Fabrication and characterization of silk/forsterite composites for tissue engineering applications

In this research, novel composite scaffolds consisting of silk fibroin and forsterite powder were prepared by a freeze-drying method. In addition, the effects of forsterite powder contents on the structure of the scaffolds were investigated to provide an appropriate composite for bone tissue engineering applications. The morphology studies using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques showed that the forsterite ceramic was well distributed throughout the structures of SF/forsterite scaffolds. Furthermore, the forsterite powder (up to 40 wt%) was homogenously distributed within the silk fibroin as a matrix.     

Synthesis and degradation of agar‐carbomer based hydrogels for tissue engineering applications

Hydrogels studied in this investigation, synthesized starting from agarose and Carbomer 974P, were chosen for their potential use in tissue engineering. The strong ability of hydrogels to mimic living tissues should be complemented with optimized degradation time profiles: a critical property for biomaterials but essential for the integration with target tissue. In this study, chosen hydrogels were characterized both from a rheological and a structural point of view before studying the chemistry of their degradation, which was performed by several analysis: infrared bond response [Fourier transform infrared (FT‐IR)], calorimetry [differential scanning Calorimetry (DSC)], and % mass loss. Degradation behaviors of Agar‐Carbomer hydrogels with different degrees of crosslinkers were evaluated monitoring peak shifts and thermal property changes. It was found that the amount of crosslinks heavily affect the time and the magnitude related to the process. The results indicate that the degradation rates of Agar‐Carbomer hydrogels can be controlled and tuned to adapt the hydrogel degradation kinetics for different cell housing and drug delivery applications. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Porous composites of hydroxyapatite‐filled poly[ethylene‐co‐(vinyl acetate)] for tissue engineering

A novel porous composite of hydroxyapatite/poly[ethylene‐co‐vinyl acetate)] (HAP/EVA) having better osteointegration was fabricated by gas foaming technique using a non toxic gas blowing agent intended for bone replacement applications. Combined techniques of scanning electronic microscopy (SEM) and X‐ray microcomputed tomography (µCT) analysis showed that the pore size and pore volume of the porous composite decrease with the increase of HAP content. The gravimetric analysis evidenced for good pore interconnectivity within the porous composites. Energy dispersive X‐ray analysis (EDX) studies inveterated the even scattering of Ca ions which in turn indicate the uniform dispersion of HAP particles in the composites. The significant gradation in Ca ion concentration seen in EDX studies is well accordance with the amount of HAP loading in the sample. Mechanical properties of the porous composite having different HAP content were measured to have the compressive strength varying from 1.06 to 2.2 MPa. Non‐cytotoxic character of the material was observed by the cytocompatibility studies. The metabolic activity of L929 cells seeded on the material assessed by [3‐(4,5‐dimethylthiazol)‐2‐yl]‐2,5‐diphenyltertrazolium bromide (MTT) assay was found to be 91.8%. The adhesion and migration of the cells inside the pore walls were visualized by confocal microscopy. Copyright © 2010 Society of Chemical Industry     

Thiol–norbornene photoclick hydrogels for tissue engineering applications

Thiol–norbornene (thiol–ene) photoclick hydrogels have emerged as a diverse material system for tissue engineering applications. These hydrogels are crosslinked through light‐mediated orthogonal reactions between multifunctional norbornene‐modified macromers [e.g., poly(ethylene glycol) (PEG), hyaluronic acid, gelatin] and sulfhydryl‐containing linkers (e.g., dithiothreitol, PEG–dithiol, biscysteine peptides) with a low concentration of photoinitiator. The gelation of thiol–norbornene hydrogels can be initiated by long‐wave UV light or visible light without an additional coinitiator or comonomer. The crosslinking and degradation behaviors of thiol–norbornene hydrogels are controlled through material selections, whereas the biophysical and biochemical properties of the gels are easily and independently tuned because of the orthogonal reactivity between norbornene and the thiol moieties. Uniquely, the crosslinking of step‐growth thiol–norbornene hydrogels is not oxygen‐inhibited; therefore, gelation is much faster and highly cytocompatible compared with chain‐growth polymerized hydrogels with similar gelation conditions. These hydrogels have been prepared as tunable substrates for two‐dimensional cell cultures as microgels and bulk gels for affinity‐based or protease‐sensitive drug delivery, and as scaffolds for three‐dimensional cell encapsulation. Reports from different laboratories have demonstrated the broad utility of thiol–norbornene hydrogels in tissue engineering and regenerative medicine applications, including valvular and vascular tissue engineering, liver and pancreas‐related tissue engineering, neural regeneration, musculoskeletal (bone and cartilage) tissue regeneration, stem cell culture and differentiation, and cancer cell biology. This article provides an up‐to‐date overview on thiol–norbornene hydrogel crosslinking and degradation mechanisms, tunable material properties, and the use of thiol–norbornene hydrogels in drug‐delivery and tissue engineering applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41563.     

Preparation and characterization of Chitosan and PLGA‐based scaffolds for tissue engineering applications

Three dimensional (3D) biodegradable porous scaffolds play a crucial role in bone tissue repair. In this study, four types of 3D polymer/hydroxyapatite (HAp) composite scaffolds were prepared by freeze drying technique in order to mimic the organic/inorganic nature of the bone. Chitosan (CH) and poly(lactic acid‐co‐glycolic acid) (PLGA) were used as the polymeric part and HAp as the inorganic component. Properties of the resultant scaffolds, such as morphology, porosity, degradation, water uptake, mechanical and thermal stabilities were examined. 3D scaffolds having interconnected macroporous structure and 77–89% porosity were produced. The pore diameters were in the range of 6 and 200 µm. PLGA and HAp containing scaffolds had the highest compressive modulus. PLGA maintained the strength by decreasing water uptake but increased the degradation rate. Scaffolds seeded with SaOs‐2 osteoblast cells showed that all scaffolds were capable of encouraging cell adhesion and proliferation. The presence of HAp particles caused an increase in cell number on CH‐HAp scaffolds compared to CH scaffolds, while cell number decreased when PLGA was incorporated in the structure. CH‐PLGA scaffolds showed highest cell number on days 7 and 14 compared to others. Based on the properties such as interconnected porosity, high mechanical strength, and in vitro cell proliferation, blend scaffolds have the potential to be applied in hard tissue treatments. POLYM. COMPOS., 36:1917–1930, 2015. © 2014 Society of Plastics Engineers     

Oxygen‐releasing biomaterials for tissue engineering

Due to the increasing demand to generate thick and vascularized tissue‐engineered constructs, novel strategies are currently being developed. An emerging example is the generation of oxygen‐releasing biomaterials to tackle mass transport and diffusion limitations within engineered tissue constructs. Biomaterials containing oxygen‐releasing molecules can be fabricated in various forms, such as hybrid thin films, microparticles or three dimensional scaffolds. In this perspective, we summarize various oxygen‐releasing reagents and their potential applications in regenerative engineering. Moreover, we review the main approaches for fabricating oxygen‐releasing biomaterials for a range of tissue engineering applications. © 2013 Society of Chemical Industry     

Plasticization of poly‐L‐lactide for tissue engineering

Plasticization of medical grade poly‐L ‐lactide (PLLA) by addition of polyethylene glycol (PEG) with various molar masses has been evaluated as means of producing low stiffness matrices for bioresorbable scaffolds for soft‐tissue engineering applications. As reported previously, the T_g of injection molded specimens of the PLLA/PEG blends decreased strongly with PEG content, so that at PEG contents of 15 and 25 wt % it became significantly lower than normal human body temperature, implying an essentially rubber‐like mechanical response in vivo. The degree of crystallinity of the moldings also increased strongly with PEG content, reaching a maximum of about 60 wt % at 25 wt % PEG. Moreover, after the immersion in phosphate‐buffered saline for 5 days in 37°C to simulate conditions in vivo, the moldings with the highest PEG contents showed increased water uptake and, for relatively low molar mass PEG, significant mass loss, associated with phase separation and leaching of the PEG. Blends with relatively low PEG contents also showed large increases in their degree of crystallinity. The implications of these changes for the in vivo performance of the blends and their potential for development as matrices for bioresorbable scaffolds are discussed in the light of results from a series of PLLA/PEG copolymers. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Polymers for medical and tissue engineering applications

Recent decades have seen great advancements in medical research into materials, both natural and synthetic, that facilitate the repair and regeneration of compromised tissues through the delivery and support of cells and/or biomolecules. Biocompatible polymeric materials have become the most heavily investigated materials used for such purposes. Naturally‐occurring and synthetic polymers, including their various composites and blends, have been successful in a range of medical applications, proving to be particularly suitable for tissue engineering (TE) approaches. The increasing advances in polymeric biomaterial research combined with the developments in manufacturing techniques have expanded capabilities in tissue engineering and other medical applications of these materials. This review will present an overview of the major classes of polymeric biomaterials, highlight their key properties, advantages, limitations and discuss their applications. © 2014 Society of Chemical Industry     

Albumin-based biomaterial for lung tissue engineering applications

The role of albumin-based biomaterials in tissue engineering (TE) cannot be overemphasized. The authors review the role of albumin in lungs scaffold grafting, which promotes cell seeding. Albumin grafted on decellularized lungs scaffold is presented as a great support material for cell-tissue interaction as well as for ease in attachment, growth, and differentiation when seeded with different types of cells. Albumin scaffold fabrication from different sources is a promising approach that may facilitate medical treatments from bench-to-bed, although the role of this scaffold in lungs surfactant proteins regeneration and binding needs to be fully elucidated.     

A library of tunable agarose carbomer‐based hydrogels for tissue engineering applications: The role of cross‐linkers

The role of the crosslinking agents was studied for a series of agarose–carbomer‐based hydrogels, specifically developed for tissue engineering applications, and was quantified using the most typical polycondensation parameter; the ratio between the reacting moieties, i.e., hydroxyl (A) and carboxyl (B) groups. Because of the bonds among hydrophilic groups, as A/B ratio was increased, the gel network showed higher compactness and less ability to swell. The role of crosslinkers was also further analyzed using environmental scanning electron microscopy (E/SEM) and rheological measurements. SEM analysis underlined the presence of different structures as well as the erosion due to the presence of cosolvents in hydrogel synthesis. Rheological measurements showed the dependence of crossover strain value and yield stress upon the ratio of hydroxyl/carboxyl groups and, generally, a clear pseudoplastic behavior. Such detailed characterizations were essential to investigate the design of an optimized formulation capable of being a proper hosting environment for glial cells, which were here used as they are a promising cell type in several central nervous system repair strategies. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123:2211–2221, 2012     

Studies on unsaturated polyester composites for high‐temperature applications

Unsaturated polyesters are widely used in a number of applications. However, they fall short in areas where high thermal stability and performance at higher temperatures are required. Previous investigations have studied the kinetics and degradation behavior of bismaleimide‐based unsaturated polyester composites. The current study aimed to investigate the effects of bismaleimide on the mechanical properties and thermal class of a bismaleimide unsaturated polyester composition. Addition of bismaleimide to the composition resulted in an increase in the thermal index of the material, thus making it useful in applications where high temperature stability is required. However, once degradation was initiated, the addition of bismaleimide had a detrimental effect on the stability of the composites. J. VINYL ADDIT. TECHNOL., 2012. © 2012 Society of Plastics Engineers     

Bio‐inspired materials for biosensing and tissue engineering

This review gives an overview of the research presented in the lecture by Professor Molly Stevens given on the occasion of the 2010 Polymer International‐IUPAC award for creativity in polymer science. Herein we describe some highlights of our biomaterials‐based approaches in the fields of regenerative medicine and biosensing. We have developed a range of polymeric and inorganic materials for use in tissue engineering scaffolds as well as for elucidating the impact of various materials‐based cues on cell behaviour and tissue formation. Specific examples in the field of bone repair are outlined. Furthermore, recent achievements in the creation of sensitive, simple and robust assays for enzyme detection are presented. Our approaches in this field are based on the combination of various nanoparticles with designer polypeptides to provide quantitative colorimetric read‐outs where a specific active enzyme is present. These enzyme assays are likely to be useful for portable point‐of‐care diagnoses of a range of diseases with significant global impact. Copyright © 2012 Society of Chemical Industry     

New halogen‐free fire retardant for engineering plastic applications

A comparative study of the fire‐retardant efficiency of three commercial aryl phosphates—triphenyl phosphate (TPP), resorcinol bis(diphenyl phosphate) (RDP) and bisphenol A bis(diphenyl phosphate) (BDP)—in PC/ABS blends was carried out. The thermal and hydrolytic stability of the fire‐retardant resins, as well as their physical properties, was also studied. The use of RDP and BDP is preferred over TPP because of superior properties, whereas BDP shows better fire‐retardant efficiency, hydrolytic stability, and thermal stability than RDP.     

Lateritic soil geopolymer composites for ceramics and engineering construction applications

Characterization of an Amazonian, laterite-doped, kaolinitic soil (LK) or “lateritic soil” and laterite-doped metakaolin (LMK) calcined at two distinct rates, as well as granite-marble (GM) particulate industrial wastes was performed by thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray fluorescence (XRF) spectrometry, and particle size and distribution analysis. In addition, an LMK geopolymer (GP) and a lateritic metakaolin-based GP reinforced with granite-marble composite (LMKGP-GM) were tested for water resistance and for mechanical strength. XRD and XRF were used to investigate the composition of the composite materials, while XRD confirmed the formation of GP. Just as in the case of highly reactive commercial metakaolin used in construction, according to this study, lateritic soil-based metakaolin presented similar characteristics. Therefore, it could be used in the development of more sustainable ceramics and construction materials, including the use of GM waste as a reinforcing phase/aggregate.     

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.     

Covalently linked biocompatible graphene/polycaprolactone composites for tissue engineering

Two synthesis routes to graphene/polycaprolactone composites are introduced and the properties of the resulting composites compared. In the first method, mixtures are produced using solution processing of polycaprolactone and well dispersed, chemically reduced graphene oxide and in the second, an esterification reaction covalently links polycaprolactone chains to free carboxyl groups on the graphene sheets. This is achieved through the use of a stable anhydrous dimethylformamide dispersion of graphene that has been highly chemically reduced resulting in mostly peripheral ester linkages. The resulting covalently linked composites exhibit far better homogeneity and as a result, both Young’s modulus and tensile strength more than double and electrical conductivities increase by ≈ 14 orders of magnitude over the pristine polymer at less than 10% graphene content. In vitro cytotoxicity testing of the materials showed good biocompatibility resulting in promising materials for use as conducting substrates for the electrically stimulated growth of cells.     

Molecular thermodynamics of soft self‐assembling structures for engineering applications

Controlling self‐assembly is a key issue in many applications such as encapsulation of drugs, micelle separation, and fabrication of nanoporous materials. For providing guidance to control self‐assembly, a reliable prognosis of aggregation behavior is indispensable. Molecular thermodynamic models have been developed for different types of soft mesoscale structures formed by aggregating chainlike amphiphilic molecules. Examples include nonionic and ionic copolymer gels swelling in selective solvents, surfactant micellar solutions and amphiphilic membranes. Though rather different in chemical nature and applications, these systems are all characterized by self‐assembly into soft mesoscale structures that are sensitive to external conditions or applied stimuli. The models predict a number of thermodynamic and structural characteristics (equilibrium size and stability of different morphologies, equilibrium swelling, elastic properties, solute partitioning, etc.) in terms of several adjustable parameters and molecular characteristics of components. Consideration of nanoscale morphology gives rise to interesting structure–property relations reflected by relatively simple models. New findings help estimate how variations of controllable factors such as pH, salinity and additives affect self‐assembly patterns and aggregate properties. Recent advances in the development of molecular thermodynamic aggregation models, factors restricting implementation of these models and trends in the field are discussed. © 2015 Society of Chemical Industry     

Characterization of nanosilica‐filled epoxy composites for electrical and insulation applications

We report in this article the results of nanosilica (SiO₂)‐filled epoxy composites with different loadings and their electrical, thermal, mechanical, and free‐volume properties characterized with different techniques. The morphological features were studied by transmission electron microscopy, and differential scanning calorimetry was used to investigate the glass‐transition temperature (T_g) of the nanocomposites. The properties of the nanocomposites showed that the electrical resistivity (ρ), ultimate tensile strength, and hardness of the composites increased with SiO₂ weight fraction up to 10 wt % and decreased thereafter; this suggested that the beneficial properties occurred up to this weight fraction. The temperature and seawater aging had a negative influence on ρ; that is, ρ decreased with increases in the temperature and aging. The free‐volume changes (microstructural) in the composite systems correlated with seawater aging but did not correlate so well with the mechanical properties. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Thin‐film polyimide/indium tin oxide composites for photovoltaic applications

Soluble polyimides were prepared from suitable monomers and were evaluated for their thermal and mechanical properties. The polymers were processed into films for use as supports for transparent, conductive indium tin oxide (ITO) layers. After deposition, annealing in vacuo at temperatures up to 400°C was performed to test the ability of the materials to endure typical device fabrication temperatures without damage to the ITO‐coated polymeric substrate. The evolution of the structural, optical, and electrical characteristics with the annealing temperature was analyzed and compared with that of polymeric and conventional glass substrates as references. Polyimide 6F6F, synthesized from hexafluoroisopropylidene diphthalic dianhydride and hexafluoroisopropylidene dianiline, had optimal characteristics for photovoltaic applications, permitting the achievement of conductive, ITO‐coated samples with optical transmission greater than 75% in the visible and near‐infrared wavelength ranges, without significant deterioration of their properties after vacuum annealing at temperatures up to 350°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3491–3497, 2007     

Numerical simulations of bioextruded polymer scaffolds for tissue engineering applications

Scaffolds provide a temporary mechanical and vascular support for tissue regeneration while shaping the in‐growth tissues. These scaffolds must be biocompatible, biodegradable, enclose appropriate porosity, pore structure and pore distribution, and have optimal structural and vascular performance, with both surface and structural compatibility. Surface compatibility means a chemical, biological and physical suitability to the host tissue. Structural compatibility corresponds to an optimal adaptation to the mechanical behaviour of the host tissue. Recent advances in the design of tissue engineering scaffolds are increasingly relying on computer‐aided design modelling and numerical simulations. The design of optimized scaffolds based on fundamental knowledge of their macro microstructure is a relevant topic of research. This research work presents a comparison between experimental compressive data and numerical simulations of bioextruded polymer scaffolds with different pore sizes for the elastic and plastic domain. Constitutive behaviour models of cellular structures are used in numerical simulations to compare numerical data with the experimental compressive data. Vascular simulation is also used in the design process of the extrusion‐based scaffolds in order to define an optimized scaffold design. © 2013 Society of Chemical Industry