Smooth muscle alpha-actin and calponin expression and extracellular matrix production of human coronary artery smooth muscle cells in 3D scaffolds

Embryonic Mesenchymal Multipotent Cell Differentiation on Electrospun Biodegradable Poly(ester amide) Scaffolds for Model Vascular Tissue Fabrication

Vascular differentiation of stem cells and matrix component production on electrospun tubular scaffolds is desirable to engineer blood vessels. The mouse embryonic multipotent mesenchymal progenitor cell line (10T1/2) provides an excellent tool for tissue engineering since it shares similar differentiation characteristics with mesenchymal stem cells. Although 10T1/2 cells have been widely studied in the context of skeletal tissue engineering, their differentiation to smooth muscle lineage is less known. In this study, we fabricated tubular electrospun poly(ester amide) (PEA) fibers from L-phenylalanine-derived biodegradable biomaterials and investigated cell-scaffold interactions as well as their differentiation into vascular smooth muscle cell and subsequent elastin expression. PEA scaffolds fabricated under different collector speeds did not have an impact on the fiber directionality/orientation. 10T1/2 cytocompatibility and proliferation studies showed that PEA fibres were not cytotoxic and were able to support proliferation for 14 days. Furthermore, cells were observed infiltrating the fibrous scaffolds despite the small pore sizes (~ 5 µm). Vascular differentiation studies of 10T1/2 cells using qPCR, Western blot, and immunostaining showed a TGFβ1-induced upregulation of vascular smooth muscle cell (VSMC)-specific markers smooth muscle alpha-actin (SM-α-actin) and smooth muscle myosin heavy chain (SM-MHC). Differentiated 10T1/2 cells produced both elastin and fibrillin-1 suggesting the potential of fibrous PEA scaffolds to fabricate model vascular tissues.

Overcoming scarring in the urethra: Challenges for tissue engineering

Urethral stricture disease is increasingly common occurring in about 1% of males over the age of 55. The stricture tissue is rich in myofibroblasts and multi-nucleated giant cells which are thought to be related to stricture formation and collagen synthesis. An increase in collagen is associated with the loss of the normal vasculature of the normal urethra. The actual incidence differs based on worldwide populations, geography, and income. The stricture aetiology, location, length and patient's age and comorbidity are important in deciding the course of treatment. In this review we aim to summarise the existing knowledge of the aetiology of urethral strictures, review current treatment regimens, and present the challenges of using tissue-engineered buccal mucosa (TEBM) to repair scarring of the urethra. In asking this question we are also mindful that recurrent fibrosis occurs in other tissues-how can we learn from these other pathologies?

Regulation of vascular smooth muscle cell phenotype in three-dimensional coculture system by Jagged1-selective Notch3 signaling

The modulation of vascular smooth muscle cell (VSMC) phenotype is an essential element to fabricate engineered conduits of clinical relevance. In vivo, owing to their close proximity, endothelial cells (ECs) play a role in VSMC phenotype switching. Although considerable progress has been made in vascular tissue engineering, significant knowledge gaps exist on how the contractile VSMC phenotype is induced at the conclusion of the tissue fabrication process. The objectives of this study were as follows: (1) to establish ligand presentation modes on transcriptional activation of VSMC-specific genes, (2) to develop a three-dimensional (3D) coculture model using human coronary artery smooth muscle cells (HCASMCs) and human coronary artery endothelial cells (HCAECs) on porous synthetic scaffolds and, (3) to investigate EC-mediated Notch signaling in 3D cultures and the induction of the HCASMC contractile phenotype. Whereas transcriptional activation of VSMC-specific genes was not induced by presenting soluble Jagged1 and Jagged1 bound to protein G beads, a direct link between HCAEC-bound Jagged1 and HCASMC differentiation genes was observed. Our 3D culture results showed that HCASMCs seeded to scaffolds and cultured for up to 16 days readily attached, infiltrated the scaffold, proliferated, and formed dense confluent layers. HCAECs, seeded on top of an HCASMC layer, formed a distinct, separate monolayer with cell-type partitioning, suggesting that HCAEC growth was contact inhibited. While we observed EC monolayer formation with 200,000 HCAECs/scaffold, seeding 400,000 HCAECs/scaffold revealed the formation of cord-like structures akin to angiogenesis. Western blot analyses showed that 3D coculture induced an upregulation of Notch3 receptor in HCASMCs and its ligand Jagged1 in HCAECs. This was accompanied by a corresponding induction of the contractile HCASMC phenotype as demonstrated by increased expression of smooth muscle-α-actin (SM-α-actin) and calponin. Knockdown of Jagged1 with siRNA showed a reduction in SM-α-actin and calponin in cocultures, identifying a link between Jagged1 and the expression of contractile proteins in 3D cocultures. We therefore conclude that the Notch3 signaling pathway is an important regulator of VSMC phenotype and could be targeted when fabricating engineered vascular tissues.

Biomimetic polyurethanes in nano and regenerative medicine

Nature's inspiration is a promising tool to design new biomaterials especially for frontier technological areas such as tissue engineering and nanomedicine.

The immunology of fibrosis

Fibrosis is the production of excessive amounts of connective tissue, i.e., scar formation, in the course of reactive and reparative processes. Fibrosis develops as a consequence of various underlying diseases and presents a major diagnostically and therapeutically unsolved problem. In this review, we postulate that fibrosis is always a sequela of inflammatory processes and that the many different causes of fibrosis all channel into the same final stereotypical pathways. During the inflammatory phase, both innate and adaptive immune mechanisms are operative. This concept is exemplified by fibrotic diseases that develop as a consequence of tissue damage, primary inflammatory diseases, fibrotic alterations induced by foreign body implants, "spontaneous" fibrosis, and tumor-associated fibrotic changes.

Bioactive and biodegradable nanocomposites and hybrid biomaterials for bone regeneration

Strategies for bone tissue engineering and regeneration rely on bioactive scaffolds to mimic the natural extracellular matrix and act as templates onto which cells attach, multiply, migrate and function. Of particular interest are nanocomposites and organic-inorganic (O/I) hybrid biomaterials based on selective combinations of biodegradable polymers and bioactive inorganic materials. In this paper, we review the current state of bioactive and biodegradable nanocomposite and O/I hybrid biomaterials and their applications in bone regeneration. We focus specifically on nanocomposites based on nano-sized hydroxyapatite (HA) and bioactive glass (BG) fillers in combination with biodegradable polyesters and their hybrid counterparts. Topics include 3D scaffold design, materials that are widely used in bone regeneration, and recent trends in next generation biomaterials. We conclude with a perspective on the future application of nanocomposites and O/I hybrid biomaterials for regeneration of bone.

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.

Tissue engineering and regenerative strategies to replicate biocomplexity of vascular elastic matrix assembly

Cardiovascular tissues exhibit architecturally complex extracellular matrices, of which the elastic matrix forms a major component. The elastic matrix critically maintains native structural configurations of vascular tissues, determines their ability to recoil after stretch, and regulates cell signaling pathways involved in morphogenesis, injury response, and inflammation via biomechanical transduction. The ability to tissue engineer vascular replacements that incorporate elastic matrix superstructures unique to cardiac and vascular tissues is thus important to maintaining vascular homeostasis. However, the vascular elastic matrix is particularly difficult to tissue engineer due to the inherently poor ability of adult vascular cells to synthesize elastin precursors and organize them into mature structures in a manner that replicates the biocomplexity of elastic matrix assembly during development. This review discusses current tissue engineering materials (e.g., growth factors and scaffolds) and methods (e.g., dynamic stretch and contact guidance) used to promote cellular synthesis and assembly of elastic matrix superstructures, and the limitations of these approaches when applied to smooth muscle cells, the primary elastin-generating cell type in vascular tissues. The potential application of these methods for in situ regeneration of disrupted elastic matrix at sites of proteolytic vascular disease (e.g., abdominal aortic aneurysms) is also discussed. Finally, the review describes the potential utility of alternative cell types to elastic tissue engineering and regenerative matrix repair. Future progress in the field is contingent on developing a thorough understanding of developmental elastogenesis and then mimicking the spatiotemporal changes in the cellular microenvironment that occur during that phase. This will enable us to tissue engineer clinically applicable elastic vascular tissue replacements and to develop elastogenic therapies to restore homeostasis in de-elasticized vessels.

Tissue engineering scaffolds containing embedded fluorinated-zeolite oxygen vectors

Efficient oxygen supply is a continuing challenge for the fabrication of successful tissue engineered constructs with clinical relevance. In an effort to enhance oxygen delivery we report the feasibility of using fluorinated zeolite particles embedded in three-dimensional (3-D) polyurethane scaffolds as novel oxygen vectors. First, 1H,1H,2H,2H-perfluorodecyltriethoxysilane was successfully coupled to zeolite framework particles to examine the dose-dependent dissolved oxygen concentration. Following this, the fluorinated-zeolite (FZ) particles were embedded in 3-D tissue engineering polyurethane scaffolds. Our data demonstrates an even distribution of FZ particles in the 3-D scaffolds without affecting the scaffold porosity or pore size. Human coronary artery smooth muscle cell (HCASMC) proliferation on FZ-containing polyurethane (PCU-FZ) scaffolds was significantly greater than on control scaffolds (P=0.05). Remarkably, cell infiltration depths on the PCU-FZ scaffolds was double that on PCU control scaffolds. Taken together, our data suggest the potential of PCU-FZ scaffolds for tissue engineering with enhanced oxygen delivery to cells.

Three-dimensional topography of synthetic scaffolds induces elastin synthesis by human coronary artery smooth muscle cells

Due to the important structural and signaling roles of elastin in vascular stability, engineered human vascular tissues must incorporate elastin. However, despite considerable progress toward engineering of elastin-containing vascular tissues from animal cells, currently engineered vascular tissues using human cells largely lack elastin. In this study, we evaluated the effect of scaffold topography (two dimensional [2D] vs. three dimensional [3D]) on elastogenesis in adult human coronary artery smooth muscle cells (HCASMCs). We report that elastin gene expression by HCASMCs was increased by twofold after 4 days of culture in porous 3D polyurethane scaffolds. Transforming growth factor β1 (TGF-β1) further increased elastin gene expression in 3D cultures but not in 2D cultures. To evaluate if gene expression is translated into elastin synthesis, both 2D and 3D cultures were analyzed using Western blots. We show that only HCASMCs in 3D scaffolds produced elastin, suggesting that scaffold geometry itself is an important cue for elastogenesis. Moreover, TGF-β1 enhanced elastin synthesis in 3D, but had no effect on cells grown on 2D surfaces. TGF-β1, known to induce vascular smooth muscle cells (VSMC) differentiation, upregulated contractile VSMC marker proteins smooth muscle-α-actin and calponin in cells on 2D surfaces. Interestingly, in 3D scaffolds, TGF-β1 failed to upregulate these differentiation marker proteins for at least 7 days, but did so in cells cultured for 14 days, whereas elastin synthesis was not affected. To our knowledge this study is the first to successfully demonstrate that adult human VSMC can produce elastin when seeded on 3D scaffolds and to directly compare the effect of scaffold topography on elastin synthesis. Knowledge about the conditions required to regulate the phenotype of human VSMCs is paramount to engineer elastin-containing autologous human vascular substitutes.

Synthesis and characterization of polyurethane-block-poly(2-hydroxyethyl methacrylate) hydrogels and their surface modification to promote cell affinity

Physically crosslinked hydrogels based on poly(2-hydroxyethyl methacrylate) (PHEMA) and polyurethane macroiniferter (PUMI) were prepared. The synthesis of polyurethane- block-poly(2-hydroxyethyl methacrylate) (PU-b-PHEMA) was verified by spectroscopic analyses. Due to the low fibronectin adsorption from culture media, cell attachment on PU-b-PHEMA surface was poor compared with the PUMI control. To improve the cell affinity of PU-b-PHEMA, fibronectin was conjugated via surface hydroxyl groups. These biomimetic PU-b-PHEMA hydrogel surfaces were tested for tissue engineering applications. A short-term cell culture study revealed that, compared with the unmodified PU-b-PHEMA, fibronectin-conjugated PU-b-PHEMA hydrogel showed more uniform and dense cell attachment and spreading, indicating a potential use for tissue engineering applications.

Conjugation of fibronectin onto three-dimensional porous scaffolds for vascular tissue engineering applications

Tissue engineering scaffolds provide the three-dimensional (3-D) geometry and mechanical framework required for regulating cell behavior and facilitating tissue maturation. Unfortunately, most synthetic scaffolds lack the biological recognition motifs required for seeded cell interaction. In order to impart this recognition, synthetic scaffolds should possess appropriate biological functionality. Here, for the first time, we present a comprehensive study of fibronectin (FN) conjugation onto highly porous 3-D poly(carbonate) urethane scaffolds through grafted poly(acrylic acid) spacers on the urethane backbone. Scanning electron microscopy was used to ensure that the porous structures of the scaffolds were preserved throughout the multiple conjugation steps, and Fourier transform infrared spectroscopy was used to monitor the reaction progress. Toluidine blue staining revealed that increasing acrylic acid concentration and grafting time increased the number of poly(acrylic acid) groups incorporated. High resolution X-ray photoelectron spectroscopy studies of the scaffolds demonstrated an increase in nitrogen and sulfur due to FN conjugation. Immunofluorescence microscopy studies showed an even distribution of conjugated FN on the 3-D scaffolds. Cell culture studies using human coronary artery smooth muscle cells demonstrated that FN-conjugated scaffolds had improved cell attachment and infiltration depth compared with scaffolds without FN conjugation and with those scaffolds on which FN was merely adsorbed.

Scaffolds in tissue engineering of blood vessels

Tissue engineering of small diameter (<5 mm) blood vessels is a promising approach for developing viable alternatives to autologous vascular grafts. It involves in vitro seeding of cells onto a scaffold on which the cells attach, proliferate, and differentiate while secreting the components of extracellular matrix that are required for creating the tissue. The scaffold should provide the initial requisite mechanical strength to withstand in vivo hemodynamic forces until vascular smooth muscle cells and fibroblasts reinforce the extracellular matrix of the vessel wall. Hence, the choice of scaffold is crucial for providing guidance cues to the cells to behave in the required manner to produce tissues and organs of the desired shape and size. Several types of scaffolds have been used for the reconstruction of blood vessels. They can be broadly classified as biological scaffolds, decellularized matrices, and polymeric biodegradable scaffolds. This review focuses on the different types of scaffolds that have been designed, developed, and tested for tissue engineering of blood vessels, including use of stem cells in vascular tissue engineering.

The immunology of fibrosis: innate and adaptive responses

Fibrosis is an important health problem, and its pathogenetic principles are still largely unknown. It can develop either spontaneously, or, more frequently, as a consequence of various underlying diseases. Irrespective of the primary cause, however, fibrotic tissue is always infiltrated by mononuclear immune cells. In most instances the reason for the attraction of these cells to fibrotic tissue and their proliferation remains to be determined; however their cytokine profile shows clear-cut proinflammatory and profibrotic characteristics. In this review, we discuss the innate and adaptive immune reactions associated with the development of fibrosis and the molecular basis of the profibrotic mechanisms taking place in systemic sclerosis (scleroderma), arteriosclerosis and peri-silicone mammary implant fibrosis.