Entrapment of organic fluorophores in calcium phosphate nanoparticles with slow release

Two organic fluorophores, fluorescein (F) and rhodamine B (Rd), were entrapped in calcium phosphate nanoparticles. The as-obtained nanoparticles can be used for biological release applications. For this aim, calcium phosphate nanoparticles were synthesized using the precipitation method. Structural analysis of these nanoparticles was performed using XRD, FTIR, and Raman spectroscopy, confirming that the synthesized nanoparticles were hydroxyapatite. TEM and SEM analyses demonstrated that these nanoparticles had a size of 20 nm and a well-defined morphology. F and Rd (about 0.5 wt.%) were entrapped in these nanoparticles and their release, as a function of time, was studied via UV-Vis spectroscopy. The obtained results showed that the release of both fluorophores was progressive over time. The trapping efficiencies of the fluorophores were 67.15% and 90.76% for F and Rd, respectively.     

Preparation of a biphasic calcium phosphate from Ca(H2PO4)2·H2O AND CaCO3

Sintered hydroxyapatite (HAp) and β-tricalcium phosphate (β-TCP) are the two most common bio-ceramics for bone substitute. Although their composition are analogous to the constituent of human hard tissue, but some disadvantages are always exist till now, such as they need a high temperature sintering process, and this would lose the functional groups for bioactivity and closed the micro- pores without any interconnections, that hamper the body fluid transportation and angiogenesis during regeneration. Furthermore, the sintered ceramics with block and fixed size is difficult to fit non-regular defect area. In this study, the mixtures of Ca(H₂PO₄)₂·H₂O and CaCO₃ were adjusted firstly, then distilled water were introduced in wet chemical method, and a biphasic ceramic of HAp/β-TCP will be obtained after drying and sintering, then the result product that prepared by wet chemical method will be the sample in this investigation. The physical properties of result powders were characterized by DTA/TG, XRD and SEM, respectively, the particle size of two bio-ceramics that after heat treatment were found under 5 μm in SEM examination. Powder type calcium phosphate ceramics with the Ca/P molar ratio of 1.67 can be as bone cement by mixing with polymeric binder, the fine particle product of the setting cement will possess micro-pores and macro-pores that after suitable heat treatment process, and this is good for fluid transportation and tissue regeneration.     

Rheological and thermal studies of polystyrene calcium phosphate nanocomposites

Polystyrene‐calcium phosphate nanocomposites were prepared in an internal mixer by the melt mixing technique with as synthesized calcium phosphate nanoparticles. The composites were characterized by different techniques. Rheological aspects of the composites revealed the ease of processability and viscosity characteristics of the composites. Thermogravimetric analysis of the composites showed that the thermal stability of the composites improved by the incorporation of the nanofillers especially for the 3% and 5% filled systems. Flammability tests were carried out with a microcalorimeter, and it was found that the heat release rate decreased with respect to the filler loading.     

Thermokinetic analysis of the hydration process of calcium phosphate cement

A microcalorimeter (Setaram c-80) was used to study the thermokinetics of the hydration process of calcium phosphate cement (CPC), a biocompatible biomaterial used in bone repair. The hydration enthalpy was determined to be 35.8 J g^–1 at 37.0°C when up to 80 mg CPC was dissolved in 2 mL of citric buffer. In the present study, parameters related to time constants of the calorimeter were obtained by fitting the recorded thermal curves with the function θ=Ae^–?t(1– e^–?2t). The real thermogenetic curves were then retrieved with Tian function and the transformation rate of the hydration process of CPC was found to follow the equation α=1–[1–(0.0075t)³]³. The microstructures of the hydrated CPC were examined by scanning electron microscopy. The nano-scale flake microstructures are due to crystallization of calcium phosphate and they could contribute to the good biocompatibility and high bioactivity.     

Mechanism of solid-state conversion of non-stoichiometric hydroxyapatite to diphase calcium phosphate

Two non-stoichiometric hydroxyapatites (n-HA) with Ca/P molar ratios of 1.50 and 1.58 and one stoichiometric hydroxyapatite (s-HA) with Ca/P = 1.67 were prepared from chemically pure CaHPO₄·2H₂O and KOH. After sintering at 1050 °C for 4 h, n-HA with Ca/P = 1.50 was transformed into -Ca₃(PO₄)₂, n-HA with Ca/P = 1.58 was converted to diphase calcium phosphate (DCP), while s-HA underwent no chemical transformations. The sintered and unsintered samples of hydroxyapatite were studied by IR spectroscopy, chemical analysis, and X-ray diffraction analysis. The crystallite dimensions were calculated, and a model for the DCP structure was proposed. The mechanism of the solid-state n-HA to DCP conversion was proposed on the basis of this model and published values of the volume diffusion coefficients of the OH^–, Ca²⁺, and PO₄ ^3– ions at 1000 °C.     

Controlled release of dexamethasone from porous PLGA scaffolds under cyclic loading

Poly(L-lactide)-b-poly(ethylene glycol)(PLLA-PEG) microspheres containing dexamethasone(Dex) have been fabricated using a spray-drying technique.Porous poly(lactic-co-glycolic acid)(PLGA) scaffolds were prepared using a method combining thermally induced phase separation and porogen leaching.A post-seeding technique was used to immobilize Dex-containing PLLA-PEG microspheres on porous PLGA scaffolds,and drug-containing microspheres-scaffolds(MS-S) were obtained.Simple Dex-containing scaffolds(D-S) were also...     

Fabrication of hollow porous PLGA microspheres for controlled protein release and promotion of cell compatibility

This letter reports on the fabrication of hollow,porous and non-porous poly(D,L-lactide-co-glycolide) (PLGA) microspheres(MSs) for the controlled release of protein and promotion of cell compatibility of tough hydrogels.PLGA MSs with different structures were prepared with modified double emulsion methods,using bovine serum albumin(BSA) as a porogen during emulsification.The release of the residual BSA from PLGA MSs was investigated as a function of the MS structure.The hollow PLGA MSs show a faster protein release than the porous MSs,while the non-porous MSs have the slowest protein release.Compositing the PLGA MSs with poly(vinyl alcohol)(PVA) hydrogels promoted chondrocyte adhesion and proliferation on the hydrogels.     

焦磷酸盐-磷酸盐复合催化剂高效催化乳酸脱水制丙烯酸

利用沉淀法制得焦磷酸盐与磷酸盐在浆状态下复配制备成复合催化剂,并用于催化乳酸脱水制丙烯酸.实验发现催化剂的组成对乳酸的转化率及丙烯酸的选择性有着重要的影响,当磷酸盐/焦磷酸盐质量比在30∶70～50∶50范围内,可以获得较高的乳酸的转化率和丙烯酸的选择性.催化反应条件如反应温度,乳酸进料浓度,液空速也被详细地进行了考察.此外,考察了该复合催化剂的稳定性.当催化剂连续运行56 h后,乳酸的转化率保持在96%以上,丙烯酸的选择性也高达57%.为了进一步揭示催化剂的结构与催化性能之间的关系,利用X射线粉末衍射、热重、扫描电镜和傅立叶红外等对催化剂进行了表征.     

Determination of photoelectron attenuation lengths in calcium phosphate ceramic films using XPS and RBS

Calcium phosphate (CaP) coatings are used to improve the biological performance of an implant. A technique that is often used to measure the composition of this material is XPS. When extremely thin coatings are measured, for example to study the interface between CaP and a substrate, the quantification of the XPS results is complicated by the varying attenuation lengths (ALs) of the photoelectrons at different energies. To correct for this, AL data are needed. In this work we measured these ALs by comparing XPS yields with the coating coverage (as measured by Rutherford backscattering spectrometry). We were able to determine the AL for several calcium and phosphorus peaks. Determination of the oxygen ALs was not possible owing to diffusion of oxygen into the polymeric substrates. For the peaks that are most often used for quantification of XPS yields (the Ca 2p and the P 2p peak), we found ALs of 21.8 × 10¹⁵ atoms cm^?2 and 26.8 × 10¹⁵ atoms cm^?2, respectively. Concentration profiles near the interface, growth mode and interfacial roughness appeared to have no measurable effect on the measured ALs. For the ALs, an energy dependence with an exponent of 0.55 was found. The measured ALs are best predicted by the empirical CS1 equation of Cumpson and Seah. Copyright © 2003 John Wiley & Sons, Ltd.     

Reaction of calcium and phosphate ions with titanium,zirconium, niobium,and tantalum

To understand the bone formation ability of constituent metal elements of new titanium alloys, titanium, zirconium, niobium, and tantalum, these metals were immersed in various electrolytes containing calcium and/or phosphate ions and characterized using X‐ray photoelectron spectroscopy. In addition, cathodic polarization of the metals in the electrolytes was performed to evaluate the stability of the surface oxide films on the metals in the electrolyte. The calcium phosphate layer formed on Ti in electrolytes containing calcium and phosphate ions is relatively protective against mass transfer throughout the layer. However, the zirconium phosphate layer formed on Zr is much more protective and stable than that on Ti. Therefore, calcium ions were not incorporated. Nb and Ta formed calcium phosphate, but the amount was smaller than that in Ti, because phosphates formed on Nb and Ta are somewhat protective and the incorporation of the calcium ion is inhibited. Titanium played the most important role in forming calcium phosphate, while zirconium inhibited the formation of calcium phosphate on titanium alloys. The control of bone formation is feasible by the design of titanium alloys. Copyright © 2015 John Wiley & Sons, Ltd.     

Evaluation of Chitosan/Biphasic Calcium Phosphate Scaffolds for Maxillofacial Bone Tissue Engineering

Porous, 3D chitosan/biphasic calcium phosphate (BCP) scaffolds were used to prepare tissue engineering constructs for maxillofacial bone tissue reconstruction. Mesenchymal stem cells (MSC's) were seeded and cultured on clinically relevant sized scaffolds. In vitro engineered constructs facilitated the healing of mandibular defects in pigs if accompanied with delivery of basic fibroblast growth factor (bFGF).     

Preparation and mechanical behavior of PLGA/nano-BCP composite scaffolds during in-vitro degradation for bone tissue engineering

In this paper, the yield strength and elastic modulus of Poly (lactide-co-glycolide) (PLGA) and PLGA/nano-biphasic calcium phosphate (nBCP) composite scaffolds, before and during in-vitro degradation, have been evaluated. Composite scaffolds were made by using PLGA matrix and 10-50 wt.% nBCP powder as the reinforcement material. All scaffolds, with more than 89% porosity, were fabricated by thermally-induced phase separation (TIPS). During in-vitro degradation (0-8 weeks), the PLGA/nBCP scaffolds showed both more weight loss and better mechanical properties as compared to neat PLGA scaffolds. The PLGA/nBCP scaffolds with 30 wt.% nBCP illustrated the highest value of yield strength among the composite scaffolds, before and after degradation, until 6 weeks. After 8 weeks, the yield strength values were very poor and close to each other. The values of elastic modulus for all samples were less than the half of their initial values after 6 weeks. However, after 8 weeks, the elastic moduli of all samples reduced to negligible values.     

Synergistic effects of cerium phosphate and intumescent flame retardant on EPDM/PP composites

An intumescent flame retardant system composed of ammonium polyphosphate (APP) and pentaerythritol (PER) was used for flame retarding ethylene–propylene–diene‐modified elastomer (EPDM)/polypropylene (PP) blends. Cerium phosphate (CeP) was synthesized and the effect on flame retardancy and thermal stability of EPDM/PP composites based on intumescent flame retardant (IFR) were studied by limiting oxygen index (LOI), UL‐94, and thermogravimetic analysis (TGA), respectively. Scanning electron microscopy (SEM) and Fourier transform infrared spectrometry (FTIR) were used to analyze the morphological structure and the component of the residue chars formed from the EPDM/PP composites, and the mechanical properties of the materials were also studied. The addition of CeP to the EPDM/PP/APP/PER composites gives better flame retardancy than that of EPDM/PP/APP/PER composites. TGA and RT‐FTIR studies indicated that an interaction occurs among APP, PER, and EPDM/PP. The incorporation of CeP improved the mechanical properties of the materials. Copyright © 2010 John Wiley & Sons, Ltd.     

Biodegradable polymer/clay systems for highly controlled release of NPK fertilizer

The aim of this work was to obtain biodegradable polymeric systems based on poly(hydroxybutyrate) (PHB) for use in the controlled release of agrochemicals and to analyze the relationship between the properties of polymers and the rates of release of active compounds. Two types of systems were obtained: one using nitrogen, phosphorous, and potassium (NPK) fertilizer directly mixed within the polymer matrix and another with the fertilizer previously incorporated in bentonite (Bent) and mixed with the polymer. The systems were obtained by melt processing and then evaluated by their properties. The release of the active compounds was analyzed by conductometric analysis using an aqueous solution as release medium for 240 hours. The obtained results were correlated with the biodegradation process of PHB. All of the systems presented a significant reduction in the active compounds released to the environment as compared with the direct application of NPK. The PHB/NPK systems showed a release of up to 37% of the compounds, while the PHB/m‐Bent showed greater control, with a release between 4% and 11% after 240 hours. In addition, the properties of the polymer systems presented a direct relationship with the rate of active compounds released. The type of production process, properties, and biodegradability indicate interesting potential of these systems for application in the controlled release of active compounds.     

Preparation and characterization of calcium hydroxyapatite and balloon-like calcium phosphate particles from forced hydrolysis of Ca(OH)2–triphosphate solution

Calcium phosphate particles were prepared by aging a solution of dissolved Ca(OH)₂ and sodium triphosphate (sodium tripolyphosphate, Natpp: Na₅P₃O₁₀) at 100–150 °C for 18 h in a Teflon-lined screw-capped Pyrex test tube. Large spherical and/or small aggregated spherical particles were precipitated with an extremely fast rate of reaction under 100 °C. The large spherical particles were amorphous and the small aggregated ones were α-CaNa₂P₂O₇^.4H₂O. The former amorphous ones crystallized to β-Ca₂P₂O₇ after being calcined above 600 °C. Calcium hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, Hap), with rod-like and ellipsoidal or spherical aggregated shapes, was successfully produced using polyphosphates as a source of orthophosphate ions. Time resolved TEM measurement revealed that the crystallization of Hap particles takes place on the surface of tiny amorphous particles precipitated before aging. The tiny particles played the role of nuclei for Hap crystallization. The aging temperature drastically varied the particle shape under conditions for producing uniform amorphous spherical particles; solid spherical particles were produced with an aging temperature of up to 120 °C, whilst transparent balloon-like hollow spheres were precipitated at 125 °C. Finally, fully transparent balloon-like hollow spheres were produced with mere trace amounts of small rod-like particles after aging the solution above 127 °C. The time resolved TEM observation and ICP-AES measurements revealed that the balloon-like hollow spheres were produced by dissolving the interior of solid spherical particles after reinforcing their shell by the adsorption of unhydrolyzed tpp and/or pyrophosphate (pp) ions, which are the hydrolysis product of tpp. The balloon-like hollow spheres of calcium phosphate may have the potential use as drug delivery vehicles and have biocompatibility advantages.     

Structural interaction and gas barrier properties of ethylene‐vinyl alcohol/tin phosphate glass composites

The strength of interaction between tin phosphate glass (PGlass) filler droplets and an ethylene‐vinyl alcohol (EVOH) matrix were investigated by image, thermal, and rheological analysis. 10% PGlass droplets in EVOH were smaller than those previously observed in maleated polypropylene. Analysis using the Fox equation showed that EVOH/97 °C T_g PGlass composites are not miscible systems. Dynamic shear and extensional rheology data of those composites exhibited a weak physical network, with relaxation times longer than that of pure EVOH at all strain rates. The tensile properties of the EVOH/10 vol % PGlass composite showed it to be more ductile and flexible than a typical polymer/inorganic filler system, supporting interaction between PGlass and EVOH sufficient to interrupt polymer–polymer hydrogen bonding. While undrawn EVOH/PGlass composite films showed increased oxygen gas permeability when compared to undrawn neat EVOH film, the drawn composite films exhibited oxygen permeability 6–7 times lower than that of neat EVOH, attributed to the presence of high aspect ratio PGlass particles after orientation. The concept of hydrogen bonding between polymer and PGlass can likely be applied to other polymers such as polyamides which possess numerous hydrogen bonding sites. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 989–998     

Development of temperature-responsive semi-IPN hydrogels from PVA-PNVC-PAm for controlled release of anti-cancer agent

A series of semi-interpenetrating polymeric network (semi-IPN) hydrogels were synthesized using poly(vinyl alcohol) (PVA), monomers N-vinylcaprolactam (NVC) acrylamide (Am), and cross-linker bis[2-methacryloyloxy] ethyl phosphate (BMEP). The hydrogels were synthesized by using free-radical polymerization using ammonium persulphate (APS) as an initiator at 60°C. The hydrogels were characterized by various techniques such as Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and scanning electron microscopy (SEM) to confirm the formation, crystallinity, and morphological behavior. The swelling behavior at various temperatures and pH conditions showed that the semi-IPN hydrogels were good candidates for temperature-responsive nature. 5-Flurouracil (FU), a model anticancer drug, was successfully encapsulated and the encapsulation efficiency was found in range of 50–74% for different hydrogels. Further, in-vitro release studies were performed to investigate the release mechanism. The cumulative release studies showed that the developed hydrogels are potentially efficient for the gastrointestinal drug delivery of FU.     

Preparation, characterization, and controlled release of novel nanoparticles based on MMA/beta-CD copolymers

A series of random copolymers with different beta-cyclodextrin contents were synthesized by radical copolymerization of MMA with a monovinyl beta-CD monomer. The copolymers were characterized with IR spectroscopy, elemental analysis, DSC, and TGA. Based on these copolymers, their nanoparticles were prepared by using DMF, water, and acetone as solvents. Aqueous dispersions of the nanoparticles were further obtained by dialysis against water. Zetasizer Nano-ZS dynamic light scattering and transmission electron microscopy were employed to characterize the nanoparticles. Using camptothecin as a model drug molecule, the encapsulation efficiency and release behavior of the nanoparticles were investigated.