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Extensive research into magnesium (Mg) alloys highlights their possible applications in the field of biodegradable implants. As magnesium alloys are highly electronegative, it is imperative to tailor their degradation rate for clinical safety. Surface coatings have been widely used for the corrosion protection of Mg alloys, but the presence of spatial defects limits their effectiveness. An innovative and near-defect-free hydroxyapatite (HA)-TiO2 nano-channeled (TNC) coating architecture has been developed on ZM21 Mg alloy in the present study by combining anodization and the sol-gel dip coating technique. The HA-TNC coating positively shifted the Ecorr of ZM21 Mg alloy from −1.38 to −0.61 V. Accordingly, the corrosion current density (Icorr, 5.8 × 10−6 A/cm2) was suppressed by 53.4 times compared to uncoated ZM21 Mg alloy. The polarization resistance (Rp) and charge transfer resistance (Rct) values are the highest among all other samples, indicating the superior shielding ability of the coating. During in vitro immersion for up to 28 days in simulated body fluid (SBF), the HA−TNC coating maintained the lowest degradation rate and hydrogen evolution rate (HER) of 1.10 ± 0.22 mg/cm2/day and 1.83 ± 0.41 mL/cm2/day, respectively. A compact and structurally stable 2D plate-like HA (Ca/P:1.55), mineralized on HA-TNC-coated ZM21, provides effective shielding against the penetration of aggressive ions with prolonged SBF immersion. The findings of the present study provide a rational design for the development of bioactive ceramic coatings on Mg-based bioimplants. [ABSTRACT FROM AUTHOR]

Various types of materials have been traditionally used to restore damaged bones. In the late 1960s, a strong interest was raised in studying ceramics as potential bone grafts due to their biomechanical properties. A short time later, such synthetic biomaterials were called bioceramics. Bioceramics can be prepared from diverse inorganic substances, but this review is limited to calcium orthophosphate (CaPO4)-based formulations only, due to its chemical similarity to mammalian bones and teeth. During the past 50 years, there have been a number of important achievements in this field. Namely, after the initial development of bioceramics that was just tolerated in the physiological environment, an emphasis was shifted towards the formulations able to form direct chemical bonds with the adjacent bones. Afterwards, by the structural and compositional controls, it became possible to choose whether the CaPO4-based implants would remain biologically stable once incorporated into the skeletal structure or whether they would be resorbed over time. At the turn of the millennium, a new concept of regenerative bioceramics was developed, and such formulations became an integrated part of the tissue engineering approach. Now, CaPO4-based scaffolds are designed to induce bone formation and vascularization. These scaffolds are usually porous and harbor various biomolecules and/or cells. Therefore, current biomedical applications of CaPO4-based bioceramics include artificial bone grafts, bone augmentations, maxillofacial reconstruction, spinal fusion, and periodontal disease repairs, as well as bone fillers after tumor surgery. Prospective future applications comprise drug delivery and tissue engineering purposes because CaPO4 appear to be promising carriers of growth factors, bioactive peptides, and various types of cells. [ABSTRACT FROM AUTHOR]

In recent years, significant progress has been made in the development of new technologies to meet the demand for engineered interfaces with appropriate properties for osteochondral unit repair and regeneration. In this context, we combined two methodologies that have emerged as powerful approaches for tissue engineering application: electrospinning to fabricate a nanofibrous polymeric scaffold and pulsed laser deposition to tune and control the composition and morphology of the scaffold surface. A multi-component scaffold composed of synthetic and natural polymers was proposed to combine the biocompatibility and suitable mechanical properties of poly(D,L-lactic acid) with the hydrophilicity and cellular affinity of gelatin. As part of a biomimetic strategy for the generation of bi-functional scaffolds, we coated the electrospun fibers with a thin film of a bioactive glass–ceramic material supplemented with manganese ions. The physico-chemical properties and composition of the bi-layered scaffold were investigated, and its bioactivity, in terms of induced mineralization, was tested by incubation in a simulated body fluid buffer. The processes of the inorganic film dissolution and the calcium phosphate phases growth were followed by microscopic and spectroscopic techniques, confirming that a combination of bioactive glass–ceramics and nanofibrous scaffolds has promising potential in the regeneration of osteochondral tissue due to its ability to induce mineralization in connective tissues. [ABSTRACT FROM AUTHOR]

Hydroxyapatite (HA) is a significant constituent of bones or teeth and is widely used as an artificial bone graft. It is often used to replace the lost bones or in reconstructing alveolar bones before dental implantation. HA with biological functions finds its importance in orthopedic surgery and dentistry to increase the local concentration of calcium ions, which activate the growth and differentiation of mesenchymal stem cells (MSC). To make relevant use of HA in bone transplantation, the surfaces of orthopedic and dental implants are frequently coated with nanosized hydroxyapatite (nHA), but its low dispersibility and tendency to form aggregates, the purpose of the surface modification of bone implants is defeated. To overcome these drawbacks and to improve the histocompatibility of bone implants or to use nHA in therapeutic applications of implants in the treatment of bone diseases, various studies suggested the attachment of biomolecules (growth factors) or drugs through chemical bonding at the surface of nHA. The growth factors or drugs bonded physically at the surface of nHA are mostly unstable and burst released immediately. Therefore, reported studies suggested that the surface of nHA needs to be modified through the chemical bonding of biologically active molecules at the surface of bone implants such as proteins, peptides, or naturally occurring polysaccharides to prevent the aggregation of nHA and to get homogenous dispersion of nHA in solution. The role of irradiation in producing bioactive and antibacterial nHA through morphological variations in surfaces of nHA is also summarized by considering internal structures and the formation of reactive oxygen species on irradiation. This mini-review aims to highlight the importance of small molecules such as proteins, peptides, drugs, and photocatalysts in surface property modification of nHA to achieve stable, bioactive, and antibacterial nHA to act as artificial bone implants (scaffolds) in combination with biodegradable polymers. [ABSTRACT FROM AUTHOR]

The mechanical and biological properties of bone implants need to be optimal to form a quick and firm connection with the surrounding environment in load bearing applications. Bone is a connective tissue composed of an organic collagenous matrix, a fine dispersion of reinforcing inorganic (calcium phosphate) nanocrystals, and bone-forming and -degrading cells. These different components have a synergistic and hierarchical structure that renders bone tissue properties unique in terms of hardness, flexibility and regenerative capacity. Metallic and polymeric materials offer mechanical strength and/or resilience that are required to simulate bone tissue in load-bearing applications in terms of maximum load, bending and fatigue strength. Nevertheless, the interaction between devices and the surrounding tissue at the implant interface is essential for success or failure of implants. In that respect, coatings can be applied to facilitate the process of bone healing and obtain a continuous transition from living tissue to the synthetic implant. Compounds that are inspired by inorganic (e.g., hydroxyapatite crystals) or organic (e.g., collagen, extracellular matrix components, enzymes) components of bone tissue, are the most obvious candidates for application as implant coating to improve the performance of bone implants. This review provides an overview of recent trends and strategies in surface engineering that are currently investigated to improve the biological performance of bone implants in terms of functionality and biological efficacy. [ABSTRACT FROM AUTHOR]

Biomaterials are in use for the replacement and reconstruction of several tissues and organs as treatment and enhancement. Metallic, organic, and composites are some of the common materials currently in practice. Metallic materials contribute a big share of their mechanical strength and resistance to corrosion properties, while organic polymeric materials stand high due to their biocompatibility, biodegradability, and natural availability. To enhance the biocompatibility of these metals and alloys, coatings are frequently applied. Organic polymeric materials and ceramics are extensively utilized for this purpose due to their outstanding characteristics of biocompatibility and biodegradability. Hydroxyapatite (HAp) is the material from the ceramic class which is an ultimate candidate for coating on these metals for biomedical applications. HAp possesses similar chemical and structural characteristics to normal human bone. Due to the bioactivity and biocompatibility of HAp, it is used for bone implants for regenerating bone tissues. This review covers an extensive study of the development of HAp coatings specifically for the orthopaedic applications that include different coating techniques and the process parameters of these coating techniques. Additionally, the future direction and challenges have been also discussed briefly in this review, including the coating of HAp in combination with other calcium magnesium phosphates that occur naturally in human bone. [ABSTRACT FROM AUTHOR]

In this work, an interdisciplinary approach was employed to investigate the impact on thermoplastic catheters from the deposition of a thin (180 nm), metallic silver film by a pulsed ablation technique. Our characterization firstly involved tensile and bending tests, each one accompanied by finite element modeling aiming to elucidate the contributions resulting from bulk and coating to the device's mechanical behavior. The morphological assessment of the surface before and after the deposition was performed by atomic force microscopy, specifically implemented to visualize the nanostructured character of the film surface and the extent to which the polymer was modified by the deposition process, focusing on coating delamination due to tensile stress. Finally, thermogravimetric–differential thermal analysis was carried out to evaluate whether silver deposition has affected the physiochemical structure of the polymer matrix. Our results establish that the deposition does not significantly alter the physical and chemical properties of the device. The presented characterization sets a useful precedent for elucidating how structural properties of polymeric materials may change after coating by electronic ablation techniques, highlighting the importance of employing a comprehensive approach for clarifying the effects of additive manufacturing on medical devices. [ABSTRACT FROM AUTHOR]

Bone regeneration is a complex, well-organized physiological process of bone formation observed during normal fracture healing and involved in continuous remodeling throughout adult life. An ideal medical device for bone regeneration requires interconnected pores within the device to allow for penetration of blood vessels and cells, enabling material biodegradation and bone ingrowth. Additional mandatory characteristics include an excellent resorption rate, a 3D structure similar to natural bone, biocompatibility, and customizability to multiple patient-specific geometries combined with adequate mechanical strength. Therefore, endless silk fibers were spun from native silk solution isolated from silkworm larvae and functionalized with osteoconductive bioceramic materials. In addition, transgenic silkworms were generated to functionalize silk proteins with human platelet-derived growth factor (hPDGF). Both, PDGF-silk and bioceramic modified silk were then assembled into 3D textile implants using an additive manufacturing approach. Textile implants were characterized in terms of porosity, compressive strength, and cyclic load. In addition, osteogenic differentiation of mesenchymal stem cells was evaluated. Silk fiber-based 3D textile implants showed good cytocompatibility and stem cells cultured on bioceramic material functionalized silk implants were differentiating into bone cells. Thus, functionalized 3D interconnected porous textile scaffolds were shown to be promising biomaterials for bone regeneration. [ABSTRACT FROM AUTHOR]

Electrophoretic deposition (EPD) was used to produce a multilayer coatings system based on chitosan/curcumin coatings on poly-ether-ether-ketone (PEEK)/bioactive glass (BG)/hexagonal boron nitride (h-BN) layers (previously deposited by EPD on 316L stainless steel) to yield bioactive and antibacterial coatings intended for orthopedic implants. Initially, PEEK/BG/h-BN coatings developed on 316L stainless steel (SS) substrates were analyzed for wear studies. Then, the EPD of chitosan/curcumin was optimized on 316L SS for suspension stability, thickness, and homogeneity of the coatings. Subsequently, the optimized EPD parameters were applied to produce chitosan/curcumin coatings on the PEEK/BG/h-BN layers. The multilayered coatings produced by EPD were characterized in terms of composition, microstructure, drug release kinetics, antibacterial activity, and in vitro bioactivity. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) confirmed the deposition of chitosan/curcumin on the multilayer coating system. The release of curcumin upon immersion of multilayer coatings in phosphate-buffered saline (PBS) was confirmed by ultraviolet/visible (UV/VIS) spectroscopic analysis. The antibacterial effect of chitosan/curcumin as the top coating was determined by turbidity tests (optical density measurements). Moreover, the multilayer coating system formed an apatite-like layer upon immersion in simulated body fluid (SBF), which is similar in composition to the hydroxyapatite component of bone, confirming the possibility of achieving close bonding between bone and the coating surface. [ABSTRACT FROM AUTHOR]

The main problem of orthopedic and dental titanium (Ti) implants has been poor bone-bonding to the metal. Various coatings to improve the bone-bonding, including the hydroxyapatite and titania, have been developed, and some of them have been to successfully applied clinical use. On the other hand, there are still challenges to provide antibacterial activity and promotion of bone growth on Ti. It was shown that a calcium-deficient calcium titanate coating on Ti and its alloys exhibits high bone-bonding owing to its apatite formation. In this study, Sr and Ag ions, known for their promotion of bone growth and antibacterial activity, were introduced into the calcium-deficient calcium titanate by a three-step aqueous solution treatment combined with heat. The treated metal formed apatite within 3 days in a simulated body fluid and exhibited antibacterial activity to Escherichia coli without showing any cytotoxicity in MC3T3-E1 preosteoblast cells. Furthermore, the metal slowly released 1.29 ppm of Sr ions. The Ti with calcium-deficient calcium titanate doped with Sr and Ag will be useful for orthopedic and dental implants, since it should bond to bone because of its apatite formation, promote bone growth due to Sr ion release, and prevent infection owing to its antibacterial activity. [ABSTRACT FROM AUTHOR]

Carbonated hydroxyapatite derivatives (CHAp) and its metallic derivatives (Ag, Sr, Ba, K, Zn) have been prepared and characterized in this paper and their coating capacity on some model stone samples have been evaluated and discussed. These compounds were characterized by using several analytical tools, including X-ray diffraction analysis (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), to determine the purity of the CHAp sample. The XRD and FTIR results confirmed the presence of AB-carbonated type CHAp. The thermal analysis (TGA) established two stages of weight loss that occured during the heating process: The first weight loss between 30–225 °C corresponding to the partial carbonate release from OH-channel and the second one between 226–700 °C, corresponding to some thermal reactions, possibly to the generation of calcium phosphate. The efficiency and suitability of these products on model stone samples were evaluated by monitoring the resistance to artificial weather (freeze–thaw), and pore structure changes (surface area, pore volume, pore diameter). Meanwhile, optical microscopy (OM) and Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM–EDS) techniques showed the particles size and surface morphology of the samples, as well as information on its chemical composition. Also, the compressive strength of these new compounds as coatings revealed a homogeneity and strengthen of these model stone samples. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]