Influence of isostatic compression on the stability of vancomycin loaded with a calcium phosphate-implantable drug delivery device

Impacts of compacting methods on the delivery of erythromycin and vancomycin from calcium polyphosphate hydrogel matrices

Designing hydrogels for controlled drug delivery remains a big challenge. We developed a calcium polyphosphate hydrogel (CPP) as matrix for delivery of vancomycin (VCM) and erythromycin (EM) by unique ionic binding and physical wrapping. In this continuing study, we investigated if gel discs prepared by mechanical compaction (at 3000 psi pressure, C-discs) is superior to that of discs prepared by regular manual compaction (M-discs) for the release of VCM and EM (10 wt.%). Data demonstrated a significant reduction of burst release of VCM and EM in C-discs (1.8% and 5%, respectively) as compared to that from M-discs within 72 hr (55% and 60%, respectively, p < 0.05). In addition, C-discs significantly extended the VCM release (1500 hr) and EM (800 hr) as compared to M-discs (160 and 96 hr, respectively, p < 0.05). The VCM released from C-discs retained its bactericidal activity much longer (1500 hr) than that from M-discs (700 hr, p < 0.05). Raman Spectroscopy indicated an ionic bond of both VCM and EM with fully hydrated polyphosphate chains of CPP hydrogel matrix for both M-discs and C-discs. Micro CT showed that C-discs had much denser microstructures and less number/depth of microcracks as a result of high pressure. We propose that CPP hydrogel represents an excellent tool for the controllable and sustained delivery of VCM and EM. Extensive experiments are currently underway to evaluate the potential impacts of the modification of compaction techniques, other antibiotics, gel concentrations on the drug release, degradation behavior and infection control both in vitro and in vivo.

A two-stage cold isostatic pressing and gelling approach for fabricating a therapeutically loaded amorphous calcium polyphosphate local delivery system

Local delivery systems have taken on a greater clinical focus for osteomyelitis therapy owing to their ability to overcome many disadvantages of systemic delivery. This study reports for the first time the capacity to fabricate strontium- and vancomycin-doped calcium polyphosphate beads using a two-stage cold isostatic pressing and gelling approach. The fabricated beads were of uniform shape and diameter, and upon gelling exhibited reduced porosity. Of greatest significance in the subsequent in vitro study was the improvement of bead long-term structural stability upon vancomycin incorporation; a characteristic that further encourages the extended release of therapeutically relevant levels of antibiotic. Overall, this study provides support for the inclusion of a cold isostatic pressing step in the fabrication of a therapeutically loaded calcium polyphosphate bead-based local delivery system intended for osteomyelitis treatment.

In vitro elution of vancomycin from biodegradable osteoconductive calcium phosphate-polycaprolactone composite beads for treatment of osteomyelitis

In this work, osteoconductive composite materials comprising a large volume fraction of a bioresorbable calcium phosphate ceramic (CaP) and a smaller amount of a polycaprolactone polymer (PCL) were studied as a degradable antibiotic carrier material for treatment of osteomyelitis. Beads loaded with 1 and 4wt.% vancomycin were prepared by admixing dissolved drug to an in situ synthesized dicalcium phosphate (DCP)-PCL or solution-mixed beta-tricalcium phosphate (βTCP)-PCL composite powder followed by high pressure consolidation of the blend at room temperature. Vancomycin release was measured in phosphate-buffered saline (PBS) at 37°C. All the beads gradually released the drug over the period of 4-11weeks, depending on the composite matrix homogeneity and porosity. Mathematical modeling using the Peppas equation showed that vancomycin elution was diffusion controlled. The stability of the antibiotic after high pressure application at room temperature was demonstrated by high-performance liquid chromatography-mass spectrometry (HPLC-MS) studies and MIC testing. The preservation of the structure and activity of vancomycin during the processing of composite beads and its sustained in vitro release profile suggest that high pressure consolidated CaP-PCL beads may be useful in the treatment of chronic bone infections as resorbable delivery vehicles of vancomycin and even of thermally unstable drug substances.

In vitro characterisation of calcium phosphate biomaterials loaded with lidocaine hydrochloride and morphine hydrochloride

Calcium phosphate substitutes drug delivery systems are well known substances used in minor bone void-filling to release their therapeutic agent in situ. Few studies associating anaesthetics and analgesics have been performed to date. The aim of this work was to study the association of the analgesic, morphine, and the local anaesthetic, lidocaine, with a calcium deficient apatite matrix. Three types of biomaterials i.e. powders, granules and blocks, were prepared by isostatic compression, wet granulation and a combination of the two, evaluated and compared. The chemical structure of the associated therapeutic agent was studied and the characteristics of the drug delivery systems were appraised in terms of drug release. The integrity of the lidocaine hydrochloride structure, as determined by RMN (1)H, was confirmed regardless of the formulation technique used (isostatic compression or wet granulation). However, analyses of morphine hydrochloride by RMN (1)H revealed slight structural modifications. The association and formulation techniques that were used made it possible to obtain an in vitro release time varying from 1 to 4 days for lidocaine hydrochloride and from 1 to 3 days for morphine hydrochloride.

Comparing the efficacy of three bioceramic matrices for the release of vancomycin hydrochloride

A number of calcium phosphate materials have been investigated as drug release matrices for the prophylactic treatment of implant-related osteomyelitis. However, some studies have shown the influence of processing on the efficacy of the delivered drug. The objective of this study was to evaluate the influence of pH during processing on the efficacy of vancomycin hydrochloride (VH) against Staphylococcus aureus. VH was loaded into a brushite cement (CaHPO(4).2H(2)O; pH 2.4); a hydroxyapatite cement (Ca(10)(PO(4))(6)OH(2); pH 9.4); and an apatite xerogel (pH 7.4). The pH of the material during processing had a significant influence on the mechanism of release from the cement. VH released from the apatite cement (pH 9.4) was not released in accordance with the Higuchi model. In addition to affecting release, the basic pH was shown to diminish the antibacterial potency of the released VH. Despite exceeding the minimum inhibitory concentration, the eluent from the apatite cement was ineffective against a culture of S. aureus. The findings of this study reinforce the importance of evaluating not only the release of the drug from the material matrix but also the antibacterial potency of the released drug.

Antibiotic delivery system using nano-hydroxyapatite/chitosan bone cement consisting of berberine

Different concentrations of berberine were mixed with nano-hydroxyapatite/chitosan (n-HA/CS) bone cement to generate an antibiotic drug delivery system for treatment of bone defects. Properties of the system such as setting time, compressive strength, surface morphology, phase compositions, drug release profiles and antimicrobial activity were also characterized. It was shown that the setting time of the cement ranged from 17.03 +/- 0.50 min to 28.47 +/- 0.96 min and the compressive strength changed from 184.00 +/- 7.94 MPa to 120.33 +/- 9.02 MPa with the increase of berberine. The XRD, IR, and SEM analyses suggested that berberine powders were stable in the bone cement in simulated body fluid (SBF). In vitro release of berberine from the bioactive bone cement pellets in SBF could last more than 4 weeks. The release profiles of 1.0 wt % berberine loaded bone cement followed the Higuchi equation at the infusion stage. The drug loaded pellets can inhibit bacterial growth (Staphylococcus aureus) at the standardized berberine minimum inhibitory concentration of 0.02 mg/mL during berberine release from 1 to 28 days. The n-HA/CS bone cement only with 1.0 wt % berberine proved to be an efficient antibiotic drug delivery system.

Effect of metal-ion-to-fuel ratio on the phase formation of bioceramic phosphates synthesized by self-propagating combustion

Synthetic calcium hydroxyapatite (HAP, Ca₁₀ (PO₄)₆ (OH)₂) is a well-known bioceramic material used in orthopedic and dental applications because of its excellent biocompatibility and bone-bonding ability due to its structural and compositional similarity to human bone. Here we report, for the first time, the synthesis of HAP by combustion employing tartaric acid as a fuel. Calcium nitrate is used as the source of calcium and diammonium hydrogen phosphate serves as the source of phosphate ions. Reaction processing parameters such as the pH, fuel-oxidant ratio and autoignition temperature are controlled and monitored. The products were characterized by powder x-ray diffraction, which revealed the formation of a hexagonal hydroxyapatite phase. Fourier transform infrared spectroscopy (FT-IR) spectra showed that the substitution of a carbonate ion occurs at the phosphate site. The morphology of the particles was imaged by scanning electron microscopy, which also revealed that the particles are of submicron size. Thermal analysis showed that the phase formation takes place at the time of combustion. Surface area and porosity analysis showed that the surface area is high and that the pores are of nanometer size. The mean grain size of the HAP powder, determined by the Debye-Scherrer formula, is in the range 20-30 nm. Chemical analyses to determine the Ca : P atomic ratio in synthesized ceramics were performed, and it was found to be 1 : 1.66.

Compaction strategies for modifying the drug delivery capabilities of gelled calcium polyphosphate matrices

Calcium polyphosphates (CPPs) have shown potential as drug delivery matrices, particularly in treating bone-related chronic diseases such as osteomyelitis, where maintenance of sufficient bactericidal concentrations at the infected bone site is essential. The objective of this study was to incorporate an additional compaction step as part of a gelling protocol to optimize CPP matrix properties while enhancing their drug delivery capabilities. Vancomycin-loaded CPP powders were produced using a previously established gelling and drying protocol, G1, and then subsequently compacted at prescribed levels (30, 113 or 452MPa) before subjecting to an additional gelling and drying protocol (G2). The resulting G2 disks were found to be more homogeneous and dense (p=0.0013) when compared with corresponding G1 disks, though increases in matrix density did not translate into subsequent increases in tensile strength. The compaction regelling protocol did, however, eliminate the burst release phenomena observed with the G1 disks and further extended the release of vancomycin into a clinically acceptable therapeutic range of 3weeks. These changes were associated with the increase in visual homogeneity, the increase in density and a more homogenous dispersion of vancomycin within the G2 disks. The ability to modulate this release profile to a limited extent by altering compaction stress, particle size distribution and regelling time was also demonstrated. Overall, the compaction regelling protocol described here, when used in conjunction with an initial gelling step to achieve matrix drug loading, enhances the flexibility and long-term drug delivery capability of this CPP matrix.

Vancomycin release behaviour from amorphous calcium polyphosphate matrices intended for osteomyelitis treatment

Calcium polyphosphate (CPP) antibiotic delivery matrices were prepared using a unique processing technique involving the exposure of antibiotic-loaded CPP pastes to high humidity for 0, 5, or 24 h. After the designated gelling period, samples were dried for a minimum of 24 h. At several time points out to 130 h, the elution medium was monitored for vancomycin, Ca2+ ion and ortho and poly phosphate release levels. Vancomycin activity was also assessed after 1, 24 and 130 h, while solution 31P-NMR was used to monitor changes in chain length within a 24 hr gelled VCM disc throughout the elution process. The gelling and drying process significantly reduced the rate of vancomycin release during the initial 2-4 h of elution, while extending the effective antibiotic release period by an additional 80 h. The mild conditions associated with matrix fabrication readily allowed for vancomycin incorporation within an environment that did not disrupt antibiotic activity. Throughout the elution process, all sample groups experienced considerable swelling followed by some apparent bulk erosion. Phosphate chain lysis was clearly observed by the end of the elution period. Generally, no strong or consistent correlation existed between matrix degradation and antibiotic release for the treatment groups investigated. An ability to delay antibiotic release using CPPs in conjunction with this protocol supports further investigations into the potential of this matrix as a localized drug delivery system.

Preparation, characterization and in vitro release of gentamicin from PHBV/wollastonite composite microspheres

Composite microspheres have been prepared from bioactive wollastonite (W) and biodegradable poly (hydroxybutyrate-polyhydroxyvalerate) (PHBV) in the present study. Gentamicin was encapsulated into the microspheres by the absorption method and the in vitro release of the gentamicin from the microspheres was performed in distilled water, modified simulated body fluid (SBF) and phosphate buffered saline (PBS) at 37 degrees C for 22 days, respectively. The results showed that the release behavior of gentamicin from PHBV/W composite microspheres was similar to that from the pure PHBV microspheres when the experiment was performed in distilled water. However, in the PBS and SBF solutions, gentamicin released from the PHBV/W composite microspheres at a relatively lower rate as compared to that of the pure PHBV microspheres and 90% of the total amount of gentamicin released from the composite microspheres after soaking for 22 days, which was much longer than that for the release of the same amount gentamicin from the pure PHBV microspheres (8 days). Scanning electron microscopy (SEM) and energy-dispersive spectrometer (EDS) analysis on the microspheres after release in SBF and PBS revealed that a microporous apatite layer was formed on the composite microspheres surface, which resulted in a controlled release behavior of the gentamicin from the PHBV/W composite microspheres. All of these results provided the possibility that the PHBV/W composite microspheres could be applied as alternative drug controlled release systems, especially as bone fillings for bone repair due to their advantages of controlled releasing antibiotics and apatite-formation ability, through which the implanted microspheres could chemically bond to the surrounding tissue in vivo.

The effect of processing on the structural characteristics of vancomycin-loaded amorphous calcium phosphate matrices

Calcium polyphosphate antibiotic delivery matrices were prepared using a unique processing technique involving the exposure of calcium polyphosphate pastes to high humidity for 0, 5, 24 or 48 h to induce gelling. Subsequently, samples were dried for a minimum of 24 h. The mild conditions associated with matrix fabrication readily allowed for vancomycin incorporation within an environment that did not disrupt antibiotic activity. While reproducible from a processing standpoint, the gelling and drying process did contribute to a decrease in matrix tensile strength and the formation of significant pores near the surface of the matrices. Generally, the core of the gelled matrices appeared to be denser than their non-gelled counterparts. The degree of phosphate chain lysis during the gelling and drying stages was quantified using solution 31P nuclear magnetic resonance (NMR) spectroscopy. Both NMR and Raman spectroscopy indicated that the presence of vancomycin did not appreciably alter the matrix formation process. The ability to incorporate clinically relevant levels of antibiotic within this degradable bone substitute matrix suggests the potential of this approach for creating a localized antibiotic delivery system to treat osteomyelitis infections.

In vitro and in vivo bactericidal activities of vancomycin dispersed in porous biodegradable poly(epsilon-caprolactone) microparticles

Treatment of methicillin-resistant Staphylococcus aureus osteomyelitis requires a prolonged antibiotic therapy with vancomycin. Because of its weak diffusion, the in situ implantation of vancomycin could be interesting. The activity of vancomycin encapsulated in microparticles was evaluated in vitro and in vivo on rabbit osteomyelitis and showed a good activity compared to intravenous administration.

Nanoporous delivery system to treat osteomyelitis and regenerate bone: Gentamicin release kinetics and bactericidal effect

Conventional treatment of osteomyelitis involves the repeated surgical removal of dead bone tissue coupled with repeated irrigation of the wound and prolonged systemic administration of antibiotics. Therapy of bone infections could easily last the rest of the patient's life because of the poor accessibility of the infection site by common systemically administered antibiotics. The objective of the present study is to develop a novel bone bioactive resorbable nanocomposite that can serve as a delivery system for antibiotics. We synthesized three different samples of porous bioactive resorbable silica-calcium phosphate nanocomposite (C3S1, C1S1, and C1S3) that has the ability to provide a sustained release of effective dose of gentamicin for 28 days. Porosity measurements showed that the average pore diameter of C3S1, C1S1, and C1S3 samples is 44.8, 54.4, and 70.9 nm, respectively. Moreover, the silica-rich composite (C1S3) is characterized by a significantly higher surface area (155.8 m(2)/g) than the silica-poor samples (C3S1) (42.9 m(2)/g). For all samples, the release profile study showed initial burst release followed by a sustained release of gentamicin. The released gentamicin has a strong inhibitory effect on Staphylococcus aureus bacteria. In addition FTIR analysis showed the formation of a biological apatite layer on the material surface after 24 h of immersion in simulated body fluid. Results of the study suggest that the silica-calcium phosphate nanocomposite can serve as a delivery vehicle for gentamicin to treat osteomyelitis and regenerate bone.

Biaxial flexure testing of calcium phosphate bioceramics for use in tissue engineering

This study analyzes data from 206 CaP specimens (68 HA, 70 BCP, and 68 beta-TCP) fractured via biaxial flexure testing. Specimens were divided into four groups: (a) Group I, dry; (b) Group II, wet (day 0, immersion time approximately 5-10 s); (c) Group III, after immersion in media for 21 days (day 21); and (d) Group IV, after culturing osteoblasts (OBs) on the surface for 21 days (day 21 with cells). X-ray diffraction verified the presence of minor second phases in HA and beta-TCP while BCP was a biphasic mixture of HA and beta-TCP with minor phases present. The statistical significance (p < 0.05) of differences in the measured biaxial flexure fracture strength, S, between groups was assessed via one-way ANOVA with Tukey's test. Also, a two-parameter Weibull analysis assessed the mechanical reliability of each group. Osteoblasts increase the biaxial flexure fracture strength in a statistically significant way compared to both the HA discs in Groups II and III. Scanning electron microscope examination revealed grain boundary grooving on the sintered surfaces and with thermal expansion anisotropy, likely leads to the observed rapid strength decline upon exposure to media found in Groups II, III and IV.

Development of hydroxyapatite bone scaffold for controlled drug release via poly(?-caprolactone) and hydroxyapatite hybrid coatings

A scaffold-coating design, the hydroxyapatite (HA) porous bone scaffold coated with poly(epsilon-)caprolactone (PCL) and HA powder hybrids, was developed for use as tissue-regeneration and controlled-release system. An antibiotic drug, tetracycline hydrochloride (TCH), was encapsulated within the hybrid coating layer through a dip-coating and solvent-casting method. Coating cycle and drug loading amount differed to control the level of drug-release rate. The HA scaffold framework, obtained by a polymeric foam reticulate method, exhibited a highly porous structure, with porosity and pore size of approximately 87% and 180 microm, respectively. The hybrid layer, consisting of PCL sheet and HA fine powders, was uniformly coated on the scaffold surface. The coating layer exhibited only PCL and HA phases and structures, revealing no chemical interaction among the coating components, as observed by X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) analyses. The coated-HA scaffolds showed an effective stress distribution behavior in response to an applied load, as confirmed by the compressive stress-strain curve. The mechanical properties of the coated scaffolds were improved highly with coatings; the compressive strength and elastic modulus of the cyclic coated scaffolds were approximately 3-4 times, and the energy absorption were approximately 8 times, higher than those without coating. These improvements were attributed mainly to the shielding of framework flaws by a flexible coating layer and partially to the thicker stems (porosity reduction). The dissolution of the coated scaffolds in a phosphate-buffered saline (PBS) solution increased with incubation time. The drug was released sharply within the initial several hours ( approximately 2 h), but the rate decreased further, showing a sustained release. The release amount was well controlled via coating-cycle and initial drug loading amount, suggesting the effectiveness of the coating-scaffold design as a drug-delivery system.

Preparation, characterization, and in vitro release of gentamicin from coralline hydroxyapatite-alginate composite microspheres

In this work, composite microspheres were prepared from bioactive ceramics such as coralline hydroxyapatite [Ca(10)(PO(4))(6)(OH)(2)] granules, a biodegradable polymer, sodium alginate, and an antibiotic, gentamicin. Previously, we have shown a gentamicin release from coralline hydroxyapatite granules-chitosan composite microspheres. In the present investigation, we attempted to prepare composite microspheres containing coralline hydroxyapatite granules and sodium alginate by the dispersion polymerization technique with gentamicin incorporated by absorption method. The crystal structure of the composite microspheres was analyzed using X-ray powder diffractometer. Fourier transform infrared spectra clearly indicated the presence of per-acid of sodium alginate, phosphate, and hydroxyl groups in the composite microspheres. Scanning electron micrographs and optical micrographs showed that the composite microspheres were spherical in shape and porous in nature. The particle size of composite microspheres was analyzed, and the average size was found to be 15 microns. The thermal behavior of composite microspheres was studied using thermogravimetric analysis and differential scanning calorimetric analysis. The cumulative in vitro release profile of gentamicin from composite microspheres showed near zero order patterns.

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.

Preparation, characterization and in vitro release of gentamicin from coralline hydroxyapatite-gelatin composite microspheres

Composite microspheres have been prepared from bioactive ceramics such as coralline hydroxyapatite [CHA, Ca10(PO4)6(OH)2] granules, a biodegradable polymer, gelatin and an antibiotic, gentamicin. In our earlier work, we have shown a gentamicin release from CHA granules--chitosan composite microspheres. In the present investigation, an attempt was made to prepare the composite microspheres containing coralline hydroxyapatite and gelatin (CHA-G), which were prepared by the dispersion polymerization technique and the gentamicin was incorporated by the absorption method. The crystal structure of the composite microspheres was analyzed using X-ray powder diffractometer. The Fourier transformed infrared spectrum clearly indicated the presence of amide and hydroxyl groups in the composite microspheres. Scanning electron micrographs and optical micrographs show that the composite microspheres are spherical in shape and porous in nature. The particle size of composite microspheres was analyzed and the average size was found to be 16 microm. The thermal behavior of composite microspheres was studied using thermogravimetric analysis and differential scanning calorimetric analysis. The cumulative in vitro release profile of gentamicin from composite microspheres showed near zero order patterns.

Association of vancomycin and calcium phosphate by dynamic compaction: in vitro characterization and microbiological activity

Dynamic compaction has rarely been used to produce drug-delivery devices in granule form. This report considered four processes associating vancomycin and compared dynamic compaction with wet granulation, a classical method. In the wet granulation study, vancomycin was associated with biphasic calcium-phosphate (BCP) granules either by adsorption or incorporation with a new granulation. In the dynamic compaction study, BCP powder was compacted at 1.1, 1.5 and 1.9 MPa. The compacts obtained were crushed and sieved (200-500 microm), and the vancomycin solution was adsorbed on the resulting granules. After crushing and sieving, the compaction of BCP and vancomycin powders produced vancomycin-loaded granules. In each study, 4.76% of vancomycin was associated with BCP. Granules were characterized in terms of porosity, vancomycin release and vancomycin biological activity. Physicochemical studies of BCP and vancomycin showed their structural integrity after dynamic compaction, which prolonged vancomycin release time from 1 to 6 days. However, a microbiological assay indicated that vancomycin had been altered since only 27.7% was found to be active.