A novel skeletal drug delivery system using a self-setting calcium phosphate cement. 5. Drug release behavior from a heterogeneous drug-loaded cement containing an anticancer drug

Calcium phosphate bone cements as local drug delivery systems for bone cancer treatment

Bone cancer is usually a metastatic disease, affecting people of all ages. Its effective therapy requires a targeted drug administration locally at the cancer site so that the surrounding healthy organs and tissues stay unharmed. Upon a thorough literature search, a tremendous number of published articles are reporting on development of calcium phosphate cements (CPCs) for the treatment of a variety of diseases, such as osteoporosis, osteoarthritis, osteomyelitis, and other musculoskeletal disorders. However, just a limited number of research employs CPCs specifically for bone cancer treatment. In this review article, we study the factors influencing the local drug release from CPCs and particularly focus on bone cancer therapy. Finally, we locate the deficiencies in the literature regarding this specific topic and propose which other perspectives should be considered and discussed in future articles.

Synthesis, physical properties, and biomedical applications of magnetic nanoparticles: a review

Recent innovations in nanotechnology have opened the applicability of multifunctional nanoparticles (NPs) in biomedical diagnosis and treatment. The examples of NPs which have attracted considerable attention in recent years are metals (e.g., Au, Ag, Mg), alloys (e.g., Fe-Co, Fe-Pd, Fe-Pt, Co-Pt), iron oxides (e.g., Fe₂O₃ and Fe₃O₄), substituted ferrites (e.g., MnFe₂O₄ and CoFe₂O₄), manganites (e.g., [Formula: see text]), etc. Special attention has been paid to magnetic NPs (MNPs), as they are the potential candidates for several biomedical appliances, such as hyperthermia applications, magnetic resonance imaging, contrast imaging, and drug delivery. To achieve effective MNPs, a thorough investigation on the synthesis, and characteristic properties, including size, magnetic properties, and toxicity, is required. Furthermore, the surfaces of the NPs must be tailored to improve the biocompatibility properties and reduce agglomeration. The present review focuses on different mechanisms to develop biocompatible MNPs. The utility of these MNPs in various biomedical applications, especially in treating and diagnosing human diseases, such as targeted drug delivery, hyperthermia treatment for cancer, and other biomedical diagnoses, is thoroughly discussed in this article. Different synthetic processes and important physical properties of these MNPs and their biocomposites are presented.

Oridonin-loaded lipid-coated calcium phosphate nanoparticles: preparation, characterization, and application in A549 lung cancer

In this study, the feasibility of using the novel anisamide-lipid calcium phosphate nanoparticles (AS-LCPs) as a nanocarrier for the delivery of biologically active oridonin (ORD) was evaluated on lung cancer models. In addition to the characterization, release behaviors, and stability of AS-ORD LCPs, we also studied their pharmacokinetics and targeting ability by in vivo imaging. Finally, we investigated the effect of ORD on the anti-tumor efficiency of the AS-LCPs based on weight, tumor inhibition, and the survival time of mice. The average particle size of the AS-ORD LCPs was 129.5 ± 23.7 nm, the polydispersity index (PDI) was 0.16 ± 0.03, and the zeta potential was 23.6 ± 3.4 mV. The AS-ORD LCPs were proved to be stable under both long-term and accelerated storage conditions. The AS-ORD LCPs showed sustained release in vivo and faster release in acidic environment, which was favorable to drug release in tumor environment. In vivo studies showed that depending on surface modification, AS-ORD LCPs which suggested that cell internalization was change and more drugs entered the cells successfully. Therefore, AS-ORD LCPs could be a promising formulation for the treatment of lung cancer.

Bone cement as a local chemotherapeutic drug delivery carrier in orthopedic oncology: A review

Metastatic bone lesions are common among patients with advanced cancers. While chemotherapy and radiotherapy may be prescribed immediately after diagnosis, the majority of severe metastatic bone lesions are treated by reconstructive surgery, which, in some cases, is followed by postoperative radiotherapy or chemotherapy. However, despite recent advancements in orthopedic surgery, patients undergoing reconstruction still have the risk of developing severe complications such as tumor recurrence and reconstruction failure. This has led to the introduction and evaluation of poly (methyl methacrylate) and inorganic bone cements as local carriers for chemotherapeutic drugs (usually, antineoplastic drugs (ANPDs)). The present work is a critical review of the literature on the potential use of these cements in orthopedic oncology. While several studies have demonstrated the benefits of providing high local drug concentrations while minimizing systemic side effects, only six studies have been conducted to assess the local toxic effect of these drug-loaded cements and they all reported negative effects on healthy bone structure. These findings do not close the door on chemotherapeutic bone cements; rather, they should assist in materials selection when designing future materials for the treatment of metastatic bone disease.

Enhanced antineoplastic/therapeutic efficacy using 5-fluorouracil-loaded calcium phosphate nanoparticles

In the past few decades, the successful theranostic application of nanomaterials in drug delivery systems has significantly improved the antineoplastic potency of conventional anticancer therapy. Several mechanistic advantages of nanomaterials, such as enhanced permeability, retention, and low toxicity, as well as surface engineering with targeting moieties, can be used as a tool in enhancing the therapeutic efficacy of current approaches. Inorganic calcium phosphate nanoparticles have the potential to increase the therapeutic potential of antiproliferative drugs due to their excellent loading efficiency, biodegradable nature and controlled-release behaviour. Herein, we report a novel system of 5-fluorouracil (5-FU)-loaded calcium phosphate nanoparticles (CaP@5-FU NPs) synthesized via a reverse micelle method. The formation of monodispersed, spherical, crystalline nanoparticles with an approximate diameter of 160-180 nm was confirmed by different methods. The physicochemical characterization of the synthesized CaP@5-FU NPs was done with transmission electron microscopy (TEM), dynamic light scattering (DLS), field emission scanning electron microscopy (FE-SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The antineoplastic potential of the CaP@5-FU NPs against colorectal and lung cancer cells was reported. The CaP@5-FU NPs were found to inhibit half the population (IC50) of lung adenocarcinoma (A549) cells at 32 μg/mL and colorectal (HCT-15) cancer cells at 48.5 μg/mL treatment. The apoptotic induction of CaP@5-FU NPs was confirmed with acridine orange/ethidium bromide (AO/EB) staining and by examining the morphological changes with Hoechst and rhodamine B staining in a time-dependent manner. The apparent membrane bleb formation was observed in FE-SEM micrographs. The up-regulated proapoptotic and down-regulated antiapoptotic gene expressions were further confirmed with semiquantitative reverse transcriptase polymerase chain reaction (PCR). The increased intracellular reactive oxygen species (ROS) were quantified via flow cytometry upon CaP@5-FU NP treatment. Likewise, the cell cycle analysis was performed to confirm the enhanced apoptotic induction. Our study concludes that the calcium phosphate nanocarriers system, i.e. CaP@5-FU NPs, has higher antineoplastic potential as compared to 5-FU alone and can be used as an improved alternative to the antimitotic drug, which causes severe side effects when administrated alone.

Design and properties of novel gallium-doped injectable apatitic cements

Different possible options were investigated to combine an apatitic calcium phosphate cement with gallium ions, known as bone resorption inhibitors. Gallium can be either chemisorbed onto calcium-deficient apatite or inserted in the structure of β-tricalcium phosphate, and addition of these gallium-doped components into the cement formulation did not significantly affect the main properties of the biomaterial, in terms of injectability and setting time. Under in vitro conditions, the amount of gallium released from the resulting cement pellets was found to be low, but increased in the presence of osteoclastic cells. When implanted in rabbit bone critical defects, a remodeling process of the gallium-doped implant started and an excellent bone interface was observed.

STATEMENT OF SIGNIFICANCE

The integration of drugs and materials is a growing force in the medical industry. The incorporation of pharmaceutical products not only promises to expand the therapeutic scope of biomaterials technology but to design a new generation of true combination products whose therapeutic value stem equally from both the structural attributes of the material and the intrinsic therapy of the drug. In this context, for the first time an injectable calcium phosphate cement containing gallium was designed with properties suitable for practical application as a local delivery system, implantable by minimally invasive surgery. This important and original paper reports the design and in-depth chemical and physical characterization of this groundbreaking technology.

Self-setting calcium orthophosphate formulations

In early 1980s, researchers discovered self-setting calcium orthophosphate cements, which are bioactive and biodegradable grafting bioceramics in the form of a powder and a liquid. After mixing, both phases form pastes, which set and harden forming either a non-stoichiometric calcium deficient hydroxyapatite or brushite. Since both of them are remarkably biocompartible, bioresorbable and osteoconductive, self-setting calcium orthophosphate formulations appear to be promising bioceramics for bone grafting. Furthermore, such formulations possess excellent molding capabilities, easy manipulation and nearly perfect adaptation to the complex shapes of bone defects, followed by gradual bioresorption and new bone formation. In addition, reinforced formulations have been introduced, which might be described as calcium orthophosphate concretes. The discovery of self-setting properties opened up a new era in the medical application of calcium orthophosphates and many commercial trademarks have been introduced as a result. Currently such formulations are widely used as synthetic bone grafts, with several advantages, such as pourability and injectability. Moreover, their low-temperature setting reactions and intrinsic porosity allow loading by drugs, biomolecules and even cells for tissue engineering purposes. In this review, an insight into the self-setting calcium orthophosphate formulations, as excellent bioceramics suitable for both dental and bone grafting applications, has been provided.

Controlling the biological function of calcium phosphate bone substitutes with drugs

There is a growing interest in bone tissue engineering for bone repair after traumatic, surgical or pathological injury, such as osteolytic tumor or osteoporosis. In this regard, calcium phosphate (CaP) bone substitutes have been used extensively as bone-targeting drug-delivery systems. This localized approach improves the osteogenic potential of bone substitutes by delivering bone growth factors, thus extending their biofunctionality to any pathological context, including infection, irradiation, tumor and osteoporosis. This review briefly describes the physical and chemical processes implicated in the preparation of drug-delivering CaPs. It also describes the impact of these processes on the intrinsic properties of CaPs, especially in terms of the drug-release profile. In addition, this review focuses on the potential influence of drugs on the resorption rate of CaPs. Interestingly, by modulating the resorption parameters of CaP biomaterials, it should be possible to control the release of bone-stimulating ions, such as inorganic phosphate, in the vicinity of bone cells. Finally, recent in vitro and in vivo evaluations are extensively reported.

RNA therapeutics targeting osteoclast-mediated excessive bone resorption

RNA interference (RNAi) is a sequence-specific post-transcriptional gene silencing technique developed with dramatically increasing utility for both scientific and therapeutic purposes. Short interfering RNA (siRNA) is currently exploited to regulate protein expression relevant to many therapeutic applications, and commonly used as a tool for elucidating disease-associated genes. Osteoporosis and their associated osteoporotic fragility fractures in both men and women are rapidly becoming a global healthcare crisis as average life expectancy increases worldwide. New therapeutics are needed for this increasing patient population. This review describes the diversity of molecular targets suitable for RNAi-based gene knock down in osteoclasts to control osteoclast-mediated excessive bone resorption. We identify strategies for developing targeted siRNA delivery and efficient gene silencing, and describe opportunities and challenges of introducing siRNA as a therapeutic approach to hard and connective tissue disorders.

Calcium phosphate cements as drug delivery materials

Calcium phosphate cements are used as synthetic bone grafts, with several advantages, such as their osteoconductivity and injectability. Moreover, their low-temperature setting reaction and intrinsic porosity allow for the incorporation of drugs and active principles in the material. It is the aim of the present work to: a) provide an overview of the different approaches taken in the application of calcium phosphate cements for drug delivery in the skeletal system, and b) identify the most significant achievements. The drugs or active principles associated to calcium phosphate cements are classified in three groups, i) low molecular weight drugs; ii) high molecular weight biomolecules; and iii) ions.

Calcium orthophosphate-based bone cements (CPCs): Applications, antibiotic release and alternatives to antibiotics

Calcium orthophosphate bone cements (CPCs) are widely used in orthopedic surgery. Implants are highly susceptible to infection and often lead to the formation of microbial biofilms. Antibiotics are often incorporated into bone cement to prevent infection. The increase in the number of microorganisms acquiring or developing resistance to antibiotics, such as methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE), is a major concern. Bacteriocins (antimicrobial peptides) offer an alternative to antibiotics. Their mode of activity involves permanent destabilization of the plasma membrane of target cells. A number of broad-spectrum bacteriocins produced by lactic acid bacteria and Bacillus spp. have recently been reported. In this REVIEW the major characteristics of calcium phosphate bone cements, prosthetic joint-associated infections, and treatment of these infections is discussed. The role of antimicrobial agents in CPCs is discussed and the possibility of incorporating bacteriocins in prosthetic devices is investigated.

Analgesic properties of calcium phosphate apatite loaded with bupivacaine on postoperative pain

Synthetic calcium-deficient apatites (CDA) are structurally similar to biological apatites and are well known as chemical precursors of biphasic calcium phosphates (BCP). BCP are mixtures of hydroxyapatite and beta-tricalcium phosphate and are widely used as bone substitutes in human surgery. Bupivacaine, a local anesthetic, has been loaded onto CDA using isostatic compaction. The purpose of this study was to evaluate the in vivo performance of such a local release on pain after having previously defined the in vitro release profile of bupivacaine. CDA was loaded with 1%, 4%, and 16% of bupivacaine using an isostatic compaction process. In vitro release profile assays performed indicated the complete release of bupivacaine after 24 h. Wistar male rats received 50 mg implants of CDA associated, respectively, with 0, 1%, 4%, and 16% of bupivacaine into the distal femur. Analgesia was measured using the electronic version of the Von Frey monofilament test, assessing the inflammatory response and a neurological score. During the first postoperative days, a dose-dependent analgesic effect was observed with the bupivacaine adsorbed on the resorbable implant. This combined device system thus appears to release local anesthetic in a manner that prevents or limits postoperative pain following bone surgery. This innovative approach could be integrated into a global pain management program, for example, in the context of bone harvesting where bone reconstruction is required.

Calcium Orthophosphate Cements and Concretes

In early 1980s, researchers discovered self-setting calcium orthophosphate cements, which are a bioactive and biodegradable grafting material in the form of a powder and a liquid. Both phases form after mixing a viscous paste that after being implanted, sets and hardens within the body as either a non-stoichiometric calcium deficient hydroxyapatite (CDHA) or brushite, sometimes blended with unreacted particles and other phases. As both CDHA and brushite are remarkably biocompartible and bioresorbable (therefore, in vivo they can be replaced with newly forming bone), calcium orthophosphate cements represent a good correction technique for non-weight-bearing bone fractures or defects and appear to be very promising materials for bone grafting applications. Besides, these cements possess an excellent osteoconductivity, molding capabilities and easy manipulation. Furthermore, reinforced cement formulations are available, which in a certain sense might be described as calcium orthophosphate concretes. The concepts established by calcium orthophosphate cement pioneers in the early 1980s were used as a platform to initiate a new generation of bone substitute materials for commercialization. Since then, advances have been made in the composition, performance and manufacturing; several beneficial formulations have already been introduced as a result. Many other compositions are in experimental stages. In this review, an insight into calcium orthophosphate cements and concretes, as excellent biomaterials suitable for both dental and bone grafting application, has been provided.

Antibacterial and osteogenic properties of silver-containing hydroxyapatite coatings produced using a sol gel process

Since bacterial infection is a rising complication following the wide use of implant, there is considerable attention on the effect of implant surface properties on bacterial adhesion. In this study, the effect of silver (Ag) doped hydroxyapatite (HA) coatings on initial antibacterial adhesion and osteoblast cell proliferation and differentiation was investigated. Using a sol-gel process, HA coatings doped with 1 wt % AgNO(3) (AgHA1.0) and 1.5 wt % Ag (AgHA1.5) were prepared. Coated surfaces were characterized using X-ray diffraction (XRD) and contact angles measurements. The initial bacteria adhesion was evaluated using a RP12 strain of Staphylococcus epidermidis (ATCC 35984) and the Cowan I strain of Staphylococcus aureus, whereas osteoblast proliferation and differentiation were evaluated using human embryonic palatal mesenchyme cells (HEPM), an osteoblast precursor cell line. In this study, XRD analysis of all surfaces indicated peaks corresponding to HA. Contact angles for AgHA surfaces were observed to be significantly lower when compared to HA surfaces. In vitro initial bacterial adhesion study indicated a significantly reduced number of S. epidermidis and S. aureus on AgHA surfaces when compared to HA surface. The use of HEPM cells indicated no significant difference in double-stranded DNA (dsDNA) production between all surfaces. Additionally, no differences in alkaline phosphatase specific activity were observed between HA and AgHA1.0 surfaces. Overall, it was concluded that AgHA1.0 has the similar biological activity as HA, with respect to bone cell proliferation and differentiation. In addition, the AgHA1.0 was also concluded to have the ability to minimize the initial bacteria adhesion. (c) 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007.

Low temperature direct 3D printed bioceramics and biocomposites as drug release matrices

The aim of this study was to investigate the adsorption and desorption kinetics of antibiotics to microporous bioceramics fabricated by a novel low temperature 3D powder direct printing process. The adsorption of vancomycin, ofloxacin and tetracycline onto hydroxyapatite, brushite and monetite showed a linear correlation with the drug concentration in the immersion solution, whereas a non-linear relationship was found between the immersion time and the amount of adsorbed drug. Differences in the total amount of adsorbed drugs were correlated to the specific surface areas of the matrices, which varied between 2.4-13.1 m(2)/g. Normalised drug loadings were found to be in the range of 1.5-1.8 mg/m(2) for vancomycin and ofloxacin, whereas higher loads of up to 5-7 mg/m(2) were obtained for tetracycline. Vancomycin and ofloxacin were rapidly released into PBS buffer within 1-2 days, while tetracycline showed a much slower release rate of approximately 25% after 5 days of immersion. Additional polymer impregnation of the drug loaded matrix with PLA/PGA polymer solutions enabled the release kinetics to be delayed such that sustained release was achieved in polymer ceramic biocomposites.

Preparation and characterization of nano‐hydroxyapatite/chitosan/konjac glucomannan composite

Nano-hydroxyapatite (n-HA)/chitosan (CS)/konjac glucomannan (KGM) composite was prepared by coprecipitation method and investigated by thermal gravitivity/differentiate thermal analysis, Fourier transform infrared spectroscopy, X-ray diffraction, inductively coupled plasma emission spectroscopy, scanning electron microscopy, and energy dispersive X-ray analyzer. The analyses showed that the three phases of n-HA, CS, and KGM combined closely to each other. Further, in vitro tests were conducted to investigate the degradation and bioactivity of the composite. During immersion in simulated body fluid (SBF), pores appeared and a new substance containing Ca and P formed on the surface of the composite. Also, the concentration of Ca and P in SBF changed and weight loss of the composite was observed during time. The composite revealed a high degradation in SBF. Evidently, the new composite has a potential to be used as a carrier of implantable drug delivery system. The biodegradation rate and route could be different from CS and KGM, which will provide an opportunity to control the degradation rate or drug releasing rate by simply adjusting the ratio of CS and KGM.

Calcium phosphate cements as bone drug delivery systems: A review

Since calcium phosphate cements were proposed, several formulations have been developed, some of them commercialised, and they have proven to be very efficient bone substitutes in different applications. Some of their properties, such as the injectability, or the low-temperature setting, which allows the incorporation of different drugs, make them very attractive candidates as drug carriers. In this article, the performance of calcium phosphate cements as carriers of different types of drugs, such as antibiotics, analgesics, anticancer, anti-inflammatory, as well as growth factors is reviewed.

Mechanical Behavior of Complex 3D Calcium Phosphate Cement Scaffolds Fabricated by Indirect Solid Freeform Fabrication In Vivo

Calcium phosphate cement is a bioceramic with potential applications for bone-tissue engineering. In this work, controlled porous calcium phosphate scaffolds with interconnected pores were computationally designed by an image-based approach and fabricated by indirect solid freeform fabrication (ISFF) or ‘lost mold’ technique. Voxel finite-element analysis (FEA) showed that mechanical properties of design and fabricated scaffold can be predicted computationally. Scaffolds were then implanted subcutaneously to demonstrate tissue in-growth. Previously, we showed the ability of porous calcium phosphate cement scaffolds to have sufficiently strong mechanical properties for bone tissue engineering applications. This work shows the image-based FEAs from micro-CT scans in vivo (four- and eight weeks). Extensive new bone apposition was noted with micro-CT technique after four- and eight weeks. FEA models of the original design and scaffolds with newly bone formed were compared.

Preparation of massive anti-infective reconstituted bone xenograft and related studies

The purpose of this study was to develop a new type of anti-infective bone transplantation material. A massive anti-infective reconstituted bone xenograft with calcium phosphate drug core (CPC-MARBX) was prepared; a drug delivery profile and capability of repairing large segmental infected bony defect were characterized with drug delivery tests and in the rabbit model with large segmental infected bony defect. CPC-MARBX was produced with relatively simple procedures. The duration of the drug delivery was about 25 days in vitro and 30 days in vivo. The infected bony defect was successfully repaired with good healing. CPC-MARBX is readily available and can be applied in repairing the large segmental infected bony defect.

Vancomycin covalently bonded to titanium beads kills Staphylococcus aureus

Periprosthetic infections are life-threatening complications that occur in about 6% of medical device insertions. Stringent sterile techniques have reduced the incidence of infections, but many implant patients are at high risk for infection, especially the elderly, diabetic, and immune compromised. Moreover, because of low vascularity at the site of the new implant, antibiotic prophylaxis is often not effective. To address this problem, we designed a covalent modification to titanium implant surfaces to render them bactericidal. Specifically, we aminopropylated titanium, a widely used implant material and extended a tether by solid phase coupling of ethylene glycol linkers, followed by solid phase coupling of vancomycin. Vancomycin covalently attached to titanium still bound soluble bacterial peptidoglycan, reduced Staphylococcus aureus colony-forming units by 88% +/- 16% over 2 hr, and retained antibacterial activity upon a repeated challenge.

Block copolymer-coated calcium phosphate nanoparticles sensing intracellular environment for oligodeoxynucleotide and siRNA delivery

The organic-inorganic hybrid nanoparticles entrapping oligodeoxynucleotide (ODN) or siRNA were prepared through the self-associating phenomenon of the block copolymer, poly(ethylene glycol)-block-poly(aspartic acid) (PEG-PAA), with calcium phosphate. The nanoparticles have diameters in the range of several hundreds of nanometers depending on the PEG-PAA concentration and revealed excellent colloidal stability due to the steric repulsion effect of the PEG layer surrounding the calcium phosphate core. The loading capacities of ODN and siRNA were fairly high, reaching almost 100% under optimal conditions. The flowcytometric analysis and confocal microscopy observation indicated that the hybrid nanoparticles loaded with ODN were taken up by the cells through the endocytosis mechanism. Furthermore, the calcium phosphate core dissociates in the intracellular environment with appreciably lowered calcium ion concentration compared to the exterior, allowing the release of the incorporated ODN and siRNA in a controlled manner. Eventually, effective intracellular delivery and nuclear localization of these nucleic acid-based drugs were evidenced through the observation of laser confocal microscopy using FITC-labeled ODN. This smart ion-sensitive characteristic of hybrid nanoparticles was further demonstrated by the appreciable silencing of reporter gene expression by siRNA incorporated in the nanoparticles.

Fabrication of low temperature macroporous hydroxyapatite scaffolds by foaming and hydrolysis of an α-TCP paste

The development of the new technologies of bone tissue engineering requires the production of bioresorbable macroporous scaffolds. Calcium phosphate cements are good candidate materials for the development of these scaffolds, as an alternative to the traditional porous sintered ceramics. In this work a novel two-step method, based in the foaming of an alpha-tricalcium phosphate (alpha-TCP) cement paste and its subsequent hydrolysis to a calcium deficient hydroxyapatite (CDHA) is presented. The foaming agent was a hydrogen peroxide (H2O2) solution, which decomposes in water and oxygen gas. CDHA foams, which combined an interconnected macroporosity with a high microporosity were obtained. The apatitic phase obtained by the hydrolysis reaction was more similar to the biologic one, in terms of chemical composition, crystallinity and specific surface than the hydroxyapatites obtained by sintering. The percentage of porosity in the foams reached a 66%. It was shown that it was possible to control the porosity, and pore size and shape by different processing parameters such as the liquid-to-powder ratio, the concentration of the H2O2 solution and the particle size of the powder.

Immobilization of Chinese herbal medicine onto the surface-modified calcium hydrogenphosphate

To accelerate the healing of bone defects or for healing to take place, it is often necessary to fill them with suitable substance. Various artificial materials defects have been developed. Among these, calcium phosphates and bioactive glass have been proven to be biocompatibile and bioactive materials that can chemically bond with bone, and have been successfully used clinically for repair of bone defects and augmentation of osseous tissue. However, those bioceramics have only the property of osteoconduction without any osteoinduction. Many ligands have been physicochemically absorbed onto substrates to enhance cell-substrate interactions. Although widely developed, they are still limited to use in long-term implantation because of their half-life period. Thus, some interfacial modification will be required for enhancing the efficacy of the delivery system. These models involve the immobilization of biologically active ligands of natural and synthetic origin onto various substrates to produce an interface with stronger chemical bond between ligand and substrate. The advantage of covalently immobilizing a ligand is that a chemical bond is present to prevent ligand or medicine from desorption. In our study, a two-step chemical immobilization was performed to surface-modified calcium hydrogenphosphate powders. The first was to modify the surface of calcium hydrogen-phosphate (CHP) with a coupling agent of hexanmethylene diisocyanate (HMDI). CHP surface modified by HMDI is abbreviated as MCHP. The linkage between CHP and HMDI will be characterized by FTIR. The second step was to immobilize chemically Gusuibu onto MCHP. Moreover, the sorption and desorption of Gusuibu was evaluated and quantitatively analyzed by spectrophotometer and HPLC. Bioceramic CHP was surface-modified by a two-step chemical immobilization. First, the surface of calcium hydrogen-phosphate (CHP) was successfully modified with coupling agent of hexanmethylene diisocyanate (HMDI). The first step was also activated the surface of CHP to induce primary amine terminator. The reaction of this functional group with Gusuibu was the second step. We confirmed simultaneously that Gusuibu could be immobilized chemically onto the surface of MCHP. Although some immobilized Gusuibu was also released rapidly at the first 12h, the degree of the released Gusuibu was lower than both by Gusuibu-adsorbing MCHP and Gusuibu-adsorbing CHP.

Calcium-deficient apatite: influence of granule size and consolidation mode on release and in vitro activity of vancomycin

The use of dynamic compaction and isostatic compression to consolidate calcium phosphate powder loaded with a therapeutic agent avoids a sintering step that could destroy the drug. The present study applied these consolidation methods to vancomycin-loaded calcium-deficient apatite powder, using three granulometric fractions (40-80, 80-200 and 200-500 micrometer). In vitro release profiles were determined via an original system derived from low-pressure liquid chromatography. The biological activity of vancomycin was measured by an in vitro standardized bacteriologic assay, which showed that the drug is completely active after association with calcium phosphate. Regardless of the consolidation method and granulometric fraction used, release profiles were not significantly different and therefore adaptable to injectable suspensions.

Diffusional release of a solute from a spherical reservoir into a finite external volume

An exact solution has been obtained for the release kinetics of a solute from a spherical reservoir with the burst effect initial condition into a finite external volume. The exact solution is derived based on the time Laplace transform method. The results presented here indicate that as the external fluid volume increases, the cumulative release at any time and the releasable amount of the solute at infinite time increase. In addition, for a given external volume, as the polymeric coat thickness increases the fractional release at any time decreases. Experimentally, cumulative release profiles of theophylline microspheres coated with ethylene vinyl acetate copolymer into different external volumes agreed with the mathematical predictions.

In vitro behavior of albumin-loaded carbonate hydroxyapatite gel

Hydroxyapatite (HA) powder, porous HA, plasma-sprayed HA, apatite cements, and sintered HA have all been investigated as delivery systems for compounds such as human growth hormone and vancomycin. However, many previous studies showed that the period of release was limited to 2-3 weeks. The concept of using a nanoporous matrix as a means of immobilizing proteins is well known but has largely been confined to silica-based systems. Carbonate hydroxyapatite (CHA) is more soluble in vivo than HA, and when formed as an aqueous precipitate, it is often formed as nanocrystals. This study investigated the release profiles of ovine albumin (OVA) from CHA gel stored in phosphate-buffered saline (PBS) and double distilled water (DDW) for times of up to 1 year. It was found that 7.9% OVA could be loaded onto apatitic gels by means of a purely aqueous process. This process provided a simple low-temperature method of protein adsorption on a high surface area apatitic matrix at physiological pH. The rate of short-term release of OVA was lower from CHA gels than from microcrystalline HA powder. However, the period of release from the CHA gel was short term and may have been associated with recrystallization of the gel. OVA loaded into CHA gel was found to remain undegraded in vitro at 37 degrees C for periods of up to 1 year.

Dissolution tests for self-setting calcium phosphate cement-containing nifedipine

Nifedipine-containing calcium phosphate cement (CPC) was prepared, and nifedipine (NF) release from this preparation was evaluated by the shaking method (SK), Japanese Pharmacopoeia XIV (JPXIV) paddle method (PD), and JPXIV flow-through cell method (FT). The release of NF from the CPC preparation continued for 7 d or longer by all these methods. This suggests that the release of NF can be controlled by preparing NF-containing CPC. The release pattern of NF from CPC in these tests was found to follow the Higuchi equation. However, the Higuchi constant differed among the three dissolution tests, probably because the apparent tortuosity of capillary system (tau) varied.

Effect of porosity reduction by compaction on compressive strength and microstructure of calcium phosphate cement

Hydroxyapatite (HA) calcium phosphate cements (CPCs) are attractive materials for orthopedic applications because they can be molded into shape during implantation. However their low strength and brittle nature limits their potential applications to principally non-load-bearing applications. Little if any use has been made of the HA cement systems as manufacturing routes for preset HA bone grafts, which although not moldable pastes, are resorbable, unlike HA sintered ceramic. It is known that the strength of cements can be increased beyond that attainable from slurry systems by compaction, and this study investigates whether compaction significantly alters the specific surface area and pore-size distribution of CPC prepared according to the method of Brown and Chow. Compaction pressures of between 18 and 106 MPa were used to decrease the porosity from 50 to 31%, which resulted in an increase in the wet compressive strength from 4 to 37 MPa. The Weibull modulus was found to increase as porosity decreased; in addition the amount of porosity larger than the reactant particle size increased as porosity decreased. It is proposed that this was caused by a combination of voids created by the aqueous solvent used in fabrication and shrinkage that occurs on reaction. The specific surface area was unchanged by compaction.

Fabrication of Zn containing apatite cement and its initial evaluation using human osteoblastic cells

Recently, the effects of Zn2+ on osteogenesis stimulation have become major topics in the research fields of bone formation and organism essential elements. Based on the fundamental finding of Zn2+ with respect to osteogenesis stimulation, Ito et al. have prepared Zn doped beta-tricalcium phosphate (ZnTCP) and have reported that ZnTCP enhances the proliferation of MC3T3-E1 cells. In this investigation, we studied the effects of ZnTCP added to apatite cement (AC) with respect to its setting reaction and proliferation of human osteoblastic cells as an initial evaluation for the feasibility of AC containing ZnTCP. Compositional analysis using powder X-ray diffractometer revealed that ZnTCP shows no reactivity with the setting reaction of AC. As a result, the mechanical strength of set AC decreased increasing amounts of added ZnTCP as if ZnTCP acts as a pore in AC. The setting time of AC was not affected by addition of ZnTCP up to 10%. When AC containing ZnTCP was immersed in alpha-MEM containing 10% bovine serum, Zn2+ was released from AC. Larger amounts of Zn2+ were released from AC containing larger amounts of ZnTCP. When human osteoblastic cells were incubated on the surface of AC discs, proliferation of human osteoblastic cells was significantly increased on the surface of AC that contained 5% ZnTCP when compared with that containing no ZnTCP. In contrast, proliferation of human osteoblastic cells decreased on the surface of AC that contained 10% ZnTCP when compared with that free from ZnTCP; indicating cytotoxicity. We concluded therefore, that addition of ZnTCP to AC is useful to enhance the osteoconductivity of AC when release of Zn2+ can be carefully regulated.

Calcium orthophosphates in medicine: from ceramics to calcium phosphate cements

Calcium phosphate (CaP) compounds are becoming of increasingly great importance in the field of biomaterials and, in particular, as bone substitutes. Recent discoveries have accelerated this process, but have simultaneously rendered the field more complicated for the everyday user. Subtle differences in composition and structure of CaP compounds may have a profound effect on their in vivo behaviour. Therefore, the main goal of this article is to provide a simple, but comprehensive presentation of CaP compounds. Reference is made to the most important commercial products.

The kinetics of pentoxifylline release from drug-loaded hydroxyapatite implants

Hydroxyapatite (HAP) was synthesized by the aqueous precipitation method from CaO and H3 PO4 as the reagents. The HAP powders, either subjected or not subjected to preliminary calcination, were mixed with a pore-creating medium and isostatically shaped at a pressure of 350 MPa to form cylindrical samples. A natural product such as flour served as a pore-creating medium. Sintering was performed in the air, at 1200 or 1250 degrees C. The employed procedure allowed for achieving microporous materials of pore sizes ranging from 0.1 to 15 microm and with open porosity values of 23-44%. It was demonstrated that the porosity of the obtained materials depended mainly on the amount of the added pore-creating medium and the temperature of sintering. The implants, shaped as hollow cylinders, were filled with 50 mg of pentoxifylline (PTX) as a model drug. Internal wells for drug placement were drilled in the samples using a high precision drill. The drug release study was performed in pH = 7.35 phosphate buffer, at 37 degrees C. The results showed that the amount and time of PTX release, as well as the lag time were mainly controlled by the open porosity of the carriers.

Adsorption and release of insulin-like growth factor-I on porous tricalcium phosphate implant

In order to develop bone substitutes, the design of biomaterials like calcium phosphate ceramic loaded with bone growth factor are of great interest. However, it is necessary to control the amount of growth factor adsorbed onto ceramics and the kinetics of its release. Radiolabeling of insulin-like growth factor-I (IGF-I) with 125-iodine ([(125)I]-IGF-I) and its adsorption onto porous tricalcium phosphate (TCP) cylinders enabled us to establish the time-adsorption and time-release curves using various concentrations of IGF-I. The adsorption curve increased rapidly and then flattened out at 72 h; 90% of the maximum was already reached at 24 h; and 20% of the adsorbed IGF-I was released in water within 4 days. In human serum the release was faster at 82% within 4 days. In vivo evaluation on an animal model was then performed. Rabbits' bilateral femoral cylindrical bone defects were filled with the TCP cylinders, which were either carrying IGF-I or implanted alone as a control in each rabbit. Bone turnover and ceramic resorption were stimulated by IGF-I loaded TCP according to standard radiography, dual-energy X-ray absorptiometry, histology, and histomorphometry.

Effects of added antibiotics on the basic properties of anti-washout-type fast-setting calcium phosphate cement

The effect of added antibiotics on the basic properties of anti-washout-type fast-setting calcium phosphate cement (aw-FSCPC) was investigated in a preliminary evaluation of aw-FSCPC containing drugs. Flomoxef sodium was employed as the antibiotic and was incorporated into the powder-phase aw-FSCPC at up to 10%. The setting time, consistency, wet diametral tensile strength (DTS) value, and porosity were measured for aw-FSCPC containing various amounts of flomoxef sodium. X-ray diffraction (XRD) analysis was also conducted for the identification of products. To evaluate the drug-release profile, set aw-FSCPC was immersed in saline and the released flomoxef sodium was determined at regular intervals. The spread area of the cement paste as an index of consistency of the cement increased progressively with the addition of flomoxef sodium, and it doubled when the aw-FSCPC contained 8% flomoxef sodium. In contrast, the wet DTS value decreased with increase in flomoxef sodium content. Bulk density measurement and scanning electron microscopic observation revealed that the set mass was more porous with the amount of flomoxef sodium contained in the aw-FSCPC. The XRD analysis revealed that formation of hydroxyapatite (HAP) from aw-FSCPC was reduced even after 24 h, when the aw-FSCPC contained flomoxef sodium at > or = 6%. Therefore, the decrease of wet DTS value was thought to be partly the result of the increased porosity and inhibition of HAP formation in aw-FSCPC containing large amounts of flomoxef sodium. The flomoxef sodium release from aw-FSCPC showed the typical profile observed in a skeleton-type drug delivery system (DDS). The rate of drug release from aw-FSCPC can be controlled by changing the concentration of sodium alginate. Although flomoxef sodium addition has certain disadvantageous effects on the basic properties of aw-FSCPC, we conclude that aw-FSCPC is a good candidate for potential use as a DDS carrier that may be useful in surgical operations.

Gentamicin-loaded hydraulic calcium phosphate bone cement as antibiotic delivery system

A hydraulic calcium phosphate cement made of beta-tricalcium phosphate [beta-Ca3(PO4)2], monocalcium phosphate monohydrate [Ca(H2PO4)2-H2O], and water was used as a delivery system for the antibiotic gentamicin sulfate (GS). GS, added as powder or as aqueous solution, was very beneficial to the physicochemical properties of the cement. The setting time increased from 2 to 4.5 min with 3% (w/w) GS and then slowly decreased to 3.75 min with 16% (w/w) GS. The tensile strength increased from 0.4 to 1.6 MPa with 16% (w/w) GS. These effects were attributed to the presence of sulfate ions in GS. The release of GS from the cement was measured in a pH 7.4 phosphate-buffered saline solution at 37 degrees C by USP paddle method. Factors such as cement porosity, GS content and presence of sulfate ions or polymeric additives were investigated. The amount of GS released was roughly proportional to the square root of time up to approximately 50% release. Afterwards, the release rate markedly slowed down to zero. In all but two cement formulations, the total dose of GS was released within 7 days, indicating that no irreversible binding occurred between the cement paste and the antibiotic. When small amounts of hydroxypropylcellulose or poly(acrylic acid) were added to the cement, the maximum fraction released was a few percent lower than the total GS dose, suggesting some binding between the polymer and GS. The GS release rate was strongly influenced by the presence of sulfate ions in the cement paste and by the cement porosity. The higher the sulfate ion content of the cement paste, the lowe the GS release rate. This influence was attributed to the finer cement micro-structure induced by the presence of sulfate ions. Furthermore, when the initial cement porosity was increased from 38 to 69%, the release rate almost tripled (0.16 to 0.45 h-1/2). Finally, the biological activity of GS in the cement was maintained, as measured by assaying the release medium.

Preparation and evaluation of chitosan microspheres containing bisphosphonates

Local implantation or injection of microspheres containing bisphosphonates for site-specific therapy may aid in treating several pathological conditions associated with bone destruction. Chitosan microspheres containing two antiresorption and anticalcification agents, pamidronate and suberoylbisphosphonate (SuBP), were prepared from a w/o emulsion. Various formulation variables were studied for their effect on the release rate profile of these bone-seeking agents. Polymer coating of micromatrices yielded microspheres with the most retarded release rate, and the drug delivery system was found biocompatible in endothelial cell culture. The microspheres were examined in vitro and in vivo for release kinetics and drug disposition. The release of bisphosphonate from the microspheres was faster in vitro than in vivo. Drug disposition following implantation of microspheres in the tibialis muscle resulted in a relatively increased disposition in the adjacent tibia while injection of drug solution in the tibialis muscle resulted in uniform disposition of the drug in the femorae and tibiae. Bisphosphonate released from chitosan microspheres effectively inhibited bioprosthetic tissue calcification in the rat subdermal model.

Sustained release of adriamycin from implanted hydroxyapatite blocks for the treatment of experimental osteogenic sarcoma in mice

A sustained-release drug delivery system was developed using a hydroxyapatite (HA) block loaded with adriamycin (ADR) by cenrifugation. Release of ADR was sustained for 66 days in vitro and for 4 weeks in vivo following intramuscular implantation in mice. ADR concentrations in plasma, liver, and kidney were from 0.25% to 10% of that at the implantation site. ADR-HA blocks implanted into osteogenic sarcomas in mice markedly inhibited tumor growth. This drug delivery system provides sustained release of the cancer chemotherapeutic agent and may prove useful for treating malignant tumours while minimising systemic side effects.