3D-printed tracheal grafts are better than the decellularized tracheal grafts. Nonetheless, the decellularized tracheal graft exhibited better biocompatibility than the 3D-printed tracheal graft.

Review: Application of chitosan and its derivatives in medical materials

Chitin is a natural polymeric polysaccharide extracted from marine crustaceans, and chitosan is obtained by removing part of the acetyl group (usually more than 60 %) in chitin's structure. Chitosan has attracted wide attention from researchers worldwide due to its good biodegradability, biocompatibility, hypoallergenic and biological activities (antibacterial, immune and antitumor activities). However, research has shown that chitosan does not melt or dissolve in water, alkaline solutions and general organic solvents, which greatly limits its application range. Therefore, researchers have carried out extensive and in-depth chemical modification of chitosan and prepared a variety of chitosan derivatives, which have expanded the application field of chitosan. Among them, the most extensive research has been conducted in the pharmaceutical field. This paper summarizes the application of chitosan and chitosan derivatives in medical materials over the past five years.

Changes of Age-related Auricular Cartilage Plasticity and Biomechanical Property in a Rabbit Model

OBJECTIVES

Ear molding is an emerging technique that can correct auricular deformities. Treatment initiation time is the most important prognostic determinant of ear molding. Here, we aimed to examine why auricular cartilage plasticity appeared to diminish with age. Thus, we characterized age-related changes in the biomechanical, biochemical, and morphological properties of auricular cartilage.

METHODS

New Zealand rabbits were used as the experimental animal. We examined immature [postnatal 0 day (P0), 5 days (P5), 15 days (P15)], young [2 months (2M)], and mature [6 months (6M)] rabbits. Rabbits' ears were splinted and folded using adhesive fixation strips. Folding duration ranged from 1 day to 5 days to 10 days. Photographs were taken to calculate the retained fold angle. Cartilage morphology and extracellular matrix (ECM) content were examined histologically (using hematoxylin-eosin, Safranin O, elastic Van Gieson, and Masson's trichrome). Water content, DNA content, and cell density were also analyzed. Biomechanical properties were measured using a Nano indenter.

RESULTS

Immature ears had smaller angles after strip removal, and the angled deformation lasted a longer time. Cartilage matrix compositions, including glycosaminoglycan (GAG), elastin fiber, and collagen, increased over development. The water content, DNA content, and cell density decreased with age. Young's modulus was significantly higher in mature cartilage.

CONCLUSIONS

Here, we successfully established an animal model of ear molding and demonstrated that immature cartilage was associated with better plasticity. We also found that the cartilage's biomechanical property increased with the accumulation of ECM. The biomechanical change could underlie age-related shape plasticity.

LEVEL OF EVIDENCE

NA Laryngoscope, 133:88-94, 2023.

Decellularized tracheal scaffolds in tracheal reconstruction: An evaluation of different techniques

In humans, the trachea is a conduit for ventilation connecting the throat and lungs. However, certain congenital or acquired diseases may cause long-term tracheal defects that require replacement. Tissue engineering is considered a promising method to reconstruct long-segment tracheal lesions and restore the structure and function of the trachea. Decellularization technology retains the natural structure of the trachea, has good biocompatibility and mechanical properties, and is currently a hotspot in tissue engineering studies. This article lists various recent representative protocols for the generation of decellularized tracheal scaffolds (DTSs), as well as their validity and limitations. Based on the advancements in decellularization methods, we discussed the impact and importance of mechanical properties, revascularization, recellularization, and biocompatibility in the production and implantation of DTS. This review provides a basis for future research on DTS and its application in clinical therapy.

Biomechanical strength dependence on mammalian airway length

Background

The trachea is the uppermost respiratory airway element connecting the larynx to the bronchi Airway reconstructions in humans are often developed from animal models but there is limited knowledge comparing tracheal biomechanics between species. We aimed to assess the structure and biomechanics of porcine, canine, caprine and human airways.

Methods

Tracheas from pigs (n=15), goats (n=9) and canines (n=9) were divided into three groups (4, 6 and 8-ringswhile human left principal brochi (n=12) were divided into two groups (3and-rings). Airway structures were compared using histology and scanning electron microscopy. Biomechanical properties were measured subjecting samples to uniaxial tension and compression, recording the elastic modulus and (tensile and compressive) strengths.

Results

The structures of animal tracheal and human bronchia appeared similar. Biomechanical testing revealed that the elastic modulus of 8-ring tracheas was 1,190.48±363.68, 2,572.00±608.19 and 1,771.27±145.54 kPa, for porcine, canine and caprine samples, respectively, while corresponding tensile strengths were 437.63±191.41, 808.38±223.48 and 445.76±44.00 kPa. Comparable measures of anterior-posterior (A-P) compression strengths were 7.94±0.82, 7.54±0.07 and 8.10±1.87 N, respectively, whereas lateral compression strengths were 8.75±0.82, 14.55±2.29 and 11.12±0.40 N. Compression testing of human samples showed significant differences (P<0.05) between the 3-ring (A-P, 1.06±0.02 N; lateral, 0.55±0.06 N) and 5-ring groups (A-P, 1.08±0.64 N; lateral, 2.32±1.95 N).

Conclusions

The tensile and compressive strengths of mammalian airways show positive correlations with the cartilage ring number (length). On the basis of structural and biomechanical comparisons, porcine, canine and caprine species appear suitable models for the study of airway reconstruction in human.

Evaluation of Antigenicity of Components of Tracheal Allotransplant and Effect of Immunosuppressant Regime in a Rodent Model

Background  Tracheal transplantation seems to be the logical step in the process of reconstruction of the trachea following a long-segment resection, which is usually done to treat malignant disease or benign stenosis of the airway caused by a traumatic, congenital, inflammatory, or iatrogenic lesion. Immunosuppression following transplant is essential but not ideal after oncoresection. Methods  The tracheal allografts, harvested from Sprague Dawley rats, were implanted in the Wistar strain rat. The harvested tracheal grafts were divided into groups and subgroups, based on the layers of trachea, method of decellularization, and immunosuppression. The antigenicity of different layers of trachea and the effect of various decellularization methods were studied within three time frames, that is, day 3, 9, and 15. Result  On structural analysis, the day 3 and day 15 samples showed no meaningful comparison could be made, due to extensive neutrophil infiltration in all three layers. The day 9 tracheal grafts showed loss of epithelium, with no signs of regeneration in most of the allografts. The subepithelial lymphoid infiltration was found to be severe in nonimmunosuppressed allografts. The group in which both inner and outer layers were removed showed moderate-to-severe infiltrate of lymphoid cells in all the allografts, but there was no cartilage loss, irrespective of the method of decellularization. The irradiated specimens retained the cartilage but showed extensive ischemic damage. Conclusion  Rat trachea is a good model for tracheal transplant research but not adequately sturdy to sustain mechanical debridement. Irradiation and chemical decellularization eliminates the immune response but causes intense ischemic damage. Out of the three time frames, day 9 seemed to be the best to study the immune response. To substantiate the results obtained in this study, the immunohistochemical study of the allografts is needed to be performed among a larger group of animals.

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.

An in vivo evaluation of induced chondrogenesis by decellularized extracellular matrix particles

Bioengineered scaffolds composed of synthetic materials and extracellular matrix (ECM) components can offer a tissue-specific microenvironment capable of regulating cells to regenerate the structure and function of the native cartilage. Here, given the potential preservation of biomechanical and biochemical cues found in the native cartilage, particulate decellularized ECM (DC-ECM) was utilized for immobilization on the surface of nanofibrous scaffolds. Afterward, the chondro-inductive potential and ectopic cartilage formation after subcutaneous implantation of bioengineered DC-ECM scaffolds were investigated in mice model. Eight weeks post-implantation, no growth of considerable inflammatory response and neovascularization was observed in histological images of bioengineered DC-ECM scaffolds. Pre-seeded bioengineered scaffolds with human adipose-derived stem cells exhibited high levels of chondro-induction capability, indicated with immunohistochemical and gene expression results. In both interval times, we also observed chondrogenesis and tissue formation after implanting unseeded bioengineered scaffolds, which denote that the presence of DC-ECM particles can even enhance attachment and migration of the host cells and induce chondrogenesis to them. To sum up, the incorporation of DC-ECM materials to tissue engineered constructs is a promising avenue to mimic the native tissue environment for regulation of cartilage regeneration in both in vivo and in vitro settings.

Development of Acellular Respiratory Mucosal Matrix Using Porcine Tracheal Mucosa

BACKGROUND

Respiratory mucosa defects result in airway obstruction and infection, requiring subsequent functional recovery of the respiratory epithelium. Because site-specific extracellular matrix (ECM) facilitates restoration of organ function by promoting cellular migration and engraftment, previous studies considered decellularized trachea an ideal ECM; however, incomplete cell removal from cartilage and mucosal-architecture destruction are frequently reported. Here, we developed a decellularization protocol and applied it to the respiratory mucosa of separated porcine tracheas.

METHODS

The trachea was divided into groups according to decellularization protocol: native mucosa, freezing-thawing (FT), FT followed by the use of Perasafe-based chemical agents before mucosal separation (wFTP), after mucosal separation (mFTP), and followed by DNase decellularization (mFTD). Decellularization efficacy was evaluated by DNA quantification and hematoxylin and eosin staining, and ECM content of the scaffold was evaluated by histologic analysis and glycosaminoglycan and collagen assays. Biocompatibility was assessed by cell-viability assay and in vivo transplantation.

RESULTS

The mFTP mucosa showed low antigenicity and maintained the ECM to form a proper microstructure. Additionally, tonsil-derived stem cells remained viable when cultured with or seeded onto mFTP mucosa, and the in vivo host response showed a constructive pattern following implantation of the mFTP scaffolds.

CONCLUSION

These results demonstrated that xenogenic acellular respiratory mucosa matrix displayed suitable biocompatibility as a scaffold material for respiratory mucosa engineering.

Chondrogenic response in presence of cartilage extracellular matrix nanoparticles

Current studies based on regenerative medicine suggest, decellularized extracellular matrix (DC-ECM) components can regulate cell phenotype. In this regard, it is believed, presence of cartilage extracellular matrix particles in culture condition could produce physical and biochemical supportive cues for chondrogenesis. In this study, DC-ECM nanoparticles with average size of 61.5± 22.4 nm were produced by decellularization and mechanical processing. Homogenous distribution and nanoscale size of yield particles were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) microscopy imaging. Chemical structure preservation of cartilage ECM after decellularization was also confirmed by typical Fourier transform infrared (FTIR) spectrum mapping. The influence these nanoparticles on chondrogenic response of chondrocyte cells was investigated by direct and indirect addition of nanoparticles to culture medium. A clinical devitalized cartilage powder (DV-ECM) was also used as a positive control. Totally, MTS results showed that direct and indirect presence of both DC-ECM and DV-ECM particles in culture medium enhanced cellular metabolic activity except on day one of culture. Furthermore, on day 21, SOX9 and COL2 expression of cultured chondrocytes in the medium containing DC-ECM nanoparticles were up-regulated in comparison to negative control, which was further confirmed by presence more frequent number of larger size lacunae in micromass spheroids. Our findings support the use of ECM nanoparticles as condition supplement in culture medium and injectable biomaterials, especially for cell-based therapies for cartilage regeneration. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A:2463-2471, 2018.

Repair of osteonecrosis of the femoral head : 3D printed Cervi cornus Colla deproteinized bone scaffolds

Background

Osteonecrosis of the femoral head (ONFH) is a common joint disease and a major cause of morbidity.

Objective

In this study Cervi cornus Colla (CCC) deproteinized bone scaffolds were designed and three dimensional (3D)-printed for the repair of ONFH in rats.

Material and methods

The CCC-deproteinized bone scaffolds were 3D-printed using polycaprolactone mixed with the CCC-deproteinized bone powder. The scaffolds were viewed under a scanning electron microscope and subjected to compression analysis. Osteoblasts were isolated from rats and coated onto the scaffolds. Cell proliferation assays were performed with the MTT (3‑[4,5-dimethylthiazole‑2]-2,5-diphenyltetrazolium bromide) kit from Promega. An ONFH was induced in rats and a CCC-deproteinized bone scaffold was implanted into the necrotic femoral head. General observations, X‑ray imaging, and pathological examination of the femoral head were performed to evaluate the treatment of ONFH in the rats.

Results

The scaffolds were porous with a mean pore diameter of 315.70 ± 41.52 nm and a porosity of 72.86 ± 5.45% and exhibited favorable mechanical properties and degradation. In vitro assays showed that osteoblasts accumulated in the pores and adhered to the scaffolds. The CCC-deproteinized bone scaffolds enhanced the proliferation of osteoblasts. The in vivo experiments revealed that the general observation score of rats in the CCC-scaffold implanted group was significantly higher than that in the control group. The X‑ray images showed significant alleviation of ONFH in the CCC-deproteinized bone scaffold implanted rats. The femoral heads of rats in the treatment group showed less destruction or ossification of cartilage cells, few bone cement lines, very little necrosis or irregularities on the cartilage surface and only a small amount of inflammatory cell infiltration in the medullary cavity.

Conclusion

These results suggest that CCC-deproteinized bone scaffold implants facilitated the repair of ONFH in rats. This research provides a new therapeutic approach for the repair of early and mid-term ONFH.

Experimental Tracheal Replacement Using 3-dimensional Bioprinted Artificial Trachea with Autologous Epithelial Cells and Chondrocytes

Various treatment methods for tracheal defects have been attempted, such as artificial implants, allografts, autogenous grafts, and tissue engineering; however, no perfect method has been established. We attempted to create an effective artificial trachea via a tissue engineering method using 3D bio-printing. A multi-layered scaffold was fabricated using a 3D printer. Polycaprolactone (PCL) and hydrogel were used with nasal epithelial and auricular cartilage cells in the printing process. An artificial trachea was transplanted into 15 rabbits and a PCL scaffold without the addition of cells was transplanted into 6 rabbits (controls). All animals were followed up with radiography, CT, and endoscopy at 3, 6, and 12 months. In the control group, 3 out of 6 rabbits died from respiratory symptoms. Surviving rabbits in control group had narrowed tracheas due to the formation of granulation tissue and absence of epithelium regeneration. In the experimental group, 13 of 15 animals survived, and the histologic examination confirmed the regeneration of epithelial cells. Neonatal cartilage was also confirmed at 6 and 12 months. Our artificial trachea was effective in the regeneration of respiratory epithelium, but not in cartilage regeneration. Additional studies are needed to promote cartilage regeneration and improve implant stability.

Selection of the optimum 3D-printed pore and the surface modification techniques for tissue engineering tracheal scaffold in vivo reconstruction

The influences of pore sizes and surface modifications on biomechanical properties and biocompatibility (BC) of porous tracheal scaffolds (PTSs) fabricated by polycaprolactone (PCL) using 3D printing technology. The porous grafts were surface-modified through hydrolysis, amination, and nanocrystallization treatment. The surface properties of the modified grafts were characterized by energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). The materials were cocultured with bone marrow mesenchymal stem cells (BMSCs). The effect of different pore sizes and surface modifications on the cell proliferation behavior was evaluated by the cell counting kit-8 (CCK-8). Compared to native tracheas, the PTS has good biomechanical properties. A pore diameter of 200 μm is the optimum for cell adhesion, and the surface modifications successfully improved the cytotropism of the PTS. Allogeneic implantation confirmed that it largely retains its structural integrity in the host, and the immune rejection reaction of the PTS decreased significantly after the acute phase. Nano-silicon dioxide (NSD)-modified PTS is a promising material for tissue engineering tracheal reconstruction. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 360-370, 2019.

Utility of extracellular matrix powders in tissue engineering

Extracellular matrix (ECM) materials have had remarkable success as scaffolds in tissue engineering (TE) and as therapies for tissue injury whereby the ECM microenvironment promotes constructive remodeling and tissue regeneration. ECM powder and solubilized derivatives thereof have novel applications in TE and RM afforded by the capacity of these constructs to be dynamically modulated. The powder form allows for effective incorporation and penetration of reagents; hence, ECM powder is an efficacious platform for 3D cell culture and vehicle for small molecule delivery. ECM powder offers minimally invasive therapy for tissue injury and successfully treatment for wounds refractory to first-line therapies. Comminution of ECM and fabrication of powder-derived constructs, however, may compromise the biological integrity of the ECM. The current lack of optimized fabrication protocols prevents a more extensive and effective clinical application of ECM powders. Further study on methods of ECM powder fabrication and modification is needed.

Functionality of decellularized matrix in cartilage regeneration: A comparison of tissue versus cell sources

Increasing evidence indicates that decellularized extracellular matrices (dECMs) derived from cartilage tissues (T-dECMs) or chondrocytes/stem cells (C-dECMs) can support proliferation and chondrogenic differentiation of cartilage-forming cells. However, few review papers compare the differences between these dECMs when they serve as substrates for cartilage regeneration. In this review, after an introduction of cartilage immunogenicity and decellularization methods to prepare T-dECMs and C-dECMs, a comprehensive comparison focuses on the effects of T-dECMs and C-dECMs on proliferation and chondrogenic differentiation of chondrocytes/stem cells in vitro and in vivo. Key factors within dECMs, consisting of microarchitecture characteristics and micromechanical properties as well as retained insoluble and soluble matrix components, are discussed in-depth for potential mechanisms underlying the functionality of these dECMs in regulating chondrogenesis. With this information, we hope to benefit dECM based cartilage engineering and tissue regeneration for future clinical application.

STATEMENT OF SIGNIFICANCE

The use of decellularized extracellular matrix (dECM) is becoming a promising approach for tissue engineering and regeneration. Compared to dECM derived from cartilage tissue, recently reported dECM from cell sources exhibits a distinct role in cell based cartilage regeneration. In this review paper, for the first time, tissue and cell based dECMs are comprehensively compared for their functionality in cartilage regeneration. This information is expected to provide an update for dECM based cartilage regeneration.

Beyond dilation: current concepts in endoscopic airway stenting and reconstruction

PURPOSE OF REVIEW

To discuss current modalities of endoscopic airway management beyond balloon dilation therapy.

RECENT FINDINGS

Advances continue to be made through technology and bioengineering with exciting potential in the pediatric airway. Smaller robots and instrumentation allow increased endoscopic surgical success. Biodegradable stents and bioengineered grafts are on the horizon for use in airway surgery. Dysphonia following airway reconstruction is of increasing recognition with new endoscopic treatments being performed. Supraglottoplasty is further recognized as a treatment for obstructive sleep apnea for laryngomalacia diagnosed on sleep endoscopy. Interarytenoid injection may be beneficial in the normal larynx for aspiration and dysphagia as well as diagnosing and treating type I laryngeal clefts.

SUMMARY

Endoscopic airway surgery continues to be a popular and effective method of treating the pediatric airway. Technological advances such as in robotics may have an increasing role in the future of endoscopic airway surgery in children. Bioengineered airway adjuncts including biodegradable airway stents look to be promising in the future treatment of airway stenosis.

Autologous Cell Seeding in Tracheal Tissue Engineering

Purpose of Review

There is no consensus on the best technology to be employed for tracheal replacement. One particularly promising approach is based upon tissue engineering and involves applying autologous cells to transplantable scaffolds. Here, we present the reported pre-clinical and clinical data exploring the various options for achieving such seeding.

Recent Findings

Various cell combinations, delivery strategies, and outcome measures are described. Mesenchymal stem cells (MSCs) are the most widely employed cell type in tracheal bioengineering. Airway epithelial cell luminal seeding is also widely employed, alone or in combination with other cell types. Combinations have thus far shown the greatest promise. Chondrocytes may improve mechanical outcomes in pre-clinical models, but have not been clinically tested. Rapid or pre-vascularization of scaffolds is an important consideration. Overall, there are few published objective measures of post-seeding cell viability, survival, or overall efficacy.

Summary

There is no clear consensus on the optimal cell-scaffold combination and mechanisms for seeding. Systematic in vivo work is required to assess differences between tracheal grafts seeded with combinations of clinically deliverable cell types using objective outcome measures, including those for functionality and host immune response.

Electronic supplementary material

The online version of this article (10.1007/s40778-017-0108-2) contains supplementary material, which is available to authorized users.

Airway reconstruction using decellularized tracheal allografts in a porcine model

PURPOSE

Tracheal cartilage reconstruction is an essential approach for the treatment of tracheal congenital abnormalities or injury. Here, we evaluated the use of allogeneic decellularized tracheas as novel support scaffolds.

METHODS

Six weaned pigs (4-week-old domestic males) were transplanted with allogeneic tracheal graft patches (three decellularized and three fresh tracheal scaffolds) onto artificial defects (approximately 15 × 15 mm). After 11 weeks, the tracheas were evaluated by bronchoscopy and histological studies.

RESULTS

No pigs displayed airway symptoms during the observation period. Tracheal lumen restored by fresh graft patches showed more advanced narrowing than that treated with decellularized grafts by bronchoscopy. Histologically, fresh grafts induced typical cellular rejection; this was decreased with decellularized grafts. In addition, immunohistochemistry demonstrated regenerating foci of recipient cartilage along the adjacent surface of decellularized tracheal grafts.

CONCLUSION

Decellularized allogeneic tracheal scaffolds could be effective materials for restoring impaired trachea.

Tissue-engineered trachea from a 3D-printed scaffold enhances whole-segment tracheal repair

Long segmental repair of trachea stenosis is an intractable condition in the clinic. The reconstruction of an artificial substitute by tissue engineering is a promising approach to solve this unmet clinical need. 3D printing technology provides an infinite possibility for engineering a trachea. Here, we 3D printed a biodegradable reticular polycaprolactone (PCL) scaffold with similar morphology to the whole segment of rabbits' native trachea. The 3D-printed scaffold was suspended in culture with chondrocytes for 2 (Group I) or 4 (Group II) weeks, respectively. This in vitro suspension produced a more successful reconstruction of a tissue-engineered trachea (TET), which enhanced the overall support function of the replaced tracheal segment. After implantation of the chondrocyte-treated scaffold into the subcutaneous tissue of nude mice, the TET presented properties of mature cartilage tissue. To further evaluate the feasibility of repairing whole segment tracheal defects, replacement surgery of rabbits' native trachea by TET was performed. Following postoperative care, mean survival time in Group I was 14.38 ± 5.42 days, and in Group II was 22.58 ± 16.10 days, with the longest survival time being 10 weeks in Group II. In conclusion, we demonstrate the feasibility of repairing whole segment tracheal defects with 3D printed TET.

Applications of Tissue Engineering in Joint Arthroplasty: Current Concepts Update

Research in tissue engineering has undoubtedly achieved significant milestones in recent years. Although it is being applied in several disciplines, tissue engineering's application is particularly advanced in orthopedic surgery and in degenerative joint diseases. The literature is full of remarkable findings and trials using tissue engineering in articular cartilage disease. With the vast and expanding knowledge, and with the variety of techniques available at hand, the authors aimed to review the current concepts and advances in the use of cell sources in articular cartilage tissue engineering.

Circumferential Three-Dimensional-Printed Tracheal Grafts: Research Model Feasibility and Early Results

BACKGROUND

Methods for tracheal graft research have presented persistent challenges to investigators, and three-dimensional (3D)-printed biosynthetic grafts offer one potential development platform. We aimed to develop an efficient research platform for customizable circumferential 3D-printed tracheal grafts and evaluate feasibility and early structural integrity with a large-animal model.

METHODS

Virtual 3D models of porcine subject tracheas were generated using preoperative computed tomography scans. Two designs were used to test graft customizability and the limits of the construction process. Designs I and II used 270-degree and 360-degree external polycaprolactone scaffolds, respectively, both encompassing a circumferential extracellular matrix collagen layer. The polycaprolactone scaffolds were made in a fused-deposition modeling 3D printer and customized to the recipient's anatomy. Design I was implanted in 3 pigs and design II in 2 pigs, replacing 4-ring tracheal segments. Data collected included details of graft construction, clinical outcomes, bronchoscopy, and gross and histologic examination.

RESULTS

The 3D-printed biosynthetic grafts were produced with high fidelity to the native organ. The fabrication process took 36 hours. Grafts were implanted without immediate complication. Bronchoscopy immediately postoperatively and at 1 week demonstrated patent grafts and appropriate healing. All animals lived beyond a predetermined 1-week survival period. Bronchoscopy at 2 weeks showed significant paraanastomotic granulation tissue, which, along with partial paraanastomotic epithelialization, was confirmed on pathology. Overall survival was 17 to 34 days.

CONCLUSIONS

We propose a rapid, reproducible, resource efficient method to develop various anatomically precise grafts. Further graft refinement and strategies for granulation tissue management are needed to improve outcomes.

Bio-engineered electrospun nanofibrous membranes using cartilage extracellular matrix particles

Functionalized nanofibrous scaffolds with decellularized ECM (DECM) particles can mimic the natural motifs of cartilage ECMs and enhance chondro-inductivity for tissue engineering applications.

Intraportal mesenchymal stem cell transplantation prevents acute liver failure through promoting cell proliferation and inhibiting apoptosis

BACKGROUND

Transplantation of mesenchymal stem cells (MSCs) has been regarded as a potential treatment for acute liver failure (ALF), but the optimal route was unknown. The present study aimed to explore the most effective MSCs transplantation route in a swine ALF model.

METHODS

The swine ALF model induced by intravenous injection of D-Gal was treated by the transplantation of swine MSCs through four routes including intraportal injection (InP group), hepatic intra-arterial injection (AH group), peripheral intravenous injection (PV group) and intrahepatic injection (IH group). The living conditions and survival time were recorded. Blood samples before and after MSCs transplantation were collected for the analysis of hepatic function. The histology of liver injury was interpreted and scored in terminal samples. Hepatic apoptosis was detected by TUNEL assay. Apoptosis and proliferation related protein expressions including cleaved caspase-3, survivin, AKT, phospho-AKT (Ser473), ERK and phospho-ERK (Tyr204) were analyzed by Western blotting.

RESULTS

The average survival time of each group was 10.7+/-1.6 days (InP), 6.0+/-0.9 days (AH), 4.7+/-1.4 days (PV), 4.3+/-0.8 days (IH), respectively, when compared with the average survival time of 3.8+/-0.8 days in the D-Gal group. The survival rates between the InP group and D-Gal group revealed a statistically significant difference (P<0.01). Pathological and biochemical analysis showed that liver damage was the worst in the D-Gal group, while less injury in the InP group. Histopathological scores revealed a significant decrease in the InP group (3.17+/-1.04, P<0.01) and AH group (8.17+/-0.76, P<0.05) as compared with that in the D-Gal group (11.50+/-1.32). The apoptosis rate in the InP group (25.0%+/-3.4%, P<0.01) and AH group (40.5%+/-1.0%, P<0.05) was lower than that in the D-Gal group (70.6%+/-8.5%). The expression of active caspase-3 was inhibited, while the expression of survivin, AKT, phospho-AKT (Ser473), ERK and phospho-ERK (Tyr204) was elevated in the InP group.

CONCLUSIONS

Intraportal injection was superior to other pathways for MSC transplantation. Intraportal MSC transplantation could improve liver function, inhibit apoptosis and prolong the survival time of swine with ALF. The transplanted MSCs may participate in liver regeneration via promoting cell proliferation and suppressing apoptosis during the initial stage of ALF.

3D printed polyurethane prosthesis for partial tracheal reconstruction: a pilot animal study

A ready-made, acellular patch-type prosthesis is desirable in repairing partial tracheal defects in the clinical setting. However, many of these prostheses may not show proper biological integration and biomechanical function when they are transplanted. In this study, we developed a novel 3D printed polyurethane (PU) tracheal scaffold with micro-scale architecture to allow host tissue infiltration and adequate biomechanical properties to withstand physiological tracheal condition. A half-pipe shaped PU scaffold (1.8 cm of height, 0.18 cm thickness, and 2 cm of diameter) was fabricated by 3D printing of PU 200 μm PU beam. The 3D printed tracheal scaffolds consisted of a porous inner microstructure with 200 × 200 × 200 μm³ sized pores and a non-porous outer layer. The mechanical properties of the scaffolds were 3.21 ± 1.02 MPa of ultimate tensile strength, 2.81 ± 0.58 MPa of Young's modulus, and 725% ± 41% of elongation at break. To examine the function of the 3D printed tracheal scaffolds in vivo, the scaffolds were implanted into 1.0 × 0.7 cm² sized anterior tracheal defect of rabbits. After implantation, bronchoscopic examinations revealed that the implanted tracheal scaffolds were patent for a 16 week-period. Histologic findings showed that re-epithelialization after 4 weeks of implantation and ciliated respiratory epithelium with ciliary beating after 8 weeks of implantation were observed at the lumen of the implanted tracheal scaffolds. The ingrowth of the connective tissue into the scaffolds was observed at 4 weeks after implantation. The biomechanical properties of the implanted tracheal scaffolds were continually maintained for 16 week-period. The results demonstrated that 3D printed tracheal scaffold could provide an alternative solution as a therapeutic treatment for partial tracheal defects.

[Renal transplantation in 2046: Future and perspectives]

OBJECTIVES

To report major findings that may build the future of kidney transplantation.

MATERIAL AND METHODS

Relevant publications were identified through Medline (http://www.ncbi.nlm.nih.gov) and Embase (http://www.embase.com) database from 1960 to 2016 using the following keywords, in association, "bio-engineering; heterotransplantation; immunomodulation; kidney; regenerative medicine; xenotransplantation". Articles were selected according to methods, language of publication and relevance. A total of 5621 articles were identified including 2264 for xenotransplantation, 1058 for regenerative medicine and 2299 for immunomodulation; after careful selection, 86 publications were eligible for our review.

RESULTS

Despite genetic constructs, xenotransplantation faces the inevitable obstacle of species barrier. Uncertainty regarding xenograft acceptance by recipients as well as ethical considerations due to the debatable utilization of animal lives, are major limits for its future. Regenerative medicine and tridimensional bioprinting allow successful implantation of organs. Bioengineering, using decellularized tissue matrices or synthetic scaffold, seeded with pluripotent cells and assembled using bioreactors, provide exciting results but remain far for reconstituting renal complexity and vascular patency. Immune tolerance may be achieved through a tough initial T-cell depletion or a combined haplo-identical bone marrow transplant leading to lymphohematopoietic chimerism.

CONCLUSION

Current researches aim to increase the pool of organs available for transplantation (xenotransplants and bio-artificial kidneys) and to increase allograft survival through the induction of immune tolerance. Reported results suggest the onset of a thrilling new era for renal transplantation providing end-stage renal disease-patients with an improved survival and quality of life.

Clinical Translation of Tissue Engineered Trachea Grafts

OBJECTIVE

To provide a state-of-the-art review discussing recent achievements in tissue engineered tracheal reconstruction.

DATA SOURCES AND REVIEW METHODS

A structured PubMed search of the current literature up to and including October 2015. Representative articles that discuss the translation of tissue engineered tracheal grafts (TETG) were reviewed.

CONCLUSIONS

The integration of a biologically compatible support with autologous cells has resulted in successful regeneration of respiratory epithelium, cartilage, and vascularization with graft patency, although the optimal construct composition has yet to be defined. Segmental TETG constructs are more commonly complicated by stenosis and delayed epithelialization when compared to patch tracheoplasty.

IMPLICATIONS FOR PRACTICE

The recent history of human TETG recipients represents revolutionary proof of principle studies in regenerative medicine. Application of TETG remains limited to a compassionate use basis; however, defining the mechanisms of cartilage formation, epithelialization, and refinement of in vivo regeneration will advance the translation of TETG from the bench to the bedside.

Preliminary experiences in trachea scaffold tissue engineering with segmental organ decellularization

OBJECTIVES/HYPOTHESIS

Ideal methods for reconstructing the tracheal structure and restoring tracheal function following damage to the trachea or removal of the trachea have not been developed. The purpose of this study is to evaluate the feasibility of using a whole segment decellularized tracheal scaffold to reconstruct the trachea.

STUDY DESIGN

Prospective experimental design.

SETTING

In vivo rabbit model.

METHODS

Trachea scaffolds were created using our previously developed freeze-dry-sonication-sodium dodecyl sulfate (SDS), [FDSS] decellularization process. After histological and mechanical testing, the scaffolds were transplanted orthotopically into segmental defects in New Zealand White Rabbits (n = 9). Another three rabbits receiving the sham operation with autologous trachea transplantations served as the control group. Two weeks after transplantation, the grafts were evaluated endoscopically and histologically.

RESULTS

The mechanical properties of the decellularized trachea segment did not differ significantly from the fresh native trachea. After transplantation, whereas the autograft in the control group showed full integration and functional recovery, all of the rabbits in the decellularized scaffold transplantation group died within 7∼24 days. Although significant collapse of the tracheal tubular structures was noted, full respiratory epithelium regeneration was observed in the rabbits that survived more than 2 weeks.

CONCLUSION

The FDSS decellularization process is effective in creating whole-segment, subtotally decellularized trachea scaffolds. However, although the respiratory epithelium regeneration on the inner surface appeared to be satisfactory, the tubular structures were not able to be maintained after transplantation, which ultimately led to the death of the animals.

LEVEL OF EVIDENCE

NA Laryngoscope, 126:2520-2527, 2016.

In vivo degradation profile of porcine cartilage-derived extracellular matrix powder scaffolds using a non-invasive fluorescence imaging method

We present a non-invasive fluorescence method for imaging of scaffold degradation in vivo by quantifying the degradation of porcine cartilage-derived extracellular matrix powder (PCP).Three-dimensional porous scaffolds should be biocompatible and bioresorbable, with a controllable degradation and resorption rate to match tissue growth. However, in vivo scaffold degradation and tissue ingrowth processes are not yet fully understood. Unfortunately, current analysis methods require animal sacrifice and scaffold destruction for the quantification of scaffold degradation and cannot monitor the situation in real time. In this study, Cy3, a fluorescent dye, was used for visualizing PCP and a real-time degradation profile was obtained quantitatively by a non-invasive method using an imaging system in which the reduction in fluorescence intensity depended on PCP scaffold degradation. Real-time PCP scaffold degradation was confirmed through changes in the volume and morphology of the scaffold using micro-computed tomography and microscopy. Our results suggest that extracellular matrix degradation was induced by collagen degradation because of the binding between Cy3 and collagen. This non-invasive real-time monitoring system for scaffold degradation will increase our understanding of in vivo matrix and/or scaffold degradation.