Towards Polycaprolactone-Based Scaffolds for Alveolar Bone Tissue Engineering: A Biomimetic Approach in a 3D Printing Technique

The alveolar bone is a unique type of bone, and the goal of bone tissue engineering (BTE) is to develop methods to facilitate its regeneration. Currently, an emerging trend involves the fabrication of polycaprolactone (PCL)-based scaffolds using a three-dimensional (3D) printing technique to enhance an osteoconductive architecture. These scaffolds are further modified with hydroxyapatite (HA), type I collagen (CGI), or chitosan (CS) to impart high osteoinductive potential. In conjunction with cell therapy, these scaffolds may serve as an appealing alternative to bone autografts. This review discusses research gaps in the designing of 3D-printed PCL-based scaffolds from a biomimetic perspective. The article begins with a systematic analysis of biological mineralisation (biomineralisation) and ossification to optimise the scaffold's structural, mechanical, degradation, and surface properties. This scaffold-designing strategy lays the groundwork for developing a research pathway that spans fundamental principles such as molecular dynamics (MD) simulations and fabrication techniques. Ultimately, this paves the way for systematic in vitro and in vivo studies, leading to potential clinical applications.

Optimization of the Mechanical Properties and the Cytocompatibility for the PMMA Nanocomposites Reinforced with the Hydroxyapatite Nanofibers and the Magnesium Phosphate Nanosheets

Commercial poly methyl methacrylate (PMMA)-based cement is currently used in the field of orthopedics. However, it suffers from lack of bioactivity, mechanical weakness, and monomer toxicity. In this study, a PMMA-based cement nanocomposite reinforced with hydroxyapatite (HA) nanofibers and two-dimensional (2D) magnesium phosphate MgP nanosheets was synthesized and optimized in terms of mechanical property and cytocompatibility. The HA nanofibers and the MgP nanosheets were synthesized using a hydrothermal homogeneous precipitation method and tuning the crystallization of the sodium-magnesium-phosphate ternary system, respectively. Compressive strength and MTT assay tests were conducted to evaluate the mechanical property and the cytocompatibility of the PMMA-HA-MgP nanocomposites prepared at different ratios of HA and MgP. To optimize the developed nanocomposites, the standard response surface methodology (RSM) design known as the central composite design (CCD) was employed. Two regression models generated by CCD were analyzed and compared with the experimental results, and good agreement was observed. Statistical analysis revealed the significance of both factors, namely, the HA nanofibers and the MgP nanosheets, in improving the compressive strength and cell viability of the PMMA-MgP-HA nanocomposite. Finally, it was demonstrated that the HA nanofibers of 7.5% wt and the MgP nanosheets of 6.12% wt result in the PMMA-HA-MgP nanocomposite with the optimum compressive strength and cell viability.

Fabrication of carbon and silver nanomaterials incorporated hydroxyapatite nanocomposites: Enhanced biological and mechanical performances for biomedical applications

Hydroxyapatite is widely utilized for different biomedical applications because of its outstanding biocompatibility and bioactivity. Cuttlefish bones, which are available aplenty, are both inexpensive and eco-friendly sources for calcium carbonate. In the present study, cuttlefish bones-derived HAp nanorods have been utilized to fabricate HAp nanocomposites incorporating 1, 3 and 5 wt% each of GO, MWCNTs, GONRs and Ag NPs. Characterization using such techniques as XRD, FTIR, HRSEM and EDS was performed to analyze the physicochemical properties of nanocomposites, and MTT assay, hemolysis, bioactivity and drug release to evaluate the biological properties. The XRD and HRSEM results reveal that crystallite and particle size increase with increasing wt% of carbon nanomaterials and Ag NPs. However, the addition of nanomaterials did not modify the shape of HAp. The MTT assay and hemolysis results suggest GONRs possess better biocompatibility than GO and CNTs due to their smooth edge structure. While adding carbon materials up to 3 wt% caused an increase in the hardness, adding up to 5 wt% of them caused a decrease in the hardness due to the agglomeration of the particles. Biocompatibility and Vicker's hardness studies show that adding carbon nanomaterials up to 3 wt% caused significant improvement in biocompatibility and mechanical properties. Antibacterial activity test was performed to analyze the ability to preclude the formation of biofilms. The results showed better activity for silver-incorporated nanocomposites in the presence of E. coli and S. aureus bacteria. Drug release studies were performed using lidocaine drug and the results showed nearly similar drug release profile for all the samples except HAg3. Finally, nanocomposite HRA3 could be a suitable candidate for biomedical applications since it shows better biological and mechanical properties than GO and MWCNTs nanocomposites.

TEM Studies on Antibacterial Mechanisms of Black Phosphorous Nanosheets

PURPOSE

Recently, two-dimensional (2D) nanomaterials are gaining tremendous attention as novel antibacterial platforms to combat against continuously evolving antimicrobial resistance levels. Among the family of 2D nanomaterials, black phosphorus (BP) nanosheets have demonstrated promising potential for biomedical applications. However, there is a need to gain nanoscale insights of the antibacterial activity of BP nanosheets which lies at the center of technical challenges.

METHODS

Ultra-large BP nanosheets were synthesized by liquid-exfoliation method in the eco-friendly deoxygenated water. Synthesized BP nanosheets were characterized by TEM, AFM, and Raman spectroscopy techniques and their chemical stability was evaluated by EDS and EELS elemental analysis. The antibacterial activity of BP nanosheets was evaluated at nanoscale by the ultramicrotome TEM technique. Further, HAADF-STEM image and EDS elemental line map of the damaged bacterium were utilized to analyze the presence of diagnostic ions. Supportive SEM and ATR-FTIR studies were carried out to confirm the bacterial cell wall damage. In vitro colony counting method was utilized to evaluate the antibacterial performance of ultra-large BP nanosheets.

RESULTS

Elemental EELS and EDS analysis of BP nanosheets stored in deoxygenated water confirmed the absence of oxygen peak. TEM studies indicate the various events of bacterial cell damage with the lost cellular metabolism and structural integrity. Colony counting test results show that as-synthesized BP nanosheets (100 μg/mL) can kill ~95% bacteria within 12 hours.

CONCLUSION

TEM studies demonstrate the various events of E. coli membrane damage and the loss of structural integrity. These events include the BP nanosheets interaction with the bacterial cell wall, cytoplasmic leakage, detachment of cytoplasm from the cell membrane, reduced density of lipid bilayer and agglomerated DNA structure. The EDS elemental line mapping of the damaged bacterium confirms the disrupted cell membrane permeability and the lost cellular metabolism. SEM micrographs and ATR-FTIR supportive results confirm the bacterial cell wall damage.

Polyglutamic acid-coordinated assembly of hydroxyapatite nanoparticles for synergistic tumor-specific therapy

Nanotechnology offers exciting and innovative therapeutic strategies in the fight against cancer. Nano-scale hydroxyapatite, the inorganic constituent of the hard tissues of humans and animals, is not only an ideal carrier for the delivery of drugs but also exerts selective inhibitory effects on tumor cells. To perform the dual functions, we propose polyglutamic acid-coordinated hydroxyapatite nanoparticles (HA-PGA NP) as both DOX delivery vehicle and sustained calcium flow supplier to achieve a synergistic, tumor-specific therapy in this study. With PGA as the coordinator, the HA-PGA NPs were easily assembled into spherical nano-clusters with low crystallinity. The excellent dispersibility and solubility in the tumor environment endowed the HA-PGA NPs with an improved internalization into the tumor cells, thereby causing a dramatic elevation in the intracellular calcium influx by about 40%, which further induced a cascade of mitochondrial membrane damage, ATP content reduction, and reinforced sensitivity to chemotherapy. After the encapsulation of the model drug DOX, a pH-responsive release profile was achieved via the degradation of the nanoparticles and the deprotonation of PGA in the acidic tumor micro-environment. Consequently, the hybrid system, with the synergistic effects of sustained DOX and calcium overload, exhibited selectively intensified toxicity to tumor cells. The in vivo test further confirmed that the current system exhibited highly selective tumor inhibition and reduced heart toxicity, thus representing an effective anti-tumor platform.

Anti-inflammatory and antimicrobial activity of bioactive hydroxyapatite/silver nanocomposites

Biomaterials are often used in orthopedic surgery like cavity fillings. However, related complications often require long-term systemic antibiotics, device removal, and extended rehabilitation. Hydroxyapatite/silver (HA/Ag) composites have been proposed as implantation biomaterials owing to the osteogenic properties of hydroxyapatite and to the antimicrobial efficiency of silver. Nevertheless, higher silver concentrations induce cytotoxic effects. The aim of this study was to synthesize and characterize HA/Ag nanocomposites that will allow us to use lower concentrations of silver nanoparticles with better antimicrobial efficiency and anti-inflammatory properties. The characterization of HA/Ag was performed by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, Fourier-transform infrared spectra, X-ray photoelectron spectroscopy, and laser diffraction. Bioactivity was evaluated under a simulated body fluid. The viability of osteoblast like-cells (MG-63) was determined by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide) and the antimicrobial activity was evaluated by the standard McFarland method. The detection of nitric oxide was measured by a colorimetric assay and the inflammatory cytokines by flow cytometry. We obtained particulate composites of calcium phosphates identified as hydroxyapatite and silver nanoparticles. The bioactivity of the HA/Ag nanocomposites on SFB was confirmed by apatite formations. The viability of MG-63 cells was not affected. We also found antimicrobial activity against Escherichia coli, Staphylococcus aureus, and Candida albicans owing to the presence of silver nanoparticles at non-cytotoxic concentrations. HA/Ag reduced the release of nitric oxide and decreased the secretion of IL-1 and TNF-α in cells stimulated with Lipopolysaccharide (LPS). In conclusion, the inflammatory and antimicrobial capacity of the HA/Ag nanocomposites, as well as its bioactivity and low cytotoxicity make it a candidate as an implantation biomaterial for bone tissues engineering and clinical practices in orthopedic, oral and maxillofacial surgery.

Biomimetic mineralization of a hydroxyapatite crystal in the presence of a zwitterionic polymer

The biomimetic mineralization of nano-hydroxyapatite using a zwitterionic polymer as a template to cognize the biomineralization of natural bone in vivo.