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.

Sustainable phosphorylated microcrystalline cellulose toward enhanced removal performance of methylene blue.

In this study, microcrystalline cellulose (MCC) was phosphorylated using phosphoric acid in the presence of urea and used as an adsorbent for methylene blue (MB) dye removal from an aqueous solution. The obtained products were characterized by different techniques. Batch adsorption experiments were conducted under varying conditions of incubation time, initial MB concentration, pH, and phosphorylation degree. All the samples exhibited similar and fast adsorption kinetics, described by pseudo-second-order model for MB adsorption, whereas the retention capacity depended significantly on the phosphate content and the surface charge of the adsorbents. The experimental adsorption data in the examined MB initial concentrations (0-2000 mg/L) were best suited by the Langmuir isotherm model. The study revealed that the presence of phosphates groups in the cellulose structure significantly enhanced the adsorption of the MB pollutant. The maximum dye removal capacity at pH of 7 was obtained for the phosphorylated microcrystalline cellulose (284.03 mg/g) with a high phosphorylation degree (1.92 % of P), which is 20 times higher than unmodified MCC (15.29 mg/g). This property increased from 284.03 to 328.32 mg/g when increasing the pH from 7 to 11. The MB adsorption mechanism involves hydrogen bonding, electrostatic and ion-dipole interactions. These findings are relevant to a better understanding of the role of cellulose phosphorylation in the recovery of organic dyes from the waste liquid of many industries.

Adsorption on apatitic calcium phosphates for drug delivery: interaction with bisphosphonate molecules.

Bisphosphonates (BPs) are well established as an important class of drugs for the treatment and prevention of several bone disorders including osteoporosis. This work investigated the interaction of two bisphosphonates, risedronate and tiludronate, with several apatitic supports, a well-crystallised hydroxyapatite (HA) and nanocrystalline apatites with varying maturation times, chemical composition and surface characteristics. The purpose was to fully understand the adsorption mechanism and desorption process, by the evaluation of the effect of several physicochemical parameters (temperature, pH and concentration of calcium and phosphate ions). Whatever the nature of the BP and the structure and composition of the apatite, the adsorption of such anti-resorptive agents can be well described as an ion exchange-reaction between phosphates species on the apatitic surface and BP molecules in solution. However, the parameters of adsorption can vary depending on the physicochemical conditions of the adsorption reaction. In addition, the structure and composition of the apatitic surface also influence the adsorption properties. Finally, BPs molecules are slowly released from apatitic supports, because most of the adsorbed molecules are irreversibly bound and not spontaneously released by dilution or simple washing. Moreover, similar to their adsorption, the release of bisphosphonates is strongly affected not only by the chemical properties of the molecule, but also by the chemical and structural characteristics of the apatitic substrates. The understanding of the adsorption and release processes provides fundamental tools for the development of drug delivery systems using apatite materials.

Infrared, Raman and NMR investigations of risedronate adsorption on nanocrystalline apatites.

The aim of the current work was to study the physico-chemical interactions of a bisphosphonate molecule, risedronate, with a well-characterised synthetic nanocrystalline apatite (NCA) as a model bone mineral. We adopted a global approach, using complementary physico-chemical techniques such as FTIR, RAMAN and NMR spectroscopies in order to learn more about the interaction process of risedronate with the apatitic surface. The results obtained suggest that risedronate adsorption corresponds to an ion substitution reaction with phosphate ions occurring at the crystal surface. This mechanism explains the greater amount adsorbed (N) for NCA, compared to well crystallised stoichiometric hydroxyapatite, attributable to the well-developed hydrated layer at the surface of the nanocrystals. However, most calcium ions remain attached to the solid phase and the formation of insoluble risedronate calcium salts must also be considered as a competitive reaction to the adsorption. Thus a calcium risedronate salt was synthesised and fully characterised for comparison to the solids after adsorption. Following spectroscopic results, it can be concluded that a strong interaction was established between risedronate ions and calcium ions at the apatitic surface. However, under these experimental conditions there is no nucleation of a distinct calcium risedronate salt and the apatite crystals retain their integrity.

Removal of the herbicide 2,4-dichlorophenoxyacetate from water to zinc-aluminium-chloride layered double hydroxides.

Batch sorption studies were conducted to investigate the potential of [Zn-Al-Cl] layered double hydroxides (LDHs) for the removal of the herbicide 2,4-dichlorophenoxyacetate (2,4-D) from contaminated aqueous solutions. Experiments were performed at different pH values, initial pesticide concentration, solid/pesticide ratio and anion exchange capacity of LDHs. The LDH samples evaluated had very high retention capacity for 2,4-D whose removal was a rapid process, as a quasi-equilibrium state was reached after 1-h reaction time. The adsorption can be described by Langmuir-type isotherms, with an average affinity constant of 12.5 L mmol(-1). At initial 2,4-D concentrations between 0.08 and 4 m molL(-1), the solids removed up to 98% of the pesticide. Physicochemical characterization of the LDH solids, both fresh and after removal of 2,4-D, by X-ray diffraction, infrared spectroscopy and thermogravimetry, indicates that the retention of 2,4-D is done by adsorption on the surface of the solid for low 2,4-D concentrations. However, a combination of surface adsorption and interlayer ion exchange takes place when the 2,4-D concentration is high.

Interactions of cisplatin with calcium phosphate nanoparticles: in vitro controlled adsorption and release.

A new system for the local delivery of chemotherapy to malignant solid tumors has been developed based on calcium phosphate (CaP) nanoparticles. The adsorption of the anti-neoplastic drug cis-diamminedichloroplatinum (cisplatin) was characterized on three types of apatitic CaP (poorly and well crystallized hydroxyapatite, and carbonated apatite). Adsorption isotherms obtained in chloride-free phosphate solutions at pH = 7.4 (24 and 37 degrees C) indicate that cisplatin adsorption increases with temperature and increases with decreasing crystallinity. Release studies in phosphate buffer saline (containing the chloride ion essential for release) showed that while the cumulative amount of released drug was the same for all apatites at 20 days (approximately 70% of the total bound), the least crystalline material released the drug more slowly. The drug release rate increased slightly with temperature. Cytotoxicity testing was conducted in a K8 clonal murine osteosarcoma cell line to verify that drug activity was retained after adsorption onto the apatite crystals. K8 cells were plated onto dried films of the apatite/cisplatin conjugates and after 24 h, viability was measured with tritiated uridine. The apatite/cisplatin formulations exhibited cytotoxic effects with a dose dependent diminishment of cell viability.

Adsorption of Catalase on Hydroxyapatite.

The adsorption of catalase on calcium hydroxyapatite is reported in this study. In all the solutions investigated, catalase adsorption takes place under conditions where the adsorbent and the adorbate are both negatively charged and is accompanied by the release of phosphate ions. This suggests that electrostatic attraction does not play a leading role in the adsorption process. However, electrostatic repulsion does play a role as evidenced by the influence of the solution composition on the maximum amount adsorbed. In fact, the amount adsorbed increases when the surface charge tends to be less negative (decrease of pH and phosphate concentration, presence of calcium) or when the electrical charges are screened as a result of the ionic strength increase. This was confirmed by the electrophoretic mobility which becomes more negative after protein adsorption. The rate of catalase adsorption is extremely low; the time required to reach a stationary concentration is 60 and 125 h in potassium nitrate and phosphate solution, respectively. The reversibility of catalase was examined with respect to changes in the bulk solution concentration. No significant desorption was obtained after several days of observation. The adsorption, desorption, and kinetic aspects have been discussed in relation to changes in the the protein structure upon interaction and to the microstructural characteristics of the mineral. Copyright 1998 Academic Press.