Poly-3-hydroxyoctanoate P(3HO), a medium chain length polyhydroxyalkanoate homopolymer from Pseudomonas mendocina.

Pseudomonas mendocina was found to produce a unique homopolymer of poly(3-hydroxyoctanoate), P(3HO), rather than a copolymer, when grown on sodium octanoate as the sole carbon source. Although this polymer has been produced by other organisms, interestingly this is the first time an absolute homopolymer has been produced by a wild type organism. In addition, a detailed study on the effects of different extraction methods on the yield, molecular weight, thermal properties, and lipopolysaccharide content of P(3HO) has been carried out. The organism was able to accumulate P(3HO) up to 31.38% of its dry cell weight within 48 h in mineral salt medium. Characterization of the monomer was carried out using FTIR, GC-MS, (13)C, (1)H, and HSQC NMR spectroscopy. The polymer had a crystallinity of 37.5%, Young's modulus value of 11.6 MPa and contact angle of 77.3°. Microstructural studies of solvent cast polymer films revealed a smooth surface topography with a root-mean-square roughness value of 0.238 µm.

Effect of substrate mechanics on cardiomyocyte maturation and growth.

Cardiac tissue engineering constructs are a promising therapeutic treatment for myocardial infarction, which is one of the leading causes of death. In order to further advance the development and regeneration of engineered cardiac tissues using biomaterial platforms, it is important to have a complete overview of the effects that substrates have on cardiomyocyte (CM) morphology and function. This article summarizes recent studies that investigate the effect of mechanical cues on the CM differentiation, maturation, and growth. In these studies, CMs derived from embryos, neonates, and mesenchymal stem cells were seeded on different substrates of various elastic modulus. Measuring the contractile function by force production, work output, and calcium handling, it was seen that cell behavior on substrates was optimized when the substrate stiffness mimicked that of the native tissue. The contractile function reflected changes in the sarcomeric protein confirmation and organization that promoted the contractile ability. The analysis of the literature also revealed that, in addition to matrix stiffness, mechanical stimulation, such as stretching the substrate during cell seeding, also played an important role during cell maturation and tissue development.

Poly(glycerol sebacate)/poly(butylene succinate-butylene dilinoleate) fibrous scaffolds for cardiac tissue engineering.

The present article investigates the use of a novel electrospun fibrous blend of poly(glycerol sebacate) (PGS) and poly(butylene succinate-butylene dilinoleate) (PBS-DLA) as a candidate for cardiac tissue engineering. Random electrospun fibers with various PGS/PBS-DLA compositions (70/30, 60/40, 50/50, and 0/100) were fabricated. To examine the suitability of these fiber blends for heart patches, their morphology, as well as their physical, chemical, and mechanical properties were measured before examining their biocompatibility through cell adhesion. The fabricated fibers were bead-free and exhibited a relatively narrow diameter distribution. The addition of PBS-DLA to PGS resulted in an increase of the average fiber diameter, whereas increasing the amount of PBS-DLA decreased the hydrophilicity and the water uptake of the nanofibrous scaffolds to values that approached those of neat PBS-DLA nanofibers. Moreover, the addition of PBS-DLA significantly increased the elastic modulus. Initial toxicity studies with C2C12 myoblast cells up to 72 h confirmed nontoxic behavior of the blends. Immunofluorescence analyses and scanning electron microscopy analyses confirmed that C2C12 cells showed better cell attachment and proliferation on electrospun mats with higher PBS-DLA content. However, immunofluorescence analyses of the 3-day-old rat cardiomyocytes cultured for 2 and 5 days demonstrated better attachment on the 70/30 fibers containing well-aligned sarcomeres and expressing high amounts of connexin 43 in cellular junctions indicating efficient cell-to-cell communication. It can be concluded, therefore, that fibrous PGS/PBS-DLA scaffolds exhibit promising characteristics as a biomaterial for cardiac patch applications.

Strategies for the chemical and biological functionalization of scaffolds for cardiac tissue engineering: a review.

The development of biomaterials for cardiac tissue engineering (CTE) is challenging, primarily owing to the requirement of achieving a surface with favourable characteristics that enhances cell attachment and maturation. The biomaterial surface plays a crucial role as it forms the interface between the scaffold (or cardiac patch) and the cells. In the field of CTE, synthetic polymers (polyglycerol sebacate, polyethylene glycol, polyglycolic acid, poly-l-lactide, polyvinyl alcohol, polycaprolactone, polyurethanes and poly(N-isopropylacrylamide)) have been proven to exhibit suitable biodegradable and mechanical properties. Despite the fact that they show the required biocompatible behaviour, most synthetic polymers exhibit poor cell attachment capability. These synthetic polymers are mostly hydrophobic and lack cell recognition sites, limiting their application. Therefore, biofunctionalization of these biomaterials to enhance cell attachment and cell material interaction is being widely investigated. There are numerous approaches for functionalizing a material, which can be classified as mechanical, physical, chemical and biological. In this review, recent studies reported in the literature to functionalize scaffolds in the context of CTE, are discussed. Surface, morphological, chemical and biological modifications are introduced and the results of novel promising strategies and techniques are discussed.

Bioactive electrospun fibers of poly(glycerol sebacate) and poly(ε-caprolactone) for cardiac patch application.

Scaffolds for cardiac patch application must meet stringent requirements such as biocompatibility, biodegradability, and facilitate vascularization in the engineered tissue. Here, a bioactive, biocompatible, and biodegradable electrospun scaffold of poly(glycerol sebacate)-poly(ε-caprolactone) (PGS-PCL) is proposed as a potential scaffold for cardiac patch application. The fibers are smooth bead free with average diameter = 0.8 ± 0.3 µm, mean pore size = 2.2 ± 1.2 µm, porosity = 62 ± 4%, and permeability higher than that of control biological tissue. For the first time, bioactive PGS-PCL fibers functionalized with vascular endothelial growth factor (VEGF) are developed, the approach used being chemical modification of the PGS-PCL fibers followed by subsequent binding of VEGF via amide bonding. The approach results in uniform immobilization of VEGF on the fibers; the concentrations are 1.0 µg cm(-2) for the PGS-PCL (H) and 0.60 µg cm(-2) for the PGS-PCL (L) samples. The bioactive scaffold supports the attachment and growth of seeded myogenic and vasculogenic cell lines. In fact, rat aortic endothelial cells also display angiogenic features indicating potential for the formation of vascular tree in the scaffold. These results therefore demonstrate the prospects of VEGF-functionalized PGS-PCL fibrous scaffold as promising matrix for cardiac patch application.

Tissue engineering of electrically responsive tissues using polyaniline based polymers: a review.

Conducting polymers have found numerous applications as biomaterial components serving to effectively deliver electrical signals from an external source to the seeded cells. Several cell types including cardiomyocytes, neurons, and osteoblasts respond to electrical signals by improving their functional outcomes. Although a wide variety of conducting polymers are available, polyaniline (PANI) has emerged as a popular choice due to its attractive properties such as ease of synthesis, tunable conductivity, environmental stability, and biocompatibility. PANI in its pure form has exhibited biocompatibility both in vitro and in vivo, and has been combined with a host of biodegradable polymers to form composites having a range of mechanical, electrical, and surface properties. Moreover, recent studies in literature report on the functionalization of polyaniline oligomers with end segments that make it biodegradable and improve its biocompatibility, two properties which make these materials highly desirable for applications in tissue engineering. This review will discuss the features and properties of PANI based composites that make them effective biomaterials, and it provides a comprehensive summary of studies where the use of PANI as a biomaterial component has enhanced cellular function and behavior. We also discuss recent studies utilizing functionalized PANI oligomers, and conclude that electroactive PANI and its derivatives show great promise in eliciting favorable responses from various cell lines that respond to electrical stimuli, and are therefore effective biomaterials for the engineering of electrically responsive biological tissues and organs.

Preparation and characterization of PHBV microsphere/45S5 bioactive glass composite scaffolds with vancomycin releasing function.

PHBV microsphere/45S5 bioactive glass (BG) composite scaffolds with drug release function were developed for bone tissue engineering. BG-based glass-ceramic scaffolds with high porosity (94%) and interconnected pore structure prepared by foam replication method were coated with PHBV microspheres (nominal diameter=3.5 µm) produced by water-in-oil-in-water double emulsion solvent evaporation method. A homogeneous microsphere coating throughout the porous structure of scaffolds was obtained by a simple dip coating method, using the slurry of PHBV microspheres in hexane. Compressive strength tests showed that the microsphere coating slightly improved the mechanical properties of the scaffolds. It was confirmed that the microsphere coating did not inhibit the bioactivity of the scaffolds in SBF. Hydroxyapatite crystals homogeneously grew not only on the struts of the scaffolds but also on the surface of microspheres within 7 days of immersion in SBF. Vancomycin was successfully encapsulated into the PHBV microspheres. The encapsulated vancomycin was released with a dual release profile involving a relatively low initial burst release (21%) and a sustained release (1 month), which is favorable compared to the high initial burst release (77%) and short release period (4 days) measured on uncoated scaffolds. The developed bioactive composite scaffold with drug delivery function has thus the potential to be used advantageously in bone tissue engineering.

Development and characterization of novel electrically conductive PANI-PGS composites for cardiac tissue engineering applications.

Cardiovascular diseases, especially myocardial infarction, are the leading cause of morbidity and mortality in the world, also resulting in huge economic burdens on national economies. A cardiac patch strategy aims at regenerating an infarcted heart by providing healthy functional cells to the injured region via a carrier substrate, and providing mechanical support, thereby preventing deleterious ventricular remodeling. In the present work, polyaniline (PANI) was doped with camphorsulfonic acid and blended with poly(glycerol-sebacate) at ratios of 10, 20 and 30vol.% PANI content to produce electrically conductive composite cardiac patches via the solvent casting method. The composites were characterized in terms of their electrical, mechanical and physicochemical properties. The in vitro biodegradability of the composites was also evaluated. Electrical conductivity increased from 0Scm(-1) for pure PGS to 0.018Scm(-1) for 30vol.% PANI-PGS samples. Moreover, the conductivities were preserved for at least 100h post fabrication. Tensile tests revealed an improvement in the elastic modulus, tensile strength and elasticity with increasing PANI content. The degradation products caused a local drop in pH, which was higher in all composite samples compared with pure PGS, hinting at a buffering effect due to the presence of PANI. Finally, the cytocompatibility of the composites was confirmed when C2C12 cells attached and proliferated on samples with varying PANI content. Furthermore, leaching of acid dopants from the developed composites did not have any deleterious effect on the viability of C2C12 cells. Taken together, these results confirm the potential of PANI-PGS composites for use as substrates to modulate cellular behavior via electrical stimulation, and as biocompatible scaffolds for cardiac tissue engineering applications.

Biomimetic poly(glycerol sebacate) (PGS) membranes for cardiac patch application.

In this study biomimetic poly(glycerol sebacate) PGS matrix was developed for cardiac patch application. The rationale was that such matrices would provide conducive environment for the seeded cells at the interphase with PGS. From the microstructural standpoint, PGS was fabricated into dense films and porous PGS scaffolds. From the biological aspect, biomimetic PGS membranes were developed via covalently binding peptides Tyr-Ile-Gly-Ser-Arg (YIGSR) and Gly-Arg-Gly-Asp-Ser-Pro (GRGDSP), corresponding to the epitope sequences of laminin and fibronectin, respectively onto the surface. To improve and enhance homogenous binding of peptides onto the PGS surface, chemical modification of its surface was carried out. A sequential regime of alkaline hydrolysis with 0.01 M NaOH for 5 min and acidification with 0.01 M HCl for 25s was optimal. More COOH chemical group was exposed without causing deleterious effect on the bulk properties of the polymer as revealed by the physicochemical analysis carried out. HPLC analysis, chemical imaging and ToF-SIMS were able to establish the successful homogenous functionalization of PGS membranes with the peptides. Finally, the developed biomimetic membranes supported the adhesion and growth of rat and human cardiac progenitor cells.

Imaging internal features of whole, unfixed bacteria.

Wet scanning-transmission electron microscopy (STEM) is a technique that allows high-resolution transmission imaging of biological samples in a hydrated state, with minimal sample preparation. However, it has barely been used for the study of bacterial cells. In this study, we present an analysis of the advantages and disadvantages of wet STEM compared with standard transmission electron microscopy (TEM). To investigate the potential applications of wet STEM, we studied the growth of polyhydroxyalkanoate and triacylglycerol carbon storage inclusions. These were easily visible inside cells, even in the early stages of accumulation. Although TEM produces higher resolution images, wet STEM is useful when preservation of the sample is important or when studying the relative sizes of different features, since samples do not need to be sectioned. Furthermore, under carefully selected conditions, it may be possible to maintain cell viability, enabling new types of experiments to be carried out. To our knowledge, internal features of bacterial cells have not been imaged previously by this technique.