Polymeric scaffolds for cardiac tissue engineering: requirements and fabrication technologies

Cardiac tissue engineering (TE) is an emerging field, whose main goal is the development of innovative strategies for the treatment of heart diseases, with the aim of overcoming the drawbacks of traditional therapies. One of these strategies involves the implantation of three‐dimensional matrices (scaffolds) capable of supporting tissue formation. Scaffolds designed and fabricated for such application should meet several requirements, concerning both the scaffold‐forming materials and the properties of the scaffold itself. A scaffold for cardiac TE should be biocompatible and biodegradable, mimic the properties of the native cardiac tissue, provide a mechanical support to the regenerating heart and possess an interconnected porous structure to favour cell migration, nutrient and oxygen diffusion, and waste removal. Moreover, the mimesis of myocardium characteristic anisotropy is attracting increasing interest to provide engineered constructs with the possibility to be structurally and mechanically integrated in native tissue. Several conventional and non‐conventional fabrication techniques have been explored in the literature to produce polymeric scaffolds meeting all these requirements. This review describes these techniques, with a focus on their advantages and disadvantages, and their flexibility, with the final goal of providing the reader with the primal knowledge necessary to develop an effective strategy in cardiac TE. © 2013 Society of Chemical Industry     

Gelatin electrospun nanofibrous matrices for cardiac tissue engineering applications

The generation of in vitro tissue constructs using biomaterials and cardiac cells is a promising strategy for screening novel therapeutics and their effects on cardiac regeneration. Current cardiac mimetic tissue constructs are unable to stably maintain functional characteristics of cardiomyocytes for long-term cultures. The objective of our study was to fabricate and characterize nanofibrous matrices of gelatin for prolonged cultures of primary cardiomyocytes which previously has been used as copolymer or hydrogels. Gelatin nanofibrous matrices were successfully electrospun using a benign binary solvent, cross-linked without swelling and fusing and evaluated by scanning electron microscopy (SEM) and uniaxial tensile measurement. Scaffolds exhibited modulus 19.6 ± 3.6 kPa similar to native human myocardium tissue with fiber diameters of 200–600 nm and average porosity percentage of 49.9 ± 5.6. Myoblasts showed good cell adhesion and proliferation. Neonatal rat cardiomyocytes cultured on gelatin nanofibrous matrices showing synchronized contracting cardiomyocytes (beating) for 27 days were studied by video microscopy. Confocal microscopic analysis of immunofluorescence stained sections indicated the presence of cardiac specific Troponin T in long-term cultures. Semiquantitative RT-PCR analysis of 3D versus 2D cultures revealed enhanced expression of contractile protein desmin. Our studies show that the biophysical and mechanical properties of electrospun gelatin nanofibers are ideal for in vitro engineered cardiac constructs (ECC), to explore cardiac function in drug testing and tissue replacement. Together with stem cell techniques, they may be an ideal platform for prolongedin vitro studies in alternatives to animal usage for the pharmaceutical industry.     

Exceptional biocompatibility of 3D fibrous scaffold for cardiac tissue engineering fabricated from biodegradable polyurethane blended with cellulose

The auhtors report 3D biomimetic scaffolds using polymer blend of polyurethane and cellulose for cardiac tissue engineering. The biocompatible and biodegradable polyurethane is designed, synthesized and characterized. By incorporating 10 wt% of naturally ordered cellulose into the polyurethane and electrospinning them into 3D scaffold, the scaffold exhibits good biocompatibility and mechanical property to support and accommodate constant cycles of contraction/expansion of cardiac tissue. The biocompatibility is further improved using scaffold fabricated from aligned fibers due to synergistic effects between cells and ordered macromolecules. The anisotropic structured scaffold is mimicked the extracellular matrix and has therapeutic potential in reconstruction of damaged myocardium.     

Silicon-doped hydroxyapatite prepared by a thermal technique for hard tissue engineering applications

Hydroxyapatite (HA, Ca₅(PO₄)₃OH) has been extensively used for bone implantation due to its similarity to the mineral component of bone, which makes it strongly osteoconductive. However, HA has low resorbability, and it is difficult to replace by a newly regenerated bone. Si doping can enhance the resorbability of HA by modifying its crystal structure. Here, we developed a simple thermal technique for preparing Si-doped HA from silica (SiO₂) and HA precursors, both of which are inexpensive and commercially available. This method included the physical binding of SiO₂ and HA particles, followed by pressing and sintering the mixture at an elevated temperature, which enhanced the atomic diffusion of Si into HA unit cells. We also evaluated the simulated body fluid (SBF) activity of the Si-doped HA prepared by this technique and showed that it significantly had higher resorbability and mineralizing potential compared to the pure HA. Our experimental design including, the individual precipitation and resorption assays enabled us to explain the mechanism behind the improved activity of Si-doped HA in SBF. This was attributed to the formation of new phases, such as β-tricalcium phosphate (β-TCP) and calcium silicate (Ca₂SiO₄) with higher solubility than HA on the SiO₂-contating HA during the sintering stage. This can provide some guidelines for designing new calcium phosphate-based materials for hard tissue engineering applications.     

A study on the effect of the collector properties on the fabrication of magnetic polystyrene nanocomposite fibers using the electrospinning technique

The role of the collector properties in changing the fiber morphology in electrospinning has not been completely understood yet. In this work, we studied the effect of different collectors on the helicity of the magnetic polystyrene nanocomposite fibers containing superparamagnetic magnetite nanoparticles. Aluminum and ice were used as solid collectors. Ethanol, ethanol-deionized (DI) water mixture, sodium dodecyl sulfate, Triton X-100, deionized water, and NaCl baths were used as liquid collectors. Ice, when surrounded by a conductive foil, produced excellent fiber alignment, but increased local humidity, inhibiting the continuous jet formation. The deionized water and NaCl bath exhibited minimum helicity. The surfactant bath produced different structures such as coiled, helical, and zig-zag with varied diameters. Ethanol and DI/Ethanol baths were found to retain the structure of the deformed fiber formed due to jet instability. The helicity of the fibers was observed to increase with decreasing surface tension. Incorporation of the magnetic phase affected the viscosity of the polymer solution and the hydrophobicity of the polystyrene fibers further influencing the obtained morphologies.     

Magnetic-field assisted mixing of liquids using magnetic nanoparticles

Size and magnetic properties of magnetic nanoparticles (MNPs) in fluids allow special remote control of fluid flow using appropriate externally applied magnetic fields, especially when submicronic mixing is critical, inter alia, for catalytic reactions, separation and drug delivery. This work explores MNPs as nanoscale devices to control mixing at microscale by submitting the system of interest to a rotating magnetic field (RMF). Magnetic nanoparticles are harnessed by RMF and converted into nanostirrers thereby generating MNP-pinned localized agitation in the liquid phase. Using this technique, self-diffusion coefficient of water in a static diffusion cell was intensified up to 200 folds. Also, axial dispersion of capillary Poiseuille flows under RMF underwent a reduction prompted by MNP-mediated intensification of lateral mixing relative to that in absence of magnetic field. Finally a multiphase flow case concerned gas–liquid mass transfer from oxygen Taylor bubbles to the liquid in capillaries where dilute MNP solutions led to measurable enhancement of k_La under RMF.     

Cardiac tissue engineering: effects of bioreactor flow environment on tissue constructs

The limited ability of cardiac muscle to regenerate after injury and the small number of organs available for transplantation motivate studies aimed at curative treatment options. Tissue engineering based on the integrated use of cells on biomaterial scaffolds in bioreactors may offer cardiac grafts suitable for surgical attachment to the myocardium or for basic research. In one of the current approaches, neonatal rat cardiomyocytes are combined with collagen sponges, gels or polyglycolic acid scaffolds (PGA). Cultivations performed in dishes, static or mixed flasks or rotating bioreactors yield constructs with a thin (100–200 µm) peripheral layer of tissue expressing markers of cardiac differentiation and able to propagate electrical signals. The non‐uniform cell distribution is a result of oxygen diffusional limitations within the constructs. Cultivations with perfusion of culture medium through the construct enhance the convective‐diffusive oxygen supply and yield 1–2 mm thick constructs with physiologically high and spatially uniform distribution of viable cells expressing cardiac markers. We review here a series of studies we conducted using cells seeded on three‐dimensional scaffolds and cultured in several different bioreactors, to demonstrate that the bioreactor flow environment can have substantial effects on structural and functional properties of cardiac constructs. Copyright © 2006 Society of Chemical Industry     

Homology of selenium (Se) and tellurium (Te) endow the functional similarity of Se-doped and Te-doped mesoporous bioactive glass nanoparticles in bone tissue engineering

The focus of bone tissue engineering is to realize the regeneration of new functional bone through the synergistic combination of biomaterials, therapeutic agents and cells. Doping of mesoporous bioactive glass (MBG) nanoparticles with therapeutic ions to give them special properties is gaining increasing interest in the design of biomaterials for bone tissue engineering. In this study, we synthesized Se-doped and Te-doped MBG nanoparticles using the sol-gel method, and demonstrated for the first time that the homology of Se and Te endows the functional similarity of bone tissue engineering, and also obtains the desired properties by guiding cell behavior and changing the physicochemical properties of the biomaterial. Results found that MBG nanoparticles doped with Se and Te respectively can be gained similar structure, and thus endowed their similar properties as expected, such as drug sustained release, anticancer and antibacterial properties in a dose-dependent manner. This study provides a feasible strategy for the development of homologous group ions doped nanobiomaterials and their evaluation and basic research in bone tissue engineering.     

Immobilization of Wnt Fragment Peptides on Magnetic Nanoparticles or Synthetic Surfaces Regulate Wnt Signaling Kinetics

Wnt signaling plays an important role in embryogenesis and adult stem cell homeostasis. Its diminished activation is implicated in osteoporosis and degenerative neural diseases. However, systematic administration of Wnt-signaling agonists carries risk, as aberrantly activated Wnt/β-catenin signaling is linked to cancer. Therefore, technologies for local modulation and control of Wnt signaling targeted to specific sites of disease or degeneration have potential therapeutic value in the treatment of degenerative diseases. We reported a facile approach to locally activate the canonical Wnt signaling cascade using nanomagnetic actuation or ligand immobilized platforms. Using a human embryonic kidney (HEK293) Luc-TCF/LEF reporter cell line, we demonstrated that targeting the cell membrane Wnt receptor, Frizzled 2, with peptide-tagged magnetic nanoparticles (MNPs) triggered canonical Wnt signaling transduction when exposed to a high-gradient, time-varying magnetic field, and the induced TCF/LEF signal transduction was shown to be avidity-dependent. We also demonstrated that the peptide retained signaling activity after functionalization onto glass surfaces, providing a versatile platform for drug discovery or recreation of the cell niche. In conclusion, these results showed that peptide-mediated Wnt signaling kinetics depended not only on ligand concentration but also on the presentation method of the ligand, which may be further modulated by magnetic actuation. This has important implications when designing future therapeutic platforms involving Wnt mimetics.     

Experimental investigation on possibility of oxygen enrichment by using gradient magnetic fields

This paper presents a novel method that uses the interception effect of gradient magnetic field on oxygen molecules to realize enrichment. The use of two opposite magnetic poles of two magnets at a certain distance forms a magnetic space having a field intensity gradient near its borders. When air injected into the magnetic space outflows from the magnetic space via its borders, oxygen molecules in the air will experience the interception effect of the gradient magnetic field, but nitrogen molecules will outflow from the magnetic space without hindrance. Thus, continuous oxygen enrichment is realized. The enrichment degree of oxygen reaches 0.65% when the inlet and outlet air flows are 40 mL/min and 20 mL/min, respectively, and the gas temperature is 298 K and the maximal product of magnetic flux density and its gradient is 563 T²/m (the distance between two magnetic poles is 1 mm). When the gas temperature rises to 343 K, the enrichment degree drops to 0.32%; and when the maximal product of magnetic flux density and field intensity gradient drops to 101 T²/m (the distance between two magnetic poles is 4 mm), the enrichment degree drops to 0.23%. The experimental results show that there is an optimal ratio between the inlet air flow and the outlet air flow. Under the experimental conditions in this paper, the value is about 2.0. It is demonstrated that the method presented in this paper can continuously enrich oxygen and has a higher enrichment degree than other oxygen-enrichment methods using magnetic separation. Translated from Journal of Beijing University of Chemical Technology, 2006, 33(5): 62–66 [译自: 北京化工大学学报]     

Microfluidics for selective concentration of nanofluid streams containing magnetic nanoparticles

Microfluidics is well-known for many Lab-on-a-Chip applications including sensing, cell sorting, separation, chemical reaction, emulsification, de-emulsification, droplet generation, energy generation and similar applications. The current research scenario in the field of interfacial science and colloidal technology has facilitated the advancement of microfluidics as a miniaturized option for many targeted tasks. Here we show how the microfluidics offers a low-cost solution for concentrating the dispersion of magnetic nanoparticles. The synthesized nanofluids were fed to the microchannels subjected to magnetic field. It has been found that the feed flow rate is one of the very crucial factors which affect the control of concentration of the nanofluids.     

Electrospun polyurethane patch in combination with cedarwood and cobalt nitrate for cardiac applications

The growth in nanotechnology led to the fabrication of scaffold at a low cost with high productivity and high surface area. The present research aims to fabricate a novel cardiac scaffold utilizing polyurethane (PU) added with cedarwood (CW) and cobalt nitrate (CoNO₃) nanofibers. Morphological analysis showed that the mean fiber diameter of the PU nanofibers was reduced owing to the incorporation of CW and CoNO₃. Infrared and thermal analysis revealed the interaction of PU with CW and CoNO₃. Contact angle studies showed that the electrospun PU/CW displayed hydrophobic nature while PU/CW/CoNO₃ showed hydrophilic behavior compared to the pristine PU. The tensile strength of PU nanofibers increased with CW and CoNO₃ addition. Atomic force microscopy analysis depicted that the PU/CW was rougher while the PU/CW/CoNO₃ as smoother surfaces than the pristine PU. According to the coagulation assay data, the blood compatibility of the electrospun composites was enhanced compared to the pristine PU. In addition, PU and its composite nanofibers exhibited non-toxic to human dermal fibroblast cells and improved cell proliferation rates compared to the control plates. To conclude, the improved physicochemical and biological response of the electrospun composites would be putative for cardiac tissue engineering. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48226.     

Bioreactors for heart valve tissue engineering: a review

Bioreactors have great potential in the successful development of tissue‐engineered heart valve replacements, both at the research stage and in commercial platforms. Their ability to mimick the chemical and physiological conditions of the body has allowed researchers to study in vitro cellular responses, and this has helped in the fabrication of better and more efficient tissues in vivo. Use of different bioreactors, such as, rotating, dynamic flexure, cyclic stretch and pulsatile bioreactors, in tissue engineering of heart valves has been widely investigated. However, this research is still at its early stage, and many critical issues need to be resolved to make tissue engineered heart valves sufficiently reliable for clinical applications. In the following article, after a brief introduction to the structure and role of heart valves, the efforts of tissue engineers in designing heart valves using different bioreactors is described. © 2015 Society of Chemical Industry     

双功能荧光磁性复合物的合成及应用

荧光磁性复合物兼有磁性微粒的快速分离和量子点的优异荧光特性,集选择、标记、分离、检测等功能为一体,在生物、化学、医学等交叉科学领域具有广泛的应用。介绍了磁性纳米颗粒、量子点和荧光磁性复合物的应用前景;综述了用层层自组装法、微乳液法、Stber法等方法制备荧光磁性复合物并进一步阐释了其在细胞分离、药物运输等方面的应用,结合当前的研究现状,分析了其主要的发展方向和仍需解决的问题。     

超临界法制备多孔纳米Fe_3O_4/SiO_2复合磁性微球及性能

为了制备具有纳米多孔结构的磁性复合微球,采用正硅酸四乙酯(TEOS)和金属氯盐分别作为SiO2和铁氧体的前驱体,通过溶胶凝胶法制备将Fe3O4纳米颗粒分散于SiO2基体中的Fe3O4/SiO2磁性纳米复合微球,并用超临界干燥法对其进行干燥。利用X线衍射(XRD)、红外光谱(IR)、透射电镜(TEM)和振动试样磁场计(VSM)等分析测试手段对合成的材料进行性能表征。结果表明:复合粒子包覆完好、性能优良、分散性良好,制备颗粒的粒径为30 nm,比饱和磁化强度为84.09 A.m2/kg。     

Electrospun polycaprolactone scaffolds for tissue engineering: a review

Polycaprolactone is a biodegradable and biocompatible polyester which has a wide range of applications in tissue engineering. Electrospinning, the versatile technique, used for the fabrication of fibrous scaffolds, which is widely used in tissue engineering, due to the ability of fabrication of nano/micro-scale fiber scaffolds. Polycaprolactone nanofiber scaffolds are widely used in tissue engineering and drug delivery. Polycaprolactone can be used in a wide variety of scaffolds construction. In this review, we will discuss the recent advances in the electrospinning of polycaprolactone nanofiber scaffolds in bone, cardiovascular, nerve, and skin tissue engineering.     

不同磁场作用下Fe3O4/water纳米流体层流流动对流传热系数的实验研究

对体积分数为3%的Fe₃O₄/water纳米流体在不同温度、不同磁场大小和方向的均匀磁场和梯度磁场作用下的对流换热进行了详细的实验研究。首先,开展了纳米流体能量方程的量纲1分析,讨论了纳米流体强化换热的机理。发现磁性纳米粒子所受到的磁力远远大于布朗运动力。实验测试结果与量纲1分析相吻合,在垂直均匀磁场作用下,纳米流体层流流动的平均对流传热系数提高了5.2%;在垂直梯度磁场作用下,平均对流传热系数提高了9.2%。而在水平均匀磁场作用下,纳米流体平均对流传热系数下降了4.8%。另外,随着温度的升高,对流传热系数均逐渐升高。     

Biodegradable polymers applied in tissue engineering research: a review

Typical applications and research areas of polymeric biomaterials include tissue replacement, tissue augmentation, tissue support, and drug delivery. In many cases the body needs only the temporary presence of a device/biomaterial, in which instance biodegradable and certain partially biodegradable polymeric materials are better alternatives than biostable ones. Recent treatment concepts based on scaffold‐based tissue engineering principles differ from standard tissue replacement and drug therapies as the engineered tissue aims not only to repair but also regenerate the target tissue. Cells have been cultured outside the body for many years; however, it has only recently become possible for scientists and engineers to grow complex three‐dimensional tissue grafts to meet clinical needs. New generations of scaffolds based on synthetic and natural polymers are being developed and evaluated at a rapid pace, aimed at mimicking the structural characteristics of natural extracellular matrix. This review focuses on scaffolds made of more recently developed synthetic polymers for tissue engineering applications. Currently, the design and fabrication of biodegradable synthetic scaffolds is driven by four material categories: (i) common clinically established polymers, including polyglycolide, polylactides, polycaprolactone; (ii) novel di‐ and tri‐block polymers; (iii) newly synthesized or studied polymeric biomaterials, such as polyorthoester, polyanhydrides, polyhydroxyalkanoate, polypyrroles, poly(ether ester amide)s, elastic shape‐memory polymers; and (iv) biomimetic materials, supramolecular polymers formed by self‐assembly, and matrices presenting distinctive or a variety of biochemical cues. This paper aims to review the latest developments from a scaffold material perspective, mainly pertaining to categories (ii) and (iii) listed above. Copyright © 2006 Society of Chemical Industry     

Pore collapse during the fabrication process of rubber‐like polymer scaffolds

Rubbery polymer scaffolds for tissue engineering were produced using templates of the pore structure. The last step in the fabrication process consists of dissolving the template using a solvent that, at the same time, swells the scaffolding matrix that was a polymer network. Sometimes the polymer matrix is stretched so strongly that when the solvent is eliminated, i.e., the network is dried, it shrinks and is not able to recover its original shape and, consequently, the porous structure collapses. In this work we prepared, using the same fabrication process (the same template and the same solvent), a series of polymer scaffolds that results in collapsed or noncollapsed porous structures, depending on the polymer network composition. We explain the collapse process as a consequence of the huge volume increase in the swelling process during the template extraction due to the large distance between crosslinking points in the scaffolding matrix. By systematically increasing the crosslinking density the porous structure remains after network drying and the final interconnected pores were observed. It is shown that this problem does not take place when the scaffolding matrix consists of a glassy polymer network. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1475–1481, 2007     

Receptor-Targeted,Magneto-Mechanical Stimulation of Osteogenic Differentiation of Human Bone Marrow-Derived Mesenchymal Stem Cells

Mechanical cues are employed to promote stem cell differentiation and functional tissue formation in tissue engineering and regenerative medicine. We have developed a Magnetic Force Bioreactor (MFB) that delivers highly targeted local forces to cells at a pico-newton level, utilizing magnetic micro- and nano-particles to target cell surface receptors. In this study, we investigated the effects of magnetically targeting and actuating specific two mechanical-sensitive cell membrane receptors—platelet-derived growth factor receptor α (PDGFRα) and integrin α_νβ₃. It was found that a higher mineral-to-matrix ratio was obtained after three weeks of magneto-mechanical stimulation coupled with osteogenic medium culture by initially targeting PDGFRα compared with targeting integrin α_νβ₃ and non-treated controls. Moreover, different initiation sites caused a differentiated response profile when using a 2-day-lagged magneto-mechanical stimulation over culture periods of 7 and 12 days). However, both resulted in statistically higher osteogenic marker genes expression compared with immediate magneto-mechanical stimulation. These results provide insights into important parameters for designing appropriate protocols for ex vivo induced bone formation via magneto-mechanical actuation.