Implantable porous gelatin microspheres sustained release of bFGF and improved its neuroprotective effect on rats after spinal cord injury

A Review of Basic Fibroblast Growth Factor Delivery Strategies and Applications in Regenerative Medicine

Basic fibroblast growth factor (bFGF) is a significant member of the fibroblast growth factor (FGF) family. The bFGF has a three-dimensional structure comprising 12 reverse parallel β-folds. This structure facilitates tissue wound repair, angiogenesis, bone formation, cartilage repair, and nerve regeneration. Consequently, it has garnered significant attention from scholars both domestically and internationally. However, the instability and degradation properties of bFGF in vivo have limited its clinical application. Significant interest has arisen in the development of novel bFGF delivery systems that can address the shortcomings of bFGF and enhance its bioavailability by controlling the release amount, timing, and location. This article offers a comprehensive overview of the research and recent advances in various bFGF delivery systems, including hydrogels, liposomes, microspheres, and nanoparticles. Subsequently, the applications of bFGF pharmaceutical preparations in various fields are described. Finally, the current clinical applications of bFGF drug formulations and those in clinical trials are discussed, along with their clinical translation and future trends.

Microfiber-reinforced hydrogels prolong the release of human induced pluripotent stem cell-derived extracellular vesicles to promote endothelial migration

Extracellular vesicle (EV)-based approaches for promoting angiogenesis have shown promising results. Yet, further development is needed in vehicles that prolong EV exposure to target organs. Here, we hypothesized that microfiber-reinforced gelatin methacryloyl (GelMA) hydrogels could serve as sustained delivery platforms for human induced pluripotent stem cell (hiPSC)-derived EV. EV with 50-200 nm size and typical morphology were isolated from hiPSC-conditioned culture media and tested negative for common co-isolated contaminants. hiPSC-EV were then incorporated into GelMA hydrogels with or without a melt electrowritten reinforcing mesh. EV release was found to increase with GelMA concentration, as 12 % (w/v) GelMA hydrogels provided higher release rate and total release over 14 days in vitro, compared to lower hydrogel concentrations. Release profile modelling identified diffusion as a predominant release mechanism based on a Peppas-Sahlin model. To study the effect of reinforcement-dependent hydrogel mechanics on EV release, stress relaxation was assessed. Reinforcement with highly porous microfiber meshes delayed EV release by prolonging hydrogel stress relaxation and reducing the swelling ratio, thus decreasing the initial burst and overall extent of release. After release from photocrosslinked reinforced hydrogels, EV remained internalizable by human umbilical vein endothelial cells (HUVEC) over 14 days, and increased migration was observed in the first 4 h. EV and RNA cargo stability was investigated at physiological temperature in vitro, showing a sharp decrease in total RNA levels, but a stable level of endothelial migration-associated small noncoding RNAs over 14 days. Our data show that hydrogel formulation and microfiber reinforcement are superimposable approaches to modulate EV release from hydrogels, thus depicting fiber-reinforced GelMA hydrogels as tunable hiPSC-EV vehicles for controlled release systems that promote endothelial cell migration.

Enhanced spinal cord regeneration by gelatin/alginate hydrogel scaffolds containing human endometrial stem cells and curcumin-loaded PLGA nanoparticles in rat

Spinal cord injury (SCI) is a serious problem with a high prevalence worldwide. The weak capability of the spinal cord for regeneration in association with upregulation of inflammatory factors is two key obstacles against a full SCI repair. Curcumin is a natural substance with anti-inflammatory and neuroprotective effects. Here, we have used a combined strategy using stem cells and hybrid hydrogel scaffolds loaded with curcumin for SCI repair. Curcumin-loaded PLGA nanoparticles were prepared, characterized, and encapsulated into gelatin/alginate hydrogel scaffolds, which were then seeded by human endometrial stem cells (hEnSCs). The resulting construct was studied using in vitro and in vivo experiments on rat models. DLS, SEM, Zeta potential, and FTIR data confirmed the successful addition of curcumin to PLGA nanoparticles. SEM analyses indicated the successful addition of curcumin-loaded nanoparticles into the gelatin/alginate scaffold, as well as the adherence of the seeded EnSCs. Based on the results, the prepared constructs not only allowed the controlled release of curcumin but also could support the survival and growth of hEnSCs. Based on the results of BBB and histological experiments, the highest BBB score was related to the combined strategy, consistent with histological outcomes, in which our hEnSC-seeded gelatin/alginate scaffold containing curcumin-loaded nanoparticles led to improved structures of the white and gray matters in the SCI site, being indicative of the superior nerve fiber regeneration, compared to other studied groups. These results indicate the efficiency of the proposed method for SCI repair and broaden the scope for subsequent studies on spinal cord regeneration.

Biomimetic engineered approaches for neural tissue engineering: Spinal cord injury

The healing process for spinal cord injuries is complex and presents many challenges. Current advances in nerve regeneration are based on promising tissue engineering techniques, However, the chances of success depend on better mimicking the extracellular matrix (ECM) of neural tissue and better supporting neurons in a three-dimensional environment. The ECM provides excellent biological conditions, including desirable morphological features, electrical conductivity, and chemical compositions for neuron attachment, proliferation and function. This review outlines the rationale for developing a construct for neuron regrowth in spinal cord injury using appropriate biomaterials and scaffolding techniques.

Biomaterial-Based bFGF Delivery for Nerve Repair

Diseases in the nervous system are common in the human body. People have to suffer a great burden due to huge economic costs and poor prognosis of the diseases. Many treatment modalities are now available that can make recovery better. Managing nutritional factors is also helpful for such diseases. The basic fibroblast growth factor (bFGF) is one of the major nutritional factors, which plays a crucial role in organogenesis and tissue homeostasis. It plays a role in cell proliferation, migration, and differentiation, thereby regulating angiogenesis and wound healing and repair of the muscle, bone, and nerve. The study on how to improve the stability of bFGF to increase the treatment effect for different diseases has garnered tremendous attention. Biomaterials are the popular methods to improve the stability of bFGF because they are safe for the living body as they are biocompatible. Biomaterials can be loaded with bFGF and delivered locally to achieve the goal of sustained bFGF release. In the present review, we report different types of biomaterials that are used for bFGF delivery for nerve repair and briefly report how the introduced bFGF can function in the nervous system. We aim to provide summative guidance for future studies about nerve injury using bFGF.

3D Gelatin Microsphere Scaffolds Promote Functional Recovery after Spinal Cord Hemisection in Rats

Spinal cord injury (SCI) damages signal connections and conductions, with the result that neuronal circuits are disrupted leading to neural dysfunctions. Such injuries represent a serious and relatively common central nervous system condition and current treatments have limited success in the reconstruction of nerve connections in injured areas, especially where sizeable gaps are present. Biomaterial scaffolds have become an effective alternative to nerve transplantation in filling these gaps and provide the foundation for simulating the 3D structure of solid organs. However, there remain some limitations with the application of 3D bioprinting for preparation of biomaterial scaffolds. Here, the approach in constructing and testing mini-tissue building blocks and self-assembly, solid 3D gelatin microsphere (GM) scaffolds with multiple voids as based on the convenient preparation of gelatin microspheres by microfluidic devices is described. These 3D GM scaffolds demonstrate suitable biocompatibility, biodegradation, porosity, low preparation costs, and relative ease of production. Moreover, 3D GM scaffolds can effectively bridge injury gaps, establish nerve connections and signal transductions, mitigate inflammatory microenvironments, and reduce glial scar formation. Accordingly, these 3D GM scaffolds can serve as a novel and effective bridging method to promote nerve regeneration and reconstruction and thus recovery of nerve function after SCI.

Mechanisms of ginsenosides exert neuroprotective effects on spinal cord injury: A promising traditional Chinese medicine

Spinal cord injury (SCI) is a devastating disorder of the central nervous system (CNS). It is mainly caused by trauma and reduces the quality of life of the affected individual. Ginsenosides are safe and effective traditional Chinese medicines (TCMs), and their efficacy against SCI is being increasingly researched in many countries, especially in China and Korea. This systematic review evaluated the neuroprotective effects of ginsenosides in SCI and elucidated their properties.

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.

Polymeric Fibers as Scaffolds for Spinal Cord Injury: A Systematic Review

Spinal cord injury (SCI) is a complex neurological condition caused by trauma, inflammation, and other diseases, which often leads to permanent changes in strength and sensory function below the injured site. Changes in the microenvironment and secondary injuries continue to pose challenges for nerve repair and recovery after SCI. Recently, there has been progress in the treatment of SCI with the use of scaffolds for neural tissue engineering. Polymeric fibers fabricated by electrospinning have been increasingly used in SCI therapy owing to their biocompatibility, complex porous structure, high porosity, and large specific surface area. Polymer fibers simulate natural extracellular matrix of the nerve fiber and guide axon growth. Moreover, multiple channels of polymer fiber simulate the bundle of nerves. Polymer fibers with porous structure can be used as carriers loaded with drugs, nerve growth factors and cells. As conductive fibers, polymer fibers have electrical stimulation of nerve function. This paper reviews the fabrication, characterization, and application in SCI therapy of polymeric fibers, as well as potential challenges and future perspectives regarding their application.

Potent Particle-Based Vehicles for Growth Factor Delivery from Electrospun Meshes: Fabrication and Functionalization Strategies for Effective Tissue Regeneration

Functionalization of electrospun meshes with growth factors (GFs) is a common strategy for guiding specific cell responses in tissue engineering. GFs can exert their intended biological effects only when they retain their bioactivity and can be subsequently delivered in a temporally controlled manner. However, adverse processing conditions encountered in electrospinning can potentially disrupt GFs and diminish their biological efficacy. Further, meshes prepared using conventional approaches often promote an initial burst and rely solely on intrinsic fiber properties to provide extended release. Sequential delivery of multiple GFs─a strategy that mimics the natural tissue repair cascade─is also not easily achievable with traditional fabrication techniques. These limitations have hindered the effective use and translation of mesh-based strategies for tissue repair. An attractive alternative is the use of carrier vehicles (e.g., nanoparticles, microspheres) for GF incorporation into meshes. This review presents advances in the development of particle-integrated electrospun composites for safe and effective delivery of GFs. Compared to traditional approaches, we reveal how particles can protect GF activity, permit the incorporation of multiple GFs, decouple release from fiber properties, help achieve spatiotemporal control over delivery, enhance surface bioactivity, exert independent biological effects, and augment matrix mechanics. In presenting innovations in GF functionalization and composite engineering strategies, we also discuss specific in vitro and in vivo biological effects and their implications for diverse tissue engineering applications.

Cross-linked Porous Gelatin Microparticles with Tunable Shape, Size, and Porosity

Gelatin particles are relevant to many applications in the biomedical field due to their excellent biocompatibility and versatility. When prepared by double emulsion methods, porous microparticles with different architectures can be obtained. Controlling the shape, size, porosity, swelling, and stability against dissolution is fundamental toward their application under physiological conditions. We prepared porous gelatin microparticles from oil-in-water-in-oil emulsions, modifying the gelatin/surfactant ratio and the stirring speed. The effect on structural properties, including surface and inner porosities, was thoroughly assessed by multiple microscopy techniques (optical, electron, and confocal Raman). Selected samples were cross-linked with glutaraldehyde or glyceraldehyde, and their swelling properties and stability against dissolution were evaluated, while the influence of the cross-linking at the nanoscale was studied by scattering of X-rays. Depending on the preparation protocol, we obtained particles with different shapes (irregular or spherical), radii within ∼40 to 90 μm, and porosities up to 10 μm. The cross-linking extends the stability in water from a few minutes up to several days while the swelling ability and the mesh size at the nanoscale of the gelatin network are preserved. The analysis of the experimental results as a function of the preparation parameters demonstrates that microparticles with tunable features can be designed.

Microencapsulation of growth factors by microfluidic system

The encapsulation of growth factors is an important component of tissue engineer- ing. Using microspheres is a convenient approach in which the dose of factors can be regulated by increasing or decreasing the number of encapsulated microspheres. Moreover, microspheres offer the possibility of delivering the growth factors directly to the target site. However, the fabrication of microspheres by traditional emulsion methods is largely variable due to the experimental procedure. We have developed a protocol using a commercially available microfluidic system that allows formation of tunable particle-size droplets loaded with growth factors. The methodology includes a guide for preparing an alginate-growth factors solution followed by the specific set-up needed for using the microfluidic system to form the microspheres. The pro- cedure also includes a unique post-crosslinking process without pH modification. These methods allow the preservation of integrity and bioactivity of the growth factors tested (BMP-6 and TGFβ -3) and their subsequent sustained delivery.•The protocol can be tuned to form particles of various sizes.•The gentle post-crosslinking process allows conformational integrity of various bioactive molecules.

AAV2-mediated and hypoxia response element-directed expression of bFGF in neural stem cells showed therapeutic effects on spinal cord injury in rats

Neural stem cell (NSCs) transplantation has been one of the hot topics in the repair of spinal cord injury (SCI). Fibroblast growth factor (FGF) is considered a promising nerve injury therapy after SCI. However, owing to a hostile hypoxia condition in SCI, there remains a challenging issue in implementing these tactics to repair SCI. In this report, we used adeno-associated virus 2 (AAV2), a prototype AAV used in clinical trials for human neuron disorders, basic FGF (bFGF) gene under the regulation of hypoxia response element (HRE) was constructed and transduced into NSCs to yield AAV2-5HRE-bFGF-NSCs. Our results showed that its treatment yielded temporally increased expression of bFGF in SCI, and improved scores of functional recovery after SCI compared to vehicle control (AAV2-5HRE-NSCs) based on the analyses of the inclined plane test, Basso-Beattie-Bresnahan (BBB) scale and footprint analysis. Mechanistic studies showed that AAV2-5HRE-bFGF-NSCs treatment increased the expression of neuron-specific neuronal nuclei protein (NeuN), neuromodulin GAP43, and neurofilament protein NF200 while decreased the expression of glial fibrillary acidic protein (GFAP) as compared to the control group. Further, the expressions of autophagy-associated proteins LC3-II and Beclin 1 were decreased, whereas the expression of P62 protein was increased in AAV2-5HRE-bFGF-NSCs treatment group. Taken together, our data indicate that AAV2-5HRE-bFGF-NSCs treatment improved the recovery of SCI rats, which is accompanied by evidence of nerve regeneration, and inhibition of SCI-induced glial scar formation and cell autophagy. Thus, this study represents a step forward towards the potential use of AAV2-5HRE-bFGF-NSCs for future clinical trials of SCI repair.

Endocrine Therapy for the Functional Recovery of Spinal Cord Injury

Spinal cord injury (SCI) is a major cause of physical disability and leads to patient dissatisfaction with their quality of life. Patients with SCI usually exhibit severe clinical symptoms, including sensory and motor dysfunction below the injured levels, paraplegia, quadriplegia and urinary retention, which can exacerbate the substantial medical and social burdens. The major pathological change observed in SCI is inflammatory reaction, which induces demyelination, axonal degeneration, and the apoptosis and necrosis of neurons. Traditional medical treatments are mainly focused on the recovery of motor function and prevention of complications. To date, numerous studies have been conducted to explore the cellular and molecular mechanism of SCI and have proposed lots of effective treatments, but the clinical applications are still limited due to the complex pathogenesis and poor prognosis after SCI. Endocrine hormones are kinds of molecules that are synthesized by specialized endocrine organs and can participate in the regulation of multiple physiological activities, and their protective effects on several disorders have been widely discussed. In addition, many studies have identified that endocrine hormones can promote nerve regeneration and functional recovery in individuals with central nervous system diseases. Therefore, studies investigating the clinical applications of endocrine hormones as treatments for SCI are necessary. In this review, we described the neuroprotective roles of several endocrine hormones in SCI; endocrine hormone administration reduces cell death and promotes functional repair after SCI. We also proposed novel therapies for SCI.

Gelatin Microsphere for Cartilage Tissue Engineering: Current and Future Strategies

The gelatin microsphere (GM) provides an attractive option for tissue engineering due to its versatility, as reported by various studies. This review presents the history, characteristics of, and the multiple approaches to, the production of GM, and in particular, the water in oil emulsification technique. Thereafter, the application of GM as a drug delivery system for cartilage diseases is introduced. The review then focusses on the emerging application of GM as a carrier for cells and biologics, and biologics delivery within a cartilage construct. The influence of GM on chondrocytes in terms of promoting chondrocyte proliferation and chondrogenic differentiation is highlighted. Furthermore, GM seeded with cells has been shown to have a high tendency to form aggregates; hence the concept of using GM seeded with cells as the building block for the formation of a complex tissue construct. Despite the advancement in GM research, some issues must still be addressed, particularly the improvement of GM’s ability to home to defect sites. As such, the strategy of intraarticular injection of GM seeded with antibody-coated cells is proposed. By addressing this in future studies, a better-targeted delivery system, that would result in more effective intervention, can be achieved.

HGF and bFGF Secreted by Adipose-Derived Mesenchymal Stem Cells Revert the Fibroblast Phenotype Caused by Vocal Fold Injury in a Rat Model

OBJECTIVE

To investigate how adipose-derived mesenchymal stem cells (ADSCs), secreted hepatocyte growth factor (HGF), and basic fibroblast growth factor (bFGF) affect the fibroblast phenotype after vocal fold injury.

METHODS

We cultured primary normal (uninjured) and injured vocal fold fibroblasts (VFFs). A transwell co-culture system of ADSCs and injured VFFs was constructed in vitro, then the effects of HGF or bFGF were inhibited. The proliferation, extracellular matrix (ECM) secretion and transformation of VFFs were observed.

RESULTS

Compared with uninjured VFFs, the secretion of collagen by injured VFFs increased significantly, hyaluronan synthase 1 (HAS1) secretion decreased, and VFF transformation increased significantly. After co-culture with ADSCs, the proliferation of VFFs was accelerated and the transformation was inhibited. Co-culture inhibited the expression of type I and III collagen and promoted the expression of HAS1. When HGF or bFGF secretion was inhibited, the proliferation of injured VFFs was inhibited. The inhibitory effect on collagen was reduced by both groups, but this was more obvious with the anti-HGF group. The anti-bFGF group had a more prominent effect on HAS1 secretion after injury than the anti-HGF group but the difference was not statistically significant. The inhibition of the transformation of injured VFFs was reduced while α-smooth muscle actin was upregulated, which was more obvious with the anti-HGF group.

CONCLUSIONS

ADSCs and secreted HGF and bFGF can revert the fibroblast phenotype caused by vocal fold injury. The effects of HGF are more significant than bFGF on collagen secretion and the transformation of VFFs into myofibroblasts. However, bFGF is more effective than HGF in upregulating HAS1.

Recombinant canine basic fibroblast growth factor-induced differentiation of canine bone marrow mesenchymal stem cells into voltage- and glutamate-responsive neuron-like cells

Introduction

Basic fibroblast growth factor (bFGF) is a promising cytokine in regenerative therapy for spinal cord injury. In this study, recombinant canine bFGF (rc-bFGF) was synthesized for clinical use in dogs, and the ability of rc-bFGF to differentiate canine bone marrow mesenchymal stem cells (BMSCs) into functional neurons was investigated.

Methods

The rc-bFGF was synthesized using a wheat germ cell-free protein synthesis system. The expression of rc-bFGF mRNA in the purification process was confirmed using a reverse transcription-polymerase chain reaction (RT-PCR). Western blotting was performed to confirm the antigenic property of the purified protein. To verify function of the purified protein, phosphorylation of extracellular signal-regulated kinase (ERK) was examined by in vitro assay using HEK293 cells. To compare the neuronal differentiation capacity of canine BMSCs in response to treatment with rc-bFGF, the cells were divided into the following four groups: control, undifferentiated, rh-bFGF, and rc-bFGF groups. After neuronal induction, the percentage of cells that had changed to a neuron-like morphology and the mRNA expression of neuronal markers were evaluated. Furthermore, to assess the function of the canine BMSCs after neuronal induction, changes in the intracellular Ca²⁺ concentrations after stimulation with KCl and l-glutamate were examined.

Results

The protein synthesized in this study was rc-bFGF and functioned as bFGF, from the results of RT-PCR, western blotting, and the expression of pERK in HEK293 cells. Canine BMSCs acquired a neuron-like morphology and expressed mRNAs of neuronal markers after neuronal induction in the rh-bFGF and the rc-bFGF groups. These results were more marked in the rc-bFGF group than in the other groups. Furthermore, an increase in intracellular Ca²⁺ concentrations was observed after the stimulation of KCl and l-glutamate in the rc-bFGF group, same as in the rh-bFGF group.

Conclusions

A functional rc-bFGF was successfully synthesized, and rc-bFGF induced the differentiation of canine BMSCs into voltage- and glutamate-responsive neuron-like cells. Our purified rc-bFGF may contribute, on its own, or in combination with canine BMSCs, to regenerative therapy for spinal cord injury in dogs.

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Functional rc-bFGF was successfully synthesized.

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rc-bFGF induced the differentiation of canine BMSCs into neuron-like cells.

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rc-bFGF may aid in regenerative therapy of spinal cord injury in dogs.

PLGA Microspheres of hGH of Preserved Native State Prepared Using a Self-Regulated Process

The challenges of formulating recombinant human growth hormone (rhGH) into sustained-release polymeric microspheres include two mutual causal factors, protein denaturing by the formulation process and severe initial burst release related with relative high dose. The stabilizers to protect the proteins must not evoke osmotic pressure inside the microspheres, and the contact of the protein with the interface between water and organic solution of the polymer must be minimized. To meet these criteria, rhGH was pre-formulated into polysaccharide particles via an aqueous–aqueous emulsion in the present study, followed by encapsulating the particles into microspheres through a self-regulated process to minimize the contact of the protein with the water–oil interface. Polysaccharides as the protein stabilizer did not evoke osmotic pressure as small sugar stabilizers, the cause of severe initial burst release. Reduced initial burst enabled reduced protein loading to 9% (from 22% of the once commercialized Nutropin depot), which in turn reduced the dosage form index from 80 to 8.7 and eased the initial burst. A series of physical chemical characterizations as well as biologic and pharmacokinetic assays confirmed that the present method is practically feasible for preparing microspheres of proteins.

tDCS Accelerates the Rehabilitation of MCAO-Induced Motor Function Deficits via Neurogenesis Modulated by the Notch1 Signaling Pathway

Background. Ischemic stroke carries a high mortality rate and is a leading cause of severe neurological disability. However, the efficacy of current therapeutic options remains limited. Objective. We aimed to investigate the treatment efficacy of transcranial direct current stimulation (tDCS) in motor function rehabilitation after ischemic stroke and explore the underlying mechanisms. Methods. Male Sprague-Dawley rats with epicranial electrodes were used to establish pathogenetic model through temporary right middle cerebral artery occlusion (MCAO). Subsequently, animals were randomly divided into 4 groups: MCAO + tDCS/sham tDCS, Control + tDCS/sham tDCS. Animals in the groups with tDCS underwent 10 days of cathodal tDCS totally (500 µA, 15 minutes, once a day). During and after tDCS treatment, the motor functions of the animals, ischemic damage area, proliferation and differentiation of neural stem cells (NSCs), and distribution, and protein expression of Notch1 signaling molecules were detected. Results. The rehabilitation of MCAO-induced motor function deficits was dramatically accelerated by tDCS treatment. NSC proliferation in the subventricular zone (SVZ) was significantly increased after MCAO surgery, and tDCS treatment promoted this process. Additionally, NSCs probably migrated from the SVZ to the ischemic striatum and then differentiated into neurons and oligodendrocytes after MCAO surgery, both of which processes were accelerated by tDCS treatment. Finally, tDCS treatment inhibited the activation of Notch1 signaling in NSCs in the ischemic striatum, which may be involved in NSC differentiation in the MCAO model. Conclusion. Our results suggest that tDCS may exert therapeutic efficacy after ischemic stroke in a regenerative medical perspective.

Thermosensitive heparin-poloxamer hydrogel encapsulated bFGF and NGF to treat spinal cord injury

The application of growth factors (GFs) for treating chronic spinal cord injury (SCI) has been shown to promote axonal regeneration and functional recovery. However, direct administration of GFs is limited by their rapid degradation and dilution at the injured sites. Moreover, SCI recovery is a multifactorial process that requires multiple GFs to participate in tissue regeneration. Based on these facts, controlled delivery of multiple growth factors (GFs) to lesion areas is becoming an attractive strategy for repairing SCI. Presently, we developed a GFs‐based delivery system (called GFs‐HP) that consisted of basic fibroblast growth factor (bFGF), nerve growth factor (NGF) and heparin‐poloxamer (HP) hydrogel through self‐assembly mode. This GFs‐HP was a kind of thermosensitive hydrogel that was suitable for orthotopic administration in vivo. Meanwhile, a 3D porous structure of this hydrogel is commonly used to load large amounts of GFs. After single injection of GFs‐HP into the lesioned spinal cord, the sustained release of NGF and bFGF from HP could significantly improve neuronal survival, axon regeneration, reactive astrogliosis suppression and locomotor recovery, when compared with the treatment of free GFs or HP. Moreover, we also revealed that these neuroprotective and neuroregenerative effects of GFs‐HP were likely through activating the phosphatidylinositol 3 kinase and protein kinase B (PI3K/Akt) and mitogen‐activated protein kinase/extracellular signal‐regulated kinase (MAPK/ERK) signalling pathways. Overall, our work will provide an effective therapeutic strategy for SCI repair.

Ginsenoside Rg1-induced activation of astrocytes promotes functional recovery via the PI3K/Akt signaling pathway following spinal cord injury

AIMS

To determine whether ginsenoside Rg1 is involved in scratch wound healing through altered expression of related molecules in astrocytes and improved functional recovery after spinal cord injury (SCI).

MATERIALS AND METHODS

Astrocytes were isolated from rats, followed by Rg1 treatment. The wound healing test was performed to observe the scratch wound healing in different groups. The expression of nerve growth factor (NGF), glial cell line-derived neurotrophic factor (GDNF), basic fibroblast growth factor (bFGF), and components of the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) signaling pathway were detected by western blot. Reverse transcription-polymerase chain reaction (RT-PCR) was used to measure the altered expression of laminin (LN) and fibronectin (FN). A revised Allen's method for the SCI model was performed, followed by Rg1 treatment. Then, functional scoring was conducted to evaluate the functional recovery. Hematoxylin-eosin (HE) staining showed changes in the void area. Finally, western blot assessed the expression of glial fibrillary acidic protein (GFAP) and chondroitin sulfate proteoglycans (CSPGs).

KEY FINDINGS

Rg1 mediated scratch wound healing through inducing an increased release of LN, FN, NGF, GDNF, and bFGF in vitro. Additionally, Rg1 activated the PI3K/Akt signaling pathway and promoted the functional recovery of hindlimb movement in rats. Furthermore, Rg1 significantly reduced the void area and downregulated the expression of GFAP and CSPGs.

SIGNIFICANCE

Rg1 not only enhanced the scratch wound repair in vitro through the release of astroglial neurotrophic factors, adhesion factors, and inhibitory factors, but it also improved the functional recovery in vivo following SCI.

Orthogonal test design for the optimization of superparamagnetic chitosan plasmid gelatin microspheres that promote vascularization of artificial bone

The optimal conditions for the preparation of superparamagnetic chitosan plasmid (pReceiver‐M29‐VEGF165/DH5a) gelatin microspheres (SPCPGMs) were determined. Then, the performance of the SPCPGMs during neovascularization was evaluated in vivo. The SPCPGMs were prepared through a cross‐linking curing method and then filled into the hollow scaffold of an artificial bone. Neovascularization at the bone defect position was histologically examined in samples collected 2, 4, 6, and 8 weeks after the operation. The cellular magnetofection rate of superparamagnetic chitosan nanoparticles/plasmid (pReceiver‐M29‐VEGF165/DH5a) complexes reached 1–3% under static magnetic field (SMF). Meanwhile, the optimal conditions for SPCPGM fabrication were 20% Fe₃O₄ (w/v), 4 mg of plasmid, 5.3 mg of glutaraldehyde, and 500 rpm of emulsification rotate speed. Under oscillating magnetic fields (OMFs), 4–6 μg of plasmids was released daily for 21 days. Under the combined application of SMF and OMF, evident neovascularization occurred at the bone defect position 6 weeks after the operation. This result is expected to provide a new type of angiogenesis strategy for the research of bone tissue engineering.

Role and prospects of regenerative biomaterials in the repair of spinal cord injury

Axonal junction defects and an inhibitory environment after spinal cord injury seriously hinder the regeneration of damaged tissues and neuronal functions. At the site of spinal cord injury, regenerative biomaterials can fill cavities, deliver curative drugs, and provide adsorption sites for transplanted or host cells. Some regenerative biomaterials can also inhibit apoptosis, inflammation and glial scar formation, or further promote neurogenesis, axonal growth and angiogenesis. This review summarized a variety of biomaterial scaffolds made of natural, synthetic, and combined materials applied to spinal cord injury repair. Although these biomaterial scaffolds have shown a certain therapeutic effect in spinal cord injury repair, there are still many problems to be resolved, such as product standards and material safety and effectiveness.

Application of PLGA/FGF-2 coaxial microfibers in spinal cord tissue engineering: an in vitro and in vivo investigation

Aim: Scaffolds are a promising approach for spinal cord injury (SCI) treatment. FGF-2 is involved in tissue repair but is easily degradable and presents collateral effects in systemic administration. In order to address the stability issue and avoid the systemic effects, FGF-2 was encapsulated into core–shell microfibers by coaxial electrospinning and its in vitro and in vivo potential were studied. Materials & methods: The fibers were characterized by physicochemical and biological parameters. The scaffolds were implanted in a hemisection SCI rat model. Locomotor test was performed weekly for 6 weeks. After this time, histological analyses were performed and expression of nestin and GFAP was quantified by flow cytometry. Results: Electrospinning resulted in uniform microfibers with a core–shell structure, with a sustained liberation of FGF-2 from the fibers. The fibers supported PC12 cells adhesion and proliferation. Implanted scaffolds into SCI promoted locomotor recovery at 28 days after injury and reduced GFAP expression. Conclusion: These results indicate the potential of these microfibers in SCI tissue engineering.

[Formula: see text]

Sustained-release of FGF-2 from a hybrid hydrogel of heparin-poloxamer and decellular matrix promotes the neuroprotective effects of proteins after spinal injury

Introduction

The short lifetime of protein-based therapies has largely limited their therapeutic efficacy in injured nervous post-spinal cord injury (post-SCI).

Methods

In this study, an affinity-based hydrogel delivery system provided sustained-release of proteins, thereby extending the efficacy of such therapies. The affinity-based hydrogel was constructed using a novel polymer, heparin-poloxamer (HP), as a temperature-sensitive bulk matrix and decellular spinal cord extracellular matrix (dscECM) as an affinity depot of drug. By tuning the concentration of HP in formulation, the cold ternary fibroblast growth factor-2 (FGF2)-dscECM-HP solution could rapidly gelatinize into a hydrogel at body temperature. Due to the strong affinity for FGF2, hybrid FGF2-dscECM-HP hydrogel enabled sustained-release of encapsulated FGF2 over an extended period in vitro.

Results

Compared to free FGF2, it was observed that both neuron functions and tissue morphology after SCI were clearly recovered in rats treated with FGF2-dscECM-HP hydrogel. Moreover, the expression of neurofilament protein and the density of axons were increased after treatment with hybrid FGF2-dscECM-HP. In addition, the neuroprotective effects of FGF2-dscECM-HP were related to inhibition of chronic endoplasmic reticulum stress-induced apoptosis.

Conclusion

The results revealed that a hybrid hydrogel system may be a potential carrier to deliver macromolecular proteins to the injured site and enhance the therapeutic effects of proteins.

Recombinant human collagen-based microspheres mitigate cardiac conduction slowing induced by adipose tissue-derived stromal cells

Background

Stem cell therapy to improve cardiac function after myocardial infarction is hampered by poor cell retention, while it may also increase the risk of arrhythmias by providing an arrhythmogenic substrate. We previously showed that porcine adipose tissue-derived-stromal cells (pASC) induce conduction slowing through paracrine actions, whereas rat ASC (rASC) and human ASC (hASC) induce conduction slowing by direct coupling. We postulate that biomaterial microspheres mitigate the conduction slowing influence of pASC by interacting with paracrine signaling.

Aim

To investigate the modulation of ASC-loaded recombinant human collagen-based microspheres, on the electrophysiological behavior of neonatal rat ventricular myocytes (NRVM).

Method

Unipolar extracellular electrograms, derived from microelectrode arrays (8x8 electrodes) containing NRVM, co-cultured with ASC or ASC loaded microspheres, were used to determine conduction velocity (CV) and conduction heterogeneity. Conditioned medium (Cme) of (co)cultures was used to assess paracrine mechanisms.

Results

Microspheres did not affect CV in control (NRVM) monolayers. In co-cultures of NRVM and rASC, hASC or pASC, CV was lower than in controls (14.4±1.0, 13.0±0.6 and 9.0± 1.0 vs. 19.5±0.5 cm/s respectively, p<0.001). Microspheres loaded with either rASC or hASC still induced conduction slowing compared to controls (13.5±0.4 and 12.6±0.5 cm/s respectively, p<0.001). However, pASC loaded microspheres increased CV of NRVM compared to pASC and NRMV co-cultures (16.3±1.3 cm/s, p< 0.001) and did not differ from controls (p = NS). Cme of pASC reduced CV in control monolayers of NRVM (10.3±1.1 cm/s, p<0.001), similar to Cme derived from pASC-loaded microspheres (11.1±1.7 cm/s, p = 1.0). The presence of microspheres in monolayers of NRVM abolished the CV slowing influence of Cme pASC (15.9±1.0 cm/s, p = NS vs. control).

Conclusion

The application of recombinant human collagen-based microspheres mitigates indirect paracrine conduction slowing through interference with a secondary autocrine myocardial factor.