Vascular Remodeling of Clinically Used Patches and Decellularized Pericardial Matrices Recellularized with Autologous or Allogeneic Cells in a Porcine Carotid Artery Model.

Background: Cardiovascular surgery is confronted by a lack of suitable materials for patch repair. Acellular animal tissues serve as an abundant source of promising biomaterials. The aim of our study was to explore the bio-integration of decellularized or recellularized pericardial matrices in vivo. Methods: Porcine (allograft) and ovine (heterograft, xenograft) pericardia were decellularized using 1% sodium dodecyl sulfate ((1) Allo-decel and (2) Xeno-decel). We used two cell types for pressure-stimulated recellularization in a bioreactor: autologous adipose tissue-derived stromal cells (ASCs) isolated from subcutaneous fat of pigs ((3) Allo-ASC and (4) Xeno-ASC) and allogeneic Wharton's jelly mesenchymal stem cells (WJCs) ((5) Allo-WJC and (6) Xeno-WJC). These six experimental patches were implanted in porcine carotid arteries for one month. For comparison, we also implanted six types of control patches, namely, arterial or venous autografts, expanded polytetrafluoroethylene (ePTFE Propaten® Gore®), polyethylene terephthalate (PET Vascutek®), chemically stabilized bovine pericardium (XenoSure®), and detoxified porcine pericardium (BioIntegral® NoReact®). The grafts were evaluated through the use of flowmetry, angiography, and histological examination. Results: All grafts were well-integrated and patent with no signs of thrombosis, stenosis, or aneurysm. A histological analysis revealed that the arterial autograft resembled a native artery. All other control and experimental patches developed neo-adventitial inflammation (NAI) and neo-intimal hyperplasia (NIH), and the endothelial lining was present. NAI and NIH were most prominent on XenoSure® and Xeno-decel and least prominent on NoReact®. In xenografts, the degree of NIH developed in the following order: Xeno-decel > Xeno-ASC > Xeno-WJC. NAI and patch resorption increased in Allo-ASC and Xeno-ASC and decreased in Allo-WJC and Xeno-WJC. Conclusions: In our setting, pre-implant seeding with ASC or WJC had a modest impact on vascular patch remodeling. However, ASC increased the neo-adventitial inflammatory reaction and patch resorption, suggesting accelerated remodeling. WJC mitigated this response, as well as neo-intimal hyperplasia on xenografts, suggesting immunomodulatory properties.

pH Modification of High-Concentrated Collagen Bioinks as a Factor Affecting Cell Viability, Mechanical Properties, and Printability.

The 3D bioprinting of cell-incorporated gels is a promising direction in tissue engineering applications. Collagen-based hydrogels, due to their similarity to extracellular matrix tissue, can be a good candidate for bioink and 3D bioprinting applications. However, low hydrogel concentrations of hydrogel (<10 mg/mL) provide insufficient structural support and, in highly concentrated gels, cell proliferation is reduced. In this study, we showed that it is possible to print highly concentrated collagen hydrogels with incorporated cells, where the viability of the cells in the gel remains very good. This can be achieved simply by optimizing the properties of the bioink, particularly the gel composition and pH modification, as well as by optimizing the printing parameters. The bioink composed of porcine collagen hydrogel with a collagen concentration of 20 mg/mL was tested, while the final bioink collagen concentration was 10 mg/mL. This bioink was modified with 0, 5, 9, 13, 17 and 20 µL/mL of 1M NaOH solution, which affected the resulting pH and gelling time. Cylindrical samples based on the given bioink, with the incorporation of porcine adipose-derived stromal cells, were printed with a custom 3D bioprinter. These constructs were cultivated in static conditions for 6 h, and 3 and 5 days. Cell viability and morphology were evaluated. Mechanical properties were evaluated by means of a compression test. Our results showed that optimal composition and the addition of 13 µL NaOH per mL of bioink adjusted the pH of the bioink enough to allow cells to grow and divide. This modification also contributed to a higher elastic modulus, making it possible to print structures up to several millimeters with sufficient mechanical resistance. We optimized the bioprinter parameters for printing low-viscosity bioinks. With this experiment, we showed that a high concentration of collagen gels may not be a limiting factor for cell proliferation.

Collagen Bioinks for Bioprinting: A Systematic Review of Hydrogel Properties, Bioprinting Parameters, Protocols, and Bioprinted Structure Characteristics.

Bioprinting is a modern tool suitable for creating cell scaffolds and tissue or organ carriers from polymers that mimic tissue properties and create a natural environment for cell development. A wide range of polymers, both natural and synthetic, are used, including extracellular matrix and collagen-based polymers. Bioprinting technologies, based on syringe deposition or laser technologies, are optimal tools for creating precise constructs precisely from the combination of collagen hydrogel and cells. This review describes the different stages of bioprinting, from the extraction of collagen hydrogels and bioink preparation, over the parameters of the printing itself, to the final testing of the constructs. This study mainly focuses on the use of physically crosslinked high-concentrated collagen hydrogels, which represents the optimal way to create a biocompatible 3D construct with sufficient stiffness. The cell viability in these gels is mainly influenced by the composition of the bioink and the parameters of the bioprinting process itself (temperature, pressure, cell density, etc.). In addition, a detailed table is included that lists the bioprinting parameters and composition of custom bioinks from current studies focusing on printing collagen gels without the addition of other polymers. Last but not least, our work also tries to refute the often-mentioned fact that highly concentrated collagen hydrogel is not suitable for 3D bioprinting and cell growth and development.

Human osteoblast-like SAOS-2 cells on submicron-scale fibers coated with nanocrystalline diamond films.

A unique composite nanodiamond-based porous material with a hierarchically-organized submicron-nano-structure was constructed for potential bone tissue engineering. This material consisted of submicron fibers prepared by electrospinning of silicon oxide (SiOx), which were oxygen-terminated (O-SiOx) and were hermetically coated with nanocrystalline diamond (NCD) films. The NCD films were then terminated with hydrogen (H-NCD) or oxygen (O-NCD). The materials were tested as substrates for the adhesion, growth and osteogenic differentiation of human osteoblast-like Saos-2 cells. The number and the spreading area of the initially adhered cells, their growth rate during 7 days after seeding and the activity of alkaline phosphatase (ALP) were significantly higher on the NCD-coated samples than on the uncoated O-SiOx samples. In addition, the concentration of type I collagen was significantly higher in the cells on the O-NCD-coated samples than on the bare O-SiOx samples. The observed differences could be attributed to the tunable wettability of NCD and to the more appropriate surface morphology of the NCD-coated samples in contrast to the less stable, rapidly eroding bare SiOx surface. The H-NCD coatings and the O-NCD coatings both promoted similar initial adhesion of Saos-2 cells, but the subsequent cell proliferation activity was higher on the O-NCD-coated samples. The concentration of beta-actin, vinculin, type I collagen and alkaline phosphatase (ALP), the ALP activity, and also the calcium deposition tended to be higher in the cells on the O-NCD-coated samples than on the H-NCD-coated samples, although these differences did not reach statistical significance. The improved cell performance on the O-NCD-coated samples could be attributed to higher wettability of these samples (water drop contact angle less than 10°), while the H-NCD-coated samples were hydrophobic (contact angle >70°). NCD-coated porous SiOx meshes can therefore be considered as appropriate scaffolds for bone tissue engineering, particularly those with an O-terminated NCD coating.

Accelerated in vitro recellularization of decellularized porcine pericardium for cardiovascular grafts.

An ideal decellularized allogenic or xenogeneic cardiovascular graft should be capable of preventing thrombus formation after implantation. The antithrombogenicity of the graft is ensured by a confluent endothelial cell layer formed on its surface. Later repopulation and remodeling of the scaffold by the patient's cells should result in the formation of living autologous tissue. In the work presented here, decellularized porcine pericardium scaffolds were modified by growing a fibrin mesh on the surface and inside the scaffolds, and by attaching heparin and human vascular endothelial growth factor (VEGF) to this mesh. Then the scaffolds were seeded with human adipose tissue-derived stem cells (ASCs). While the ASCs grew only on the surface of the decellularized pericardium, the fibrin-modified scaffolds were entirely repopulated in 28 d, and the scaffolds modified with fibrin, heparin and VEGF were already repopulated within 6 d. Label free mass spectrometry revealed fibronectin, collagens, and other extracellular matrix proteins produced by ASCs during recellularization. Thin layers of human umbilical endothelial cells were formed within 4 d after the cells were seeded on the surfaces of the scaffold, which had previously been seeded with ASCs. The results indicate that an artificial tissue prepared by in vitro recellularization and remodeling of decellularized non-autologous pericardium with autologous ASCs seems to be a promising candidate for cardiovascular grafts capable of accelerating in situ endothelialization. ASCs resemble the valve interstitial cells present in heart valves. An advantage of this approach is that ASCs can easily be collected from the patient by liposuction.

Applications of Nanocellulose/Nanocarbon Composites: Focus on Biotechnology and Medicine.

Nanocellulose/nanocarbon composites are newly emerging smart hybrid materials containing cellulose nanoparticles, such as nanofibrils and nanocrystals, and carbon nanoparticles, such as "classical" carbon allotropes (fullerenes, graphene, nanotubes and nanodiamonds), or other carbon nanostructures (carbon nanofibers, carbon quantum dots, activated carbon and carbon black). The nanocellulose component acts as a dispersing agent and homogeneously distributes the carbon nanoparticles in an aqueous environment. Nanocellulose/nanocarbon composites can be prepared with many advantageous properties, such as high mechanical strength, flexibility, stretchability, tunable thermal and electrical conductivity, tunable optical transparency, photodynamic and photothermal activity, nanoporous character and high adsorption capacity. They are therefore promising for a wide range of industrial applications, such as energy generation, storage and conversion, water purification, food packaging, construction of fire retardants and shape memory devices. They also hold great promise for biomedical applications, such as radical scavenging, photodynamic and photothermal therapy of tumors and microbial infections, drug delivery, biosensorics, isolation of various biomolecules, electrical stimulation of damaged tissues (e.g., cardiac, neural), neural and bone tissue engineering, engineering of blood vessels and advanced wound dressing, e.g., with antimicrobial and antitumor activity. However, the potential cytotoxicity and immunogenicity of the composites and their components must also be taken into account.

Treatments for enhancing the biocompatibility of titanium implants.

Titanium surface treatment is a crucial process for achieving sufficient osseointegration of an implant into the bone. If the implant does not heal sufficiently, serious complications may occur, e.g. infection, inflammation, aseptic loosening of the implant, or the stress-shielding effect, as a result of which the implant may need to be reoperated. After a titanium graft has been implanted, several interactions are crucial in order to create a strong bone-implant connection. It is essential that cells adhere to the surface of the implant. Surface roughness has a significant influence on cell adhesion, and also on improving and accelerating osseointegration. Other highly important factors are biocompatibility and resistance to bacterial contamination. Bio-inertness of titanium is ensured by the protective film of titanium oxides that forms spontaneously on its surface. This film prevents the penetration of metal compounds, and it is well-adhesive for calcium and phosphate ions, which are necessary for the formation of the mineralized bone structure. Since the presence of the film alone is not sufficient for the biocompatibility of titanium, a suitable surface finish is required to create a firm bone-implant connection. In this review, we explain and compare the most widely-used methods for modulating the surface roughness of titanium implants in order to enhance cell adhesion on the surface of the implant, e.g. plasma spraying, sandblasting, acid etching, laser treatment, sol-gel etc., The methods are divided into three overlapping groups, according to the type of modification.

Nanocrystalline diamond-based impedance sensors for real-time monitoring of adipose tissue-derived stem cells.

Cell-based impedance spectroscopy is a promising label-free method for electrical monitoring of cell activity. Here we present a diamond-based impedance sensor with built-in gold interdigitated electrodes (IDT) as a promising platform for simultaneous electrical and optical monitoring of adipose tissue-derived stem cells (ASCs). The impedance spectra were collected in a wide frequency range (from 100 Hz to 50 kHz) for 90 h of cell cultivation in chambers designed for static cultivation. Absolute impedance spectra were analyzed in terms of measured frequencies and cell properties monitored by a high-resolution digital camera. The control commercially-available impedance system, based on gold electrodes exposed to the cultivation media, and also our specially developed sensor with gold electrodes built into a diamond thin film detected three phases of cell growth, namely the phase of cell attachment and spreading, the phase of cell proliferation, and the stationary phase without significant changes in cell number. These results were confirmed by simultaneous live cell imaging. The design of the sensing electrode is discussed, pointing out its enhanced sensitivity for a certain case. The diamond-based sensor appeared to be more sensitive for detecting the cell-substrate interaction in the first phase of cell growth, while the control system was more sensitive in the second phase of cell growth.

Iterative reconstruction of pulmonary MDCT angiography: effects on image quality, effective dose and estimated organ dose to the breast.

AIMS: To compare the image characteristics, effective dose and estimated organ dose to the female breast in pulmonary MDCT angiography (MDCTA), reconstructed with either standard filtered back projection (FBP), or iterative reconstruction in image space (IRIS). METHODS: Pulmonary MDCTA performed in 116 females (age 18 - 77 years; body mass index 15 - 48) was reconstructed with FBP (n=52) or IRIS (n=64). Scans were acquired on a 128-row MDCT system using automatic tube current modulation, 100 kV tube voltage, and a quality reference mAs value of 120 (FBP) and 80 (IRIS). Dose was calculated from CT dose index (CTDIvol) and dose length product (DLP) values utilising ImPACT software. Image noise was measured within the pulmonary artery. Qualitative visual assessment of the scans was performed (1=negligible noise, 5=noise obscuring diagnostic information). RESULTS: The average CTDIvol yielded 4.33 mGy for FBP and 3.54 mGy for IRIS, respectively (18.2% decrease). The average effective scan dose was 2.73±0.57 mSv (FBP) and 2.29±0.68 mSv (IRIS), respectively (16.1% decrease). The estimated average organ dose to the breast decreased from 5.1±1.1 mGy (FBP) to 4.2±1.2 mGy (IRIS, 17.6% decrease). No non-diagnostic scans (score 5) were encountered in either group. Significant improvement in image noise levels (P<0.01) and subjective image quality (P<0.02) were noted in IRIS group. CONCLUSION: Pulmonary MDCTA utilizing a 100 kV technique, automatic tube current modulation, and iterative image reconstruction offers robust results in routine conditions among an unselected female population, with breast doses being comparable to two-view digital mammography. Moreover, iterative reconstruction offers improvements in both image noise and visual perception of the scans, thus suggesting a potential for further dose reduction.