Hydroxyapatite Nanorods Function as Safe and Effective Growth Factors Regulating Neural Differentiation and Neuron Development

Construction Form and Application of Three-Dimensional Bioprinting Ink Containing Hydroxyapatite

With the increasing prevalence of bone tissue diseases, three-dimensional (3D) bioprinting applied to bone tissue engineering for treatment has received a lot of interests in recent years. The research and popularization of 3D bioprinting in bone tissue engineering require bioinks with good performance, which is closely related to ideal material and appropriate construction form. Hydroxyapatite (HAp) is the inorganic component of natural bone and has been widely used in bone tissue engineering and other fields due to its good biological and physicochemical properties. Previous studies have prepared different bioinks containing HAp and evaluated their properties in various aspects. Most bioinks showed significant improvement in terms of rheology and biocompatibility; however, not all of them had sufficiently favorable mechanical properties and antimicrobial activity. The deficiencies in properties of bioink and 3D bioprinting technology limited the applications of bioinks containing HAp in clinical trials. This review article summarizes the construction forms of bioinks containing HAp and its modifications in previous studies, as well as the 3D bioprinting techniques adopted to print bioink containing HAp. In addition, this article summarizes the advantages and underlying mechanisms of bioink containing HAp, as well as its limitations, and suggests possible improvement to facilitate the development of bone tissue engineering bioinks containing HAp in the future.

Electromagnetic Cellularized Patch with Wirelessly Electrical Stimulation for Promoting Neuronal Differentiation and Spinal Cord Injury Repair

Although stem cell therapy holds promise for the treatment of spinal cord injury (SCI), its practical applications are limited by the low degree of neural differentiation. Electrical stimulation is one of the most effective ways to promote the differentiation of stem cells into neurons, but conventional wired electrical stimulation may cause secondary injuries, inflammation, pain, and infection. Here, based on the high conductivity of graphite and the electromagnetic induction effect, graphite nanosheets with neural stem cells (NSCs) are proposed as an electromagnetic cellularized patch to generate in situ wirelessly pulsed electric signals under a rotating magnetic field for regulating neuronal differentiation of NSCs to treat SCI. The strength and frequency of the induced voltage can be controlled by adjusting the rotation speed of the magnetic field. The generated pulsed electrical signals promote the differentiation of NSCs into functional mature neurons and increase the proportion of neurons from 12.5% to 33.7%. When implanted in the subarachnoid region of the injured spinal cord, the electromagnetic cellularized patch improves the behavioral performance of the hind limbs and the repair of spinal cord tissue in SCI mice. This work opens a new avenue for remote treatment of SCI and other nervous system diseases.

Cellular and Molecular Insights into the Divergence of Neural Stem Cells on Matrigel and Poly-l-lysine Interfaces

Poly-l-lysine (PLL) and Matrigel, both classical coating materials for culture substrates in neural stem cell (NSC) research, present distinct interfaces whose effect on NSC behavior at cellular and molecular levels remains ambiguous. Our investigation reveals intriguing disparities: although both PLL and Matrigel interfaces are hydrophilic and feature amine functional groups, Matrigel stands out with lower stiffness and higher roughness. Based on this diversity, Matrigel surpasses PLL, driving NSC adhesion, migration, and proliferation. Intriguingly, PLL promotes NSC differentiation into astrocytes, whereas Matrigel favors neural differentiation and the physiological maturation of neurons. At the molecular level, Matrigel showcases a wider upregulation of genes linked to NSC behavior. Specifically, it enhances ECM-receptor interaction, activates the YAP transcription factor, and heightens glycerophospholipid metabolism, steering NSC proliferation and neural differentiation. Conversely, PLL upregulates genes associated with glial cell differentiation and amino acid metabolism and elevates various amino acid levels, potentially linked to its support for astrocyte differentiation. These distinct transcriptional and metabolic activities jointly shape the divergent NSC behavior on these substrates. This study significantly advances our understanding of substrate regulation on NSC behavior, offering novel insights into optimizing and targeting the application of these surface coating materials in NSC research.

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.

Bioprinting of inorganic-biomaterial/neural-stem-cell constructs for multiple tissue regeneration and functional recovery

Tissue regeneration is a complicated process that relies on the coordinated effort of the nervous, vascular and immune systems. While the nervous system plays a crucial role in tissue regeneration, current tissue engineering approaches mainly focus on restoring the function of injury-related cells, neglecting the guidance provided by nerves. This has led to unsatisfactory therapeutic outcomes. Herein, we propose a new generation of engineered neural constructs from the perspective of neural induction, which offers a versatile platform for promoting multiple tissue regeneration. Specifically, neural constructs consist of inorganic biomaterials and neural stem cells (NSCs), where the inorganic biomaterials endows NSCs with enhanced biological activities including proliferation and neural differentiation. Through animal experiments, we show the effectiveness of neural constructs in repairing central nervous system injuries with function recovery. More importantly, neural constructs also stimulate osteogenesis, angiogenesis and neuromuscular junction formation, thus promoting the regeneration of bone and skeletal muscle, exhibiting its versatile therapeutic performance. These findings suggest that the inorganic-biomaterial/NSC-based neural platform represents a promising avenue for inducing the regeneration and function recovery of varying tissues and organs.

Occlusive membranes for guided regeneration of inflamed tissue defects

Guided bone regeneration aided by the application of occlusive membranes is a promising therapy for diverse inflammatory periodontal diseases. Symbiosis, homeostasis between the host microbiome and cells, occurs in the oral environment under normal, but not pathologic, conditions. Here, we develop a symbiotically integrating occlusive membrane by mimicking the tooth enamel growth or multiple nucleation biomineralization processes. We perform human saliva and in vivo canine experiments to confirm that the symbiotically integrating occlusive membrane induces a symbiotic healing environment. Moreover, we show that the membrane exhibits tractability and enzymatic stability, maintaining the healing space during the entire guided bone regeneration therapy period. We apply the symbiotically integrating occlusive membrane to treat inflammatory-challenged cases in vivo, namely, the open and closed healing of canine premolars with severe periodontitis. We find that the membrane promotes symbiosis, prevents negative inflammatory responses, and improves cellular integration. Finally, we show that guided bone regeneration therapy with the symbiotically integrating occlusive membrane achieves fast healing of gingival soft tissue and alveolar bone.

Hydroxyapatite nanoparticles induced calcium overload-initiated cancer cell-specific apoptosis through inhibition of PMCA and activation of calpain

Hydroxyapatite nanoparticles (HAPNs) have been reported to specifically induce apoptosis and sustained elevation of intracellular Ca2+ concentration ([Ca2+]i) in cancer cells. However, it remains unclear whether calcium overload, the abnormal intracellular accumulation of Ca2+, is the intrinsic cause of cell apoptosis, how HAPNs specifically evoke calcium overload in cancer cells, and which potential pathways were involved in apoptosis initiation in response to calcium overload. In this study, using various cancer and normal cells, we observed a positive correlation between the degree of increased [Ca2+]i and the specific toxicity of HAPNs. Moreover, chelating intracellular Ca2+ with BAPTA-AM inhibited HAPN-induced calcium overload and apoptosis, thus demonstrating that calcium overload was the main cause of HAPN-induced cytotoxicity in cancer cells. Notably, the dissolution of particles outside the cells did not affect cell viability or [Ca2+]i. In contrast, internalized HAPNs dissolved more readily in cancer cells than in normal cells and inhibited the activity of plasma membrane calcium-ATPase solely in cancer cells to prevent extrusion of excessive Ca2+, hence leading to calcium overload in tumor cells. Upon exposure to HAPNs, the Ca2+-sensitive cysteine protease calpain was activated and then cleaved the BH3-only protein Bid. Consequently, cytochrome c was released, and caspase-9 and -3 were activated, leading to mitochondrial apoptosis. However, these effects were alleviated by the calpain inhibitor calpeptin, confirming the involvement of calpain in HANP-induced apoptosis. Therefore, our results demonstrated that calcium overload induced by HAPNs caused cancer cell-specific apoptosis by inhibiting PMCA and activating calpain in tumor cells and thus may contribute to a more comprehensive understanding of biological effects of this nanomaterial and facilitate the development of calcium overload cancer therapy.

Bifunctional MXene-Augmented Retinal Progenitor Cell Transplantation for Retinal Degeneration

Retinal degeneration, characterized by the progressive loss of retinal neurons, is the leading cause of incurable visual impairment. Retinal progenitor cells (RPCs)-based transplantation can facilitate sight restoration, but the clinical efficacy of this process is compromised by the imprecise neurogenic differentiation of RPCs and undermining function of transplanted cells surrounded by severely oxidative retinal lesions. Here, it is shown that ultrathin niobium carbide (Nb2 C) MXene enables performance enhancement of RPCs for retinal regeneration. Nb2 C MXene with moderate photothermal effect markedly improves retinal neuronal differentiation of RPCs by activating intracellular signaling, in addition to the highly effective RPC protection by scavenging free radicals concurrently, which has been solidly evidenced by the comprehensive biomedical assessments and theoretical calculations. A dramatically increased neuronal differentiation is observed upon subretinal transplantation of MXene-assisted RPCs into the typical retinal degeneration 10 (rd10) mice, thereby contributing to the efficient restoration of retinal architecture and visual function. The dual-intrinsic function of MXene synergistically aids RPC transplantation, which represents an intriguing paradigm in vision-restoration research filed, and will broaden the multifunctionality horizon of nanomedicine.

Porous hydroxyapatite carrier enables localized and sustained delivery of honokiol for glioma treatment

The objective of this study is to develop hydroxyapatite (HAp) particles for targeted delivery of honokiol to tumor sites after glioma surgical management. Honokiol is released from the HAp-honokiol particles inside cancer cells through endocytosis and subsequent acid lysosomal dissolution. HAp is synthesized using a co-precipitation method, and egg white is added to create porous structures. The HAp is then surface-modified with stearic acid to enhance its hydrophobicity and loaded with honokiol to form HAp-honokiol particles. The synthesized particles are of appropriate size and characteristics for cancer cell uptake. Honokiol remains attached on to the HAp particles in neutral environments due to its hydrophobic nature, but undergoes rapid burst release in acidic environments such as lysosomes. The HAp-honokiol treatment shows a delayed effect on cell viability and cytotoxicity, indicating sustained drug release without compromising drug efficacy. Flow cytometry analysis demonstrates the apoptosis pathway induced by HAp-honokiol in ALTS1C1 glioma cells. In an in vivo study using a mouse glioma model, MRI results showed a 40% reduction in tumor size after HAp-honokiol treatment. These findings suggest that HAp-honokiol particles have potential as an effective drug delivery system for the treatment of glioma.

CD44 and HAP-Conjugated hADSCs as Living Materials for Targeted Tumor Therapy and Bone Regeneration

Combining targeted tumor therapy with tissue regeneration represents a promising strategy for synergistic tumor therapy. In this study, a multifunctional living material is constructed with human-derived adipose stem cells (hADSCs) and antibody-modified hydroxyapatite nanorods (nHAP) for targeted drug delivery and bone regeneration following surgery. The living material delivers the therapeutics to the tumor site efficiently based on the strength of the inherent tumor tropism of hADSCs. The bioconjugation of nHAP with hADSCs via specific antibody modification is found to be biocompatible, even when loaded with the chemotherapeutic drug doxorubicin (Dox). The endocytosis of nHAP stimulates the osteogenic differentiation of hADSCs, promoting bone tissue regeneration. Moreover, the antibody-modified nHAP-hADSC conjugate exhibits targeted tumor delivery, which is further facilitated by pH-triggered release of Dox, inducing apoptosis of tumor cells with low toxicity to healthy tissues. Therefore, the present study provides a general strategy for engineering living materials to achieve targeted tumor therapy and bone tissue regeneration after surgery, which can be extended to other disease types.

The enhanced generation of motor neurons from mESCs by MgAl layered double hydroxide nanoparticles

The committed differentiation of stem cells into neurons is a promising therapeutic strategy for neurological diseases. Predifferentiation of transplanted stem cells into neural precursors could enhance their utilization and control the direction of differentiation. Embryonic stem cells with totipotency can differentiate into specific nerve cells under appropriate external induction conditions. Layered double hydroxide (LDH) nanoparticles have been proven to regulate the pluripotency of mouse ESCs (mESCs), and LDH could be used as carrier in neural stem cells for nerve regeneration. Hence, we sought to study the effects of LDH without loaded factors on mESCs neurogenesis in this work. A series of characteristics analyses indicated the successful construction of LDH nanoparticles. LDH nanoparticles that may adhere to the cell membranes had insignificant effect on cell proliferation and apoptosis. The enhanced differentiation of mESCs into motor neurons by LDH was systematically validated by immunofluorescent staining, quantitative real-time PCR analysis and western blot analysis. In addition, transcriptome sequencing analysis and mechanism verification elucidated the significant regulatory roles of focal adhesion signaling pathway in the enhanced mESCs neurogenesis by LDH. Taken together, the functional validation of inorganic LDH nanoparticles promoting motor neurons differentiation provide a novel strategy and therapeutic prospect for the clinical transition of neural regeneration.

Nanotherapeutic and Stem Cell Therapeutic Strategies in Neurodegenerative Diseases: A Promising Therapeutic Approach

Neurodegeneration is characterized by progressive, disabling, and incurable neurological disorders with the massive loss of specific neurons. As one of the most promising potential therapeutic strategies for neurodegenerative diseases, stem cell therapy exerts beneficial effects through different mechanisms, such as direct replacement of damaged or lost cells, secretion of neurotrophic and growth factors, decreased neuroinflammation, and activation of endogenous stem cells. However, poor survival and differentiation rates of transplanted stem cells, insufficient homing ability, and difficulty tracking after transplantation limit their further clinical use. The rapid development of nanotechnology provides many promising nanomaterials for biomedical applications, which already have many applications in neurodegenerative disease treatment and seem to be able to compensate for some of the deficiencies in stem cell therapy, such as transport of stem cells/genes/drugs, regulating stem cell differentiation, and real-time tracking in stem cell therapy. Therefore, nanotherapeutic strategies combined with stem cell therapy is a promising therapeutic approach to treating neurodegenerative diseases. The present review systematically summarizes recent advances in stem cell therapeutics and nanotherapeutic strategies and highlights how they can be combined to improve therapeutic efficacy for the treatment of neurodegenerative diseases.

Osteogenic and anti-inflammatory effect of the multifunctional bionic hydrogel scaffold loaded with aspirin and nano-hydroxyapatite

Although tissue engineering offered new approaches to repair bone defects, it remains a great challenge to create a bone-friendly microenvironment and rebuild bone tissue rapidly by a scaffold with a bionic structure. In this study, a multifunctional structurally optimized hydrogel scaffold was designed by integrating polyvinyl alcohol (PVA), gelatin (Gel), and sodium alginate (SA) with aspirin (ASA) and nano-hydroxyapatite (nHAP). The fabrication procedure is through a dual-crosslinking process. The chemical constitution, crystal structure, microstructure, porosity, mechanical strength, swelling and degradation property, and drug-release behavior of the hydrogel scaffold were analyzed. Multi-hydrogen bonds, electrostatic interactions, and strong "egg-shell" structure contributed to the multi-network microstructure, bone tissue-matched properties, and desirable drug-release function of the hydrogel scaffold. The excellent performance in improving cell viability, promoting cell osteogenic differentiation, and regulating the inflammatory microenvironment of the prepared hydrogel scaffold was verified using mouse pre-osteoblasts (MC3T3-E1) cells. And the synergistic osteogenic and anti-inflammatory functions of aspirin and nano-hydroxyapatite were also verified. This study provided valuable insights into the design, fabrication, and biological potential of multifunctional bone tissue engineering materials with the premise of constructing a bone-friendly microenvironment.

Sustained delivery of gambogic acid from mesoporous rod-structure hydroxyapatite for efficient in vitro cancer therapy

Inspired by the critical role of nanocarrier in biomaterials modification, we synthesized a mesoporous rod-structure hydroxyapatite (MR-HAp) nanoparticles for boosting gambogic acid (GA) bioavailability in cells and improving the tumor therapy. As expected, the GA loading ratio of MR-HAp was up to about 96.97% and GA-loaded MR-HAp (MR-HAp/GA) demonstrates a sustained release performance. Furthermore, a substantial improvement was observed in inhibiting the cell proliferation and inducing the apoptosis of HeLa cells, as the cell viability was decreased to 89.6% and the apoptosis was increased to 49.2% when the cells treated with MR-HAp/GA at a GA concentration of 1 μg/mL for 72 h. The remarkable inhibition effect of cell proliferation and the enhanced inducing apoptosis are attributed to the increasing intracellular reactive oxygen species level and reduced mitochondrial membrane potential. This result provides a promising and facile approach for highly efficient tumor treatment.

Stemness Maintenance and Massproduction of Neural Stem Cells on Poly L-Lactic Acid Nanofibrous Membrane Based on Piezoelectriceffect

Neural stem cells (NSCs) therapy is promising for treating neurodegenerative disorders and neural injuries. However, the limited in vitro expansion, spontaneous differentiation, and decrease in stemness obstruct the acquisition of high quantities of NSCs, restricting the clinical application of cell-based therapies and tissue engineering. This article reports a facile method of promoting NSCs expansion and maintaining stemness using wireless electrical stimulation triggered by piezoelectric nanomaterials. A nanofibrous membrane of poly L-lactic acid (PLLA) is prepared by electrostatic spinning, and the favorable piezoelectric property of PLLA facilitates the freeing of electrons after transformation. These self-powered electric signals generated by PLLA significantly enhance NSCs proliferation. Further, an undifferentiated cellular state is maintained in the NSCs cultured on the surfaces of PLLA nanofibers exposed to ultrasonic vibration. In addition, the neural differentiation potencies and functions of NSCs expanded by piezoelectric-driven localized electricity are not attenuated. Moreover, cell stemness can be maintained by wireless electric stimulation. Taken together, the electronic signals mediated by PLLA nanofibers facilitate NSCs proliferation. This efficient and simple strategy can maintain the stemness of NSCs during proliferation, which is essential for their clinical application, and opens up opportunities for the mass production of NSCs for use in cell therapy.

Osteogenic Property Regulation of Stem Cells by a Hydroxyapatite 3D-Hybrid Scaffold With Cancellous Bone Structure

Cancellous bone plays an indispensable role in the skeletal system due to its various functions and high porosity. In this work, chitosan and hydroxyapatite nanowires (CS@HAP NWs) hybrid nanostructured scaffolds with suitable mechanical properties, high porosity and a fine porous structure were prepared to simulate the 3-dimensional structure of cancellous bone. The 3D-hybrid scaffolds promote cell adhesion and the migration of human adipose-derived stem cells (hADSCs) inside the scaffolds. The cavities in the scaffolds provide space for the hADSCs proliferation and differentiation. Moreover, the various contents of HAP and the induced mechanical property changes regulate the differentiation of hADSCs toward osteoblasts. Overall, cellular fate regulation of hADSCs via rationally engineered HAP-based hybrid scaffolds is a facile and effective approach for bone tissue engineering.