Preparation and biological effects of apatite nanosheet-constructed porous ceramics

Nano-/micro-scaled hydroxyapatite ceramic construction and the regulation of immune-associated osteogenic differentiation

Hydroxyapatite (HA) bioceramic is a promising substitute for bone defects, and the surface properties are major factors that influence bioactivity and osteoinductivity. In this study, two kinds of HA bioceramics with nanoscale (n-HA) and microscale (m-HA) surface topography were designed to mimic the natural bone, thus enhancing the stimulation of osteogenic differentiation and revealing the potential mechanism. Compared to m-HA, n-HA owned a larger surface roughness, a stronger wettability, and reduced hardness and indentation modulus. Based on these properties, n-HA could maintain the conformation of vitronectin better than m-HA, which may contribute to higher cellular activities and a stronger promotion of osteogenic differentiation of mesenchymal stem cells (MSCs). Further RNA sequencing analysis compared the molecular expression between n-HA and m-HA. Six hundred twenty-seven differentially expressed genes were identified in MSCs, and 17 upregulated genes and 610 downregulated genes were included when n-HA compared to m-HA. The GO cluster analysis and enriched Kyoto encyclopedia of genes and genome signaling pathways revealed a close correlation with the immune process in both upregulated (chemokine signaling pathway and cytokine-cytokine receptor interaction) and downregulated pathways (osteoclasts differentiation). It suggested that the nanoscale surface topography of HA enhanced the osteoinductivity of MSCs and could not be separated from its regulation of immune function and the retention of adsorbed protein conformation.

A novel porous hydroxyapatite scaffold (pHAMG) enhances angiogenesis and osteogenesis around dental implants by regulating the immune microenvironment

OBJECTIVE

The purpose was to evaluate whether a novel porous hydroxyapatite (HA) scaffold with a 25-30-µm groove structure (pHAMG) may improve bone osteogenesis, angiogenesis, and bone integration of titanium dental implants in animal models.

METHODS

The pHAMG was prepared by chemical precipitation method and its elemental composition and crystal structure were evaluated. The ability of the scaffolds to induce ectopic osteogenesis and the ability of scaffolds combined with titanium dental implants to induce orthotopic peri-implant angiogenesis, osteogenesis, and osteointegration were tested after implantation into the femur muscle pocket in rats and the mandibular defects in beagle dogs, respectively. The elemental composition was evaluated by SEM-EDS; the expression of the relevant osteogenic/inflammation marker and the anti-/pro-inflammation markers was evaluated by immunostaining and immunofluorescence, respectively.

RESULTS

In animal experiments with ectopic and peri-implant osteogenesis, pHAMG resulted in significantly larger neovascularization by hematoxylin-eosin staining, as well as deposition of collagen fibers by Masson staining than HA. Meanwhile, microgrooves in pHAMG upregulate more bone morphogenetic protein (BMP) 2 and interleukin-4 (IL-4) and -10 (IL-10) and downregulate more IL-1β and tumor necrosis factor-α (TNF-α) than that in HA. The pHAMG showed greater expression of arginase (Arg)-1 and lower expression of inducible nitric oxide synthase (iNOS) than HA.

CONCLUSION

The novel pHAMG can better repair bone defects in ectopic and orthotopic model. It also transfers macrophages to anti-inflammatory phenotypes, promoting angiogenic and osteogenesis in scaffolds, and bone integration in implants.

CLINICAL RELEVANCE

The novel pHAMG induce greater osteogenesis and angiogenesis which could be utilized in the clinical treatment.

Construction of a drug-containing microenvironment for in situ bone regeneration

Bioactive glass-coated hierarchical porous tricalcium phosphate ceramics were constructed as both bone scaffolds and drug delivery devices to treat S. aureus-infected bone defects.

Construction of Antimicrobial Material-Loaded Porous Tricalcium Phosphate Beads for Treatment of Bone Infections

Due to low success rates of antibiotic therapy in most osteomyelitis diseases, continuous efforts have been made to fabricate local delivery systems with high antimicrobial effects. Here, we reported a kind of ε-polylysine(PL)/Ag-loaded porous tricalcium phosphate (TCP) bead instead of antibiotics as local delivery systems for the treatment of Staphylococcus aureus-caused osteomyelitis. Such local delivery systems were prepared by the fabrication of porous TCP beads at first and then the loading of Ag and PL in turn into porous TCP beads via in situ Ag-doping and layer-by-layer methods. In vitro experiments demonstrated that the release of PL and Ag was controllable. Especially, the release dosage of Ag could be controlled to be less than 0.05 ppm 28 days later. The surface coating of PL improved the cytocompatibility and antibacterial activity of local delivery systems. In vivo experiments demonstrated that the Ag/PL-loaded porous TCP beads displayed strong antibacterial activity and good osteoconductivity, and the combination of Ag and PL was better than the use of single antibacterial materials to treat S. aureus-caused osteomyelitis. The implantation of Ag into the infected marrow had low toxicity because Ag has been integrated into the TCP grains, which could be absorbed in marrow. Therefore, the Ag/PL-loaded porous TCP beads presented potential for treating osteomyelitis, especially sequestrum-debrided osteomyelitis.

Construction of the Gypsum-Coated Scaffolds for In Situ Bone Regeneration

It is significant to use functional biomaterials to rationally engineer microenvironments for in situ bone regeneration in the field of bone tissue engineering. To this end, we constructed the gypsum-coated β-tricalcium phosphate (G-TCP) scaffolds by combing a three-dimensional printing technique and an epitaxial gypsum growth method. In vitro simulation experiments showed that the as-prepared scaffolds could establish a dynamic and weakly acidic microenvironment in a simulated body liquid, in which the pH and the calcium ion concentration always changed due to the gypsum degradation and growth of bone-like apatite nanoplates on the scaffold surfaces. The cell experiments confirmed that the microenvironment established by the G-TCP surfaces promoted rapid osteogenic differentiation and proliferation of bone marrow mesenchymal stem cells (BM-MSCs). In vivo experiments confirmed that the G-TCP scaffolds had high bioactivity in modulating in situ regeneration of bone, and the bioactivity of the G-TCP scaffolds was endowed by correct pore structures, degradation of gypsum, and growth of a bone-like apatite layer. The microenvironment established by the gypsum degradation could stimulate tissue inflammation and recruit white blood cells and BM-MSCs and thus accelerating native healing cascades of the bone defects via a bone growth/remodeling-absorption cycle process. Furthermore, in vivo experiments demonstrated that after the bone defects had healed completely, the as-prepared scaffolds also degraded completely within 24 weeks.

Programmed BMP-2 release from biphasic calcium phosphates for optimal bone regeneration

This study aimed to fabricate a multi-layered biphasic calcium phosphate (BCP) platform for programmed bone morphogenetic protein-2 (BMP-2) release, which means to block the initial burst release and promote releasing during the differentiation phase of osteogenic cells. And it is to confirm in vivo whether this platform has osteogenic inductivity even when extremely low doses of BMP-2 are loaded compared to the conventional soaking method. Our strategy consisted of preparing a multilayer coating on BCP to minimize the contact between BMP-2 and BCP and allow the loading of BMP-2. The multilayer, which is surface-modified on BCP, is composed of an organosilicate and a natural polymer-based layer-by-layer (LbL) film. We applied (3-Aminopropyl)triethoxysilane (APTES) as an organosilicate was used for amine-functionalized BCP and (collagen/heparin)₅ film was used to delay and sustain BMP-2 release. The coated multilayer not only reduced the initial burst release by more than 50% but also loaded more BMP-2. For in vivo experiment, histomorphometric analysis, it was observed that the BCP platform loaded with extremely low concentration BMP-2 (0.01 mg/ml) induced a significantly larger amount of new bones at 8 weeks compared to the conventional soaking method in the rabbit calvarium onlay graft model.

Design of hydroxyapatite bioceramics with micro-/nano-topographies to regulate the osteogenic activities of bone morphogenetic protein-2 and bone marrow stromal cells

Biomimicking the nanostructure of natural bone apatite to enhance the bioactivity of hydroxyapatite (HA) biomaterials is an eternal topic in the bone regeneration field. In the present study, we designed four kinds of HA bioceramics with micro- to nanosized grains and investigated the effects of bioceramic topographies on the structures of bone morphogenetic protein-2 (BMP-2) and the effects on the responses of bone marrow stromal cells (BMSCs). Compared to the samples with submicron-scale crystalline particles, HA bioceramics with grain sizes of 104.6 ± 27.8 nm exhibited increased roughness, improved hydrophilicity and enhanced mechanical properties. The synergistic effects of these surface characteristics could well maintain the conformation of BMP-2, facilitate cell adhesion and spreading, and activate the osteogenic differentiation of BMSCs. Furthermore, SBF immersion and in vivo canine intramuscular implantation confirmed that the HA bioceramics with nanotopography also processed excellent bone-like apatite forming ability and outstanding osteoinductivity. In summary, these findings suggest that the nanotopography of HA bioceramics is a critical factor to enhance their bioactivity and osteoinductivity.

Biological effects of apatite nanoparticle-constructed ceramic surfaces in regulating behaviours of mesenchymal stem cells

HCA nanoparticle-constructed nanotopography in vivo mediates bone marrow MSCs to condensate and spontaneously differentiate towards the osteogenic lineage.

Stabilization of Ca-deficient hydroxyapatite in biphasic calcium phosphate ceramics by adding alginate to enhance their biological performances

It is of significance to further improve the bioactivity of existing calcium phosphate (Ca–P) biomaterials to satisfy the needs of regenerative medicine.

Enhanced osteoinductivity of porous biphasic calcium phosphate ceramic beads with high content of strontium-incorporated calcium-deficient hydroxyapatite

Further biomimicking natural bone and enhancing osteoinductivity to meet the requirements of regenerative medicine is the key development direction of biphasic calcium phosphate (BCP) ceramics.