Hydroxyapatite coatings with oriented nanoplate and nanorod arrays: Fabrication, morphology, cytocompatibility and osteogenic differentiation

Histochemical analysis of osteoclast and osteoblast distributions on hydroxyapatite/collagen bone-like nanocomposite embedded in rat tibiae

OBJECTIVES

Hydroxyapatite (HAp)/collagen (Col) cylinders with laminated collagen layers were implanted into the tibial diaphysis of rats and examined histochemically to clarify how the orientation of HAp and Col bone-like nanocomposite fibers in HAp/Col blocks affects bone resorption and formation.

METHODS

HAp/Col fibers were synthesized and compressed into cylindrical blocks to mimic bone nanostructures. These were implanted into the cortical bone cavities of 10-week-old male Wistar rats with fiber bundles parallel to the tibial surface. The implants were histologically analyzed at 3, 5, 7, 14, and 28 days after implantation.

RESULTS

TRAP-positive osteoclasts appeared after 3-5 days in the lateral region of the graft, where the fiber ends were exposed, but not in the bottom region, where the HAp/Col fibers were parallel to the surface. Osteoclasts were observed in both regions by day 14. PHOSPHO1-positive osteoblasts were first detected on day 5, appearing slightly away from the cylinder laterally but directly on the bottom surface. A few osteoblasts contacted the block laterally, whereas many were observed on the new bone tissue at the bottom, between days 7 and 14. Bone formation was induced earlier in the bottom region, whereas lateral resorption was dominant. This suggested the uncoupling of bone resorption and formation in the early postimplantation stages. However, bone remodeling shifted to coupling between osteoclasts and osteoblasts throughout the cylinder by day 28.

CONCLUSION

The orientation of HAp/Col fibers in HAp/Col graft materials substantially affected the preferential induction of bone resorption or formation during the early stages of bone regeneration.

Surface-modified electrospun poly-ε-caprolactone incorporating ZnO NPs and QK peptide to repair bone defect via osteogenesis, angiogenesis and antibacterial

Revealing excellent materials for bone defect repair or bionic periosteum fabrication, as well as addressing infection post orthopedic implantation, continue to pose challenges in bone tissue engineering. Reaping the benefits of electrospinning technology, poly-ε-caprolactone (PCL) nanofibers have been fabricated, exhibiting excellent biocompatibility and plasticity. In this study, electrospun PCL nanofiber was employed as a substrate to generate an alternative with promising clinical potential. The incorporation of zinc oxide nanoparticles (ZnO NPs) enhances the antibacterial properties of PCL nanofiber, thereby addressing infection-related concerns through releasing Zn2+. Moreover, dual surface modifications of polydopamine (PDA) and vascular endothelial growth factor mimics peptide (QK) were utilized, in combination with Zn2+, to promote osteogenesis and angiogenesis. After a comprehensive characterization process, the successful synthesis of composite nanofibers with ZnO NPs and dual surface modifications was confirmed. The in vitro studies have shown that the composite nanofibers have excellent biocompatibility and antibacterial activity. The composite nanofibers also demonstrate the capacity to enhance osteogenesis and angiogenesis. The results of subcutaneous infection experiment confirm the composite nanofibers can still play a role in vivo. These findings suggest that the composite nanofibers possess significant potential as an orthopedic implant for addressing clinical challenges.

Comparison of the differentiation of ovine fetal bone-marrow mesenchymal stem cells towards osteocytes on chitosan/alginate/CuO-NPs and chitosan/alginate/FeO-NPs scaffolds

In the current study, the creation of a chitosan/alginate scaffold hydrogel with and without FeO-NPs or CuO-NPs was studied. From fetal ovine bone marrow mesenchymal stem cells (BM-MSCs) were isolated and cultivated. Their differentiation into osteocyte and adipose cells was investigated. Also, on the scaffolds, cytotoxicity and apoptosis were studied. To investigate the differentiation, treatment groups include: (1) BM-MSCs were plated in DMEM culture medium with high glucose containing 10% FBS and antibiotics (negative control); (2) BM-MSCs were plated in osteogenic differentiation medium (positive control); (3) positive control group + FeO-NPs, (4) positive control group + CuO-NPs; (5) BM-MSCs were plated in osteogenic differentiation medium on chitosan/alginate scaffold; (6) BM-MSCs were plated in osteogenic differentiation medium on chitosan/alginate/FeO-NPs scaffold; and (7) BM-MSCs were plated in osteogenic differentiation medium on chitosan/alginate/CuO-NPs scaffold. Alkaline phosphatase enzyme concentrations, mineralization rate using a calcium kit, and mineralization measurement by alizarin staining quantification were evaluated after 21 days of culture. In addition, qRT-PCR was used to assess the expression of the ALP, ColA, and Runx2 genes. When compared to other treatment groups, the addition of CuO-NPs in the chitosan/alginate hydrogel significantly increased the expression of the ColA and Runx2 genes (p < 0.05). However, there was no significant difference between the chitosan/alginate hydrogel groups containing FeO-NPs and CuO-NPs in the expression of the ALP gene. It appears that the addition of nanoparticles, in particular CuO-NPs, has made the chitosan/alginate scaffold more effective in supporting osteocyte differentiation.

Morphology-Dependent Immunomodulatory Coating of Hydroxyapatite/PEO for Magnesium-Based Bone Implants

One of the most critical issues concerning orthopedic implants is the risk of chronic inflammation, which poses a threat to the bone healing process. Osteo-immunomodulation plays a pivotal role in implant technology by influencing proinflammatory and anti-inflammatory responses, ultimately promoting bone healing. This study aims to investigate the morphology-dependent osteo-immunomodulatory properties of a hydroxyapatite (HA)/plasma electrolytic oxidation (PEO)-coated WE43 alloy. In this context, following the PEO process with various operational parameters (duty cycles of 50-40, 50-20, 70-40%, and frequencies of 0.5, 0.8, and 1 kHz), a layer of HA was applied as the top coating using a straightforward hot-dip process. The results revealed the formation of the PEO layer with distinct morphologies and pore sizes, depending on the operational parameters. Specifically, a uniform PEO coating with small pore sizes (5.2-5.3 μm) led to the creation of plate-like HA particles, while a random-like HA structure formed on nonuniform surfaces with large pores (7.0-11.1 μm) of PEO. Moreover, it was observed that the plate-like HA coating exhibited higher adhesion strength than the random one (classified as class 2 vs class 3 based on cross-cut standards). Furthermore, electrochemical impedance spectroscopy (EIS) and polarization studies confirmed a substantial increase in the polarization resistance (680 kΩ) and total impedance (48 559.6 Ω) for the plate-like HA/PEO as compared to the substrate (an increase of 1511-fold and 311-fold, respectively) and the random HA/PEO samples (an increase of 85-fold and 18-fold, respectively). In addition, compared to random HA coatings, there was a significant enhancement in the viability (150% control vs 96% control), proliferation, and differentiation of MG63 cells when exposed to plate-like HA coatings. Moreover, surface morphology and chemistry pronouncedly impacted macrophages' viability, morphology, and phenotype. Notably, plate-like HA coatings resulted in a higher upregulation of BMP-2 and TGF-β than proinflammatory cytokines (IL-6 and M-CSF), indicating a polarization of macrophage type 1 (M1) toward type 2 (M2). In summary, the bilayer HA/PEO coating exhibited remarkable osteo-immunomodulatory activity, making it highly appealing for use in bone implant applications.

There Are over 60 Ways to Produce Biocompatible Calcium Orthophosphate (CaPO4) Deposits on Various Substrates

A The present overview describes various production techniques for biocompatible calcium orthophosphate (abbreviated as CaPO4) deposits (coatings, films and layers) on the surfaces of various types of substrates to impart the biocompatible properties for artificial bone grafts. Since, after being implanted, the grafts always interact with the surrounding biological tissues at the interfaces, their surface properties are considered critical to clinical success. Due to the limited number of materials that can be tolerated in vivo, a new specialty of surface engineering has been developed to desirably modify any unacceptable material surface characteristics while maintaining the useful bulk performance. In 1975, the development of this approach led to the emergence of a special class of artificial bone grafts, in which various mechanically stable (and thus suitable for load-bearing applications) implantable biomaterials and artificial devices were coated with CaPO4. Since then, more than 7500 papers have been published on this subject and more than 500 new publications are added annually. In this review, a comprehensive analysis of the available literature has been performed with the main goal of finding as many deposition techniques as possible and more than 60 methods (double that if all known modifications are counted) for producing CaPO4 deposits on various substrates have been systematically described. Thus, besides the introduction, general knowledge and terminology, this review consists of two unequal parts. The first (bigger) part is a comprehensive summary of the known CaPO4 deposition techniques both currently used and discontinued/underdeveloped ones with brief descriptions of their major physical and chemical principles coupled with the key process parameters (when possible) to inform readers of their existence and remind them of the unused ones. The second (smaller) part includes fleeting essays on the most important properties and current biomedical applications of the CaPO4 deposits with an indication of possible future developments.

A dual aperture (mesoporous and macroporous) system loaded with cell-free fat extract to optimize bone regeneration microenvironment

Injured bone regeneration requires a systemically and carefully orchestrated series of events involving inflammation, angiogenesis, and osteogenesis. Thus, we designed a multifunctional cell-supporting and drug-retarding dual-pore system: cell-free fat extract (Ceffe)-mesoporous silica nanoparticle (MSN)@poly(lactic-co-glycolic acid) (PLGA) (Ceffe-MSN@PLGA) to mimic the developmental spatial structure, the microenvironment of bone regeneration and integration during injured bone regeneration. In this system, a macroporous scaffold (pore size 200-250 μm) of PLGA is combined with mesoporous MSN (pore size 2-50 nm), aiming at realizing the slow release of Ceffe. Besides, PLGA and MSN are used to recruit the temporary support of cells that are able to degrade simultaneously with bone regeneration and provide space for bone tissue regeneration. And the Ceffe isolated from fresh human adipose tissue has a therapeutic effect in regulating the important functions of early inflammatory cell transformation, neovascularization and eventual osteogenic differentiation. Our results suggest that the mesoporous and macroporous Ceffe-MSN@PLGA system represents a promising strategy to better fit the regeneration of injured bone tissue.

Investigation on [OH−]-responsive systems for construction of one-dimensional hydroxyapatite via a solvothermal method

The concentration of OH⁻ can directly influence the crystal growth of flexible hydroxyapatite nanofibers in oleic acid-assisted solvothermal reaction systems.

Tunable Microstructure and Morphology of the Self-Assembly Hydroxyapatite Coatings on ZK60 Magnesium Alloy Substrates Using Hydrothermal Methods

Hydroxyapatite coatings have been widely used to improve the corrosion resistance of biodegradable magnesium alloys. In this paper, in order to manufacture the ideal hydroxyapatite (HA) coating on the ZK60 magnesium substrate by hydrothermal method, formation mechanism of enhanced hydroxyapatite (HA) coatings, influence of pH values of the precursor solution on the HA morphology, corrosion resistance and cytotoxicity of HA coatings have been investigated. Results show that the growth pattern of the HA is influenced by the local pH value. HA has a preferential c-axis and higher crystallinity in the alkaline environment developing a nanorod-like structure, while in acid and neutral environments it has a preferential growth along the a(b)-plane with a lower crystallinity, developing a nanosheet-like structure. The different morphology and microstructure lead to different degradation behavior and performance of HA coatings. Immersion and electrochemical tests show that the neutral environment promote formation of HA coatings with high corrosion resistance. The cell culture experiments confirm that the enhanced corrosion resistance assure the biocompatibility of the substrate-coating system. In general, the HA coating prepared in neutral environment shows great potential in surface modification of magnesium alloys.

The morphological effect of nanostructured hydroxyapatite coatings on the osteoinduction and osteogenic capacity of porous titanium

Weak osteogenic activity affects the long-term fixation and lifespan of titanium (Ti) implants. Surface modification along with a built-in porous structure is a highly considerable approach to improve the osteoinduction and osseointegration capacity of Ti. Herein, the osteoinduction and osteogenic activities of electrochemically deposited (ED) nanoplate-like, nanorod-like and nanoneedle-like hydroxyapatite (HA) coatings (named EDHA-P, EDHA-R, and EDHA-N, respectively) were evaluated in vitro and in vivo by comparison with those of acid/alkali (AA) treatment. The results revealed that the apatite forming ability of all nanostructured EDHA coatings was excellent, and only 12 h of soaking in SBF was needed to induce a complete layer of apatite. More serum proteins adsorbed on EDHA-P than others. In cellular experiments, different from those on EDHA-R and EDHA-N, the cells on EDHA-P presented a polygonal shape with lamellipodia extension, and thus exhibited a relatively larger spreading area. Furthermore, EDHA-P was more favorable for the enhancement of the proliferation and ALP activity of BMSCs, and the up-regulation of OPN gene expression. Based on the good biological performance in vitro, EDHA-P was selected to further evaluate its osteoinduction and osteogenic activities in vivo by comparison with AA treatment. Interestingly, a greater ability of ectopic osteoinduction was observed in the EDHA-P group compared to that in the AA group. At the osseous site, EDHA-P promoted more bone on/ingrowth, and had a higher area percentage of newly formed bone in the bone-implant interface and inner pores of the implants than in the AA group. Thus, a nanoplate-like HA coating has good potential in improving the osteoinductivity and osteogenic activity of porous Ti implants in clinical applications.

Two-in-one strategy: a remineralizing and anti-adhesive coating against demineralized enamel

Tooth enamel is prone to be attacked by injurious factors, leading to a de/remineralization imbalance. To repair demineralized enamel and prevent pulp inflammation caused by biofilm accumulation, measures are needed to promote remineralization and inhibit bacterial adhesion on the tooth surface. An innovative material, poly (aspartic acid)-polyethylene glycol (PASP-PEG), was designed and synthesized to construct a mineralizing and anti-adhesive surface that could be applied to repair demineralized enamel. A cytotoxicity assay revealed the low cytotoxicity of synthesized PASP-PEG. Adsorption results demonstrated that PASP-PEG possesses a high binding affinity to the hydroxyapatite (HA)/tooth surface. In vitro experiments and scanning electron microscopy (SEM) demonstrated a strong capacity of PASP-PEG to induce in situ remineralization and direct the oriented growth of apatite nanocrystals. Energy dispersive X-ray spectroscopy (EDS), X-ray diffraction analysis (XRD) and Vickers hardness tests demonstrated that minerals induced by PASP-PEG were consistent with healthy enamel in Ca/P ratio, crystal form and surface micro-hardness. Contact angle tests and bacterial adhesion experiments demonstrated that PASP-PEG yielded a strong anti-adhesive effect. In summary, PASP-PEG could achieve dual effects for enamel repair and anti-adhesion of bacteria, thereby widening its application in enamel repair.

Magnetic lanthanum-doped hydroxyapatite/chitosan scaffolds with endogenous stem cell-recruiting and immunomodulatory properties for bone regeneration

Magnetic lanthanum hydroxyapatite/chitosan scaffolds can better repair bone defects through stem cell recruitment and immunomodulation.

Role of citrate in the formation of enamel-like calcium phosphate oriented nanorod arrays

The effect of citrate on the formation of oriented fluoride doped hydroxyapatite nanorods grown on an amorphous calcium phosphate substrate was investigated.

Characteristics of (002) Oriented Hydroxyapatite Coatings Deposited by Atmospheric Plasma Spraying

Hydroxyapatite (HA) coatings with strong (002) preferred orientation were successfully prepared on Ti-6Al-4V substrates with conventional atmospheric plasma spraying (APS). The intensity changes of (002) preferred orientation along the coating depth were investigated and the mechanical properties of these coatings were analyzed. Results indicated that the intensity of (002) preferred orientation at a distance of longer than ~90 mm from the interface showed a high value, where uniformly distributed columnar grains in a direction perpendicular to the coating surface were observed. The results obtained from experiments on the mechanical properties revealed that the (002) oriented coatings prepared by conventional APS technique exhibited excellent mechanical properties. Meanwhile, this study provided a simple and rapid method for the preparation of HA coatings with (002) preferred orientation.

Titanium-based implant comprising a porous microstructure assembled with nanoleaves and controllable silicon-ion release for enhanced osseointegration

Osseointegration is crucial for early fixation as well as for long-term implantation success, hence numerous efforts have been made to tune the surface topography or chemical composition of biomedical implants to improve osseointegration. In this work, various nanostructures, including nanoflocs, nanobundles, nanorods, and nanoleaves, were introduced to the surface of silicon (Si)-incorporated microporous structure to form Si-incorporated micro-nano hierarchical structures on titanium (Ti)-based implants. The osseointegration of the implants were systemically assessed in vivo and in vitro. The in vitro evaluations showed that the nanostructures promoted the protein adsorption, thus modulating the early cellular responses, including the attachment and spreading of osteoblasts and human endothelial cells (HUVECs), and subsequent cell proliferation and differentiation. Furthermore, compared with the single microporous structure, the nanostructures located over the microporous structure protected the Si ions from quick release and allowed the long-term sustained Si-ions release, which further contributed to the proliferation and differentiation of osteoblasts and vascular endothelial growth factor (VEGF) secretion as well as the tube formation of HUVECs. Collectively, the favorable nano-surface structures, especially the nanoleaves structure, and the constant Si-ion release together led to robust osteogenic and angiogenic activities. More importantly, in vivo micro-CT evaluation and histological observations further verified that the Si-incorporated micro-nano hierarchical implant with nanoleaves structure could efficiently promote new bone formation, thus indicating it was an attractive candidate as a next-generation bone-implant material.

Progress of Regenerative Therapy in Orthopedics

PURPOSE OF REVIEW

To conduct a thorough appraisal of recent and inventive advances in the field of bone tissue engineering using biomaterials, cell-based research, along with the incorporation of biomimetic properties using surface modification of scaffolds.

RECENT FINDINGS

This paper will provide an overview on different biomaterials and emerging techniques involved in the fabrication of scaffolds, brief description of signaling pathways involved in osteogenesis, and the effect of surface modification on the fate of progenitor cells. The current strategies used for regenerative medicine like cell therapy, gene transfer, and tissue engineering have opened numerous therapeutic avenues for the treatment of various disabling orthopedic disorders. Precise strategy utilized for the reconstruction, restoration, or repair of the bone-related tissues exploits cells, biomaterials, morphogenetic signals, and appropriate mechanical environment to provide the basic constituents required for creating new tissue. Combining all the above strategies in clinical trials would pave the way for successful "bench to bedside" transformation in bone healing.

Artificial enamel induced by phase transformation of amorphous nanoparticles

Human tooth enamel has tightly packed c-axis-oriented hydroxyapatite (HAP: Ca10(PO4)6(OH)2) nanorods with high elastic modulus. Fabrication of an enamel architecture in vitro supports the repair of teeth using HAP; however, existing methods require complex and laborious steps to form an enamel-like structure. Here we present a very simple and effective technique for forming artificial enamel in near-physiological solution using a substrate composed of amorphous calcium phosphate (ACP) nanoparticles. Without any functionalized modification of the substrate surface, faint dissolution and successive phase transformation automatically induce formation of an intermediate layer of low-crystalline HAP nanoparticles, on which highly oriented HAP nanorods grow by geometrical selection. We also show that an enamel structure forms on a substrate of amorphous calcium carbonate when the surface nanoparticles react so as to form an intermediate layer similar to that in ACP. Our results demonstrate that there is a wide range of substrate choices for nanorod array formation. Contrary to current understanding, a stable surface designed in nanoscale is not essential for the growth of arranged guest crystals. Reactive amorphous nanoparticles and their transformation efficiently induce a nanorod array structure.