Biodegradable and Biocompatible Systems Based on Hydroxyapatite Nanoparticles

Enhanced Release of Calcium Ions from Hydroxyapatite Nanoparticles with an Increase in Their Specific Surface Area

Synthetic calcium phosphates, e.g., hydroxyapatite (HAP) and tricalcium phosphate (TCP), are the most commonly used bone-graft materials due to their high chemical similarity to the natural hydroxyapatite-the inorganic component of bones. Calcium in the form of a free ion or bound complexes plays a key role in many biological functions, including bone regeneration. This paper explores the possibility of increasing the Ca2+-ion release from HAP nanoparticles (NPs) by reducing their size. Hydroxyapatite nanoparticles were obtained through microwave hydrothermal synthesis. Particles with a specific surface area ranging from 51 m2/g to 240 m2/g and with sizes of 39, 29, 19, 11, 10, and 9 nm were used in the experiment. The structure of the nanomaterial was also studied by means of helium pycnometry, X-ray diffraction (XRD), and transmission-electron microscopy (TEM). The calcium-ion release into phosphate-buffered saline (PBS) was studied. The highest release of Ca2+ ions, i.e., 18 mg/L, was observed in HAP with a specific surface area 240 m2/g and an average nanoparticle size of 9 nm. A significant increase in Ca2+-ion release was also observed with specific surface areas of 183 m2/g and above, and with nanoparticle sizes of 11 nm and below. No substantial size dependence was observed for the larger particle sizes.

Particelle nanostrutturate di idrossiapatite biomimetica come sistema di delivery di micro e macro elementi nelle colture biologiche

Nanoparticelle biomimetiche di idrossiapatite drogate con ioni metallici (Cu, Fe, Mg, Zn, K) sono state utilizzate in formulazioni contenenti basse concentrazioni di rame (Cu) e zolfo (S) per controllare la peronospora (plasmopara viticola) e l'oidio (erysiphe necator) della vite. I formulati sono stati testati in campo sulla varietà di vino "Dolcetto" coltivata secondo tecniche di agricoltura biologica, e la loro efficacia è stata confrontata con prodotti commerciali contenenti miscela bordolese e zolfo.

I dati indicano che le formulazioni contenenti bassi dosaggi di rame e zolfo possono essere trasportati in modo efficiente dalle nanoparticelle di idrossiapatite biomimetica e possono ridurre la presenza di micota sulle foglie della vite. Nessun residuo di rame e zolfo è stato rilevato in campioni di vino ottenuti da viti in cui è stata utilizzata l'idrossiapatite biomimetica. Il drogaggio di nanoparticelle di idrossiapatite biomimetica con metalli di transizione è un modo efficiente per fornire micro e macro-elementi alle piante a basso livello di dosaggio. Le formulazioni contenenti idrossiapatite funzionano anche come supporti a lento rilascio di macronutrienti come elementi di calcio e fosforo.

Manufacturing hydroxyapatite scaffold from snapper scales with green phenolic granules as the space holder material

Hydroxyapatite (HA) scaffold was made using the powder metallurgy with an use of a space holder method with a pore-forming agent from green phenolic (GP) granules. The novelty of this study was the use of GP granules as an agent that does not melt at high temperatures to avoid damaging the tangential contact between the HA powder during the sintering process. HA from snapper scales was added and mixed with polyvinyl alcohol (PVA) and ethanol to form a slurry. The ethanol content was then removed by drying at room temperature. The HA, which contained PVA, was added with GP granules as a pore-forming agent in various amounts to get the desired porosity. The green body was made using a stainless steel mold with the uniaxial pressing process under a pressure of 100 MPa. To make a scaffold sintered body, a sintering process ran at 1200 °C with a holding time of 2 h while maintaining the heating and cooling rates at 5 °C/min. The physical properties of the scaffold sintered body were characterized through linear shrinkage test, pore measurement, porosity test, phase observation by X-ray diffraction (XRD), and microstructure observation by scanning electron microscopy (SEM) and digital microscopy (DM). So were the mechanical ones through a compressive strength test. The results showed that the sintered body had a compressive strength value of 1.6 MPa at a porosity of 60.7% with a pore size of 129-394 μm. The scaffold contained interconnections between pores at a HA:GP ratio of 55:45 wt%, which matched the condition required for cell tissue growth. The conclusion is that GP granules are good enough to be used as a pore-making agent on scaffolds using the space holder method because they do not damage the tangential contact between the HA powder during the sintering process. However, efforts are needed to remove the remaining GP ash on the scaffold.

Zinc- and magnesium-doped hydroxyapatite-urea nanohybrids enhance wheat growth and nitrogen uptake

The ongoing and unrestrained application of nitrogen fertilizer to agricultural lands has been directly linked to climate change and reductions in biodiversity. The agricultural sector needs a technological upgrade to adopt sustainable methods for maintaining high yield. We report synthesis of zinc and magnesium doped and undoped hydroxyapatite nanoparticles, and their urea nanohybrids, to sustainably deliver nitrogen to wheat. The urea nanohybrids loaded with up to 42% nitrogen were used as a new source of nitrogen and compared with a conventional urea-based fertilizer for efficient and sufficient nitrogen delivery to pot-grown wheat. Doping with zinc and magnesium manipulated the hydroxyapatite crystallinity for smaller size and higher nitrogen loading capacity. Interestingly, 50% and 25% doses of urea nanohybrids significantly boosted the wheat growth and yield compared with 100% doses of urea fertilizer. In addition, the nutritional elements uptake and grain protein and phospholipid levels were significantly enhanced in wheat treated with nanohybrids. These results demonstrate the potential of the multi-nutrient complexes, the zinc and magnesium doped and undoped hydroxyapatite-urea nanoparticles, as nitrogen delivery agents that reduce nitrogen inputs by at least 50% while maintaining wheat plant growth and nitrogen uptake to the same level as full-dose urea treatments.

Hydroxyapatite Biobased Materials for Treatment and Diagnosis of Cancer

Great advances in cancer treatment have been undertaken in the last years as a consequence of the development of new antitumoral drugs able to target cancer cells with decreasing side effects and a better understanding of the behavior of neoplastic cells during invasion and metastasis. Specifically, drug delivery systems (DDS) based on the use of hydroxyapatite nanoparticles (HAp NPs) are gaining attention and merit a comprehensive review focused on their potential applications. These are derived from the intrinsic properties of HAp (e.g., biocompatibility and biodegradability), together with the easy functionalization and easy control of porosity, crystallinity and morphology of HAp NPs. The capacity to tailor the properties of DLS based on HAp NPs has well-recognized advantages for the control of both drug loading and release. Furthermore, the functionalization of NPs allows a targeted uptake in tumoral cells while their rapid elimination by the reticuloendothelial system (RES) can be avoided. Advances in HAp NPs involve not only their use as drug nanocarriers but also their employment as nanosystems for magnetic hyperthermia therapy, gene delivery systems, adjuvants for cancer immunotherapy and nanoparticles for cell imaging.

Rotary Jet-Spun Polycaprolactone/Hydroxyapatite and Carbon Nanotube Scaffolds Seeded with Bone Marrow Mesenchymal Stem Cells Increase Bone Neoformation

Clinically, bone tissue replacements and/or bone repair are challenging. Strategies based on well-defined combinations of osteoconductive materials and osteogenic cells are promising to improve bone regeneration but still require improvement. Herein, we combined polycaprolactone (PCL) fibers, carbon nanotubes (CNT), and hydroxyapatite (nHap) nanoparticles to develop the next generation of bone regeneration material. Fibers formed by rotary jet spinning (RJS) instead of traditional electrospinning (ES) with embedded bone marrow mesenchymal stem cells (BMMSCs) showed the best outcomes to repair rat calvarial defects after 6 weeks. To understand this, it was observed that different morphologies were formed depending on the manufacturing method used. RJS fibers presented a particular topography with rough fibers, which allowed for better cellular growth and cell spreading in vitro around and into a three-dimensional (3D) mesh, while fibers made by ES were more smooth and cellular growth was only measured on the 3D mesh surface. The fibers with incorporated nHap/CNT nanoparticles enhanced in vitro cell performance as indicated by more cellular proliferation, alkaline phosphatase activity, proliferation, and deposition of calcium. Greater bone neoformation occurred by combining three characteristics: the presence of nHap and CNT nanoparticles, the topography of the RJS fibers, and the addition of BMMSCs. RJS fibers with nanoparticles and seeded with BMMSCs showed 10 136 mm³ of bone neoformation, meaning a 10-fold increase compared to using RJS only and BMMSCs (0.853 mm³) and a 5-fold increase from using ES only (2054 mm³) after 6 weeks of implantation. Conversely, none of these approaches used individually showed any significant difference for in vivo bone neoformation, suggesting that their combination is essential for optimizing bone formation. In summary, our work generated a potential material composed of well-defined combinations of suitable scaffolds seeded with BMMSCs for enhancing numerous orthopedic tissue engineering applications.

Valorization of porcine by-products: a combined process for protein hydrolysates and hydroxyapatite production

The meat industry generates large amounts of by-products that are costly to be treated and discarded ecologically; moreover, they could be used to extract high added-value compounds. In this work, we present an innovative combined process which allowed the parallel extraction of both organic and mineral compounds; more specifically protein hydrolysates and single-phase hydroxyapatite were obtained. The protein hydrolysates, extracted through an enzymatic hydrolysis with alcalase, showed a degree of hydrolysis of 53.3 ± 5.1%; moreover, they had a high protein content with peptides with molecular weight lower than 1.2 kDa. Their antioxidant activities, measured with ABTS and ORAC tests, were 21.1 ± 0.5 mg ascorbic acid equivalent/g of dry extract and 87.7 ± 6.3 mg Trolox equivalent/g of dry extract, respectively. Single-phase hydroxyapatite, obtained with a simple calcination at 700 °C on the residues of the hydrolysis process, showed a Ca/P ratio close to the stoichiometric one (1.65 vs. 1.67) and presented a nanometric structure. This study reports a simple and feasible process for the valorization of porcine by-products in a large-scale up generating products with potential applications for environment remediation, biomedicine, nutrition and catalysis/bioenergy.

Graphic Abstract

New Horizons for Hydroxyapatite Supported by DXA Assessment-A Preliminary Study

Dual Energy X-ray Absorptiometry (DXA) is a tool that allows the assessment of bone density. It was first presented by Cameron and Sorenson in 1963 and was approved by the Food and Drug Administration. Misplacing the femoral neck box, placing a trochanteric line below the midland and improper placement of boundary lines are the most common errors made during a DXA diagnostic test made by auto analysis. Hydroxyapatite is the most important inorganic component of teeth and bone tissue. It is estimated to constitute up to 70% of human bone weight and up to 50% of its volume. Calcium phosphate comes in many forms; however, studies have shown that only tricalcium phosphate and hydroxyapatite have the characteristics that allow their use as bone-substituted materials. The purpose of this study is aimed at analyzing the results of hip densitometry and hydorxyapatite distribution in order to better assess the structure and mineral density of the femoral neck. However, a detailed analysis of the individual density curves shows some qualitative differences that may be important in assessing bone strength in the area under study. To draw more specific conclusions on the therapy applied for individual patients, we need to determine the correct orientation of the bone from the resulting density and document the trends in the density distribution change. The average results presented with the DXA method are insufficient.

Investigation of the Effect of Nanocrystalline Calcium Carbonate-Substituted Hydroxyapatite and L-Lysine and L-Arginine Surface Interactions on the Molecular Properties of Dental Biomimetic Composites

Differences in the surface interactions of non-stoichiometric nanocrystalline B-type carbonate-substituted hydroxyapatite (n-cHAp) with the amino acids L-Lysine hydrochloride (L-LysHCl) and L-Arginine hydrochloride (L-ArgHCl) in acidic and alkaline media were determined using structural and spectroscopic analysis methods. The obtained data confirm that hydroxyapatite synthesized using our technique, which was used to develop the n-cHAp/L-LysHCl and n-cHAp/L-ArgHCl composites, is nanocrystalline. Studies of molecular composition of the samples by Fourier transform infrared spectroscopy under the change in the charge state of L-Lysine in environments with different alkalinity are consistent with the results of X-ray diffraction analysis, as evidenced by the redistribution of the modes' intensities in the spectra that is correlated with the side chains, i.e., amide and carboxyl groups, of the amino acid. During the formation of a biomimetic composite containing L-Lysine hydrochloride and n-cHAp, the interaction occurred through bonding of the L-Lysine side chain and the hydroxyl groups of hydroxyapatite, which created an anionic form of L-Lysine at pH ≤ 5. In contrast, in biocomposites based on L-Arginine and n-cHAp, the interaction only slightly depends on pH value, and it proceeds by molecular orientation mechanisms. The X-ray diffraction and infrared spectroscopy results confirm that changes in the molecular composition of n-cHAp/L-ArgHCl biomimetic composites are caused by the electrostatic interaction between the L-ArgHCl molecule and the carbonate-substituted calcium hydroxyapatite. In this case, the bond formation was detected by Fourier transform infrared (FTIR) spectroscopy; the vibrational modes attributed to the main carbon chain and the guanidine group of L-Arginine are shifted during the interaction. The discovered interaction mechanisms between nanocrystalline carbonate-substituted hydroxyapatite that has physicochemical properties characteristic of the apatite in human dental enamel and specific amino acids are important for selecting the formation conditions of biomimetic composites and their integration with the natural dental tissue.

Comparison of the Morphological and Structural Characteristic of Bioresorbable and Biocompatible Hydroxyapatite-Loaded Biopolymer Composites

Calcium phosphate (CaP)-based ceramic–biopolymer composites can be regarded as innovative bioresorbable coatings for load-bearing implants that can promote the osseointegration process. The carbonated hydroxyapatite (cHAp) phase is the most suitable CaP form, since it has the highest similarity to the mineral phase in human bones. In this paper, we investigated the effect of wet chemical preparation parameters on the formation of different CaP phases and compared their morphological and structural characteristics. The results revealed that the shape and crystallinity of CaP particles were strongly dependent on the post-treatment methods, such as heat or alkaline treatment of as-precipitated powders. In the next step, the optimised cHAp particles have been embedded into two types of biopolymers, such as polyvinyl pyrrolidone (PVP) and cellulose acetate (CA). The pure polymer fibres and the cHAp–biopolymer composites were produced using a novel electrospinning technique. The SEM images showed the differences between the morphology and network of CA and PVP fibres as well as proved the successful attachment of cHAp particles. In both cases, the fibres were partially covered with cHAp clusters. The SEM measurements on samples after one week of immersion in PBS solution evidenced the biodegradability of the cHAp–biopolymer composites.

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.

The impact of calcium phosphate on FITC-BSA loading of sonochemically prepared PLGA nanoparticles for inner ear drug delivery elucidated by two different fluorimetric quantification methods

Although therapeutically active proteins are highly efficacious, their content in protective nanoparticles is often too low to elicit adequate plasma levels. A strategy to increase protein loading is the in-situ generation of calcium phosphate as a protein adsorbent. To verify this approach, a highly sensitive and reliable fluorimetric method for quantification of incorporated fluorescein-labelled bovine serum albumin (FITC-BSA) as a model protein drug was developed. Dequenching the fluorescein label by pronase E, which digests the protein backbone, and dissolving the nanoparticle matrix in acetonitrile enabled FITC-BSA quantification in the nanogram per milliliter range. This test was confirmed by a second assay involving alkaline hydrolysis of FITC-BSA and the matrix. Nanoparticles prepared with calcium phosphate contained 40 µg FITC-BSA/mg and nanoparticles without calcium phosphate only 15 µg FITC-BSA/mg, representing a 2.7-fold increase in model protein loading. In this work the nanoparticle preparation procedure was optimized in terms of size for administration in the inner ear, but the range of applications is not limited.

Dental Applications of Systems Based on Hydroxyapatite Nanoparticles—An Evidence-Based Update

Hydroxyapatite is one of the most studied biomaterials in the medical and dental field, because of its biocompatibility; it is the main constituent of the mineral part of teeth and bones. In dental science, hydroxyapatite nanoparticles (HAnps) or nano-hydroxyapatite (nano-HA) have been studied, over the last decade, in terms of oral implantology and bone reconstruction, as well in restorative and preventive dentistry. Hydroxyapatite nanoparticles have significant remineralizing effects on initial enamel lesions, and they have also been used as an additive material in order to improve existing and widely used dental materials, mainly in preventive fields, but also in restorative and regenerative fields. This paper investigates the role of HAnps in dentistry, including recent advances in the field of its use, as well as their advantages of using it as a component in other dental materials, whether experimental or commercially available. Based on the literature, HAnps have outstanding physical, chemical, mechanical and biological properties that make them suitable for multiple interventions, in different domains of dental science. Further well-designed randomized controlled trials should be conducted in order to confirm all the achievements revealed by the in vitro or in vivo studies published until now.

A nano-biomimetic transformation system enables in planta expression of a reporter gene in mature plants and seeds

Plant genetic engineering will be essential to decipher the genomic basis of complex traits, optimize crop genomics, and enable plant-based production of recombinant proteins. However, established plant transformation approaches for bioengineering are fraught with limitations. Although nanoparticle-mediated methods show great promise for advancing plant biotechnology, many engineered nanomaterials can have cytotoxic and ecological effects. Here, we demonstrate the efficient uptake of a nano-biomimetic carrier of plasmid DNA and transient expression of a reporter gene in leaves of Arabidopsis, common ice plant and tobacco, as well as in the developing seed tissues of Arabidopsis, field mustard, barley, and wheat. The nano-biomimetic transformation system described here has all the advantages of other nanoparticle-mediated approaches for passive delivery of genetic cargo into a variety of plant species and is also nontoxic to cells and to the environment for diverse biotechnological applications in plant biology and crop science.

Emerging marine derived nanohydroxyapatite and their composites for implant and biomedical applications

Implant materials must mimic natural human bones with biocompatibility, osteoconductivity and mechanical stability to successfully replace damaged or disease-affected bones. Synthetic hydroxyapatite was incorporated with bioglass to mimic natural bones for replacing conventional implant materials which has led to certain toxicity issues. Hence, hydroxyapatite (HAp) are recently gaining applicational importance as they are resembling the structure and function of natural bones. Further, nanosized HAp is under extensive research to utilize them as a potential replacement for traditional implants with several exclusive properties. However, chemical synthesis of nano-HAp exhibited toxicity towards normal and healthy cells. Recently, biogenic Hap synthesis from marine and animal sources are introduced as a next generation implant materials, due to their mineral ion and significant porous architecture mediated biocompatibility and bone bonding ability, compared to synthetic HAp. Thus, the purpose of the paper is to give a bird's eye view into the conventional approaches for fabricating nano-HAp, its limitations and the significance of using marine organisms and marine food wastes as a precursor for biogenic nano-Hap production. Moreover, in vivo and in vitro analyses of marine source derived nano-HAp and their potential biomedical applications were also discussed.

Influence of nanoscale-modified apatite-type calcium phosphates on the biofilm formation by pathogenic microorganisms

Nanoparticles (25–50 nm) of chemically modified calcium phosphates Ca10−x−y M ii x Na y (PO4)6−z (CO3) z (OH)2 (M ii  – Cu2+, Zn2+) were synthesized via a wet precipitation method at room temperature. The Fourier-transform infrared spectroscopy data confirmed the partial substitution of PO 4 3 − {\text{PO}}_{4}^{3-} → CO 3 2 − {\text{CO}}_{3}^{2-} (B-type) in apatite-type structure. The influence of prepared phosphates on biofilm formation by pathogenic microorganisms was investigated. It was found that the samples Na+, CO 3 2 − {\text{CO}}_{3}^{2-} -hydroxyapatite (HAP) and Na+, Zn2+, CO 3 2 − {\text{CO}}_{3}^{2-} -HAP (5–20 mM) had the highest inhibitory effect on biofilm formation by Staphylococcus aureus strains. The sample Na+, CO 3 2 − {\text{CO}}_{3}^{2-} -HAP had the slight influence on the formation of the biofilm by Pseudomonas aeruginosa, while for the samples Na+, Cu2+, CO 3 2 − {\text{CO}}_{3}^{2-} -HAP and Na+, Zn2+, CO 3 2 − {\text{CO}}_{3}^{2-} -HAP such an effect was not detected. According to transmission electron microscopy data, a correlation between the activity of synthesized apatite-related modified calcium phosphates in the processes of biofilm formation and their ability to adhere to the surface of bacterial cells was established. The prepared samples can be used for the design of effective materials with antibacterial activity for medicine.

Zn-doped mesoporous hydroxyapatites and their antimicrobial properties

Recently, zinc-based materials have gained immense attention as antimicrobial agents. In this study, zinc-doped mesoporous hydroxyapatites (HAps) with various Zn contents were prepared by co-precipitation using a phosphoprotein as the porous template. The use of the phosphoprotein as the porous template resulted in the formation of zinc-doped mesoporous HAps (mHAps) with large pores and specific surface area (182 m² g^-1), as indicated by the nitrogen adsorption/desorption measurements. The formation of the zinc-doped HAps was confirmed by various analytical techniques such as X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The biomaterials prepared in this study were used as antimicrobial agents against gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) bacteria. The Zn2%-mHAp sample showed the maximum bacterial inhibitory concentrations of 50 ± 5% and 77 ± 5% for the Gram-positive and Gram-negative bacteria, respectively. The antibacterial activity of the mHAp samples depended strongly on their Zn²⁺ content. Thus, the use of a biotemplate and Zn²⁺ ions is an efficient approach for the formation of novel HAp-based biomaterials with promising antibacterial properties. This synthesis approach will pave a new pathway for the functionalization of other materials for different biomedical applications.

Polyetheretherketone and Its Composites for Bone Replacement and Regeneration

In this article, recent advances in the development, preparation, biocompatibility and mechanical properties of polyetheretherketone (PEEK) and its composites for hard and soft tissue engineering are reviewed. PEEK has been widely employed for fabricating spinal fusions due to its radiolucency, chemical stability and superior sterilization resistance at high temperatures. PEEK can also be tailored into patient-specific implants for treating orbital and craniofacial defects in combination with additive manufacturing process. However, PEEK is bioinert, lacking osseointegration after implantation. Accordingly, several approaches including surface roughening, thin film coating technology, and addition of bioactive hydroxyapatite (HA) micro-/nanofillers have been adopted to improve osseointegration performance. The elastic modulus of PEEK is 3.7-4.0 GPa, being considerably lower than that of human cortical bone ranging from 7-30 GPa. Thus, PEEK is not stiff enough to sustain applied stress in load-bearing orthopedic implants. Therefore, HA micro-/nanofillers, continuous and discontinuous carbon fibers are incorporated into PEEK for enhancing its stiffness for load-bearing applications. Among these, carbon fibers are more effective than HA micro-/nanofillers in providing additional stiffness and load-bearing capabilities. In particular, the tensile properties of PEEK composite with 30wt% short carbon fibers resemble those of cortical bone. Hydrophobic PEEK shows no degradation behavior, thus hampering its use for making porous bone scaffolds. PEEK can be blended with hydrophilic polymers such as polyglycolic acid and polyvinyl alcohol to produce biodegradable scaffolds for bone tissue engineering applications.

Novel formulation of antimicrobial peptides enhances antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA)

Antimicrobial peptides (AMPs) have the ability to penetrate as well as transport cargo across bacterial cell membranes, and they have been labeled as exceptional candidates to function in drug delivery. The aim of this study was to investigate the effectiveness of novel formulation of AMPs for enhanced MRSA activity. The strategy was carried out through the formulation of liposomes by thin-layer film hydration methodology, containing phosphatidylcholine, cholesterol, oleic acid, the novel AMP, as well as vancomycin (VCM). Characterization of the AMPs and liposomes included HPLC and LCMS for peptide purity and mass determination; DLS (size, polydispersity, zeta potential), TEM (surface morphology), dialysis (drug release), broth dilution, and flow cytometry (antibacterial activity); MTT assay, haemolysis and intracellular antibacterial studies. The size, PDI, and zeta potential of the drug-loaded AMP₂-Lipo-1 were 102.6 ± 1.81 nm, 0.157 ± 0.01, and - 9.81 ± 1.69 mV, respectively, while for AMP₃-Lipo-2 drug-loaded formulation, it was 146.4 ± 1.90 nm, 0.412 ± 0.05, and - 4.27 ± 1.25 mV respectively at pH 7.4. However, in acidic pH for both formulations, we observed an increase in size, PDI, and a switch to positive zeta potential, which indicated the pH responsiveness of our liposomal systems. The in vitro drug release studies demonstrated that liposomal formulations released VCM-HCl at a faster rate at pH 6.0 compared to pH 7.4. In vitro antibacterial activity against S. aureus and MRSA revealed that liposomes had enhanced activity at pH 6 compared to pH 7.4. The study revealed that the formulation can potentially be used to enhance activity and penetration of AMPs, thereby improving the treatment of bacterial infections.

Biomimetic Hybrid Systems for Tissue Engineering

Tissue engineering approaches appear nowadays highly promising for the regeneration of injured/diseased tissues. Biomimetic scaffolds are continuously been developed to act as structural support for cell growth and proliferation as well as for the delivery of cells able to be differentiated, and also of bioactive molecules like growth factors and even signaling cues. The current research concerns materials employed to develop biological scaffolds with improved features as well as complex preparation techniques. In this work, hybrid systems based on natural polymers are discussed and the efforts focused to provide new polymers able to mimic proteins and DNA are extensively explained. Progress on the scaffold fabrication technique is mentioned, those processes based on solution and melt electrospinning or even on their combination being mainly discussed. Selection of the appropriate hybrid technology becomes vital to get optimal architecture to reasonably accomplish the final applications. Representative examples of the recent possibilities on tissue regeneration are finally given.

Synthesis of Graphene Nanoribbons–Hydroxyapatite Nanocomposite Applicable in Biomedicine and Theranostics

In order to investigate the effect of graphene nanoribbons on the final properties of hydroxyapatite-based nanocomposites, a solvothermal method was used at 180 °C and 5 h for the synthesis of graphene nanoribbons–hydroxyapatite nanopowders by employing hydrogen gas injection. Calcium nitrate tetrahydrate and diammonium hydrogenphosphate were used as calcium and phosphate precursors, respectively. To synthesize the powders, a solvent containing diethylene glycol, anhydrous ethanol, dimethylformamide, and water was used. Graphene oxide nanoribbons were synthesized by chemical unzipping of carbon nanotubes under oxidative conditions. The synthesized powders were consolidated by spark plasma sintering methodat 950 °C and a pressure of 50 MPa. The powders and sintered samples were then evaluated using X-ray diffraction, Raman spectroscopy, high-resolution transmission electron microscopy, Vickers microindentation techniques, and biocompatibility assay. The findings of this study showed that the final powders synthesized by the solvothermal method had calcium to phosphate ratio of about 1.67. By adding a small amount of graphene nanoribbon (0.5%W), elastic modulus and hardness of hydroxyapatite increased dramatically. In biological experiments, the difference of hydroxyapatite effect in comparison with the nanocomposite was not significant. The findings of this study showed that graphene nanoribbons have a positive effect on the properties of hydroxyapatite, and these findings would be useful for the medical and theranostic application of this type of nanocomposites.

The Design of Poly(lactide-co-glycolide) Nanocarriers for Medical Applications

Polymeric biomaterials have found widespread applications in nanomedicine, and poly(lactide-co-glycolide), (PLGA) in particular has been successfully implemented in numerous drug delivery formulations due to its synthetic malleability and biocompatibility. However, the need for preconception in these formulations is increasing, and this can be achieved by selection and elimination of design variables in order for these systems to be tailored for their specific applications. The starting materials and preparation methods have been shown to influence various parameters of PLGA-based nanocarriers and their implementation in drug delivery systems, while the implementation of computational simulations as a component of formulation studies can provide valuable information on their characteristics. This review provides a critical summary of the synthesis and applications of PLGA-based systems in bio-medicine and outlines experimental and computational design considerations of these systems.

Calcium Phosphate Nanoparticles-Based Systems for RNAi Delivery: Applications in Bone Tissue Regeneration

Bone-related injury and disease constitute a significant global burden both socially and economically. Current treatments have many limitations and thus the development of new approaches for bone-related conditions is imperative. Gene therapy is an emerging approach for effective bone repair and regeneration, with notable interest in the use of RNA interference (RNAi) systems to regulate gene expression in the bone microenvironment. Calcium phosphate nanoparticles represent promising materials for use as non-viral vectors for gene therapy in bone tissue engineering applications due to their many favorable properties, including biocompatibility, osteoinductivity, osteoconductivity, and strong affinity for binding to nucleic acids. However, low transfection rates present a significant barrier to their clinical use. This article reviews the benefits of calcium phosphate nanoparticles for RNAi delivery and highlights the role of surface functionalization in increasing calcium phosphate nanoparticles stability, improving cellular uptake and increasing transfection efficiency. Currently, the underlying mechanistic principles relating to these systems and their interplay during in vivo bone formation is not wholly understood. Furthermore, the optimal microRNA targets for particular bone tissue regeneration applications are still unclear. Therefore, further research is required in order to achieve the optimal calcium phosphate nanoparticles-based systems for RNAi delivery for bone tissue regeneration.

Calcium Phosphate Nanoparticles for Therapeutic Applications in Bone Regeneration

Bone injuries and diseases constitute a burden both socially and economically, as the consequences of a lack of effective treatments affect both the patients' quality of life and the costs on the health systems. This impended need has led the research community's efforts to establish efficacious bone tissue engineering solutions. There has been a recent focus on the use of biomaterial-based nanoparticles for the delivery of therapeutic factors. Among the biomaterials being considered to date, calcium phosphates have emerged as one of the most promising materials for bone repair applications due to their osteoconductivity, osteoinductivity and their ability to be resorbed in the body. Calcium phosphate nanoparticles have received particular attention as non-viral vectors for gene therapy, as factors such as plasmid DNAs, microRNAs (miRNA) and silencing RNA (siRNAs) can be easily incorporated on their surface. Calcium phosphate nanoparticles loaded with therapeutic factors have also been delivered to the site of bone injury using scaffolds and hydrogels. This review provides an extensive overview of the current state-of-the-art relating to the design and synthesis of calcium phosphate nanoparticles as carriers for therapeutic factors, the mechanisms of therapeutic factors' loading and release, and their application in bone tissue engineering.

Incorporation of Chloramphenicol Loaded Hydroxyapatite Nanoparticles into Polylactide

Chloramphenicol (CAM) has been encapsulated into hydroxyapatite nanoparticles displaying different morphologies and crystallinities. The process was based on typical precipitation of solutions containing phosphate and calcium ions and the addition of CAM once the hydroxyapatite nuclei were formed. This procedure favored a disposition of the drug into the bulk parts of the nanoparticles and led to a fast release in aqueous media. Clear antibacterial activity was derived, being slightly higher for the amorphous samples due to their higher encapsulation efficiency. Polylactide (PLA) microfibers incorporating CAM encapsulated in hydroxyapatite nanoparticles were prepared by the electrospinning technique and under optimized conditions. Drug release experiments demonstrated that only a small percentage of the loaded CAM could be delivered to an aqueous PBS medium. This amount was enough to render an immediate bacteriostatic effect without causing a cytotoxic effect on osteoblast-like, fibroblasts, and epithelial cells. Therefore, the prepared scaffolds were able to retain CAM-loaded nanoparticles, being a reservoir that should allow a prolonged release depending on the polymer degradation rate. The studied system may have promising applications for the treatment of cancer since CAM has been proposed as a new antitumor drug.

Ionic Liquid-Assisted Hydrothermal Synthesis of a Biocompatible Filler for Photo-Curable Dental Composite: From Theory to Experiment

Nanostructured hydroxyapatite (HA) is a new class of biocompatible fillers which has been recently utilized in bio hybrid materials by virtue of its excellent tissue bioactivity and biocompatibility. However, the need for higher thermal stability, solubility, surface bioactivity, radiopacity, and remineralization ability suggests a divalent cation substitution of HA for use in light curable dental restorative composites. In this work, structural and optical properties of Sr-doped hydroxyapatite were studied using first-principle calculations based on density functional theory (DFT). Next, Sr-doped hydroxyapatite (HA) was prepared via a new ionic liquid-assisted hydrothermal (ILH) route. Samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM)/energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), dynamic light scattering (DLS), Brunauer–Emmett–Teller (BET) surface area analysis, and cell viability. The obtained experimental data showed that the nucleation and crystal growth process controlled by [BMIM]Br molecules results in uniform products with small and regular particles and high specific surface areas. Finally, cytotoxicity tests showed that the as-prepared Sr-doped HA nanoparticles have good biocompatibility (≥91%), confirming their potential for use in photo-curable dental restorative composites.

Peptide Self-Assembly into Hydrogels for Biomedical Applications Related to Hydroxyapatite

Amphiphilic peptides can be self-assembled by establishing physical cross-links involving hydrogen bonds and electrostatic interactions with divalent ions. The derived hydrogels have promising properties due to their biocompatibility, reversibility, trigger capability, and tunability. Peptide hydrogels can mimic the extracellular matrix and favor the growth of hydroxyapatite (HAp) as well as its encapsulation. Newly designed materials offer great perspectives for applications in the regeneration of hard tissues such as bones, teeth, and cartilage. Furthermore, development of drug delivery systems based on HAp and peptide self-assembly is attracting attention.

Silver nanoparticles coated with dodecanethiol used as fillers in non-cytotoxic and antifungal PBAT surface based on nanocomposites

In the present study, we report the preparation of antifungal and non-cytotoxic polymer nanocomposites with potential application in biomedical materials. Dodecanethiol-protected silver nanoparticles (AgNPs-DDT) were synthesized by a reduction/precipitation method and dispersed in chloroform to obtain stable colloidal dispersions. PBAT-based nanocomposites containing 0.25, 0.5 and 2 wt% AgNPs-DDT were prepared by casting method. The incorporation of AgNPs-DDT in PBAT matrix resulted in nanocomposites which combine improved mechanical performance and antifungal properties with a non-cytotoxic characteristic.

New approach to modification of poly (l-lactic acid) with nano-hydroxyapatite improving functionality of human adipose-derived stromal cells (hASCs) through increased viability and enhanced mitochondrial activity

The aim of this study was to determine the cytocompatibility of poly (l-lactide) (PLLA) scaffolds fabricated using co-rotating twin screw extrusion technique and functionalized with different concentrations of nano-hydroxyapatite (nHAp). The efforts were aimed on the designing bioactive scaffolds improving the viability and metabolic activity of human adipose-derived multipotent stromal cells (hASCs). The in vitro study was designed to determine the optimal nHAp concentration, based on analysis of hASCs morphology, adhesion rate, as well as metabolic and proliferative potential. Initially, the PLLA filled with three different concentrations of the nHAp were tested i.e. 5%, 10% and 15 wt%. The obtained results indicated that the 10 wt% nHAp in the PLLA (10% nHAp/PLLA) matrices improved the adhesion and proliferation of the hASCs, what was in good agreement with the results of tensile properties of the composites. Further, we performed profound studies regarding the cytotoxicity of 10% nHAp/PLLA. The analysis included the evaluation of the biomaterial influence on viability, apoptosis-related markers expression profile and mitochondrial function. The cytocompatibility of 10% nHAp/PLLA scaffolds toward the hASCs was confirmed. The hASCs propagated on 10% nHAp/PLLA were more viable then those propagated on the plain PLLA. The level of pro-apoptotic markers, i.e. caspase-3 and Bax in cultures on 10% nHAp/PLLA was significantly decreased. Obtained results correlated with higher mitochondrial membrane potential of hASCs in those cultures. The obtained composites may improve therapeutic potential of hASCs via directing their adhesion, enhancing proliferation and viability as well as increasing mitochondrial potential, thus may find potential application in tissue engineering.

Covalent immobilization of doxorubicin in glycine functionalized hydroxyapatite nanoparticles for pH-responsive release

Development and therapeutic evaluation of glycine functionalized hydroxyapatite nanoparticles having a covalently conjugated anticancer drug, doxorubicin hydrochloride.