A potential platform for developing 3D tubular scaffolds for paediatric organ development

Small diameter polycaprolactone vascular grafts are patent in sheep carotid bypass but require antithrombotic therapy

Background: Polycaprolactone (PCL) scaffolds exhibit high biocompatibility and are attractive as vascular conduits. Materials & methods: PCL tubes were cultivated in bioreactor with human adipose regenerative cells to assess ex vivo cytocompatibility, whereas in vivo PCL tube patency was evaluated in sheep carotid bypass with and without antithrombotic treatment. Results: Ex vivo results revealed increasing adipose regenerative cells on PCL using dynamic bioreactor culturing. In vivo data showed that 67% (2/3) of grafts in the antithrombotic group were patent at day 28, while 100% (3/3) of control grafts were occluded already during the first week due to thrombosis. Histology showed that patent PCL grafts were recellularized by host cells. Conclusion: PCL tubes may work as small diameter vascular scaffolds under antithrombotic treatment.

Composite Scaffolds Based on Intestinal Extracellular Matrices and Oxidized Polyvinyl Alcohol: A Preliminary Study for a New Regenerative Approach in Short Bowel Syndrome

Pediatric Short Bowel Syndrome is a rare malabsorption disease occurring because of massive surgical resections of the small intestine. To date, the issues related to current strategies including intestinal transplantation prompted the attention towards tissue engineering (TE). This work aimed to develop and compare two composite scaffolds for intestinal TE consisting of a novel hydrogel, that is, oxidized polyvinyl alcohol (OxPVA), cross-linked with decellularized intestinal wall as a whole (wW/OxPVA) or homogenized (hW/OxPVA). A characterization of the supports was performed by histology and Scanning Electron Microscopy and their interaction with adipose mesenchymal stem cells occurred by MTT assay. Finally, the scaffolds were implanted in the omentum of Sprague Dawley rats for 4 weeks prior to being processed by histology and immunohistochemistry (CD3; F4/80; Ki-67; desmin; α-SMA; MNF116). In vitro studies proved the effectiveness of the decellularization, highlighting the features of the matrices; moreover, both supports promoted cell adhesion/proliferation even if the wW/OxPVA ones were more effective (p < 0.01). Analysis of explants showed a continuous and relatively organized tissue wall around the supports with a connective appearance, such as myofibroblastic features, smooth muscle, and epithelial cells. Both scaffolds, albeit with some difference, were promising; nevertheless, further analysis will be necessary.

Dual-acting biofunctionalised scaffolds for applications in regenerative medicine

Off the shelf scaffolds for replacing ultra-small diameter vascular grafts are valuable for reconstruction of diseased or damaged vessels. The limitations for such grafts include optimal handling with ready availability of varied lengths of grafts, graft patency with the ability to replace the function of active cellular mechanisms and adequate mechanical properties to maintain physicochemical function. We used a well-established, solvent casting method for potential tissue replacement scaffold fabrication with incorporated bioactive molecules, which we have previously explored to confer haemocompatibility. These grafts were tested in-vivo within the abdominal aorta of 10 Wistar rats and the patency was clinically and echographically evaluated. Haemocompatibility and endothelialisation were assessed on explants. Biofunctionalised scaffolds were also grafted subcutaneously and intraperitoneally to evaluate integration, inflammation and angiogenesis reactions. The potential wider applications of this dual acting scaffold were evaluated for its interactions with human dermal fibroblasts as well as bronchial epithelial cells. Physicochemical property evaluation of the functionalised grafts has clarified the mechanical strength and permeability. This study confirmed the microsurgical suturability of tubular grafts and graft patency of functionalized scaffolds. The study demonstrated the potential of a dual acting biofunctionalised scaffold's use for a wide range of tissue engineering applications where micro-porous, yet impermeable scaffolds are needed.

Additive Manufacturing of Patient-Customizable Scaffolds for Tubular Tissues Using the Melt-Drawing Method

Polymeric fibrous scaffolds for guiding cell growth are designed to be potentially used for the tissue engineering (TE) of tubular organs including esophagi, blood vessels, tracheas, etc. Tubular scaffolds were fabricated via melt-drawing of highly elastic poly(l-lactide-co-ε-caprolactone) (PLC) fibers layer-by-layer on a cylindrical mandrel. The diameter and length of the scaffolds are customizable via 3D printing of the mandrel. Thickness of the scaffolds was varied by changing the number of layers of the melt-drawing process. The morphology and tensile properties of the PLC fibers were investigated. The fibers were highly aligned with a uniform diameter. Their diameters and tensile properties were tunable by varying the melt-drawing speeds. These tailorable topographies and tensile properties show that the additive-based scaffold fabrication technique is customizable at the micro- and macro-scale for different tubular tissues. The merits of these scaffolds in TE were further shown by the finding that myoblast and fibroblast cells seeded onto the scaffolds in vitro showed appropriate cell proliferation and distribution. Human mesenchymal stem cells (hMSCs) differentiated to smooth muscle lineage on the microfibrous scaffolds in the absence of soluble induction factors, showing cellular shape modulation and scaffold elasticity may encourage the myogenic differentiation of stem cells.

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.

Transdifferentiation of human endothelial progenitors into smooth muscle cells

Access to smooth muscle cells (SMC) would create opportunities for tissue engineering, drug testing, and disease modeling. Herein we report the direct conversion of human endothelial progenitor cells (EPC) to induced smooth muscle cells (iSMC) by induced expression of MYOCD. The EPC undergo a cytoskeletal rearrangement resembling that of mesenchymal cells within 3 days post initiation of MYOCD expression. By day 7, the reprogrammed cells show upregulation of smooth muscle markers ACTA2, MYH11, and TAGLN by qRT-PCR and ACTA2 and MYH11 expression by immunofluorescence. By two weeks, they resemble umbilical artery SMC in microarray gene expression analysis. The iSMC, in contrast to EPC control, show calcium transients in response to phenylephrine stimulation and a contractility an order of magnitude higher than that of EPC as determined by traction force microscopy. Tissue-engineered blood vessels constructed using iSMC show functionality with respect to flow- and drug-mediated vasodilation and vasoconstriction.

Tubular organ epithelialisation

Hollow, tubular organs including oesophagus, trachea, stomach, intestine, bladder and urethra may require repair or replacement due to disease. Current treatment is considered an unmet clinical need, and tissue engineering strategies aim to overcome these by fabricating synthetic constructs as tissue replacements. Smart, functionalised synthetic materials can act as a scaffold base of an organ and multiple cell types, including stem cells can be used to repopulate these scaffolds to replace or repair the damaged or diseased organs. Epithelial cells have not yet completely shown to have efficacious cell-scaffold interactions or good functionality in artificial organs, thus limiting the success of tissue-engineered grafts. Epithelial cells play an essential part of respective organs to maintain their function. Without successful epithelialisation, hollow organs are liable to stenosis, collapse, extensive fibrosis and infection that limit patency. It is clear that the source of cells and physicochemical properties of scaffolds determine the successful epithelialisation. This article presents a review of tissue engineering studies on oesophagus, trachea, stomach, small intestine, bladder and urethral constructs conducted to actualise epithelialised grafts.