Different Concentrations Of Hydroxyapatite Research Articles

Improving bone regeneration with electrospun antibacterial polycaprolactone/collagen/polyvinyl pyrrolidone scaffolds coated with hydroxyapatite and cephalexin delivery capability

Electrospinning is a facile popular method for the creation of nano-micro fibers tissue engineering scaffolds. Here, polycaprolactone (PCL)/collagen (COL): polyvinyl pyrrolidone (PVP) scaffolds (PCL/COL: PVP) were fabricated for bone regeneration. Various concentrations of Cephalexin (CEF) (0.5, 1, 1.5 wt. %) were added to PCL/COL: PVP scaffold to provide an antibacterial scaffold, and different concentrations of hydroxyapatite (HA) (1, 2, 5 wt. %) was electrospray on the surface of the scaffolds. The PCL/COL: PVP scaffold contained 1.5% CEF and coated with 2% HA was introduced as the best sample and in-vitro tests were performed on this scaffold based on the antibacterial and MTT test results. Morphology observations demonstrated a bead-free uniform combined nano-micro fibrous structure. Fourier transform infrared spectroscopy and X-ray diffraction tests confirmed the successful formation of the scaffolds and the wettability, swelling, and biodegradability evaluations of the scaffolds confirmed the hydrophilicity nature of the scaffold with high swelling properties and suitable biodegradation ratio. The scaffolds supported cell adhesion and represented high alkaline phosphatase activity. CEF loading led to antibacterial properties of the designed scaffolds and showed a suitable sustained release rate within 48 h. It seems that the electrospun PCL/COL: PVP scaffold loaded with 1.5% CEF and coated with 2% HA can be useful for bone regeneration applications that need further evaluation in the near future.

Triphasic 3D In Vitro Model of Bone-Tendon-Muscle Interfaces to Study Their Regeneration.

The transition areas between different tissues, known as tissue interfaces, have limited ability to regenerate after damage, which can lead to incomplete healing. Previous studies focussed on single interfaces, most commonly bone-tendon and bone-cartilage interfaces. Herein, we develop a 3D in vitro model to study the regeneration of the bone-tendon-muscle interface. The 3D model was prepared from collagen and agarose, with different concentrations of hydroxyapatite to graduate the tissues from bones to muscles, resulting in a stiffness gradient. This graduated structure was fabricated using indirect 3D printing to provide biologically relevant surface topographies. MG-63, human dermal fibroblasts, and Sket.4U cells were found suitable cell models for bones, tendons, and muscles, respectively. The biphasic and triphasic hydrogels composing the 3D model were shown to be suitable for cell growth. Cells were co-cultured on the 3D model for over 21 days before assessing cell proliferation, metabolic activity, viability, cytotoxicity, tissue-specific markers, and matrix deposition to determine interface formations. The studies were conducted in a newly developed growth chamber that allowed cell communication while the cell culture media was compartmentalised. The 3D model promoted cell viability, tissue-specific marker expression, and new matrix deposition over 21 days, thereby showing promise for the development of new interfaces.

In vitro characterization of hydroxyapatite and cobalt ferrite nanoparticles compounds and their biocompatibility in vivo

Bioactive materials in combination with antibiotics have been widely developed for the treatment of bone infection. Thus, this work aims to characterize six biomaterials formulated with different concentrations of hydroxyapatite and cobalt ferrite nanoparticles, in addition to the antibiotic ciprofloxacin, using X-ray diffraction (XRD), scanning electron microscopy (SEM), and the antibiotic diffusion test on agar. Furthermore, in vivo biocompatibility and the reabsorption process of these materials were analyzed. XRD showed that both hydroxyapatite and cobalt ferrite present high crystallinity. The photomicrographs obtained by SEM revealed that composites have a complex surface, evidenced by the irregular arrangement of the hydroxyapatite and cobalt ferrite granules, besides demonstrating the interaction between their components. The antibiotic-diffusion test showed that all biomaterials produced an inhibition halo in Staphylococcus aureus cultures. For the biocompatibility study, composites were surgically implanted in the dorsal region of rabbits. At 15, 30, 70, and 100 days, biopsies of the implanted regions were performed. The biomaterials were easily identified during histological analysis and no significant inflammatory process, nor histological signs of toxicity or rejection by the adjacent tissue were observed. We can conclude that the biomaterials analyzed are biocompatible, degradable, and effective in inhibiting the in vitro growth of Staphylococcus aureus.Graphical abstract

Mechanical and histological properties of an electrospun scaffold with a modified surface by plasma polymerization implanted in an in vivo model

This article presents the construction of scaffolds composed of polylactic acid (PLA) with different concentrations of hydroxyapatite (HA) by electrospinning, which were superficially modified with polypyrrole (PPy/I) by plasma polymerization. A preliminary study was conducted of the biological and mechanical behavior of the scaffolds when they were implanted in the back of rabbits for 30 days; bone cells differentiated from mesenchymal stem cells (MSCs) were used. The bone cell and scaffold structures were characterized by histological, immunohistochemical, and mechanical stress tests. Hematoxylin–eosin staining showed good tissue conformation. The immunohistochemical tests highlighted the presence of the main bone tissue proteins, such as collagen, osteocalcin, and osteopontin. The PLA/HA scaffolds were observed to exhibit cell adhesion and proliferation properties; however, the response was much better in the scaffolds that had a higher concentration of HA and that were coated with PPy/I. The results of the mechanical tests of the scaffolds indicated that the plasma treatment improved the adhesion and cell proliferation properties and contributed to the mechanical support, allowing the formation of neotissues with good viability of cell growth.

Development of porous guar gum-hydroxyapatite composite scaffolds via freeze-drying method

This paper intends the development of a composite scaffold by a simple freeze-drying technique where the naturally available guar gum (GG) was reacted with that of hydroxyapatite (HA). During the synthesis, the GG suspension was allowed to react with different concentrations of HA (10–30 wt%) and the formed porous scaffolds are expected to have better control of the scaffold microstructure and can enhance the mechanical characteristics of GG. The morphology of prepared scaffolds was analyzed by using stereo zoom optical microscopy and the mechanical properties (compressive strength) by the universal testing machine. The analysis of results indicated that the concentration of polysaccharide solution plays a dynamic part in controlling the morphological and compressive strength of the scaffold by bringing changes to the pore architecture and total solid content.

Multiscale micromechanical modeling of the elastic properties of dentin

The paper focuses on multiscale modeling of the elastic properties of dentin. It is modeled as a hierarchical structure consisting of collagen fibers and hydroxyapatite particles at the lower level. Different concentrations of hydroxyapatite in this tissue correspond to peritubular and intertubular dentins. Then, the overall material is modeled as intertubular dentin matrix containing parallel cylindrical holes (the tubules) surrounded by layers of peritubular dentin. At each microstructural level, the model accounts for anisotropy of the constituents. The model predictions are compared with experimental data available in literature.

Characterization and in vitro and in vivo assessment of poly(butylene adipate-co-terephthalate)/nano-hydroxyapatite composites as scaffolds for bone tissue engineering

The polyester for bone tissue engineering is produced using different concentrations of hydroxyapatite. Poly(butylene adipate-co-terephthalate) (PBAT) solutions containing different concentrations of nano-hydroxyapatite (nHAp) (1, 2, 3, 4, 5 and 6% wt) were evaluated to assess their potential to produce scaffolds via electrospinning. The characteristics of these solutions were evaluated using surface tension analysis. Different solutions were electrospun and characterized using scanning electron microscopy, X-ray diffractometry (XRD), infrared spectroscopy (FTIR), and differential scanning calorimetry analysis. In vitro and in vivo experiments were performed using MG-63 osteoblast cells and male Wistar rats. The MTT assay was used to evaluate the cytotoxicity of scaffolds. Microtomography and a three-point bend test were used to analyze parameters of bone neoformation 4 weeks after implantation. We observed a requirement for solutions containing nHAp to reach chemical stability to produce ultrathin fibers. FTIR and XRD data demonstrated the presence of carbonate and phosphate groups, and thermal analysis showed a reduction in crystallinity of the nanocomposites when the concentration of nHAp was increased. None of the scaffolds analyzed demonstrated cytotoxicity when compared to controls. All of the PBAT/nHAp scaffolds analyzed promoted bone repair; however, a solution of PBAT with 3% nHAp improved bone volume, force, and stiffness when compared to controls.

Sensitivity of Streptococcus Mutans to Selected Nanoparticles : In Vitro Study

Background: Nanoparticles are clusters of atoms in a size range from (1-100) nm. Nano dentistry creates amazing useful structures from individual atoms or molecules (nanoparticles), which provides a new alternative and a possibly superior strategy in prevention and treatment of dental caries through management of dental plaque biofilms. The aim of the study was to test the sensitivity of Streptococcus mutans to different concentrations of hydroxyapatite and iron oxide nanoparticles suspension solutions, in comparison to chlorhexidine, and de-ionized water, in vitro. Materials and methods: Agar well technique was applied to test the sensitivity of Streptococcus mutans to different concentrations of hydroxyapatite and iron oxide nanoparticles compared with chlorhexidine 0.2% as a control positive and de-ionized water as control negative. Zone of inhibitions which is clear zone of no growth of the bacteria were measured across the diameter of each well, no zone indicated a complete resistance of bacteria to the agents. Results: Values of mean of inhibition zone for all concentrations of hydroxyapatite nanoparticles were zero. While for iron oxide nanoparticles, they were zero until reaching the last three concentrations, in which there was a respective increase with a highly significant difference between groups (p>0.01). When making multiple comparisons of the inhibition zones of iron oxide nanoparticles between groups, findings showed that the inhibition zones of 17%, 20% and 22.5% of iron oxide nanoparticles were more than all other concentrations that had no inhibition zones with a significant difference (p>0.05). There was a highly significant difference between each concentration of hydroxyapatite and iron oxide nanoparticles with chlorhexidine and de-ionized water (p>0.01). Conclusion: Streptococcus mutans were not sensitive to hydroxyapatite nanoparticles, as there was a complete resistance for the agent. While for iron oxide nanoparticles, Streptococcus mutans were sensitive to 17.5%, 20% and 22.5% and sensitivity increased with the increase in concentration with a statistically highly significant difference and this indicates an antibacterial activity of this material. Keywords: Hydroxyapatite nanoparticles, Iron oxide nanoparticles, streptococcus mutans, Inhibition zone. (J Bagh Coll Dentistry 2018; 30(1): 69-75)

The properties of hydroxyapatite ceramic coatings produced by plasma electrolytic oxidation

Calcium phosphate coatings produced on the surface of Ti6Al4V by plasma electrolytic oxidation (PEO) using different concentrations of hydroxyapatite (HA) in a 0.12M Na3PO4 (NAP) electrolyte solution was investigated. It was found that the amount of calcium phosphate particles infiltrated into the coating layer as well as the thickness and the surface roughness of the coating increased with increasing HA concentration. The porosity of the ceramic coatings indicated an inverse relationship with the concentration of HA particles dispersed in the NAP solution. The result also demonstrates that higher scratch adhesive strength was achieved using 1.5g/L HA solution, producing a critical load of 2099mN, while 0g/L HA only produced a critical load of 1247mN. The adhesion becomes independent of thickness when the concentration of HA exceeds 1.5g/L. The failure of the coating was characterized by large periodic hemispherical chipping, while intermittent delamination was noticed with the coating embedded with HA particles. This study demonstrate the viability of using PEO to produce a thin layer of HA ceramic coating on Ti6Al4V suitable for biomedical applications.

Synthesis and characterization of cellulose acetate-hydroxyapatite micro and nano composites membranes for water purification and biomedical applications

In this work, we report facile synthesis and characterization of new cellulose acetate-hydroxyapatite membranes for water purification and biomedical applications. The membranes were synthesized from a polymer solution in N, N’-dimethylformamide (12% wt.) where different concentrations of hydroxyapatite (1, 2, 4% wt. based on the amount of polymer) were dispersed using sonication. The synthesis of membranes was carried out by precipitation employing phase inversion using deionized water. The morphological and structural characterization of the synthesized membranes was carried out using SEM, EDS and FT-IR. Thermal characterization (TGA & DTG) and water flows analysis of the synthesized membranes was also carried out. The SEM analysis confirmed the presence of hydroxyapatite micro/nanostructured particles in the membrane as well as significant changes in the morphology of the membranes surface. The presence of inorganic compounds was also found to influence the thermal or hydrodynamic properties of the composite membranes, leading to a more stable hydrodynamic behavior, flow variation in time being much lower compared to the control membrane of cellulose acetate.

Implants of composite scaffolds of PLA/HA coated with polypyrrole by plasma for bone neo-tissue in rabbit

Event Abstract Back to Event Implants of composite scaffolds of PLA/HA coated with polypyrrole by plasma for bone neo-tissue in rabbit Maria Flores1, Roberto Olayo2, Juan Morales2, Atlántida M. Raya3 and Diego R. Esquiliano3 1 Universidad Autonoma Metropolitana, Biomedical Engineering, Mexico 2 Universidad Autonoma Metropolitana, Physics, Mexico 3 Child Hospital of México Federico Gómez, Tissue Engineering, Mexico Introduction: Composites of hydroxyapatite (HA) and biodegradable polymers had been tasted as scaffolds for bone implants with several problems to solve, two of this problems are the cell adhesion and morphology, pore size and accessibility of the HA are important and than the cell interaction with bought materials must be good[1]-[3]. In this work we study a scaffold made by electrospinning from a suspension of HA in polylactic acid (PLA) solutions, to made a material with large porosity and a large surface area. We increased the surface cell interaction by plasma polymerization of pyrrole[4],[5]. Scaffolds were tested with rabbit osteoblasts in vitro and in vivo, showing excellent bone neo-tissue formation. Materials and Methods: Electrospinning, was used to manufacture porous matrices. Solutions of polylactic acid and two different concentrations of hydroxyapatite, 18wt% and 36wt% were electrospunned. Samples were characterized by scanning electron microscopy (SEM) and probed as a support for cell multiplication of mesenchymal stem cells (MSC´s) differentiated into osteoblasts. Cells were obtained by a biopsy of rabbit’s femur marrow. The differentiation evaluation of MSC´s was performed using antibodies and flow cytometry, also by observing alkaline phosphatase in cells. To further induce cell adhesion and stimulation, a thin layer of polypyrrole doped with iodine (PPy-I), by plasma polymerization, was deposited in the matrices. Samples of PLA/HA/PPy-I underwent in vitro cell culture. Culture was maintained in vitro for 7, 14, 21, and 28 days. At day 7, cells were implanted in vivo, in the back of a rabbit (subcutaneous) for 30 days. Their cell viability was characterized by MTT cell proliferation assay in both cultures. Results: Fibrous porous matrices were obtained of PLA/HA and PLA/HA/PPy-I fiber diameters varied from 800 nm up to 50 µm and pore size from 10 µm to 100 µm which allows passage of osteoblasts and culture medium within the matrices, as the diameter of osteoblasts is 10 μm. The differentiation of mesenchymal stem cells into osteogenic lineage was confirmed. Matrices showed good cell adhesion and proliferation in vitro and in vivo culture. Discussion: In the matrices of interest with osteoblasts at day 7 of culture, we can see the beginning of the adhesion of these bone cells. Figure 1. a) SEM of scaffolds at 7 day of in vitro culture of osteoblasts. a) PLA/HA(18 wt%), b) PLA/HA(18 wt%)/PPy-I, c) PLA/HA(36 wt%) , d) PLA/HA(36 wt%)/PPy-I Such cells tend to be in the hydroxyapatite rich areas, adherence is enhanced in the matrices with PPy-I. Also, samples were compared at 7, 14, 21, and 28 days, and, in this case MTT assay showed that samples with PPy-I and 36wt% of hydroxyapatite presented higher cell viability. Figure 2. Results of MTT assay When implanted in vivo samples were implanted for 30 days and there was no rejection of the material by the animal, there was vascularization and tissue formation in the matrix, indicating that the material effectively allowed the adhesion and proliferation of cells. Conclusion: This study confirms that the technique of electrospinning produces porous matrices of PLA/HA. Neotissue is achieved using PLA/HA and PLA/HA/Ppy-I. Better viability was observed when Ppy-I was added to the scaffolds. Increasing the concentration of HA further improved cell viability. The authors thank the support to CONACYT (Instituto Nacional de Ciencia y Tecnología) for the scholarship.

Preparation of silver-hydroyapatite/PVA nanocomposites: Giant dielectric material for industrial and clinical applications

Pure hydroxyappatite Ca10(PO4)6(OH)2 (or HAP) was prepared from eggshell and potassium dihydrogen phosphate (KH2PO4) by a simple self-chemical reaction method. The clean eggshell was heated at 800 °C in air giving the source of CaO. Appropriate amount of CaO was dissolved in KH2PO4 solution at 37°C for few days. The PH value decreases with increasing the duration of preparation of HAP. Silver nanoparticles derived from silver nitrate solution using black tea leaf extract had been introduced to hydroxyapatite due to its biocompatibility. The unique size- dependent properties of nanomaterials make them superior and indispensable. In this work, hydroxyapatite-silver nanoparticles/polyvinyl alcohol (PVA) composites with 4 different concentrations of hydroxyapatite (1-4 wt %) were prepared by bio-reduction method. Several techniques like XRD and SEM were used to characterize the prepared samples. Frequency dependent capacitance and conductance of the samples were measured using an impedance analyzer. The results showed a remarkable increase in dielectric permittivity (~5117) with low loss (~0.23) at1000 HZ and room temperature (300K) for 4wt% Hydroxapatie-Silver/PVA nanocomposite. Such nanocomposite might be directly applied in manufacturing clinical devices and also for embedding capacitor applications.

Tunable hydrogel composite with two-step processing in combination with innovative hardware upgrade for cell-based three-dimensional bioprinting

Three-dimensional (3-D) bioprinting is the layer-by-layer deposition of biological material with the aim of achieving stable 3-D constructs for application in tissue engineering. It is a powerful tool for the spatially directed placement of multiple materials and/or cells within the 3-D sample. Encapsulated cells are protected by the bioink during the printing process. Very few materials are available that fulfill requirements for bioprinting as well as provide adequate properties for cell encapsulation during and after the printing process. A hydrogel composite including alginate and gelatin precursors was tuned with different concentrations of hydroxyapatite (HA) and characterized in terms of rheology, swelling behavior and mechanical properties to assess the versatility of the system. Instantaneous as well as long-term structural integrity of the printed hydrogel was achieved with a two-step mechanism combining the thermosensitive properties of gelatin with chemical crosslinking of alginate. Novel syringe tip heaters were developed for improved temperature control of the bioink to avoid clogging. Human mesenchymal stem cells mixed into the hydrogel precursor survived the printing process and showed high cell viability of 85% living cells after 3days of subsequent in vitro culture. HA enabled the visualization of the printed structures with micro-computed tomography. The inclusion of HA also favors the use of the bioink for bone tissue engineering applications. By adding factors other than HA, the composite could be used as a bioink for applications in drug delivery, microsphere deposition or soft tissue engineering.

Electrophoretic deposition of hydroxyapatite nanostructured coatings with controlled porosity

Abstract Hydroxyapatite (HA) coatings with controlled porosity were prepared by electrophoretic deposition (EPD) method. Carbon black (CB) particles were used as the sacrificial template (porogen agent). Two component suspensions containing different concentrations of HA and CB particles were prepared in isopropanol. It was found that the finer and positively charged HA nanoparticles are heterocoagulated on the coarser and negatively charged CB particles to form CB–HA composite particles with net positive charge. The deposition rate from the suspensions with WR (CCB/CHA ratio) of 0.25 was faster than that of those with WR: 0.5 at initial times of EPD. However the situation was reversed at longer EPD times. It was also found that the amount of porosity in the coatings increases as the CB concentration in the suspension increases (15%, 24%, 31%, 43% for the coatings deposited from the suspensions with 20 g/L HA nanoparticles and 0, 5, 10 and 20 g/L CB particles, respectively).

Hybrid hydroxyapatite nanoparticles-loaded PCL/GE blend fibers for bone tissue engineering

In order to augment bone formation, a new biodegradable scaffold system was fabricated using different ratios of hydroxyapatite (HAp) blended with synthetic polymer polycaprolactone (PCL) and natural polymer gelatin (GE) followed by electrospinning method. Three different concentrations of HAp were used in PCL/GE to obtain a blend of 10, 30, and 50% (w/v) HAp–PCL/GE. These HAp-loaded PCL/GE blends were then compared with PCL/GE blends by different mechanical and biological in vitro and in vivo studies to understand the applicability of the system. Scanning electron microscopy, X-ray diffraction analysis, and tensile strength measurement were done to obtain physical properties. Fifty Percent HAp–PCL/GE blends possessed the highest mechanical strength. In vitro cytotoxicity and proliferation of osteoblast cells on the PCL/GE and HAp–PCL/GE scaffolds were examined and shown that addition of HAp in PCL/GE was beneficial by increasing cell viability (>85%) proliferation and cell-surface attachment. Expression of collagen and osteopontin was also found higher in 50% HAp–PCL/GE blends than the others. On the other hand, in vivo bone formation was examined using rat models and increased bone formation was observed in 50% HAp–PCL/GE blends within 6 weeks. Based on the combined results of this study, HAp–PCL/GE membranes were found to hold great promise for use in tissue engineering applications, especially in bone tissue engineering.

Electrospun Scaffolds Composed of Poly(L-lactic acid) and Hydroxyapatite

Tissue engineering is an important emerging area for creating biological alternatives for harvested tissues, implants, and prostheses. Biocompatible and biodegradable polymeric materials are considered an important class of materials that can be used as scaffolds in tissue engineering applications. In this work, the system studied was nanocomposites of hydroxyapatite (HA) dispersed in a matrix of PLLA. Scaffolds have to present similar structure and also function as an artificial extracellular matrix for cell attachment and growth. Hydroxyapatite is a bioactive ceramic and has been used in applications of repairing bone tissue due to its biocompatibility and osteoconductivity. Poly(L- lactic acid) is a biodegradable and biocompatible polymer and has been used in different applications in the biomedical field. In this work, polymer solutions were prepared with different percentages of hydroxyapatite and porous membranes consisting of non-woven nanostructured fibers were obtained by electrospinning. The process parameters were: voltage of 13kV, flow rate of 0.5 ml/h and distance from the tip of the needle to the collector of 12 cm. By using these process parameter, fibrous membranes were obtained with different concentrations of HA (1.96, 4.76, 9 [wt %]). The morphology of the samples was observed by SEM and the characteristic physic-chemical were analyzed by XRF, XRD, DSC and FTIR.

Microtomographic images of rat's lumbar vertebra microstructure using [formula omitted] synchrotron X-rays: an analysis in terms of 3D visualization

Microtomographic images of rat's lumbar vertebra of different age groups varying from 8, 56 and 78 weeks were obtained at 30 keV using synchrotron X-rays with a spatial resolution of 12 μm . The images are analyzed in terms of 3D visualization and micro-architecture. Density histogram of rat's lumbar vertebra is compared with test phantoms. Rat's lumbar volume and phantom volume are studied at different concentrations of hydroxyapatite with slice number. With the use of 2D slices, 3D images are reconstructed, in order to know the evolution and a state of decline of bone microstructure with aging. Cross-sectional μ-CT images shows that the bone of young rat has a fine trabecular microstructure while that of the old rat has large meshed structure.

Evaluation of hydroxyapatite as a metal immobilizing soil additive for the remediation of polluted soils. Part 1. Influence of hydroxyapatite on metal exchangeability in soil, plant growth and plant metal accumulation

In order to evaluate the possible use of hydroxyapatite (HA) as a soil additive for the in situ remediation of metal contaminated soils, the immobilizing capacity of this product was investigated. Three different concentrations of HA (0.5%, 1%, and 5% by weight (w/w)) were applied to a metal (Zn, Pb, Cu, Cd) and As contaminated soil originating from an old zinc smelter site in Belgium. After a three weeks equilibration period, exchangeable metal concentrations of the soils were determined using 0.1 M Ca(NO 3) 2 extraction. Test plants ( Zea Mays cv. Volga and Phaseolus vulgaris cv. Limburgse vroege) were grown on all soils. Growth parameters were determined and mineral analysis (Cu, Zn, Pb, Cd, Ni, Mn, Mg, Ca, K, As and P) of plants was performed. Exchangeable metal contents in soil decreased with increasing HA application. Plant growth was partly restored on the 0.5% and 1% HA treated soils. However, at the 5% HA application rate growth was inhibited again. Plant mineral analysis showed that concentrations of `toxic' metals in the leaves of the test plants decreased after HA application. However, the uptake of essential trace elements also decreased and probably led to Mn-deficiency in maize. In bean, addition of 0.5% and 1% HA resulted in a gradual decrease of metal uptake. At the 5% application level an increase of Zn, Cu, and Ni uptake was observed compared to the 0.5% and 1% application rate. In contrast to metal uptake, As uptake was found to increase after HA treatment. The increased PO 4 2− concentration in the soil may be responsible for this. These results illustrate that HA application for the remediation of metal contaminated soils can be effective, but is not self evident. Strong immobilization of essential nutrients may lead to deficiency problems and mobilization of As may lead to an increased transfer to plants and animals and to an increased percolation of this element to the ground water.