In vitro analysis of nanoparticulate hydroxyapatite/chitosan composites as potential drug delivery platforms for the sustained release of antibiotics in the treatment of osteomyelitis

A comprehensive review on recent progress in chitosan composite gels for biomedical uses

Chitosan (CS) composite gels have emerged as promising materials with diverse applications in biomedicine. This review provides a concise overview of recent advancements and key aspects in the development of CS composite gels. The unique properties of CS, such as biocompatibility, biodegradability, and antimicrobial activity, make it an attractive candidate for gel-based composites. Incorporating various additives, such as nanoparticles, polymers, and bioactive compounds, enhances the mechanical, thermal, and biological and other functional properties of CS gels. This review discusses the fabrication methods employed for CS composite gels, including blending and crosslinking, highlighting their influence on the final properties of the gels. Furthermore, the uses of CS composite gels in tissue engineering, wound healing, drug delivery, and 3D printing highlight their potential to overcome a number of the present issues with drug delivery. The biocompatibility, antimicrobial properties, electroactive, thermosensitive and pH responsive behavior and controlled release capabilities of these gels make them particularly suitable for biomedical applications. In conclusion, CS composite gels represent a versatile class of materials with significant potential for a wide range of applications. Further research and development efforts are necessary to optimize their properties and expand their utility in pharmaceutical and biomedical fields.

Targeted Clindamycin Delivery Systems: Promising Options for Preventing and Treating Bacterial Infections Using Biomaterials

Targeted therapy represents a real opportunity to improve the health and lives of patients. Developments in this field are confirmed by the fact that the global market for drug carriers was worth nearly $40 million in 2022. For this reason, materials engineering and the development of new drug carrier compositions for targeted therapy has become a key area of research in pharmaceutical drug delivery in recent years. Ceramics, polymers, and metals, as well as composites, are of great interest, as when they are appropriately processed or combined with each other, it is possible to obtain biomaterials for hard tissues, soft tissues, and skin applications. After appropriate modification, these materials can release the drug directly at the site requiring a therapeutic effect. This brief literature review characterizes routes of drug delivery into the body and discusses biomaterials from different groups, options for their modification with clindamycin, an antibiotic used for infections caused by aerobic and anaerobic Gram-positive bacteria, and different methods for the final processing of carriers. Examples of coating materials for skin wound healing, acne therapy, and bone tissue fillers are given. Furthermore, the reasons why the use of antibiotic therapy is crucial for a smooth and successful recovery and the risks of bacterial infections are explained. It was demonstrated that there is no single proven delivery scheme, and that the drug can be successfully released from different carriers depending on the destination.

Tunable Release of Calcium from Chitosan-Coated Bioglass

Bioglass presents a standard biomaterial for regeneration of hard tissues in orthopedics and dentistry. The notable osteo-inductive properties of bioglass are largely due to the release of calcium ions from it. However, this release is not easily controllable and can often be excessive, especially during the initial interaction of the biomaterial with the surrounding tissues. Consequently, this excessive release can deplete the calcium content of the bioglass, ultimately reducing its overall bioactivity. In this study, we have tested if applying biopolymer chitosan coatings of different thicknesses would be able to mitigate and regulate the calcium ion release from monodisperse bioglass nanoparticles. Calcium release was assessed for four different chitosan coating thicknesses at different time points over the period of 28 days using a fluorescence quencher. Expectedly, chitosan-coated particles released less calcium as the concentration of chitosan in the coating solution increased, presumably due to the increased thickness of the chitosan coating around the bioglass particles. The mechanism of release remained constant for each coating thickness, corresponding to anomalous, non-Fickian diffusion, but the degree of anomalousness increased with the deposition of chitosan. Zeta potential testing showed an expected increase in the positive double layer charge following the deposition of the chitosan coating due to the surface exposure of the amine groups of chitosan. Less intuitively, the zeta potential became less positive as thickness of the chitosan coating increased, attesting to the lower density of the surface charges within thicker coatings than within the thinner ones. Overall, the findings of this study demonstrate that chitosan coating efficiently prevents the early release of calcium from bioglass. This coating procedure also allows for the tuning of the calcium release kinetics by controlling the chitosan concentration in the parent solution.

3D and 4D printing hydroxyapatite-based scaffolds for bone tissue engineering and regeneration

The osseous tissue can be classified as a nanocomposite that encompasses a complex interweaving of organic and inorganic matrices. This intricate amalgamation consists of a collagen component and a mineral phase that are intricately arranged to form elaborate and perforated configurations. Hydroxyapatite, whether synthesized artificially or obtained from natural sources, has garnered considerable attention as a composite material in the field of bone tissue engineering due to its striking resemblance to bone in terms of structure and characteristics. Hydroxyapatite (HA) constitutes the predominant ceramic biomaterial for biomedical applications due to its ability to replicate the mineral composition of vertebrate bone. Nonetheless, it is noteworthy that the present biomimetic substance exhibits unfavorable mechanical characteristics, characterized by insufficient tensile and compressive strength, thus rendering it unsuitable for effective employment in the field of bone tissue engineering. Due to its beneficial attributes, hydroxyapatite (HA) is frequently employed in conjunction with various polymers and crosslinkers as composites to enhance mechanical properties and overall efficacy of implantable biomaterials engineered. The restoration of skeletal defects through the use of customized replacements is an effective way to replace damaged or lost bone structures. This method not only restores the bones' original functions but also reinstates their initial aesthetic appearance. The utilization of hydroxyapatite-polymer composites within 3D-printed grafts necessitates meticulous optimization of both mechanical and biological properties, in order to ensure their suitability for employment in medical devices. The utilization of 3D-printing technology represents an innovative approach in the manufacturing of HA-based scaffolds, which offers advantageous prospects for personalized bone regeneration. The expeditious prototyping method, with emphasis on the application of 3D printing, presents a viable approach in the development of bespoke prosthetic implants, grounded on healthcare data sets. 4D printing approach is an evolved form of 3D printing that utilizes programmable materials capable of altering the intended shape of printed structures, contingent upon single or dual stimulating factors. These factors include aspects such as pH level, temperature, humidity, crosslinking degree, and leaching factors.

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.

Hydroxyapatite-based carriers for tumor targeting therapy

At present, targeted drug delivery is regarded as the most effective means of tumor treatment, overcoming the lack of conventional chemotherapeutics that are difficult to reach or enter into cancer cells. Hydroxyapatite (HAP) is the main component of biological hard tissue, which can be regarded as a suitable drug carrier due to its biocompatibility, nontoxicity, biodegradation, and absorbability. This review focuses on the cutting edge of HAP as a drug carrier in targeted drug delivery systems. HAP-based carriers can be obtained by doping, modification, and combination, which benefit to improve the loading efficiency of drugs and the response sensitivity of the microenvironment in the synthesis process. The drug adsorbed or in situ loaded on HAP-based carriers can achieve targeted drug delivery and precise treatment through the guidance of the in vivo microenvironment and the stimulation of the in vitro response. In addition, HAP-based drug carriers can improve the cellular uptake rate of drugs to achieve a higher treatment effect. These advantages revealed the promising potential of HAP-based carriers from the perspective of targeted drug delivery for tumor treatment.

Hierarchy of hybrid materials. Part-II: The place of organics-on-inorganics in it, their composition and applications

Hybrid materials or hybrids incorporating organic and inorganic constituents are emerging as a very potent and promising class of materials due to the diverse but complementary nature of their properties. This complementarity leads to a perfect synergy of properties of the desired materials and products as well as to an extensive range of their application areas. Recently, we have overviewed and classified hybrid materials describing inorganics-in-organics in Part-I (Saveleva, et al., Front. Chem., 2019, 7, 179). Here, we extend that work in Part-II describing organics-on-inorganics, i.e., inorganic materials modified by organic moieties, their structure and functionalities. Inorganic constituents comprise of colloids/nanoparticles and flat surfaces/matrices comprise of metallic (noble metal, metal oxide, metal-organic framework, magnetic nanoparticles, alloy) and non-metallic (minerals, clays, carbons, and ceramics) materials; while organic additives can include molecules (polymers, fluorescence dyes, surfactants), biomolecules (proteins, carbohydtrates, antibodies and nucleic acids) and even higher-level organisms such as cells, bacteria, and microorganisms. Similarly to what was described in Part-I, we look at similar and dissimilar properties of organic-inorganic materials summarizing those bringing complementarity and composition. A broad range of applications of these hybrid materials is also presented whose development is spurred by engaging different scientific research communities.

Polymeric Nanotechnologies for the Treatment of Periodontitis: A Chronological Review

Periodontitis is a chronic infectious and inflammatory disease of periodontal tissues estimated to affect 70 - 80 % of all adults. At the same time, periodontium, the site of periodontal pathologies, is an extraordinarily complex plexus of soft and hard tissues, the regeneration of which using even the most advanced forms of tissue engineering continues to be a challenge. Nanotechnologies, meanwhile, have provided exquisite tools for producing biomaterials and pharmaceutical formulations capable of elevating the efficacies of standard pharmacotherapies and surgical approaches to whole new levels. A bibliographic analysis provided here demonstrates a continuously increasing research output of studies on the use of nanotechnologies in the management of periodontal disease, even when they are normalized to the total output of studies on periodontitis. The great majority of biomaterials used to tackle periodontitis, including those that pioneered this interesting field, have been polymeric. In this article, a chronological review of polymeric nanotechnologies for the treatment of periodontitis is provided, focusing on the major conceptual innovations since the late 1990s, when the first nanostructures for the treatment of periodontal diseases were fabricated. In the opening sections, the etiology and pathogenesis of periodontitis and the anatomical and histological characteristics of the periodontium are being described, along with the general clinical manifestations of the disease and the standard means of its therapy. The most prospective chemistries in the design of polymers for these applications are also elaborated. It is concluded that the amount of innovation in this field is on the rise, despite the fact that most studies are focused on the refinement of already established paradigms in tissue engineering rather than on the development of revolutionary new concepts.

When Nothing Turns Itself Inside out and Becomes Something: Coating Poly (Lactic-Co-Glycolic Acid) Spheres with Hydroxyapatite Nanoparticles vs. the Other Way Around

To stabilize drugs physisorbed on the surface of hydroxyapatite (HAp) nanoparticles and prevent burst release, these nanoparticles are commonly coated with polymers. Bioactive HAp, however, becomes shielded from the surface of such core/shell entities, which partially defeats the purpose of using it. The goal of this study was to assess the biological and pharmacokinetic effects of inverting this classical core/shell structure by coating poly(lactic-co-glycolic acid) (PLGA) spheres with HAp nanoparticles. The HAp shell did not hinder the release of vancomycin; rather, it increased the release rate to a minor degree, compared to that from undecorated PLGA spheres. The decoration of PLGA spheres with HAp induced lesser mineral deposition and lesser upregulation of osteogenic markers compared to those induced by the composite particles where HAp nanoparticles were embedded inside the PLGA spheres. This was explained by homeostatic mechanisms governing the cell metabolism, which ensure than the sensation of a product of this metabolism in the cell interior or exterior is met with the reduction in the metabolic activity. The antagonistic relationship between proliferation and bone production was demonstrated by the higher proliferation rate of cells challenged with HAp-coated PLGA spheres than of those treated with PLGA-coated HAp. It is concluded that the overwhelmingly positive response of tissues to HAp-coated biomaterials for bone replacement is unlikely to be due to the direct induction of new bone growth in osteoblasts adhering to the HAp coating. Rather, these positive effects are consequential to more elementary aspects of cell attachment, mechanotransduction, and growth at the site of contact between the HAp-coated material and the tissue.

Improving the Mechanical Resistance of Hydroxyapatite/Chitosan Composite Materials Made of Nanofibers with Crystalline Preferential Orientation

The stability and mechanical properties of hydroxyapatite (HAp)/Chitosan composite materials depend on the dispersion of HAp aggregates in the chitosan matrix and on the chemical interaction between them. Therefore, hexagonal cross-sectioned HAp nanofibers were produced using a microwave-assisted hydrothermal method. Glutamic acid was used to control the HAp crystal growth; thereby, nanofibers were obtained with a preferential crystalline orientation, and they were grown along the “c” axis of HAp crystal structures. This morphology exposed the (300) and (100) crystal planes on the surface, and several phosphate groups and calcium ions were also exposed; they were able to form numerous chemical interactions with the amine, hydroxyl, and carbonyl groups of chitosan. Consequently, the final mechanical resistance of the composite materials was synergistically increased. Nanofibers were mixed with commercial chitosan using a sonotrode to improve their dispersion within the biopolymer matrix and prevent migration. The HAp nanofiber/Chitosan composite materials showed higher mechanical resistance than that observed in similar materials with the same chemical composition that were made of commercial HAp powders, which were used as reference materials. The mechanical resistance under tension of the composite materials made of nanofibers was similar to that reported for cortical bone.

Understanding Zinc-Doped Hydroxyapatite Structures Using the First-Principles Calculations and Convolutional Neural Network Algorithm

Element doping is widely used to improve the performance of materials by changing their intrinsic properties. However, the lack of direct crystallographic structures for dopants has restricted the effective high-throughput...

Control Release Coating for Urinary Catheters with Enhanced Released Profile for Sustained Antimicrobial Protection

Catheter-associated urinary tract infections (CAUTIs) are common and pose significant costs to healthcare systems. To date, this problem is largely unsolved as commercially available antimicrobial catheters are still lacking in functionality and performance. A prior study by Lim et al. ( Biotechnol. Bioeng. 2018, 115 (8), 2000-2012) reported the development of a novel anhydrous polycaprolactone (PCL) polymer formulation with controlled-release functionality for antimicrobial peptides. In this follow-up study, we developed an improved antimicrobial peptide (AMP)-impregnated poly(ethylene glycol) (PEG)-polycaprolactone (PCL) anhydrous polymer coating for enhanced sustained controlled-release functionality to provide catheters with effective antimicrobial properties. Varying the ratio of PEG and PEG-PCL copolymers resulted in polymers with different morphologies, consequently affecting the AMP release profiles. The optimal coating, formulated with 10% (w/w) PEG-PCL in PCL, achieved a controlled AMP release rate of 31.65 ± 6.85 μg/mL daily for up to 19 days, with a moderate initial burst release. Such profile is desired for antimicrobial coating as the initial burst release acts as a sterilizer to kill the bacteria present in the urinary tract upon insertion, and the subsequent linear release functions as a prophylaxis to deter opportunistic microbial infections. As a proof-of-concept application, our optimized coating was then applied to a commercial silicone catheter for further antibacterial tests. Preliminary results revealed that our coated catheters outperformed commercial silver-based antimicrobial catheters in terms of antimicrobial performance and sustainability, lasting for 4 days. Application of the controlled-release coating also aids in retarding biofilm formation, showing a lower extent of biofilm formation at the end of seven inoculation cycles.

Hydroxyapatite grafted chitosan/laponite RD hydrogel: Evaluation of the encapsulation capacity, pH-responsivity, and controlled release behavior

In this study, a pH-responsive drug carrier was developed for the controllable release of drugs in the gastric environment. Chitosan (CS), a pH-sensitive biopolymer, and laponite RD (LAP), a nano-clay with a high drug-loading capability, were used to design the new carrier. Hydroxyapatite (HA) was grafted into CS/LAP matrix through a simple co-precipitation technique to overcome the burst release of the CS/LAP. The structural analysis and swelling tests of products demonstrated that the co-precipitation method has led to the penetration of HA nanoparticles inside the CS/LAP matrix and occupying its hollow pores. Occupation of the empty pores can lead to the entrapment of drug molecules, thereby reducing the release rate. The nanocomposite showed a high loading capacity to ofloxacin as a drug model. The effects of HA content on release behavior of nanocomposite were investigated at simulated gastric (pH 1.2) and intestine (pH 7.4) environments. The results indicated a high pH sensitivity for CS/LAP/HA. HA grafting reduced the release rate remarkably regardless of pH. The release rate of CS/LAP/HA decreased by 44-63% in pH 1.2 and 41-51% in pH 7.4 compared to CS/LAP. Kinetic studies indicated that grafting the HA in CS/LAP has changed the drug release mechanism.

In vitro evaluation of curcumin-loaded chitosan-coated hydroxyapatite nanocarriers as a potential system for effective treatment of cancer

Nanotechnology has many potential applications in cancer treatment. For example, nano-drug delivery systems (NDDS) with high bioavailability, biodegradability, and biocompatibility have been developed, in order to increase the therapeutic effects of anticancer drugs. Among these NDDS, high-performance hydroxyapatite (HA) nanoparticles are rapidly advancing in the targeted cancer treatment due to their numerous benefits. Curcumin is an herbal metabolite that acts as a chemical inhibitor through the inhibition of tumor cells and the progression of many cancers. However, the poor bioavailability of curcumin is the most important challenge in using this substance. In this study, HA nanoparticles coated by chitosan were used as a pH-sensitive biopolymer to improve the efficiency and bioavailability of curcumin. For this purpose, HA nanoparticles were first synthesized by the sol-gel method. Then, a layer of chitosan was coated on it, and the curcumin drug was encapsulated in the nanocarrier, under controlled conditions. Techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) were used to characterize the nanocarriers. In the second part, nano-drugs prepared by various bioassays were examined. For this purpose, the rate of cytotoxicity by the methyl-thiazol-tetrazolium (MTT) assay and the rate of apoptosis induction by the acridine orange and ethidium bromide (AO/EB) staining method on the brain carcinoma U87MG cell line were investigated.

Formulation and characterization of hydroxyapatite-based composite with enhanced compressive strength and controlled antibiotic release

A composite based on hydroxyapatite (HA) and chitosan (CS) combined with ciprofloxacin (CIP) was formulated by the solid-liquid mixing method. The optimization of the solid to the liquid ratio and the use of chitosan in a small amount (≤5 wt%) promoted the preparation of stable and rigid monoliths. A synergistic effect of CS and CIP contents on the compressive strength of the CIP-loaded composite was evidenced. The compressive strength of the fabricated biocomposite ranged in values from 1 to 6 MPa, comparable to those reported for cancellous bone. The improvement of the mechanical properties with the increase of the rate of organic components was correlated with the diminution of the surface area and the reduction in the pore volume of the specimens. On the other hand, the in vitro release experiments of the antibiotic indicated a sustained and controlled release of CIP over 10 days. Moreover, in vitro antibacterial tests performed on the biocomposite HA-CS5-CIP showed significant inhibition of Staphylococcus aureus and Escherichia coli pathogens. According to the showed results, the formulated composite with three-phase components could be a promising material for bone repair and local antibiotic release for the treatment of bone infections.

Chitosan-based drug delivery systems: From synthesis strategy to osteomyelitis treatment - A review

Osteomyelitis is a complex disease in orthopedics mainly caused by bacterial pathogens invading bone or bone marrow. The treatment of osteomyelitis is highly difficult and it is a major challenge in orthopedic surgery. The long-term systemic use of antibiotics may lead to antibiotic resistance and has limited effects on eradicating local biofilms. Localized antibiotic delivery after surgical debridement can overcome the problem of antibiotic resistance and reduce systemic toxicity. Chitosan, a special cationic polysaccharide, is a product extracted from the deacetylation of chitin. It has numerous advantages, such as nontoxicity, biocompatibility, and biodegradability. Recently, chitosan has attracted significant attention in bacterial inhibition and drug delivery. Because chitosan contains many functional bioactive groups conducive to chemical reaction and modification, some chitosan-based biomaterials have been applied as the local antibiotic delivery systems in the treatment of osteomyelitis. This review aims to introduce recent advances in the biomedical applications of chitosan-based drug delivery systems in osteomyelitis treatment and to highlight the perspectives for further studies.

Why have nanotechnologies been underutilized in the global uprising against the coronavirus pandemic?

Prior research on nanotechnologies in diagnostics, prevention and treatment of coronavirus infections is reviewed. Gold nanoparticles and semiconductor quantum dots in colorimetric and immunochromatographic assays, silica nanoparticles in the polymerase chain reaction and spike protein nanospheres as antigen carriers and adjuvants in vaccine formulations present notable examples in diagnostics and prevention, while uses of nanoparticles in coronavirus infection treatments have been merely sporadic. The current absence of antiviral therapeutics that specifically target human coronaviruses, including SARS-CoV-2, might be largely due to the underuse of nanotechnologies. Elucidating the interface between nanoparticles and coronaviruses is timely, but presents the only route to the rational design of precisely targeted therapeutics for coronavirus infections. Such a fundamental approach is also a viable prophylaxis against future pandemics of this type.

Bone Diseases: Current Approach and Future Perspectives in Drug Delivery Systems for Bone Targeted Therapeutics

Bone diseases include a wide group of skeletal-related disorders that cause mobility limitations and mortality. In some cases, e.g., in osteosarcoma (OS) and metastatic bone cancer, current treatments are not fully effective, mainly due to low patient compliance and to adverse side effects. To overcome these drawbacks, nanotechnology is currently under study as a potential strategy allowing specific drug release kinetics and enhancing bone regeneration. Polymers, ceramics, semiconductors, metals, and self-assembled molecular complexes are some of the most used nanoscale materials, although in most cases their surface properties need to be tuned by chemical or physical reactions. Among all, scaffolds, nanoparticles (NPs), cements, and hydrogels exhibit more advantages than drawbacks when compared to other nanosystems and are therefore the object of several studies. The aim of this review is to provide information about the current therapies of different bone diseases focusing the attention on new discoveries in the field of targeted delivery systems. The authors hope that this paper could help to pursue further directions about bone targeted nanosystems and their application for bone diseases and bone regeneration.

Role of nanoparticles in osteogenic differentiation of bone marrow mesenchymal stem cells

The present study aimed to investigate the osteoinductive potentiality of some selected nanostructures; Hydroxyapatite (HA-NPs), Gold (Au-NPs), Chitosan (C-NPs), Gold/hydroxyapatite (Au/HA-NPs) and Chitosan/hydroxyapatite (CH-NPs) on bone marrow- derived mesenchymal stem cells (BM-MSCs). These nanostructures were characterized using transmission electron microscope and Zetasizer. MSCs were isolated from bone marrow of rat femur bones and their identity was documented by morphology, flow cytometry and multi-potency capacity. The influence of the selected nanostructures on the viability, osteogenic differentiation and subsequent matrix mineralization of BM-MSCs was determined by MTT assay, molecular genetic analysis and alizarin red S staining, respectively. MTT analysis revealed insignificant toxicity of the tested nanostructures on BM-MSCs at concentrations ranged from 2 to 25 µg/ml over 48 h and 72 h incubation period. Notably, the tested nanostructures potentiate the osteogenic differentiation of BM-MSCs as evidenced by a prominent over-expression of runt-related transcription factor 2 (Runx-2) and bone morphogenetic protein 2 (BMP-2) genes after 7 days incubation. Moreover, the tested nanostructures induced matrix mineralization of BM-MSCs after 21 days as manifested by the formation of calcium nodules stained with alizarin red S. Conclusively, these data provide a compelling evidence for the functionality of the studied nanostructures as osteoinductive materials motivating the differentiation of BM-MSCs into osteoblasts with the most prominent effect observed with Au-NPs and Au/HA-NPs, followed by CH-NPs.

Novel chitosan-based pH-responsive lipid-polymer hybrid nanovesicles (OLA-LPHVs) for delivery of vancomycin against methicillin-resistant Staphylococcus aureus infections

The development of novel materials is necessary for adequate delivery of drugs to combat the Methicillin-resistant Staphylococcus aureus (MRSA) burden due to the limitations of conventional methods and challenges associated with antimicrobial resistance. Hence, this study aimed to synthesise a novel oleylamine based zwitterionic lipid (OLA) and explore its potential to formulate chitosan-based pH-responsive lipid-polymer hybrid nanovesicles (VM-OLA-LPHVs1) to deliver VM against MRSA. The OLA was synthesised, and the structure characterised by ¹H NMR, ¹³C NMR, FT-IR and HR-MS. The preliminary biocompatibility of OLA and VM-OLA-LPHVs1 was evaluated on HEK-293, A-549, MCF-7 and HepG-2 cell lines using in vitro cytotoxicity assay. The VM-OLA-LPHVs1 were formulated by ionic gelation method and characterised in order to determine the hydrodynamic diameter (D_H), morphology in vitro and in vivo antibacterial efficacy. The result of the in vitro cytotoxicity study revealed cell viability of above 75% in all cell lines when exposed to OLA and VM-OLA-LPHVs1, thus indicating their biosafety. The VM-OLA-LPHVs1 had a D_H, polydispersity index (PDI), and EE% of 198.0 ± 14.04 nm, 0.137 ± 0.02, and 45.61 ± 0.54% respectively at physiological pH, with surface-charge (ζ) switching from negative at pH 7.4 to positive at pH 6.0. The VM release from the VM-OLA-LPHVs1 was faster at pH 6.0 compared to physiological pH, with 97% release after 72-h. The VM-OLA-LPHVs1 had a lower minimum inhibitory concentration (MIC) value of 0.59 μg/mL at pH 6.0 compared to 2.39 μg/mL at pH 7.4, against MRSA with 52.9-fold antibacterial enhancement. The flow cytometry study revealed that VM-OLA-LPHVs1 had similar bactericidal efficacy on MRSA compared to bare VM, despite an 8-fold lower VM concentration in the nanovesicles. Additionally, fluorescence microscopy study showed the ability of the VM-OLA-LPHVs1 to eliminate biofilms. The electrical conductivity, and protein/DNA concentration, increased and decreased respectively, as compared to bare VM which indicated greater MRSA membrane damage. The in vivo studies in a BALB/c mouse-infected skin model treated with VM-OLA-LPHVs1 revealed 95-fold lower MRSA burden compared to the group treated with bare VM. These findings suggest that OLA can be used as an effective novel material for complexation with biodegradable polymer chitosan (CHs) to form pH-responsive VM-OLA-LPHVs1 nanovesicles which show greater potential for enhancement and improvement of treatment of bacterial infections.

The future application of nanomedicine and biomimicry in plastic and reconstructive surgery

Plastic surgery encompasses a broad spectrum of reconstructive challenges and prides itself upon developing and adopting new innovations. Practice has transitioned from microsurgery to supermicrosurgery with a possible future role in even smaller surgical frontiers. Exploiting materials on a nanoscale has enabled better visualization and enhancement of biological processes toward better wound healing, tumor identification and viability of tissues, all cornerstones of plastic surgery practice. Recent advances in nanomedicine and biomimicry herald further reconstructive progress facilitating soft and hard tissue, nerve and vascular engineering. These lay the foundation for improved biocompatibility and tissue integration by the optimization of engineered implants or tissues. This review will broadly examine each of these technologies, highlighting areas of progress that reconstructive surgeons may not be familiar with, which could see adoption into our armamentarium in the not-so-distant future.

Calcium phosphate nanoparticles as intrinsic inorganic antimicrobials: In search of the key particle property

One of the main goals of materials science in the 21st century is the development of materials with rationally designed properties as substitutes for traditional pharmacotherapies. At the same time, there is a lack of understanding of the exact material properties that induce therapeutic effects in biological systems, which limits their rational optimization for the related medical applications. This study sets the foundation for a general approach for elucidating nanoparticle properties as determinants of antibacterial activity, with a particular focus on calcium phosphate nanoparticles. To that end, nine physicochemical effects were studied and a number of them were refuted, thus putting an end to frequently erred hypotheses in the literature. Rather than having one key particle property responsible for eliciting the antibacterial effect, a complex synergy of factors is shown to be at work, including (a) nanoscopic size; (b) elevated intracellular free calcium levels due to nanoparticle solubility; (c) diffusivity and favorable electrostatic properties of the nanoparticle surface, primarily low net charge and high charge density; and (d) the dynamics of perpetual exchange of ultrafine clusters across the particle/solution interface. On the positive side, this multifaceted mechanism is less prone to induce bacterial resistance to the therapy and can be a gateway to the sphere of personalized medicine. On a more problematic side, it implies a less intense effect compared to single-target molecular therapies and a difficulty of elucidating the exact mechanisms of action, while also making the rational design of theirs for this type of medical application a challenge.

Bacteriocin Isolated from Lactobacillus Rhamnosus L34 Has Antibacterial Effects in a Rabbit Model of Infection After Mandible Fracture Fixation

BACKGROUND Rigid internal fixation (RIF) technology is a recently developed fracture fixation technique in which use of specific antibiotics before and after the operation and timely treatment of local infections is necessary. MATERIAL AND METHODS The bacteriocins were isolated from Lactobacillus rhamnosus L34. Twenty-four New Zealand White female rabbits were divided into 2 groups: bacteriocins and control group. After mandible fracture fixation, the rabbits were infected with S. aureus and subsequently injected with either bacteriocins or saline. The biofilm samples were harvested from rabbits euthanized on the 1st, 3rd, and 5th days and observed using a fluorescence microscope. Blood samples were collected at 1 h, 12 h, 1 day, 3 days, and 5 days after the injection of either bacteriocin or saline to test the level of C-reactive protein and TNF-α. RESULTS Significant differences in the biofilm formation were evident between the bacteriocins and saline treatment group on days 1, 3, and 5. Moreover, the serum levels of TNF-α and CRP after treatment with bacteriocins were significantly lower than in controls. CONCLUSIONS Use of bacteriocins isolated from Lactobacillus rhamnosus L34 may be a promising way to control infections of mandible fracture after internal fixation in vivo.

Coatings as the useful drug delivery system for the prevention of implant-related infections

Implant-related infections (IRIs) which led to a large amount of medical expenditure were caused by bacteria and fungi that involve the implants in the operation or in ward. Traditional treatments of IRIs were comprised of repeated radical debridement, replacement of internal fixators, and intravenous antibiotics. It needed a long time and numbers of surgeries to cure, which meant a catastrophe to patients. So how to prevent it was more important than to cure it. As an excellent local release system, coating is a good idea by its local drug infusion and barrier effect on resisting biofilms which were the main cause of IRIs. So in this review, materials used for coatings and evidences of prevention were elaborated.

Biowaste-Derived Hydroxyapatite for Effective Removal of Reactive Yellow 4 Dye: Equilibrium, Kinetic, and Thermodynamic Studies

This study examines the application of poultry eggshell (PES) as a source of calcium for the synthesis of hydroxyapatite (HA) via annealation. The synthesized powder (poultry eggshell hydroxyapatite (PESHA)) was characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), EDAX, and transmission electron microscopy (TEM) analytical techniques. This powder was used for adsorptive removal of the Reactive Yellow 4 (RY4) dye in a batch process. Results from morphological analysis by SEM and TEM revealed that the microstructure of the apatite is made up of needle-rod-like particles with the length of 15-60 nm, breadth of 4-6 nm, and crystallite size of 86.32 nm. EDAX revealed that HA has Ca/P ratio of 1.63, indicating a nonstoichiometric apatite, whereas XRD analysis presented it as a pure monophasic hydroxyapatite powder. Fourier Transform Infrared (FTIR) spectroscopy indicated that the adsorption is due to the electrostatic interaction between the functional groups of the dye and those on the apatite surface. The maximum adsorption capacity (Q _max) of 127.9 mg g^-1 was obtained for the adsorption process, whereas the pseudo-first-order model with R ² > 0.99 best described the adsorption mechanism. Furthermore, the thermodynamic studies revealed that the adsorption process was exothermic and spontaneous in nature with ΔH and ΔS values of 120.79 kJ mol^-1 and 0.395 kJ mol^-1 K^-1, respectively. Thus, hydroxyapatite fabricated from the poultry waste of eggshell can be effectively utilized as an excellent nontoxic and cheap adsorbent for the removal of RY4 dye from aqueous medium.

Novel calcitonin gene-related peptide/chitosan-strontium-calcium phosphate cement: Enhanced proliferation of human umbilical vein endothelial cells in vitro

Bone cement materials have some disadvantages, including slow degradation and no biological activity, which greatly weakens their clinical application. Therefore, the search for a multifunctional bioactive bone cement has become urgent. In this study, a novel bone cement sample of calcitonin gene-related peptide (CGRP)/chitosan-strontium (Sr)-calcium phosphate cement (CPC) was developed. The structure and morphology were observed by scanning electron microscope (SEM). The cytotoxicity and proliferation of CGRP/chitosan-Sr-CPC were also measured. The expression of CGRP receptor 1 was measured using an immunofluorescence assay. Real-time polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA) were employed to quantify the VEGF mRNA and protein levels, respectively. Finally, the ability of the material to improve angiogenesis was assessed by using human umbilical vein endothelial cells (HUVECs) tube formation assay. The results showed that CGRP/Chitosan-Sr-CPC had the characteristics of a good orthopedic material without showing cell cytotoxicity to HUVECs. Meanwhile, CGRP/chitosan-Sr-CPC could release CGRP and enhance the proliferation of HUVECs via CGRP receptors. Moreover, CGRP/chitosan-Sr-CPC significantly upregulated the expression of the VEGF gene and protein in HUVECs, which might help improve the angiogenesis microenvironment. Besides, CGRP/chitosan-Sr-CPC could significantly improve angiogenesis of HUVECs. These findings provide new therapeutic material for the treatment of osteoporotic bone injury. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 107B: 19-28, 2019.

Nanomedicine for safe healing of bone trauma: Opportunities and challenges

Historically, high-energy extremity injuries resulting in significant soft-tissue trauma and bone loss were often deemed unsalvageable and treated with primary amputation. With improved soft-tissue coverage and nerve repair techniques, these injuries now present new challenges in limb-salvage surgery. High-energy extremity trauma is pre-disposed to delayed or unpredictable bony healing and high rates of infection, depending on the integrity of the soft-tissue envelope. Furthermore, orthopedic trauma surgeons are often faced with the challenge of stabilizing and repairing large bony defects while promoting an optimal environment to prevent infection and aid bony healing. During the last decade, nanomedicine has demonstrated substantial potential in addressing the two major issues intrinsic to orthopedic traumas (i.e., high infection risk and low bony reconstruction) through combatting bacterial infection and accelerating/increasing the effectiveness of the bone-healing process. This review presents an overview and discusses recent challenges and opportunities to address major orthopedic trauma through nanomedical approaches.

Synthesis of hydroxyapatite for biomedical applications

The current need for long lasting implants and bone substitutes characterized by biocompatibility, bioactivity and mechanical properties, without the immune rejection is a great challenge for scientists. These bone substitute structures should be prepared for individual patients with all details controlled on the micrometer level. Similarly, nontoxic, biocompatible targeted drug delivery systems which allow controlling the rate and time period of the drug delivery and simultaneously eliminating toxic and side effects on the healthy tissues, are of great interest. Extensive attempts have been made to develop a simple, efficient, and green method to form biofunctional scaffolds and implant coatings possessing the above mentioned significant biocompatibility, bioactivity and mechanical strength. Moreover, that could also serve as drug delivery systems. Hydroxyapatite (HA) which is a major mineral component of vertebrate bones and teeth is an excellent material for these purposes. In this literature review the biologically inspired scaffolds, bone substitutes, implants characterized by mechanical strength and biocompatibility, as well the drug delivery systems, based on hydroxyapatite are discussed.

Nonlinear Oscillatory Dynamics of the Hardening of Calcium Phosphate Bone Cements

Here we report on the nonlinear, oscillatory dynamics detected in the evolution of phase composition during the setting of different calcium phosphate cements, two of which evolved toward brushite and one toward hydroxyapatite as the final product. Whereas both brushite-forming cements contained ion-doped β-tricalcium phosphate as the initial phase, the zinc-containing one yielded scholzite as an additional phase during setting and the oscillations between these two products were pronounced throughout the entire 80 h setting period, long after the hardening processes was over from the mechanical standpoint. Oscillations in the copper-containing system involved the amount of brushite as the main product of the hardening reaction and they progressed faster toward an equilibrium point than in the zinc-containing system. Initially detected with the use of in situ energy-dispersive X-ray diffractometry, the oscillations were confirmed with a sufficient level of temporal matching in an in situ Fourier transform infrared spectroscopic analysis. The kinetic reaction analysis based on the Johnson-Mehl-Avrami-Kolmogorov model indicated an edge-controlled nucleation mechanism for brushite. The hydroxyapatite-forming cement comprised gelatin as an additional phase with a role of slowing down diffusion and allowing the detection of otherwise rapid oscillations in crystallinity and in the amount of the apatitic phase on the timescale of minutes. A number of possible causes for these dynamic instabilities were discussed. The classical chemical oscillatory model should not apply to these systems unless in combination with less exotic mechanisms of physicochemical nature. One possibility is that the variations in viscosity, directly affecting diffusion and nucleation rates and accompanying growth and transformation from the lower to the higher interfacial energy per the Ostwald-Lussac rule, are responsible for the oscillatory dynamics. The conception of bone replacement materials and tissue engineering constructs capable of engaging in the dynamics of integration with the natural tissues in compliance with this oscillatory nature may open a new avenue for the future of this type of medical devices. To succeed in this goal, the mechanism of these and similar instabilities must be better understood.

Bisphosphonate-Functionalized Hydroxyapatite Nanoparticles for the Delivery of the Bromodomain Inhibitor JQ1 in the Treatment of Osteosarcoma

Osteosarcoma (OS) is one of the most common neoplasia among children, and its survival statistics have been stagnating since the combinatorial anticancer therapy triad was first introduced. Here, we report on the assessment of the effect of hydroxyapatite (HAp) nanoparticles loaded with medronate, the simplest bisphosphonate, as a bone-targeting agent and JQ1, a small-molecule bromodomain inhibitor, as a chemotherapeutic in different 2D and 3D K7M2 OS in vitro models. Both additives decreased the crystallinity of HAp, but the effect was more intense for medronate because of its higher affinity for HAp. As the result of PO₄^3--NH⁺ binding, JQ1 shielded the surface phosphates of HAp and pushed its surface charge to more positive values, exhibiting the opposite effect from calcium-blocking medronate. In contrast to the faster and more exponential release of JQ1 from monetite, its release from HAp nanoparticles followed a zero-order kinetics, but 98% of the payload was released after 48 h. The apoptotic effect of HAp nanoparticles loaded with JQ1, with medronate and with both JQ1 and medronate, was selective in 2D culture: pronounced against the OS cells and nonexistent against the healthy fibroblasts. While OS cell invasion was significantly inhibited by all of the JQ1-containing HAp formulations, that is, with and without medronate, all of the combinations of the targeting compound, medronate, and the chemotherapeutic, JQ1, delivered using HAp, but not HAp alone, inhibited OS cell migration from the tumor spheroids. JQ1 delivered using HAp had an effect on tumor migration, invasion, and apoptosis even at extremely low, subnanomolar concentrations, at which no effect of JQ1 per se was observed, meaning that this form of delivery could help achieve a multifold increase of this drug's efficacy. More than 80% of OS cells internalized JQ1-loaded HAp nanoparticles after 24 h of coincubation, suggesting that this augmentation of the activity of JQ1 may be due to the intracellular delivery and sustained release of the drug enabled by HAp. In addition to the reduction of the OS cell viability, the reduction of the migration and invasion radii was observed in OS tumor spheroids challenged with even JQ1-free medronate-functionalized HAp nanoparticles, demonstrating a definite anticancer activity of medronate alone when combined with HAp. The effect of medronate-functionalized JQ1-loaded HAp nanoparticles was most noticeable against OS cells differentiated into an osteoblastic lineage, in which case they surpassed in effect pure JQ1 and medronate-free compositions. The activity of JQ1 was mediated through increased Ezrin expression and decreased RUNX2 expression and was MYC and FOSL1 independent, but these patterns of gene expression changed in cells challenged with the nanoparticulate form of delivery, having been accompanied by the upregulation of RUNX2 and downregulation of Ezrin in OS cells treated with medronate-functionalized JQ1-loaded HAp nanoparticles.

Recent coating developments for combination devices in orthopedic and dental applications: A literature review

Orthopedic and dental implants have been used successfully for decades to replace or repair missing or damaged bones, joints, and teeth, thereby restoring patient function subsequent to disease or injury. However, although device success rates are generally high, patient outcomes are sometimes compromised due to device-related problems such as insufficient integration, local tissue inflammation, and infection. Many different types of surface coatings have been developed to address these shortcomings, including those that incorporate therapeutic agents to provide localized delivery to the surgical site. While these coatings hold enormous potential for improving device function, the list of requirements that an ideal combination coating must fulfill is extensive, and no single coating system today simultaneously addresses all of the criteria. Some of the primary challenges related to current coatings are non-optimal release kinetics, which most often are too rapid, the potential for inducing antibiotic resistance in target organisms, high susceptibility to mechanical abrasion and delamination, toxicity, difficult and expensive regulatory approval pathways, and high manufacturing costs. This review provides a survey of the most recent developments in the field, i.e., those published in the last 2-3years, with a particular focus on technologies that have potential for overcoming the most significant challenges facing therapeutically-loaded coatings. It is concluded that the ideal coating remains an unrealized target, but that advances in the field and emerging technologies are bringing it closer to reality. The significant amount of research currently being conducted in the field provides a level of optimism that many functional combination coatings will ultimately transition into clinical practice, significantly improving patient outcomes.

Encapsulation of epigallocatechin gallate in zein/chitosan nanoparticles for controlled applications in food systems

The objective of this study was to prepare chitosan nanoparticles (CS NPs) coated with zein as a promising encapsulation and delivery system for epigallocatechin gallate (EGCG). The factors influencing the nanoparticle fabrication, including zein concentration, zein/chitosan weight ratio and EGCG encapsulation percentage, were systematically investigated. The physicochemical and structural analysis showed that the electrostatic interactions and hydrogen bonds were the major forces responsible for nanoparticles formation. The transmission electron microscopy study revealed the spherical nature with smooth surface of obtained nanoparticles. The release profile of EGCG showed a burst effect, followed by slow release. EGCG release was relatively higher from zein/chitosan nanoparticles (zein/CS NPs) with higher DPPH scavenging activity, than that of NPs without zein coating in 95% ethanol fatty simulant. These results indicated that controlled-release of EGCG from zein/CS NPs and its corresponding antioxidant activities in 95% ethanol fatty simulant may provide long-term protection against oxidation for fatty foods.

One Ion to Rule Them All: Combined Antibacterial, Osteoinductive and Anticancer Properties of Selenite-Incorporated Hydroxyapatite

Although hydroxyapatite (HAp) has been doped with dozens of different ions, the quest for an ion imparting a combination of properties conducive to bone healing is still ongoing. Because of its protean potency and the similarity in size and shape to the phosphate tetrahedron, selenite ion presents a natural ionic substitute in HAp. The incorporation of selenite into synthetic HAp using two different methods - co-precipitation and ion-exchange sorption - was studied for its effect on crystal properties and on a triad of biological responses: antibacterial, anticancer and osteoinductive. Co-precipitation yielded HAp with higher selenite contents than sorption and the stoichiometry of HAp richest in selenite was represented as Ca_9.75(PO₄)_5.75(SeO₃)_0.25(OH)_1.75. Crystallinity of HAp decreased in direct proportion with the amount of selenite incorporated. Because of their lower selenite content, HAp powders prepared by ion-exchange exhibited a consistently higher crystallinity compared to the co-precipitated ones. Annealing partially recovered the crystallinity, yet the difference in crystallinity between powders prepared by co-precipitation and by ion-exchange remained, suggesting that the amorphization is mainly due to structural incorporation of selenite, not its effect on the crystal growth kinetics. The addition of selenite changed the morphology of HAp nanoparticles from acicular to rounded and affected the crystal lattice parameters in different ways depending on whether the powders were annealed or not. As for the annealed powders, the incorporation of selenite contracted the lattice in both a and c crystallographic directions. In the agar diffusion assay, the effectiveness of HAp was more dependent on the presence or absence of selenite in it than on its concentration and was highest against E. coli and S. aureus, moderately high against S. enteritidis and ineffective against P. aeruginosa. In liquid inoculation tests, on the other hand, the antibacterial activity of HAp was directly proportional to the amount of selenite contained in it. The viability of K7M2 osteosarcoma cells decreased in direct proportion with the amount of selenite in HAp and was significantly different from the untreated control and from pure HAp at contents equal to or higher than 1.9 wt.%. In contrast, no reduction was observed in the viability of primary fibroblasts treated with HAp incorporating different amounts of selenite ions, suggesting their potentially selective anticancer activity: lethal for the cancer cells and harmless for the healthy cells. Finally, mRNA expression of bone gamma-carboxyglutamate protein (BGLAP3) was higher in differentiated MC3T3-E1 osteoblastic cells treated with selenite-incorporated HAp particles than in cells treated with pure HAp. The osteoinductive effect was due to an overall higher metabolic activity of cells treated with the particles and not due to increased proliferation. In such a way, a triad of antibacterial, osteoinductive and anticancer activities was attributed to selenite-incorporated HAp.

A novel composite scaffold comprising ultralong hydroxyapatite microtubes and chitosan: preparation and application in drug delivery

The composite scaffold comprising ultralong hydroxyapatite microtubes and chitosan with high drug loading capacity and sustained drug release properties has been successfully prepared.

Selective anticancer activity of hydroxyapatite/chitosan-poly(d,l)-lactide-co-glycolide particles loaded with an androstane-based cancer inhibitor

In an earlier study we demonstrated that hydroxyapatite nanoparticles coated with chitosan-poly(d,l)-lactide-co-glycolide (HAp/Ch-PLGA) target lungs following their intravenous injection into mice. In this study we utilize an emulsification process and freeze drying to load the composite HAp/Ch-PLGA particles with 17β-hydroxy-17α-picolyl-androst-5-en-3β-yl-acetate (A), a chemotherapeutic derivative of androstane and a novel compound with a selective anticancer activity against lung cancer cells. ¹H NMR and ¹³C NMR techniques confirmed the intact structure of the derivative A following its entrapment within HAp/Ch-PLGA particles. The thermogravimetric and differential thermal analyses coupled with mass spectrometry were used to assess the thermal degradation products and properties of A-loaded HAp/Ch-PLGA. The loading efficiency, as indicated by the comparison of enthalpies of phase transitions in pure A and A-loaded HAp/Ch-PLGA, equaled 7.47wt.%. The release of A from HAp/Ch-PLGA was sustained, neither exhibiting a burst release nor plateauing after three weeks. Atomic force microscopy and particle size distribution analyses were used to confirm that the particles were spherical with a uniform size distribution of d₅₀=168nm. In vitro cytotoxicity testing of A-loaded HAp/Ch-PLGA using MTT and trypan blue dye exclusion assays demonstrated that the particles were cytotoxic to the A549 human lung carcinoma cell line (46±2%), while simultaneously preserving high viability (83±3%) of regular MRC5 human lung fibroblasts and causing no harm to primary mouse lung fibroblasts. In conclusion, composite A-loaded HAp/Ch-PLGA particles could be seen as promising drug delivery platforms for selective cancer therapies, targeting malignant cells for destruction, while having a significantly lesser cytotoxic effect on the healthy cells.

The use of nanomaterials to treat bone infections

A new era of osteomyelitis treatment has been taking strides towards efficient, local administration of antibiotics at the site of infection. By having them localized to the site of infection, this toxicity is no longer an issue and actually has shown to be a more productive treatment for osteomyelitis. Researchers have focused the production of non-biodegradable, antibiotic, infused bone cements specifically designed for proficient osteocyte binding, useful antibiotic release over a desirable period of time, and promotion of bone regeneration. These cements are then surgically placed on the infected site following debridement and irrigation. The problem, however, is that the use of ineffective cements and the overuse of antibiotics has led to the development of resistant bacteria. Due to this, further research is being done in the field of antibiotic discovery and delivery. Specifically, the development of biodegradable materials capable of efficiently delivering antibiotics and also eliminating the need for follow-up surgery to remove the delivery material is being done, thus reducing exposure risk. Nanoparticles have been developed in the forms of scaffolds and injections to deliver a higher degree and longer lasting duration of antibiotic release, while promoting bone regeneration.

Natural polysaccharides leading to super adsorbent hydroxyapatite nanoparticles for the removal of heavy metals and dyes from aqueous solutions

Water pollution has created a major impact on the environment mainly due to contaminated industrial effluents with toxic substances such as heavy metals and textile dyes.

When 1+1>2: Nanostructured composites for hard tissue engineering applications

Multicomponent, synergistic and multifunctional nanostructures have taken over the spotlight in the realm of biomedical nanotechnologies. The most prospective materials for bone regeneration today are almost exclusively composites comprising two or more components that compensate for the shortcomings of each one of them alone. This is quite natural in view of the fact that all hard tissues in the human body, except perhaps the tooth enamel, are composite nanostructures. This review article highlights some of the most prospective breakthroughs made in this research direction, with the hard tissues in main focus being those comprising bone, tooth cementum, dentin and enamel. The major obstacles to creating collagen/apatite composites modeled after the structure of bone are mentioned, including the immunogenicity of xenogeneic collagen and continuously failing attempts to replicate the biomineralization process in vitro. Composites comprising a polymeric component and calcium phosphate are discussed in light of their ability to emulate the soft/hard composite structure of bone. Hard tissue engineering composites created using hard material components other than calcium phosphates, including silica, metals and several types of nanotubes, are also discoursed on, alongside additional components deliverable using these materials, such as cells, growth factors, peptides, antibiotics, antiresorptive and anabolic agents, pharmacokinetic conjugates and various cell-specific targeting moieties. It is concluded that a variety of hard tissue structures in the body necessitates a similar variety of biomaterials for their regeneration. The ongoing development of nanocomposites for bone restoration will result in smart, theranostic materials, capable of acting therapeutically in direct feedback with the outcome of in situ disease monitoring at the cellular and subcellular scales. Progress in this research direction is expected to take us to the next generation of biomaterials, designed with the purpose of fulfilling Daedalus' dream - not restoring the tissues, but rather augmenting them.

Sustained release of VH and rhBMP-2 from nanoporous magnesium-zinc-silicon xerogels for osteomyelitis treatment and bone repair

Nanoporous magnesium-zinc-silicon (n-MZS) xerogels with a pore size ∼4 nm, a surface area of 718 cm(2)/g, and a pore volume of 1.24 cm(3)/g were synthesized by a sol-gel method. The n-MZS xerogels had high capacity to load vancomycin hydrochloride (VH) and human bone morphogenetic protein-2 (rhBMP-2), after soaking in phosphate buffered saline (PBS) for 24 hours (1.5 and 0.8 mg/g, respectively). Moreover, the n-MZS xerogels exhibited the sustained release of VH and rhBMP-2 as compared with magnesium-zinc-silicon (MZS) xerogels without nanopores (showing a burst release). The VH/rhBMP-2/n-MZS system not only exhibited a good antibacterial property but also promoted the MG63 cell proliferation and differentiation demonstrating good bactericidal activity and cytocompatibility. The results suggested that n-MZS with larger surface area and high pore volume might be a promising carrier for loading and sustained release of VH and rhBMP-2. Hence, the VH/rhBMP-2/n-MZS system might be one of the promising biomaterials for osteomyelitis treatment and bone repair.