A Conductive polylactic acid/polyaniline porous scaffold via freeze extraction for potential biomedical applications

This paper reports for the first time a simple yet effective method for fabricating a conductive and highly porous scaffold material made up of polylactic acid (PLA) and conducting polyaniline (PANI). The electrical percolation state was successfully obtained at 3 wt% of PANI inclusions and reached a conductivity level of useable tissue engineering applications at 4 wt%. In addition, preliminary bioactivity test results indicated that the protonating agent could form a chelate at the scaffold surface leading to good in-vitro apatite forming ability during biomimetic immersion. This new conductive scaffold has potential as a suitable biomedical material that requires electrical conductivity.     

Biofabrication of a flexible and conductive 3D polymeric scaffold for neural tissue engineering applications; physical,chemical, mechanical,and biological evaluations

Tissue engineering approach aims to overcome the transplant drawbacks and facilitate tissue repair and regeneration. Here, a new conductive, highly porous, and flexible polycaprolactone/gelatin/polypyrrole/graphene 3D scaffolds for nerve tissue repair is presented. A simple and efficient porogen leaching fabrication method is applied to create a 3D network with a pore radius of 3.8 ± 0.7 to 4.2 ± 0.8 μm with an exceptional uniform circular porous structure. The conductivity of the polymeric scaffold without graphene, in wet conditions, was found to be 0.78 ± 0.1 S.m⁻¹ and it increased to 3.3 ± 0.2 S.m⁻¹ for the optimized sample containing 3wt% graphene (G3). Tensile strength was measured at 163 KPa for the base sample (without graphene) and improved to 526 KPa for G3 sample. Following 42 days of incubation in PBS, 32.5% degradation for the base sample (without graphene) was observed. The cell study demonstrated a non-cytotoxic nature of all scaffolds tested and the cells had mostly stretched and covered the surface. Overall, the sum of results presented in this study demonstrate a simple fabrication platform with extraordinary aspects that can be utilized to mimic the native conductive tissue properties, and also because of its flexibility it can easily be rolled into a nerve conduit to fill gaps in nerve tissue regeneration.     

Microengineered PEG Hydrogels: 3D Scaffolds for Guided Cell Growth

Designing three‐dimensional (3D) scaffolds for selective manipulation of cell growth is of high relevance for applications in regenerative medicine. Especially, scaffolds with oriented morphologies bear high potential to guide the restoration of specific tissues. The fabrication of hydrogel scaffolds that support long‐term survival, proliferation, and unidirectional growth of embedded cells is presented here. Parallel channel structures are introduced into the bulk hydrogels by uniaxial freezing, providing stable, and uniform porosity suitable for cell invasion (pore diameters of 5–15 µm). In vitro assessment of the scaffolds with murine fibroblasts (NIH L929) shows a remarkable unidirectional movement along the channels, with the cells traveling several millimeters through the hydrogel.

     

Cell(MC3T3‐E1)‐Printed Poly(ϵ‐caprolactone)/Alginate Hybrid Scaffolds for Tissue Regeneration

A new cell‐printed scaffold consisting of poly(ϵ‐caprolactone) (PCL) and cell‐embedded alginate struts is designed. The PCL and alginate struts are stacked in an interdigitated pattern in successive layers to acquire a three‐dimensional (3D) shape. The hybrid scaffold exhibits a two‐phase structure consisting of cell (MC3T3‐E1)‐laden alginate struts able to support biological activity and PCL struts able to provide controllable mechanical support of the cell‐laden alginate struts. The hybrid scaffolds exhibit an impressive increase in tensile modulus and maximum strength compared to pure alginate scaffolds. Laden cells are homogeneously distributed throughout the alginate struts and the entire scaffold, resulting in cell viability of approximately 84%.     

Preparation and modification of collagen-based porous scaffold for tissue engineering

In the effort to generate cartilage tissues using mesenchymal stem cells, porous scaffolds with prescribed biomechanical properties were prepared. Scaffolds with interconnected pores were prepared via lyophilisation of frozen hydrogels made from collagen modified with chitosan nanofibres, hyaluronic acid, copolymers based on poly(ethylene glycol) (PEG), poly(lactic-co-glycolic acid) (PLGA), and itaconic acid (ITA), and hydroxyapatite nanoparticles. The modified collagen compositions were cross-linked using N-(3-dimethylamino propyl)-N′-ethylcarbodiimide hydrochloride (EDC) combined with N-hydroxysuccinimide (NHS) in water solution. Basic physicochemical and mechanical properties were measured and an attempt to relate these properties to the molecular and supermolecular structure of the modified collagen compositions was carried out. Scaffolds containing hydrophilic chitosan nanofibres showed the highest swelling ratio (SR = 20–25) of all the materials investigated, while collagen modified with an amphiphilic PLGA-PEG-PLGA copolymer or functionalised with ITA exhibited the lowest swelling ratio (SR = 5–8). The best resistance to hydrolytic degradation was obtained for hydroxyapatite containing scaffolds. On the other hand, the fastest degradation rate was observed for synthetic copolymer-containing scaffolds. The results showed that the addition of hydroxyapatite or hyaluronic acid to the collagen matrix increases the rigidity in comparison to the collagen-chitosan scaffold. Collagen scaffold modified with hyaluronic acid presented reduced deformation at break while the presence of hydroxypatatite enhanced the scaffold deformation under tensile loading. The tensile elastic modulus of chitosan nanofibre collagen scaffold was the lowest but closest to the articular cartilage; however, the strength and deformation to failure increased up to 200 %. Presented at the 1st Bratislava Young Polymer Scientists Workshop, Bratislava, 20–23 August 2007.     

Acrylic‐Acid‐Functionalized PolyHIPE Scaffolds for Use in 3D Cell Culture

This study describes the development of a functional porous polymer for use as a scaffold to support 3D hepatocyte culture. A high internal phase emulsion (HIPE) is prepared containing the monomers styrene (STY), divinylbenzene (DVB), and 2‐ethylhexyl acrylate (EHA) in the external oil phase and the monomer acrylic acid (Aa) in the internal aqueous phase. Upon thermal polymerization with azobisisobutyronitrile (AIBN), the resulting porous polymer (polyHIPE) is found to have an open‐cell morphology and a porosity of 89%, both suitable characteristics for 3D cell scaffold applications. X‐ray photo­electron spectroscopy reveals that the polyHIPE surface contained 7.5% carboxylic acid functionality, providing a useful substrate for subsequent surface modifications and bio‐conjugations. Initial bio‐compatibility assessments with human hepatocytes show that the acid functionality does not have any detrimental effect on cell adhesion. It is therefore believed that this material can be a useful precursor scaffold towards 3D substrates that offer tailored surface functionality for enhanced cell adhesion.

     

Preparation and characterization of 3D collagen materials with magnetic properties

In this study 3D collagen materials with magnetic properties were prepared by lyophilization technique. Magnetic particles were synthesized by precipitation of iron (II) sulfate heptahydrate and iron (III) chloride hexahydrate in an aqueous solution of chitosan and then added to a collagen solution. Starch dialdehyde (DAS) was used as a cross-linking agent for the materials. The properties of the obtained materials were studied using infrared spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Additionally, mechanical properties, porosity, density, swelling and moisture content were measured.It was found that 3D composites made from collagen with magnetic particles are hydrophilic with a high swelling ability. Cross-linking of such collagen materials with dialdehyde starch (DAS) alters the swelling degree, porosity and density of materials. The addition of magnetic particles to collagen materials decreases its porosity, and increases the density of the studied materials. Collagen 3D materials with magnetic particles are rigid and inflexible. Magnetic properties of the 3D collagen materials containing magnetic particles were confirmed by the interaction of this material with a magnet.     

3‐D Interdigitated electrodes for uniform stimulation of electro‐responsive hydrogels for biomedical applications

Stimuli‐responsive hydrogels are continuing to increase in demand in biomedical applications. Occluding a blood vessel is one possible application which is ideal for a hydrogel because of their ability to expand in a fluid environment. However, typically stimuli‐responsive hydrogels focus on bending instead of radial uniform expansion, which is required for an occlusion application. This article focuses on using an interdigitated electrode device to stimulate an electro‐responsive hydrogel in order to demonstrate a uniform swelling/deswelling of the hydrogel. A Pluronic‐bismethacrylate (PF127‐BMA) hydrogel modified with hydrolyzed methacrylic acid, in order to make it electrically responsive, is used in this article. An interdigitated electrode device was manufactured containing Platinum electrodes. The results in this paper show that the electrically biased hydrogels deswelled 230% more than the non‐biased samples on average. The hydrogels deswelled uniformly and showed no visual deformations due to the electrical bias. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1523–1528     

PEG‐dialdehyde–the new cross‐linking agent for collagen/elastin hydrogels

Collagen and elastin are the major proteins of an extracellular matrix. They possess attractive, complementary mechanical properties in their native state, but during isolation, its unique structure is destroyed, which affects the parameters of the materials. However, they still have excellent biological properties. The cross‐linking process improves the physicochemical properties of protein materials. The ideal cross‐linking agent should be effective and does not impair the biological properties of the material. Therefore, poly(ethylene) glycol‐dialdehyde was used in the study. The results show that the addition of poly(ethylene) glycol‐dialdehyde in combination with the neutralization of a collagen/elastin solution is a useful method for preparation of protein hydrogels. The gels are transparent and relatively stiff. They exhibit good mechanical properties, surface properties and are attractive for 3 T3 cells. Copyright © 2016 John Wiley & Sons, Ltd.     

Segmented polyurethanes derived from novel siloxane–carbonate soft segments for biomedical applications

A novel macrodiol based on mixed silicone and carbonate chemistries was synthesized and used as a soft segment precursor in the synthesis of two series of segmented polyurethane (PU) copolymers varying in hard segment content and soft segment molecular weight. The hard segments in these copolymers were derived from 4,4‐methylene diphenyl diisocyanate and 1,4‐butane diol. The phase transitions, microphase separation behavior, and mechanical properties of the copolymers were investigated using a variety of experimental methods. When compared with segmented PU copolymers having predominately poly(dimethyl siloxane) soft segments, these siloxane–carbonate soft segment copolymers exhibit enhanced intersegment mixing, and consequently relatively low mechanical modulus. With relatively low modulus and siloxane units in the soft phase, the siloxane–carbonate PUs have potential for use in cardiac and orthopedic biomedical applications. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Preparation of bio‐based keratin‐derived magnetic molecularly imprinted polymer nanoparticles for the facile and selective separation of bisphenol A from water

In this study, new bio‐based magnetic molecularly imprinted polymer nanoparticles (∼23 nm) were synthesized from keratin extracted from chicken feathers and methacrylate‐functionalized Fe₃O₄ nanoparticles for its potential application in separation and removal of bisphenol A from water. The prepared magnetic molecularly imprinted polymer was characterized by Fourier‐transform infrared spectroscopy, field‐emission scanning electron microscopy, thermogravimetric analysis, alternative gradient field magnetometry, and energy‐dispersive X‐ray spectroscopy. The sorption of bisphenol A was investigated by changing the influencing factors such as pH, immersion time, Fe₃O₄ nanoparticles dosage, and the initial concentration of bisphenol A. Results illustrated that sorption was very fast and efficient (Q_m = 600 mg/g) having a removal efficiency of ∼98% in 40 min of immersion. The adsorption process showed better conformity with the Weber−Morris kinetics and the Freundlich isotherm model. The selectivity of bisphenol A by adsorbent was checked in the presence of hydroquinone, phenol, tetrabromobisphenol, and 4,4′‐biphenol as interferences.     

Fabrication of biodegradable poly(trimethylene carbonate) networks for potential tissue engineering scaffold applications

Biodegradable poly(trimethylene carbonate) (PTMC) networks were prepared by photopolymerization of linear (L)‐ and star (S)‐shaped PTMC macromonomers for potential tissue engineering scaffold applications. The L‐ (M_n, 6400) and S‐shaped (M_n, 5880) PTMC macromonomers were synthesized using 1,4‐butane diol and 2‐ethyl‐ 2‐hydroxyl‐propane‐1,3‐diol co‐initiated ring‐opening polymerization of trimethylene carbonate (TMC) in the presence of stannous octoate and subsequent acrylation with acryloyl chloride. Chemical structures of the PTMC macromonomers and their corresponding networks were characterized by ¹H NMR and ¹³C NMR spectroscopy. The human endothelial cell line, EA.hy926 was used to test the biocompatibility, cell adhesion, and proliferation behavior of both PTMC networks. The PTMC networks made from the S‐shaped macromonomers exhibited superior cell adhesion and proliferation behavior than those made of the linear macromonomers. Copyright © 2008 John Wiley & Sons, Ltd.     

3D printed biodegradable composites: An insight into mechanical properties of PLA/chitosan scaffold

Three-dimensional (3D) printing is a frontier manufacturing approach with great potential to benefit biomedical and patient care sectors. In the last decades, different types of biomedical materials were investigated in purpose of developing medical tools and devices. The present study attempts to assess mechanical performances (namely: tensile, compression, and flexural) of the newly developed chitosan-reinforced poly-lactic-acid (PLA) scaffolds by using fused filament fabrication (FFF) based 3D printing technology. Specifically, the effects of chitosan loading, infill density and annealing temperature on mechanical behavior of PLA composite scaffolds are investigated via design of experiments. Moreover, fracture behavior under various load types is studied with the help of selective electron microscopy. It is found that the strength of the produced composite samples depends significantly on the loading of chitosan and infill density, while annealing temperature does not affect mechanical response. Overall, the developed PLA composite scaffolds are mechanically efficient and they appear suitable for clinical purposes.     

The effect of 3D printing on the morphological and mechanical properties of polycaprolactone filament and scaffold

Three‐dimensional (3D) printing becomes an attractive technique to fabricate tissue engineering scaffolds through its high control on fabrication and repeatability using the printing parameters. This technique can be combined by the finite element method (FEM), and tissue‐specific scaffolds with desirable morphological and mechanical properties can be designed and manufactured. In this study, the influential 3D printing parameters on the morphological and mechanical properties of polycaprolactone (PCL) filament and scaffold were studied experimentally and numerically. First, the effects of printing parameters and process on the properties of extruded PCL filament were investigated. Then, using FEM, the effects of filament specifications on the overall characteristics of the scaffold were evaluated. Results showed that both the printing process in terms of resting time and remaining time and the printing parameters like pressure, printing speed, and printing path length have influenced the filament properties. In addition, both the filament diameter and elastic modulus had significant effects on the properties of scaffold especially, a 20% increase in the filament diameter caused the scaffold compressive elastic modulus to rise by around 72%. It is concluded that the printing parameters and process must be tuned very well in fabricating scaffolds with the desired morphology and mechanical property.     

3D–2D–0D Stepwise Deconstruction of a Water Framework Templated by a Nanoporous Organic–Inorganic Hybrid Host

The supramolecular salt [H₂pip]₃[Ge(hedp)₂]?14 H₂O ( 1 ) [H₂pip²⁺=piperazine cation C₄H₁₂N₂²⁺; hedp^5?=deprotonated form of etidronic acid, C₂H₃P₂O₇^5?) is reported. This consists of an organic–inorganic hybrid hydrogen‐bonded nanoporous framework, the internal surface of which acts as a template for the three‐dimensional (3D) clustering of water molecules. The structure and molecular dynamics of this material are characterised by single‐crystal X‐ray diffraction, thermogravimetric analysis, Raman (H/D isotopic substitution) spectroscopy, and ²H solid‐state (wide‐line and MAS) NMR spectroscopy. Material 1 is shown to be unusual because 1) few nanoporous materials exhibit a well‐organised 3D framework of water molecules, 2) it provides a unique opportunity to follow experimentally and to rationalise the deconstruction of a 3D water framework and 3) despite the fact that the hybrid framework is a supramolecular salt, the structure does not collapse after dehydration and the final material is crystalline.     

Injectable Biodegradable Chitosan‐Alginate 3D Porous Gel Scaffold for mRNA Vaccine Delivery

mRNA vaccines have proven to be more stable, effective, and specific than protein/peptide‐based vaccines in stimulating both humoral and cellular immune response. However, mRNA's fast degradation rate and low‐transfection efficiency in vivo impede its potential in vaccination. Recent research in gene delivery has focused on nonviral vaccine carriers and either implantable or injectable delivery systems to improve transgene expression in vivo. Here, an injectable chitosan‐alginate gel scaffold for the local delivery of mRNA vaccines is reported. Gel scaffold biodegradation rates and biocompatibility are quantified. Scaffold‐mediated mRNA in vivo transgene expression as well as ovalbumin antigen specific cellular and humoral immune responses are evaluated in vivo. Luciferase reporter protein expression resulting from mRNA lipoplex‐loaded gel scaffolds is five times higher than systemic injection. Compared to systemic injections of naked mRNA or mRNA:lipoplexes, elevated levels of T cell proliferation and IFN‐γ secretion are seen with in vivo scaffold‐mediated mRNA lipoplex delivery. Furthermore, a humoral response (ovalbumin antigen specific IgG levels) is observed as early as week 1 for scaffold‐mediated mRNA lipoplex delivery, while protein‐based immunization did not elicit IgG production until 2 weeks post‐injection. Results suggest that injectable scaffold mRNA vaccine delivery maybe a viable alternative to traditional nucleic acid immunization methods.     

3D Plotted PCL Scaffolds for Stem Cell Based Bone Tissue Engineering

The ability to control the architecture and strength of a bone tissue engineering scaffold is critical to achieve a harmony between the scaffold and the host tissue. Rapid prototyping (RP) technique is applied to tissue engineering to satisfy this need and to create a scaffold directly from the scanned and digitized image of the defect site. Design and construction of complex structures with different shapes and sizes, at micro and macro scale, with fully interconnected pore structure and appropriate mechanical properties are possible by using RP techniques. In this study, RP was used for the production of poly(ε-caprolactone) (PCL) scaffolds. Scaffolds with four different architectures were produced by using different configurations of the fibers (basic, basic-offset, crossed and crossed-offset) within the architecture of the scaffold. The structure of the prepared scaffolds were examined by scanning electron microscopy (SEM), porosity and its distribution were analyzed by micro-computed tomography (µ-CT), stiffness and modulus values were determined by dynamic mechanical analysis (DMA). It was observed that the scaffolds had very ordered structures with mean porosities about 60%, and having storage modulus values about 1 × 10⁷ Pa. These structures were then seeded with rat bone marrow origin mesenchymal stem cells (MSCs) in order to investigate the effect of scaffold structure on the cell behavior; the proliferation and differentiation of the cells on the scaffolds were studied. It was observed that cell proliferation was higher on offset scaffolds (262000 vs 235000 for basic, 287000 vs 222000 for crossed structure) and stainings for actin filaments of the cells reveal successful attachment and spreading at the surfaces of the fibers. Alkaline phosphatase (ALP) activity results were higher for the samples with lower cell proliferation, as expected. Highest MSC differentiation was observed for crossed scaffolds indicating the influence of scaffold structure on cellular activities.     

PSAQ™ standards for accurate MS–based quantification of proteins: from the concept to biomedical applications

Absolute protein quantification, i.e. determining protein concentrations in biological samples, is essential to our understanding of biological and physiopathological phenomena. Protein quantification methods based on the use of antibodies are very effective and widely used. However, over the last ten years, absolute protein quantification by mass spectrometry has attracted considerable interest, particularly for the study of systems biology and as part of biomarker development. This interest is mainly linked to the high multiplexing capacity of MS analysis, and to the availability of stable‐isotope‐labelled standards for quantification. This article describes the details of how to produce, control the quality and use a specific type of standard: Protein Standard Absolute Quantification (PSAQ?) standards. These standards are whole isotopically labelled proteins, analogues of the proteins to be assayed. PSAQ standards can be added early during sample treatment, thus they can correct for protein losses during sample prefractionation and for incomplete sample digestion. Because of this, quantification of target proteins is very accurate and precise using these standards. To illustrate the advantages of the PSAQ method, and to contribute to the increase in its use, selected applications in the biomedical field are detailed here. Copyright © 2012 John Wiley & Sons, Ltd.     

One‐Step Synthesis and Characterization of Gold–Hollow PbSx Hybrid Nanoparticles

Turing lead into gold : Hollow hybrid PbS_x–Au nanostructures of about 10 nm in diameter were synthesized using a one‐step reaction under mild experimental conditions. The redox reaction of gold precursors with PbS nanocrystals in the presence of dodecylamine leads to the hollow feature of hybrid nanostructures (see picture).

     

Characterization of Collagen/Lipid Nanoparticle–Curcumin Cryostructurates for Wound Healing Applications

Curcumin‐loaded collagen cryostructurates have been devised for wound healing applications. Curcumin displays strong antioxidant, antiseptic, and anti‐inflammatory properties, while collagen is acknowledged for promoting cell adhesion, migration and differentiation. However, when curcumin is loaded directly into collagen hydrogels, it forms large molecular aggregates and clogs the matrix pores. A double‐encapsulation strategy is therefore developed by loading curcumin into lipid nanoparticles (LNP), and embedding these particles inside collagen scaffolds. The resulting collagen/LNP cryostructurates have an optimal fibrous structure with ≈100 µm average pore size for sustaining cell migration. Results show that collagen is structurally unaltered and that nanoparticles are homogeneously distributed amidst collagen fibers. Hydrogels soaked in saline buffer release about 20 to 30% of their nanoparticles content within 24 h, while achieved 100% release after 25 days. When exposed to NIH 3T3 fibroblasts, these hydrogels provide a satisfactory scaffold for cell interaction as early as 4 h after seeding, with no cytotoxic counter effect. These positive features make the collagen/lipid cryostructurates a promising material for further use in wound healing.