The crystallization of Hydroxyapatite in the presence of sodium alginate

Biomechanical Evaluation of an Injectable Alginate / Dicalcium Phosphate Cement Composites for Bone Tissue Engineering

Biocompatible dicalcium phosphate (DCP) cements are widely used as bone repair materials. In this study, we aimed to investigate the impact of different amounts of sodium alginate (SA) on the microstructural, mechanical, and biological properties of DCP cements. Beta-tricalcium phosphate (β-TCP) was prepared using a microwave-assisted wet precipitation system. Lattice parameters of the obtained particles determined from X-ray diffraction (XRD), were in good match with a standard phase of β-TCP. Scanning electron microscopy (SEM) examination revealed that the particles were in globular shape. Furthermore, all functional groups of β-TCP were also detected using Fourier-transform infrared spectroscopy (FTIR) spectra. DCP cement (pure phase) was synthesized using monocalcium phosphate monohydrate (MCPM)/β-TCP powder mixture blended with 1.0 mL of water. SA/DCP cement composites were synthesized by dissolving different amounts of SA into water (1.0 mL) to obtain different final concentrations (0.5%, 1%, 2% and 3%). The prepared cements were characterized with XRD, SEM, FTIR and Thermogravimetric analysis (TGA). XRD results showed that pure DCP and SA/DCP cements were in a good match with Monetite phase. SEM results confirmed that addition of SA inhibited the growth of DCP particles. Setting time and injectability behaviour were significantly improved upon increasing the SA amount into DCP cements. In vitro biodegradation was evaluated using Simulated body fluid (SBF) over 21 days at 37 °C. The highest cumulative weight loss (%) in SBF was observed for 2.0% SA/DCP (about 26.52%) after 21 days of incubation. Amount of Ca²⁺ ions released in SBF increased with the addition of SA. DCP and SA/DCP cements showed the highest mechanical strength after 3 days of incubation in SBF and declined with prolonged immersion periods. In vitro cell culture experiments were conducted using Dental pulp stem cells (DPSCs). Viability and morphology of cells incubated in extract media of DCP and SA/DCP discs after 24 h incubation was studied with MTT assay and fluorescence microscopy imaging, respectively. All cements were cytocompatible and viability of cells incubated in extracts of cements was higher than observed in the control group. Based on the outcomes, SA/DCP bone cements have a promising future to be utilized as bone filler.

Effect of sodium alginate on phosphorus recovery by vivianite precipitation

There are good prospects for phosphorus recovery from excess sludge by vivianite crystallization while a large number of extracellular polymeric substances in sludge will have impact on vivianite precipitation. In this study, as a representative of extracellular polymeric substance, the effect of sodium alginate (SA) on phosphorus recovery by vivianite precipitation under different initial SA concentrations (0-800 mg/L), pH values (6.5-9.0) and Fe/P molar ratios (1:1-2.4:1) was investigated using synthetic wastewater. The results showed that SA in low concentrations (≤400 mg/L) had little inhibitory effect on the phosphorus recovery rate. However, when the concentration of SA was larger than 400 mg/L, the phosphorus recovery rate decreased significantly with increasing SA concentrations. The inhibition rate of 800 mg/L SA was about 3 times as large as that of 400 mg/L SA. It was worth noting that the inhibitory effect of SA on vivianite precipitation decreased with increasing initial pH and Fe/P molar ratios. Additionally, SA has no obvious influence on the composition of products, but the morphology of harvested crystals was transformed from branches to plates or rods in uneven sizes.

A correlative spatiotemporal microscale study of calcium phosphate formation and transformation within an alginate hydrogel matrix

The modification of soft hydrogels with hard inorganic components is a method used to form composite materials with application in non-load-bearing bone tissue engineering. The inclusion of an inorganic component may provide mechanical enhancement, introduce osteoconductive or osteoinductive properties, or change other aspects of interactions between native or implanted cells and the material. A thorough understanding of the interactions between such components is needed to improve the rational design of such biomaterials. To achieve this goal, model systems which could allow study of the formation and transformation of mineral phases within a hydrogel network with a range of experimental methods and high spatial and time resolution are needed. Here, we report a detailed investigation of the formation and transformation process of calcium phosphate mineral within an alginate hydrogel matrix. A combination of optical microscopy, confocal Raman microspectroscopy and electron microscopy was used to investigate the spatial distribution, morphology and crystal phase of the calcium phosphate mineral, as well as to study transformation of the mineral phases during the hydrogel mineralization process and upon incubation in a simulated body fluid. It was found, that under the conditions used in this work, mineral initially formed as a metastable amorphous calcium phosphate phase (ACP). The ACP particles had a distinctive spherical morphology and transformed within minutes into brushite in the presence of brushite seed crystals or into octacalcium phosphate, when no seeds were present in the hydrogel matrix. Incubation of brushite-alginate composites in simulated body fluid resulted in formation of hydroxyapatite. The characterization strategy presented here allows for non-destructive, in situ observation of mineralization processes in optically transparent hydrogels with little to no sample preparation.

STATEMENT OF SIGNIFICANCE

The precipitation and transformations of calcium phosphates (CaP) is a complex process, where both formation kinetics and the stability of different mineral phases control the outcome. This situation is even more complex if CaP is precipitated in a hydrogel matrix, where one can expect the organic matrix to modulate crystallization by introducing supersaturation gradients or changing the nucleation and growth kinetics of crystals. In this study we apply a range of characterization techniques to study the mineral formation and transformations of CaP within an alginate matrix with spatiotemporal resolution. It demonstrates how a detailed investigation of the mineral precipitation and transformations can aid in the future rational design of hydrogel-based materials for bone tissue engineering and studies of biomineralization processes.

Evaluation of novel in situ synthesized nano-hydroxyapatite/collagen/alginate hydrogels for osteochondral tissue engineering

Collagen hydrogel has been widely used for osteochondral repair, but its mechanical properties cannot meet the requirements of clinical application. Previous studies have shown that the addition of either polysaccharide or inorganic particles could reinforce the polymer matrix. However, their synergic effects on collagen-based hydrogel have seldom been studied, and the potential application of triple-phased composite gel in osteochondral regeneration has not been reported. In this study, nano-hydroxyapatite (nano-HA) reinforced collagen-alginate hydrogel (nHCA) was prepared by the in situ synthesis of nano-HA in collagen gel followed by the addition of alginate and Ca(2+). The properties of triple-phased nHCA hydrogel were studied and compared with pure collagen and biphasic gels, and the triple-phased composite of collagen-alginate-HA gels showed a superiority in not only mechanical but also biological features, as evidenced by the enhanced tensile and compressive modulus, higher cell viability, faster cell proliferation and upregulated hyaline cartilage markers. In addition, it was found that the synthesis process could also affect the properties of the triple-phased composite, compared to blend-mixing HCA. The in situ-synthesized nHCA hydrogel showed an enhanced tensile modulus, as well as enhanced biological features compared with HCA. Our study demonstrated that the nHCA composite hydrogel holds promise in osteochondral regeneration. The addition of alginate and nano-HA contribute to the increase in both mechanical and biological properties. This study may provide a valuable reference for the design of an appropriate composite scaffold for osteochondral tissue engineering.

Bioactive silica-based drug delivery systems containing doxorubicin hydrochloride: in vitro studies

This study reports the applicability of sol-gel derived silica and silica-polydimethylsiloxane (silica-PDMS) composites as a potential bioactive implantable drug delivery system for doxorubicin hydrochloride (DOX). These composites also contain calcium chloride (CaCl(2)) and triethylphosphate as precursors of Ca(2+) and (PO(4))(3-) ions. These composites were immersed for 20 days in a simulated body fluid (SBF) at 37°C to study the release rate of the DOX, dissolution of the silica and the formation of hydroxyapatite on the composites' surface. The results show that the release rate of the DOX can be effectively tailored by either the addition of a polydimethylsiloxane (PDMS), or by varying the amount of CaCl(2), where the elution rate of DOX increases with increasing amount of the CaCl(2) precursor. Importantly, irrespective of the amount of CaCl(2), no burst release of DOX has been observed in any of the silica-PDMS system investigated. On the other hand, a slow release of DOX has been observed with a trend that followed a zero (0)-order kinetics for a total of 20 days of elusion. The dissolution of silica in SBF was ca. two-times faster than that of silica-PDMS, with the former reaching an average saturation level of 80 μg/mL whilst the latter reached 46 μg/mL within 20 days. Both the silica and the silica-PDMS composites show bioactivity i.e. they absorb calcium phosphate from SBF. Within 10 days, a ten-fold increase in the concentration of calcium phosphate deposit has been observed on the silica-PDMS relative to the silica. The constant rates of DOX release observed for the silica-PDMS composites indicate that the calcium phosphate deposit do not obstruct controlled release of the drug.

Nanoscale hydroxyapatite particles for bone tissue engineering

Hydroxyapatite (HAp) exhibits excellent biocompatibility with soft tissues such as skin, muscle and gums, making it an ideal candidate for orthopedic and dental implants or components of implants. Synthetic HAp has been widely used in repair of hard tissues, and common uses include bone repair, bone augmentation, as well as coating of implants or acting as fillers in bone or teeth. However, the low mechanical strength of normal HAp ceramics generally restricts its use to low load-bearing applications. Recent advancements in nanoscience and nanotechnology have reignited investigation of nanoscale HAp formation in order to clearly define the small-scale properties of HAp. It has been suggested that nano-HAp may be an ideal biomaterial due to its good biocompatibility and bone integration ability. HAp biomedical material development has benefited significantly from advancements in nanotechnology. This feature article looks afresh at nano-HAp particles, highlighting the importance of size, crystal morphology control, and composites with other inorganic particles for biomedical material development.

Aqueous microgels for the growth of hydroxyapatite nanocrystals

In present article, we demonstrate that aqueous microgels can be used as containers for the in-situ synthesis of hydroxyapatite. The hydroxyapatite nanocrystals (HAp NCs) become integrated into microgels forming hybrid colloids. The HAp NCs loaded in the microgel can be varied over a broad range. The HAp NCs are localized within the microgel corona. The deposition of the inorganic nanocrystals decreases the colloidal stability of the microgels and leads to particle aggregation at high HAp NCs loading. Because of the strong interactions between HAp NCs and polymer chains, the swelling degree of microgels decreases, and temperature-sensitive properties disappear at high loading of the inorganic component. We demonstrate that hybrid colloids can be used as building blocks for the preparation of nanostructured films on solid substrates.

Influence of anti-washout agents on the rheological properties and injectability of a calcium phosphate cement

Anti-washout-type calcium phosphate cement (aw-CPC) was prepared by introducing chitosan, sodium alginate, or modified starch into the powder phase of CPC, respectively. The results showed that these cements cannot be washed out and set within approximately 10-30 min even if the pastes were immersed in distilled water immediately and were shaken in a shaker after mixing and moulding. To our knowledge, it is the first report about the influence of the content of these anti-washout additives on the rheological properties and injectability of the cement. Moreover, novel approach of yield stress measurement was used to evaluate the injectability of the pastes. A modified starch was originally used as anti-washout agent for CPC. This study provided a convenient way to use the injectable CPC with good anti-washout performance when the paste was exposed to blood. The aw-CPC had potential prospects for the wider applications in surgery such as orthopaedics, oral, and maxillofacial surgery.