Nano-hydroxyapatite-alginate-gelatin microcapsule as a potential osteogenic building block for modular bone tissue engineering

Fabricating vascularized, anatomically accurate bone grafts using 3D bioprinted sectional bone modules, in-situ angiogenesis, BMP-2 controlled release, and bioassembly

Bone grafting is the most common treatment for repairing bone defects. However, current bone grafting methods have several drawbacks. Bone tissue engineering emerges as a promising solution to these problems. An ideal engineered bone graft should exhibit high mechanical strength, osteogenic properties, and pre-vascularization. Both top-down (using bulk scaffold) and bottom-up (using granular modules) approaches face challenges in fulfilling these requirements. In this paper, we propose a novel sectional modular bone approach to construct osteogenic, pre-vascularized bone grafts in anatomical shapes. We 3D-printed a series of rigid, thin, sectional, porous scaffolds from a biodegradable polymer, tailored to the dimensions of a femur bone shaft. These thin sectional modules promote efficient nutrition and waste removal due to a shorter diffusion distance. The modules were pre-vascularized viain-situangiogenesis, achieved through endothelial cell sprouting from the scaffold struts. Angiogenesis was further enhanced through co-culture with bioprinted fibroblast microtissues, which secreted pre-angiogenic growth factors. Sectional modules were assembled around a porous rod incorporated with Bone Morphogenetic Protein-2 (BMP-2), which released over 3 weeks, demonstrating sustained osteogenic activity. The assembled scaffold, in the anatomical shape of a human femur shaft, was pre-vascularized, osteogenic, and possessed high mechanical strength, supporting 12 times the average body weight. The feasibility of implanting the assembled bone graft was demonstrated using a 3D-printed femur bone defect model. Our method provides a novel modular engineering approach for regenerating tissues that require high mechanical strength and vascularization.

Fanganiello R. Design of Alginate/Gelatin Hydrogels for Biomedical Applications: Fine-Tuning Osteogenesis in Dental Pulp Stem Cells While Preserving Other Cell Behaviors

Alginate/gelatin (Alg-Gel) hydrogels have been used experimentally, associated with mesenchymal stromal/stem cells (MSCs), to guide bone tissue formation. One of the main challenges for clinical application is optimizing Alg-Gel stiffness to guide osteogenesis. In this study, we investigated how Alg-Gel stiffness could modulate the dental pulp stem cell (DPSC) attachment, morphology, proliferation, and osteogenic differentiation, identifying the optimal conditions to uncouple osteogenesis from the other cell behaviors. An array of Alg-Gel hydrogels was prepared by casting different percentages of alginate and gelatin cross-linked with 2% CaCl2. We have selected two hydrogels: one with a stiffness of 11 ± 1 kPa, referred to as "low-stiffness hydrogel", formed by 2% alginate and 8% gelatin, and the other with a stiffness of 55 ± 3 kPa, referred to as "high-stiffness hydrogel", formed by 8% alginate and 12% gelatin. Hydrogel analyses showed that the average swelling rates were 20 ± 3% for the low-stiffness hydrogels and 35 ± 2% for the high-stiffness hydrogels. The degradation percentage was 47 ± 5% and 18 ± 2% for the low- and high-stiffness hydrogels, respectively. Both hydrogel types showed homogeneous surface shape and protein (Alg-Gel) interaction with CaCl2 as assessed by physicochemical characterization. Cell culture showed good adhesion of the DPSCs to the hydrogels and proliferation. Furthermore, better osteogenic activity, determined by ALP activity and ARS staining, was obtained with high-stiffness hydrogels (8% alginate and 12% gelatin). In summary, this study confirms the possibility of characterizing and optimizing the stiffness of Alg-Gel gel to guide osteogenesis in vitro without altering the other cellular properties of DPSCs.

Droplet Microfluidics Powered Hydrogel Microparticles for Stem Cell-Mediated Biomedical Applications

Stem cell-related therapeutic technologies have garnered significant attention of the research community for their multi-faceted applications. To promote the therapeutic effects of stem cells, the strategies for cell microencapsulation in hydrogel microparticles have been widely explored, as the hydrogel microparticles have the potential to facilitate oxygen diffusion and nutrient transport alongside their ability to promote crucial cell-cell and cell-matrix interactions. Despite their significant promise, there is an acute shortage of automated, standardized, and reproducible platforms to further stem cell-related research. Microfluidics offers an intriguing platform to produce stem cell-laden hydrogel microparticles (SCHMs) owing to its ability to manipulate the fluids at the micrometer scale as well as precisely control the structure and composition of microparticles. In this review, the typical biomaterials and crosslinking methods for microfluidic encapsulation of stem cells as well as the progress in droplet-based microfluidics for the fabrication of SCHMs are outlined. Moreover, the important biomedical applications of SCHMs are highlighted, including regenerative medicine, tissue engineering, scale-up production of stem cells, and microenvironmental simulation for fundamental cell studies. Overall, microfluidics holds tremendous potential for enabling the production of diverse hydrogel microparticles and is worthy for various stem cell-related biomedical applications.

Betulin Stimulates Osteogenic Differentiation of Human Osteoblasts-Loaded Alginate-Gelatin Microbeads

Osteoporosis, a terminal illness, has emerged as a global public health problem in recent years. The long-term use of bone anabolic drugs to treat osteoporosis causes multi-morbidity in elderly patients. Alternative therapies, such as allogenic and autogenic tissue grafts, face important issues, such as a limited source of allogenic grafts and tissue rejection in autogenic grafts. However, stem cell therapy has been shown to increase bone regeneration and decrease osteoporotic bone formation. Stem cell therapy combined with betulin (BET) supplementation might be adequate for bone remodeling and new bone tissue generation. In this study, the effect of BET on the viability and osteogenic differentiation of hFOB 1.19 cells was investigated. The cells were encapsulated in alginate-gelatin (AlGel) microbeads. In vitro tests were conducted during the 12 d of incubation. While BET showed cytotoxic activity (>1 µM) toward non-encapsulated hFOB 1.19 cells, encapsulated cells retained their functionality for up to 12 days, even at 5 µM BET. Moreover, the expression of osteogenic markers indicates an enhanced osteo-inductive effect of betulin on encapsulated hFOB 1.19, compared to the non-encapsulated cell culture. The 3D micro-environment of the AlGel microcapsules successfully protects the hFOB 1.19 cells against BET cytotoxicity, allowing BET to improve the mineralization and differentiation of osteoblast cells.

Alginate: Microbial production, functionalization, and biomedical applications

Alginates are natural polysaccharides widely participating in food, pharmaceutical, and environmental applications due to their excellent gelling capacity. Their excellent biocompatibility and biodegradability further extend their application to biomedical fields. The low consistency in molecular weight and composition of algae-based alginates may limit their performance in advanced biomedical applications. It makes microbial alginate production more attractive due to its potential for customizing alginate molecules with stable characteristics. Production costs remain the primary factor limiting the commercialization of microbial alginates. However, carbon-rich wastes from sugar, dairy, and biodiesel industries may serve as potential substitutes for pure sugars for microbial alginate production to reduce substrate costs. Fermentation parameter control and genetic engineering strategies may further improve the production efficiency and customize the molecular composition of microbial alginates. To meet the specific needs of biomedical applications, alginates may need functionalization, such as functional group modifications and crosslinking treatments, to achieve enhanced mechanical properties and biochemical activities. The development of alginate-based composites incorporated with other polysaccharides, gelatin, and bioactive factors can integrate the advantages of each component to meet multiple requirements in wound healing, drug delivery, and tissue engineering applications. This review provided a comprehensive insight into the sustainable production of high-value microbial alginates. It also discussed recent advances in alginate modification strategies and alginate-based composites for representative biomedical applications.

Multi-scale cellular PLA-based bionic scaffold to promote bone regrowth and repair

Large bone defects have presented a significant challenge in orthopedic treatments, and the emergence of tissue-engineered scaffolds has introduced new avenues for treatment. Nonetheless, the clinical application of such scaffolds has been hindered by drawbacks like inadequate mechanical properties, and deficient osteogenesis. Herein, a biocompatible polylactic acid (PLA) based composite was proposed to emulate cancellous bone's morphology by incorporating nano-hydroxyapatite (nHA). In addition, a quantity of Mg²⁺ and chitosan (CS) as active osteogenic factors were adopted to imitate the bone marrow mesenchymal components in vivo. Using a pre-evaporated solvent and sacrificial multi-template techniques, the cellular PLA-based tissue engineering scaffolds containing macropores larger than 100 μm and micropores smaller than 10 μm were developed. The scaffold's bionic structure, osteogenic active component, and multi-scale cellular make it comparable to cancellous bone, with favorable mechanical properties and hydrophilicity. Vitro tests using Sprague-Dawley (SD) rat bone marrow mesenchymal stem cells (rBMSCs) demonstrated the scaffold's excellent biocompatibility to induce high efficiency of osteogenic differentiation. The bionic porous scaffold with multi-scale cellular structure also can recruit rBMSCs, promote bone regrowth and osteogenic differentiation, and facilitate the regeneration of defective bone tissue for repair. This contribution presented a promising strategy for future advancements in bone tissue engineering.

Structure and drug delivery relationship of acidic polysaccharides: A review

Scientists from across the world are being inspired by recent development in polysaccharides and their use in medical administration. Due to their extraordinary physical, chemical, and biological characteristics, polysaccharides are excellent materials for use in medicine. Acidic polysaccharides, which include Pectin, Xanthan gum, Carrageenan, Alginate, and Glycosaminoglycan, are natural polymers with carboxyl groups that are being researched for their potential as drug delivery systems. Most publications do not discuss how the different polysaccharides interact structurally in terms of drug delivery, which limits the scope of their use. The purpose of this review is to inform readers about the structural activity correlations between acidic polysaccharides, their different modification process and effects of combination of various acidic polysaccharides which have been used in drug delivery systems and expanding their potential applications, and bringing new perspectives to the fore.

Frontiers of Hydroxyapatite Composites in Bionic Bone Tissue Engineering

Bone defects caused by various factors may cause morphological and functional disorders that can seriously affect patient's quality of life. Autologous bone grafting is morbid, involves numerous complications, and provides limited volume at donor site. Hence, tissue-engineered bone is a better alternative for repair of bone defects and for promoting a patient's functional recovery. Besides good biocompatibility, scaffolding materials represented by hydroxyapatite (HA) composites in tissue-engineered bone also have strong ability to guide bone regeneration. The development of manufacturing technology and advances in material science have made HA composite scaffolding more closely related to the composition and mechanical properties of natural bone. The surface morphology and pore diameter of the scaffold material are more important for cell proliferation, differentiation, and nutrient exchange. The degradation rate of the composite scaffold should match the rate of osteogenesis, and the loading of cells/cytokine is beneficial to promote the formation of new bone. In conclusion, there is no doubt that a breakthrough has been made in composition, mechanical properties, and degradation of HA composites. Biomimetic tissue-engineered bone based on vascularization and innervation show a promising future.

Scaffold Fabrication Techniques of Biomaterials for Bone Tissue Engineering: A Critical Review

Bone tissue engineering (BTE) is a promising alternative to repair bone defects using biomaterial scaffolds, cells, and growth factors to attain satisfactory outcomes. This review targets the fabrication of bone scaffolds, such as the conventional and electrohydrodynamic techniques, for the treatment of bone defects as an alternative to autograft, allograft, and xenograft sources. Additionally, the modern approaches to fabricating bone constructs by additive manufacturing, injection molding, microsphere-based sintering, and 4D printing techniques, providing a favorable environment for bone regeneration, function, and viability, are thoroughly discussed. The polymers used, fabrication methods, advantages, and limitations in bone tissue engineering application are also emphasized. This review also provides a future outlook regarding the potential of BTE as well as its possibilities in clinical trials.

A novel gelatin/carboxymethyl chitosan/nano-hydroxyapatite/β-tricalcium phosphate biomimetic nanocomposite scaffold for bone tissue engineering applications

Hydroxyapatite (HA) and tricalcium phosphate (TCP) constitute 60% of the content of the bone, and their combination has a better effect on bone tissue engineering than either single element. This study demonstrates a new degradable gelatin/carboxymethyl chitosan (CMC) bone scaffold loaded with both nano-HA and β-TCP (hereinafter referred to as HCP), and freeze drying combined with stir foaming was used to obtain highly connected macropores. Only a few studies have used these components to synthesize a four-component osteogenic scaffold. The aim of this study was to comprehensively assess the biocompatibility and osteoinductivity of the nanocomposites. Three HCP/CMC/gelatin scaffolds were made with different HCP contents: group A (10 wt% HCP), group B (30 wt% HCP), and group C (50 wt% HCP) (the ratio of nano-HA and β-TCP was fixed at 3:2). The scaffolds were macroporous with a high porosity and pore connectivity, as observed by morphological analysis by scanning electron microscopy. Additionally, the pore size of groups A and B was more homogeneous than that of group C. There were no significant differences in physicochemical characterization among the three groups. The Fourier-transform infrared (FTIR) spectroscopy test indicated that the scaffold contained active groups, such as hydroxyl, amino, or peptide bonds, corresponding to gelatin and CMC. The XRD results showed that the phase structures of HA and β-TCP did not change in the nanocomposite. The scaffolds had biodegradation potential and an appreciable swelling ratio, as demonstrated with the in vitro test. The scaffolds were cultured in vitro with MC3T3-E1 cells, showing that osteoinduction and osteoconduction increased with the HCP content. None of the scaffolds showed cytotoxicity. However, cell adhesion and growth in group B were better than those in group A and group C. Therefore, freeze drying combined with a stir foaming method may have a solid component limit. This study demonstrates a novel four-component scaffold via a simple manufacturing process. Group B (30% HCP) had the best characteristics for bone scaffold materials.

Interaction of alginate with nano-hydroxyapatite-collagen using strontium provides suitable osteogenic platform

Background

Hydrogels based on organic/inorganic composites have been at the center of attention for the fabrication of engineered bone constructs. The establishment of a straightforward 3D microenvironment is critical to maintaining cell-to-cell interaction and cellular function, leading to appropriate regeneration. Ionic cross-linkers, Ca²⁺, Ba²⁺, and Sr²⁺, were used for the fabrication of Alginate-Nanohydroxyapatite-Collagen (Alg-nHA-Col) microspheres, and osteogenic properties of human osteoblasts were examined in in vitro and in vivo conditions after 21 days.

Results

Physicochemical properties of hydrogels illustrated that microspheres cross-linked with Sr²⁺ had reduced swelling, enhanced stability, and mechanical strength, as compared to the other groups. Human MG-63 osteoblasts inside Sr²⁺ cross-linked microspheres exhibited enhanced viability and osteogenic capacity indicated by mineralization and the increase of relevant proteins related to bone formation. PCR (Polymerase Chain Reaction) array analysis of the Wnt (Wingless-related integration site) signaling pathway revealed that Sr²⁺ cross-linked microspheres appropriately induced various signaling transduction pathways in human osteoblasts leading to osteogenic activity and dynamic growth. Transplantation of Sr²⁺ cross-linked microspheres with rat osteoblasts into cranium with critical size defect in the rat model accelerated bone formation analyzed with micro-CT and histological examination.

Conclusion

Sr²⁺ cross-linked Alg-nHA-Col hydrogel can promote functionality and dynamic growth of osteoblasts.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01511-9.

Synthesis and application of nanometer hydroxyapatite in biomedicine

Nano-hydroxyapatite (nano-HA) has been widely studied as a promising biomaterial because of its potential mechanical and biological properties. In this article, different synthesis methods for nano-HA were summarized. Key factors for the synthesis of nano-HA, including reactant concentration, effects of temperature, PH, additives, aging time, and sintering, were separately investigated. The biological performances of the nano-HA depend strongly on its structures, morphology, and crystallite sizes. Nano-HA with different morphologies may cause different biological effects, such as protein adsorption, cell viability and proliferation, angiogenesis, and vascularization. Recent research progress with respect to the biological functions of the nano-HA in some specific biological applications are summarized and the future development of nano-sized hydroxyapatite is prospected.

Degradation-Kinetics-Controllable and Tissue-Regeneration-Matchable Photocross-linked Alginate Hydrogels for Bone Repair

Photocross-linked alginate hydrogels, due to their biodegradability, biocompatibility, strong control for gelling kinetics in space and time, and admirable adaptability for in situ polymerization with a minimally invasive approach in surgical procedures, have created great expectations in bone regeneration. However, hydrogels with suitable degradation kinetics that can match the tissue regeneration process have not been designed, which limits their further application in bone tissue engineering. Herein, we finely developed an oxidation strategy for alginate to obtain hydrogels with more suitable degradation rates and comprehensively explored their physical and biological performances in vitro and in vivo to further advance the clinical application for the hydrogels in bone repair. The physical properties of the gels can be tuned via tailoring the degree of alginate oxidation. In particular, in vivo degradation studies showed that the degradation rates of the gels were significantly increased by oxidizing alginate. The activity, proliferation, initial adhesion, and osteogenic differentiation of rat and rabbit bone marrow stromal cells (BMSCs) cultured with/in the hydrogels were explored, and the results demonstrated that the gels possessed excellent biocompatibility and that the encapsulated BMSCs were capable of osteogenic differentiation. Furthermore, in vivo implantation of rabbit BMSC-loaded gels into tibial plateau defects of rabbits demonstrated the feasibility of hydrogels with appropriate degradation rates for bone repair. This study indicated that hydrogels with increasingly controllable and matchable degradation kinetics and satisfactory bioproperties demonstrate great clinical potential in bone tissue engineering and regenerative medicine and could also provide references for drug/growth-factor delivery therapeutic strategies for diseases requiring specific drug/growth-factor durations of action.

A Review on Current Designation of Metallic Nanocomposite Hydrogel in Biomedical Applications

In the past few decades, nanotechnology has been receiving significant attention globally and is being continuously developed in various innovations for diverse applications, such as tissue engineering, biotechnology, biomedicine, textile, and food technology. Nanotechnological materials reportedly lack cell-interactive properties and are easily degraded into unfavourable products due to the presence of synthetic polymers in their structures. This is a major drawback of nanomaterials and is a cause of concern in the biomedicine field. Meanwhile, particulate systems, such as metallic nanoparticles (NPs), have captured the interest of the medical field due to their potential to inhibit the growth of microorganisms (bacteria, fungi, and viruses). Lately, researchers have shown a great interest in hydrogels in the biomedicine field due to their ability to retain and release drugs as well as to offer a moist environment. Hence, the development and innovation of hydrogel-incorporated metallic NPs from natural sources has become one of the alternative pathways for elevating the efficiency of therapeutic systems to make them highly effective and with fewer undesirable side effects. The objective of this review article is to provide insights into the latest fabricated metallic nanocomposite hydrogels and their current applications in the biomedicine field using nanotechnology and to discuss the limitations of this technology for future exploration. This article gives an overview of recent metallic nanocomposite hydrogels fabricated from bioresources, and it reviews their antimicrobial activities in facilitating the demands for their application in biomedicine. The work underlines the fabrication of various metallic nanocomposite hydrogels through the utilization of natural sources in the production of biomedical innovations, including wound healing treatment, drug delivery, scaffolds, etc. The potential of these nanocomposites in relation to their mechanical strength, antimicrobial activities, cytotoxicity, and optical properties has brought this technology into a new dimension in the biomedicine field. Finally, the limitations of metallic nanocomposite hydrogels in terms of their methods of synthesis, properties, and outlook for biomedical applications are further discussed.

Advances of Hydroxyapatite Hybrid Organic Composite Used as Drug or Protein Carriers for Biomedical Applications: A Review

Hydroxyapatite (HA), especially in the form of HA nanoparticles (HANPs), has excellent bioactivity, biodegradability, and osteoconductivity and therefore has been widely used as a template or additives for drug delivery in clinical applications, such as dentistry and orthopedic repair. Due to the atomically anisotropic distribution on the preferred growth of HA crystals, especially the nanoscale rod-/whisker-like morphology, HA can generally be a good candidate for carrying a variety of substances. HA is biocompatible and suitable for medical applications, but most drugs carried by HANPs have an initial burst release. In the adsorption mechanism of HA as a carrier, specific surface area, pore size, and porosity are important factors that mainly affect the adsorption and release amounts. At present, many studies have developed HA as a drug carrier with targeted effect, porous structure, and high porosity. This review mainly discusses the influence of HA structures as a carrier on the adsorption and release of active molecules. It then focuses on the benefits and effects of different types of polymer-HA composites to re-examine the proteins/drugs carry and release behavior and related potential clinical applications. This literature survey can be divided into three main parts: 1. interaction and adsorption mechanism of HA and drugs; 2. advantages and application fields of HA/organic composites; 3. loading and drug release behavior of multifunctional HA composites in different environments. This work also presents the latest development and future prospects of HA as a drug carrier.

Collagen and nano-hydroxyapatite interactions in alginate-based microcapsule provide an appropriate osteogenic microenvironment for modular bone tissue formation

The addition of nano-hydroxyapatite (nHA) and collagen (Col) to the alginate (Alg) microcapsule hydrogel reduced swelling and degradation ratios while the compressive strength increased compared to Alg, Alg-Col, and Alg-nHA groups. MTT assay and Calcein-AM staining revealed an enhanced MG-63 osteoblasts viability in the Alg-nHA-Col hydrogel compared to the other groups. SEM showed the attachment of MG-63 osteoblasts inside Alg-Col hydrogels. Non-significant differences were found in antioxidant capacity of cells inside the Alg-nHA-Col hydrogel compared to the Alg group. Hematoxylin-Eosin staining showed the distribution of MG-63 osteoblasts inside microspheres. Calcium deposits, alkaline phosphatase (ALP) activity with the increase of intracellular calcium were found in Alg-nHA-Col group. Western blotting showed that levels of osteocalcin, ColA2, Sox-9, and ColA1 also significantly increased compared to the Alg, Alg-Col, Alg-nHA groups. The present study demonstrated that the addition of mineral nHA and protein (Col) into the Alg improves osteogenic potential and provides a 3D platform for modular bone tissue engineering.

Bioactive chitosan biguanidine-based injectable hydrogels as a novel BMP-2 and VEGF carrier for osteogenesis of dental pulp stem cells

Nowadays, vascularization and mineralization of bone defects is the main bottleneck in the bone regeneration field that is needed to be overcome and developed. Here, we prepared novel in-situ formed injectable hydrogels based on chitosan biguanidine and carboxymethylcellulose loaded with vascular endothelial growth factor (VEGF) and recombinant Bone morphogenetic protein 2 (BMP-2) and studied its influence on osteoblastic differentiation of dental pulp stem cells (DPSCs). The sequential release behavior of the VEGF and BMP-2 from hydrogels adjusted with the pattern of normal human bone growth. MTT assay exhibited that these hydrogels were non-toxic and significantly increased DPSCs proliferation. The Real-time PCR and Western blot analysis on CG11/BMP2-VEGF showed significantly higher gene and protein expression of ALP, COL1α1, and OCN. These results were confirmed by mineralization assay by Alizarin Red staining and Alkaline phosphatase enzyme activity. Based on these evaluations, these hydrogel holds potential as an injectable bone tissue engineering platform.

Comparative Study of Crystallization, Mechanical Properties, and In Vitro Cytotoxicity of Nanocomposites at Low Filler Loadings of Hydroxyapatite for Bone-Tissue Engineering Based on Poly(l-lactic acid)/Cyclo Olefin Copolymer

A poly(l-lactic acid)/nanohydroxyapatite (PLLA/nHA) scaffold works as a bioactive, osteoconductive scaffold for bone-tissue engineering, but its low degradation rate limits embedded HA in PLLA to efficiently interact with body fluids. In this work, nano-hydroxyapatite (nHA) was added in lower filler loadings (1, 5, 10, and 20 wt%) in a poly(l-lactic acid)/cyclo olefin copolymer10 wt% (PLLA/COC10) blend to obtain novel poly(l-lactic acid)/cyclo olefin copolymer/nanohydroxyapatite (PLLA/COC10-nHA) scaffolds for bone-tissue regeneration and repair. Furthermore, the structure-activity relationship of PLLA/COC10-nHA (ternary system) nanocomposites in comparison with PLLA/nHA (binary system) nanocomposites was systematically studied. Nanocomposites were evaluated for structural (morphology, crystallization), thermomechanical properties, antibacterial potential, and cytocompatibility for bone-tissue engineering applications. Scanning electron microscope images revealed that PLLA/COC10-nHA had uniform morphology and dispersion of nanoparticles up to 10% of HA, and the overall nHA dispersion in matrix was better in PLLA/COC10-nHA as compared to PLLA/nHA. Fourier transformation infrared spectroscopy (FTIR), powder X-ray diffraction (XRD), and differential scanning calorimetry (DSC) studies confirmed miscibility and transformation of the α-crystal form of PLLA to the ά-crystal form by the addition of nHA in all nanocomposites. The degree of crystallinity (%) in the case of PLLA/COC10-nHA 10 wt% was 114% higher than pure PLLA/COC10 and 128% higher than pristine PLLA, indicating COC and nHA are acting as nucleating agents in the PLLA/COC10-nHA nanocomposites, causing an increase in the degree of crystallinity (%). Moreover, PLLA/COC10-nHA exhibited 140 to 240% (1-20 wt% HA) enhanced mechanical properties in terms of ductility as compared to PLLA/nHA. Antibacterial activity results showed that 10 wt% HA in PLLA/COC10-nHA showed substantial activity against P. aeruginosa, S. aureus, and L. monocytogenes. In vitro cytocompatibility of PLLA/COC10 and PLLA nanocomposites with nHA osteoprogenitor cells (MC3T3-E1) and bone mesenchymal stem cells (BMSC) was evaluated. Both cell lines showed two- to three-fold enhancement in cell viability and 10- to 30-fold in proliferation upon culture on PLLA/COC10-nHA as compared to PLLA/nHA composites. It was observed that the ternary system PLLA/COC10-nHA had good dispersion and interfacial interaction resulting in improved thermomechanical and enhanced osteoconductive properties as compared to PLLA/nHA.

Functionalized Porous Hydroxyapatite Scaffolds for Tissue Engineering Applications: A Focused Review

Biomaterials have been widely used in tissue engineering applications at an increasing rate in recent years. The increased clinical demand for safe scaffolds, as well as the diversity and availability of biomaterials, has sparked rapid interest in fabricating diverse scaffolds to make significant progress in tissue engineering. Hydroxyapatite (HAP) has drawn substantial attention in recent years owing to its excellent physical, chemical, and biological properties and facile adaptable surface functionalization with other innumerable essential materials. This focused review spotlights a brief introduction on HAP, scope, a historical outline, basic structural features/properties, various synthetic strategies, and their scientific applications concentrating on functionalized HAP in the diverse area of tissue engineering fields such as bone, skin, periodontal, bone tissue fixation, cartilage, blood vessel, liver, tendon/ligament, and corneal are emphasized. Besides clinical translation aspects, the future challenges and prospects of HAP based biomaterials involved in tissue engineering are also discussed. Furthermore, it is expected that researchers may find this review expedient in gaining an overall understanding of the latest advancement of HAP based biomaterials.

6-deoxy-aminocellulose derivatives embedded soft gelatin methacryloyl (GelMA) hydrogels for improved wound healing applications: In vitro and in vivo studies

Hydrogels were prepared by mixing protein and carbohydrate-based biopolymers to increase the mechanical properties and efficient cell adhesion and proliferation for wound healing applications. Microcrystalline cellulose (MCC) and its 6-deoxy-aminocellulose derivatives (6-deoxy-6-hydrazide Cellulose (Cell-Hyd), 6-deoxy-6-diethylamide Cellulose (Cell-DEA), and 6-deoxy-6-diethyltriamide Cellulose (Cell-DETA)) were embedded in methacrylated gelatin (GelMA). GelMA and 6-deoxy-aminocellulose derivatives were synthesized and characterized by spectroscopic techniques. MCC and cellulose derivatives embedded GelMA gels were characterized by FTIR, SEM and Tensile mechanical testing. SEM images revealed that, porosity of the amine MCC incorporated GelMA was decreased compared to GelMA and MCC incorporated GelMA. Tensile strain of GelMA 61.30% at break was increased to 64.3% in case of GelMA/Cell-HYD. In vitro cytocompatibility and cell proliferation using NIH-3T3 cell lines showed cell density trend on scaffold as GelMA/Cell-DETA>GelMA/Cell-Hyd > GelMA. Scratch assay for wound healing revealed that GelMA/Cell-DETA showed complete wound closure, while GelMA/Cell-Hyd and GelMA exhibited 85.7%, and 66.1% wound healing, respectively in 8 h. In vivo tests on rats revealed that GelMA/Cell-DETA exhibited 98% wound closure on day 9, whereas GelMA/Cell-Hyd exhibited 97.7% and GelMA 66.1% wound healing on day 14. Our findings revealed that GelMA embedded amine MCC derivatives hydrogels can be applied for achieving accelerated wound healing.

Enhancing Tissue Adhesion and Osteoblastic Differentiation of MC3T3-E1 Cells on Poly(aryl ether ketone) by Chemically Anchored Hydroxyapatite Nanocomposite Hydrogel Coating

Tissue adhesion to bone implant and osteoblastic differentiation are the key factors to achieve poly(aryl ether ketone) (PAEK) implant osseointegration. However, physical interaction of implant with tissue and hydroxyapatite coating suffers from slow implant tissue integration and lack of long-term stability. In this study, a novel poly(phthalazinone ether sulfone ketone) containing allyl groups (APPBAESK) is coated onto PPBESK sheet for reacting with the allyl groups of the hydrogel coating to enhance its stability. N-Succinimidyl (NHS)-ester activated group and nano-hydroxyapatite (nano-HA) are introduced into the hydrogel synthesized from gelatin methacrylate (GelMA) and acrylic acid to construct a nanocomposite hydrogel coating on PPBESK which is a promising PAEK implant material. The hydrophilicity of the PPBESK sheet is improved by the hydrogel coating. The chemical components of the nanocomposite hydrogel coating are confirmed by X-ray photoelectron spectroscope, Attenuated total reflection infrared, and X-ray powder diffraction. The tissue shear adhesion strength of the hydrogel coating toward pig skin is enhanced due to the synergism of NHS-ester activated group and nano-HA. The osteogenic differentiation of MC3T3-E1 preosteoblasts is promoted by nano-HA in nanocomposite hydrogel coating. Therefore, the bifunctional nanocomposite hydrogel coating provides a great application prospect in the surface modification of PAEK implants in bone tissue engineering.

Preparation and characterization of polycaprolactone/chitosan-g-polycaprolactone/hydroxyapatite electrospun nanocomposite scaffolds for bone tissue engineering

Chitosan (CS) and poly (ε-caprolactone) (PCL) are two most usable polymers in biomedical applications. In this study, chitosan has been modified and incorporated with poly (ε-caprolactone) to fabricate bone tissue engineering scaffold. Moreover, hydroxyapatite nanoparticles were added to enhance bioactivity and mechanical properties of scaffold. Bulk and fibrous comparative results showed significant effect of fiber diameter and distribution on mechanical properties. Moreover, the incorporation of chitosan-g-poly (ε-caprolactone) (CS-g-PCL) significantly decreases fiber diameter of pure PCL scaffold. Furthermore, both CS-g-PCL and nHA enhance mineralization and degradation of the scaffold soaked in simulated body fluid (SBF) and phosphate buffered saline (PBS), respectively. In vitro cytocompatibility assays also confirmed high cell viability and proliferation on the samples. Taken together, the results suggest that the microfabricated nanocomposite scaffolds could be used in bone tissue engineering.

Alginate-chitosan core-shell microcapsule cultures of hepatic cells in a small scale stirred bioreactor: impact of shear forces and microcapsule core composition

A small scale stirred bioreactor was designed and the effect of different agitation rates (30, 60 and 100 rpm) was investigated on HepG2 cells cultured in alginate-chitosan (AC) core-shell microcapsule in terms of the cell proliferation and liver-specific function. The microencapsulated hepatic cells could proliferate well when they were cultured for 10 days at 30 rpm while the cell-laden microcapsules showed no cell proliferation at 100 rpm in the bioreactor system. Albumin production rate, as an important liver function, increased also 1.8- and 1.5- fold under stirring rate of 30 rpm compared to the static culture and 60 rpm of agitation, respectively. Moreover, In comparison with the static culture, about 1.5-fold increment in urea production was observed at 30 rpm. Similarly, the highest expressions of albumin and P450 genes were found at 30 rpm stirring rate, which were 4.9- and 19.2-fold of the static culture. Addition of collagen to the microcapsule core composition (ACol/C) could improve the cell proliferation and functionality at 60 rpm in comparison with the cell-laden microcapsules without collagen. The study demonstrated the hepatic cell-laden ACol/C microcapsule hydrogel cultured in the small scale stirred bioreactor at low mixing rate has a great potential for mass production of the hepatic cells while maintaining liver-specific functions.

In vivo evaluation of biocompatibility and immune modulation potential of poly(caprolactone)-poly(ethylene glycol)-poly(caprolactone)-gelatin hydrogels enriched with nano-hydroxyapatite in the model of mouse

Biocompatible, biodegradable, and injectable hydrogels are a novel and promising approach for bone regeneration. In this study, poly(caprolactone)-poly(ethylene glycol)-poly(caprolactone) (PCL-PEG-PCL), PCL-PEG-PCL-gelatin (Gel), PCL-PEG-PCL-Gel/nano-hydroxyapatite (nHA) injectable hydrogels were synthesized and evaluated in a mouse model of subcutaneous transplantation after 14 days. PCL-PEG-PCL-Gel and PCL-PEG-PCL-Gel/nHA hydrogels were fabricated with in situ precipitation method. Structure, intermolecular interaction, and the reaction between the PCL-PEG-PCL, Gel, and nHA were evaluated using a scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance (H-NMR), and carbon nuclear magnetic resonance (C-NMR). Fourteen days after subcutaneous injection, the existence of an immune system reaction was investigated using Hematoxylin and Eosin (H&E) staining. Using immunofluorescence imaging, the number of CD68⁺ cells was determined in the periphery of the hydrogel. The CD8/CD4 lymphocyte ratio was also calculated in blood samples. We monitored the expression of CCL-2, BCL-2, IL-10, and CD31 using real-time PCR assay. The chemical evaluation revealed the successful integration of Gel and nHA to the PCL-PEG-PCL backbone. Histological examination showed the lack of inflammation at the site of injection. No toxicological effects were determined in hepatic and renal tissues. The addition of nHA to the PCL-PEG-PCL-Gel decreased biodegradation time. None of the hydrogels caused statistically significant differences in the number of CD68 cells (p > 0.05). The CD8/CD4 lymphocyte ratio remained unchanged in all groups (p > 0.05). Compared to the PCL-PEG-PCL group, the addition of nHA and Gel increased the expression of CCL-2, BCL-2, IL-10, and CD31 (p < 0.05). In conclusion, the current study showed that PCL-PEG-PCL-Gel/nHA hydrogels could be used in in vivo conditions without prominent toxic effects and inflammatory responses.

Progress of gelatin-based microspheres (GMSs) as delivery vehicles of drug and cell

Gelatin has various attractive features as biomedical materials, for instance, biocompatibility, low immunogenicity, biodegradability, and ease of manipulation. In recent years, various gelatin-based microspheres (GMSs) have been fabricated with innovative technologies to serve as sustained delivery vehicles of drugs and genetic materials as well as beneficial bacteria. Moreover, GMSs have exhibited promising potentials to act as both cell carriers and 3D scaffold components in tissue engineering and regenerative medicine, which not only exhibit excellent injectability but also could be integrated into a macroscale construct with the laden cells. Herein, we aim to thoroughly summarize the recent progress in the preparations and biomedical applications of GMSs and then to point out the research direction in future. First, various methods for the fabrication of GMSs will be described. Second, the recent use of GMSs in tumor embolization and in the delivery of cells, drugs, and genetic material as well as bacteria will be presented. Finally, several key factors that may enhance the improvement of GMSs were suggested as delivery vehicles.

The osteogenic differentiation of human dental pulp stem cells in alginate-gelatin/Nano-hydroxyapatite microcapsules

Background

Microcapsule is considered as a promising 3D microenvironment for Bone Tissue Engineering (BTE) applications. Microencapsulation of cells in an appropriate scaffold not only protected the cells against excess stress but also promoted cell proliferation and differentiation. Through the current study, we aimed to microcapsulate the human Dental Pulp Stem Cells (hDPSCs) and evaluated the proliferation and osteogenic differentiation of those cells by using MTT assay, qRT-PCR, Alkaline phosphatase, and Alizarine Red S.

Results

The SEM results revealed that Alg/Gel microcapsules containing nHA showed a rough and more compact surface morphology in comparison with the Alg/Gel microcapsules. Moreover, the microencapsulation by Alg/Gel/nHA could improve cell proliferation and induce osteogenic differentiation. The cells cultured in the Alg/Gel and Alg/Gel/nHA microcapsules showed 1.4-fold and 1.7-fold activity of BMP-2 gene expression more in comparison with the control group after 21 days. The mentioned amounts for the BMP-2 gene were 2.5-fold and 4-fold more expression for the Alg/Gel and Alg/Gel/nHA microcapsules after 28 days. The nHA, addition to hDPSCs-laden Alg/Gel microcapsule, could up-regulate the bone-related gene expressions of osteocalcin, osteonectin, and RUNX-2 during the 21 and 28 days through the culturing period, too. Calcium deposition and ALP activities of the cells were observed in accordance with the proliferation results as well as the gene expression analysis.

Conclusion

The present study demonstrated that microencapsulation of the hDPSCs inside the Alg/Gel/nHA hydrogel could be a potential approach for regenerative dentistry in the near future.

Graphical abstract

Shapable bulk agarose-gelatine-hydroxyapatite-minocycline nanocomposite fabricated using a mineralising system aided with electrophoresis for bone tissue regeneration

To develop a shapable bulk antibacterial nanocomposite biomaterial for bone regeneration. A bulk agarose-gelatine hydrogel was through mineralised using a hydrogel mineralising system aided with electrophoresis, and the mineralised hydrogel was loaded with minocycline to obtain the agarose-gelatine-hydroxyapatite-minocycline nanocomposite. The nanocomposite had a large BET surface area of 44.4518m2/g and a high porosity of 76.9%. Hydroxyapatite crystals were well developed in the hydrogel matrix and exhibited a hybrid structure of microscale and nanoscale motifs. The addition of minocycline resulted in a continuous antibiotic release, inhibiting the growth of Staphylococcus aureus over two weeks in vitro. Exposed to rabbit bone marrow mesenchymal stem cells, the nanocomposite revealed good cytocompatibility in vitro. Furthermore, the biomaterial could effectively enhance the bone regeneration in a critical-size rabbit cranial defect model in vivo. These findings depicted that the nanocomposite, with good biocompatibility and good antibacterial property, is a promising candidate for future clinical application in bone tissue engineering or as a prospective bone replacement biomaterial.

Progress in Modern Marine Biomaterials Research

The growing demand for new, sophisticated, multifunctional materials has brought natural structural composites into focus, since they underwent a substantial optimization during long evolutionary selection pressure and adaptation processes. Marine biological materials are the most important sources of both inspiration for biomimetics and of raw materials for practical applications in technology and biomedicine. The use of marine natural products as multifunctional biomaterials is currently undergoing a renaissance in the modern materials science. The diversity of marine biomaterials, their forms and fields of application are highlighted in this review. We will discuss the challenges, solutions, and future directions of modern marine biomaterialogy using a thorough analysis of scientific sources over the past ten years.

Advancement of Nanobiomaterials to Deliver Natural Compounds for Tissue Engineering Applications

Recent advancement in nanotechnology has provided a wide range of benefits in the biological sciences, especially in the field of tissue engineering and wound healing. Nanotechnology provides an easy process for designing nanocarrier-based biomaterials for the purpose and specific needs of tissue engineering applications. Naturally available medicinal compounds have unique clinical benefits, which can be incorporated into nanobiomaterials and enhance their applications in tissue engineering. The choice of using natural compounds in tissue engineering improves treatment modalities and can deal with side effects associated with synthetic drugs. In this review article, we focus on advances in the use of nanobiomaterials to deliver naturally available medicinal compounds for tissue engineering application, including the types of biomaterials, the potential role of nanocarriers, and the various effects of naturally available medicinal compounds incorporated scaffolds in tissue engineering.

N-(9-Fluorenylmethoxycarbonyl)-L-Phenylalanine/nano-hydroxyapatite hybrid supramolecular hydrogels as drug delivery vehicles with antibacterial property and cytocompatibility

The intrinsic fragility of hydroxyapatite (HAP) restricts its wider applications for local delivery of antibiotics. The composites formed by integrating HAP with hydrogels can improve the properties of HAP. However, these reported composites not only require tedious preparation and employ organic solvent and toxic reagents, but also hardly have inherent antimicrobial property. In this study, N-(9-Fluorenylmethoxycarbonyl)-L-Phenylalanine/nano-hydroxyapatite (Fmoc-L-Phe/nHAP) hybrid supramolecular hydrogels with antibacterial property and cytocompatibility was prepared by integrating nHAP as reinforcement with Fmoc-L-Phe supramolecular hydrogels. The results showed that nHAP bounds in the chamber of the gel network and adheres to the fiber of Fmoc-L-Phe due to intermolecular interaction, remarkably improving the mechanical strength of Fmoc-L-Phe supramolecular hydrogels. The results of inhibition zone experiment and MTT experiment showed that the Fmoc-L-Phe/nHAP hybrid supramolecular hydrogels possess antimicrobial property and cytocompatibility. In vitro release experiment of chlorogenic acid (CGA) from the hybrid supramolecular hydrogels was performed. The study of the release kinetics indicated that the release behavior of CGA from the hybrid supramolecular hydrogels is following Weibull model and release mechanism involved Fickian diffusion and erosion of the surface of hydrogel matrix. The release of CGA shows a good inhibition effect on S. aureus. The results show that the Fmoc-L-Phe/nHAP hybrid hydrogels with antibacterial property and cytocompatibility have promising applications as drug delivery carrier. Due to the intrinsic fragility of hydroxyapatite (HAP), the properties of HAP could be improved by incorporation into hydrogels. However, these reported composites not only require tedious preparation and employ organic solvent and toxic reagents, but also hardly have inherent antimicrobial property. We prepared N-(9-Fluorenylmethoxycarbonyl)-L-Phenylalanine/nano-hydroxyapatite (Fmoc-L-Phe/nHAP) hybrid supramolecular hydrogels by integrating nHAP as reinforcement with Fmoc-L-Phe supramolecular hydrogels. The results showed that nHAP bounds in the chamber of the gel network and adheres to the fiber of Fmoc-L-Phe due to intermolecular interaction, remarkably improving the mechanical strength of Fmoc-L-Phe supramolecular hydrogels. The results of inhibition zone experiment and MTT experiment showed that the Fmoc-L-Phe/nHAP hybrid supramolecular hydrogels possess antibacterial property and cytocompatibility. In vitro release experiment of chlorogenic acid (CGA) from the hybrid supramolecular hydrogels was performed. The study of the release kinetics indicated that the release behavior of CGA from the hybrid supramolecular hydrogels is following Weibull model and release mechanism involved Fickian diffusion and erosion of the surface of hydrogel matrix. The release of CGA shows a good inhibition effect on S. aureus. The results show that the Fmoc-L-Phe/nHAP hybrid hydrogels with antibacterial property and cytocompatibility have promising applications as drug delivery carrier.

Three-dimensional cell printing of gingival fibroblast/acellular dermal matrix/gelatin-sodium alginate scaffolds and their biocompatibility evaluation in vitro

Tissue engineering has emerged as a promising approach for soft tissue regeneration. Three-dimensional (3D) cell printing showed great potential for producing cell-encapsulated scaffolds to repair tissue defects. The advantage of 3D cell printing technology is precise cell loading in scaffolds to achieve tissue regeneration instead of only relying on the cells from surrounding tissue or blood. A new acellular dermal matrix/gelatin-sodium alginate (ADM/A/G) scaffold with living gingival fibroblasts was constructed by 3D cell printing technology for potential oral soft tissue regeneration in this study, and the biological characteristics of the 3D cell printing scaffolds were evaluated. The residue of nucleic acid and growth factors in ADM were detected. Three biomaterials were mixed at an appropriate radio with human gingival fibroblasts (hGFs) to prepare bioinks. Two kinds of layer scaffolds were fabricated by 3D cell printing technology. The mechanical strength and degradability of the scaffolds were determined by measuring their compressive modulus and mass loss. CCK-8 assay and calcein-AM/PI staining were conducted to detect the cell proliferation and viability in 3D cell printing scaffolds. The morphology of the hGFs in the scaffolds were observed using SEM and FITC-phalloidin staining. The expression of COL1A1, PECAM1, and VEGF-A of hGFs in the scaffolds were quantified by qRT-PCR. The gelatin-sodium alginate (A/G) scaffolds were used as control group in all experiments. Compared with the control group, 3D cell printing ADM/A/G scaffolds showed better mechanical strength and longer degradation time. The ADM/A/G scaffolds obviously had a better promotion effect on cell proliferation and viability. Most of the hGFs observed had a fully extended spindle morphology in the ADM/A/G scaffolds but oval morphology in the control group. The expression of COL1A1 was significantly higher than in the control group with time, and the expression of PECAM1 and VEGF-A was slightly higher in ADM/A/G scaffolds on day 14. 3D cell printing gingival fibroblast-ADM/A/G scaffolds showed excellent biological properties, which could be potentially useful in oral soft tissue regeneration.

Polysaccharide-Based Systems for Targeted Stem Cell Differentiation and Bone Regeneration

Bone tissue engineering is an ever-changing, rapidly evolving, and highly interdisciplinary field of study, where scientists try to mimic natural bone structure as closely as possible in order to facilitate bone healing. New insights from cell biology, specifically from mesenchymal stem cell differentiation and signaling, lead to new approaches in bone regeneration. Novel scaffold and drug release materials based on polysaccharides gain increasing attention due to their wide availability and good biocompatibility to be used as hydrogels and/or hybrid components for drug release and tissue engineering. This article reviews the current state of the art, recent developments, and future perspectives in polysaccharide-based systems used for bone regeneration.

Enzymatically gellable gelatin improves nano-hydroxyapatite-alginate microcapsule characteristics for modular bone tissue formation

To maintain gelatin (Gel) as adhesive motifs inside alginate microcapsule as building blocks of modular approach, phenol moiety (Ph) was introduced into gelatin (Gel Ph). Addition of Gel Ph to alginate (Alg-Gel Ph) dramatically altered the physical properties of alginate-based hydrogels as compared to unmodified gelatin (Alg-Gel) addition. Alg-Gel Ph hydrogels revealed a dramatically lower swelling ratios (63%) as compared to Alg-Gel hydrogels (150%). Moreover, Gel Ph decreased 40% degradation rate of alginate-based hydrogels after 72 hr, while increasing compressive modulus 3.5-fold as compared to Alg-Gel hydrogels. Introducing nano-hydroxyapatite (nHA) to Alg-Gel Ph hydrogel (Alg-Gel Ph-nHA) could reduce degradation rate to 41.5% and improve compressive modulus of hydrogels significantly, reaching to 294 ± 2.5 kPa. The microencapsulated osteoblast-like cells proliferated considerably and showed more metabolic activities (two times) in Alg-Gel Ph-nHA microcapsules during a 21-day culture period, resulting in more calcium deposition and alkaline phosphatase (ALP) activities. The subcutaneous microcapsules could also be identified readily without complete absorption and signs of toxicity or any untoward reactions and viable osteoblast-like cells were seen as red colored areas in the central regions of cell-laden microcapsules after 1 month. The study demonstrated Alg-Gel Ph-nHA microcapsule as a promising 3D microenvironment for modular bone tissue formation.

Status of Plant Protein-Based Green Scaffolds for Regenerative Medicine Applications

In recent decades, regenerative medicine has merited substantial attention from scientific and research communities. One of the essential requirements for this new strategy in medicine is the production of biocompatible and biodegradable scaffolds with desirable geometric structures and mechanical properties. Despite such promise, it appears that regenerative medicine is the last field to embrace green, or environmentally-friendly, processes, as many traditional tissue engineering materials employ toxic solvents and polymers that are clearly not environmentally friendly. Scaffolds fabricated from plant proteins (for example, zein, soy protein, and wheat gluten), possess proper mechanical properties, remarkable biocompatibility and aqueous stability which make them appropriate green biomaterials for regenerative medicine applications. The use of plant-derived proteins in regenerative medicine has been especially inspired by green medicine, which is the use of environmentally friendly materials in medicine. In the current review paper, the literature is reviewed and summarized for the applicability of plant proteins as biopolymer materials for several green regenerative medicine and tissue engineering applications.

Adsorption, recovery, and regeneration of Cd by magnetic phosphate nanoparticles

Adsorption plays an important role in removing cadmium (Cd²⁺) from water, and magnetic adsorbents are increasingly being used due to their ease of separation and recovery. Magnetic Fe₃O₄-coated hydroxyapatite (HAP) nanoparticles (nHAP-Fe₃O₄) were developed by co-precipitation and then used for the removal of Cd²⁺ from water. The properties of these nanoparticles were characterized by transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and magnetization curves. Experiments were conducted to investigate the effects of adsorption and mechanisms. Results illustrated that kinetic data were well fitted by a pseudo-second-order model. The adsorption capacity of nHAP-Fe₃O₄ was 62.14 mg/g. The mechanisms for the adsorption of Cd²⁺ on nHAP-Fe₃O₄ included rapid surface adsorption, intraparticle diffusion, and internal particle bonding, with the ion exchange with Ca²⁺ and chemical complexation being the most dominant. The regeneration efficiency and recovery rate of nHAP-Fe₃O₄ eluted by EDTA-Na₂ after the fifth cycle were 63.04% and 40.2%, respectively. Results revealed that the feasibility of nHAP-Fe₃O₄ as an adsorbent of Cd²⁺ and its environmental friendliness make it an ideal focus for future research.