Marine biological waste as a source of hydroxyapatite for bone tissue engineering applications

The demand for bone graft substitutes for orthopedics and dentistry is constantly growing due to the increase of ageing-related diseases. Synthetic hydroxyapatite (HA) is largely used as a bone graft material thanks to its biocompatibility, osteointegration, osteoconductive and osteoinductive properties and similarity to biological apatite, the main mineral component of bones and teeth. Biogenic apatite has gained attention due to its peculiar intrinsic characteristics: multi-doped ion composition and micro- and nano-scale architecture make natural-derived HA particularly promising for biomedical applications.At the same time, the growing interest in green materials is pushing towards the use of more sustainable biomaterials precursors, including re-use materials: marine waste, such as mollusk-shells, shellfish carapaces, cuttlefish bone, and fishbone have become widely studied sources of biogenic HA. Indeed, they are rich in calcium carbonate (CaCO₃), which can be converted into HA by environmentally sustainable processes. This allows the transformation of waste into valuable materials, while paying attention to the issues of sustainability and circular economy.In this review, we listed and discussed the methods to produce HA starting from shell-derived CaCO₃, describing all the steps and synthesis routes proposed for the conversion procedure, with a special focus on the different species of marine shells used. We discussed the use of HA alone or in combination with other materials (natural and synthetic polymers), used to enhance the mechanical and biological properties.We summarized the types of devices obtained by marine-derived HA, including nanorods, particulates and scaffolds and we described their in vitro and in vivo behavior.The up-to-date literature was summarized in tables with a special focus on the in vitro and in vivo biological evaluation of such materials.In conclusion, composite biomaterials based on marine-derived biogenic HA are reported as potential candidates for synthetic bone substitutes highlighting their potential, limitations and future perspectives.     

Porous wollastonite-hydroxyapatite bioceramics from a preceramic polymer and micro- or nano-sized fillers

Wollastonite-hydroxyapatite ceramics have been successfully prepared by a novel method, corresponding to the thermal treatment in air of a silicone embedding micro- and nano-sized fillers. CaCO₃ nano-sized particles, providing CaO upon decomposition, acted as “active” filler, whereas different commercially available or synthesised hydroxyapatite particles were used as “passive” filler. The homogeneous distribution of CaO, at a quasi-molecular level, favoured the reaction with silica derived from the polymer, at only 900 °C, preventing extensive decomposition of hydroxyapatite. Open-celled porous ceramics suitable for scaffolds for bone-tissue engineering applications were easily prepared from filler-containing silicone resin mixed with sacrificial PMMA microbeads as templates. The pore size (in the range of 80-400 μm) and the open porosity percentage (40-50%) were evaluated by means of micro-computerized tomographic analysis. A preliminary assessment of the biocompatibility and cell activity of the produced ceramics was performed successfully by in vitro tests using human osteoblast cells.     

Electrophoretic deposition (EPD) of nanohydroxyapatite - nanosilver coatings on Ti13Zr13Nb alloy

Titanium and its alloys are the biomaterials most frequently used in medical engineering, especially as parts of orthopedic and dental implants. The surfaces of titanium and its alloys are usually modified to improve their biocompatibility and bioactivity, for example, in connection with the deposition of hydroxyapatite coatings.The objective of the present research was to elaborate the technology of electrophoretic deposition (EPD) of nanohydroxyapatite (nanoHAp) coatings decorated with silver nanoparticles (nanoAg) and to investigate the mechanical and chemical properties of these coatings as determined by EPD voltage and the presence of nanoAg. The deposition of nanoHAp was carried out at two voltage values, 15 and 30 V. The decoration of nanoHAp coatings with nanoAg was carried out using the EPD process at a voltage value of 60 V and a deposition time of 5 min. The thickness of the undecorated coatings was found to be 2.16 and 5.14 µm for applied EPD voltages of 15- and 30-V, respectively. The release rate of silver nanoparticles into an artificial saliva solution increased with exposure time and EPD voltage. The corrosion current, between 1 and 10 nA/cm², was significantly higher for undecorated nanoHAp coatings and close to that of the substrate for decorated nanoHAp coatings. The hardness of the undecorated nanoHAp coatings obtained at 15 and 30 V of EPD voltage attained 0.2245±0.036 and 0.0661±0.008 GPa, respectively. Resistance to nanoscratching was higher for thicker coatings. The wettability angle was lower for coatings decorated with nanoAg.     

Fabrication,characterization and cellular biocompatibility of porous biphasic calcium phosphate bioceramic scaffolds with different pore sizes

Facile wet-chemical methods are applied to synthesize hydroxyapatite and β-tricalcium phosphate nanoparticles, respectively. Porous biphasic calcium phosphate (BCP) bioceramic scaffolds are then fabricated using as-prepared HA and β-tricalcium phosphate nanoparticle powders. The macro pore diameter of BCP bioceramic scaffolds can be controlled by adjusting the amount of surfactants. The average diameter of the macro pores in BCP bioceramic scaffolds increases from 100 to 600 µm with the decrease amount of sodium dodecyl sulfate from 0.8 to 0.5 g, respectively. The BCP bioceramic scaffolds gradually degrade and the calcium-phosphate compounds fully deposit when soaking in simulated body fluid solution. Moreover, The BCP bioceramic scaffolds have outstanding biocompatibility to promote the cellular growth and proliferation of human dental pulp stem cells (hDPSCs). The hDPSCs also demonstrate favorable cellular adhering capacity on the pore surface of scaffolds, especially on the scaffolds with 100–200 µm pore diameter. The porous BCP bioceramic scaffold with inter-connected pore structure, outstanding in vitro cellular biocompatibility, favorable cell viability and adhesion ability will be a promising biomaterial for bone or dentin tissue regeneration.     

Soft chemistry routes for the preparation of Ag-CoFe2O4 nanocomposites

Silver-cobalt ferrite nanocomposites (Ag-CoFe₂O₄) were synthesized through wet ferritization process and self-propagating combustion method. The structure, morphology, surface chemistry and magnetic properties of the nanocomposites were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometer (VSM). X-ray diffraction patterns confirmed the formation of CoFe₂O₄ and Ag nanoparticles with cubic symmetry. The average crystallite size of CoFe₂O₄ by wet ferritization ranged between 60 Å and 87 Å; for those obtained by self-propagating combustion was in the range 232–290 Å. SEM micrographs revealed different morphological features of nanocomposites. Ag-CoFe₂O₄ obtained by wet ferritization exhibited typical superparamagnetic behaviour. The antimicrobial and anti-biofilm properties of all silver-cobalt ferrites were evaluated. The results revealed that the Ag-CoFe₂O₄ nanocomposites exhibited good microbicidal and anti-biofilm features.     

Studies on novel bioactive glasses and bioactive glass-nano-HAp composites suitable for coating on metallic implants

A series of novel zinc oxide (ZnO) containing bioactive glass compositions in SiO₂-Na₂O-CaO-P₂O₅ system and composite with hydroxyapatite (HAp) nano-particles were developed and applied as coating on Ti-6Al-4V substrates. The bioactive glasses and their composites were also processed to yield dense scaffolds, porous scaffolds and porous bone filler materials. The coating materials and the coatings were characterized and evaluated by different in vitro techniques to establish their superior mechanical properties. The cytotoxicity test of the coating material, porous and dense scaffolds and coated specimens showed non-cytotoxicity, biocompatibility and promising in vitro bioactivity for all tested samples. The dissolution behaviour studies of the bioactive glasses and the composites in simulated body fluid showed promising in vitro release pattern and bioactivity for all tested samples. Addition of nanosized HAp improves mechanical properties of the bioactive glass coating without affecting the in vitro bioactivity.     

Sodium dodecyl sulfate mediated microwave synthesis of biocompatible superparamagnetic mesoporous hydroxyapatite nanoparticles using black Chlamys varia seashell as a calcium source for biomedical applications

Designing biocompatible superparamagnetic mesoporous nanoparticles for advanced healthcare applications has received much attention. In this research, we have synthesized intrinsic mesoporous superparamagnetic hydroxyapatite (HAp) nanoparticles using bio-waste of black Chlamys varia seashell as a calcium source by sodium dodecyl sulfate (SDS)–enabled microwave-assisted synthesis approach. The synthesized Fe-doped HAp nanoparticles were characterized using various characterization techniques to know the phase purity and morphological features. The incorporation of Fe greatly affected the morphology of HAp nanoparticles without affecting their crystalline phase. Superparamagnetic behavior was observed with the incorporation of Fe in the HAp nanoparticles. Further, saturation magnetization was enhanced with higher incorporation of Fe ions. The cytotoxicity studies of the synthesized pure and Fe-doped HAp samples conducted using a human osteoblasts cell line (MG63), which indicated that Fe-doped HAp nanoparticles are biocompatible. Further, antibacterial activity analysis also confirmed their excellent antibacterial performance against different pathogens. Hence, SDS-enabled microwave-assisted synthesis approach using seashell as a calcium source would be a better approach for the production of intrinsic mesoporous superparamagnetic HAp nanoparticles for various biomedical applications, such as drug targeting, hyperthermia cancer therapy, and magnetic resonance imaging.     

Macroporous Bioglass-derived scaffolds for bone tissue regeneration

Since it was introduced at the end of the ‘60s, the 45S5 Bioglass^® has played a fundamental role among the materials for orthopedic applications because of its ability to build a stable bond with the surrounding bone. The recent development of bone tissue engineering has led the interest of many scientists in the design of Bioglass^®-based scaffolds, i.e. porous systems able to drive and foster the bone tissue regrowth. Among the available techniques to realize scaffolds, the polymer burning out method, which employs organic particles as pore generating agents in a ceramic matrix, combines versatility and low cost. In spite of the advantages of the polymer burning out method, this technique has been rarely applied to 45S5 Bioglass^® and a systematic feasibility study has not been carried out on this issue yet. In order to fill this gap, in the present contribution the polymer burning out method was employed to design macroporous scaffolds based on 45S5 Bioglass^®. Different amounts of organic phase were used to obtain samples with different porosity. The samples were characterized from a microstructural point of view, in order to evaluate the pore morphology, dimension and degree of interconnectivity. Such findings proved that a proper setting of the processing parameters made it possible to achieve very high porosity values, among the best ones obtained in the literature with the same technique, together with an appreciable mechanical behaviour, according to compression tests. Finally, the scaffolds bioactivity was assessed by means of in vitro tests in a simulated body fluid (SBF) solution. Moreover, in the view of a potential application for bone tissue engineering, a preliminary biological evaluation of the obtained scaffolds to sustain cell proliferation was carried out.     

Potassium based bioactive glass for bone tissue engineering

A fundamental issue for the restoration of bone defects according to a tissue engineering approach is the development of highly porous bioactive scaffolds. The polymer burning out method is widely employed to fabricate bioceramic scaffolds because of its versatility, simplicity and low cost. However, the resulting scaffolds may suffer low porosity and non-interconnected pores. In the present contribution a new fabrication method is presented. Thanks to a recently developed potassium-based bioactive glass, which has the peculiarity to be sintered at a relatively low temperature (i.e. ∼750 °C), it was possible to use sodium chloride particles as pore generating agents, which helped to maintain the shape of the struts during the entire sintering process. The salt particles can be easily removed by immersing the scaffold in water, giving place to a structure that combines high porosity (in the 70–80 vol.% range) with interconnected pores and an appreciable mechanical behaviour (Young's modulus in the 3.4–3.7 MPa range according to compression tests).     

Development of macroporous nanocomposite scaffolds of gelatin/bioactive glass prepared through layer solvent casting combined with lamination technique for bone tissue engineering

In this study, macroporous bioactive nanocomposite scaffolds were developed using cross-linked gelatin and bioactive glass (BaG) nanoparticles. First, BaG nanoparticles were synthesized via sol–gel method and characterized. Then, macroporous nanocomposites were prepared through layer solvent casting combined with freeze-drying and lamination techniques. This research has developed a new composition to produce a new bioactive nanocomposite which is porous with three-dimensional (3D) inter-connected microstructure, pore sizes are 200–500 μm, porosity are 72–86% and BaG nanoparticles are dispersed evenly among cross-linked gelatin matrices. It is mentionable that in this study, we have reported the formation of chemical bonds between BaG nanoparticles and gelatin for the first time. Finally, the in vitro cytocompatibility of the nanocomposite scaffolds was tested using SaOS-2 cell line.     

Solution combustion synthesis of bioceramic calcium phosphates by single and mixed fuels—A comparative study

Calcium phosphate based bioceramics have been synthesized by a modified combustion synthetic route using both citric acid and succinic acid separately and in mixture as fuels and nitrate and nitric acid as oxidants. Calcium nitrate and diammonium hydrogen phosphate were used as calcium and phosphate sources. The effects of citric acid to succinic acid ratio on the phase formation have been investigated. The precursors and the calcined products have been characterized by powder X-ray diffraction, Fourier-transform infrared spectroscopy and scanning electron microscopy. Succinic acid has been used as a fuel for the first time to synthesize hydroxyapatite.     

High thermally stable Mg-substituted tricalcium phosphate via precipitation

Tricalcium phosphates incorporating small amounts of Mg show attractive biological performances in terms of enhanced bone apposition, bone in-growth and cell-mediated degradation. A systematic investigation on Mg-stabilized β-TCP (β-tricalcium phosphate, β-Ca₃(PO₄)₂) is presented. Microstructure, composition and thermal behaviour were investigated by means of thermogravimetry and differential thermal analysis (TG-DTA), induced coupled plasma-atomic emission spectroscopy (ICP-AES), Fourier transform infrared spectroscopy (FT-IR), N₂ adsorption isotherms, X-ray diffraction (XRD and HT-XRD), and scanning electron microscopy (SEM). Pure and Mg-substituted tricalcium phosphate precursors consisted of calcium-deficient hydroxyapatite, the specific surface area being 128 m²/g and 87 m²/g, respectively. Tricalcium phosphate nanostructured powders were obtained by thermal treatment above 800 °C. The incorporation of Mg within the calcium phosphate lattice promoted the formation of the β-TCP phase at slightly lower temperature and resulted in the stabilization of the β-polymorph at high temperature (i.e. 1600 °C).     

Osseointegration of sputtered SiC-added hydroxyapatite for orthopaedic applications

Over the last few years, a trend in medical applications is to find solutions for metallic implants using coatings that can improve bioactivity and osseointegration. The goal of this study was to obtain and investigate sputtered hydroxyapatite coatings enriched with SiC to enhance the bioactivity and osseointegration of Ti alloys used in orthopaedic applications. The films were characterized in terms of phase composition, roughness, corrosion resistance in a synthetic body fluid (SBF) and in vitro biocompatibility with MG 63 osteoblast-like cells. All of the investigations were conducted using XRD, AFM, cell viability assays and proliferation tests. The results revealed that the addition of SiC had a positive influence on the properties of the sputtered hydroxyapatite. The addition of SiC led to an improvement in coating adhesion and corrosion resistance in an SBF solution over the HAP coating. All of the coatings presented cell viability values over 90%, revealing their suitability for medical applications.     

Synthesis and characterization of chlorinated hydroxyapatite as novel synthetic bone substitute with negative zeta potential

In the present work, chlorine doped hydroxyapatite (ClHA), with varying degrees of ion replacement was successfully synthesized by a simple ball milling technique. The resulting powders were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Field emission scanning electron microscopy and particle size analyzer. The zeta potential of the powders was performed in physiological saline (0.154 M). The results confirmed the formation of apatite as the main phase in all chlorine substituted powders except for some incremental changes in the lattice parameter ‘a’ and unit cell volumes of the resultant powders. However, the crystallinity of the powders declined from 96% to 83%. Fourier transform infrared spectroscopy results confirmed the incorporation of Cl ions in the apatite lattice by the appearance of new bands at 677 cm^-1. FESEM results revealed that the crystallites have grown into grains with no major agglomeration. Vicker hardness test results revealed a hardness value of 2.65 ± 0.258 GPa for ClHA4 dense bodies at a load of 200g. Zeta potential analysis of the powders suggested that ClHA nanopowders can prove to be a potential bone implant material.     

Enhanced photocatalytic performance of ZnO/multi-walled carbon nanotube nanocomposites for dye degradation

The ZnO nanowire/multi-walled carbon nanotube (MWNT) nanocomposites have been successfully synthesized by one-step hydrothermal method using zinc chloride as Zn source. Their photocatalytic degradation performances on methylene blue and Rhodamine 6G have been investigated under UV irradiation. Experimental results show that the photocatalytic efficiency of the as-synthesized ZnO/MWNT nanocomposites is 3 times higher than that of pure ZnO nanowires. The enhanced photocatalytic activity is attributed to the fast transfer of photo-generated electrons from ZnO to MWNTs, leading to low recombination rate of photo-induced electron–hole pairs.     

Synthesis and characterization of spinel–forsterite nanocomposites

Although micron size forsterite is biocompatible, the degradation rate of this ceramic is extremely low, and the apatite formation ability is poor as well. In this study, the influence of nanostructure and the degree of crystallinity on the apatite formation ability and degradation rate were investigated. Forsterite was synthesized by 5 h of milling of talc and magnesium carbonate and subsequent annealing at 1000 °C in the presence of chloride ion. To investigate the in vitro bioactivity and degradability, the prepared forsterite powder was pressed in the form of tablets and then immersed in simulated body fluid (SBF) and Ringer's solution, respectively. The results showed that nanostructure forsterite powder with crystallite size of about 20 nm was bioactive and released magnesium ions in the SBF solution. With increasing crystallinity degree of nanostructure forsterite, the apatite formation ability and degradation rate decreased.     

Size and morphology-controlled synthesis of mesoporous hydroxyapatite nanocrystals by microwave-assisted hydrothermal method

We report the rapid microwave-assisted hydrothermal synthesis of mesoporous hydroxyapatite (HAp) nanocrystals with controlled size, morphology, and surface area using various organic modifiers as regulators. The products were analyzed for their crystalline nature, phase purity, morphology, particle size and pore size distribution. Results indicated that ascorbic acid, cetyltrimethyl ammonium bromide (CTAB) and polyvinylpyrrolidone (PVP) play an important role to obtain needle like, rod like and fiber like mesoporous HAp nanocrystals with different specific surface area by controlling growth habit of HAp along c-axis. In addition, the prepared samples were B-type carbonated HAp similar to bone minerals. Therefore, the present approach can be a promising way to obtain precursor for making tissue engineering scaffolds, drug/protein delivery carriers and bone fillers with tunable characteristics.     

Influence of concentration of hydroxyapatite surface modifier agent on bioactive composite characteristics

The characterization of chitosan – hydroxyapatite (CH – HAp) composite sponges prepared via freeze-drying methodology is reported in this study. Stearic acid (SA), added as a surface modifier of the HAp nanoparticles, induced changes in the TG/DTG results, particle size distribution and particle morphology. Composite sponges prepared with SA coated HAp demonstrated enhanced biocompatibility and structural properties, as compared to the composites prepared with uncoated HAp. SA coating modified the morphology of the composite, promoting a better dispersion of HAp particles within the composite sponges, and better homogeneity of the polymeric cover with HAp particles. The viability of the composites for cell culture applications was analyzed, and the results suggest that the sponges are biocompatible. Therefore, SA proved to be a good candidate for surface coating of HAp nanoparticles prevent agglomerations, and could be used effectively in the preparation of biocompatible composite sponges with chitosan.     

One step method to synthesize flower-like hydroxyapatite architecture using mussel shell bio-waste as a calcium source

Mussel shell, a calcium-rich resource, is found plenty in nature. We have developed a novel and facile method to convert mussel shell bio-waste into hydroxyapatite (HAp) biomaterial using microwave irradiation with the aid of ethylenediaminetetraacetic acid (EDTA) as chelating agent. The obtained HAp had flower-like morphology which can be a potential candidate for developing biomaterial for orthopedic applications. Moreover, the developed method has the potential to recover the bio-waste and reduce environment pollution.