Platform technologies for tubular organ regeneration

Preparation of a Cellulosic Photosensitive Hydrogel for Tubular Tissue Engineering

Since the concept of tissue engineering was proposed, biocompatible hydrogel materials have attracted the attention of researchers. With the help of three-dimensional (3D) printing technology, precise shaping of hydrogels can be realized. In this paper, we synthesized a cellulosic photosensitive acrylamide (AM)/N,N-methylenebisacrylamide (MBA) hydrogel. With the high-efficiency water-soluble photoinitiator TPO@Tw developed by our research group, the efficient photocuring cross-linking process of the hydrogel can be realized under 405 nm visible light. In consideration of the viscosity, curing mass, curing depth, and break distance of the hydrogel, we screened out hydroxypropyl cellulose (HPC) as the preferred tackifier of the material. The addition of HPC greatly improved the mechanical properties of the hydrogel. The compressive modulus of the optimal sample AM-HPC-5 increased by 709.2% and the tensile strength increased by 76.7% compared with the blank control group. By adding a PEGDA shell to the surface of the material, the water retention capacity of the hydrogel was effectively improved. The water loss rate was greatly reduced. The 3D wooden-pile structure model was printed by a DIW 3D printer. Further, through coaxial extrusion, the microtubule structure that may be applied in tissue engineering was obtained. Cell experiment results showed high biocompatibility of the hydrogel. NIH 3T3 cells could adhere and grow on the surface of microtubules.

Recent Advances in Hydroxyapatite-Based Biocomposites for Bone Tissue Regeneration in Orthopedics

Bone tissue is a nanocomposite consisting of an organic and inorganic matrix, in which the collagen component and the mineral phase are organized into complex and porous structures. Hydroxyapatite (HA) is the most used ceramic biomaterial since it mimics the mineral composition of the bone in vertebrates. However, this biomimetic material has poor mechanical properties, such as low tensile and compressive strength, which make it not suitable for bone tissue engineering (BTE). For this reason, HA is often used in combination with different polymers and crosslinkers in the form of composites to improve their mechanical properties and the overall performance of the implantable biomaterials developed for orthopedic applications. This review summarizes recent advances in HA-based biocomposites for bone regeneration, addressing the most widely employed inorganic matrices, the natural and synthetic polymers used as reinforcing components, and the crosslinkers added to improve the mechanical properties of the scaffolds. Besides presenting the main physical and chemical methods in tissue engineering applications, this survey shows that HA biocomposites are generally biocompatible, as per most in vitro and in vivo studies involving animal models and that the results of clinical studies on humans sometimes remain controversial. We believe this review will be helpful as introductory information for scientists studying HA materials in the biomedical field.

Identification of functional pathways for regenerative bioactivity of selected renal cells

Background

Selected renal cells (SRC) are in Phase II clinical trials as a kidney-sourced, autologous, tubular epithelial cell-enriched cell-based therapy for chronic kidney disease (CKD). In preclinical studies with rodent models of CKD, SRC have been shown to positively modulate key renal biomarkers associated with development of the chronic disease condition.

Methods

A comparative bioinformatic analysis of transcripts specifically enriched or depleted in SRC component sub-populations relative to the initial, biopsy-derived cell source was conducted.

Results

Outcomes associated with therapeutically relevant bioactivity from a systematic, genome-wide transcriptomic profiling of rodent SRC are reported. Key transcriptomic networks and concomitant signaling pathways that may underlie SRC mechanism of action as manifested by reparative, restorative, and regenerative bioactivity in rodent models of chronic kidney disease are identified. These include genes and gene networks associated with cell cycle control, transcriptional control, inflammation, ECM–receptor interaction, immune response, actin polymerization, regeneration, cell adhesion, and morphogenesis.

Conclusions

These data indicate that gene networks associated with development of the kidney are also leveraged for SRC regenerative bioactivity, providing evidence of potential mechanisms of action.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02713-6.

Integrated 3D Printing-Based Framework-A Strategy to Fabricate Tubular Structures with Mechanocompromised Hydrogels

Several hollow organs perform various crucial functions in the body and must be replaced, repaired, or augmented in many disease conditions. Fabrication of tissue analogues to these hollow organs is incredibly challenging. Still, recent advancements in biofabrication have allowed researchers to pursue the development of several hollow organs such as blood vessels, esophagus, trachea, urethra, and others. Materials like collagen, alginate, elastin, silk, fibrin, etc., have been predominantly used for organ development. However, the focus has been duly shifted toward decellularized extracellular matrix (dECM) to develop tissue-specific hydrogels because they provide relevant biochemical cues to promote cellular activity. Still, the dECM-based hydrogels are mechanically weak to fabricate self-supporting tubular structures. Here, an innovative approach using the stereolithography apparatus (SLA) 3D printed framework has been implemented to achieve a self-supporting tubular structure using caprine esophagus muscle dECM hydrogel. A significant improvement in the mechanical stability of the biofabricated tissue has been observed within 7 days of culture. Interestingly, the encapsulated L929 mouse fibroblasts transdifferentiated into myofibroblasts because of the cues provided by the muscle dECM. Overall, the potential of an SLA-based 3D printing strategy to fabricate frameworks, especially for fabricating tubular organs/tissues using mechanocompromised hydrogel, has been demonstrated here.

Fabrication of a dual-layer cell-laden tubular scaffold for nerve regeneration and bile duct reconstruction

Tubular scaffolds serve as a controllable extracellular environment to guide the repair and regeneration of tissues. But it is still a challenge to achieve both excellent mechanical properties and cell compatibility of artificial scaffolds for long-term structural and biological stability. In this study, a four-step solution casting method was developed to fabricate dual-layer cell-laden tubular scaffolds for nerve and bile duct regeneration. The dual-layer tubular scaffold consisted of a bone marrow mesenchymal stem cells (BMSCs)-laden hydrogel inner layer and an outer layer of gelatin methacrylate (GelMA)/polyethylene glycol diacrylate. While the inner layer had a good biocompatibility, the outer layer had desired mechanical properties. The interfacial toughness, Young's modulus, maximum tensile strain, and compressive modulus of dual-layer tubular scaffolds were 65 J m^-2, 122.37 ± 23.21 kPa, 100.87 ± 40.10%, and 39.14 ± 18.56 N m^-1, respectively. More importantly, the fabrication procedure was very cell-friendly, since the BMSC viability encapsulated in the inner layer of 10% (w/v) GelMA reached 94.68 ± 0.43% after 5 d of culture. Then, a preliminary evaluation of the potential application of dual-layer tubular scaffolds as nerve conduits and biliary scaffolds was performed, and demonstrated that the cell-laden dual-layer tubular scaffolds proposed in this work are expected to extend the application of tubular scaffolds in tissue engineering.

One-Step Formation of Protein-Based Tubular Structures for Functional Devices and Tissues

Tubular biological structures consisting of extracellular matrix (ECM) proteins and cells are basic functional units of all organs in animals and humans. ECM protein solutions at low concentrations (5-10 milligrams per milliliter) are abundantly used in 3D cell culture. However, their poor "printability" and minute-long gelation time have made the direct extrusion of tubular structures in bioprinting applications challenging. Here, this limitation is overcome and the continuous, template-free conversion of low-concentration collagen, elastin, and fibrinogen solutions into tubular structures of tailored size and radial, circumferential and axial organization is demonstrated. The approach is enabled by a microfabricated printhead for the consistent circumferential distribution of ECM protein solutions and lends itself to scalable manufacture. The attached confinement accommodates minute-long residence times for pH, temperature, light, ionic and enzymatic gelation. Chip hosted ECM tubular structures are amenable to perfusion with aqueous solutions and air, and cyclic stretching. Predictive collapse and reopening in a crossed-tube configuration promote all-ECM valves and pumps. Tissue level function is demonstrated by factors secreted from cells embedded within the tube wall, as well as endothelial or epithelial barriers lining the lumen. The described approaches are anticipated to find applications in ECM-based organ-on-chip and biohybrid structures, hydraulic actuators, and soft machines.

Biofabrication of a Functional Tubular Construct from Tissue Spheroids Using Magnetoacoustic Levitational Directed Assembly

In traditional tissue engineering, synthetic or natural scaffolds are usually used as removable temporal support, which involves some biotechnology limitations. The concept of "scaffield" approach utilizing the physical fields instead of biomaterial scaffold has been proposed recently. In particular, a combination of intense magnetic and acoustic fields can enable rapid levitational bioassembly of complex-shaped 3D tissue constructs from tissue spheroids at low concentration of paramagnetic agent (gadolinium salt) in the medium. In the current study, the tissue spheroids from human bladder smooth muscle cells (myospheres) are used as building blocks for assembling the tubular 3D constructs. Levitational assembly is accomplished at low concentrations of gadolinium salts in the high magnetic field at 9.5 T. The biofabricated smooth muscle constructs demonstrate contraction after the addition of vasoconstrictive agent endothelin-1. Thus, hybrid magnetoacoustic levitational bioassembly is considered as a new technology platform in the emerging field of formative biofabrication. This novel technology of scaffold-free, nozzle-free, and label-free bioassembly opens a unique opportunity for rapid biofabrication of 3D tissue and organ constructs with complex geometry.

Artificial Intelligence and Machine Learning in Computational Nanotoxicology: Unlocking and Empowering Nanomedicine

Advances in nanomedicine, coupled with novel methods of creating advanced materials at the nanoscale, have opened new perspectives for the development of healthcare and medical products. Special attention must be paid toward safe design approaches for nanomaterial-based products. Recently, artificial intelligence (AI) and machine learning (ML) gifted the computational tool for enhancing and improving the simulation and modeling process for nanotoxicology and nanotherapeutics. In particular, the correlation of in vitro generated pharmacokinetics and pharmacodynamics to in vivo application scenarios is an important step toward the development of safe nanomedicinal products. This review portrays how in vitro and in vivo datasets are used in in silico models to unlock and empower nanomedicine. Physiologically based pharmacokinetic (PBPK) modeling and absorption, distribution, metabolism, and excretion (ADME)-based in silico methods along with dosimetry models as a focus area for nanomedicine are mainly described. The computational OMICS, colloidal particle determination, and algorithms to establish dosimetry for inhalation toxicology, and quantitative structure-activity relationships at nanoscale (nano-QSAR) are revisited. The challenges and opportunities facing the blind spots in nanotoxicology in this computationally dominated era are highlighted as the future to accelerate nanomedicine clinical translation.

3D Bioprinting Strategies for the Regeneration of Functional Tubular Tissues and Organs

It is difficult to fabricate tubular-shaped tissues and organs (e.g., trachea, blood vessel, and esophagus tissue) with traditional biofabrication techniques (e.g., electrospinning, cell-sheet engineering, and mold-casting) because these have complicated multiple processes. In addition, the tubular-shaped tissues and organs have their own design with target-specific mechanical and biological properties. Therefore, the customized geometrical and physiological environment is required as one of the most critical factors for functional tissue regeneration. 3D bioprinting technology has been receiving attention for the fabrication of patient-tailored and complex-shaped free-form architecture with high reproducibility and versatility. Printable biocomposite inks that can facilitate to build tissue constructs with polymeric frameworks and biochemical microenvironmental cues are also being actively developed for the reconstruction of functional tissue. In this review, we delineated the state-of-the-art of 3D bioprinting techniques specifically for tubular tissue and organ regeneration. In addition, this review described biocomposite inks, such as natural and synthetic polymers. Several described engineering approaches using 3D bioprinting techniques and biocomposite inks may offer beneficial characteristics for the physiological mimicry of human tubular tissues and organs.

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

Despite recent developments in the tracheal tissue engineering field, the creation of a patient specific substitute possessing both appropriate mechanical and biointerfacial properties remains challenging. Most tracheal replacement therapies fail due to restenosis at the anastomosis site. In this study, we designed a robust, biodegradable, 3D tubular scaffold by combining electrospinning (ELSP) and 3D (three-dimensional) printing techniques for use in transplantation therapy. After that, we loaded dexamethasone (DEX) onto the 3D tubular scaffold using mild surface modification reactions by using polydopamine (PDA), polyethyleneimine (PEI), and carboxymethyl-β-cyclodextrin (βCD). As a result, the fabricated 3D tubular scaffold had robust mechanical properties and the chemical modifications were confirmed to have proceeded successfully by physico-chemical analysis. The surface treatments allowed for a larger amount of DEX to be loaded onto the βCD modified scaffold as compared to the bare group. In vitro and in vivo studies demonstrated that the DEX loaded 3D tubular scaffold exhibited significantly enhanced anti-inflammation activity, enhanced tracheal mucosal regeneration, and formation of a patent airway. From our results, we believe that our system may represent an innovative paradigm in tracheal tissue engineering by providing proper mechanical properties and successful formation of tracheal tissue as a means of remodeling and healing tracheal defects for use in transplantation therapy.

3D biofabrication for tubular tissue engineering

The therapeutic replacement of diseased tubular tissue is hindered by the availability and suitability of current donor, autologous and synthetically derived protheses. Artificially created, tissue engineered, constructs have the potential to alleviate these concerns with reduced autoimmune response, high anatomical accuracy, long-term patency and growth potential. The advent of 3D bioprinting technology has further supplemented the technological toolbox, opening up new biofabrication research opportunities and expanding the therapeutic potential of the field. In this review, we highlight the challenges facing those seeking to create artificial tubular tissue with its associated complex macro- and microscopic architecture. Current biofabrication approaches, including 3D printing techniques, are reviewed and future directions suggested.

Concise Review: Biomimetic Functionalization of Biomaterials to Stimulate the Endogenous Healing Process of Cartilage and Bone Tissue

Musculoskeletal reconstruction is an ongoing challenge for surgeons as it is required for one out of five patients undergoing surgery. In the past three decades, through the close collaboration between clinicians and basic scientists, several regenerative strategies have been proposed. These have emerged from interdisciplinary approaches that bridge tissue engineering with material science, physiology, and cell biology. The paradigm behind tissue engineering is to achieve regeneration and functional recovery using stem cells, bioactive molecules, or supporting materials. Although plenty of preclinical solutions for bone and cartilage have been presented, only a few platforms have been able to move from the bench to the bedside. In this review, we highlight the limitations of musculoskeletal regeneration and summarize the most relevant acellular tissue engineering approaches. We focus on the strategies that could be most effectively translate in clinical practice and reflect on contemporary and cutting‐edge regenerative strategies in surgery. Stem Cells Translational Medicine2017;6:2186–2196

Evaluation of different crosslinking agents on hybrid biomimetic collagen-hydroxyapatite composites for regenerative medicine

This study focuses on the development of novel bone-like scaffolds by bio-inspired, pH-driven, mineralization of type I collagen matrix with magnesium-doped hydroxyapatite nanophase (MgHA/Coll). To this aim, this study evaluates the altered modifications in the obtained composite due to different crosslinkers such as dehydrothermal treatment (DHT), 1,4-butanediol diglycidyl ether (BDDGE) and ribose in terms of morphological, physical-chemical and biological properties. The physical-chemical properties of the composites evaluated by XRD, FTIR, ICP and TGA demonstrated that the chemical mimesis of bone was effectively achieved using the in-lab biomineralization process. Furthermore, the presence of various crosslinkers greatly promoted beneficial enzymatic resistivity and swelling ability. The morphological results revealed highly porous and fibrous micro-architecture with total porosity above 85% with anisotropic pore size within the range of 50-200μm in all the analysed composites. The mechanical behaviour in response to compressive forces demonstrated enhanced compressive modulus in all crosslinked composites, suggesting that mechanical behaviour is largely dependent on the type of crosslinker used. The biomimetic compositional and morphological features of the composites elicited strong cell-material interaction. Therefore, the results showed that by activating specific crosslinking mechanisms, hybrid composites can be designed and tailored to develop tissue-specific biomimetic biomaterials for hard tissue engineering.

Vacuum-assisted decellularization: an accelerated protocol to generate tissue-engineered human tracheal scaffolds

Patients with large tracheal lesions unsuitable for conventional endoscopic or open operations may require a tracheal replacement but there is no present consensus of how this may be achieved. Tissue engineering using decellularized or synthetic tracheal scaffolds offers a new avenue for airway reconstruction. Decellularized human donor tracheal scaffolds have been applied in compassionate-use clinical cases but naturally derived extracellular matrix (ECM) scaffolds demand lengthy preparation times. Here, we compare a clinically applied detergent-enzymatic method (DEM) with an accelerated vacuum-assisted decellularization (VAD) protocol. We examined the histological appearance, DNA content and extracellular matrix composition of human donor tracheae decellularized using these techniques. Further, we performed scanning electron microscopy (SEM) and biomechanical testing to analyze decellularization performance. To assess the biocompatibility of scaffolds generated using VAD, we seeded scaffolds with primary human airway epithelial cells in vitro and performed in vivo chick chorioallantoic membrane (CAM) and subcutaneous implantation assays. Both DEM and VAD protocols produced well-decellularized tracheal scaffolds with no adverse mechanical effects and scaffolds retained the capacity for in vitro and in vivo cellular integration. We conclude that the substantial reduction in time required to produce scaffolds using VAD compared to DEM (approximately 9 days vs. 3–8 weeks) does not compromise the quality of human tracheal scaffold generated. These findings might inform clinical decellularization techniques as VAD offers accelerated scaffold production and reduces the associated costs.

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.

Selected renal cells modulate disease progression in rodent models of chronic kidney disease via NF-κB and TGF-β1 pathways

AIM

Identification of mechanistic pathways for selected renal cell (SRC) therapeutic bioactivity in rodent models of chronic kidney disease.

MATERIALS & METHODS

In vivo and in vitro functional bioassays applied to investigate regenerative outcomes associated with delivery of SRC to diseased rodent kidney.

RESULTS

In vivo, SRC reduces chronic infiltration by monocytes/macrophages. SRC attenuates NF-κB and PAI-1 responses while simultaneously promoting host tubular cell expansion through trophic cues. In vitro, SRC-derived conditioned media attenuates TNF-α-induced NF-κB response, TGF-β-mediated PAI-1 response and increases expression of transcripts associated with cell cycle regulation. Observed bioactive responses were from vesicle and nonvesicle-associated factors, including specific miRNAs.

CONCLUSION

We identify a paracrine mechanism for SRC immunomodulatory and trophic cues on host renal tissues, catalyzing long-term functional benefits in vivo.

Cell-based therapeutic products: potency assay development and application

Potency is a critical quality attribute of biological products, defined by the US FDA as the specific ability or capacity of the product, as indicated by appropriate laboratory tests or by adequately controlled clinical data obtained through the administration of the product in the manner intended, to effect a given result. Ideally, a potency assay will leverage the product's mechanism of action. Alternatively, the assay may focus on a therapeutically relevant biological activity. The absence of rigorous mechanistic data for the majority of cell-based therapeutics currently in the process research pipeline has impeded efforts to design and validate indices of product potency. Development of a systematic battery of parallel functional assays that, taken together, can address all potential mechanisms of action believed to be relevant for the product platform is recommended. Such an approach is especially important during preclinical development. Here, we summarize the principal and unique challenges facing the development of functionally relevant and rigorous potency assays for cell-based therapeutics. We present perspectives regarding potency assay development for these products as illustrated by our experiences in process R&D of cryopreserved hepatocytes (Incara Pharmaceuticals) and selected renal cells (Tengion).

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

Children suffer from damaged or loss of hollow organs i.e. trachea, oesophagus or arteries from birth defects or diseases. Generally these organs possess an outer matrix consisting of collagen, elastin, and cells such as smooth muscle cells (SMC) and a luminal layer consisting of endothelial or epithelial cells, whilst presenting a barrier to luminal content. Tissue engineering research enables the construction of such organs and this study explores this possibility with a bioabsorbable nanocomposite biomaterial, polyhedral oligomeric silsesquioxane poly(ε-caprolactone) urea urethane (POSS-PCL).Our established methods of tubular graft extrusion were modified using a porogen-incorporated POSS-PCL and a new lamination method was explored. Porogen (40, 60 or 105 µm) were introduced to POSS-PCL, which were fabricated into a bilayered, dual topography matching the exterior and luminal interior of tubular organs. POSS-PCL with different amounts of porogen were tested for their suitability as a SMC layer by measuring optimal interactions with human adipose derived stem cells. Angiogenesis potential was tested with the chorioallantoic membrane assay. Tensile strength and burst pressures of bilayared tubular grafts were determined. Scaffolds made with 40 µm porogen demonstrated optimal adipose derived stem cell integration and the scaffolds were able to accommodate angiogenesis. Mechanical properties of the grafts confirmed their potential to match the relevant physiological and biophysical parameters. This study presents a platform for the development of hollow organs for transplantation based on POSS-PCL. These bilayered-tubular structures can be tailor-made for cellular integration and match physico-mechanical properties of physiological systems of interest. More specific luminal cell integration and sources of SMC for the external layer could be further explored.

Fabrication of a myocardial patch with cells differentiated from human-induced pluripotent stem cells

The incidence of cardiovascular disease represents a significant and growing health-care challenge to the developed and developing world. The ability of native heart muscle to regenerate in response to myocardial infarct is minimal. Tissue engineering and regenerative medicine approaches represent one promising response to this difficulty. Here, we present methods for the construction of a cell-seeded cardiac patch with the potential to promote regenerative outcomes in heart muscle with damage secondary to myocardial infarct. This method leverages iPS cells and a fibrin-based scaffold to create a simple and commercially viable tissue-engineered cardiac patch. Human-induced pluripotent stem cells (hiPSCs) can, in principle, be differentiated into cells of any lineage. However, most of the protocols used to generate hiPSC-derived endothelial cells (ECs) and cardiomyocytes (CMs) are unsatisfactory because the yield and phenotypic stability of the hiPSC-ECs are low, and the hiPSC-CMs are often purified via selection for expression of a promoter-reporter construct. In this chapter, we describe an hiPSC-EC differentiation protocol that generates large numbers of stable ECs and an hiPSC-CM differentiation protocol that does not require genetic manipulation, single-cell selection, or sorting with fluorescent dyes or other reagents. We also provide a simple but effective method that can be used to combine hiPSC-ECs and hiPSC-CMs with hiPSC-derived smooth muscle cells to engineer a contracting patch of cardiac cells.

Preclinical biosafety evaluation of cell-based therapies: emerging global paradigms

Cell-based therapies have the potential to treat a diversity of disease conditions, many representing significant and long-standing unmet medical needs. Certain properties of cell-based therapies, such as differentiation potential and proliferative potential, present safety concerns uniquely distinct from those of small molecule drugs and other macromolecule biologics. These cellular products carry risks associated with localized host tissue response, long-term persistence, ectopic tissue formation, differentiation to undesirable cell and tissue types, uncontrollable biodistribution, tumorigenicity, and immunogenicity. Such risks are generally evaluated in preclinical animal model studies as part of a comprehensive safety program prior to administration in humans. However, safety assessment for these products can be challenging because of inconsistent approaches to product characterization, inadequately defined product parameters that anticipate adverse events, and the lack of standardized approaches in evaluating in vivo host responses. In this symposium, we introduced cell-based therapies as an emerging product class to the Society of Toxicologic Pathology (STP) and highlighted key challenges for consideration during product biosafety evaluation.

Regenerative medicine of the gastrointestinal tract

Regenerative biology/tissue engineering offers potential solutions for the repair and augmentation of diseased tissues and organs. Tissue engineering technology platforms currently under development for organ regeneration may function in part by recapitulating key mechanistic and signaling pathways associated with embryonic organogenesis. Temporal observations of observed morphological outcomes from the regeneration of tubular organs provide insights into the mechanisms of action associated with the activation of regenerative pathways in preclinical animal models and humans. These include induction of a neo-blastema, regeneration of laminarily organized mural elements (i.e., lamina propria, sub-mucosa, and muscularis), and formation of context appropriate transitional junctions at the point of anastomosis with other tissue elements. These results provide the foundation for a regenerative technology applicable to hollow organs of the gastrointestinal (GI) tract including esophagus and small intestine. Factors affecting the efficacy of observed regenerative outcomes within the GI tract include the roles of vascularization, innervations, and mesenchymal signaling. These will be discussed in the context of an overall mechanism of adult regeneration potentially applicable by the tissue engineering and regenerative medicine industry for continued development of hollow neo-organ products.

Isolation of smooth muscle cells from bladder for generation of engineered urologic organs

The isolation of smooth muscle cells from bladder tissue is a valuable technique used in cell biology research and tissue engineering. Smooth muscle cells can be used for analysis in many areas including, but not limited to, cell function and genotype experimentation. Smooth muscle cells can also be used in tissue engineering applications for research and/or regenerative medicine. Replacement tissue or tissue for augmentation can be created to stem or remediate problems in the urologic system.

Fabrication of a multi-layer three-dimensional scaffold with controlled porous micro-architecture for application in small intestine tissue engineering

Various methods can be employed to fabricate scaffolds with characteristics that promote cell-to-material interaction. This report examines the use of a novel technique combining compression molding with particulate leaching to create a unique multi-layered scaffold with differential porosities and pore sizes that provides a high level of control to influence cell behavior. These cell behavioral responses were primarily characterized by bridging and penetration of two cell types (epithelial and smooth muscle cells) on the scaffold in vitro. Larger pore sizes corresponded to an increase in pore penetration, and a decrease in pore bridging. In addition, smaller cells (epithelial) penetrated further into the scaffold than larger cells (smooth muscle cells). In vivo evaluation of a multi-layered scaffold was well tolerated for 75 d in a rodent model. This data shows the ability of the components of multi-layered scaffolds to influence cell behavior, and demonstrates the potential for these scaffolds to promote desired tissue outcomes in vivo.

Isolation of urothelial cells from bladder tissue

Presented below is a methodology for the isolation, expansion, and maintenance of urothelial cells derived from human bladder. Such bladder-derived urothelial cells, taken together with bladder or alternately sourced smooth muscle cells, may be complexed with an appropriately shaped biodegradable scaffold to create regenerative constructs capable of seeding formation of new bladder or bladder-like neo-organs upon implantation in human cystectomy patients.

Preparation and evaluation of natural scaffold materials for kidney regenerative applications

Tissue engineering involves the concerted action of biomaterials, cells, and growth factors. Kidney -regeneration relies on the same combination of ingredients. Here, we describe an example of gelatin-based biomaterial preparation and its evaluation in the context of kidney biocompatibility and integration. This biomaterial manufacturing technique is simple, cost-effective, highly reproducible and the in vivo evaluation procedure highly informative on the biocompatibility and regenerative potential of the tested construct.

Epithelial machines of morphogenesis and their potential application in organ assembly and tissue engineering

Sheets of embryonic epithelial cells coordinate their efforts to create diverse tissue structures such as pits, grooves, tubes, and capsules that lead to organ formation. Such cells can use a number of cell behaviors including contractility, proliferation, and directed movement to create these structures. By contrast, tissue engineers and researchers in regenerative medicine seeking to produce organs for repair or replacement therapy can combine cells with synthetic polymeric scaffolds. Tissue engineers try to achieve these goals by shaping scaffold geometry in such a way that cells embedded within these scaffold self-assemble to form a tissue, for instance aligning to synthetic fibers, and assembling native extracellular matrix to form the desired tissue-like structure. Although self-assembly is a dominant process that guides tissue assembly both within the embryo and within artificial tissue constructs, we know little about these critical processes. Here, we compare and contrast strategies of tissue assembly used by embryos to those used by engineers during epithelial morphogenesis and highlight opportunities for future applications of developmental biology in the field of tissue engineering.

The use of regenerative medicine in the management of invasive bladder cancer

Muscle invasive and recurrent nonmuscle invasive bladder cancers have been traditionally treated with a radical cystectomy and urinary diversion. The urinary diversion is generally accomplished through the creation of an incontinent ileal conduit, continent catheterizable reservoir, or orthotopic neobladder utilizing small or large intestine. While radical extirpation of the bladder is often successful from an oncological perspective, there is a significant morbidity associated with enteric interposition within the genitourinary tract. Therefore, there is a great opportunity to decrease the morbidity of the surgical management of bladder cancer through utilization of novel technologies for creating a urinary diversion without the use of intestine. Clinical trials using neourinary conduits (NUC) seeded with autologous smooth muscle cells are currently in progress and may represent a significant surgical advance, potentially eliminating the complications associated with the use of gastrointestinal segments in the urinary reconstruction, simplifying the surgical procedure, and greatly facilitating recovery from cystectomy.

Developmental engineering the kidney: leveraging principles of morphogenesis for renal regeneration

Multiple methodological approaches are currently under active development for application in tissue engineering and regenerative medicine of tubular and solid organs. Most recently, developmental engineering (TE/RM), or the leveraging of embryonic and morphological paradigms to recapitulate aspects of organ development, has been proposed as a strategy for the sequential, iterative de novo assembly of tissues and organs as discrete developmental modules ex vivo, prior to implantation in vivo. In this article, we focus on the kidney to highlight in detail how principles of developmental biology are impacting approaches to TE of this complex solid organ. Ultimately, such methodologies may facilitate the establishment of clinically relevant therapeutic strategies for regeneration of renal structure and function, greatly impacting treatment regimens for chronic kidney disease.

Characterization of the human smooth muscle cell secretome for regenerative medicine

Smooth muscle cells (SMC) play a central role in maintaining the structural and functional integrity of muscle tissue. Little is known about the early in vitro events that guide the assembly of 'bioartificial tissue' (constructs) and recapitulate the key aspects of smooth muscle differentiation and development before surgical implantation. Biomimetic approaches have been proposed that enable the identification of in vitro processes which allow standardized manufacturing, thus improving both product quality and the consistency of patient outcomes. One essential element of this approach is the description of the SMC secretome, that is, the soluble and deposited factors produced within the three-dimensional (3D) extracellular matrix (ECM) microenvironment. In this study, we utilized autologous SMC from multiple tissue types that were expanded ex vivo and generated with a rigorous focus on operational phenotype and genetic stability. The objective of this study was to characterize the spatiotemporal dynamics of the first week of organoid maturation using a well-defined in vitro-like, 3D-engineered scale model of our validated manufacturing process. Functional proteomics was used to identify the topological properties of the networks of interacting proteins that were derived from the SMC secretome, revealing overlapping central nodes related to SMC differentiation and proliferation, actin cytoskeleton regulation, and balanced ECM accumulation. The critical functions defined by the Ingenuity Pathway Analysis included cell signaling, cellular movement and proliferation, and cellular and organismal development. The results confirm the phenotypic and functional similarity of the SMC generated by our platform technology at the molecular level. Furthermore, these data validate the biomimetic approaches that have been established to maintain manufacturing consistency.

Immediate production of a tubular dense collagen construct with bioinspired mechanical properties

The intrinsic complexity of tissues and organs demands tissue engineering approaches that extend beyond planar constructs currently in clinical use. However, the engineering of cylindrical or tubular tissue constructs with a hollow lumen presents significant challenges arising from geometrical and architectural considerations required to tailor biomaterials for tissue and organ repair. Type I collagen is an ideal scaffolding material due to its outstanding biocompatibility and high processability. However, the highly hydrated nature of collagen hydrogels results in their lack of mechanical properties and instability, as well as extensive cell-mediated contraction, which must be overcome to achieve process control. Herein, tubular dense collagen constructs (TDCCs) were produced simply and rapidly (in less than 1h) by circumferentially wrapping plastically compressed dense collagen gel sheets around a cylindrical support. The effects of collagen source, i.e. rat-tail tendon and bovine dermis-derived acid solubilized collagen, and concentration on TDCC properties were investigated through morphological, mechanical and chemical characterizations. Both tensile strength and apparent modulus correlated strongly with physiologically relevant collagen gel fibrillar densities. The clinical potential of TDCC as a tubular tissue substitute was demonstrated mechanically, through circumferential tensile properties, theoretical burst pressure, which ranged from 1225 to 1574 mm Hg, compliance values of between 8.3% to 14.2% per 100mm Hg and suture retention strength in the range of 116-151 grams-force, which were compatible with surgical procedures. Moreover, NIH/3T3 fibroblast viability and uniform distribution within the construct wall were confirmed up to day 7 in culture. TDCCs with fibrillar densities equivalent to native tissues can be readily engineered in various dimensions with tunable morphological and mechanical properties, which can be easily handled for use as tissue models and adapted to clinical needs.

Microfluidic synthesis of microfibers for magnetic-responsive controlled drug release and cell culture

This study demonstrated the fabrication of alginate microfibers using a modular microfluidic system for magnetic-responsive controlled drug release and cell culture. A novel two-dimensional fluid-focusing technique with multi-inlets and junctions was used to spatiotemporally control the continuous laminar flow of alginate solutions. The diameter of the manufactured microfibers, which ranged from 211 µm to 364 µm, could be well controlled by changing the flow rate of the continuous phase. While the model drug, diclofenac, was encapsulated into microfibers, the drug release profile exhibited the characteristic of a proper and steady release. Furthermore, the diclofenac release kinetics from the magnetic iron oxide-loaded microfibers could be controlled externally, allowing for a rapid drug release by applying a magnetic force. In addition, the successful culture of glioblastoma multiforme cells in the microfibers demonstrated a good structural integrity and environment to grow cells that could be applied in drug screening for targeting cancer cells. The proposed microfluidic system has the advantages of ease of fabrication, simplicity, and a fast and low-cost process that is capable of generating functional microfibers with the potential for biomedical applications, such as drug controlled release and cell culture.

Construction of a tubular scaffold that mimics J-shaped stress/strain mechanics using an innovative electrospinning technique

Soft tissues such as blood vessel, lung, ureter, skin, etc., possess mechanical behavior characterized by a "J"-shaped curve on a stress-strain diagram with a low-stiffness highly elastic zone giving rise to a high-stiffness zone. This mechanical behavior may be adaptive and protective against aneurysm formation in tissues whose primary loading is pressure-based. "J"-shaped behavior arises from the synergistic interplay of two main structural proteins: collagen and elastin. An innovative electrospinning technique has been utilized to form tubular scaffold composites with structural features reminiscent of the corrugated laminae seen in blood vessels. In doing so, tubular scaffolds have been fabricated with complex "J"-shaped behavior through the use of elastic polyurethane and reinforcing poly-glycolic acid (PGA) woven mesh. In these studies, corrugated laminae were formed on the 175 μm and 1.5 mm scale. Initial moduli were 0.5±0.17 MPa (mean±standard deviation) giving rise to stiffer moduli of 36.09±6.72 MPa at a strain of 1.31±0.15. Burst pressures were physiologically relevant at 3095±1016 mmHg. The toughness of these prototypes was 6.3±1.9 MJ/m(3). The ability to employ different materials and different formation parameters utilizing this technique promises the ability to match complex stress-strain behaviors in soft tissues with a high degree of fidelity.

Regeneration of native-like neo-urinary tissue from nonbladder cell sources

Urinary pathology requiring urinary diversion, partial or full bladder replacement, is a significant clinical problem affecting ~14,000 individuals annually in the United States alone. The use of gastrointestinal tissue for urinary diversion or bladder reconstruction/replacement surgeries is frequently associated with complications. To try and alleviate or reduce the frequency of these complications, tissue engineering and regenerative medicine strategies have been developed using bio-absorbable materials seeded with cells derived from the bladder. However, bladder-sourced cells may not always be suitable for such applications, especially in patients with bladder cancer. In this study, we describe the isolation and characterization of smooth muscle cells (SMCs) from porcine adipose and peripheral blood that are phenotypically and functionally indistinguishable from bladder-derived SMCs. In a preclinical Good Laboratory Practice study, we demonstrate that autologous adipose- and peripheral blood-derived SMCs may be used to seed synthetic, biodegradable tubular scaffold structures and that implantation of these seeded scaffolds into a porcine cystectomy model leads to successful de novo regeneration of a tubular neo-organ composed of urinary-like neo-tissue that is histologically identical to native bladder. The ability to create urologic structures de novo from scaffolds seeded by autologous adipose- or peripheral blood-derived SMCs will greatly facilitate the translation of urologic tissue engineering technologies into clinical practice.

The future of regenerative medicine: urinary system

Regeneration of tissues and organs is now within the technological reach of modern medicine. With such advancements, substantial improvements to existing standards-of-care are very real possibilities. This review will focus on regenerative medicine approaches to treating specific maladies of the bladder and kidney, including the biological basis of regeneration and the history of regenerative medicine in the urinary system. Current clinical management approaches will be presented within the context of future directions including cell-based regenerative therapies.

Functional Evaluation of Primary Renal Cell/Biomaterial Neo-Kidney Augment Prototypes for Renal Tissue Engineering

Development of a tissue-engineered neo-kidney augment (NKA) requires evaluation of defined, therapeutically relevant cell and cell/biomaterial composites (NKA constructs) for regenerative potential in mammalian kidney. Previous work identified primary renal cell populations that extended survival and improved renal function in a rodent model of chronic kidney disease (CKD). This study extends that work toward the goal of developing NKA by (i) screening in vivo inflammatory and fibrotic responses to acellular biomaterials delivered to healthy rodent renal parenchyma, (ii) evaluating the functionality of renal cell/biomaterial combinations in vitro, (iii) generating NKA constructs by combining therapeutically relevant cell populations with biocompatible biomaterial, and (iv) evaluating in vivo neokidney tissue development in response to NKA constructs delivered to healthy rodent renal parenchyma. Gelatin and hyaluronic acid (HA)-based hydrogels elicited the least inflammatory and fibrotic responses in renal parenchyma relative to polycaprolactone (PCL) and poly(lactic- co-glycolic acid) (PLGA) beads or particles and were associated with neovascularization and cellular infiltration by 4 weeks postimplantation. Renal cell populations seeded onto gelatin or HA-based hydrogels were viable and maintained a tubular epithelial functional phenotype during an in vitro maturation of 3 days as measured by transcriptomic, proteomic, secretomic, and confocal immunofluorescence assays. In vivo delivery of cell-seeded NKA constructs (bioactive renal cells + gelatin hydrogels) to healthy rodent renal parenchyma elicited neokidney tissue formation at 1 week postimplantation. To investigate a potential mechanism by which NKA constructs could impact a disease state, the effect of conditioned media on TGF-β signaling pathways related to tubulo-interstitial fibrosis associated with CKD progression was evaluated. Conditioned medium was observed to attenuate TGF-β-induced epithelial–mesenchymal transition (EMT) in vitro in a human proximal tubular cell line (HK2).

Extension of bladder-based organ regeneration platform for tissue engineering of esophagus

Recent successes in regenerative medicine and tissue engineering of bladder and bladder-like neo-organs have leveraged regenerative constructs composed of a biodegradable scaffold seeded with a population of smooth muscle cells. We have shown that such smooth muscle cells are isolatable from adipose and other sources alternate to the primary organ. We hypothesize that this regenerative platform is not limited to regeneration of bladder and bladder-like neo-organs, but rather represents a foundational technology platform broadly applicable for regeneration of laminarly organized hollow organs. Using esophagus as an illustrative example in support of this hypothesis, we demonstrate that patch constructs composed of adipose-derived smooth muscle cells seeded on a biodegradable matrix catalyze complete regeneration of the esophageal wall in a rodent model of esophageal injury. By implication, such regenerative constructs may potentially be used to mediate the regeneration of any laminarly organized tubular organ.

Regeneration of rodent small intestine tissue following implantation of scaffolds seeded with a novel source of smooth muscle cells

Aims: To apply an organ regeneration platform technology of autologous smooth muscle cell/biomaterial combination products, previously demonstrated to be successful for urinary tissue regeneration, to the regeneration of the small intestine. Materials & methods: Patch and tubular constructs were implanted in rodent small intestines and histologically evaluated over a time course for evidence of regeneration of the laminarly organized neo-mucosa and muscle layers. Results: Laminarly organized neo-mucosa and muscle layer bundles are demonstrated as early as 8 weeks postimplantation. Conclusion: An organ regeneration technology platform of autologous smooth muscle cell/biomaterial combination products can be extended to the regeneration of the small intestine.

Organ specific regenerative markers in peri-organ adipose: kidney

Background

Therapeutically bioactive cell populations are currently understood to promote regenerative outcomes in vivo by leveraging mechanisms of action including secretion of growth factors, site specific engraftment and directed differentiation. Constitutive cellular populations undoubtedly participate in the regenerative process. Adipose tissue represents a source of therapeutically bioactive cell populations. The potential of these cells to participate in various aspects of the regenerative process has been demonstrated broadly. However, organ association of secretory and developmental markers to specific peri-organ adipose depots has not been investigated. To characterize this topographical association, we explored the potential of cells isolated from the stromal vascular fraction (SVF) of kidney sourced adipose to express key renal associated factors.

Results

We report that renal adipose tissue is a novel reservoir for EPO expressing cells. Kidney sourced adipose stromal cells demonstrate hypoxia regulated expression of EPO and VEGF transcripts. Using iso-electric focusing, we demonstrate that kidney and non-kidney sourced adipose stromal cells present unique patterns of EPO post-translational modification, consistent with the idea that renal and non-renal sources are functionally distinct adipose depots. In addition, kidney sourced adipose stromal cells specifically express the key renal developmental transcription factor WT1.

Conclusions

Taken together, these data are consistent with the notion that kidney sourced adipose stromal (KiSAS) cells may be primed to recreate a regenerative micro-environment within the kidney. These findings open the possibility of isolating solid-organ associated adipose derived cell populations for therapeutic applications in organ-specific regenerative medicine products.

Expansion of the human adipose-derived stromal vascular cell fraction yields a population of smooth muscle-like cells with markedly distinct phenotypic and functional properties relative to mesenchymal stem cells

Adipose tissue contains a heterogeneous cell population composed of endothelial cells, adipocytes, smooth muscle cells (SMC), and mesenchymal progenitors and stromal cells that meet the criteria put forth by the International Society for Cellular Therapy as defining mesenchymal stem cells (MSC). In this study, we expanded the stromal vascular fraction (SVF) of human adipose tissue and characterized the resulting adherent primary cell cultures by quantitative reverse transcription-polymerase chain reaction, antigen expression, protein fingerprinting, growth kinetics, in vitro tri-lineage differentiation bioactivity, and functional responses to small molecules modulating SMC-related developmental pathways and compared the results to those obtained with functionally validated MSC cultures. SVF-derived initial cultures (P0) were expanded in a defined medium that was not optimized for MSC growth conditions, neither were recombinant cytokines or growth factors added to the media to direct differentiation. The adherent cell cultures derived from SVF expansion under these conditions had markedly distinct phenotypic and biological properties relative to functionally validated MSC cultures. SVF-derived adherent cell cultures retained characteristics consistent with the SMC subpopulation within adipose tissue--phenotype, gene, and protein expression--that were independent of passage number and source of SVF (n=4 independent donors). SVF-derived cells presented significantly less robust in vitro tri-lineage differentiation bioactivity relative to validated MSC. Expanded SVF cells and MSC had opposite responses to the thromboxane A2 mimetic U46619, demonstrating an unambiguous functional distinction between the two cell types. Taken together, these data support the conclusions that SVF cells expanded under the conditions described in these studies are accurately described as adipose-derived SMC and represent a cellular subpopulation of adipose SVF that is separate and distinct from other classes of adipose-derived cells.