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

Design and preparation of hydrogel microspheres for spinal cord injury repair

A severe disorder known as spinal cord damage causes both motor and sensory impairment in the limbs, significantly reducing the patients' quality of life. After a spinal cord injury, functional recovery and therapy have emerged as critical concerns. Hydrogel microspheres have garnered a lot of interest lately because of their enormous promise in the field of spinal cord injury rehabilitation. The material classification of hydrogel microspheres (natural and synthetic macromolecule polymers) and their synthesis methods are examined in this work. This work also covers the introduction of several kinds of hydrogel microspheres and their use as carriers in the realm of treating spinal cord injuries. Lastly, the study reviews the future prospects for hydrogel microspheres and highlights their limitations and problems. This paper can offer feasible ideas for researchers to advance the application of hydrogel microspheres in the field of spinal cord injury.

Amino acid-crosslinked 4arm-PLGA Janus patch with anti-adhesive and anti-bacterial properties for hernia repair

Presently, the non-biodegradable polypropylene (PP) patches frequently used for hernia repair can cause fibrous tissue growth and adhesions. This study created a Janus Patch with anti-adhesion and antimicrobial properties to improve hernia repair while promoting tissue repair. The biologically active 4arm-PLGA-BLPD was initially synthesized through the modification of 4arm-PLGA with lysine, followed by the fabrication of a Janus patch using a layer-by-layer electrostatic spinning technique. This patch consisted of three layers: a repair layer composed of 4arm-PLGA-BLPD/PCL fiber membrane, a mechanical layer of 4arm-PLGA/PCL fiber membrane, and an antimicrobial layer of EMO-4arm-PLGA/PCL fiber membrane loaded with Emodin (EMO). The results showed that Janus patch exhibited notable tensile strength and elongation at break, enabling it to offer enhanced mechanical reinforcement for abdominal wall defects. In addition, it slowly releases lysine for repair and inhibits bacterial growth with EMO. In vivo experiments demonstrated that the patch effectively induced neovascularization, reduced collagen ac-cumulation, and stabilized the expression of relevant proteins through the up-regulation of MMP1 and MMP9. This facilitated successful repair of the abdominal wall defect model and prevented adhesions. In summary, the Janus patch offers both practical application and theoretical insight for hernia repair.

Hyaluronic acid/lactoferrin-coated polydatin/PLGA nanoparticles for active targeting of CD44 receptors in lung cancer

Traditional chemotherapeutic drugs lack optimal efficacy and invoke severe adverse effects in cancer patients. Polydatin (PD), a phytomedicine, has gradually gained attention due to its antitumor activity. However, its low solubility and poor bioavailability are still cornerstone issues. The present study aimed to fabricate and develop hyaluronic acid/lactoferrin-double coated PD/PLGA nanoparticles via a layer-by-layer self-assembly technique for active targeting of CD44 receptors in lung cancer. Different molecular weights (M.wt.) of HA (32 and 110 kDa) were exploited to study the relationship between the HA M.wt. and the NPs targeting efficacy. The optimized formulations were fully characterized. Their cytotoxicity and cellular uptake were investigated against A549 cell line by CCK-8 kit and fluorescence imaging, respectively. Finally, HA110/Lf-coated PD/PLGA NPs (F9) were subjected to a competitive inhibition study to prove internalization through CD44 overexpressed receptors. The results verified the fabrication of F9 with a particle size of 174.87 ± 3.97 nm and a zeta potential of -24.37 ± 1.19 mV as well as spherical NPs architecture. Importantly, it provoked enhanced cytotoxicity (IC50 = 0.57 ± 0.02 µg/mL) and superior cellular uptake efficacy. To conclude, the current investigation lays the foundation for the prospective therapeutic avenue of F9 for active targeting of CD44 receptors in lung cancer.

NGF-BMSC-SF/CS composites for repairing knee joint osteochondral defects in rabbits: evaluation of the repair effect and potential underlying mechanisms

BACKGROUND

With the rapid growth of the ageing population, chronic diseases such as osteoarthritis have become one of the major diseases affecting the quality of life of elderly people. The main pathological manifestation of osteoarthritis is articular cartilage damage. Alleviating and repairing damaged cartilage has always been a challenge. The application of cartilage tissue engineering methods has shown promise for articular cartilage repair. Many studies have used cartilage tissue engineering methods to repair damaged cartilage and obtained good results, but these methods still cannot be used clinically. Therefore, this study aimed to investigate the effect of incorporating nerve growth factor (NGF) into a silk fibroin (SF)/chitosan (CS) scaffold containing bone marrow-derived mesenchymal stem cells (BMSCs) on the repair of articular cartilage defects in the knees of rabbits and to explore the possible underlying mechanism involved.

MATERIALS AND METHODS

Nerve growth factor-loaded sustained-release microspheres were prepared by a double emulsion solvent evaporation method. SF/CS scaffolds were prepared by vacuum drying and chemical crosslinking. BMSCs were isolated and cultured by density gradient centrifugation and adherent culture. NGF-SF/CS-BMSC composites were prepared and implanted into articular cartilage defects in the knees of rabbits. The repair of articular cartilage was assessed by gross observation, imaging and histological staining at different time points after surgery. The repair effect was evaluated by the International Cartilage Repair Society (ICRS) score and a modified Wakitani score. In vitro experiments were also performed to observe the effect of different concentrations of NGF on the proliferation and directional differentiation of BMSCs on the SF/CS scaffold.

RESULTS

In the repair of cartilage defects in rabbit knees, NGF-SF/CS-BMSCs resulted in higher ICRS scores and lower modified Wakitani scores. The in vitro results showed that there was no significant correlation between the proliferation of BMSCs and the addition of different concentrations of NGF. Additionally, there was no significant difference in the protein and mRNA expression of COL2a1 and ACAN between the groups after the addition of different concentrations of NGF.

CONCLUSION

NGF-SF/CS-BMSCs improved the repair of articular cartilage defects in the knees of rabbits. This repair effect may be related to the early promotion of subchondral bone repair.

Engineering Innervated Musculoskeletal Tissues for Regenerative Orthopedics and Disease Modeling

Musculoskeletal (MSK) disorders significantly burden patients and society, resulting in high healthcare costs and productivity loss. These disorders are the leading cause of physical disability, and their prevalence is expected to increase as sedentary lifestyles become common and the global population of the elderly increases. Proper innervation is critical to maintaining MSK function, and nerve damage or dysfunction underlies various MSK disorders, underscoring the potential of restoring nerve function in MSK disorder treatment. However, most MSK tissue engineering strategies have overlooked the significance of innervation. This review first expounds upon innervation in the MSK system and its importance in maintaining MSK homeostasis and functions. This will be followed by strategies for engineering MSK tissues that induce post-implantation in situ innervation or are pre-innervated. Subsequently, research progress in modeling MSK disorders using innervated MSK organoids and organs-on-chips (OoCs) is analyzed. Finally, the future development of engineering innervated MSK tissues to treat MSK disorders and recapitulate disease mechanisms is discussed. This review provides valuable insights into the underlying principles, engineering methods, and applications of innervated MSK tissues, paving the way for the development of targeted, efficacious therapies for various MSK conditions.

Optimizing Process Parameters for Controlled Drug Delivery: A Quality by Design (QbD) Approach in Naltrexone Microspheres

The formulation of microspheres involves a complex manufacturing process with multiple steps. Identifying the appropriate process parameters to achieve the desired quality attributes poses a significant challenge. This study aims to optimize the critical process parameters (CPPs) involved in the preparation of naltrexone microspheres using a Quality by Design (QbD) methodology. Additionally, the research aims to assess the drug release profiles of these microspheres under both in vivo and in vitro conditions. Critical process parameters (CPPs) and critical quality attributes (CQAs) were identified, and a Box-Behnken design was utilized to delineate the design space, ensuring alignment with the desired Quality Target Product Profile (QTPP). The investigated CPPs comprised polymer concentration, aqueous phase ratio to organic phase ratio, and quench volume. The microspheres were fabricated using the oil-in-water emulsion solvent extraction technique. Analysis revealed that increased polymer concentration was correlated with decreased particle size, reduced quench volume resulted in decreased burst release, and a heightened aqueous phase ratio to organic phase ratio improved drug entrapment. Upon analyzing the results, an optimal formulation was determined. In conclusion, the study conducted in vivo drug release testing on both the commercially available innovator product and the optimized test product utilizing an animal model. The integration of in vitro dissolution data with in vivo assessments presents a holistic understanding of drug release dynamics. The QbD approach-based optimization of CPPs furnishes informed guidance for the development of generic pharmaceutical formulations.

Impact of transcranial electrical stimulation on serum neurotrophic factors and language function in patients with speech disorders

BACKGROUND

Speech disorders have a substantial impact on communication abilities and quality of life. Traditional treatments such as speech and psychological therapies frequently demonstrate limited effectiveness and patient compliance. Transcranial electrical stimulation (TES) has emerged as a promising non-invasive treatment to improve neurological functions. However, its effectiveness in enhancing language functions and serum neurofactor levels in individuals with speech disorders requires further investigation.

AIM

To investigate the impact of TES in conjunction with standard therapies on serum neurotrophic factor levels and language function in patients with speech disorders.

METHODS

In a controlled study spanning from March 2019 to November 2021, 81 patients with speech disorders were divided into a control group (n = 40) receiving standard speech stimulation and psychological intervention, and an observation group (n = 41) receiving additional TES. The study assessed serum levels of ciliary neurotrophic factor (CNTF), glial cell-derived neurotrophic factor (GDNF), brain-derived neurotrophic factor (BDNF), and nerve growth factor (NGF), as well as evaluations of motor function, language function, and development quotient scores.

RESULTS

After 3 wk of intervention, the observation group exhibited significantly higher serum levels of CNTF, GDNF, BDNF, and NGF compared to the control group. Moreover, improvements were noted in motor function, cognitive function, language skills, physical abilities, and overall development quotient scores. It is worth mentioning that the observation group also displayed superior performance in language-specific tasks such as writing, reading comprehension, retelling, and fluency.

CONCLUSION

This retrospective study concluded that TES combined with traditional speech and psychotherapy can effectively increase the levels of neurokines in the blood and enhance language function in patients with speech disorders. These results provide a promising avenue for integrating TES into standard treatment methods for speech disorders.

Gastrointestinal delivery of codfish Skin-Derived collagen Hydrolysates: Deep eutectic solvent extraction and bioactivity analysis

The fishing industry produces substantial by-products, such as heads, skins, bones, and scales, rich in collagen-a prevalent protein in these materials. However, further application of deep eutectic solvent-based extraction remains unexplored. In this study, we extracted collagen with urea: propanoic acid mixture (U:PA; 1:2) with a 2.2 % yield, followed by enzymatic hydrolysis with alcalase for 120 min. The resulting bioactive peptides demonstrated notable antioxidant activity (961 µmol TE) and antihypertensive properties (39.3 % ACE inhibition). Subsequently, we encapsulated 39.3 % of these hydrolysates in chitosan-TPP capsules, which released about 58 % of their content, primarily in the intestine, as mimicked in the in vitro model of the gastrointestinal tract. Although the digestion process did not significantly alter the size of the non-encapsulated collagen peptides, it did influence their health benefits. The promising results suggest that further research could optimize the use of collagen from fish by-products, potentially offering a sustainable source for health products.

Growth factors: Bioactive macromolecular drugs for peripheral nerve injury treatment - Molecular mechanisms and delivery platforms

Bioactive macromolecular drugs known as Growth Factors (GFs), approved by the Food and Drug Administration (FDA), have found successful application in clinical practice. They hold significant promise for addressing peripheral nerve injuries (PNIs). Peripheral nerve guidance conduits (NGCs) loaded with GFs, in the context of tissue engineering, can ensure sustained and efficient release of these bioactive compounds. This, in turn, maintains a stable, long-term, and effective GF concentration essential for treating damaged peripheral nerves. Peripheral nerve regeneration is a complex process that entails the secretion of various GFs. Following PNI, GFs play a pivotal role in promoting nerve cell growth and survival, axon and myelin sheath regeneration, cell differentiation, and angiogenesis. They also regulate the regenerative microenvironment, stimulate plasticity changes post-nerve injury, and, consequently, expedite nerve structure and function repair. Both exogenous and endogenous GFs, including NGF, BDNF, NT-3, GDNF, IGF-1, bFGF, and VEGF, have been successfully loaded onto NGCs using techniques like physical adsorption, blend doping, chemical covalent binding, and engineered transfection. These approaches have effectively promoted the repair of peripheral nerves. Numerous studies have demonstrated similar tissue functional therapeutic outcomes compared to autologous nerve transplantation. This evidence underscores the substantial clinical application potential of GFs in the domain of peripheral nerve repair. In this article, we provide an overview of GFs in the context of peripheral nerve regeneration and drug delivery systems utilizing NGCs. Looking ahead, commercial materials for peripheral nerve repair hold the potential to facilitate the effective regeneration of damaged peripheral nerves and maintain the functionality of distant target organs through the sustained release of GFs.

The microspheres/hydrogels scaffolds based on the proteins, nucleic acids, or polysaccharides composite as carriers for tissue repair: A review

There are many studies on specific macromolecules and their contributions to tissue repair. Macromolecules have supporting and protective effects in organisms and can help regrow, reshape, and promote self-repair and regeneration of damaged tissues. Macromolecules, such as proteins, nucleic acids, and polysaccharides, can be constructed into hydrogels for the preparation of slow-release drug agents, carriers for cell culture, and platforms for gene delivery. Hydrogels and microspheres are fabricated by chemical crosslinking or mixed co-deposition often used as scaffolds, drug carriers, or cell culture matrix, provide proper mechanical support and nutrient delivery, a well-conditioned environment that to promote the regeneration and repair of damaged tissues. This review provides a comprehensive overview of recent developments in the construction of macromolecules into hydrogels and microspheres based on the proteins, nucleic acids, polysaccharides and other polymer and their application in tissue repair. We then discuss the latest research trends regarding the advantages and disadvantages of these composites in repair tissue. Further, we examine the applications of microspheres/hydrogels in different tissue repairs, such as skin tissue, cartilage, tumor tissue, synovial, nerve tissue, and cardiac repair. The review closes by highlighting the challenges and prospects of microspheres/hydrogels composites.

Advances in Large Gap Peripheral Nerve Injury Repair and Regeneration with Bridging Nerve Guidance Conduits

Peripheral nerve injury is a common complication of accidents and diseases. The traditional autologous nerve graft approach remains the gold standard for the treatment of nerve injuries. While sources of autologous nerve grafts are very limited and difficult to obtain. Nerve guidance conduits are widely used in the treatment of peripheral nerve injuries as an alternative to nerve autografts and allografts. However, the development of nerve conduits does not meet the needs of large gap peripheral nerve injury. Functional nerve conduits can provide a good microenvironment for axon elongation and myelin regeneration. Herein, the manufacturing methods and different design types of functional bridging nerve conduits for nerve conduits combined with electrical or magnetic stimulation and loaded with Schwann cells, etc., are summarized. It summarizes the literature and finds that the technical solutions of functional nerve conduits with electrical stimulation, magnetic stimulation and nerve conduits combined with Schwann cells can be used as effective strategies for bridging large gap nerve injury and provide an effective way for the study of large gap nerve injury repair. In addition, functional nerve conduits provide a new way to construct delivery systems for drugs and growth factors in vivo.

Cyclosporine A-loaded chitosan extra-fine particles for deep pulmonary drug delivery: In vitro and in vivo evaluation

In this study, the extra-fine dry powder inhalers (DPIs) with chitosan (CS) as carrier were successfully prepared by ionic gel method combined with spray drying technique for deep pulmonary drug delivery of Cyclosporine A (CsA), using sodium hyaluronate (SHA) and sodium polyglutamate (SPGA) as polyanions. The CsA-loaded DPIs of CS-SHA-CsA and CS-SPGA-CsA were spherical particles with wrinkles on the surface, which were more conducive to improving the aerosol properties. The aerodynamic evaluation of CS-SHA-CsA and CS-SPGA-CsA showed that the fine particle fraction (FPF) reached up to 79.22 ± 2.12% and 81.55 ± 0.43%, while the emitted fraction (EF) reached 77.15 ± 1.46% and 78.29 ± 2.10%. In addition, the mass median aerodynamic diameter (MMAD) was calculated as 1.58 ± 0.04 μm and 1.94 ± 0.02 μm for CS-SHA-CsA and CS-SPGA-CsA, indicating that they were all extra-fine particles (d < 2 μm). These in vitro aerodynamic results showed that CS-SHA-CsA and CS-SPGA-CsA could reach the smaller airways, further improving therapeutic efficiency. The cell viability on A549 cell line results showed that CS-SHA-CsA and CS-SPGA-CsA were safe to deliver CsA to lungs. The in vivo pharmacokinetics consequence proved that inhalation administration of CS-SHA-CsA and CS-SPGA-CsA could significantly improve the bioavailability of CsA in vivo compared with oral administration of Neoral®, effectively reducing the risk of a series of adverse effects caused by systemic overexposure. In addition, the safety and compatibility of DPIs using SHA, SPGA, and CS as carriers for pulmonary drug delivery was verified by in vivo repeated dose inhalation toxicity. From these findings, the extra-fine DPIs with CS as carrier could be a viable delivery option for the deep pulmonary drug delivery of CsA relative to orally administered drug.

Ropivacaine microsphere-loaded electroconductive nerve dressings for long-acting analgesia and functional recovery following diabetic peripheral nerve injury

In recent years, electroconductive hydrogels (ECHs) have shown great potential in promoting nerve regeneration and motor function recovery following diabetic peripheral nerve injury (PNI), attributed to their similar electrical and mechanical characteristics to innate nervous tissue. It is well-established that PNI causes motor deficits and pain, especially in diabetics. Current evidence suggests that ropivacaine (ROP) encapsulated in poly lactic-co-glycolic acid (PLGA) microspheres (MSs) yield a sustained analgesic effect. In this study, an ECH electroconductive network loaded with MS/ROP (ECH-MS/ROP) was designed as a promising therapeutic approach for diabetic PNI to exert lasting analgesia and functional recovery. This dual delivery system allowed ROP's slow and sequential release, achieving sustained analgesia as demonstrated by our in vivo experiments. Meanwhile, this system was designed like a lamellar dressing, with desirable adhesive and self-curling properties, convenient for treating injured nerve tissues via automatically wrapping tube-like structures, facilitating the process of implantation. Our in vitro assays verified that ECH-MS/ROP was able to enhance the adhesion and motility of Schwann cells. Besides, both in vitro and in vivo studies substantiated that ECH-MS/ROP stimulated myelinated axon regeneration through the MEK/ERK signaling pathway, thereby improving muscular denervation atrophy and facilitating functional recovery. Therefore, this study suggests that the ECH-MS/ROP dressing provides a promising strategy for treating diabetic PNI to facilitate nerve regeneration, functional recovery and pain relief.

Chitosan-poly(lactide-co-glycolide)/poloxamer mixed micelles as a mucoadhesive thermo-responsive moxifloxacin eye drop to improve treatment efficacy in bacterial keratitis

A mucoadhesive self-assembling polymeric system was developed to carry moxifloxacin (M) for treating bacterial keratitis (BK). Chitosan-PLGA (C) conjugate was synthesized, and poloxamers (F68/127) were mixed in different proportions (1: 5/10) to prepare moxifloxacin (M)-encapsulated mixed micelles (M@CF68/127(5/10)Ms), including M@CF68(5)Ms, M@CF68(10)Ms, M@CF127(5)Ms, and M@CF127(10)Ms. The corneal penetration and mucoadhesiveness were determined biochemically, in vitro using human corneal epithelial (HCE) cells in monolayers and spheroids, ex vivo using goat cornea, and in vivo via live-animal imaging. The antibacterial efficacy was studied on planktonic biofilms of P. aeruginosa and S. aureus (in vitro) and Bk-induced mice (in vivo). Both M@CF68(10)Ms and M@CF127(10)Ms demonstrated high cellular uptake, corneal retention, muco-adhesiveness, and antibacterial effect, with M@CF127(10)Ms exhibiting superior therapeutic effects in P. aeruginosa and S. aureus-infected BK mouse model by reducing the corneal bacterial load and preventing corneal damage. Therefore, the newly developed nanomedicine is promising for clinical translation in treating BK.

Preparation, characterization and protective effect of chitosan - Tripolyphosphate encapsulated dihydromyricetin nanoparticles on acute kidney injury caused by cisplatin

Dihydromyricetin (DMY) is a natural dihydroflavonol compound known for its diverse pharmacological benefits. However, its limited stability and bioavailability posed significant challenges for further applications. To address these issues, in this study, an ion crosslinking method was utilized to prepare chitosan nanoparticles that were loaded with DMY. The synthesized chitosan nanoparticles (CS-DMY-NPs) were spherical in shape with particle size and ζ potential of 198.7 nm and 45.05 mV, respectively. Furthermore, in vitro release experiments demonstrated that CS-DMY-NPs had sustained release and protective effects in simulated gastric and intestinal fluids. CS-DMY-NPs exhibited better antioxidant activity by ABTS and DPPH radical scavenging activity than free DMY. In vivo study showed that CS-DMY-NPs alleviated cisplatin-induced kidney damage by inhibiting oxidative stress and proinflammatory cytokines, and had better activity compared to DMY (free). Immunofluorescence data showed that CS-DMY-NPs activated the Nrf2 signaling pathways in a dose-dependent manner to combat cisplatin-induced kidney damage. Our results demonstrate that CS-TPP has good compatibility with DMY, and CS-DMY-NPs exhibited better protective effects against cisplatin-induced acute kidney injury (AKI) than free DMY.

Fabrication of biodegradable hollow microsphere composites made of polybutylene adipate co-terephthalate/polyvinylpyrrolidone for drug delivery and sustained release

Sustained drug release has attracted increasing interest in targeted drug therapy. However, existing methods of drug therapy suffer drug action time, large fluctuations in the effective concentration of the drug, and the risk of side effects. Here, a biodegradable composite of polybutylene adipate co-terephthalate/polyvinylpyrrolidone (PBAT/PVP) consisting of electrospun hollow microspheres as sustained-released drug carriers is presented. The as-prepared PBAT/PVP composites show faster degradation rate and drug (Erlotinib) release than that of PBAT. Furthermore, PBAT/PVP composites loaded with Erlotinib provide sustained release effect, thus achieving a better efficacy than that after the direct injection of erlotinib due to the fact that the composites allow a high drug concentration in the tumor for a longer period. Hence, this work provides a potential effective solution for clinical drug therapy and tissue engineering using drug microspheres with a sustained release.

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.

Current Status of Polysaccharides-Based Drug Delivery Systems for Nervous Tissue Injuries Repair

Neurological disorders affecting both CNS and PNS still represent one of the most critical and challenging pathologies, therefore many researchers have been focusing on this field in recent decades. Spinal cord injury (SCI) and peripheral nerve injury (PNI) are severely disabling diseases leading to dramatic and, in most cases, irreversible sensory, motor, and autonomic impairments. The challenging pathophysiologic consequences involved in SCI and PNI are demanding the development of more effective therapeutic strategies since, as yet, a therapeutic strategy that can effectively lead to a complete recovery from such pathologies is not available. Drug delivery systems (DDSs) based on polysaccharides have been receiving more and more attention for a wide range of applications, due to their outstanding physical-chemical properties. This review aims at providing an overview of the most studied polysaccharides used for the development of DDSs intended for the repair and regeneration of a damaged nervous system, with particular attention to spinal cord and peripheral nerve injury treatments. In particular, DDSs based on chitosan and their association with alginate, dextran, agarose, cellulose, and gellan were thoroughly revised.

Progress in the application of sustained-release drug microspheres in tissue engineering

Sustained-release drug-loaded microspheres provide a long-acting sustained release, with targeted and other effects. There are many types of sustained-release drug microspheres and various preparation methods, and they are easy to operate. For these reasons, they have attracted widespread interest and are widely used in tissue engineering and other fields. In this paper, we provide a systematic review of the application of sustained-release drug microspheres in tissue engineering. First, we introduce this new type of drug delivery system (sustained-release drug carriers), describe the types of sustained-release drug microspheres, and summarize the characteristics of different microspheres. Second, we summarize the preparation methods of sustained-release drug microspheres and summarize the materials required for preparing microspheres. Third, various applications of sustained-release drug microspheres in tissue engineering are summarized. Finally, we summarize the shortcomings and discuss future prospects in the development of sustained-release drug microspheres. The purpose of this paper was to provide a further systematic understanding of the application of sustained-release drug microspheres in tissue engineering for the personnel engaged in related fields and to provide inspiration and new ideas for studies in related fields.

Fabrication of a controlled-release delivery system for relieving sciatica nerve pain using an ultrasound-responsive microcapsule

Lidocaine, a potent local anesthetic, is clinically used in nerve block and pain management. However, due to its short half-life, repeated administration is required. For this reason, here we designed and prepared a lidocaine-encapsulated polylactic acid-glycolic acid (Lidocaine@PLGA) microcapsule with ultrasound responsiveness to relieve the sciatica nerve pain. With a premixed membrane emulsification strategy, the fabricated lidocaine-embedded microcapsules possessed uniform particle size, good stability, injectability, and long-term sustained release both in vitro and in vivo. More importantly, Lidocaine@PLGA microcapsules had the function of ultrasonic responsive release, which made the drug release controllable with the effect of on-off administration. Our research showed that using ultrasound as a trigger switch could promote the rapid release of lidocaine from the microcapsules, achieving the dual effects of long-term sustained release and short-term ultrasound-triggered rapid release, which can enable the application of ultrasound-responsive Lidocaine@PLGA microcapsules to nerve root block and postoperative pain relief.

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.

Ti3C2Tx MXene-Coated Electrospun PCL Conduits for Enhancing Neurite Regeneration and Angiogenesis

An electrical signal is the key basis of normal physiological function of the nerve, and the stimulation of the electric signal also plays a very special role in the repair process of nerve injury. Electric stimulation is shown to be effective in promoting axonal regeneration and myelination, thereby promoting nerve injury repair. At present, it is considered that electric conduction recovery is a key aspect of regeneration and repair of long nerve defects. Conductive neural scaffolds have attracted more and more attention due to their similar electrical properties and good biocompatibility with normal nerves. Herein, PCL and MXene-PCL nerve guidance conduits (NGCs) were prepared; their effect on nerve regeneration was evaluated in vitro and in vivo. The results show that the NGCs have good biocompatibility in vitro. Furthermore, a sciatic nerve defect model (15 mm) of SD rats was made, and then the fabricated NGCs were implanted. MXene-PCL NGCs show similar results with the autograft in the sciatic function index, electrophysiological examination, angiogenesis, and morphological nerve regeneration. It is possible that the conductive MXene-PCL NGC could transmit physiological neural electric signals, induce angiogenesis, and stimulate nerve regeneration. This paper presents a novel design of MXene-PCL NGC that could transmit self-originated electric stimulation. In the future, it can be combined with other features to promote nerve regeneration.

The balanced microenvironment regulated by the degradants of appropriate PLGA scaffolds and chitosan conduit promotes peripheral nerve regeneration

Tissue-engineered nerve grafts (TENGs) are the most promising way for repairing long-distance peripheral nerve defects. Chitosan and poly (lactic-co-glycolic acid) (PLGA) scaffolds are considered as the promising materials in the pharmaceutical and biomedical fields especially in the field of tissue engineering. To further clarify the effects of a chitosan conduit inserted with various quantity of poly (lactic-co-glycolic acid) (PLGA) scaffolds, and their degrades on the peripheral nerve regeneration, the chitosan nerve conduit inserted with different amounts of PLGA scaffolds were used to repair rat sciatic nerve defects. The peripheral nerve regeneration at the different time points was dynamically and comprehensively evaluated. Moreover, the influence of different amounts of PLGA scaffolds on the regeneration microenvironment including inflammatory response and cell state were also revealed. The modest abundance of PLGA is more instrumental to the success of nerve regeneration, which is demonstrated in terms of the structure of the regenerated nerve, reinnervation of the target muscle, nerve impulse conduction, and overall function. The PLGA scaffolds aid the migration and maturation of Schwann cells. Furthermore, the PLGA and chitosan degradation products in a correct ratio neutralize, reducing the inflammatory response and enhancing the regeneration microenvironment. The balanced microenvironment regulated by the degradants of appropriate PLGA scaffolds and chitosan conduit promotes peripheral nerve regeneration. The findings represent a further step towards programming TENGs construction, applying polyester materials in regenerative medicine, and understanding the neural regeneration microenvironment.

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Guide scaffolds are necessary for construction of TENGs to benefeat Schwann cell migration and maturation.

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A large number of acid degradation products of PLGA scaffolds adversely affect cell proliferation, migration and apoptosis.

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Appropriate amount of PLGA scaffolds balance positive cell guidance and negative degradation inflammation.

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Dosage of PLGA and its combination with complementary biomaterials are key factors that affect regeneration effects.

Fabrication of Injectable Chitosan-Chondroitin Sulfate Hydrogel Embedding Kartogenin-Loaded Microspheres as an Ultrasound-Triggered Drug Delivery System for Cartilage Tissue Engineering

Ultrasound-responsive microspheres (MPs) derived from natural polysaccharides and injectable hydrogels have been widely investigated as a biocompatible, biodegradable, and controllable drug delivery system and cell scaffolds for tissue engineering. In this study, kartogenin (KGN) loaded poly (lactide-co-glycolic acid) (PLGA) MPs (MPs@KGN) were fabricated by premix membrane emulsification (PME) method which were sonicated by an ultrasound transducer. Furthermore, carboxymethyl chitosan-oxidized chondroitin sulfate (CMC-OCS) hydrogel were prepared via the Schiff’ base reaction-embedded MPs to produce a CMC-OCS/MPs scaffold. In the current work, morphology, mechanical property, porosity determination, swelling property, in vitro degradation, KGN release from scaffolds, cytotoxicity, and cell bioactivity were investigated. The results showed that MPs presented an obvious collapse after ultrasound treatment. The embedded PLGA MPs could enhance the compressive elastic modulus of soft CMC-OCS hydrogel. The cumulative release KGN from MPs exhibited a slow rate which would display an appropriate collapse after ultrasound, allowing KGN to maintain a continuous concentration for at least 28 days. Moreover, the composite CMC-OCS@MPs scaffolds exhibited faster gelation, lower swelling ratio, and lower in vitro degradation. CCK-8 and LIVE/DEAD staining showed these scaffolds did not influence rabbit bone marrow mesenchymal stem cells (rBMMSCs) proliferation. Then these scaffolds were cultured with rBMMSCs for 2 weeks, and the immunofluorescent staining of collagen II (COL-2) showed that CMC-OCS hydrogel embedded with MPs@KGN (CMC-OCS@MPs@KGN) with ultrasound had the ability to increase the COL-2 synthesis. Overall, due to the improved mechanical property and the ability of sustained KGN release, this injectable hydrogel with ultrasound-responsive property is a promising system for cartilage tissue engineering.

Nanocellulose for peripheral nerve regeneration in rabbits using citric acid as crosslinker with chitosan and freeze/thawed PVA

This work investigates peripheral nerve regeneration using membranes consisting of pure chitosan (CHI), which was further blended with nanofibrillated cellulose, with citric acid as crosslinker, with posterior addition of polyvinyl alcohol, with subsequent freeze thawing. Nanocellulose improves the mechanical and thermal resistance, as well as flexibility of the film, which is ideal for the surgical procedure. The hydrogel presented a slow rate of swelling, which is adequate for cell and drug delivery. A series ofin vitrotests revealed to be non-toxic for neuronal Schwann cell from the peripheral nervous system of Rattus norvegicus, while there was a slight increase in toxicity if crosslink is performed-freeze-thaw. Thein vivoresults, using rabbits with a 5 mm gap nerve defect, revealed that even though pure CHI was able to regenerate the nerve, it did not present functional recovery with only the deep pain attribute being regenerated. When autologous implant was used jointly with the biomaterial membrane, as a covering agent, it revealed a functional recovery within 15 d when cellulose and the hydrogel were introduced, which was attributed to the film charge interaction that may help influence the neuronal axons growth into correct locations. Thus, indicating that this system presents ideal regeneration as nerve conduits.