Nacre-mimetic hydroxyapatite/chitosan/gelatin layered scaffolds modifying substance P for subchondral bone regeneration

Design and synthesis of bioinspired nanomaterials for biomedical application

Natural materials and bioprocesses provide abundant inspirations for the design and synthesis of high-performance nanomaterials. In the past several decades, bioinspired nanomaterials have shown great potential in the application of biomedical fields, such as tissue engineering, drug delivery, and cancer therapy, and so on. In this review, three types of bioinspired strategies for biomedical nanomaterials, that is, inspired by the natural structures, biomolecules, and bioprocesses, are mainly introduced. We summarize and discuss the design concepts and synthesis approaches of various bioinspired nanomaterials along with their specific roles in biomedical applications. Additionally, we discuss the challenges for the development of bioinspired biomedical nanomaterials, such as mechanical failure in wet environment, limitation in scale-up fabrication, and lack of deep understanding of biological properties. It is expected that the development and clinical translation of bioinspired biomedical nanomaterials will be further promoted under the cooperation of interdisciplinary subjects in future. This article is categorized under: Implantable Materials and Surgical Technologies > Nanomaterials and Implants Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Recent advances in biopolymer-based hydrogels and their potential biomedical applications

Hydrogels are three-dimensional networks of polymer chains containing large amounts of water in their structure. Hydrogels have received significant attention in biomedical applications owing to their attractive physicochemical properties, including flexibility, softness, biodegradability, and biocompatibility. Different natural and synthetic polymers have been intensely explored in developing hydrogels for the desired applications. Biopolymers-based hydrogels have advantages over synthetic polymers regarding improved cellular activity and weak immune response. These properties can be further improved by grafting with other polymers or adding nanomaterials, and they structurally mimic the living tissue environments, which opens their broad applicability. The hydrogels can be physically or chemically cross-linked depending on the structure. The use of different biopolymers-based hydrogels in biomedical applications has been reviewed and discussed earlier. However, no report is still available to comprehensively introduce the synthesis, advantages, disadvantages, and biomedical applications of biopolymers-based hydrogels from the material point of view. Herein, we systematically overview different synthesis methods of hydrogels and provide a holistic approach to biopolymers-based hydrogels for biomedical applications, especially in bone regeneration, wound healing, drug delivery, bioimaging, and therapy. The current challenges and prospects of biopolymers-based hydrogels are highlighted rationally, giving an insight into the progress of these hydrogels and their practical applications.

Neuro-bone tissue engineering: emerging mechanisms, potential strategies, and current challenges

The skeleton is a highly innervated organ in which nerve fibers interact with various skeletal cells. Peripheral nerve endings release neurogenic factors and sense skeletal signals, which mediate bone metabolism and skeletal pain. In recent years, bone tissue engineering has increasingly focused on the effects of the nervous system on bone regeneration. Simultaneous regeneration of bone and nerves through the use of materials or by the enhancement of endogenous neurogenic repair signals has been proven to promote functional bone regeneration. Additionally, emerging information on the mechanisms of skeletal interoception and the central nervous system regulation of bone homeostasis provide an opportunity for advancing biomaterials. However, comprehensive reviews of this topic are lacking. Therefore, this review provides an overview of the relationship between nerves and bone regeneration, focusing on tissue engineering applications. We discuss novel regulatory mechanisms and explore innovative approaches based on nerve-bone interactions for bone regeneration. Finally, the challenges and future prospects of this field are briefly discussed.

Photothermal Carbon Dots Chelated Hydroxyapatite Filler: High Photothermal Conversion Efficiency and Enhancing Adhesion of Hydrogel

The synthesis of photothermal carbon/hydroxyapatite composites poses challenges due to the binding modes and relatively low photothermal conversion efficiency. To address these challenges, the calcium ions chelated by photothermal carbon dots (PTC-CDs) served as the calcium source for the synthesis of photothermal carbon dots chelated hydroxyapatite (PTC-HA) filler via the coprecipitation method. The coordination constant K and chelation sites of PTC-HA were 7.20 × 102 and 1.61, respectively. Compared to PTC-CDs, the coordination constant K and chelation sites of PTC-HA decreased by 88 and 35% due to chelating to hydroxyapatite, respectively. PTC-HA possesses fluorescence and photothermal performance with a 62.4% photothermal conversion efficiency. The incorporation of PTC-HA filler significantly enhances as high as 76% the adhesion performance of the adhesive hydrogel. PTC-HA with high photothermal conversion efficiency and enhancing adhesion performance holds promise for applications in high photothermal conversion efficiency, offering tissue adhesive properties and fluorescence capabilities to the hydrogel.

The ratio of alpha-calcitonin gene-related peptide to substance P is associated with the transition of bone metabolic states during aging and healing

Alpha-calcitonin gene-related peptide (αCGRP) and substance P (SP) are functionally correlated sensory neuropeptides deeply involved in bone homeostasis. However, they are usually studied individually rather than as an organic whole. To figure out whether they are interdependent, we firstly recorded the real-time αCGRP and SP levels in aging bone and healing fracture, which revealed a moderate to high level of αCGRP coupled with a low αCGRP/SP ratio in an anabolic state, and a high level of αCGRP coupled with a high αCGRP/SP ratio in a catabolic state, suggesting the importance of αCGRP/SP ratio in driving aging and healing scenarios. During facture healing, increase in αCGRP/SP ratio by adding αCGRP led to better callus formation and faster callus remodeling, while simultaneous addition of αCGRP and SP resulted in hypertrophic callus and delayed remodeling. The characteristics in inflammation and osteoclast activation further confirmed the importance of high αCGRP/SP ratio during catabolic bone remodeling. In vitro assays using different mixtures of αCGRP-SP proved that the osteogenic potential of the mixtures depended mostly on αCGRP, while their effects on osteoclasts and neutrophils relied on both peptides. These results demonstrated that αCGRP and SP were spatiotemporally interdependent. The αCGRP/SP ratio may be more important than the dose of a single neuropeptide in managing age-related and trauma-related bone diseases.

Current application and modification strategy of marine polysaccharides in tissue regeneration: A review

Marine polysaccharides (MPs) are exceptional bioactive materials that possess unique biochemical mechanisms and pharmacological stability, making them ideal for various tissue engineering applications. Certain MPs, including agarose, alginate, carrageenan, chitosan, and glucan have been successfully employed as biological scaffolds in animal studies. As carriers of signaling molecules, scaffolds can enhance the adhesion, growth, and differentiation of somatic cells, thereby significantly improving the tissue regeneration process. However, the biological benefits of pure MPs composite scaffold are limited. Therefore, physical, chemical, enzyme modification and other methods are employed to expand its efficacy. Chemically, the structural properties of MPs scaffolds can be altered through modifications to functional groups or molecular weight reduction, thereby enhancing their biological activities. Physically, MPs hydrogels and sponges emulate the natural extracellular matrix, creating a more conducive environment for tissue repair. The porosity and high permeability of MPs membranes and nanomaterials expedite wound healing. This review explores the distinctive properties and applications of select MPs in tissue regeneration, highlighting their structural versatility and biological applicability. Additionally, we provide a brief overview of common modification strategies employed for MP scaffolds. In conclusion, MPs have significant potential and are expected to be a novel regenerative material for tissue engineering.

Substance P promote macrophage M2 polarization to attenuate secondary lymphedema by regulating NF-kB/NLRP3 signaling pathway

Secondary lymphedema often occurs after filariasis, trauma, lymph node dissection and radiation therapy, which is manifested by infiltration of inflammatory cells and fibrosis formation in pathologically. Substance P is a widely used neuropeptide in the field of tissue repair, while the regenerative potential of the substance P has not been proven in the secondary lymphedema. In this study, animal model of secondary lymphedema was constructed by excising the skin and subcutaneous lymphatic network in the tail of mice, and the degree of swelling in the tail of mice was evaluated after 6 weeks under the treatment with substance P. Immunofluorescence staining was also performed to assess immune cell infiltration, subcutaneous fibrosis and lymphangiogenesis. The results revealed that substance P significantly alleviated post-surgical lymphedema in mice. Furthermore, we found that substance P promoted macrophages M2 polarization, a process associated with downregulation of the NF-kB/NLRP3 pathway. After application of disodium clodronate (macrophage scavenger, CLO), the positive effect of substance P in lymphedema is significantly inhibited. In vitro experiments, we further demonstrated the polarizing effect of substance P on bone marrow-derived macrophages (BMDMs), while substance P inhibited the activation of the NF-kB/NLRP3 pathway in BMDMs after the treatment of lipopolysaccharide (LPS). In addition, polarized macrophages were demonstrated to promote the proliferation, tube-forming and migratory functions of human lymphatic endothelial cells (hLEC). In conclusion, our study provides preliminary evidence that substance P alleviates secondary lymphedema by promoting macrophage M2 polarization, and this therapeutic effect may be associated with downregulation of the NF-kB/NLRP3 pathway.

Recent progressions in biomedical and pharmaceutical applications of chitosan nanoparticles: A comprehensive review

Nowadays, the most common approaches in the prognosis, diagnosis, and treatment of diseases are along with undeniable limitations. Thus, the ever-increasing need for using biocompatible natural materials and novel practical modalities is required. Applying biomaterials, such as chitosan nanoparticles (CS NPs: FDA-approved long-chain polymer of N-acetyl-glucosamine and D-glucosamine for some pharmaceutical applications), can serve as an appropriate alternative to overcome these limitations. Recently, the biomedical applications of CS NPs have extensively been investigated. These NPs and their derivatives can not only prepare through different physical and chemical approaches but also modify with various molecules and bioactive materials. The potential properties of CS NPs, such as biocompatibility, biodegradability, serum stability, solubility, non-immunogenicity, anti-inflammatory properties, appropriate pharmacokinetics and pharmacodynamics, and so forth, have made them excellent candidates for biomedical applications. Therefore, CS NPs have efficiently applied for various biomedical applications, like regenerative medicine and tissue engineering, biosensors for the detection of microorganisms, and drug delivery systems (DDS) for the suppression of diseases. These NPs possess a high level of biosafety. In summary, CS NPs have the potential ability for biomedical and clinical applications, and it would be remarkably beneficial to develop new generations of CS-based material for the future of medicine.

Gadolinium-doped whitlockite/chitosan composite scaffolds with osteogenic activity for bone defect treatment: In vitro and in vivo evaluations

Reducing the incidence of bone defects caused by trauma and other primary diseases is an urgent task in modern society. In the present study, we developed a gadolinium-doped whitlockite/chitosan (Gd-WH/CS) scaffold and assessed its biocompatibility, osteoinductivity, and bone regeneration capacity for the treatment of calvarial defect in a Sprague-Dawley (SD) rat model. The Gd-WH/CS scaffolds possessed a macroporous structure, with a pore size ranging 200-300 μm, which facilitated the growth of bone precursor cells and tissues into scaffold. Results of cytological and histological biosafety experiments showed that both WH/CS and Gd-WH/CS scaffolds were non-cytotoxic to human adipose-derived stromal cells (hADSCs) and bone tissue, which demonstrated the excellent biocompatibility of Gd-WH/CS scaffolds. Results of western blotting and real-time PCR analysis provided a possible mechanism that Gd³⁺ ions in the Gd-WH/CS scaffolds promoted the osteogenic differentiation of hADSCs through the GSK3β/β-catenin signaling pathway and significantly upregulated the expression of osteogenic related genes (OCN, OSX and COL1A1). Finally, in animal experiments, SD rat cranial defects were effectively treated and repaired with Gd-WH/CS scaffolds due to its appropriate degradation rate and excellent osteogenic activity. This study suggests the potential utility of the Gd-WH/CS composite scaffolds in treating bone defect disease.

Bioactive Nanocomposite Microsponges for Effective Reconstruction of Critical-Sized Calvarial Defects in Rat Model

Introduction

Micro-sized sponge particulates have attracted extensive attention because of their potential to overcome the intrinsic limitations of conventional monolithic scaffolds in tissue engineering. Bioactive nanocomposite microsponges are regarded as potential bone substitute materials for bone regeneration.

Methods

Based on a combination of microfluidic emulsion with further freezing and in situ thawing, chitosan (CS)-hydroxyapatite (HAP) microsponges were prepared and characterized in terms of their morphology and elemental distribution using a scanning electron microscope equipped with an X-ray detector. The swelling ratio, porosity, degradability, antibacterial activity, and bioactivity were detected and analyzed. The biological functions of the CS-HAP microsponges were examined to assess the adhesion, proliferation, and differentiation of in vitro co-cultured rat bone marrow mesenchymal stem cells (rBMSCs). Furthermore, the CS-HAP microsponges were used as cell-free scaffolds and implanted into calvarial defects in a rat model to evaluate the in vivo osteogenesis.

Results

The CS-HAP microsponges have a porous structure with high porosity (~76%), good swelling capacity (~1900%), and shape-memory properties. The results of in vitro experiments show that the CS-HAP microsponges achieve good bioactivity and promote osteogenic differentiation of rBMSCs. Furthermore, the CS-HAP microsponges significantly promote bone regeneration in rat calvarial defects.

Conclusion

The bioactive CS-HAP microsponges have the potential to be used as bone substitute materials for bone tissue engineering.

3D printed-electrospun PCL/hydroxyapatite/MWCNTs scaffolds for the repair of subchondral bone

Osteochondral defect caused by trauma or osteoarthritis exhibits a major challenge in clinical treatment with limited symptomatic effects at present. The regeneration and remodeling of subchondral bone play a positive effect on cartilage regeneration and further promotes the repair of osteochondral defects. Making use of the strengths of each preparation method, the combination of 3D printing and electrospinning is a promising method for designing and constructing multi-scale scaffolds that mimic the complexity and hierarchical structure of subchondral bone at the microscale and nanoscale, respectively. In this study, the 3D printed-electrospun poly(ɛ-caprolactone)/nano-hydroxyapatites/multi-walled carbon nanotubes (PCL/nHA/MWCNTs) scaffolds were successfully constructed by the combination of electrospinning and layer-by-layer 3D printing. The resulting dual-scale scaffold consisted of a dense layer of disordered nanospun fibers and a porous microscale 3D scaffold layer to support and promote the ingrowth of subchondral bone. Herein, the biomimetic PCL/nHA/MWCNTs scaffolds enhanced cell seeding efficiency and allowed for higher cell-cell interactions that supported the adhesion, proliferation, activity, morphology and subsequently improved the osteogenic differentiation of bone marrow mesenchymal stem cells in vitro. Together, this study elucidates that the construction of 3D printed-electrospun PCL/nHA/MWCNTs scaffolds provides an alternative strategy for the regeneration of subchondral bone and lays a foundation for subsequent in vivo studies.

CaCO3 Crystals with Unique Morphologies Controlled by the Hydrogen-Bonded Supramolecular Assemblies of Ureido-Pyrimidinone-Amino Acid Derivatives

Biomineral materials such as nacre of shells exhibit high mechanical strength and toughness on account of their unique "brick-mortar" multilayer structure. 2-Ureido-4[1H]-pyrimidinone (UPy) derivatives with different types of end groups, due to the self-complementary quadruple hydrogen bonds and abundant Ca²⁺ binding sites, can easily self-assemble into supramolecular aggregates and act as templates and skeleton in the process of inducing mineral crystallization. In this work, UPy derivatives were used as templates to induce the mineralization and growth of CaCO₃ through a CO₂ diffusion method. The morphology of CaCO₃ crystals was modulated and analyzed by adjusting the synthesizing parameters including Ca²⁺ concentration, pH, and end groups. The results showed that, by the regulatory role of the mineralization template, it was easier to realize the multilayer crystal structure at a lower concentration of Ca²⁺ (less than 0.01 mol L^-1). Under alkaline regulation, the quadruple hydrogen bonds would be destroyed, and the template's regulation effect on the morphology of CaCO₃ crystals would be weakened. Moreover, by comparing different types of end groups, it was proven that the UPy derivatives with carboxylic acid groups (-COOH) played a crucial role in the process of CaCO₃ crystallization with unique morphologies.