Marwa Tallawi

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.

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.

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.

Novel PGS/PCL electrospun fiber mats with patterned topographical features for cardiac patch applications.

Nano- and micro-scale topographical features play a critical role in the induction and maintenance of various cellular properties and functions, including morphology, adhesion, gene regulation, and cell-to-cell communication. In addition, recent studies have indicated that the structure and function of heart tissue are also sensitive to mechanical cues at the nano- and micro-scale. Although fabrication methods exist for generating topographical features on polymeric scaffolds for cell culture, current techniques, especially those with nano-scale resolution, are typically complex, prohibitively expensive and not accessible to most biology laboratories. Here, we present a simple and tunable fabrication method for the production of patterned electrospun fibers that simulate the complex anisotropic and multi-scale architecture of cardiac tissue, to promote cardiac cell alignment. This method is based on the combination of electrospinning and soft lithography techniques, in which electrospun fibers, based on a blend of poly(glycerol sebacate) and poly(caprolactone), were collected on a patterned Teflon-coated silicon wafer with imprinted topographical features. Different surface topographies were investigated, such as squares and grooves, with constant or different interspatial distances. In vitro cell culture studies successfully demonstrated the alignment of both C2C12 myoblasts and neonatal rat cardiomyocytes on fabricated electrospun patterned surfaces. C2C12 cells were cultured over a period of 72h to study the effect of topographical cues on cell morphology. Cells attached within the first 8h after seeding and after 24h most of the cells started to align responding to the topographical cues. Similarly, cardiomyocytes responded to the topographical features by aligning themselves and by expressing Connexin 43 along cellular junctions. Summarizing, we have developed a new method with the potential to significantly promote cardiac tissue engineering by fabricating electrospun fibers with defined topographical features to guide and instruct donor and/or host cells.

Biodegradable poly(glycerol sebacate)/poly(3-hydroxybutyrate)-TiO2 nanocomposites: fabrication and characterisation

Abstract Novel Nanocomposite films containing TiO2 nanoparticles incorporated in blend matrices of biocompatible and bioresorbable polymers, namely poly(glycerol sebacate) (PGS) and poly(3-hydroxybutyrate) P(3HB), were developed. The samples were fabricated via a sequential step of solvent casting followed by cross-linking. PGS/P(3HB) blends (controls) were fabricated in two different ratios, i.e. 7∶1 and 8∶1. Varying amounts of TiO2 nanoparticles (1 and 2 vol.-%) were incorporated into the matrices. SEM studies revealed that the TiO2 particles were distributed both within the matrix and on the surface of the films thus imparting surface nanotopography and increasing the surface roughness. These microstructural features combined with the cumulative effect of blending of the two polymeric systems influenced the wettability, chemical and mechanical properties of the films. In vitro degradation of the fabricated matrices in PBS medium over a 30 day period confirmed that the composites undergo weight loss and mechanical, chemical and surface topography changes. The nanocomposites constitute model biodegradable organic–inorganic systems suitable for tissue engineering applications.

POLY(GLYCEROL SEBACATE) FILMS MODIFIED BY THERMAL PROTEINS FOR CARDIAC TISSUE ENGINEERING

Scaffolds for cardiac tissue engineering must be designed to achieve adequate degradation kinetics and mechanical properties. In this study, bulk modification of poly(glycerol sebacate) (PGS) with different concentrations of thermal proteins (TP) was investigated to tailor the degradation properties of PGS. TP are polyamino acids formed by heating a mixture of amino acids with minimal proportions of glutamic or aspartic acid. The degradation study of TP-PGS was performed in vitro in phosphate buffered saline (PBS) solution over a 21 day period. Results showed that the degradation rate of PGS increased with increasing content of TP. After 21 days in PBS, degradation weight loss values of 9.40% ± 0.07, 7.3% ± 0.8 and 6.0% ± 0.4 were determined for PGS-TP2g, PGS-TP-0.01g and PGS-control, respectively. The studies also showed that TP altered the mechanical properties and surface hydrophilicity of PGS.