Development and characterization of cores–shell poly(lactide-co-glycolide)-chitosan microparticles for sustained release of GDNF

Chitosan-Based Particulate Carriers: Structure, Production and Corresponding Controlled Release

The state of the art in the use of chitosan (CS) for preparing particulate carriers for drug delivery applications is reviewed. After evidencing the scientific and commercial potentials of CS, the links between targeted controlled activity, the preparation process and the kinetics of release are detailed, focusing on two types of particulate carriers: matrix particles and capsules. More precisely, the relationship between the size/structure of CS-based particles as multifunctional delivery systems and drug release kinetics (models) is emphasized. The preparation method and conditions greatly influence particle structure and size, which affect release properties. Various techniques available for characterizing particle structural properties and size distribution are reviewed. CS particulate carriers with different structures can achieve various release patterns, including zero-order, multi-pulsed, and pulse-triggered. Mathematical models have an unavoidable role in understanding release mechanisms and their interrelationships. Moreover, models help identify the key structural characteristics, thus saving experimental time. Furthermore, by investigating the close relation between preparation process parameters and particulate structural characteristics as well as their effect on release properties, a novel "on-demand" strategy for the design of drug delivery devices may be developed. This reverse strategy involves designing the production process and the related particles' structure based on the targeted release pattern.

Recent Advances in Polymeric Drug Delivery Systems for Peripheral Nerve Regeneration

When a traumatic event causes complete denervation, muscle functional recovery is highly compromised. A possible solution to this issue is the implantation of a biodegradable polymeric tubular scaffold, providing a biomimetic environment to support the nerve regeneration process. However, in the case of consistent peripheral nerve damage, the regeneration capabilities are poor. Hence, a crucial challenge in this field is the development of biodegradable micro- nanostructured polymeric carriers for controlled and sustained release of molecules to enhance nerve regeneration. The aim of these systems is to favor the cellular processes that support nerve regeneration to increase the functional recovery outcome. Drug delivery systems (DDSs) are interesting solutions in the nerve regeneration framework, due to the possibility of specifically targeting the active principle within the site of interest, maximizing its therapeutical efficacy. The scope of this review is to highlight the recent advances regarding the study of biodegradable polymeric DDS for nerve regeneration and to discuss their potential to enhance regenerative performance in those clinical scenarios characterized by severe nerve damage.

Sustain release of loaded insulin within biomimetic hydrogel microsphere for sciatic tissue engineering in vivo

We developed insulin loaded biomimetic microsphere by laccase-mediated crosslinking using a microfluidic device in the water-in-oil emulsion system as an injectable vehicle for the repair of sciatic tissue. Aqueous polymeric solution of phenol-substituted hyaluronic acid (HAPh) and collagen (ColPh) containing insulin and laccase flowed from the inner channel into oil flow within an outer channel which leads formation of hydrogel microsphere. The physical properties of prepared specimens including swelling rate, mechanical resistance and the prolonged release rate of microspheres proved applicability of fabricated vehicles for tissue engineering and drug delivery systems. The growth profile and behavior of cells in microspheres indicated cytocompatibility of the method and prepared vehicles for microtissue development. Histopathological examination revealed a significant increase in axonal regeneration, and remyelination process in injured sciatic nerve following treatment with HAPh/ColPh microspheres containing insulin compared to control groups. Also, the functional characteristic of sciatic tissue showed that the presence of biomimetic microsphere and insulin simultaneously had improved sciatic tissue functions including functional sciatic index (SFI) values, reaction to hot plate and muscle weight of rats. In summary, the results proved that composite biomimetic microspheres containing insulin effectively improved nerve regeneration in the rat model.

Natural Polymer‐Derived Bioscaffolds for Peripheral Nerve Regeneration

In recent decades, artificial nerve scaffolds have become a promising substitute for peripheral nerve repair. Considerable efforts have been devoted to improving the therapeutic effectiveness of artificial scaffolds. Among numerous biomaterials for tissue engineering scaffolds fabrication, natural polymers are considered as tremendous candidates because of their excellent biocompatibility, low toxicity, high cell affinity, wide source, and environmental protection. With the development of engineering technology, a variety of natural polymer‐derived nerve scaffolds have emerged, which are endowed with biological properties and appropriate physicochemical performances to gradually adapt to the needs of nerve regeneration. Significantly, the intergradation of exogenous biomolecules onto the artificial scaffolds is able to avoid low stability, rapid degradation, and redistribution of direct therapeutic drugs in vivo, thereby enhancing nerve regeneration and functional reconstruction. Here, the development of nerve scaffolds derived from natural polymers, and their applications in continuous administration and peripheral nerve regeneration are comprehensively and carefully reviewed, providing an advanced perspective of the field.

Functional microspheres for tissue regeneration

As a new type of injectable biomaterials, functional microspheres have attracted increasing attention in tissue regeneration because they possess some advantageous properties compared to other biomaterials, including hydrogels. A variety of bio-inspired microspheres with unique structures and properties have been developed as cellular carriers and drug delivery vehicles in recent years. In this review, we provide a comprehensive summary of the progress of functional and biodegradable microspheres that have been used for tissue regeneration over the last two decades. First, we briefly introduce the biomaterials and general methods for microsphere fabrication. Next, we focus on the newly developed technologies for preparing functional microspheres, including macroporous microspheres, nanofibrous microspheres, hollow microspheres, core-shell structured microspheres, and surface-modified functional microspheres. After that, we discuss the application of functional microspheres for tissue regeneration, specifically for bone, cartilage, dental, neural, cardiac, and skin tissue regeneration. Last, we present our perspectives and future directions of functional microspheres as injectable carriers for the future advancement of tissue regeneration.

Gentiopicroside PLGA Nanospheres: Fabrication, in vitro Characterization, Antimicrobial Action, and in vivo Effect for Enhancing Wound Healing in Diabetic Rats

Purpose

Gentiopicroside (GPS), an adequate bioactive candidate, has a promising approach for enhancing wound healing due to its antioxidant and antimicrobial properties. Its poor aqueous solubility negatively affects oral absorption accompanied by low bioavailability due to intestinal/hepatic first-pass metabolism. Our aim in this study is to fabricate GPS into appropriate nanocarriers (PLGA nanospheres, NSs) to enhance its solubility and hence its oral absorption would be improved.

Methods

Normal and ODS silica gel together with Sephadex LH20 column used for isolation of GPS from Gentiana lutea roots. Crude GPS would be further processed for nanospheres fabrication using a single o/w emulsion solvent evaporation technique followed by in vitro optimization study to examine the effect of two formulation variables: polymer (PLGA) and stabilizer (PVA) concentrations on the physical characterizations of prepared NSs. Possible GPS-PLGA chemical and physical interactions have been analyzed using Fourier-transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The optimum GPS-PLGA NSs have been chosen for antimicrobial study to investigate its inhibitory action on Staphylococcus aureus compared with unloaded GPS NSs. Also, a well-designed in vivo study on streptozotocin-induced diabetic rats has been performed to examine the wound healing effect of GPS-PLGA NSs followed by histological examination of wound incisions at different day intervals throughout the study.

Results

The optimum GPS PLGA NSs (F5) with well-controlled particle size (250.10±07.86 nm), relative high entrapment efficiency (83.35±5.71), and the highest % cumulative release (85.79±8.74) have increased the antimicrobial activity as it exhibited a higher inhibitory effect on bacterial growth than free GPS. F5 showed a greater enhancing impact on wound healing and a significant stimulating effect on the synthesis of collagen fibers compared with free GPS.

Conclusion

These findings demonstrate that loading GPS into PLGA NSs is considered a promising strategy ensuring optimum GPS delivery for potential management of wounds.

PLGA Core-Shell Nano/Microparticle Delivery System for Biomedical Application

Core-shell particles are very well known for their unique features. Their distinctive inner core and outer shell structure allowed promising biomedical applications at both nanometer and micrometer scales. The primary role of core-shell particles is to deliver the loaded drugs as they are capable of sequence-controlled release and provide protection of drugs. Among other biomedical polymers, poly (lactic-co-glycolic acid) (PLGA), a food and drug administration (FDA)-approved polymer, has been recognized for the vehicle material. This review introduces PLGA core-shell nano/microparticles and summarizes various drug-delivery systems based on these particles for cancer therapy and tissue regeneration. Tissue regeneration mainly includes bone, cartilage, and periodontal regeneration.

TPP ionically cross-linked chitosan/PLGA microspheres for the delivery of NGF for peripheral nerve system repair

To control the release of nerve growth factor (NGF) in the injured peripheral nerve, NGF-loaded chitosan/PLGA composite microspheres ionically cross-linked by tripolyphosphate (TPP/Chitosan/PLGA-NGF) were prepared. The encapsulation efficiency of NGF ranged from 83.4 ± 1.5 % to 72.1 ± 1.6 % with TPP concentrations from 1 % to 10 %. Zeta potential and FT-IR analyses together with confocal microscopy demonstrated that multiple NGF-loaded PLGA microspheres were embedded in chitosan matrix, the mean size of TPP/Chitosan/PLGA-NGF microspheres ranged from 40.2 ± 3.4 to 49.3 ± 3.1 μm. The increase of TPP concentration improved the network stability and decreased the swelling ratio, resulting in the decreased NGF release from 67.7 ± 1.2 % to 45.7 ± 0.8 % in 49 days. The sustained release of NGF could promote PC12 cells differentiation and neurite growth in vitro. Moreover, in comparison with NGF solution without microencapsulation, TPP/Chitosan/PLGA-NGF microspheres enhanced sciatic nerve regeneration and prevented gastrocnemius muscle atrophy in rats. These results demonstrate the feasibility of using TPP/Chitosan/PLGA-NGF microspheres for neural tissue repair.

Design and applications of protein delivery systems in nanomedicine and tissue engineering

Proteins are biological macromolecules involved in a wide range of biological functions, which makes them very appealing as therapeutics agents. Indeed, compared to small molecule drugs, their endogenous nature ensures their biocompatibility and biodegradability, they can be used in a large range of applications and present a higher specificity and activity. However, they suffer from unfolding, enzymatic degradation, short half-life and poor membrane permeability. To overcome such drawbacks, the development of protein delivery systems to protect, carry and deliver them in a controlled way have emerged importantly these last years. In this review, the formulation of a wide panel of protein delivery systems either in the form of polymer or inorganic nanoengineered colloids and scaffolds are presented and the protein loading and release mechanisms are addressed. A section is also dedicated to the detection of proteins and the characterization methods of their release. Then, the main protein delivery systems developed these last three years for anticancer, tissue engineering or diabetes applications are presented, as well as the major in vivo models used to test them. The last part of this review aims at presenting the perspectives of the field such as the use of protein-rich material or the sequestration of proteins. This part will also deal with less common applications and gene therapy as an indirect method to deliver protein.

[The fabrication and related properties study of chitosan-poly (lactide-co-glycolide) double-walled microspheres loaded with nerve growth factor]

Objective

To evaluate the feasibility of the chitosan-poly (lactide-co-glycolide) (PLGA) double-walled microspheres for sustained release of bioactive nerve growth factor (NGF) in vitro.

Methods

NGF loaded chitosan-PLGA double-walled microspheres were prepared by emulsion-ionic method with sodium tripolyphosphate (TPP) as an ionic cross-linker. The double-walled microspheres were cross-linked by different concentrations of TPP [1%, 3%, 10% ( W/ V)]. NGF loaded PLGA microspheres were also prepared. The outer and inner structures of double-walled microspheres were observed by light microscopy, scanning electron microscopy, confocal laser scanning microscopy, respectively. The size and distribution of microspheres and fourier transform infra red spectroscopy (FT-IR) were analyzed. PLGA microspheres with NGF or chitosan-PLGA double-walled microspheres cross-linked by 1%, 3%, and 10%TPP concentration (set as groups A, B, C, and D respectively) were used to determine the degradation ratio of microspheres in vitro and the sustained release ratio of NGF in microspheres at different time points. The bioactivity of NGF (expressed as the percentage of PC12 cells with positive axonal elongation reaction) in the sustained release solution of chitosan-PLGA double-walled microspheres without NGF (set as group A1) was compared in groups B, C, and D.

Results

The chitosan-PLGA double-walled microspheres showed relative rough and spherical surfaces without aggregation. Confocal laser scanning microscopy showed PLGA microspheres were evenly uniformly distributed in the chitosan-PLGA double-walled microspheres. The particle size of microspheres ranged from 18.5 to 42.7 μm. The results of FT-IR analysis showed ionic interaction between amino groups and phosphoric groups of chitosan in double-walled microspheres and TPP. In vitro degradation ratio analysis showed that the degradation ratio of double-walled microspheres in groups B, C, and D appeared faster in contrast to that in group A. In addition, the degradation ratio of double-walled microsphere in groups B, C, and D decreased when the TPP concentration increased. There were significant differences in the degradation ratio of each group ( P<0.05). In vitro sustained release ratio of NGF showed that when compared with PLGA microspheres in group A, double-walled microspheres in groups B, C, and D released NGF at a relatively slow rate, and the sustained release ratio decreased with the increase of TPP concentration. Except for 84 days, there was significant difference in the sustained release ratio of NGF between groups B, C, and D ( P<0.05). The bioactivity of NGF results showed that the percentage of PC12 cells with positive axonal elongation reaction in groups B, C, and D was significantly higher than that in group A1 ( P<0.05). At 7 and 28 days of culture, there was no significant difference between groups B, C, and D ( P>0.05); at 56 and 84 days of culture, the percentage of PC12 cells with positive axonal elongation reaction in groups C and D was significantly higher than that in group B ( P<0.05), and there was no significant difference between groups C and D ( P>0.05).

Conclusion

NGF loaded chitosan-PLGA double-walled microspheres have a potential clinical application in peripheral nerve regeneration after injury.

Electrospun acid-neutralizing fibers for the amelioration of inflammatory response

Biodegradable aliphatic polyesters, especially polylactide (PLA), polyglycolide (PGA), and their copolymer poly(lactide-co-glycolide) (PLGA), are the most representative and widely used synthetic polymers in the field of tissue engineering and regenerative medicine. However, these polyesters often give rise to aseptic inflammation because of their acidic degradation products after implantation. Here, unidirectional shell-core structured fibers of chitosan/poly(lactide-co-glycolide) (i.e., CTS/PLGA) with acid-neutralizing capability were developed for addressing the noted issue by coating the PLGA fiber surfaces with a layer of the alkaline chitosan by coaxial electrospinning. Our results showed that during a period of 8-week degradation, the shell-layer of chitosan with its unique alkaline nature for acid-neutralization obviously hindered the pH decrease as a result of the degradation of PLGA-core. In a mocked acidic environment testing of the human dermal fibroblasts, chitosan-enabled acidity neutralization could significantly reduce in vitro the secretion of inflammatory factors and downregulate the expression of related inflammatory genes. Thereafter, biocompatibility assessment in vitro showed that the CTS/PLGA fibers had poorer cell adhesion capacity than the PLGA fibers but were cytocompatible and promoted cell migration and secretion of collagen. Moreover, subcutaneous embedding for two and four weeks in vivo revealed that the CTS/PLGA fibers significantly reduced the recruitment of inflammatory cells and the formation of foreign body giant cells (FBGCs). This study thereby demonstrated the evident acid-neutralizing effect of the chitosan-coating layer on alleviating the inflammatory responses caused by the acidic degradation products of the PLGA-core. Our highly aligned CTS/PLGA fibers, as a kind of quasi "pH-neutral fibers" with the acid-neutralizing capability, could be potentially applied for engineering those architecturally anisotropic tissues (e.g., tendon/ligament) toward improved efficacy of regeneration. STATEMENT OF SIGNIFICANCE: It is well known that acidic degradation products from representative aliphatic polyesters (e.g., PLA, PGA, and PLGA) give rise to the problem of aseptic inflammation. Various alkaline components acting as neutralizing agents have been used to address the noted issue. However, rather less attention has been paid to engineer these polyesters into a fibrous form with acid-neutralizing functionality. The present study proposes the concept of "pH-neutral fibers" and develops shell-core structured unidirectional fibers of chitosan/poly(lactide-co-glycolide) with acid-neutralizing capability for ameliorating inflammatory responses caused by the acidic degradation products of PLGA. It provides a comprehensive study encompassing fiber characterization and in vitro and in vivo evaluation, which would pave the way for developing sophisticated pH-neutral fibers for functional tissue regeneration.

Application of stem cells and chitosan in the repair of spinal cord injury

Cytology and histology obstacles have been the main barriers to multiple tissues injury repair. In search of the most promising treatment strategies for spinal cord injury (SCI), stem cell-based transplantation coupled with various materials/technologies have been explored extensively to enhance SCI repair. Chitosan (CS) has demonstrated immense potential for widespread application in the form of scaffolds and micro-particles for SCI repair. The current review summarizes the evidences for stem cell-based transplantation and CS in SCI repair. Stem cells transplantation, which plays a key role in the repair of SCI, mainly results from its neural differentiation potential and neurotrophic effects. Application of CS enhances the survival of grafted stem cells, upregulates the expression level of neurotrophic factors and heightens the neural differentiation of stem cells as well as the functional recovery of spinal cord. Meanwhile, CS can also be exploited as growth factors/RNA carriers to control the release of regenerating molecules which are beneficial to damage spinal cord repair.

Nanomaterial-Based Approaches for Neural Regeneration

Mechanical, thermal, chemical, or ischemic injury of the central or peripheral nervous system results in neuron loss, neurite damage, and/or neuronal dysfunction, almost always accompanied by sensorimotor impairment which alters the patient's life quality. The regenerative strategies for the injured nervous system are currently limited and mainly allow partial functional recovery, so it is necessary to develop new and effective approaches for nervous tissue regenerative therapy. Nanomaterials based on inorganic or organic and composite or hybrid compounds with tunable physicochemical properties and functionality proved beneficial for the transport and delivery/release of various neuroregenerative-relevant biomolecules or cells. Within the following paragraphs, we will emphasize that nanomaterial-based strategies (including nanosized and nanostructured biomaterials) represent a promising alternative towards repairing and regenerating the injured nervous system.