Magnetic alginate microspheres: system for the position controlled delivery of nerve growth factor

Stimuli-responsive microcarriers and their application in tissue repair: A review of magnetic and electroactive microcarrier

Microcarrier applications have made great advances in tissue engineering in recent years, which can load cells, drugs, and bioactive factors. These microcarriers can be minimally injected into the defect to help reconstruct a good microenvironment for tissue repair. In order to achieve more ideal performance and face more complex tissue damage, an increasing amount of effort has been focused on microcarriers that can actively respond to external stimuli. These microcarriers have the functions of directional movement, targeted enrichment, material release control, and providing signals conducive to tissue repair. Given the high controllability and designability of magnetic and electroactive microcarriers, the research progress of these microcarriers is highlighted in this review. Their structure, function and applications, potential tissue repair mechanisms, and challenges are discussed. In summary, through the design with clinical translation ability, meaningful and comprehensive experimental characterization, and in-depth study and application of tissue repair mechanisms, stimuli-responsive microcarriers have great potential in tissue repair.

Nanoparticles for neurotrophic factor delivery in nerve guidance conduits for peripheral nerve repair

Peripheral nerve injuries are a major source of disabilities, and treatment of long nerve gap autografts is the gold standard. However, due to poor availability and donor-site morbidity, research is directed towards the development of regenerative strategies based on the use of artificial nerve guidance conduits (NGCs). Several properties and characteristics of the NGCs can be fine-tuned, such as the architecture of the conduit, the surface topography and the addition of bioactive molecules and cells to speed up nerve regeneration. In this review, US FDA-approved NGCs are described. The recent works, in which polymeric, magnetic, silica-based and lipidic NPs are employed to introduce growth factors (GFs) to NGCs, are overviewed and discussed in depth herein.

Externally triggered release of growth factors - A tissue regeneration approach

Tissue regeneration aims to achieve functional restoration following injury by creating an environment to enable the body to self-repair. Strategies for regeneration rely on the introduction of biomaterial scaffolding, cells and bioactive molecules into the body, at or near the injury site. Of these bioactive molecules, growth factors (GFs) play a pivotal role in directing regenerative pathways for many cell populations. However, the therapeutic use of GFs has been limited by the complexity of biological injury and repair, and the properties of the GFs themselves, including their short half-life, poor tissue penetration, and off-target side effects. Externally triggered delivery systems have the potential to facilitate the delivery of GFs into the target tissues with considerations of the timing, sequence, amount, and location of GF presentation. This review briefly discusses the challenges facing the therapeutic use of GFs, then, we discuss approaches to externally trigger GF release from delivery systems categorised by stimulation type; ultrasound, temperature, light, magnetic fields and electric fields. Overall, while the use of GFs for tissue regeneration is still in its infancy, externally controlled GF delivery technologies have the potential to achieve robust and effective solutions to present GFs to injured tissues. Future technological developments must occur in conjunction with a comprehensive understanding of the biology at the injury site to ensure translation of promising technologies into real world benefit.

Preparation and evaluation of microfluidic magnetic alginate microparticles for magnetically templated hydrogels

Our aim is to develop a hydrogel-based scaffold containing porous microchannels that mimic complex tissue microarchitecture and provide physical cues to guide cell growth for scalable, cost-effective tissue repair. These hydrogels are patterned through the novel process of magnetic templating where magnetic alginate microparticles (MAMs) are dispersed in a hydrogel precursor and aligned in a magnetic field before hydrogel crosslinking and subsequent MAM degradation, leaving behind an aligned, porous architecture. Here, a protocol for fabricating uniform MAMs using microfluidics was developed for improved reproducibility and tunability of templated microarchitecture. Through iron quantification, we find that this approach allows control over magnetic iron oxide loading of the MAMs. Using Brownian dynamics simulations and nano-computed tomography of templated hydrogels to examine MAM chain length and alignment, we find agreement between simulated and measured areal densities of MAM chains. Oscillatory rheology and stress relaxation experiments demonstrate that magnetically templated microchannels alter bulk hydrogel mechanical properties. Finally, in vitro studies where rat Schwann cells were cultured on templated hydrogels to model peripheral nerve injury repair demonstrate their propensity for providing cell guidance along the length of the channels. Our results show promise for a micro-structured biomaterial that could aid in tissue repair applications.

Magnetogel Nanospheres Composed of Cisplatin-Loaded Alginate/B-Cyclodextrin as Controlled Release Drug Delivery

Purpose: The main aim of the present study was to design, fabrication and physicochemical characteristics of the magnetogel nanospheres as carriers for Cisplatin in the in vitro environment.

Methods: Magnetic nanospheres were synthesized by using a chemical co-precipitation method and coated by sodium alginate through double emulsion method. Then cisplatin was encapsulated into β-cyclodextrin -sodium alginate grafted magnetic nanospheres. The physicochemical properties of the sodium alginate grafted magnetic nanospheres were characterized by using FTIR, particle size analyzing, vibrating sample magnetometry, thermogravimetric and SEM analysis. Also the drug entrapment efficiency, content and in vitro release profile were investigated.

Results: Size distribution results revealed that the particles size was distributed in the range of 50± nm. Also morphological properties showed that particles are separated and spherical with the grafted layers of the polymer. The release profile data were in the acceptable range compared to the blank (cisplatin solution).

Conclusion: It could be concluded that the sodium alginate grafted magnetic nanospheres could act as a slow and controlled release system to deliver cisplatin.

Magnetic Composite Biomaterials for Neural Regeneration

Nervous system damage caused by physical trauma or degenerative diseases can result in loss of sensory and motor function for patients. Biomaterial interventions have shown promise in animal studies, providing contact guidance for extending neurites or sustained release of various drugs and growth factors; however, these approaches often target only one aspect of the regeneration process. More recent studies investigate hybrid approaches, creating complex materials that can reduce inflammation or provide neuroprotection in addition to stimulating growth and regeneration. Magnetic materials have shown promise in this field, as they can be manipulated non-invasively, are easily functionalized, and can be used to mechanically stimulate cells. By combining different types of biomaterials (hydrogels, nanoparticles, electrospun fibers) and incorporating magnetic elements, magnetic materials can provide multiple physical and chemical cues to promote regeneration. This review, for the first time, will provide an overview of design strategies for promoting regeneration after neural injury with magnetic biomaterials.

Magnetic Targeting of Growth Factors Using Iron Oxide Nanoparticles

Growth factors play an important role in nerve regeneration and repair. An attractive drug delivery strategy, termed “magnetic targeting”, aims to enhance therapeutic efficiency by directing magnetic drug carriers specifically to selected cell populations that are suitable for the nervous tissues. Here, we covalently conjugated nerve growth factor to iron oxide nanoparticles (NGF-MNPs) and used controlled magnetic fields to deliver the NGF–MNP complexes to target sites. In order to actuate the magnetic fields a modular magnetic device was designed and fabricated. PC12 cells that were plated homogenously in culture were differentiated selectively only in targeted sites out of the entire dish, restricted to areas above the magnetic “hot spots”. To examine the ability to guide the NGF-MNPs towards specific targets in vivo, we examined two model systems. First, we injected and directed magnetic carriers within the sciatic nerve. Second, we injected the MNPs intravenously and showed a significant accumulation of MNPs in mouse retina while using an external magnet that was placed next to one of the eyes. We propose a novel approach to deliver drugs selectively to injured sites, thus, to promote an effective repair with minimal systemic side effects, overcoming current challenges in regenerative therapeutics.

Se@SiO2 nanocomposites suppress microglia-mediated reactive oxygen species during spinal cord injury in rats

Selenium (Se) is an essential trace element with strong antioxidant activity, showing a great prospect in the treatment of spinal cord injury (SCI). However, the narrow gap between the beneficial and toxic effects has limited its further clinical application. In this experiment, we used porous Se@SiO2 nanocomposites (Se@SiO2) modified by nanotechnology as a new means of release control to investigate the anti-oxidative effect in SCI. In vitro Se@SiO2 toxicity, anti-oxidative and anti-inflammatory effects on microglia were assayed. In vivo we investigated the protective effect of Se@SiO2 to SCI rats. Neurological function was evaluated by Basso, Beattie and Bresnahan (BBB). The histopathological analysis, microglia activation, oxidative stress, inflammatory factors (TNF-α, IL-1β and IL-6) and apoptosis were detected at 3 and 14 days after SCI. The favorable biocompatibility of Se@SiO2 suppressed microglia activation, which is known to be associated with oxidative stress and inflammation in vivo and in vitro. In addition, Se@SiO2 improved the rat neurological function and reduced apoptosis via caspase-3, Bax and Bcl-2 pathways in SCI. Se@SiO2 was able to treat SCI and reduce oxidative stress, inflammation and apoptosis induced by microglia activation, which may provide a novel and safe strategy for clinical application.

Modeling angiogenesis with micro- and nanotechnology

Angiogenesis plays an important role not only in the growth and regeneration of tissues in humans but also in pathological conditions such as inflammation, degenerative disease and the formation of tumors. Angiogenesis is also vital in thick engineered tissues and constructs, such as those for the heart and bone, as these can face difficulties in successful implantation if they are insufficiently vascularized or unable to connect to the host vasculature. Considerable research has been carried out on angiogenic processes using a variety of approaches. Pathological angiogenesis has been analyzed at the cellular level through investigation of cell migration and interactions, modeling tissue level interactions between engineered blood vessels and whole organs, and elucidating signaling pathways involved in different angiogenic stimuli. Approaches to regenerative angiogenesis in ischemic tissues or wound repair focus on the vascularization of tissues, which can be broadly classified into two categories: scaffolds to direct and facilitate tissue growth and targeted delivery of genes, cells, growth factors or drugs that promote the regeneration. With technological advancement, models have been designed and fabricated to recapitulate the innate microenvironment. Moreover, engineered constructs provide not only a scaffold for tissue ingrowth but a reservoir of agents that can be controllably released for therapeutic purposes. This review summarizes the current approaches for modeling pathological and regenerative angiogenesis in the context of micro-/nanotechnology and seeks to bridge these two seemingly distant aspects of angiogenesis. The ultimate aim is to provide insights and advances from various models in the realm of angiogenesis studies that can be applied to clinical situations.

Processing-Size Correlations in the Preparation of Magnetic Alginate Microspheres Through Emulsification and Ionic Crosslinking

Magnetic alginate microspheres are biocompatible due to their alginate matrix, and motion-controllable by applied magnetic fields due to their magnetic character. Therefore, they have the potential of being used as vessels to a broad variety of materials, including drugs and therapeutic agents, facilitating entry to biological systems in a relatively non-invasive manner. Here, magnetic alginate microspheres were prepared through an emulsification and ionic cross-linking process, where a mixture of alginate and iron oxide magnetic nanoparticles was initially dispersed in a continuous phase, followed by gelation of this dispersed phase into microspheres by cross-linking the dispersion with calcium ions. The resulting magnetic alginate microspheres were found to be superparamagnetic and to respond to applied magnetic fields by chain formation. The effect of shear rate, alginate concentration, and magnetic nanoparticle concentration on microsphere size was investigated with the aim to control the size of microspheres with respect to process and formulation parameters. Two of these parameters, shear rate and alginate concentration, were used to correlate experimental results with a theoretical model for the case where the dispersed phase is more viscous than the continuous phase.

Facilitation of transscleral drug delivery by drug loaded magnetic polymeric particles

A unique method was used to facilitate ocular drug delivery from periocular route by drug loaded magnetic sensitive particles. Injection of particles in periocular space along the eye axis followed by application of magnetic field in front of the eye would trigger the magnetic polymeric particles to move along the direction of magnetic force and reside against the outer surface of the sclera. This technique prevents removal of drug in the periocular space, observed in conventional transscleral drug delivery systems and hence higher amount of drug can enter the eye in a longer period of time. The experiments were performed by fresh human sclera and an experimental setup. Experimental setup was designed by side by side diffusion cell and hydrodynamic and thermal simulation of the posterior segment of the eye were applied. Magnetic polymeric particles were synthesized by alginate as a model polymer, iron oxide nanoparticles as a magnetic agent and diclofenac sodium as a model drug and characterized by SEM, TEM, DLS and FT-IR techniques. According to the SEM images, the size range of particles is around 60 to 800nm. The results revealed that the cumulative drug transfer from magnetic sensitive particles across the sclera improves by 70% in the presence of magnetic field. The results of this research show promising method of drug delivery to use magnetic properties to facilitate drug delivery to the back of the eye.

Magnetic NGF-releasing PLLA/iron oxide nanoparticles direct extending neurites and preferentially guide neurites along aligned electrospun microfibers

Nerve growth factor releasing composite nanoparticles (NGF-cNPs) were developed to direct the extension of neurite outgrowth from dorsal root ganglia (DRG). Iron oxide magnetic nanoparticles were incorporated into poly-l-lactic acid (PLLA) nanoparticles in order to position the NGF-cNPs in a culture dish. Neurites growing from DRG extended toward the NGF released from the NGF-cNPs. DRG were then cultured on aligned PLLA microfibers in the presence of NGF-cNPs, and these biomaterials combined to align DRG neurite extension along one axis and preferentially toward the NGF-cNPs. This combinatorial biomaterial approach shows promise as a strategy to direct the extension of regenerating neurites.

Magneto-responsive alginate capsules

Upon incorporation of magnetic nanoparticles (mNPs) into gels, composite materials called ferrogels are obtained. These magneto-responsive systems have a wide range of potential applications including switches and sensors as well as drug delivery systems. In this article, we focus on the properties of calcium alginate capsules, which are widely used as carrier systems in medicine and technology. We studied the incorporation of different kinds of mNPs in matrix capsules and in the core and the shell of hollow particles. We found out that not all particle-alginate or particle-CaCl2 solution combinations were suitable for a successful capsule preparation on grounds of a destabilization of the nanoparticles or the polymer. For those systems allowing the preparation of switchable beads or capsules, we systematically studied the size and microscopic structure of the capsules, their magnetic behavior and mechanical resistance.

Magnetic micro-device for manipulating PC12 cell migration and organization

Directing neuronal migration and growth has an important impact on potential post traumatic therapies. Magnetic manipulation is an advantageous method for remotely guiding cells. In the present study, we have generated highly localized magnetic fields with controllable magnetic flux densities to manipulate neuron-like cell migration and organization at the microscale level. We designed and fabricated a unique miniaturized magnetic device composed of an array of rectangular ferromagnetic bars made of permalloy (Ni80Fe20), sputter-deposited onto glass substrates. The asymmetric shape of the magnets enables one to design a magnetic landscape with high flux densities at the poles. Iron oxide nanoparticles were introduced into PC12 cells, making the cells magnetically sensitive. First, we manipulated the cells by applying an external magnetic field. The magnetic force was strong enough to direct PC12 cell migration in culture. Based on time lapse observations, we analysed the movement of the cells and estimated the amount of MNPs per cell. We plated the uploaded cells on the micro-patterned magnetic device. The cells migrated towards the high magnetic flux zones and aggregated at the edges of the patterned magnets, corroborating that the cells with magnetic nanoparticles are indeed affected by the micro-magnets and attracted to the bars' magnetic poles. Our study presents an emerging method for the generation of pre-programmed magnetic micro-'hot spots' to locate and direct cellular growth, setting the stage for implanted magnetic devices.

NGF-conjugated iron oxide nanoparticles promote differentiation and outgrowth of PC12 cells

The search for regenerative agents that promote neuronal differentiation and repair is of great importance. Nerve growth factor (NGF) which is an essential contributor to neuronal differentiation has shown high pharmacological potential for the treatment of central neurodegenerative diseases such as Alzheimer's and Parkinson's. However, growth factors undergo rapid degradation, leading to a short biological half-life. In our study, we describe a new nano-based approach to enhance the NGF activity resulting in promoted neuronal differentiation. We covalently conjugated NGF to iron oxide nanoparticles (NGF-NPs) and studied the effect of the novel complex on the differentiation of PC12 cells. We found that the NGF-NP treatment, at the same concentration as free NGF, significantly promoted neurite outgrowth and increased the complexity of the neuronal branching trees. Examination of neuronal differentiation gene markers demonstrated higher levels of expression in PC12 cells treated with the conjugated factor. By manipulating the NGF specific receptor, TrkA, we have demonstrated that NGF-NPs induce cell differentiation via the regular pathway. Importantly, we have shown that NGF-NPs undergo slower degradation than free NGF, extending their half-life and increasing NGF availability. Even a low concentration of conjugated NGF treatment has led to an effective response. We propose the use of the NGF-NP complex which has magnetic characteristics, also as a useful method to enhance NGF efficiency and activity, thus, paving the way for substantial neuronal repair therapeutics.

Cell guidance on nanogratings: a computational model of the interplay between PC12 growth cones and nanostructures

Background

Recently, the effects of nanogratings have been investigated on PC12 with respect to cell polarity, neuronal differentiation, migration, maturation of focal adhesions and alignment of neurites.

Methodology/Principal Findings

A synergistic procedure was used to study the mechanism of alignment of PC12 neurites with respect to the main direction of nanogratings. Finite Element simulations were used to qualitatively assess the distribution of stresses at the interface between non-spread growth cones and filopodia, and to study their dependence on filopodial length and orientation. After modelling all adhesions under non-spread growth cone and filopodial protrusions, the values of local stress maxima resulted from the length of filopodia. Since the stress was assumed to be the main triggering cause leading to the increase and stabilization of filopodia, the position of the local maxima was directly related to the orientation of neurites. An analytic closed form equation was then written to quantitatively assess the average ridge width needed to achieve a given neuritic alignment (R² = 0.96), and the alignment course, when the ridge depth varied (R² = 0.97). A computational framework was implemented within an improved free Java environment (CX3D) and in silico simulations were carried out to reproduce and predict biological experiments. No significant differences were found between biological experiments and in silico simulations (alignment, p = 0.3571; tortuosity, p = 0.2236) with a standard level of confidence (95%).

Conclusions/Significance

A mechanism involved in filopodial sensing of nanogratings is proposed and modelled through a synergistic use of FE models, theoretical equations and in silico simulations. This approach shows the importance of the neuritic terminal geometry, and the key role of the distribution of the adhesion constraints for the cell/substrate coupling process. Finally, the effects of the geometry of nanogratings were explicitly considered in cell/surface interactions thanks to the analytic framework presented in this work.

Polymeric theranostics: using polymer-based systems for simultaneous imaging and therapy

Polymer-based nanomedicine is a large and fast growing field. Polymer-based systems have been extensively used as therapeutic carriers as well as bioimaging agents for example in tumour diagnosis. However, fewer polymeric systems have been able to combine both therapy and imaging in a new field that is called theranostics (theragnostics). This review aims to summarise the recent developments and trends on polymeric theranostics. Four different types of therapies/treatments are examined namely drug delivery, gene delivery, photodynamic therapy and hyperthermia treatment combined with different imaging moieties like magnetic resonance imaging agents, fluorescent agents and microbubbles for ultrasound imaging.

Role of engineered nanocarriers for axon regeneration and guidance: current status and future trends

There are approximately 1.5 million people who experience traumatic injuries to the brain and 265,000 who experience traumatic injuries to the spinal cord each year in the United States. Currently, there are few effective treatments for central nervous system (CNS) injuries because the CNS is refractory to axonal regeneration and relatively inaccessible to many pharmacological treatments. Smart, remotely tunable, multifunctional micro- and nanocarriers hold promise for delivering treatments to the CNS and targeting specific neurons to enhance axon regeneration and synaptogenesis. Furthermore, assessing the efficacy of treatments could be enhanced by biocompatible nanovectors designed for imaging in vivo. Recent developments in nanoengineering offer promising alternatives for designing biocompatible micro- and nanovectors, including magnetic nanostructures, carbon nanotubes, and quantum dot-based systems for controlled release of therapeutic and diagnostic agents to targeted CNS cells. This review highlights recent achievements in the development of smart nanostructures to overcome the existing challenges for treating CNS injuries.

Polymer-based microparticles in tissue engineering and regenerative medicine

Different types of biomaterials, processed into different shapes, have been proposed as temporary support for cells in tissue engineering (TE) strategies. The manufacturing methods used in the production of particles in drug delivery strategies have been adapted for the development of microparticles in the fields of TE and regenerative medicine (RM). Microparticles have been applied as building blocks and matrices for the delivery of soluble factors, aiming for the construction of TE scaffolds, either by fusion giving rise to porous scaffolds or as injectable systems for in situ scaffold formation, avoiding complicated surgery procedures. More recently, organ printing strategies have been developed by the fusion of hydrogel particles with encapsulated cells, aiming the production of organs in in vitro conditions. Mesoscale self-assembly of hydrogel microblocks and the use of leachable particles in three-dimensional (3D) layer-by-layer (LbL) techniques have been suggested as well in recent works. Along with innovative applications, new perspectives are open for the use of these versatile structures, and different directions can still be followed to use all the potential that such systems can bring. This review focuses on polymeric microparticle processing techniques and overviews several examples and general concepts related to the use of these systems in TE and RE applications. The use of materials in the development of microparticles from research to clinical applications is also discussed.

RNA interference therapy via functionalized scaffolds

Tissue engineering aims to provide structural and biomolecular cues to compromised tissues through scaffolds. An emerging biomolecular cue is that of RNA interference by which the expression of genes can be silenced through a potent endogenous pathway. Recombinant viral-based approaches in RNAi delivery exist; however non-viral strategies offer many opportunities to exploit this mechanism of regulation in a safer way. Current RNAi therapies in clinical trials are without a vector (naked) or have slightly modified structures. Modification of these molecules with efficient backbone moieties for improved stability and potency, protecting and buffering them with delivery vehicles, and using scaffolds as reservoirs of delivery is at the frontier of current research. However, to enable an efficient sustained therapeutic effect scaffolds have a potentially significant role to play. This review presents non-viral delivery of RNAi that have been attempted via tissue engineered scaffolds. For RNAi to have a clinical impact, it is imperative to evaluate optimal delivery systems to ensure that the efficacy of this promising technology can be maximized.