Calcium Orthophosphate-Containing Biocomposites and Hybrid Biomaterials for Biomedical Applications

Synergistic effects of silica-enriched bioactive glass and tri-calcium phosphate nanocomposites on BMP2 gene expression for bone repair and regeneration applications

This study focuses on the development of biomaterials for bone regeneration highlighting 59S bioactive glass (59S BG), tri-calcium phosphate (TCP), and their 1:1 composite (59S BG/TCP). The synthesized materials demonstrated excellent properties for bone tissue engineering. Characterization revealed their thermal stability up to 900 °C, as confirmed by thermogravimetric analysis (TGA), while X-ray diffraction (XRD) identified calcium phosphate and silicate phases. Functional groups and chemical bonding were elucidated using Fourier transform infrared spectroscopy (FTIR). The composite exhibited remarkable mechanical properties, with a hardness of 167.87 HV and a strength of 680.52 MPa, indicating its suitability for load-bearing applications. Biological evaluations confirmed promising performance, with in-vitro bioactivity showing apatite formation and reduced XRD peak intensity. Biocompatibility assessments revealed hemolysis below 5 % and a 300 % cell proliferation rate by day three ensuring minimal cytotoxicity and favorable blood compatibility. Protein adsorption studies demonstrated strong interactions with bovine serum albumin (BSA) and lysozyme, supporting protein stability. Additionally, the composite showed enhanced osteogenic potential with elevated BMP2 gene expression indicating its capacity to promote robust bone regeneration. The synergy between 59S BG and TCP underscores the composite's potential as a promising material for effective bone repair and regeneration.

Two decades of continuous progresses and breakthroughs in the field of bioactive ceramics and glasses driven by CICECO-hub scientists

Over the past two decades, the CICECO-hub scientists have devoted substantial efforts to advancing bioactive inorganic materials based on calcium phosphates and alkali-free bioactive glasses. A key focus has been the deliberate incorporation of therapeutic ions like Mg, Sr, Zn, Mn, or Ga to enhance osteointegration and vascularization, confer antioxidant properties, and impart antimicrobial effects, marking significant contributions to the field of biomaterials and bone tissue engineering. Such an approach is expected to circumvent the uncertainties posed by methods relying on growth factors, such as bone morphogenetic proteins, parathyroid hormone, and platelet-rich plasma, along with their associated high costs and potential adverse side effects. This comprehensive overview of CICECO-hub's significant contributions to the forefront inorganic biomaterials across all research aspects and dimensionalities (powders, granules, thin films, bulk materials, and porous structures), follows a unified approach rooted in a cohesive conceptual framework, including synthesis, characterization, and testing protocols. Tangible outcomes [injectable cements, durable implant coatings, and bone graft substitutes (scaffolds) featuring customized porous architectures for implant fixation, osteointegration, accelerated bone regeneration in critical-sized bone defects] were achieved. The manuscript showcases specific biofunctional examples of successful biomedical applications and effective translations to the market of bone grafts for advanced therapies.

Sodium Alginate/Poly (Acrylicacid) Hydrogel Composite, Potential Carrier for Fibroblast Growth Factor1 (FGF1) Delivery

Fibroblast growth factor1 is a powerful signaling molecule that plays a critical role in injury repair of diverse tissue by stimulating cell growth and angiogenesis. FGF1 has significant role in the cell fate and regulating inflammation with short half-life and poor in vivo stability. The encapsulation of the growth factor in the hydrogel led to peptide protect from the degradation and/or immune recognition and enable controlled drug delivery over a longer period of time. The aim of this study is to develop and evaluate a hydrogel carrier with adjustable release rate while maintaining bioactivity of FGF1. Here we describe an optimal ratio of sodium alginate and polyacrylic acid without additional cross linker containing optimum amount of FGF1 with the potential of sustained release to be used as a therapeutic agent. The carrier was characterized by FTIR, contact angle and swelling ratio. The activity of FGF1 after release from the hydrogel was confirmed by ELISA and Western blot. Further assessment of genes related to inflammation were evaluated by RTPCR. This hydrogel is able to deliver growth factors by restricting the essential proteins within the matrix to prevent rapid proteolysis and explosive release and is therefore widely applicable.

Biomaterials for Protein Delivery: Opportunities and Challenges to Clinical Translation

The development of biomaterials for protein delivery is an emerging field that spans materials science, bioengineering, and medicine. In this review, we highlight the immense potential of protein-delivering biomaterials as therapeutic options and discuss the multifaceted challenges inherent to the field. We address current advancements and approaches in protein delivery that leverage stimuli-responsive materials, harness advanced fabrication techniques like 3D printing, and integrate nanotechnologies for greater targeting and improved stability, efficacy, and tolerability profiles. We also discuss the demand for highly complex delivery systems to maintain structural integrity and functionality of the protein payload. Finally, we discuss barriers to clinical translation, such as biocompatibility, immunogenicity, achieving reliable controlled release, efficient and targeted delivery, stability issues, scalability of production, and navigating the regulatory landscape for such materials. Overall, this review summarizes insights from a survey of the current literature and sheds light on the interplay between innovation and the practical implementation of biomaterials for protein delivery.

Low-Temperature Calcium Phosphate Ceramics Can Modulate Monocytes and Macrophages Inflammatory Response In Vitro

Creating bioactive materials for bone tissue regeneration and augmentation remains a pertinent challenge. One of the most promising and rapidly advancing approaches involves the use of low-temperature ceramics that closely mimic the natural composition of the extracellular matrix of native bone tissue, such as Hydroxyapatite (HAp) and its phase precursors (Dicalcium Phosphate Dihydrate-DCPD, Octacalcium Phosphate-OCP, etc.). However, despite significant scientific interest, the current knowledge and understanding remain limited regarding the impact of these ceramics not only on reparative histogenesis processes but also on the immunostimulation and initiation of local aseptic inflammation leading to material rejection. Using the stable cell models of monocyte-like (THP-1ATRA) and macrophage-like (THP-1PMA) cells under the conditions of LPS-induced model inflammation in vitro, the influence of DCPD, OCP, and HAp on cell viability, ROS and intracellular NO production, phagocytosis, and the secretion of pro-inflammatory cytokines was assessed. The results demonstrate that all investigated ceramic particles exhibit biological activity toward human macrophage and monocyte cells in vitro, potentially providing conditions necessary for bone tissue restoration/regeneration in the peri-implant environment in vivo. Among the studied ceramics, DCPD appears to be the most preferable for implantation in patients with latent inflammation or unpredictable immune status, as this ceramic had the most favorable overall impact on the investigated cellular models.

Synthesis and Characterization of a Titanium-Based Functionally Graded Material-Structured Biocomposite using Powder Metallurgy

This investigation aims at synthesizing and characterizing a biocomposite of hydroxyapatite (HA) and titanium (Ti) as a functionally graded material (FGM) via an economical powder metallurgy route. Ti particles were produced through drilling and chipping, followed by compaction and sintering. Ti foams, so obtained, were then infused with varying volume fractions of HA. The pure Ti foam control sample and the FGM composite samples were then subjected to various characterizations to validate their biocompatibility, structural strength, and integrity. The interface development between the load-bearing Ti implant and living tissue was resolved through an FGM structure, where the base of the implant consisted of load-bearing Ti and the outer periphery changed to HA gradually. HA/Ti specimens of different volume fractions were tested for density measurements, microstructure, hardness, and bioactivity. The bioactive behavior was investigated using the potentiodynamic polarization technique to measure the corrosion rate of the pure Ti foam (0/100 HA/Ti) and the FGM composite (10/90 HA/Ti) samples in a simulated body fluid (SBF). The results showed that the hardness of FGM composites, despite being less than that of 0/100 HA/Ti, was still within safe limits. The corrosion rate, however, was found to be decreased by a significant value of almost 40% for the 10/90 HA/Ti FGM composite sample compared to the pure Ti foam control sample. It was concluded that the optimum composition 10/90 HA/Ti sample offers improved corrosion resistance while maintaining a sufficient allowable hardness level.

Comparison of bovine serum albumin and chitosan effects on calcium phosphate formation in the presence of silver nanoparticles

The precipitation of calcium phosphates (CaPs) in the presence of more than one type of additive is of interest both from a fundamental point of view and as a possible biomimetic route for the preparation of multicomponent composites in which the activity of the components is preserved. In this study, the effect of bovine serum albumin (BSA) and chitosan (Chi) on the precipitation of CaPs in the presence of silver nanoparticles (AgNPs) stabilized with sodium bis(2-ethylhexyl)sulfosuccinate (AOT-AgNPs), poly(vinylpyrrolidone) (PVP-AgNPs), and citrate (cit-AgNPs) was investigated. In the control system, the precipitation of CaPs occurred in two steps. Amorphous calcium phosphate (ACP) was the first precipitated solid, which transformed into a mixture of calcium-deficient hydroxyapatite (CaDHA) and a smaller amount of octacalcium phosphate (OCP) after 60 min of ageing. Both biomacromolecules inhibited ACP transformation, with Chi being a stronger inhibitor due to its flexible molecular structure. As the concentration of the biomacromolecules increased, the amount of OCP decreased both in the absence and presence of AgNPs. In the presence of cit-AgNPs and two highest BSA concentrations, a change in the composition of the crystalline phase was observed. Calcium hydrogen phosphate dihydrate was formed in the mixture with CaDHA. An effect on the morphology of both the amorphous and crystalline phases was observed. The effect depended on the specific combination of biomacromolecules and differently stabilized AgNP. The results obtained suggest a simple method for fine-tuning the properties of precipitates using different classes of additives. This could be of interest for the biomimetic preparation of multifunctional composites for bone tissue engineering.

Manufacturing methods, properties, and potential applications in bone tissue regeneration of hydroxyapatite-chitosan biocomposites: A review

Hydroxyapatite (HA) and chitosan (CS) biopolymer are the major materials investigated for biomedical purposes. Both of these components play an important role in the orthopedic field as bone substitutes or drug release systems. Used separately, the hydroxyapatite is quite fragile, while CS mechanical strength is very weak. Therefore, a combination of HA and CS polymer is used, which provides excellent mechanical performance with high biocompatibility and biomimetic capacity. Moreover, the porous structure and reactivity of the hydroxyapatite-chitosan (HA-CS) composite allow their application not only as a bone repair but also as a drug delivery system providing controlled drug release directly to the bone site. These features make biomimetic HA-CS composite a subject of interest for many researchers. Through this review, we provide the important recent achievements in the development of HA-CS composites, focusing on manufacturing techniques, conventional and novel three-dimensional bioprinting technology, and physicochemical and biological properties. The drug delivery properties and the most relevant biomedical applications of the HA-CS composite scaffolds are also presented. Finally, alternative approaches are proposed to develop HA composites with the aim to improve their physicochemical, mechanical, and biological properties.

Biomimetic Remineralized Three-Dimensional Collagen Bone Matrices with an Enhanced Osteostimulating Effect

Bone grafts with a high potential for osseointegration, capable of providing a complete and effective regeneration of bone tissue, remain an urgent and unresolved issue. The presented work proposes an approach to develop composite biomimetic bone material for reconstructive surgery by deposition (remineralization) on the surface of high-purity, demineralized bone collagen matrix calcium phosphate layers. Histological and elemental analysis have shown reproduction of the bone tissue matrix architectonics, and a high-purity degree of the obtained collagen scaffolds; the cell culture and confocal microscopy have demonstrated a high biocompatibility of the materials obtained. Adsorption spectroscopy, scanning electron microscopy, microcomputed tomography (microCT) and infrared spectroscopy, and X-ray diffraction have proven the efficiency of the deposition of calcium phosphates on the surface of bone collagen scaffolds. Cell culture and confocal microscopy methods have shown high biocompatibility of both demineralized and remineralized bone matrices. In the model of heterotopic implantation in rats, at the term of seven weeks, an intensive intratrabecular infiltration of calcium phosphate precipitates, and a pronounced synthetic activity of osteoblast remodeling and rebuilding implanted materials, were revealed in remineralized bone collagen matrices in contrast to demineralized ones. Thus, remineralization of highly purified demineralized bone matrices significantly enhanced their osteostimulating ability. The data obtained are of interest for the creation of new highly effective osteoplastic materials for bone tissue regeneration and augmentation.

Evolution of Biomimetic Approaches for Regenerative and Restorative Dentistry

Biomimetics refers to human-made processes, substances, systems, or devices that imitate nature. The art and science of designing and building biomimetic apparatus are called biomimetics. This method can be widely used in dentistry to restore the structure and function of normal tooth structure. Traditional approaches to treating damaged and decayed teeth require more aggressive preparation to place a "strong," stiff restoration. The emphasis was made on the strength of the restoration as well as its function and mechanical properties, despite several disadvantages like tooth fracture, making future treatment more difficult and invasive. This review paper will seek to provide a clear explanation of its scope, different fields of biomimetic dentistry, and materials used in biomimetics that improve the strength of the tooth.

Injectable bone cements: What benefits the combination of calcium phosphates and bioactive glasses could bring?

Out of the wide range of calcium phosphate (CaP) biomaterials, calcium phosphate bone cements (CPCs) have attracted increased attention since their discovery in the 1980s due to their valuable properties such as bioactivity, osteoconductivity, injectability, hardening ability through a low-temperature setting reaction and moldability. Thereafter numerous researches have been performed to enhance the properties of CPCs. Nonetheless, low mechanical performance of CPCs limits their clinical application in load bearing regions of bone. Also, the in vivo resorption and replacement of CPC with new bone tissue is still controversial, thus further improvements of high clinical importance are required. Bioactive glasses (BGs) are biocompatible and able to bond to bone, stimulating new bone growth while dissolving over time. In the last decades extensive research has been performed analyzing the role of BGs in combination with different CaPs. Thus, the focal point of this review paper is to summarize the available research data on how injectable CPC properties could be improved or affected by the addition of BG as a secondary powder phase. It was found that despite the variances of setting time and compressive strength results, desirable injectable properties of bone cements can be achieved by the inclusion of BGs into CPCs. The published data also revealed that the degradation rate of CPCs is significantly improved by BG addition. Moreover, the presence of BG in CPCs improves the in vitro osteogenic differentiation and cell response as well as the tissue-material interaction in vivo.

•

Properties of injectable calcium phosphate bone cements and bioactive glasses are discussed.

•

Benefits that BG addition to CPC could bring are highlighted.

•

Desirable injectable properties of bone cements can be achieved by the inclusion of BGs into CPCs.

•

The presence of BG in CPC advances in vitro and in vivo response of the composites.

•

Future research direction of BG containing injectable CPC composites are provided.

Horizon of exosome-mediated bone tissue regeneration: The all-rounder role in biomaterial engineering

Bone injury repair has always been a tricky problem in clinic, the recent emergence of bone tissue engineering provides a new direction for the repair of bone injury. However, some bone tissue processes fail to achieve satisfactory results mainly due to insufficient vascularization or cellular immune rejection. Exosomes with the ability of vesicle-mediated intercellular signal transmission have gained worldwide attention and can achieve cell-free therapy. Exosomes are small vesicles that are secreted by cells, which contain genetic material, lipids, proteins and other substances. It has been found to play the function of material exchange between cells. It is widely used in bone tissue engineering to achieve cell-free therapy because it not only does not produce some immune rejection like cells, but also can play a cell-like function. Exosomes from different sources can bind to scaffolds in various ways and affect osteoblast, angioblast, and macrophage polarization in vivo to promote bone regeneration. This article reviews the recent research progress of exosome-loaded tissue engineering, focusing on the mechanism of exosomes from different sources and the application of exosome-loaded scaffolds in promoting bone regeneration. Finally, the existing deficiencies and challenges, future development directions and prospects are summarized.

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.

Hydroxyapatite Reinforced Polyvinyl Alcohol/Polyvinyl Pyrrolidone Based Hydrogel for Cartilage Replacement

Polyvinyl alcohol (PVA) and Polyvinyl Pyrrolidone (PVP) hydrogels are desirable biomaterials for soft tissue repair and replacement. However, the bio-inertness and poor cell adhesive potency of the PVA and PVP hinder the wide range of biomedical applications. In the present work, PVA and PVP were blended with a one-dimensional hydroxyapatite nanorod (HNr), and PVA/PVP/HNr composite hydrogel was synthesized by the freeze-thaw process. The developed hydrogels were characterized by Scanning Electron Microscope (SEM). The bio-ceramic nanohydroxyapatite content was optimized, and it was found that reinforcement improves mechanical strength as well as bioactivity. The compression strength values are 2.47 ± 0.73 MPa for the composite having 2 wt% of nanohydroxyapatite. The storage modulus was much higher than the loss modulus, which signifies the elastic dominancy similar to cartilage. Besides, the antimicrobial activity of nanohydroxyapatite reinforced PVA hydrogel towards bacterial species, Escherichia coli (E. Coli), Staphylococcus aureus (S. aureus) was satisfactory, and the in vitro biocompatibility response towards Human Mesenchymal stem cells(hMSC) after 72 h of culture confirms nanohydroxyapatite reinforced PVA/PVP hydrogels are the promising alternatives for next-generation cartilage substitutes.

Comparison between hydroxyapatite and polycaprolactone in inducing osteogenic differentiation and augmenting maxillary bone regeneration in rats

Background

The selection of appropriate scaffold plays an important role in ensuring the success of bone regeneration. The use of scaffolds with different materials and their effect on the osteogenic performance of cells is not well studied and this can affect the selection of suitable scaffolds for transplantation. Hence, this study aimed to investigate the comparative ability of two different synthetic scaffolds, mainly hydroxyapatite (HA) and polycaprolactone (PCL) scaffolds in promoting in vitro and in vivo bone regeneration.

Method

In vitro cell viability, morphology, and alkaline phosphatase (ALP) activity of MC3T3-E1 cells on HA and PCL scaffolds were determined in comparison to the accepted model outlined for two-dimensional systems. An in vivo study involving the transplantation of MC3T3-E1 cells with scaffolds into an artificial bone defect of 4 mm length and 1.5 mm depth in the rat's left maxilla was conducted. Three-dimensional analysis using micro-computed tomography (micro-CT), hematoxylin and eosin (H&E), and immunohistochemistry analyses evaluation were performed after six weeks of transplantation.

Results

MC3T3-E1 cells on the HA scaffold showed the highest cell viability. The cell viability on both scaffolds decreased after 14 days of culture, which reflects the dominant occurrence of osteoblast differentiation. An early sign of osteoblast differentiation can be detected on the PCL scaffold. However, cells on the HA scaffold showed more prominent results with intense mineralized nodules and significantly (p < 0.05) high levels of ALP activity with prolonged osteoblast induction. Micro-CT and H&E analyses confirmed the in vitro results with bone formation were significantly (p < 0.05) greater in HA scaffold and was supported by IHC analysis which confirmed stronger expression of osteogenic markers ALP and osteocalcin.

Conclusion

Different scaffold materials of HA and PCL might have influenced the bone regeneration ability of MC3T3-E1. Regardless, in vitro and in vivo bone regeneration was better in the HA scaffold which indicates its great potential for application in bone regeneration.

The Molecular and Mechanical Characteristics of Biomimetic Composite Dental Materials Composed of Nanocrystalline Hydroxyapatite and Light-Cured Adhesive

The application of biomimetic strategies and nanotechnologies (nanodentology) has led to numerous innovations and provided a considerable impetus by creating a new class of modern adhesion restoration materials, including different nanofillers. An analysis of the molecular properties of biomimetic adhesives was performed in this work to find the optimal composition that provides high polymerisation and mechanical hardness. Nanocrystalline carbonate-substituted calcium hydroxyapatite (nano-cHAp) was used as the filler of the light-cured adhesive Bis-GMA (bisphenol A-glycidyl methacrylate). The characteristics of this substance correspond to the apatite of human enamel and dentin, as well as to the biogenic source of calcium: avian eggshells. The introduction and distribution of nano-cHAp fillers in the adhesive matrix resulted in changes in chemical bonding, which were observed using Fourier transform infrared (FTIR) spectroscopy. As a result of the chemical bonding, the Vickers hardness (VH) and the degree of conversion under photopolymerisation of the nano-cHAp/Bis-GMA adhesive increased for the specified concentration of nanofiller. This result could contribute to the application of the developed biomimetic adhesives and the clinical success of restorations.

Calcium Phosphate-Based Bioceramics in the Treatment of Osteosarcoma: Drug Delivery Composites and Magnetic Hyperthermia Agents

The use of biomaterials in medicine is not recent, and in the last few decades, the research and development of biocompatible materials had emerged. Hydroxyapatite (HAp), a calcium phosphate that constitutes a large part of the inorganic composition of human bones and teeth, has been used as an interesting bioceramic material. Among its applications, HAp has been used to carry antitumor drugs, such as doxorubicin, cisplatin, and gemcitabine. Such HAp-based composites have an essential role in anticancer drug delivery systems, including the treatment of osteosarcoma. In addition, the association of this bioceramic with magnetic nanoparticles (MNPs) has also been used as an effective agent of local magnetic hyperthermia. Further, the combined approach of the aforementioned techniques (HAp scaffolds combined with anti-tumor drugs and MNPs) is also an attractive therapeutical alternative. Considering the promising role of the use of bioceramics in modern medicine, we proposed this review, presenting an updated perspective on the use of HAp in the treatment of cancer, especially osteosarcoma. Finally, after giving the current progress in this field, we highlight the urgent need for efforts to provide a better understanding of their potential applications.

The Role of High Resolution Ultrasonography in Elucidating Features of the Breast Implants in Asymptomatic Patients After Implant-based Augmentation Mammaplasty

BACKGROUND

We conducted this study to describe the feasibility of high-resolution ultrasound (HRUS) in characterizing a breast implant in patients receiving an implant-based augmentation mammaplasty.

METHODS

The current study was conducted in a total of 612 patients (n =6 12) receiving an implant-based augmentation mammaplasty at other hospitals between August 31, 2017 and August 31, 2020. Of these, 136 patients (n = 136; 272 breasts) receiving reoperation were included in the current study. We compared between the patients' subjective awareness of a breast implant and its HRUS findings and an agreement between HRUS findings of a breast implant and its findings at reoperation.

RESULTS

The proportion of the patients receiving a silicone gel-filled breast implant was increased from 65.44% (89/136) to 81.61% (111/136) on HRUS. Moreover, HRUS was effective in identifying a manufacturer of the device.

CONCLUSIONS

In conclusion, our results indicate that HRUS is feasible in characterizing a breast implant in patients receiving an implant-based augmentation mammaplasty. But further prospective, large-scale studies are warranted to corroborate our results.

LEVEL OF EVIDENCE V

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors. www.springer.com/00266 .

Synthetic amorphous calcium phosphates (ACPs): preparation, structure, properties, and biomedical applications

Amorphous calcium phosphates (ACPs) represent a metastable amorphous state of other calcium orthophosphates (abbreviated as CaPO₄) possessing variable compositional but rather identical glass-like physical properties, in which there are neither translational nor orientational long-range orders of the atomic positions. In nature, ACPs of a biological origin are found in the calcified tissues of mammals, some parts of primitive organisms, as well as in the mammalian milk. Manmade ACPs can be synthesized in a laboratory by various methods including wet-chemical precipitation, in which they are the first solid phases, precipitated after a rapid mixing of aqueous solutions containing dissolved ions of Ca²⁺ and PO₄^3- in sufficient amounts. Due to the amorphous nature, all types of synthetic ACPs appear to be thermodynamically unstable and, unless stored in dry conditions or doped by stabilizers, they tend to transform spontaneously to crystalline CaPO₄, mainly to ones with an apatitic structure. This intrinsic metastability of the ACPs is of a great biological relevance. In particular, the initiating role that metastable ACPs play in matrix vesicle biomineralization raises their importance from a mere laboratory curiosity to that of a reasonable key intermediate in skeletal calcifications. In addition, synthetic ACPs appear to be very promising biomaterials both for manufacturing artificial bone grafts and for dental applications. In this review, the current knowledge on the occurrence, structural design, chemical composition, preparation, properties, and biomedical applications of the synthetic ACPs have been summarized.

A Review on Biphasic Calcium Phosphate Materials Derived from Fish Discards

This review summarizes the results reported on the production of biphasic calcium phosphate (BCP) materials derived from fish wastes (i.e., heads, bones, skins, and viscera), known as fish discards, and offers an in-depth discussion on their promising potential for various applications in many fields, especially the biomedical one. Thus, considerable scientific and technological efforts were recently focused on the capability of these sustainable materials to be transformed into economically attractive and highly valuable by-products. As a consequence of using these wastes, plenty of beneficial social effects, with both economic and environmental impact, will arise. In the biomedical field, there is a strong and continuous interest for the development of innovative solutions for healthcare improvement using alternative materials of biogenic origin. Thus, the orthopedic field has witnessed a significant development due to an increased demand for a large variety of implants, grafts, and/or scaffolds. This is mainly due to the increase of life expectancy and higher frequency of bone-associated injuries and diseases. As a consequence, the domain of bone-tissue engineering has expanded to be able to address a plethora of bone-related traumas and to deliver a viable and efficient substitute to allografts or autografts by combining bioactive materials and cells for bone-tissue ingrowth. Among biomaterials, calcium phosphate (CaP)-based bio-ceramics are widely used in medicine, in particular in orthopedics and dentistry, due to their excellent bioactive, osteoconductive, and osteointegrative characteristics. Recently, BCP materials (synthetic or natural), a class of CaP, which consist of a mixture of two phases, hydroxyapatite (HA) and beta tricalcium phosphate (β-TCP), in different concentrations, gained increased attention due to their superior overall performances as compared to single-phase formulations. Moreover, the exploitation of BCP materials from by-products of fish industry was reported to be a safe, cheap, and simple procedure. In the dedicated literature, there are many reviews on synthetic HA, β-TCP, or BCP materials, but to the best of our knowledge, this is the first collection of results on the effects of processing conditions on the morphological, compositional, structural, mechanical, and biological properties of the fish discard-derived BCPs along with the tailoring of their features for various applications.

Nanostructure of bone tissue probed with Ca 2p and O 1s NEXAFS spectroscopy

X-ray absorption spectroscopy is applied to investigate relationships between hierarchical organization of the skeleton and nanostructure of femoral bone in knee compartments and to understand the osteoarthritis (OA) related changes at the subcellular level. Our focus is on local electronic and atomic and molecular architectonics of the medial and lateral condyles of the femur resected during total knee arthroplasty in patients with medial compartmental knee OA. The element-specific and site-dependent peculiarities in spectral distributions of oscillator strength for core-to-valence transitions are revealed. The near Ca 2p and O 1s edges x-ray absorption fine structure (Ca 2p and O 1s NEXAFS) spectra of the saw cuts demonstrate substantial redistributions in intact and OA damaged areas on the proximal side, and on the proximal and distal sides of the samples. Examining the O 1s NEXAFS spectra new chemical bonds are revealed on the proximal surface in the OA areas. Strong intra-atomic intershell Ca2+ 2 p 3 / 2 , 1 / 2 5 3 d 1 interaction specifies the great similarity of the Ca 2p NEXAFS spectra. Their analysis performed in combination with the x-ray photoelectron data has demonstrated the formation of non-apatite calcium in the OA areas of the samples. It is shown that NEXAFS spectroscopy is a powerful tool for deeper understanding relationship between hierarchical skeletal organization and nanostructure of native bone. Perspectives for development of novel methods for medical imaging and diagnosis of subchondral bone at the nanolevel are discussed.

Fabrication and Evaluation of Layered Double Hydroxide-Enriched ß-Tricalcium Phosphate Nanocomposite Granules for Bone Regeneration: In Vitro Study

One of the most important challenges facing tissue engineering researches is the scaffold design with optimum physical and mechanical properties for growth and proliferation of cells, and tissue formation. The aim of this study was to produce a novel nanocomposite containing β-tricalcium phosphate and layered double hydroxide (β-TCP-LDH) and analyzing the capacity of its osteogenic activity in vitro. In this paper, β-tricalcium phosphate and layered double hydroxide powders were synthesized by co-precipitation processes. Then, the porous nanocomposite granules were prepared by the polyurethane sponge replication method. In this study, four kinds of β-TCP granules containing LDHs nanoparticles (ranging from 0.1 to 10 wt%) have been prepared. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX) analyses were selected to study the phase structure, morphology, and phase distribution, respectively. Physicochemical characterizations demonstrated that the granules were synthesized successfully. Interconnected macro pores ranging over 200-500 μm were observed for all kinds of granules. SEM micrographs showed that human mesenchymal stem cells (hMSCs) were attached to the surfaces of the granules and proliferated in good shape. The results warranted that the synthesized granules exhibited good biocompatibility and mineralization. Based on the results of compressive strength and porosity tests, the most suitable type of granule is β-TCP/LDH 10 wt% with 77% porosity and compressive modulus of 231.4 MPa, which can be utilized in bone tissue engineering. To our knowledge, layered double hydroxides have not previously been incorporated into tricalcium phosphate granules for bone grafting. Also, this study is the first report on the effects of LDH on the mechanical properties and porosity of β-TCP granules. Our results demonstrated that β-TCP/LDH nanocomposite granule has a great potential for bone defects regeneration and tissue engineering applications.

Tailoring Pyro-and Orthophosphate Species to Enhance Stem Cell Adhesion to Phosphate Glasses

Phosphate-based glasses (PBGs) offer significant therapeutic potential due to their bioactivity, controllable compositions, and degradation rates. Several PBGs have already demonstrated their ability to support direct cell growth and in vivo cytocompatibility for bone repair applications. This study investigated development of PBG formulations with pyro- and orthophosphate species within the glass system (40 − x)P₂O₅·(16 + x)CaO·20Na₂O·24MgO (x = 0, 5, 10 mol%) and their effect on stem cell adhesion properties. Substitution of phosphate for calcium revealed a gradual transition within the glass structure from Q² to Q⁰ phosphate species. Human mesenchymal stem cells were cultured directly onto discs made from three PBG compositions. Analysis of cells seeded onto the discs revealed that PBG with higher concentration of pyro- and orthophosphate content (61% Q¹ and 39% Q⁰) supported a 4.3-fold increase in adhered cells compared to glasses with metaphosphate connectivity (49% Q² and 51% Q¹). This study highlights that tuning the composition of PBGs to possess pyro- and orthophosphate species only, enables the possibility to control cell adhesion performance. PBGs with superior cell adhesion profiles represent ideal candidates for biomedical applications, where cell recruitment and support for tissue ingrowth are of critical importance for orthopaedic interventions.

Self-Assembled Type I Collagen-Apatite Fibers with Varying Mineralization Extent and Luminescent Terbium Promote Osteogenic Differentiation of Mesenchymal Stem Cells

This work explores in depth the simultaneous self-assembly and mineralization of type I collagen by a base-acid neutralization technique to prepare biomimetic collagen-apatite fibrils with varying mineralization extent and doped with luminescent bactericidal Tb³⁺ ions. Two variants of the method are tested: base-acid titration, a solution of Ca(OH)₂ is added dropwise to a stirred solution containing type I collagen dispersed in H₃ PO₄ ; and direct mixing, the Ca(OH)₂ solution is added by fast dripping onto the acidic solution. Only the direct mixing variant yielded an effective control of calcium phosphate polymorphism. Luminescence spectroscopy reveals the long luminescence lifetime and high relative luminescence intensity of the Tb³⁺ -doped materials, while two-photon confocal fluorescence microscopy shows the characteristic green fluorescence light when using excitation wavelength of 458 nm, which is not harmful to bone tissue. Cytotoxicity/viability tests reveal that direct mixing samples show higher cell proliferation than titration samples. Additionally, osteogenic differentiation essays show that all mineralized fibrils promote the osteogenic differentiation, but the effect is more pronounced when using samples prepared by direct mixing, and more notably when using the Tb³⁺ -doped mineralized fibrils. Based on these findings it is concluded that the new nanocomposite is an ideal candidate for bone regenerative therapy.

Zn- or Cu-Containing CaP-Based Coatings Formed by Micro-arc Oxidation on Titanium and Ti-40Nb Alloy: Part I-Microstructure, Composition and Properties

Zn- and Cu-containing CaP-based coatings, obtained by micro-arc oxidation process, were deposited on substrates made of pure titanium (Ti) and novel Ti-40Nb alloy. The microstructure, phase, and elemental composition, as well as physicochemical and mechanical properties, were examined for unmodified CaP and Zn- or Cu-containing CaP coatings, in relation to the applied voltage that was varied in the range from 200 to 350 V. The unmodified CaP coatings on both types of substrates had mainly an amorphous microstructure with a minimal content of the CaHPO₄ phase for all applied voltages. The CaP coatings modified with Zn or Cu had a range from amorphous to nano- and microcrystalline structure that contained micro-sized CaHPO₄ and Ca(H₂PO₄)₂·H₂O phases, as well as nano-sized β-Ca₂P₂O₇, CaHPO₄, TiO₂, and Nb₂O₅ phases. The crystallinity of the formed coatings increased in the following order: CaP/TiNb < Zn-CaP/TiNb < Cu-CaP/TiNb < CaP/Ti < Zn-CaP/Ti < Cu-CaP/Ti. The increase in the applied voltage led to a linear increase in thickness, roughness, and porosity of all types of coatings, unlike adhesive strength that was inversely proportional to an increase in the applied voltage. The increase in the applied voltage did not affect the Zn or Cu concentration (~0.4 at%), but led to an increase in the Ca/P atomic ratio from 0.3 to 0.7.

Synthesis of Calcium Orthophosphates by Chemical Precipitation in Aqueous Solutions: The Effect of the Acidity, Ca/P Molar Ratio, and Temperature on the Phase Composition and Solubility of Precipitates

Studies on chemical precipitation of the calcium orthophosphates have shown that their phase compositions do not vary depending on molar ratio Ca/P but are sensitive to solutions acidity and temperature. These are two key factors that determine the phase transformation progress of metastable phases into less soluble precipitates of the phosphates. It was proposed to compare calcium orthophosphates solubility products with calcium cations quantities in their formulas. It was found that there was a linear correlation between calcium orthophosphates specific solubility products and their molar ratios Ca/P if hydroxyapatite and its Ca-deficient forms were excluded from consideration. It was concluded that the relatively large deviations of their solubility products from the found correlation should be thought of as erroneous data. That is why solubility products were changed in accordance with correlation dependence: pKS for hydroxyapatite was 155, pKS for Ca-deficient hydroxyapatites was 114–155. The solubility isotherms, which were calculated on the basis of the corrected pKS values, coincided with the experimental data on solid-phase titration by Pan and Darvell.

Impact of industry 4.0 to create advancements in orthopaedics

Scientists and health professional are focusing on improving the medical sciences for the betterment of patients. The fourth industrial revolution, which is commonly known as Industry 4.0, is a significant advancement in the field of engineering. Industry 4.0 is opening a new opportunity for digital manufacturing with greater flexibility and operational performance. This development is also going to have a positive impact in the field of orthopaedics. The purpose of this paper is to present various advancements in orthopaedics by the implementation of Industry 4.0. To undertake this study, we have studied the available literature extensively on Industry 4.0, technologies of Industry 4.0 and their role in orthopaedics. Paper briefly explains about Industry 4.0, identifies and discusses the major technologies of Industry 4.0, which will support development in orthopaedics. Finally, from the available literature, the paper identifies twelve significant advancements of Industry 4.0 in orthopaedics. Industry 4.0 uses various types of digital manufacturing and information technologies to create orthopaedics implants, patient-specific tools, devices and innovative way of treatment. This revolution is to be useful to perform better spinal surgery, knee and hip replacement, and invasive surgeries.

High Nanodiamond Content-PCL Composite for Tissue Engineering Scaffolds

Multifunctional scaffolds are becoming increasingly important in the field of tissue engineering. In this research, a composite material is developed using polycaprolactone (PCL) and detonation nanodiamond (ND) to take advantage of the unique properties of ND and the biodegradability of PCL polymer. Different ND loading concentrations are investigated, and the physicochemical properties of the composites are characterized. ND-PCL composite films show a higher surface roughness and hydrophilicity than PCL alone, with a slight decrease in tensile strength and a significant increase in degradation. Higher loading of ND also shows a higher osteoblast adhesion than the PCL alone sample. Finally, we show that the ND-PCL composites are successfully extruded to create a 3D scaffold demonstrating their potential as a composite material for tissue regeneration.

Bismuth-Doped Nanohydroxyapatite Coatings on Titanium Implants for Improved Radiopacity and Antimicrobial Activity

This study aims to present the possibility to obtain bismuth-doped nanohydroxyapatite coatings on the surface of the titanium implants by using a solution-derived process according to an established biomimetic methodology. The bioactivity of the titanium surface was increased by an alkali-thermal treatment. Then, under biomimetic conditions, the titanium surface was coated with a Bi-doped nanohydroxyapatite layer by using a modified supersaturated calcification solution (SCS) containing a bismuth salt. The apatite deposits were analyzed by scanning electron microscopy coupled with X-ray analysis (SEM-EDX), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and digital X-rays radiography method. The results indicate that the Bi-doped nanohydroxyapatite coatings on titanium surface were produced. These coatings exhibit a good radiopacity, thus enhancing their applications in dental and orthopedic fields. Additionally, the Bi-doped nanohydroxyapatite coatings show significant antimicrobial activity against Escherichia coli and Staphylococcus aureus bacteria.

Functionalized calcium orthophosphates (CaPO4) and their biomedical applications

Due to the chemical similarity to natural calcified tissues (bones and teeth) of mammals, calcium orthophosphates (abbreviated as CaPO₄) appear to be good biomaterials for creation of artificial bone grafts. However, CaPO₄ alone have some restrictions, which limit their biomedical applications. Various ways have been developed to improve the properties of CaPO₄ and their functionalization is one of them. Namely, since surfaces always form the interfaces between implanted grafts and surrounding tissues, the state of CaPO₄ surfaces plays a crucial role in the survival of bone grafts. Although the biomedically relevant CaPO₄ possess the required biocompatible properties, some of their properties could be better. For example, functionalization of CaPO₄ to enhance cell attachment and cell material interactions has been developed. In addition, to prepare stable formulations from nanodimensional CaPO₄ particles and prevent them from agglomerating, the surfaces of CaPO₄ particles are often functionalized by sorption of special chemicals. Furthermore, there are functionalizations in which CaPO₄ are exposed to various types of physical treatments. This review summarizes the available knowledge on CaPO₄ functionalizations and their biomedical applications.

Synthesis and characterization of biomimetic bioceramic nanoparticles with optimized physicochemical properties for bone tissue engineering

Calcium phosphate bioceramics nanoparticles such as nano-hydroxyapatite (nHA) and nano-tricalcium phosphate (nTCP) are the main focus of basic and applied research for bone tissue regeneration. In particular, a combination of these two phases (nHA + nTCP) which refers to as "nano-biphasic calcium phosphates (nBCP)" is of interest due to the preferred biodegradation nature compared to single-phase bioceramics. However, the available synthesis processes are challenging and the biomaterials properties are yet to be optimized to mimic the physiochemical properties of the natural nanoscale bone apatite. In this study, a new approach was developed for the production of optimized bioceramic nanoparticles aiming to improve their biomimecity for better biological performances. Nanoparticles were synthesized through a carefully controlled and modified wet mechano-chemical method combined with a controlled solid-state synthesis. Different processing variables have been analyzed including; milling parameters, post-synthesis treatment, and calcination phase. Detailed physicochemical characterizations of nanoparticles revealed higher crystallinity (∼100%), lower crystallite/particle size (58 nm), higher homogeneity, reduced particle agglomeration size (6 μm), and a closer molar ratio (1.8) to biological apatite compared to control and standard samples. Furthermore, the study group was confirmed as calcium-deficient carbonate-substituted BCP nanoparticles (nHA/nβ-TCP: 92/8%). As such, the introduced method can afford an easier and accurate control over nanoparticle physiochemical properties including the composition phase which can be used for better customization of biomaterials for clinical applications. The findings of this article will also help researchers in the further advancement of production strategies of biomaterials. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1654-1666, 2019.

Hybrid polymer biomaterials for bone tissue regeneration

Native tissues possess unparalleled physiochemical and biological functions, which can be attributed to their hybrid polymer composition and intrinsic bioactivity. However, there are also various concerns or limitations over the use of natural materials derived from animals or cadavers, including the potential immunogenicity, pathogen transmission, batch to batch consistence and mismatch in properties for various applications. Therefore, there is an increasing interest in developing degradable hybrid polymer biomaterials with controlled properties for highly efficient biomedical applications. There have been efforts to mimic the extracellular protein structure such as nanofibrous and composite scaffolds, to functionalize scaffold surface for improved cellular interaction, to incorporate controlled biomolecule release capacity to impart biological signaling, and to vary physical properties of scaffolds to regulate cellular behavior. In this review, we highlight the design and synthesis of degradable hybrid polymer biomaterials and focus on recent developments in osteoconductive, elastomeric, photoluminescent and electroactive hybrid polymers. The review further exemplifies their applications for bone tissue regeneration.

Silicon nitride enhances osteoprogenitor cell growth and differentiation via increased surface energy and formation of amide and nanocrystalline HA for craniofacial reconstruction

The bioactive silicon nitride (Si₃N₄) has been FDA cleared for use as spinal intervertebral arthrodesis devices. Because its surface properties promote bone ongrowth and ingrowth, it also has the potential to benefit craniofacial reconstruction. Thus, the aim of this work was to determine whether the surface properties of Si₃N₄ could enhance the osteoblast cell growth, differentiation and nucleation of hydroxyapatite (HA) crystals compared to conventional implant materials such as titanium (Ti) and polyether ether ketone (PEEK). X-ray absorbance near-edge structure analysis (XANES) indicated the presence of Si-Si, Si-O and Si-N bonding. Surface wettability studies confirmed that Si₃N₄ exhibits the lowest contact angle and highest surface energy. Cell culture studies showed that osteoblast growth was enhanced on Si₃N₄ after 1 day and up to 7 days. Si₃N₄ surface induced highest surface coverage and thickness of nanocrystalline HA (211) and (203) in cell-free in vitro studies after 7 days of culture. Raman spectroscopy analysis confirmed the presence of surface functional groups consisting of phosphate and carbonate species. Interestingly, Si₃N₄ surface showed amide and hydroxyproline groups, the precursors to collagen, which were not observed on Ti and PEEK surfaces. Furthermore, Si₃N₄ surface indicated high expression of RUNX2, enhanced cell differentiation and dense collagenous ECM after 30 days of the in vitro study. The present study concluded that Si₃N₄ surface enhances osteoprogenitor cell adhesion, growth, RUNX2 expression and ECM formation via the coupled effects of higher surface energy and the presence of amide and nanocrystalline HA functional groups.

Comparative Study on Acellular Dermal Graft Versus Propylene Mesh Both Either Loaded or Unloaded with BM-MSCs in Healing of Skull Bone Defect in Rats: Histological and Immunohistochemical Study

Bone defect occurs as a consequence of many conditions. Diseased bones don’t heal properly and defects in face area need proper bone reconstruction to avoid psychological and social problems. Tissue engineering is an emerging new modality of treatment. We thought to study different methods to fill skull bone defect in rats in order to find the most safe and effective method. So, this study was designed to evaluate the efficacy of acellular dermal graft (ADM) versus propylene mesh both either loaded or unloaded with bone marrow derived mesenchymal stem cells (BM-MSCs) in healing of skull bone defect of a 5 mm diameter. The study included 36 adult male Wistar albino rats that were divided into three groups according to the way of filling skull bone defect. Group I: Ia (sham control), Ib (negative control). Group II: IIa (unseeded propylene), IIb (seeded propylene) and Group III: IIIa (unseeded ADM), IIIb (seeded ADM). The trephine operation was done on the left parietal bone. Specimens were collected four weeks postoperative and processed for H&E, osteopontin immunohistochemistry and scanning electron microscope. Morphometric and statistical analysis were also performed. After studying the results of the experiment, we found that propylene mesh and ADM were suitable scaffolds that could support new bone formation in clavarial bone defect. Healing of skull bone defect was better in rats that received seeded scaffolds more than rats with unseeded scaffolds. The seeded ADM showed significant increase in bone forming activity as confirmed by histomorphometric and statistical results.

Artificially controlled degradable nanoparticles for contrast switch MRI and programmed cancer therapy

Background

Utilizing the permeability enhancement and irreversible biomolecule denaturation caused by hyperthermia, photothermal-chemo synergistic therapy has shown great potential in clinical cancer treatment.

Purpose

The objective of this study was to provide a novel controlled drug release method to improve the efficiency of photothermal-chemo synergistic therapy.

Patients and methods

HCT116 tumor-bearing mice were selected as modal for the study of cancer theranostics efficiency. The T2 to T1 magnetic resonance imaging contrast switch was studied in vivo. Analyses of the tumor growth of mice were carried out to evaluate the tumor therapy efficiency.

Results

We developed novel artificially controlled degradable Co₃O₄ nanoparticles and explored their potential in drug delivery/release. In the presence of ascorbic acid (AA), the designed nanomaterials can be degraded via a redox process and hence release the loaded drugs. Importantly, the AA, in the lack of l-gulonolactone oxidase, cannot be synthesized in the body of typical mammal including human, which suggested that the degradation process can be controlled artificially. Moreover, the obtained nanoparticles have outstanding photothermal conversion efficiency and their degradation can also result in an magnetic resonance imaging contrast enhancement switch from T₂ to T₁, which benefits the cancer theranostics.

Conclusion

Our results illustrated that the artificially controlled degradable nanoparticles can serve as an alternative candidate for controllable drug release as well as a platform for highly efficient photothermal-chemo synergistic cancer theranostics.

Enhanced radiographic visualization of resorbable foils for orbital floor reconstruction: A proof of principle

PURPOSE

Despite the advantages and broad applications of alloplastic resorbable implants, postoperative radiological control is challenging due to its radiolucency. The aim of the present study was to evaluate the radiographic visibility of newly developed materials for orbital floor reconstruction.

MATERIALS AND METHODS

The radiographic visibility of four different material combinations consisting of poly-(L-lactic acid)/poly-glycolic acid (PLLA/PGA) or poly(D,L-lactic acid) (PDLLA) enriched with magnesium (Mg), hydroxyapatite (HA) or β-tricalcium phosphate (β-TCP) with various layers of thicknesses (0.3, 0.6, and 1 mm), surgically placed above the orbital floor of a human head specimen, was evaluated using computed tomography (CT) and cone beam computed tomography (CBCT). The visibility was rated on a scale of 0-10 in CT/CBCT and by Hounsfield Units in CT for each subject.

RESULTS

All of the materials were clearly detectable in CT scans. Visibility was significantly higher (p < 0.001) in the standard soft tissue window (mean score: 7.3, ranging from 2 to 10) in comparison to the standard bone window (mean score: 5.2, ranging from 1 to 10). In CBCT (mean score: 3.3, ranging from 0 to 7), there was significantly lower but still sufficient visibility of the materials compared to the CT soft tissue window (p < 0.001) and CT bone window (p < 0.001). Comparing the different materials' visibility among the group of same layer thicknesses with each other, in the majority of cases, PDLLA enriched with β-TCP appeared to be most visible in both CT and CBCT.

CONCLUSION

The incorporation of radiopaque elements to PLLA/PGA and PDLLA polymers is a promising strategy to improve their visibility in CT and CBCT. Our data suggest that the reconstruction of the orbital floor with these new materials could provide an advantageous postoperative radiographic control.

Studies on adsorption of oxytetracycline from aqueous solutions onto hydroxyapatite

The presence of antibiotics in the water and wastewater has raised problems due to potential impacts on the environment and consequently their removal is of great importance. For this reason, this article aims to perform a study on the possibility of oxytetracycline (OTC) adsorption from aqueous medium by using the hydroxyapatite (HA) nanopowders as adsorbent materials. The hydroxyapatite nanopowders were synthesized by wet precipitation method by using orthophosphoric acid and calcium hydroxide as raw materials and investigated by XRD, SEM-EDX, FTIR and BET methods. The uncalcined and calcined hydroxyapatite samples have hexagonal crystal structure with crystal sizes smaller than 100nm and a specific surface area of 316m²/g and 139m²/g, respectively. The adsorption behavior of oxytetracycline, a zwitterionic antibiotic, on nanohydroxyapatite was investigated as a function of pH, contact time, adsorbent dosage and drug concentration by means of batch adsorption experiments. High oxytetracycline removal rates of about 97.58% and 89.95% for the uncalcined and calcined nanohydroxyapatites, respectively, were obtained at pH8 and ambient temperature. The adsorption process of oxytetracycline onto nanohydroxyapatite samples was found to follow a pseudo-second order and intraparticle diffusion kinetic models. The maximum adsorption capacities of 291.32mg/g and 278.27mg/g for uncalcined and calcined nanohydroxyapatite samples, respectively, have been found. The adsorption mechanism of OTC on the hydroxyapatite surface at pH8 can be established via surface complexation. The obtained results are indicative of good hydroxyapatite adsorption ability towards oxytetracycline drug.

Calcium orthophosphates (CaPO4): Occurrence and properties

The present overview is intended to point the readers' attention to the important subject of calcium orthophosphates (CaPO₄). This type of materials is of the special significance for the human beings because they represent the inorganic part of major normal (bones, teeth and antlers) and pathological (those appearing due to various diseases) calcified tissues of mammals. For example, atherosclerosis results in blood vessel blockage caused by a solid composite of cholesterol with CaPO₄, while dental caries (tooth decay) and osteoporosis (a low bone mass with microarchitectural changes) mean a partial decalcification of teeth and bones, respectively, that results in replacement of a less soluble and harder biological apatite by more soluble and softer calcium hydrogenorthophosphates. Due to the compositional similarities to the calcified tissues of mammals, CaPO₄ are widely used as biomaterials for bone grafting purposes. In addition, CaPO₄ have many other applications. Thus, there is a great significance of CaPO₄ for the humankind and, in this paper, an overview on the current knowledge on this subject is provided.

Biopolymers/poly(ε-caprolactone)/polyethylenimine functionalized nano-hydroxyapatite hybrid cryogel: Synthesis, characterization and application in gene delivery

Nano-hydroxyapatite (nHAp), surface functionalized with linear polyethylenimine (LPEI), was used for the preparation of biocomposites in combination with biopolymers and poly(ε-caprolactone) (PCL), by cryogelation technique, to yield biomimetic scaffolds with controlled interconnected macroporosity, mechanical stability, and predictable degradation behavior. The structural characteristics, swelling and degradation behavior of hydroxyapatite and hydroxyapatite/β-tricalcium phosphate (β-TCP) filled matrices were investigated as compared to the corresponding naked polymer 3D system. It was found that the homogeneity and cohesivity of the composite are significantly dependent on the size and amount of the included inorganic particles, which are thus determining the structural parameters. Surface modification with LPEI and nanodimensions favored the nHAp integration in the organic matrix, with preferential location along protein fibers, while β-TCP microparticles induced an increased disorder in the hybrid system. The biocomposite including nHAp only was further investigated targeting biomedical uses, and proved to be non-cytotoxic and capable of acting as gene-activated matrix (GAM). It allowed sustained delivery over time (until 22days) of embedded PEI₂₅-pDNA polyplexes at high levels of transgene expression, while insuring a decrease in cytotoxicity as compared to polyplexes alone. Experimental data recommend such biocomposite as an attractive material for regenerative medicine.

A history of calcium orthophosphates (CaPO4) and their biomedical applications

The historical development of a scientific knowledge on calcium orthophosphates (CaPO₄) from 1770-s till 1950 is described. Many forgotten and poorly known historical facts and approaches have been extracted from old publications and then they have been analyzed, systematized and reconsidered from the modern point of view. The chosen time scale starts with the earliest available studies of 1770-s (to the best of my findings, CaPO₄ had been unknown before), passes through the entire 19th century and finishes in 1950, because since then the amount of publications on CaPO₄ rapidly increases and the subject becomes too broad. Furthermore, since publications of the second half of the 20th century are easily accessible, the substantial amount of them has been already reviewed by other researchers. The reported historical findings clearly demonstrate that the substantial amount of the scientific facts and experimental approaches has been known for very many decades and, in fact, the considerable quantity of relatively recent investigations on CaPO₄ is just either a further development of the earlier studies or a rediscovery of the already forgotten knowledge.