Biocompatible Mn2+-doped carbonated hydroxyapatite thin films grown by pulsed laser deposition

A natural biogenic fluorapatite as a new biomaterial for orthopedics and dentistry: antibacterial activity of lingula seashell and its use for nanostructured biomimetic coatings

Calcium phosphates are widely studied in orthopedics and dentistry, to obtain biomimetic and antibacterial implants. However, the multi-substituted composition of mineralized tissues is not fully reproducible from synthetic procedures. Here, for the first time, we investigate the possible use of a natural, fluorapatite-based material, i.e., Lingula anatina seashell, resembling the composition of bone and enamel, as a biomaterial source for orthopedics and dentistry. Indeed, thanks to its unique mineralization process and conditions, L. anatina seashell is among the few natural apatite-based shells, and naturally contains ions having possible antibacterial efficacy, i.e., fluorine and zinc. After characterization, we explore its deposition by ionized jet deposition (IJD), to obtain nanostructured coatings for implantable devices. For the first time, we demonstrate that L. anatina seashells have strong antibacterial properties. Indeed, they significantly inhibit planktonic growth and cell adhesion of both Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli. The two strains show different susceptibility to the mineral and organic parts of the seashells, the first being more susceptible to zinc and fluorine in the mineral part, and the second to the organic (chitin-based) component. Upon deposition by IJD, all films exhibit a nanostructured morphology and sub-micrometric thickness. The multi-doped, complex composition of the target is maintained in the coating, demonstrating the feasibility of deposition of coatings starting from biogenic precursors (seashells). In conclusion, Lingula seashell-based coatings are non-cytotoxic with strong antimicrobial capability, especially against Gram-positive strains, consistently with their higher susceptibility to fluorine and zinc. Importantly, these properties are improved compared to synthetic fluorapatite, showing that the films are promising for antimicrobial applications.

Substituted Hydroxyapatite, Glass, and Glass-Ceramic Thin Films Deposited by Nanosecond Pulsed Laser Deposition (PLD) for Biomedical Applications: A Systematic Review

The deposition of thin films of bioactive materials is the most common approach to improve the bone bonding ability of an implant surface. With this purpose, several wet and plasma assisted deposition methods were proposed in the scientific literature. In this review, we considered films obtained by nanosecond Pulsed Laser Deposition (PLD). Since hydroxyapatite (HA) has composition and structure similar to that of the mineral component of the bone, the initial studies focused on the selection of experimental conditions that would allow the deposition of films that retain HA stoichiometry and crystallinity. However, biological apatite was found to be a poorly crystalline and multi-substituted mineral; consequently, the attention of researchers was oriented towards the deposition of substituted HA, glass (BG), and glass-ceramic (BGC) bioactive materials to exploit the biological relevance of foreign ions and crystallinity. In this work, after a description of the nanosecond ablation and film growth of ceramic materials, we reported studies on the mechanism of HA ablation and deposition, evidencing the peculiarities of PLD. The literature concerning the PLD of ion substituted HA, BG, and BGC was then reviewed and the performances of the coatings were discussed. We concluded by describing the advantages, limitations, and perspectives of PLD for biomedical applications.

Efficient antibacterial activity of hydroxyapatite through ROS generation motivated by trace Mn(iii) coupled H vacancies

Hydroxyapatite (HA) has attracted wide attention for medical application due to its biocompatibility and bioactivity. However, the infection problems of HA remain among the leading reasons for implantation failure. Thus, it is urgent to endow HA biomaterials with antibacterial activity. Herein, the high antibacterial activity was achieved by introducing trace Mn³⁺ and H vacancy couples in HA through a facile heat-treatment strategy in air. The theoretical results indicated that Mn³⁺ was preferentially substituted for the Ca(2) site in the HA structure with a charge-compensating H vacancy appearing at the adjacent OH^- site. The antibacterial tests showed that Mn-HA possessed antibacterial activity towards both E. coli and S. aureus with trace Mn content at the ppm level, and implied that Mn³⁺ and centers may play an important role in the antibacterial process. The Mn³⁺ and couples in Mn-HA, serving as oxidative and reductive centers respectively, could then collectively participate in the CoQ/CoQH₂ redox cycling and synergistically facilitate the accumulation of CoQ˙^- and ROS radicals. This enhanced ROS production was the main factor to endow Mn-HA with efficient antibacterial activity. Moreover, the in vitro bioactivity assay showed that Mn-HA materials exhibited enhanced osteogenic activity and good biocompatibility. Therefore, this work not only provides a feasible method to control the oxidation state of Mn elements in HA, but also proposes a novel trace Mn³⁺-doped HA for potential applications in tissue engineering.

Substituted hydroxyapatite coatings of bone implants

Surface modification of orthopedic and dental implants has been demonstrated to be an effective strategy to accelerate bone healing at early implantation times. Among the different alternatives, coating implants with a layer of hydroxyapatite (HAp) is one of the most used techniques, due to its excellent biocompatibility and osteoconductive behavior. The composition and crystalline structure of HAp allow for numerous ionic substitutions that provide added value, such as antibiotic properties or osteoinduction. In this article, we will review and critically analyze the most important advances in the field of substituted hydroxyapatite coatings. In recent years substituted HAp coatings have been deposited not only on orthopedic prostheses and dental implants, but also on macroporous scaffolds, thus expanding their applications towards bone regeneration therapies. Besides, the capability of substituted HAps to immobilize proteins and growth factors by non-covalent interactions has opened new possibilities for preparing hybrid coatings that foster bone healing processes. Finally, the most important in vivo outcomes will be discussed to understand the prospects of substituted HAp coatings from a clinical point of view.

A Review on Ionic Substitutions in Hydroxyapatite Thin Films: Towards Complete Biomimetism

Plasma sprayed coatings composed of stoichiometric hydroxyapatite have been extensively used to improve integration of metallic implants in the host bone, as hydroxyapatite (HA) is normally regarded as similar to the mineralized phase of bone. However, these coatings exhibited several drawbacks that limited their success. On the one hand biological apatite is a carbonated-HA, containing significant amounts of foreign ions, having low crystallinity and a small crystals size. This means that it differs from stoichiometric HA in terms of composition, stoichiometry, crystallinity degree, crystal size/morphology and, as a direct consequence, solubility, and ions release in the peri-implant environment. On the other hand, thick plasma sprayed coatings can undergo cracking and delamination and are scarcely uniform. For these reasons, research is pushing into two directions: (i) Increasing the similarity of apatite coatings to real bone, and (ii) exploring deposition by alternative plasma assisted techniques, allowing to achieve thin films, and having superior adhesion and a better control over the coating composition. In this article, we review the latest advances in the field of plasma-assisted deposition of ion-substituted hydroxyapatite thin films, highlighting the state of the art, the limitations, potentialities, open challenges, and the future scenarios for their application.

Mn-containing titanium surface with favorable osteogenic and antimicrobial functions synthesized by PIII&D

Reasonable incorporation of manganese into titanium is believed to be able to enhance the osteogenic and antibacterial activities of orthopedic implants. However, it is still a challenge to compromise Mn-induced cytotoxicity and better develop its biocompatibility and antimicrobial ability. To pinpoint this issue, a stable Mn ion release platform was created on Ti using plasma immersion ion implantation and deposition (PIII&D) technique. Compared with as-etched titanium, as a result, promoted antibacterial abilities against gram-negative bacteria species and enhanced osteogenic-related gene expressions on rBMMSC were observed on Mn-containing sample. Meanwhile, the Mn-containing samples showed no obvious cytotoxicity. Our results here provide insight to be better understanding the relationships between additives-induced biological performance and the dose, state, and stability of the doped element.

Mechanical preparation of nanocrystalline biocompatible single-phase Mn-doped A-type carbonated hydroxyapatite (A-cHAp): effect of Mn doping on microstructure

Mn substitution reduces Ca2/Mn–O bond lengths leading to structural changes in the A-cHAp lattice.

Characterisation, corrosion resistance and in vitro bioactivity of manganese-doped hydroxyapatite films electrodeposited on titanium

This work elucidated the corrosion resistance and in vitro bioactivity of electroplated manganese-doped hydroxyapatite (MnHAp) film on NaOH-treated titanium (Ti). The NaOH treatment process was performed on Ti surface to enhance the adhesion of the MnHAp coating on Ti. Scanning electron microscopy images showed that the MnHAp coating had needle-like apatite crystals, and the approximately 10 μm thick layer was denser than HAp. Energy-dispersive X-ray spectroscopy analysis revealed that the MnHAp crystals were Ca-deficient and the Mn/P molar ratio was 0.048. X-ray diffraction confirmed the presence of single-phase MnHAp, which was aligned vertically to the substrate. Fourier transform infrared spectroscopy indicated the presence of phosphate bands ranging from 500 to 650 and 900 to 1,100 cm(-1), and a hydroxyl band at 3,571 cm(-1), which was characteristic of HAp. Bond strength test revealed that adhesion for the MnHAp coating was more enhanced than that of the HAp coating. Potentiodynamic polarisation test showed that the MnHAp-coated surface exhibited superior corrosion resistance over the HAp single-coated surface. Bioactivity test conducted by immersing the coatings in simulated body fluid showed that MnHAp coating can rapidly induce bone-like apatite nucleation and growth. Osteoblast cellular tests revealed that the MnHAp coating was better at improving the in vitro biocompatibility of Ti than the HAp coating.

Physicochemical investigation of pulsed laser deposited carbonated hydroxyapatite films on titanium

Carbonated hydroxyapatite (CHA)-coated titanium can find wide applications as bone substitute implant in bone and dental surgery and orthopedics, promoting osseointegration with a host bone and ensuring biocompatibility and bioactivity. In this work, carbonated hydroxyapatite films were prepared on titanium substrates by pulsed laser deposition at different substrate temperatures ranging from 30 to 750 degrees C. The properties of films were investigated by scanning electron microscopy, atomic force microscopy, energy-dispersive X-ray diffraction, and Fourier transform infrared spectroscopy. Vickers microhardness measurements of the composite film-substrate systems were performed, and the intrinsic hardness of films was separated from the composite hardness using a "law-of-mixtures" approach and taking into account the indentation size effect. The prepared CHA films are nearly stoichiometric with a Ca/P atomic ratio of 2.0-2.2. The films deposited in the 30-500 degrees C temperature range are about 9 microm thick, amorphous, having an average roughness of 60 nm. At higher temperature, 700-750 degrees C, the films are about 4 microm thick, show a finer surface morphology and an average roughness of 20 nm. At 750 degrees C the films are amorphous, whereas at 700 degrees C they are crystalline and textured along the (202) and (212) directions. The intrinsic hardness of the films increased with an increase in substrate temperature, being as low as 5 GPa at 30 degrees C and reaching a high value of 28 GPa at 700 degrees C. The rich information gained by the joint use of the mentioned techniques allowed a comprehensive characterization of this system.

Strontium-substituted hydroxyapatite coatings synthesized by pulsed-laser deposition: in vitro osteoblast and osteoclast response

The increasing interest in strontium incorporation into biomaterials for hard tissue repair is justified by the growing evidence of its beneficial effect on bone. We successfully synthesized hydroxyapatite (HA) thin films with different extents of strontium substitution for calcium (0, 1, 3 or 7 at.%) by pulsed-laser deposition. The coatings displayed a granular surface and a good degree of crystallinity, which slightly diminished as strontium content increased. Osteoblast-like MG63 cells and human osteoclasts were cultured on the thin films up to 21 days. MG63 cells grown on the strontium-doped HA coatings displayed normal morphology, good proliferation and increased values of the differentiation parameters, whereas the number of osteoclasts was negatively influenced by the presence of strontium. The positive effect of the ion on bone cells was particularly evident in the case of coatings deposited from HA at relatively high strontium contents (3-7%), where significantly increased values of alkaline phosphatase activity, osteocalcin, type I collagen and osteoprotegerin/TNF-related activation-induced cytokine receptor ratio, and considerably reduced values of osteoclast proliferation, were observed.

Cytocompatibility of calcium phosphate coatings deposited by an ArF pulsed laser

In the current studies, we deposited ultra-thin hydroxyapatite films on a pure titanium substrate by pulsed laser deposition, and we examined the effects of these surfaces on rat bone marrow (RBM) cells. This method allowed deposition of 500-, 2,000-, and 5,000-A-thick hydroxyapatite films. X-ray diffraction showed that the amorphous films recrystallized to a hydroxyapatite crystal structure after annealing. The proliferation of RBM cells was unaffected by the hydroxyapatite films, but osteocalsin and alkaline phosphatase mRNA and protein levels were elevated in cells grown on 2,000- and 5,000-A-thick films. These results indicate that ultra-thin hydroxyapatite films generated by pulsed laser deposition are better at promoting osteogenesis than pure titanium surfaces.

Cytocompatibility of calcium phosphate coatings deposited by an ArF pulsed laser

In the current studies, we deposited ultra-thin hydroxyapatite films on a pure titanium substrate by pulsed laser deposition, and we examined the effects of these surfaces on rat bone marrow (RBM) cells. This method allowed deposition of 500-, 2000-, and 5000-Angstrom-thick hydroxyapatite films. X-ray diffraction showed that the amorphous films recrystallized to a hydroxyapatite crystal structure after annealing. The proliferation of RBM cells was unaffected by the hydroxyapatite films, but osteocalsin and alkaline phosphatase mRNA and protein levels were elevated in cells grown on 2000- and 5000-Angstrom-thick films. These results indicate that ultra-thin hydroxyapatite films generated by pulsed laser deposition are better at promoting osteogenesis than pure titanium surfaces.

Human osteoblast response to pulsed laser deposited calcium phosphate coatings

Octacalcium phosphate (OCP) and Mn(2+)-doped carbonate hydroxyapatite (Mn-CHA) thin films were deposited on pure, highly polished and chemically etched Ti substrates with pulsed laser deposition. The coatings exhibit different composition, crystallinity and morphology that might affect their osteoconductivity. Human osteoblasts were cultured on the surfaces of OCP and Mn-CHA thin films, and the cell attachment, proliferation and differentiation were evaluated up to 21 days. The cells showed a normal morphology and a very good rate of proliferation and viability in every experimental time. Alkaline phosphatase activity was always higher than the control and Ti groups. From days 7 to 21 collagen type I production was higher in comparison with control and Ti groups. The level of transforming growth factor beta 1 (TGF-beta1) was lower at 3 and 7 days, but reached the highest values during following experimental times (14 and 21 days). Our data demonstrate that both calcium phosphate coatings favour osteoblasts proliferation, activation of their metabolism and differentiation.