Pore size and LbL chitosan coating influence mesenchymal stem cellin vitrofibrosis and biomineralization in 3D porous poly(epsilon-caprolactone) scaffolds

Transcriptomic and cellular decoding of scaffolds-induced suture mesenchyme regeneration

Precise orchestration of cell fate determination underlies the success of scaffold-based skeletal regeneration. Despite extensive studies on mineralized parenchymal tissue rebuilding, regenerating and maintaining undifferentiated mesenchyme within calvarial bone remain very challenging with limited advances yet. Current knowledge has evidenced the indispensability of rebuilding suture mesenchymal stem cell niches to avoid severe brain or even systematic damage. But to date, the absence of promising therapeutic biomaterials/scaffolds remains. The reason lies in the shortage of fundamental knowledge and methodological evidence to understand the cellular fate regulations of scaffolds. To address these issues, in this study, we systematically investigated the cellular fate determinations and transcriptomic mechanisms by distinct types of commonly used calvarial scaffolds. Our data elucidated the natural processes without scaffold transplantation and demonstrated how different scaffolds altered in vivo cellular responses. A feasible scaffold, polylactic acid electrospinning membrane (PLA), was next identified to precisely control mesenchymal ingrowth and self-renewal to rebuild non-osteogenic suture-like tissue at the defect center, meanwhile supporting proper osteointegration with defect bony edges. Especially, transcriptome analysis and cellular mechanisms underlying the well-orchestrated cell fate determination of PLA were deciphered. This study for the first time cellularly decoded the fate regulations of scaffolds in suture-bony composite defect healing, offering clinicians potential choices for regenerating such complicated injuries.

Preparation of laser microporous porcine acellular dermal matrix and observation of wound transplantation

To prepare a new type of porcine acellular dermis matrix (PADM) with the new laser microporous technique and verify its safety and feasibility. A novel porcine acellular dermis matrix (ADM) was prepared by using sequential combined decellularization of trypsin, neutral protease and SDS solution method and fully rinsed with ultrasonic wave. Specific laser microporous technology was used to prepare the laser micropore porcine acellular dermal matrix (LPADM). SD rats were chose as the animal models and autologous skin was transplanted by one-step method to observe and detect the graft activity, immunogenicity and vascularization degree of the novel PADM. A porcelain white, shiny, soft and elastic dermal matrix was prepared in this study, the results showed low DNA residue and low cytotoxicity. HE staining and SEM observation revealed that the PADM had neither residual cells nor cell fragments, while the collagen bundles were intact and orderly arranged. All the SD rats survived. No infection or skin allergy was found after surgery. None of the animals lost weight. Histological examination showed that the LPADM was fully vascularized with little tissue destruction in the experiment group. Immunohistochemical staining for CD31 showed ideal vascularization in the experiment group, and immunohistochemical staining for TNF-α showed there were no statistical significance of inflammatory reaction in both groups. This study demonstrated that the novel PADM prepared by sequential combined decellularization of trypsin, neutral protease and SDS solution method and new laser microporous technique was effective and safe in animal transplantation.

Surface modification of silica nonwoven fabrics for osteogenesis of bone marrow-derived mesenchymal stem cells

Silica nonwoven fabrics (SNFs) with high mechanical strength and porosity are known to exhibit high cell proliferation and osteogenic differentiation potential of mesenchymal stem cells (MSCs) by morphologically mimicking the extracellular matrix (ECM). To further improve the osteoinductive ability of SNFs, it could be effective to increase the interaction between MSCs and ECM components because exogenous ECM components seem to modulate the fate of MSCs differentiation. In this study, we developed immobilization methods for ECM components, such as collagen, fibronectin, and chondroitin sulphate C on SNFs, to improve cell-matrix interactions and examined their suitability for bone tissue regeneration. Collagen and fibronectin were immobilized via physical adsorption and chondroitin sulphate C was also immobilized by the layer-by-layer method combined with chitosan on SNF surfaces to maintain the high porosity of SNFs. The treated SNFs were characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. In osteogenic differentiation culture, modified SNFs showed significantly increased expression of osteogenic differentiation marker genes compared to unmodified SNFs. These results suggest that the present methods improve cell-matrix interactions and enhance the cellular functions of MSCs. We are convinced that these simple modification techniques for ECM components are effective in functionalizing various 3D fabric scaffolds possessing hydrophilic groups.

Controlling scaffold conductivity and pore size to direct myogenic cell alignment and differentiation

Skeletal muscle's combination of three-dimensional (3D) anisotropy and electrical excitability is critical for enabling normal movement. We previously developed a 3D aligned collagen scaffold incorporating conductive polypyrrole (PPy) particles to recapitulate these key muscle properties and showed that the scaffold facilitated enhanced myotube maturation compared with nonconductive controls. To further optimize this scaffold design, this work assessed the influence of conductive polymer incorporation and scaffold pore architecture on myogenic cell behavior. Conductive PPy and poly(3,4-ethylenedioxythiophene) (PEDOT) particles were synthesized and mixed into a suspension of type I collagen and chondroitin sulfate prior to directional freeze-drying to produce anisotropic scaffolds. Energy dispersive spectroscopy revealed homogenous distribution of conductive PEDOT particles throughout the scaffolds that resulted in a threefold increase in electrical conductivity while supporting similar myoblast metabolic activity compared to nonconductive scaffolds. Control of freezing temperature enabled fabrication of PEDOT-doped scaffolds with a range of pore diameters from 98 to 238 μm. Myoblasts conformed to the anisotropic contact guidance cues independent of pore size to display longitudinal cytoskeletal alignment. The increased specific surface area of the smaller pore scaffolds helped rescue the initial decrease in myoblast metabolic activity observed in larger pore conductive scaffolds while also promoting modestly increased expression levels of the myogenic marker myosin heavy chain (MHC) and gene expression of myoblast determination protein (MyoD). However, cell infiltration to the center of the scaffolds was marginally reduced compared with larger pore variants. Together these data underscore the potential of aligned and PEDOT-doped collagen scaffolds for promoting myogenic cell organization and differentiation.

Directed Regeneration of Osteochondral Tissue by Hierarchical Assembly of Spatially Organized Composite Spheroids

The use of engineered scaffolds or stem cells is investigated widely in the repair of injured musculoskeletal tissue. However, the combined regeneration of hierarchical osteochondral tissue remains a challenge due to delamination between cartilage and subchondral bone or difficulty in spatial control over differentiation of transplanted stem cells. Here, two types of composite spheroids are prepared using adipose-derived stem cells (hADSCs) and nanofibers coated with either transforming growth factor-β3 or bone morphogenetic growth factor-2 for chondrogenesis or osteogenesis, respectively. Each type of spheroid is then cultured within a 3D-printed microchamber in a spatially arranged manner to recapitulate the bilayer structure of osteochondral tissue. The presence of inductive factors regionally modulates in vitro chondrogenic or osteogenic differentiation of hADSCs within the biphasic construct without dedifferentiation. Furthermore, hADSCs from each spheroid proliferate and sprout and successfully connect the two layers mimicking the osteochondral interface without apertures. In vivo transplantation of the biphasic construct onto a femoral trochlear groove defect in rabbit knee joint results in 21.2 ± 2.8% subchondral bone volume/total volume and a cartilage score of 25.0 ± 3.7. The present approach can be an effective therapeutic platform to engineer complex tissue.

Chitosan coatings with distinct innate immune bioactivities differentially stimulate angiogenesis, osteogenesis and chondrogenesis in poly-caprolactone scaffolds with controlled interconnecting pore size

This study tested whether osseous integration into poly (ε-caprolactone) (PCL) bioplastic scaffolds with fully-interconnecting 155 ± 8 μm pores is enhanced by an adhesive, non-inflammatory 99% degree of deacetylation (DDA) chitosan coating (99-PCL), or further incorporation of pro-inflammatory 83% DDA chitosan microparticles (83-99-PCL) to accelerate angiogenesis. New Zealand White rabbit osteochondral knee defects were press-fit with PCL, 99-PCL, 83-99-PCL, or allowed to bleed (drill-only). Between day 1 and 6 weeks of repair, drill-only defects repaired by endochondral ossification, with an 8-fold higher bone volume fraction (BVF) versus initial defects, compared to a 2-fold (99-PCL), 1.1-fold (PCL), or 0.4-fold (83-99-PCL) change in BVF. Hematoma innate immune cells swarmed to 83-99-PCL, elicited angiogenesis throughout the pores and induced slight bone resorption. PCL and 99-PCL pores were variably filled with cartilage or avascular mesenchyme near the bone plate, or angiogenic mesenchyme into which repairing trabecular bone infiltrated up to 1 mm deep. More repair cartilage covered the 99-PCL scaffold (65%) than PCL (18%) or 83-99-PCL (0%) (p < 0.005). We report the novel finding that non-inflammatory chitosan coatings promoted cartilage infiltration into and over a bioplastic scaffold, and were compatible with trabecular bone integration. This study also revealed that in vitro osteogenesis assays have limited ability to predict osseous integration into porous scaffolds, because (1) in vivo, woven bone integrates from the leading edge of regenerating trabecular bone and not from mesenchymal cells adhering to scaffold surfaces, and (2) bioactive coatings that attract inflammatory cells induce bone resorption.

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Porous polycaprolactone scaffolds elicited drawn-out osteochondral wound repair.

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Regenerating trabecular bone only infiltrated angiogenic mesenchyme free of inflammatory cells.

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83% DDA chitosan stimulated sterile inflammatory angiogenesis and trabecular bone resorption.

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99% DDA chitosan coatings promoted chondrogenesis inside and over the PCL articular surface.

Recent advances in chitosan-based layer-by-layer biomaterials and their biomedical applications

In recent years, chitosan-based biomaterials have been continually and extensively researched by using layer-by-layer (LBL) assembly, due to their potentials in biomedicine. Various chitosan-based LBL materials have been newly developed and applied in different areas along with the development of technologies. This work reviews the recent advances of chitosan-based biomaterials produced by LBL assembly. Driving forces of LBL, for example electrostatic interactions, hydrogen bond as well as Schiff base linkage have been discussed. Various forms of chitosan-based LBL materials such as films/coatings, capsules and fibers have been reviewed. The applications of these biomaterials in the field of antimicrobial applications, drug delivery, wound dressings and tissue engineering have been comprehensively reviewed.

Characterization of Tissue Scaffolds Using Synchrotron Radiation Microcomputed Tomography Imaging

Distinguishing from other traditional imaging, synchrotron radiation microcomputed tomography (SR-μCT) imaging allows for the visualization of three-dimensional objects of interest in a nondestructive and/or in situ way with better spatial resolution, deep penetration, relatively fast speed, and/or high contrast. SR-μCT has been illustrated promising for visualizing and characterizing tissue scaffolds for repairing or replacing damaged tissue or organs in tissue engineering (TE), which is of particular advance for longitudinal monitoring and tracking the success of scaffolds once implanted in animal models and/or human patients. This article presents a comprehensive review on recent studies of characterization of scaffolds based on SR-μCT and takes scaffold architectural properties, mechanical properties, degradation, swelling and wettability, and biological properties as five separate sections to introduce SR-μCT wide applications. We also discuss and highlight the unique opportunities of SR-μCT in various TE applications; conclude this article with the suggested future research directions, including the prospective applications of SR-μCT, along with its challenges and methods for improvement in the field of TE.

Trends in 3D bioprinting for esophageal tissue repair and reconstruction

In esophageal pathologies, such as esophageal atresia, cancers, caustic burns, or post-operative stenosis, esophageal replacement is performed by using parts of the gastrointestinal tract to restore nutritional autonomy. However, this surgical procedure most often does not lead to complete functional recovery and is instead associated with many complications resulting in a decrease in the quality of life and survival rate. Esophageal tissue engineering (ETE) aims at repairing the defective esophagus and is considered as a promising therapeutic alternative. Noteworthy progress has recently been made in the ETE research area but strong challenges remain to replicate the structural and functional integrity of the esophagus with the approaches currently being developed. Within this context, 3D bioprinting is emerging as a new technology to facilitate the patterning of both cellular and acellular bioinks into well-organized 3D functional structures. Here, we present a comprehensive overview of the recent advances in tissue engineering for esophageal reconstruction with a specific focus on 3D bioprinting approaches in ETE. Current biofabrication techniques and bioink features are highlighted, and these are discussed in view of the complexity of the native esophagus that the designed substitute needs to replace. Finally, perspectives on recent strategies for fabricating other tubular organ substitutes via 3D bioprinting are discussed briefly for their potential in ETE applications.

Multi-layered polydopamine coatings for the immobilization of growth factors onto highly-interconnected and bimodal PCL/HA-based scaffolds

For bone tissue engineering applications, scaffolds that mimic the porous structure of the extracellular matrix are highly desirable. Herein, we employ a PCL/HA-based scaffold with a double-scaled architecture of small pores coupled to larger ones. To improve the osteoinductivity of the scaffold, we incorporate two different growth factors via polydopamine (PDA) coating. As a first step, we identify the maximum amount of PDA that can be deposited onto the scaffold. Next, to allow for the deposition of a second PDA layer which, in turn, will allow to increase the loading of growth factors, we incorporate a dithiol connecting layer. The thiol groups covalently react with the first PDA coating through Michael addition while also allowing for the incorporation of a second PDA layer. We load the first and second PDA layers with bone morphogenic protein-2 (BMP2) and vascular endothelial growth factor (VEGF), respectively, and evaluate the osteogenic potential of the functionalised scaffold by cell viability, alkaline phosphatase activity and the expression of three different osteogenesis-related genes of pre-seeded human mesenchymal stem cells. Through these studies, we demonstrate that the osteogenic activity of the scaffolds loaded with both BMP2 and VEGF is greater than scaffolds loaded only with BMP2. Importantly, the osteoinductivity is higher when the scaffolds are loaded with BMP2 and VEGF in two different PDA layers. Taken together, these results indicate that the as-prepared scaffolds could be a useful construct for bone-tissue applications.

Impedance-Based Monitoring of Mesenchymal Stromal Cell Three-Dimensional Proliferation Using Aerosol Jet Printed Sensors: A Tissue Engineering Application

One of the main hurdles to improving scaffolds for regenerative medicine is the development of non-invasive methods to monitor cell proliferation within three-dimensional environments. Recently, an electrical impedance-based approach has been identified as promising for three-dimensional proliferation assays. A low-cost impedance-based solution, easily integrable with multi-well plates, is here presented. Sensors were developed using biocompatible carbon-based ink on foldable polyimide substrates by means of a novel aerosol jet printing technique. The setup was tested to monitor the proliferation of human mesenchymal stromal cells into previously validated gelatin-chitosan hybrid hydrogel scaffolds. Reliability of the methodology was assessed comparing variations of the electrical impedance parameters with the outcomes of enzymatic proliferation assay. Results obtained showed a magnitude increase and a phase angle decrease at 4 kHz (maximum of 2.5 kΩ and -9 degrees) and an exponential increase of the modeled resistance and capacitance components due to the cell proliferation (maximum of 1.5 kΩ and 200 nF). A statistically significant relationship with enzymatic assay outcomes could be detected for both phase angle and electric model parameters. Overall, these findings support the potentiality of this non-invasive approach for continuous monitoring of scaffold-based cultures, being also promising in the perspective of optimizing the scaffold-culture system.

Regenerative and engineered options for urethroplasty

Surgical correction of urethral strictures by substitution urethroplasty - the use of grafts or flaps to correct the urethral narrowing - remains one of the most challenging procedures in urology and is frequently associated with complications, restenosis and poor quality of life for the affected individual. Tissue engineering using different cell types and tissue scaffolds offers a promising alternative for tissue repair and replacement. The past 30 years of tissue engineering has resulted in the development of several therapies that are now in use in the clinic, especially in treating cutaneous, bone and cartilage defects. Advances in tissue engineering for urethral replacement have resulted in several clinical applications that have shown promise but have not yet become the standard of care.

Biomimetic Designer Scaffolds Made of D,L-Lactide-ɛ-Caprolactone Polymers by 2-Photon Polymerization

IMPACT STATEMENT

In tissue engineering (TE), the establishment of cell targeting materials, which mimic the conditions of the physiological extracellular matrix (ECM), seems to be a mission impossible without advanced materials and fabrication techniques. With this in mind we established a toolbox based on (D,L)-lactide-ɛ-caprolactone methacrylate (LCM) copolymers in combination with a nano-micromaskless lithography technique, the two-photon polymerization (2-PP) to mimic the hierarchical structured and complex milieu of the natural ECM. To demonstrate the versatility of this toolbox, we choose two completely different application scenarios in bone and tumor TE to show the high potential of this concept in therapeutic and diagnostic application.

3D gelatin-chitosan hybrid hydrogels combined with human platelet lysate highly support human mesenchymal stem cell proliferation and osteogenic differentiation

Bone marrow and adipose tissue human mesenchymal stem cells were seeded in highly performing 3D gelatin–chitosan hybrid hydrogels of varying chitosan content in the presence of human platelet lysate and evaluated for their proliferation and osteogenic differentiation. Both bone marrow and adipose tissue human mesenchymal stem cells in gelatin–chitosan hybrid hydrogel 1 (chitosan content 8.1%) or gelatin–chitosan hybrid hydrogel 2 (chitosan 14.9%) showed high levels of viability (80%–90%), and their proliferation and osteogenic differentiation was significantly higher with human platelet lysate compared to fetal bovine serum, particularly in gelatin–chitosan hybrid hydrogel 1. Mineralization was detected early, after 21 days of culture, when human platelet lysate was used in the presence of osteogenic stimuli. Proteomic characterization of human platelet lysate highlighted 59 proteins mainly involved in functions related to cell adhesion, cellular repairing mechanisms, and regulation of cell differentiation. In conclusion, the combination of our gelatin–chitosan hybrid hydrogels with hPL represents a promising strategy for bone regenerative medicine using human mesenchymal stem cells.

Design of spherically structured 3D in vitro tumor models -Advances and prospects

Three-dimensional multicellular tumor models are receiving an ever-growing focus as preclinical drug-screening platforms due to their potential to recapitulate major physiological features of human tumors in vitro. In line with this momentum, the technologies for assembly of 3D microtumors are rapidly evolving towards a comprehensive inclusion of tumor microenvironment elements. Customized spherically structured platforms, including microparticles and microcapsules, provide a robust and scalable technology to imprint unique biomolecular tumor microenvironment hallmarks into 3D in vitro models. Herein, a comprehensive overview of novel advances on the integration of tumor-ECM components and biomechanical cues into 3D in vitro models assembled in spherical shaped platforms is provided. Future improvements regarding spatiotemporal/mechanical adaptability, and degradability, during microtumors in vitro 3D culture are also critically discussed considering the realistic potential of these platforms to mimic the dynamic tumor microenvironment. From a global perspective, the production of 3D multicellular spheroids with tumor ECM components included in spherical models will unlock their potential to be used in high-throughput screening of therapeutic compounds. It is envisioned, in a near future, that a combination of spherically structured 3D microtumor models with other advanced microfluidic technologies will properly recapitulate the flow dynamics of human tumors in vitro.

STATEMENT OF SIGNIFICANCE

The ability to correctly mimic the complexity of the tumor microenvironment in vitro is a key aspect for the development of evermore realistic in vitro models for drug-screening and fundamental cancer biology studies. In this regard, conventional spheroid-based 3D tumor models, combined with spherically structured biomaterials, opens the opportunity to precisely recapitulate complex cell-extracellular matrix interactions and tumor compartmentalization. This review provides an in-depth focus on current developments regarding spherically structured scaffolds engineered into in vitro 3D tumor models, and discusses future advances toward all-encompassing platforms that may provide an improved in vitro/in vivo correlation in a foreseeable future.

Three-dimensional printed polycaprolactone-microcrystalline cellulose scaffolds

Microcrystalline cellulose (MCC) is proposed in this study as an additive in polycaprolactone (PCL) matrices to obtain three-dimensional (3D) printed scaffolds with improved mechanical and biological properties. Improving the mechanical behavior and the biological performance of polycaprolactone-based scaffolds allows to increase the potential of these structures for bone tissue engineering. Different groups of samples were evaluated in order to analyze the effect of the additive in the properties of the PCL matrix. The concentrations of MCC in the groups of samples were 0, 2, 5, and 10% (w/w). These combinations were subjected to a thermogravimetric analysis in order to evaluate the influence of the additive in the thermal properties of the composites. 3D printed scaffolds were manufactured with a commercial 3D printer based on fused deposition modelling. The operation conditions have been established in order to obtain scaffolds with a 0/90° pattern with pore sizes between 450 and 500 µm and porosity values between 50 and 60%. The mechanical properties of these structures were measured in the compression and flexural modes. The scaffolds containing 2 and 5% MCC have higher flexural and compression elastic modulus, although those containing 10% do not show this reinforcement effect. On the other hand, the proliferation of sheep bone marrow cells on the proposed scaffolds was evaluated over 8 days. The results show that the proliferation is significantly better (p < 0.05) on the group of samples containing 2% MCC. Therefore, these scaffolds (PCL:MCC 98:2) have suitable properties to be further evaluated for bone tissue engineering applications. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2018. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 521-528, 2019.

Cationic osteogenic peptide P15-CSP coatings promote 3-D osteogenesis in poly(epsilon-caprolactone) scaffolds of distinct pore size

P15-CSP is a biomimetic cationic fusion peptide that stimulates osteogenesis and inhibits bacterial biofilm formation when coated on 2-D surfaces. This study tested the hypothesis that P15-CSP coatings enhance 3-D osteogenesis in a porous but otherwise hydrophobic poly-(ɛ-caprolactone) (PCL) scaffold. Scaffolds of 84 µm and 141 µm average pore size were coated or not with Layer-by-Layer polyelectrolytes followed by P15-CSP, seeded with adult primary human mesenchymal stem cells (MSCs), and cultured 10 days in proliferation medium, then 21 days in osteogenic medium. Atomic analyses showed that P15-CSP was successfully captured by LbL. After 2 days of culture, MSCs adhered and spread more on P15-CSP coated pores than PCL-only. At day 10, all constructs contained nonmineralized tissue. At day 31, all constructs became enveloped in a "skin" of tissue that, like 2-D cultures, underwent sporadic mineralization in areas of high cell density that extended into some 141 µm edge pores. By quantitative histomorphometry, 2.5-fold more tissue and biomineral accumulated in edge pores versus inner pores. P15-CSP specifically promoted tissue-scaffold integration, fourfold higher overall biomineralization, and more mineral deposits in the outer 84 µm and inner 141 µm pores than PCL-only (p < 0.05). 3-D Micro-CT revealed asymmetric mineral deposition consistent with histological calcium staining. This study provides proof-of-concept that P15-CSP coatings are osteoconductive in PCL pore surfaces with 3-D topography. Biomineralization deeper than 150 µm from the scaffold edge was optimally attained with the larger 141 µm peptide-coated pores. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2171-2181, 2017.