Magnetic Scaffolds Research Articles

Facile and Green Synthesis of Core–Shell Structured Magnetic Chitosan Submicrospheres and Their Surface Functionalization

Submicrometer-sized magnetite colloid nanocrystal clusters (MCNCs) provide a new avenue for constructing uniformly sized and highly magnetic composite submicrospheres. Herein, a facile and eco-friendly method is described for the synthesis of Fe3O4@poly(acrylic acid) (PAA)/chitosan (CS) core-shell submicrospheres using MCNCs bearing carboxyl groups as the magnetic cores. It is based on the self-assembly of positively charged CS chains on the surface of the oppositely charged MCNCs dispersed in the aqueous solution containing acrylic acid (AA) and a cross-linker N,N'-methylenebis(acrylamide) (MBA), followed by radical induced cross-linking copolymerization of AA and MBA along the CS chains. The resulting polymer shell comprises a medium shell of cross-linked PAA/CS polyelectrolyte complexes and an outer shell of protonated CS chains. It was found that the shell thickness could be tuned by varying either the concentration of radical initiator or the molar ratio of AA to aminoglucoside units of CS. To the surface of thus obtained Fe3O4@PAA/CS particles, Au nanoparticles, a variety of functional groups such as fluorescein, carboxyl, quaternary ammonium, and aliphatic bromide, and even functional polymer chains were successfully introduced. Therefore, such Fe3O4@PAA/CS submicrospheres may be used as versatile magnetic functional scaffolds in biorelated areas like bioseparation and medical assay, considering the unique features of CS like nontoxicity and biocompatibility.

Modifying bone scaffold architecture in vivo with permanent magnets to facilitate fixation of magnetic scaffolds

The fundamental elements of tissue regeneration are cells, biochemical signals and the three-dimensional microenvironment. In the described approach, biomineralized-collagen biomaterial functions as a scaffold and provides biochemical stimuli for tissue regeneration. In addition superparamagnetic nanoparticles were used to magnetize the biomaterials with direct nucleation on collagen fibres or impregnation techniques. Minimally invasive surgery was performed on 12 rabbits to implant cylindrical NdFeB magnets in close proximity to magnetic scaffolds within the lateral condyles of the distal femoral epiphyses.Under this static magnetic field we demonstrated, for the first time in vivo, that the ability to modify the scaffold architecture could influence tissue regeneration obtaining a well-ordered tissue. Moreover, the association between NdFeB magnet and magnetic scaffolds represents a potential technique to ensure scaffold fixation avoiding micromotion at the tissue/biomaterial interface.

Evaluation of the Effects of a Moderate Intensity Static Magnetic Field Application on Human Osteoblast-Like Cells

There is a general interest in the effects of magnetic fields on human tissue, for biomedical imaging, cancer therapy or tissue engineering applications. In particular the orthopaedic field may greatly benefit from magnetic scaffolds, magnetic fixation and magnetic delivery techniques. In this study, MG-63 osteoblast-like cells were analysed <i>in vitro</i> after exposure to a 320mT static magnetic field (SMF), either continuously or applied for 1h at any 24-hour interval. Results demonstrate that SMF causes a reduction in cell number after 7 days of exposure, as demonstrated by the MTT assay. This reduction in proliferation is not associated to an increase in Lactate Dehydrogenase production, a marker of cellular stress and/or disruption of membrane integrity. Osteocalcin secretion increased at day 3 for the condition 1h/day exposure and this effect was reversed after 7 days. Instead, the continuous application of a SMF resulted in a significantly decreased osteocalcin release at day 7. Cell distribution, morphology and cytoskeleton organization were unaltered, with the typical osteoblastic morphology maintained and normal distribution of cytoplasmic actin fibrils, as demonstrated by phalloidin staining. Gene expression analysis of COL1A1, ALPL and RUNX2 show no alterations respect to control. These results suggest that such a moderate intensity static magnetic field has a detrimental effect on cell proliferation and osteocalcin secretion, while maintaining morphological features and gene expression unaltered. The <i>in vitro</i> effects of magnetic fields depend on cell type, magnetic field intensity and modality of application. This study gives a contribution to understand moderate strength static magnetic field effects on human tissue, with particular importance for the orthopaedic field.

Magnetic mesoporous bioactive glass scaffolds: preparation, physicochemistry and biological properties.

The magnetic 10Fe5Ca MBG scaffolds (Fe3O4-CaO-SiO2-P2O5 system) have been prepared by a combination of polyurethane sponge and P123 as co-templates and an evaporation-induced self-assembly (EISA) process through the substitution of Fe3O4 for CaO in the 15Ca MBG scaffolds (CaO-SiO2-P2O5 system). The structure, magnetic heating, drug release, physicochemical and biological properties were systematically investigated. The results showed that the 10Fe5Ca MBG scaffolds had the interconnected macroporous structure with pore sizes ranging from 200 to 400 μm and the mesoporous wall with a peak pore size of ca. 3.34 nm. Also, the 10Fe5Ca MBG scaffolds exhibited similar mechanical strength, apatite-forming ability and sustained drug release behavior compared to the 15Ca MBG scaffolds. Importantly, the substitution of Fe3O4 for CaO in the MBG scaffolds induced a slower ion dissolution rate and more significant potential to stabilize the pH environment, and facilitated osteoblast cell proliferation, alkaline phosphatase (ALP) activity and osteogenic expression. In particular, the 10Fe5Ca MBG scaffolds could generate heat in an alternating magnetic field. Therefore, the magnetic 10Fe5Ca MBG scaffolds have potential for the regeneration of the critical-size bone defects caused by bone tumors by a combination of magnetic hyperthermia and local drug delivery therapy.

Systematic Analysis of Injectable Materials and 3D Rapid Prototyped Magnetic Scaffolds: From CNS Applications to Soft and Hard Tissue Repair/Regeneration

Over the past years, polymer-based materials have attracted research interest in the field of tissue repair and regeneration. As reported in literature, different injectable systems have been proposed, trying to reduce surgical invasiveness. In a first step of the current research, the rheological and functional features of injecatble hydrogel-based materials for central nervous system applications or soft tissue regeneration (collagen/PEG semi-IPNs) as well as for hard tissue engineering (alginate/iron-doped hydroxyapatite) were evaluated. Then, the study was also devoted to the development of 3D nanocomposite poly(ɛ- caprolactone)/iron-doped hydroxyapatite scaffolds for bone tissue engineering, providing a preliminary approach to assess magnetic attraction forces.

Glycolic acid-functionalized chitosan–Co3O4–Fe3O4 hybrid magnetic nanoparticles-based nanohybrid scaffolds for drug-delivery and tissue engineering

In the present work, Co3O4 was prepared by hydrothermal process, which is further used for the synthesis of Co3O4–Fe3O4 hybrid nanoparticles. The formation of Co3O4–Fe3O4 nanoparticles was investigated by transmission electron microscopy and physical property measurement system. In the next step, the drug-loaded novel nanohybrid porous scaffold based on chitosan-g-glycolic acid and Co3O4–Fe3O4 nanoparticle was prepared by freeze drying technique. The grafting of glycolic acid on chitosan drug loading in porous scaffold was characterized by Fourier transform infrared spectroscopy. The nanohybrid scaffolds were found to be stable regardless of the pH of the medium and play an important role in cell adhesion, proliferation, and migration. Co3O4–Fe3O4 hybrid nanoparticles' reinforcement was found to control the drug (cyclophosphamide) release rate in phosphate buffer saline solution (pH 7.4). Therefore, Co3O4–Fe3O4 hybrid nanoparticles are viable additives for formulating sustained drug delivery systems and could be applied in the field of biomaterials.

Synthesis, characterization and in vitro assessment of the magnetic chitosan–carboxymethylcellulose biocomposite interactions with the prokaryotic and eukaryotic cells

Preparation and characterization of CS/Fe(3)O(4)/CMC composite scaffolds including the morphology, crystallinity, and the in vitro efficacy as antibiotic delivery vehicles as well as their influence on the eukaryotic cells are reported. The results demonstrated that the magnetic polymeric composite scaffolds are exhibiting structural and functional properties that recommend them for further applications in the biomedical field. They improve the activity of currently used antibiotics belonging to penicillins, macrolides, aminoglycosides, rifampicines and quinolones classes, representing potential macromolecular carriers for these antimicrobial substances, to achieve extracellular and intracellular targets. The obtained systems are not cytotoxic and do not influence the eukaryotic HCT8 cell cycle, representing potential tools for the delivery of drugs in a safe, effective and less expensive manner.

Magnetic Hydroxyapatite Bone Substitutes to Enhance Tissue Regeneration: Evaluation In Vitro Using Osteoblast-Like Cells and In Vivo in a Bone Defect

In case of degenerative disease or lesion, bone tissue replacement and regeneration is an important clinical goal. In particular, nowadays, critical size defects rely on the engineering of scaffolds that are 3D structural supports, allowing cellular infiltration and subsequent integration with the native tissue. Several ceramic hydroxyapatite (HA) scaffolds with high porosity and good osteointegration have been developed in the past few decades but they have not solved completely the problems related to bone defects. In the present study we have developed a novel porous ceramic composite made of HA that incorporates magnetite at three different ratios: HA/Mgn 95/5, HA/Mgn 90/10 and HA/Mgn 50/50. The scaffolds, consolidated by sintering at high temperature in a controlled atmosphere, have been analysed in vitro using human osteoblast-like cells. Results indicate high biocompatibility, similar to a commercially available HA bone graft, with no negative effects arising from the presence of magnetite or by the use of a static magnetic field. HA/Mgn 90/10 was shown to enhance cell proliferation at the early stage. Moreover, it has been implanted in vivo in a critical size lesion of the rabbit condyle and a good level of histocompatibility was observed. Such results identify this scaffold as particularly relevant for bone tissue regeneration and open new perspectives for the application of a magnetic field in a clinical setting of bone replacement, either for magnetic scaffold fixation or magnetic drug delivery.

Innovative magnetic scaffolds for orthopedic tissue engineering

The use of magnetism in tissue engineering is a very promising approach, in fact magnetic scaffolds are able not only to support tissue regeneration, but they can be activated and work like a magnet attracting functionalized magnetic nanoparticles (MNPs) injected close to the scaffold enhancing tissue regeneration. This study aimed to assess the in vivo biocompatibility and osteointegrative properties of novel magnetic scaffolds. Two hydroxyapatite/collagen (70/30 wt %) magnetic scaffolds were magnetized with two different techniques: direct nucleation of biomimetic phase and superparamagnetic nanoparticles (MNPs) on self-assembling collagen fibers (MAG-A) and scaffold impregnation in ferro-fluid solution (MAG-B). Magnetic scaffolds were implanted in rabbit distal femoral epiphysis and tibial mid-diaphysis. Histopathological screening showed no inflammatory reaction due to MNPs. Significantly higher bone healing rate (ΔBHR) results were observed in MAG-A in comparison to MAG-B. Significant differences were also found between experimental times with an increase in ΔBHR from 2 to 4 weeks for both scaffolds in trabecular bone, while only for MAG-B (23%, p < 0.05) in cortical bone. The proposed magnetic scaffolds seem to be promising for magnetic guiding in orthopedic tissue engineering applications and they will be suitable to treat also several pathologies in regenerative medicine area.

The promotion of in vitro vessel-like organization of endothelial cells in magnetically responsive alginate scaffolds

One of the major challenges in engineering thick, complex tissues such as cardiac muscle, is the need to pre-vascularize the engineered tissue in vitro to enable its efficient integration with host tissue upon implantation. Herein, we explored new magnetic alginate composite scaffolds to provide means of physical stimulation to cells. Magnetite-impregnated alginate scaffolds seeded with aortic endothelial cells stimulated during the first 7 days out of a total 14 day experimental course showed significantly elevated metabolic activity during the stimulation period. Expression of proliferating cell nuclear antigen (PCNA) indicated that magnetically stimulated cells had a lower proliferation index as compared to the non-stimulated cells. This suggests that the elevated metabolic activity could instead be related to cell migration and re-organization. Immunostaining and confocal microscopy analyses supported this observation showing that on day 14 in magnetically stimulated scaffolds without supplementation of any growth factors, cellular vessel-like (loop) structures, known as indicators of vasculogenesis and angiogenesis were formed as compared to cell sheets or aggregates observed in the non-stimulated (control) scaffolds. This work is the first step in our understanding of how to accurately control cellular organization to form tissue engineered constructs, which together with additional molecular signals could lead to a creation of an efficient pre-vascularized tissue construct with potential applicability for transplantation.

A new approach to scaffold fixation by magnetic forces: Application to large osteochondral defects

Scaffold fixation represents one of the most serious challenges in osteochondral defect surgery. Indeed, the fixation should firmly hold the scaffold in the implanted position as well as it should guaranty stable bone/scaffold interface for efficient tissue regeneration. Nonetheless successful results have been achieved for small defect repair, the fixation remains really problematic for large defects, i.e. defects with areas exceeding 2cm2. This paper advances an innovative magnetic fixation approach based on application of magnetic scaffolds. Finite element modeling was exploited to investigate the fixation efficiency. We considered three magnetic configurations: (1) external permanent magnet ring placed around the leg near the joint; (2) four small permanent magnet pins implanted in the bone underlying the scaffold; (3) four similarly implanted stainless steel pins which magnetization was induced by the external magnet. It was found that for most appropriate magnetic materials and optimized magnet-scaffold positioning all the considered configurations provide a sufficient scaffold fixation. In addition to fixation, we analyzed the pressure induced by magnetic forces at the bone/scaffold interface. Such pressure is known to influence significantly the bone regeneration and could be used for magneto-mechanical stimulation.

Ferroferric oxide/chitosan scaffolds with three-dimensional oriented structure

A facile approach to construct ferroferric oxide/chitosan composite scaffolds with three-dimensional oriented structure has been explored in this research. Chitosan and ferroferric oxide are co-precipitated by using an in situ precipitation method, and then lyophilized to get the composite scaffolds. XRD indicated that Fe3O4 was generated during the gel formation process, and increasing the content of magnetic particles could destruct the crystal structure of chitosan. When the content of magnetic particles is lower than 10%, the layer-by-layer structure and wheel spoke structure are coexisting in the scaffolds. Increasing the content of magnetic particles, just layer-by-layer structure could be observed in the scaffolds. Ferroferric oxide particles were uniformly distributed in the matrix, the size of which was about 0.48 μm in diameter, 2 μm in length. Porosity of magnetic chitosan composite scaffolds is about 90%. When the ratio of ferroferric oxide to chitosan is 5/100, the compressive strength of the material is 0.4367 MPa, which is much higher than that of pure chitosan scaffolds, indicating that the layer-by-layer and wheel spokes complex structure is beneficial for the improvement of the mechanical properties of chitosan scaffolds. However, increasing the content of ferroferric oxide, the compressive strength of scaffolds decreased, because of the decreasing of chitosan crystallization and aggregation of magnetic particles as stress centralized body. Another reason is that the layer-by-layer and wheel spokes complex structure makes bigger contributions for the compressive strength than the layer-by-layer structure does. Three-dimensional ferroferric oxide/chitosan scaffolds could be used as hyperthermia generator system, improving the local circulation of blood, promoting the aggradation of calcium salt and stimulating bone tissue regeneration.

Magnetic Scaffolds Enriched with Bioactive Nanoparticles for Tissue Engineering

Novel magnetic fibrin hydrogel scaffolds for cell implantation and tissue engineering are reported. The magnetic scaffolds are produced by the interaction between thrombin-conjugated maghemite nanoparticles of narrow size distribution and fibrinogen. These scaffolds, enriched with growth factor conjugated fluorescent maghemite nanoparticles, provide a supporting 3D environment for massive proliferation of various cell types, and can be successfully visualized by MRI.

Magnetic responsive hydroxyapatite composite scaffolds construction for bone defect reparation

IntroductionIn recent years, interest in magnetic biomimetic scaffolds for tissue engineering has increased considerably. A type of magnetic scaffold composed of magnetic nanoparticles (MNPs) and hydroxyapatite (HA) for bone repair has been developed by our research group.Aim and methodsIn this study, to investigate the influence of the MNP content (in the scaffolds) on the cell behaviors and the interactions between the magnetic scaffold and the exterior magnetic field, a series of MNP-HA magnetic scaffolds with different MNP contents (from 0.2% to 2%) were fabricated by immersing HA scaffold into MNP colloid. ROS 17/2.8 and MC3T3-E1 cells were cultured on the scaffolds in vitro, with and without an exterior magnetic field, respectively. The cell adhesion, proliferation and differentiation were evaluated via scanning electron microscopy; confocal laser scanning microscopy; and 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), alkaline phosphatase, and bone gla protein activity tests.ResultsThe results demonstrated the positive influence of the magnetic scaffolds on cell adhesion, proliferation, and differentiation. Further, a higher amount of MNPs on the magnetic scaffolds led to more significant stimulation.ConclusionThe magnetic scaffold can respond to the exterior magnetic field and engender some synergistic effect to intensify the stimulating effect of a magnetic field to the proliferation and differentiation of cells.

Novel magnetic fibrin hydrogel scaffolds containing thrombin and growth factors conjugated iron oxide nanoparticles for tissue engineering

Novel tissue-engineered magnetic fibrin hydrogel scaffolds were prepared by the interaction of thrombin-conjugated iron oxide magnetic nanoparticles with fibrinogen. In addition, stabilization of basal fibroblast growth factor (bFGF) was achieved by the covalent and physical conjugation of the growth factor to the magnetic nanoparticles. Adult nasal olfactory mucosa (NOM) cells were seeded in the transparent fibrin scaffolds in the absence or presence of the free or conjugated bFGF-iron oxide nanoparticles. The conjugated bFGF enhanced significantly the growth and differentiation of the NOM cells in the fibrin scaffolds, compared to the same or even five times higher concentration of the free bFGF. In the presence of the bFGF-conjugated magnetic nanoparticles, the cultured NOM cells proliferated and formed a three-dimensional interconnected network composed mainly of tapered bipolar cells. The magnetic properties of these matrices are due to the integration of the thrombin- and bFGF-conjugated magnetic nanoparticles within the scaffolds. The magnetic properties of these scaffolds may be used in future work for various applications, such as magnetic resonance visualization of the scaffolds after implantation and reloading the scaffolds via magnetic forces with bioactive agents, eg, growth factors bound to the iron oxide magnetic nanoparticles.

Field-Control, Phase-Transitions, and Life's Emergence.

Instances of critical-like characteristics in living systems at each organizational level (bio-molecules to ecosystems) as well as the spontaneous emergence of computation (Langton), do suggest the relevance of self-organized criticality (SOC). But extrapolating complex bio-systems to life’s origins, brings up a paradox: how could simple organics – lacking the “soft-matter” response properties of today’s complex bio-molecules – have dissipated energy from primordial reactions (eventually reducing CO2) in a controlled manner for their “ordering”? Nevertheless, a causal link of life’s macroscopic irreversible dynamics to the microscopic reversible laws of statistical mechanics is indicated via the “functional-takeover” of a soft magnetic scaffold by organics (c.f. Cairns-Smith’s “crystal-scaffold”). A field-controlled structure offers a mechanism for boot-strapping – bottom-up assembly with top-down control: its super-paramagnetic colloidal components obey reversible dynamics, but its dissipation of magnetic (H)-field energy for aggregation breaks time-reversal symmetry. The responsive adjustments of the controlled (host) mineral system to environmental changes would bring about mutual coupling between random organic sets supported by it; here the generation of long-range correlations within organic (guest) networks could include SOC-like mechanisms. And, such cooperative adjustments enable the selection of the functional configuration by altering the inorganic dipolar network’s capacity to assist a spontaneous process. A non-equilibrium dynamics could now drive the kinetically oriented system (trimming the phase-space via sterically coupled organics) toward a series of phase-transitions with appropriate organic replacements “taking-over” its functions. Where available, experiments are cited in support of these speculations and for designing appropriate tests.

Hybrid materials for drug delivery of rifampicin: evaluation of release profile

The aim of the present investigation was to evaluate the dissolution profile of rifampicin, to study the design parameters of magnetic scaffolds and to evaluate the in vitro release characteristics. A series of magnetic hybrid materials were developed with different release rates using chitosan (Ch) and diethylaminoethyl-cellulose (DeaeC). The duration of rifampicin release could be tailored by varying the polymer type. Rifampicin was found to follow a linear release profile with time from all magnetic polysaccharide scaffolds. Using suitable polysaccharide scaffolds and proper optimization of the processing techniques, it was possible to design the controlled release formulations of rifampicin that could provide the sufficient initial release and release extension up to 24 h for the drug despite of the wide variations in their physicochemical properties.

A route toward the development of 3D magnetic scaffolds with tailored mechanical and morphological properties for hard tissue regeneration: Preliminary study

A basic approach toward the design of three-dimensional (3D) rapid prototyped magnetic scaffolds for hard-tissue regeneration has been proposed. In particular, 3D scaffolds consisting of a poly(ε-caprolactone) (PCL) matrix and iron oxide (Fe3O4) or iron-doped hydroxyapatite (FeHA) nanoparticles were fabricated through a 3D fibre deposition technique. As a first approach, a polymer to nanoparticle weight ratio of 90/10 (wt/wt) was used. The effect of the inclusion of both kinds of nanoparticles on the mechanical, magnetic, and biological performances of the scaffolds was studied. The inclusion of Fe3O4 and FeHA nanoparticles generally improves the modulus and the yield stress of the fibres if compared to those of neat PCL, as well as the modulus of the scaffolds. Micro-computed tomography has confirmed the possibility to design morphologically-controlled structures with a fully interconnected pore network. Magnetisation analyses performed at 37°C have highlighted M-H curves that are not hysteretic; values of saturation magnetisation (Ms) of about 3.9 emu/g and 0.2 emu/g have been evaluated for PCL/Fe3O4 and PCL/FeHA scaffolds, respectively. Furthermore, results from confocal laser scanning microscopy (CLSM) carried out on cell-scaffold constructs have evidenced that human mesenchymal stem cells (hMSCs) better adhered and were well spread on the PCL/Fe3O4 and PCL/FeHA nanocomposite scaffolds in comparison with the PCL structures.

Magnetic scaffold for drug targeting: evaluation of cephalosporins controlled release profile

The great problem associated with drug administration is the inability to target a specific area of the body. To reach an acceptable therapeutic level, large doses of the drug must be administered. Only a part of the dose will actually reach the intended disease. Magnetic targeting simplifies drug administration procedures, increases the concentration of the drug at target sites and decreases the concentration of the drug at non-target sites. This study was focused to evaluate the controlled release profile of cephalosporins from magnetic diethylaminoethyl-cellulose hybrid material (magnetic scaffold). Dissolution behavior of these magnetic scaffolds was evaluated using a modified HPLC system. It was found that in all cases, at large time values, the cephalosporin’s concentration was much below the solubility plateau for the pure active compound, demonstrating that the adsorption on the surface of magnetic scaffolds is a valuable procedure to attain controlled release

Intrinsic magnetism and hyperthermia in bioactive Fe-doped hydroxyapatite

The use of magnetic activation has been proposed to answer the growing need for assisted bone and vascular remodeling during template/scaffold regeneration. With this in mind, a synthesis procedure was developed to prepare bioactive (Fe 2+/Fe 3+)-doped hydroxyapatite (Fe-HA), endowed with superparamagnetic-like properties. This new class of magnetic hydroxyapatites can be potentially employed to develop new magnetic ceramic scaffolds with enhanced regenerative properties for bone surgery; in addition, magnetic Fe-HA can find application in anticancer therapies, to replace the widely used magnetic iron oxide nanoparticles, whose long-term cytotoxicity was recently found to reach harmful levels. An extensive physicochemical, microstructural and magnetic characterization was performed on the obtained Fe-HA powders, and demonstrated that the simultaneous addition of Fe 2+ and Fe 3+ ions during apatite nucleation under controlled synthesis conditions induces intrinsic magnetization in the final product, minimizing the formation of magnetite as secondary phase. This result potentially opens new perspectives for biodevices aimed at bone regeneration and for anti-cancer therapies based on hyperthermia.