There Are over 60 Ways to Produce Biocompatible Calcium Orthophosphate (CaPO4) Deposits on Various Substrates

A The present overview describes various production techniques for biocompatible calcium orthophosphate (abbreviated as CaPO4) deposits (coatings, films and layers) on the surfaces of various types of substrates to impart the biocompatible properties for artificial bone grafts. Since, after being implanted, the grafts always interact with the surrounding biological tissues at the interfaces, their surface properties are considered critical to clinical success. Due to the limited number of materials that can be tolerated in vivo, a new specialty of surface engineering has been developed to desirably modify any unacceptable material surface characteristics while maintaining the useful bulk performance. In 1975, the development of this approach led to the emergence of a special class of artificial bone grafts, in which various mechanically stable (and thus suitable for load-bearing applications) implantable biomaterials and artificial devices were coated with CaPO4. Since then, more than 7500 papers have been published on this subject and more than 500 new publications are added annually. In this review, a comprehensive analysis of the available literature has been performed with the main goal of finding as many deposition techniques as possible and more than 60 methods (double that if all known modifications are counted) for producing CaPO4 deposits on various substrates have been systematically described. Thus, besides the introduction, general knowledge and terminology, this review consists of two unequal parts. The first (bigger) part is a comprehensive summary of the known CaPO4 deposition techniques both currently used and discontinued/underdeveloped ones with brief descriptions of their major physical and chemical principles coupled with the key process parameters (when possible) to inform readers of their existence and remind them of the unused ones. The second (smaller) part includes fleeting essays on the most important properties and current biomedical applications of the CaPO4 deposits with an indication of possible future developments.

Calcium Orthophosphate (CaPO4)-Based Bioceramics: Preparation, Properties, and Applications

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.

Characterization and Evaluation of Composite Biomaterial Bioactive Glass-Polylactic Acid for Bone Tissue Engineering Applications

The limitations associated with the clinical use of autographs and allografts are driving efforts to develop relevant and applicable biomaterial substitutes. In this research, 3D porous scaffolds composed of bioactive glass (BG) obtained through the sol-gel technique and polylactic acid (PLA) synthesized via lactic acid (LA) ring-opening polymerization were prepared by the gel-pressing technique. Two different weight compositions were evaluated, namely, BG70-PLA30 and BG30-PLA70. The structure and morphology of the resulting scaffolds were analysed by FTIR, XRD, SEM, and under ASTM F1635 standard characterizations. The results confirmed that BG promotes the formation of a hydroxy-carbonated apatite (HAp) layer on composites when immersed in simulated body fluid (SBF). Biodegradability evaluations were carried out according to the ISO 10993-13:2010 standard. In addition, electrochemical evaluations were performed in both Hank's and SBF solutions at 37 °C in order to analyse the degradation of the material. This evaluation allowed us to observe that both samples showed an activation mechanism in the early stages followed by pseudo-passivation due to physical bioactive glass characteristics, suggesting an improvement in the formation of the HAp nucleation. The described composites showed excellent resistance to degradation and outstanding suitability for bone tissue engineering applications.

Development of Bioactive Glass-Collagen-Hyaluronic Acid-Polycaprolactone Scaffolds for Tissue Engineering Applications

In this work, bioactive glass (BG) particles synthesized by a sol-gel method, hyaluronic acid (HYA) and collagen (COL) extracted from chicken eggshell membrane (ESM), and as-purchased polycaprolactone (PCL) were used to obtain a novel bioactive scaffold using the gel-pressing technique. Two composite mixtures in weight percent were obtained and identified as SCF-1 and SCF-2, and were characterized by using FTIR, XRD, and SEM techniques. Subsequently, the composite materials applied as coatings were evaluated in simulated body fluid solutions using electrochemical techniques. The results of bioactivity and biodegradability evaluations, carried out by immersing in simulated body fluid and phosphate-buffered saline solution, showed that the SCF-1 sample presented the best biocompatibility. In accordance with the potentiodynamic results, the 316L-SS and the SCF-1-coated SS showed a very similar corrosion potential (Ecorr), around −228 mV, and current density (icorr) values in close proximity, while the SCF-2-coated SS showed more positive Ecorr around −68 mV and lower icorr value in one order of magnitude. These results agree with those obtained by electrochemical impedance spectroscopy, which show a corrosion mechanism governed by activation and finite diffusion through the porous layer. In addition, results were complemented by dynamic compression testing under oscillating forces to identify the developed scaffolds’ response under external forces, where the SCF-1 scaffold presented a maximum compression. The degradation resistance, bioactivity, and mechanically obtained measurements provided interesting results for potential further studies in tissue engineering.

Bioactive Glass—An Extensive Study of the Preparation and Coating Methods

Diseases or complications that are caused by bone tissue damage affect millions of patients every year. Orthopedic and dental implants have become important treatment options for replacing and repairing missing or damaged parts of bones and teeth. In order to use a material in the manufacture of implants, the material must meet several requirements, such as mechanical stability, elasticity, biocompatibility, hydrophilicity, corrosion resistance, and non-toxicity. In the 1970s, a biocompatible glassy material called bioactive glass was discovered. At a later time, several glass materials with similar properties were developed. This material has a big potential to be used in formulating medical devices, but its fragility is an important disadvantage. The use of bioactive glasses in the form of coatings on metal substrates allows the combination of the mechanical hardness of the metal and the biocompatibility of the bioactive glass. In this review, an extensive study of the literature was conducted regarding the preparation methods of bioactive glass and the different techniques of coating on various substrates, such as stainless steel, titanium, and their alloys. Furthermore, the main doping agents that can be used to impart special properties to the bioactive glass coatings are described.

On enhancement and control of green emission of rare earth co-doped hydroxyapatite nanoparticles: synthesis and upconversion luminescence properties

In this work, low-temperature hydrothermal synthesis of a series of xMo–1%Er–10%Yb (x:mol%) doped hydroxyapatite (HA) phosphors was studied.

Evaluation of the Antibacterial Activity and Cell Response for 3D-Printed Polycaprolactone/Nanohydroxyapatite Scaffold with Zinc Oxide Coating

Among 3D-printed composite scaffolds for bone tissue engineering, researchers have been attracted to the use of zinc ions to improve the scaffold's anti-bacterial activity and prevent surgical site infection. In this study, we assumed that the concentration of zinc ions released from the scaffold will be correlated with the thickness of the zinc oxide coating on 3D-printed scaffolds. We investigated the adequate thickness of zinc oxide coating by comparing different scaffolds' characteristics, antibacterial activity, and in vitro cell response. The scaffolds' compressive modulus decreased as the zinc oxide coating thickness increased (10, 100 and 200 nm). However, the compressive modulus of scaffolds in this study were superior to those of other reported scaffolds because our scaffolds had a kagome structure and were made of composite material. In regard to the antibacterial activity and in vitro cell response, the in vitro cell proliferation on scaffolds with a zinc oxide coating was higher than that of the control scaffold. Moreover, the antibacterial activity of scaffolds with 100 or 200 nm-thick zinc oxide coating on Escherichia coli was superior to that of other scaffolds. Therefore, we concluded that the scaffold with a 100 nm-thick zinc oxide coating was the most appropriate scaffold to use as a bone-regenerating scaffold, given its mechanical property, its antibacterial activity, and its in vitro cell proliferation.

Crystallization Behavior of the Low-Temperature Mineralization Sintering Process for Glass Nanoparticles

Bioactive glasses are promising materials for various applications, such as bone grafts and implants. The development of sintering techniques for bioactive glasses is one of the most important ways to expand the application to biomaterials. In this paper, we demonstrate the low-temperature mineralization sintering process (LMSP) of glass nanoparticles and their crystallization behavior. LMSP is a novel process employed to densify glass nanoparticles at an extremely low temperature of 120 °C. For this new approach, the hydrothermal condition, mineralization, and the nanosize effect are integrated into LMSP. To induce mineralization in LMSP, bioactive glass nanoparticles (BGNPs, 55SiO2-40CaO-5P2O5, mol%), prepared by the sol-gel process, were mixed with a small amount of simulated body fluid (SBF) solution. As a result, 93% dense BGNPs were realized under a temperature of 120 °C and a uniaxial pressure of 300 MPa. Due to the effect of mineralization, crystalline hydroxyapatite (HAp) was clearly formed at the boundaries of BGNPs, filling particles and interstitials. As a result, the relative density was remarkably close to that of the BGNPs conventionally sintered at 1050 °C. Additionally, the Vickers hardness value of LMSP samples varied from 2.10 ± 0.12 GPa to 4.28 ± 0.11 GPa, and was higher than that of the BGNPs conventionally sintered at 850 °C (2.02 ± 0.11 GPa). These results suggest that, in addition to LMSP being an efficient densification method for obtaining bulk bioactive glasses at a significantly lower temperature level, this process has great potential for tissue engineering applications, such as scaffolds and implants.

Pectin Methacrylate (PEMA) and Gelatin-Based Hydrogels for Cell Delivery: Converting Waste Materials into Biomaterials

The emergence of nontoxic, eco-friendly, and biocompatible polymers derived from natural sources has added a new and exciting dimension to the development of low-cost and scalable biomaterials for tissue engineering applications. Here, we have developed a mechanically strong and durable hydrogel composed of an eco-friendly biopolymer that exists within the cell walls of fruits and plants. Its trade name is pectin, and it bears many similarities with natural polysaccharides in the native extracellular matrix. Specifically, we have employed a new pathway to transform pectin into a ultraviolet (UV)-cross-linkable pectin methacrylate (PEMA) polymer. To endow this hydrogel matrix with cell differentiation and cell spreading properties, we have also incorporated thiolated gelatin into the system. Notably, we were able to fine-tune the compressive modulus of this hydrogel in the range ∼0.5 to ∼24 kPa: advantageously, our results demonstrated that the hydrogels can support growth and viability for a wide range of three-dimensionally (3D) encapsulated cells that include muscle progenitor (C2C12), neural progenitor (PC12), and human mesenchymal stem cells (hMSCs). Our results also indicate that PEMA-gelatin-encapsulated hMSCs can facilitate the formation of bonelike apatite after 5 weeks in culture. Finally, we have demonstrated that PEMA-gelatin can yield micropatterned cell-laden 3D constructs through UV light-assisted lithography. The simplicity, scalability, processability, tunability, bioactivity, and low-cost features of this new hydrogel system highlight its potential as a stem cell carrier that is capable of bridging the gap between clinic and laboratory.

Combinatorial Screening of Nanoclay-Reinforced Hydrogels: A Glimpse of the "Holy Grail" in Orthopedic Stem Cell Therapy?

Despite the promise of hydrogel-based stem cell therapies in orthopedics, a significant need still exists for the development of injectable microenvironments capable of utilizing the  regenerative potential of donor cells. Indeed, the quest for biomaterials that can direct stem cells into bone without the need of external factors has been the "Holy Grail" in orthopedic stem cell therapy for decades. To address this challenge, we have utilized a combinatorial approach to screen over 63 nanoengineered hydrogels made from alginate, hyaluronic acid, and two-dimensional nanoclays. Out of these combinations, we have identified a biomaterial that can promote osteogenesis in the absence of well-established differentiation factors such as bone morphogenetic protein 2 (BMP2) or dexamethasone. Notably, in our "hit" formulations we observed a 36-fold increase in alkaline phosphate (ALP) activity and a 11-fold increase in the formation of mineralized matrix, compared to the control hydrogel. This induced osteogenesis was further supported by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and energy-dispersive X-ray spectroscopy. Additionally, the Montmorillonite-reinforced hydrogels exhibited high osteointegration as evident from the relatively stronger adhesion to the bone explants as compared to the control. Overall, our results demonstrate the capability of combinatorial and nanoengineered biomaterials to induce bone regeneration through osteoinduction of stem cells in a natural and differentiation-factor-free environment.

In Vivo MRI and X-Ray Bifunctional Imaging of Polymeric Composite Supplemented with GdPO4 ·H2 O Nanobundles for Tracing Bone Implant and Bone Regeneration

Homogeneous and monodisperse GdPO4 ·H2 O nanobundles are successfully synthesized via a solvothermal method. Then, GdPO4 ·H2 O are incorporated into the composite of hydroxyapatite and poly(lactic-co-glycolic acid) to obtain a biodegradable and traceable bone implant. After implanted, the GdPO4 ·H2 O/HA/PLGA implant and the newly formed bone can be easily traced and observed through the combination of magnetic resonance imaging and X-ray imaging.

Silver nanoparticle-loaded hydroxyapatite coating: structure, antibacterial properties, and capacity for osteogenic induction in vitro

AgNP-HAC has the potential to be used on the surfaces of orthopedic and dental implants for infection prophylaxis.

Hybrid nanostructured hydroxyapatite-chitosan composite scaffold: bioinspired fabrication, mechanical properties and biological properties

The fabrication of bone scaffolds with interconnected porous structure, adequate mechanical properties, excellent biocompatibility and osteoinductivity presents a great challenge. Herein, a hybrid nanostructured hydroxyapatite-chitosan (HA-CS) composite scaffold has been fabricated according to the following steps: (i) the deposition of brushite-CS on a CS fibre porous scaffold by a dip-coating method; and (ii) the formation of a hybrid nanostructured HA-CS composite scaffold by the in situ conversion of brushite to HA using a bioinspired mineralization process. The hybrid HA-CS composite scaffold possesses three-dimensional (3D) interconnected pores with pore sizes of 30-80 μm. The HA rods with a length of ∼200 nm and width of ∼50 nm are perpendicularly oriented to the CS fibres. Interestingly, the abovementioned HA rods are composed of many smaller nanorods with a length of ∼40 nm and width of ∼10 nm oriented along the c-axis. The hybrid nanostructured HA-CS composite scaffold exhibits good mechanical properties with a compression strength of 9.41 ± 1.63 MPa and an elastic modulus of 0.17 ± 0.02 GPa, which are well-matched to those of trabecular bone. The influences of the hybrid HA-CS composite scaffold on cells have been investigated using human bone marrow stem cells (hBMSCs) as cell model and the CS fibre porous scaffold as the control sample. The hybrid HA-CS composite scaffold not only supports the adhesion and proliferation of hBMSCs, but also improves the osteoinductivity. The alkaline phosphatase activity and mineralization deposition on the hybrid HA-CS composite scaffold are higher than those on the CS fibre porous scaffold. Moreover, the hybrid HA-CS composite scaffold can promote the formation of new bone in rat calvarial defects as compared with the CS fibre porous scaffold. The excellent biocompatibility, osteoinductivity and mechanical properties suggest that the hybrid nanostructured HA-CS composite scaffold has great potential for bone tissue engineering.

Calcium orthophosphate deposits: Preparation, properties and biomedical applications

Since various interactions among cells, surrounding tissues and implanted biomaterials always occur at their interfaces, the surface properties of potential implants appear to be of paramount importance for the clinical success. In view of the fact that a limited amount of materials appear to be tolerated by living organisms, a special discipline called surface engineering was developed to initiate the desirable changes to the exterior properties of various materials but still maintaining their useful bulk performances. In 1975, this approach resulted in the introduction of a special class of artificial bone grafts, composed of various mechanically stable (consequently, suitable for load bearing applications) implantable biomaterials and/or bio-devices covered by calcium orthophosphates (CaPO4) to both improve biocompatibility and provide an adequate bonding to the adjacent bones. Over 5000 publications on this topic were published since then. Therefore, a thorough analysis of the available literature has been performed and about 50 (this number is doubled, if all possible modifications are counted) deposition techniques of CaPO4 have been revealed, systematized and described. These CaPO4 deposits (coatings, films and layers) used to improve the surface properties of various types of artificial implants are the topic of this review.

Nano-hydroxyapatite promotes self-assembly of honeycomb pores in poly(l-lactide) films through breath-figure method and MC3T3-E1 cell functions

The effects of nano-hydroxyapatite particles on the formation of honeycomb poly(l-lactide) films and MC3T3-E1 cell functions were investigated.

Hydroxyapatite coatings with oriented nanoplate arrays: synthesis, formation mechanism and cytocompatibility

A novel strategy has been developed to fabricate hydroxyapatite coatings with oriented nanoplate arrays for implants of human hard tissues.

Gentamicin-loaded carbonated hydroxyapatite coatings with hierarchically porous structures: drug delivery properties, bactericidal properties and biocompatibility

Gentamicin-loaded carbonated hydroxyapatite coatings as bone substitute materials can effectively treat implant-associated infection.