Vancomycin encapsulation in biodegradable poly(epsilon-caprolactone) microparticles for bone implantation. Influence of the formulation process on size, drug loading, in vitro release and cytocompatibility

Enhanced Antibacterial Activity of Vancomycin Loaded on Functionalized Polyketones

Today, polymeric drug delivery systems (DDS) appear as an interesting solution against bacterial resistance, having great advantages such as low toxicity, biocompatibility, and biodegradability. In this work, two polyketones (PK) have been post-functionalized with sodium taurinate (PKT) or potassium sulfanilate (PKSK) and employed as carriers for Vancomycin against bacterial infections. Modified PKs were easily prepared by the Paal-Knorr reaction and loaded with Vancomycin at a variable pH. All polymers were characterized by FT-IR, DSC, TGA, SEM, and elemental analysis. Antimicrobial activity was tested against Gram-positive Staphylococcus aureus ATCC 25923 and correlated to the different pHs used for its loading (between 2.3 and 8.8). In particular, the minimum inhibitory concentrations achieved with PKT and PKSK loaded with Vancomycin were similar, at 0.23 μg/mL and 0.24 μg/mL, respectively, i.e., six times lower than that with Vancomycin alone. The use of post-functionalized aliphatic polyketones has thus been demonstrated to be a promising way to obtain very efficient polymeric DDS.

Nanoparticle-laden contact lens for controlled release of vancomycin with enhanced antibiotic efficacy

Vancomycin is the last resort antibiotic for the treatment of severe bacterial keratitis. Its clinical application is limited due to its hydrophilicity and high molecular weight. To overcome this, this study aims to develop nanoparticles-laden contact lens for controlled ocular delivery of vancomycin. Polyvinyl alcohol (PVA) was used as encapsulant material. The nanoparticles had a negative surface charge and an average size of 147.6 nm. A satisfactory encapsulation efficiency (61.24%) was obtained. The release profile was observed to be slow and sustained, with a release rate of 1.29 μL mg-1 h-1 for 48 h. Five out of 6 test bacteria were suppressed by vancomycin nanoparticles-laden contact lens. Vancomycin is generally ineffective against Gram-negative bacteria and unable to pass through the outer membrane barrier. In this study, vancomycin inhibited Proteus mirabilis and Pseudomonas aeruginosa. Nano-encapsulation enables vancomycin to penetrate the Gram-negative cell wall and further destroy the bacterial cells. On Hohenstein challenge test, all test bacteria exhibited significant reduction in growth when exposed to vancomycin nanoparticles-laden contact lens. This study created an effective and long-lasting vancomycin delivery system via silicone hydrogel contact lenses, by using PVA as encapsulant. The antibiotic efficacy and vancomycin release should be further studied using ocular in vivo models.

Carboxymethyl Chitosan Microgels for Sustained Delivery of Vancomycin and Long-Lasting Antibacterial Effects

Carboxymethyl chitosan (CMCh) is a unique polysaccharide with functional groups that can develop positive and negative charges due to the abundant numbers of amine and carboxylic acid groups. CMCh is widely used in different areas due to its excellent biocompatibility, biodegradability, water solubility, and chelating ability. CMCh microgels were synthesized in a microemulsion environment using divinyl sulfone (DVS) as a crosslinking agent. CMCh microgel with tailored size and zeta potential values were obtained in a single stem by crosslinking CMCh in a water-in-oil environment. The spherical microgel structure is confirmed by SEM analysis. The sizes of CMCh microgels varied from one micrometer to tens of micrometers. The isoelectric point of CMCh microgels was determined as pH 4.4. Biocompatibility of CMCh microgels was verified on L929 fibroblasts with 96.5 ± 1.5% cell viability at 1 mg/mL concentration. The drug-carrying abilities of CMCh microgels were evaluated by loading Vancomycin (Van) antibiotic as a model drug. Furthermore, the antibacterial activity efficiency of Van-loaded CMCh microgels (Van@CMCh) was investigated. The MIC values of the released drug from Van@CMCh microgels were found to be 68.6 and 7.95 µg/mL against E. coli and S. aureus, respectively, at 24 h contact time. Disk diffusion tests confirmed that Van@CMCh microgels, especially for Gram-positive (S. aureus) bacteria, revealed long-lasting inhibitory effects on bacteria growth up to 72 h.

Polymer type effect on PLGA-based microparticles preparation by solvent evaporation method with single emulsion system using focussed beam reflectance measurement

AIM

This study aimed to investigate the effect of polymer type on solidification rate of PLGA polymeric microparticles and particle size/distribution of the emulsion droplets/hardened PLGA polymeric microparticles during solvent evaporation process using FBRM (Focussed Beam Reflectance Measurement).

METHODS

PLGA polymeric microparticles were prepared by an O/W solvent evaporation method using various PLGA polymers, including PLGA Resomer® RG503H, RG502H and RG752H. The particle size mean, chord length distribution (CLD), and chord count of the emulsion droplets/hardened microparticles were monitored by FBRM. The morphology of polymeric microparticles were characterised by optical microscopy and scanning electron microscopy (SEM).

RESULTS

The transformation of the emulsion droplets into solid microparticles occurred within the first 30 (± 1.04), 34 (± 1.15) and 37 (± 0.82) min and square weighted mean chord lengths are 64.08 (± 3.18), 52.36 (± 5.27) and 42.18 (± 4.61) µm when PLGA Resomer® RG503H, RG502H and RG752H were used respectively. Larger square weighted mean chord length of PLGA polymeric microparticles gave lower chord counts. PLGA RG752H microparticles gave smallest square weighted mean chord length and the chord counts was the highest. The CLDs measured by FBRM showed that a larger particle size mean gave longer CLD and a lower peak of particle number. SEM data revealed that the morphology of microparticles was influenced by type and physical properties of polymer.

CONCLUSIONS

FBRM can be employed for online monitoring of the shift in the microparticle CLD and detect transformation of the emulsion droplets into solid microparticles during the solvent evaporation process. The microparticle CLD and transformation process were strongly influenced by polymer type.

Real-time particle size analysis using focused beam reflectance measurement as a process analytical technology tool for continuous microencapsulation process

The online real-time particle size analysis of the microencapsules manufacturing process using the continuous solvent evaporation method was performed using focused beam reflectance measurement (FBRM). In this paper, we use FBRM measurements to investigate the effects of polymer type and compare the size distributions to those obtained using other sizing methods such as optical microscope and laser diffraction. FBRM was also utilized to measure the length-weighted chord length distribution (CLD) and particle size distribution (PSD) online during particle solidification, which could not be done with laser diffraction or nested sieve analysis. The chord lengths and CLD data were taken at specific times using an online FBRM probe mounted below the microparticle. The timing of the FBRM determinations was coordinated with the selection of microparticle samples for particle size analysis by optical microscope and laser diffraction calculation as a reference. For all three produced batches tested, FBRM, laser diffraction, and sieve analysis yielded similar results. Hardening time for the transformation of emulsion droplets into solid microparticles occurred within the first 10.5, 19, 25, 30, and 55 min, according to FBRM results. The FBRM CLDs revealed that a larger particle size mean resulted in a longer CLD and a lower peak of particle number. The FBRM data revealed that the polymer type had a significant impact on microparticle CLD and the transformation process.

Control of Vancomycin Activity through the Encapsulation and Controlled Release from a Propargyl Acrylate-Poloxamer Nanocomposite System

Vancomycin is a potent antibacterial drug that suffers from poor bioavailability due to its poor water solubility and relatively high molecular weight. Consequently, the application of vancomycin to treat bacteria-induced disease is limited. In this study, the ability of a temperature-stimulated propargyl acrylate-poloxamer nanocomposite (PAPN) system to encapsulate and release vancomycin is investigated. A controllable encapsulation and release system can be used to not only increase and prolong the bioavailability of vancomycin but also activate vancomycin with a temperature change. The PAPN system was prepared using an emulsion polymerization of propargyl acrylate followed by a surface decoration with a poloxamer at a precisely controlled grafting density. The activity of the PAPN system loaded with vancomycin is compared to that of the free drug and unmodified propargyl acrylate nanoparticles. It is shown that the activity of the PAPN system loaded with vancomycin is comparable to that of a freshly prepared, free-floating vancomycin solution. Upon storage, the activity of the free vancomycin in solution decreases, while the PAPN system loaded with vancomycin retains its high activity. Additionally, the PAPN system is able to effectively encapsulate and deactivate vancomycin until heated above a lower critical solution temperature (LCST). At temperatures above the LCST, the PAPN system releases vancomycin restoring the activity of the drug.

An overview of polymeric nano-biocomposites as targeted and controlled-release devices

In recent years, controlled drug delivery has become an important area of research. Nano-biocomposites can fulfil the necessary requirements of a targeted drug delivery device. This review describes use of polymeric nano-biocomposites in controlled drug delivery devices. Selection of suitable biopolymer and methods of preparation are discussed.

Treating Intracranial Abscesses in Rats with Stereotactic Injection of Biodegradable Vancomycin-Embedded Microparticles

Brain abscesses are emergent and life-threating despite advances in modern neurosurgical techniques and antibiotics. The present study explores the efficacy of vancomycin embedded to 50:50 poly(lactic-co-glycolide acid) (PLGA) microparticles in the treatment of brain abscess. The vancomycin embedded microparticles (VMPs) were stereotactically introduced into the cerebral parenchyma in Staphylococcus aureus bacteria- induced brain abscess-bearing rats. Experimental rats were divided into three groups: group A (n = 13; no treatment), group B (n = 14; daily vancomycin injection (5 mg intraperitoneally), and group C (n = 12; stereotactic introduction of VMPs into the abscess cavity). Group C exhibited no inflammatory response and significantly increased survival and reduced mean abscess volumes (p <0.001) at the eighth week, compared with other groups. Vancomycin delivery via a biodegradable PLGA vehicle can easily attain Area Under the Curve (AUC)/minimum inhibitory concentration (MIC) ratios of ≥400, and strengthens the therapeutic efficacy of antibiotics without provoking any potential toxicity. Biodegradable VMPs are a safe and sustainable drug delivery vehicle for the treatment of brain abscess.

Antimicrobial Peptides and Nanotechnology, Recent Advances and Challenges

Antimicrobial peptides are sequences of amino acids, which present activity against microorganisms. These peptides were discovered over 70 years ago, and are abundant in nature from soil bacteria, insects, amphibians to mammals and plants. They vary in amino acids number, the distance between amino acids within individual peptide structure, net charge, solubility and other physical chemical properties as well as differ in mechanism of action. These peptides may provide an alternative treatment to conventional antibiotics, which encounter resistance such as the peptide nisin applied in treating methicillin resistant Staphylococcus aureus (MRSA) or may behave synergistically with known antibiotics against parasites for instance, nisin Z when used in synergy with ampicillin reported better activity against Pseudomonas fluorescens than when the antibiotic was alone. AMPs are known to be active against viruses, bacteria, fungi and protozoans. Nanotechnology is an arena which explores the synthesis, characterization and application of an array of delivery systems at a one billionth of meter scale. Such systems are implemented to deliver drugs, proteins, vaccines, and peptides. The role of nanotechnology in delivering AMPs is still at its early development stage. There are challenges of incorporating AMPs into drug delivery system. This review intends to explore in depth, the role of nanotechnology in delivering AMPs as well as presenting the current advances and accompanying challenges of the technology.

Direct plasma synthesis of nano-capsules loaded with antibiotics

Vancomycin containing nano-capsules have been synthesized in one step by means of aerosol-assisted atmospheric pressure plasma.

Activity of daptomycin- and vancomycin-loaded poly-epsilon-caprolactone microparticles against mature staphylococcal biofilms

The aim of the present study was to develop novel daptomycin-loaded poly-epsilon-caprolactone (PCL) microparticles with enhanced antibiofilm activity against mature biofilms of clinically relevant bacteria, methicillin-resistant Staphylococcus aureus (MRSA) and polysaccharide intercellular adhesin-positive Staphylococcus epidermidis. Daptomycin was encapsulated into PCL microparticles by a double emulsion-solvent evaporation method. For comparison purposes, formulations containing vancomycin were also prepared. Particle morphology, size distribution, encapsulation efficiency, surface charge, thermal behavior, and in vitro release were assessed. All formulations exhibited a spherical morphology, micrometer size, and negative surface charge. From a very early time stage, the released concentrations of daptomycin and vancomycin were higher than the minimal inhibitory concentration and continued so up to 72 hours. Daptomycin presented a sustained release profile with increasing concentrations of the drug being released up to 72 hours, whereas the release of vancomycin stabilized at 24 hours. The antibacterial activity of the microparticles was assessed by isothermal microcalorimetry against planktonic and sessile MRSA and S. epidermidis. Regarding planktonic bacteria, daptomycin-loaded PCL microparticles presented the highest antibacterial activity against both strains. Isothermal microcalorimetry also revealed that lower concentrations of daptomycin-loaded microparticles were required to completely inhibit the recovery of mature MRSA and S. epidermidis biofilms. Further characterization of the effect of daptomycin-loaded PCL microparticles on mature biofilms was performed by fluorescence in situ hybridization. Fluorescence in situ hybridization showed an important reduction in MRSA biofilm, whereas S. epidermidis biofilms, although inhibited, were not eradicated. In addition, an important attachment of the microparticles to MRSA and S. epidermidis biofilms was observed. Finally, all formulations proved to be biocompatible with both ISO compliant L929 fibroblasts and human MG63 osteoblast-like cells.

Biodegradable vancomycin-eluting poly[(d,l)-lactide-co-glycolide] nanofibres for the treatment of postoperative central nervous system infection

The incidence of postoperative central nervous system infection (PCNSI) is higher than 5%–7%. Successful management of PCNSI requires a combined therapy of surgical debridement and long-term antibiotic treatment. In this study, Duraform soaked in a prepared bacterial solution was placed on the brain surface of rats to induce PCNSI. Virgin poly[(d,l)-lactide-co-glycolide] (PLGA) nanofibrous membranes (vehicle-control group) and vancomycin-eluting PLGA membranes (vancomycin-nanofibres group) were implanted. The wound conditions were observed and serial brain MRI and pathology examinations were performed regularly. PCNSI was consistently induced in a single, simple step. In the vehicle-control group, most rats died within 1 week, and the survival rate was low (odds ratio = 0.0357, 95% confidence interval = 0.0057–0.2254). The wounds and affected cerebral tissues necrosed with purulence and increased in mass from the resulting PCNSI volumes. Initially, the mean PCNSI volumes showed no significant difference between the two groups. The PCNSI volume in the rats in the vancomycin-nanofibres group significantly decreased (P < 0.01), and the wound appearance was excellent. Pathologic examinations revealed that the necrosis and leukocyte infiltration area decreased considerably. The experimental results suggest that vancomycin-eluting PLGA nanofibres are favourable candidates for treating PCNSI after surgical debridement.

Enzymatic polymerization of cyclic monomers in ionic liquids as a prospective synthesis method for polyesters used in drug delivery systems

Biodegradable or bioresorbable polymers are commonly used in various pharmaceutical fields (e.g., as drug delivery systems, therapeutic systems or macromolecular drug conjugates). Polyesters are an important class of polymers widely utilized in pharmacy due to their biodegradability and biocompatibility features. In recent years, there has been increased interest in enzyme-catalyzed ring-opening polymerization (e-ROP) of cyclic esters as an alternative method of preparation of biodegradable or bioresorbable polymers. Ionic liquids (ILs) have been presented as green solvents in enzymatic ring-opening polymerization. The activity, stability, selectivity of enzymes in ILs and the ability to catalyze polyester synthesis under these conditions are discussed. Overall, the review demonstrates that e-ROP of lactones or lactides could be an effective method for the synthesis of useful biomedical polymers.

Microparticles produced by the hydrogel template method for sustained drug delivery

Polymeric microparticles have been used widely for sustained drug delivery. Current methods of microparticle production can be improved by making homogeneous particles in size and shape, increasing the drug loading, and controlling the initial burst release. In the current study, the hydrogel template method was used to produce homogeneous poly(lactide-co-glycolide) (PLGA) microparticles and to examine formulation and process-related parameters. Poly(vinyl alcohol) (PVA) was used to make hydrogel templates. The parameters examined include PVA molecular weight, type of PLGA (as characterized by lactide content, inherent viscosity), polymer concentration, drug concentration and composition of solvent system. Three model compounds studied were risperidone, methylprednisolone acetate and paclitaxel. The ability of the hydrogel template method to produce microparticles with good conformity to template was dependent on molecular weight of PVA and viscosity of the PLGA solution. Drug loading and encapsulation efficiency were found to be influenced by PLGA lactide content, polymer concentration and composition of the solvent system. The drug loading and encapsulation efficiency were 28.7% and 82% for risperidone, 31.5% and 90% for methylprednisolone acetate, and 32.2% and 92% for paclitaxel, respectively. For all three drugs, release was sustained for weeks, and the in vitro release profile of risperidone was comparable to that of microparticles prepared using the conventional emulsion method. The hydrogel template method provides a new approach of manipulating microparticles.

Biodegradable drug-eluting poly[lactic-co-glycol acid] nanofibers for the sustainable delivery of vancomycin to brain tissue: in vitro and in vivo studies

Successful treatment of a brain infection requires aspiration of the pus or excision of the abscess, followed by long-term (usually 4-8 weeks) parenteral antibiotic treatment. Local antibiotic delivery using biodegradable drug-impregnated carriers is effective in treating postoperative infections, thereby reducing the toxicity associated with parenteral antibiotic treatment and the expense involved with long-term hospitalization. We have developed vancomycin-loaded, biodegradable poly[lactic-co-glycol acid] nanofibrous membranes for the sustainable delivery of vancomycin to the brain tissue of rats by using the electrospinning technique. A high-performance liquid chromatography assay was employed to characterize the in vitro and in vivo release behaviors of pharmaceuticals from the membranes. The experimental results suggested that the biodegradable nanofibers can release high concentrations of vancomycin for more than 8 weeks in the cerebral cavity of rats. Furthermore, the membranes can cover the wall of the cavity after the removal of abscess more completely and achieve better drug delivery without inducing adverse mass effects in the brain. Histological examination also showed no inflammation reaction of the brain tissues. By adopting the biodegradable, nanofibrous drug-eluting membranes, we will be able to achieve long-term deliveries of various antibiotics in the cerebral cavity to enhance the therapeutic efficacy of cerebral infections.

Development of intra-vaginal matrices from polycaprolactone for sustained release of antimicrobial agents

Microporous poly(ɛ-caprolactone) matrices were loaded with an antibacterial agent, ciprofloxacin and an antifungal agent, miconazole nitrate, respectively, for investigations of their potential as controlled vaginal delivery devices. Ciprofloxacin loadings up to 15% w/w could be obtained by increasing the drug content of the poly(ɛ-caprolactone) solution, while the actual loadings of miconazole were much lower (1–3% w/w) due to drug partition into methanol during the solvent extraction. The kinetics of ciprofloxacin release in simulated vaginal fluid at 37℃ were characterised by a small burst release phase in the first 24 h, low drug release up to 7 days (10%) and gradual release of up to 80% of the drug content by day 30. Meanwhile, the release kinetics of miconazole-loaded matrices could be effectively described by the Higuchi model with 100% drug release from the highest loaded matrices (3.2% w/w) in 13 days. Ciprofloxacin or miconazole released over 30 and 13 days, respectively, from poly(ɛ-caprolactone) matrices into simulated vaginal fluid retained high levels of antimicrobial activity in excess of 80% of the activity of the free drug. This study confirms the potential of poly(ɛ-caprolactone) matrices for delivering antimicrobial agents in the form of an intra-vaginal device.

Nanoconjugated vancomycin: new opportunities for the development of anti-VRSA agents

More than 90% of Staphylococcus strains are resistant to penicillin. In 1961 S. aureus developed resistance to methicillin (MRSA), invalidating almost all antibiotics, including the most potent beta-lactams. Vancomycin, a glycopeptide antibiotic, was used for the treatment of MRSA in 1980. Vancomycin inhibits the bio-synthesis of peptidoglycan and the assembly of NAM-NAG-polypeptide into the growing peptidoglycan chain. Vancomycin resistant S. aureus (VRSA) first appeared in the USA in 2002. Folic acid tagged chitosan nanoparticles are used as Trojan horses to deliver vancomycin into bacterial cells. These nanoparticles are biocompatible and biodegradable semisynthetic polymers. These nanosized vehicles enhance the transport of vancomycin across epithelial surfaces and show its efficient drug action, which has been understood from studies of the minimum inhibitory concentration and minimum bactericidal concentration of nanoparticles of a chitosan derivative loaded with vancomycin. Tolerance values distinctly show that vancomycin loaded into nanoconjugate is very effective and has a strong bactericidal effect on VRSA.

Silica xerogel-chitosan nano-hybrids for use as drug eluting bone replacement

Silica xerogel-chitosan hybrids containing vancomycin were fabricated by the sol-gel process at room temperature and their potential as a drug eluting bone replacement was evaluated in terms of their mechanical properties and drug release behaviors. Regardless of the content of chitosan, all of the prepared hybrids had a uniform mesoporous structure, which would allow the effectual loading of vancomycin. As the content of chitosan was increased, the strength, strain to failure, and work of fracture of the hybrids were significantly enhanced, while the elastic modulus was decreased. These changes in the mechanical properties were mainly attributed to the mitigation of the brittleness of the silica xerogel through its hybridization with the flexible chitosan phase. In addition, the initial burst-effect was remarkably reduced by increasing the content of chitosan. The hybrids with more than 30% chitosan could release the vancomycin for an extended period of time in a controlled manner.

Dexamethasone-containing biodegradable superparamagnetic microparticles for intra-articular administration: physicochemical and magnetic properties, in vitro and in vivo drug release

Compared with traditional drug solutions or suspensions, polymeric microparticles represent a valuable means to achieve controlled and prolonged drug delivery into joints, but still suffer from the drawback of limited retention duration in the articular cavity. In this study, our aim was to prepare and characterize magnetic biodegradable microparticles containing dexamethasone acetate (DXM) for intra-articular administration. The superparamagnetic properties, which result from the encapsulation of superparamagnetic iron oxide nanoparticles (SPIONs), allow for microparticle retention with an external magnetic field, thus possibly reducing their clearance from the joint. Two molecular weights of poly(lactic-co-glycolic acid) (PLGA) were used, 12 and 19 kDa. The prepared batches were similar in size (around 10 microm), inner morphology, surface morphology, charge (neutral) and superparamagnetic behaviour. The SPION distribution in the microparticles assessed by TEM indicates a homogeneous distribution and the absence of aggregation, an important factor for preserving superparamagnetic properties. DXM release profiles were shown to be quite similar in vitro (ca. 6 days) and in vivo, using a mouse dorsal air pouch model (ca. 5 days).

Fabrication of an alpha-lipoic acid-eluting poly-(D,L-lactide-co-caprolactone) cuff for the inhibition of neointimal formation

The purpose of this study was to develop a novel polymer cuff for the local delivery of alpha-lipoic acid (ALA) to inhibit neointimal formation in vivo. The polymer cuff was fabricated by incorporating the ALA into poly- (D,L-lactide-co-caprolactone) 40:60 (PLC), with or without methoxy polyethylene glycol (MethoxyPEG). The release kinetics of ALA and in vitro degradation by hydrolysis were analyzed by HPLC and field emission scanning electron microscopy (FE-SEM), respectively. In vivo evaluation of the effect of the ALA-containing polymer cuff was carried out using a rat femoral artery cuff injury model. At 24 h, 48% or 87% of the ALA was released from PCL cuffs with or without MethoxyPEG. FE-SEM results indicated that ALA was blended homogenously in the PLC with MethoxyPEG, whereas ALA was distributed on the surface of the PLC cuff without MethoxyPEG. The PLC cuff with MethoxyPEG showed prolonged and controlled release of ALA in PBS, in contrast to the PLC cuff without MethoxyPEG. Both ALA-containing polymer cuffs had a significant effect on the inhibition of neointimal formation in rat femoral artery. Novel ALA-containing polymer cuffs made of PLC were found to be biocompatible and effective in inhibiting neointimal formation in vivo. Polymer cuffs containing MethoxyPEG allowed the release of ALA for one additional week, and the rate of drug release from the PLC could be controlled by changing the composition of the polymer. These findings demonstrate that polymer cuffs may be an easy tool for the evaluation of anti-restenotic agents in animal models.

Implantation of vancomycin microspheres in blend with human/rabbit bone grafts to infected bone defects

In orthopaedic applications, allografts are used for restoration of bone defects. In order to combine the effects of bone repair and to prevent the infection, antibiotic-impregnated bone grafts are under current investigation with promising early results. In this study, to preserve the stability of antibiotics and to provide appropriate release profiles for 4-6 weeks, antibiotic-loaded microspheres were administered in combination with allografts and vancomycin was the antibiotic loaded to microspheres. Particle size, surface characteristics, loading capacity and in vitro release characteristics of the microspheres with and without allografts were determined. In vivo studies were performed on rabbits and antibiotic amount was determined by a fluorescence polarization immunoassay (FPIA) method from synovial fluid sample aspirated. According to the results, although the in vitro study demonstrated effective antibiotic release of vancomycin from antibiotic-impregnated allografts for 5 weeks, in vivo conditions led to an early instability of the antibiotic (in powder form) and contrary to the high initial loading dose an effective release could not be obtained from the allografts after the first week. Following these studies, it was determined that antibiotic release over a minimum inhibitory concentration (MIC) for 6 weeks was realized from vancomycin-loaded microspheres which were implanted in a blend with allografts in bone defects. In conclusion, preservation of the antibiotic in microspheres maintained the bioactivity and provided the controlled antibiotic release, thus implantation of microspheres in a blend with allografts seemed to be a promising carrier system for the orthopaedic applications.

Sodium fusidate-poly(D,L-lactide-co-glycolide) microspheres: Preparation, characterisation andin vivoevaluation of their effectiveness in the treatment of chronic osteomyelitis

PURPOSE

The aim of this study was to prepare poly(D,L-lactide-co-glycolide) (PLGA) microspheres containing sodium fusidate (SF) using a double emulsion solvent evaporation method with varying polymer:drug ratios (1:1, 2.5:1, 5:1) and to evaluate its efficiency for the local treatment of chronic osteomyelitis.

METHODS

The particle size and distribution, morphological characteristics, thermal behaviour, drug content, encapsulation efficiency and in vitro release assessments of the formulations had been carried out. Sterilized SF-PLGA microspheres were implanted in the proximal tibia of rats with methicillin-resistant Staphylococcus aureus (MRSA) osteomyelitis. After 3 weeks of treatment, bone samples were analysed with a microbiological assay.

RESULTS

PLGA microspheres between the size ranges of 2.16-4.12 microm were obtained. Production yield of all formulations was found to be higher than 79% and encapsulation efficiencies of 19.8-34.3% were obtained. DSC thermogram showed that the SF was in an amorphous state in the microspheres and the glass transition temperature (T(g)) of PLGA was not influenced by the preparation procedure. In vitro drug release studies had indicated that these microspheres had significant burst release and their drug release rates were decreased upon increasing the polymer:drug ratio (p < 0.05). Based on the in vivo data, rats implanted with SF-PLGA microspheres and empty microspheres showed 1987 +/- 1196 and 55526 +/- 49086 colony forming unit of MRSA in 1 g bone samples (CFU/g), respectively (p < 0.01).

CONCLUSION

The in vitro and in vivo studies had shown that the implanted SF loaded microspheres were found to be effective for the treatment of chronic osteomyelitis in an animal experimental model. Hence, these microspheres may be potentially useful in the clinical setting.

pH-triggered release of vancomycin from protein-capped porous silicon films

Objective: An in vitro model system for pH-triggered release of the antibiotic vancomycin from porous Si films is studied. Method: Vancomycin is infused into a mesoporous Si film from a mixed aqueous/acetonitrile solution and trapped by a capping layer containing the protein bovine serum albumin (BSA). The protein effectively traps vancomycin in the porous nanostructure at pH 4.0; the protein dissolves and vancomycin is released into solution when the pH increases to 7.4. The surface chemistry of porous Si exerts a substantial effect on the efficacy of drug loading. The amount of drug loading is larger in freshly-etched (hydrophobic, hydrogen-terminated) porous Si and smaller in methyl-modified, undecylenic acid-modified and thermally oxidized samples. The quantity of drug loaded in a freshly etched porous Si chip is proportional to the thickness of the porous layer, which exhibits a constant volume loading efficiency of 31% (v/v). Flow-cell experiments designed to mimic the transition from pH 4 to 7 that occurs when material moves from the stomach to the upper intestinal tract were performed on the freshly etched films and vancomycin- and BSA-release rates were quantified from the effluent of the flow cell by high-pressure liquid chromatography analysis. Results & conclusion: There is a small, constant rate of vancomycin release at pH 4 that is independent of the amount of drug loaded in the pores. This is attributed to diffusion of vancomycin from the BSA-capping layer. The release rate increases five- to tenfold when the pH of the solution in the flow cell increases to 7.4; 100% of the drug is released within 3 h of this increase.

In vitro and in vivo testing of bioabsorbable antibiotic containing bone filler for osteomyelitis treatment

The use of local antibiotics from a biodegradable implant is appealing concept for treatment of chronic osteomyelitis. Our aim was to develop a new drug delivery system based on controlled ciprofloxacin release from poly(D/L-lactide). Cylindrical composite pellets (1.0 x 0.9 mm) were manufactured from bioabsorbable poly(D/L-lactide) matrix and ciprofloxacin (7.4 wt %). In vitro studies were carried out to delineate the release profile of the antibiotic and to verify its antimicrobial activity by means of MIC testing. A long-term study in rabbits was performed to validate the release of ciprofloxacin from the composite in vivo. Therapeutic level of ciprofloxacin (>2 microg/mL) was maintained between 60 and 300 days and the concentration remained below the potentially detrimental level of 20 microg/mL in vitro. The released ciprofloxacin had retained its antimicrobial properties against common pathogens. In an exploratory long-term in vivo study with three rabbits, ciprofloxacin could not be detected from the serum after moderate filling (160 mg) of the tibia (follow-up 168 days), whereas after high dosing (a total dose of 1,000 mg in both tibias) ciprofloxacin was found temporarily at low serum concentrations (14-34 ng/mL) during the follow-up of 300 days. The bone concentrations of ciprofloxacin could be measured in all samples at 168 and 300 days. The tested copolylactide matrix seems to be a promising option in selection of resorbable carriers for sustained release of antibiotics, but the composite needs modifications to promote ciprofloxacin release during the first 60 days of implantation.

Vancomycin biodegradable poly(lactide-co-glycolide) microparticles for bone implantation. Influence of the formulation parameters on the size, morphology, drug loading and in vitro release

The present study investigates vancomycin microencapsulation in biodegradable PLAGA microparticles. To optimize encapsulation efficiency by the double emulsion (w/o/w) solvent evaporation/extraction process, two parameters were studied: surfactant (Span 80) rate and external aqueous phase saturation. In vitro dissolution studies, laser granulometry and scanning electron microscopy were performed to characterize the microparticles. The best results were obtained by stabilizing the first emulsion with 0.5% Span 80 and saturating the external phase with sodium chloride. Such parameters allowed a 95% drug encapsulation efficiency. This process yielded round microparticles with a mean diameter of approximately 170 microm and presenting a smooth surface without any pores. Moreover, this formulation induces a sustained drug release at a constant rate over a period of 10 days. Such materials could be associated with biphasic calcium phosphate granules to form an antibiotic-loaded injectable bone substitute offering a long-term activity in situ.

Delivery of the antibiotic gentamicin sulphate from precipitation cast matrices of polycaprolactone

Microporous, poly(epsilon-caprolactone) (PCL) matrices were loaded with the aminoglycoside antibiotic, gentamicin sulphate (GS) using the precipitation casting technique by suspension of powder in the PCL solution prior to casting. Improvements in drug loading from 1.8% to 6.7% w/w and distribution in the matrices were obtained by pre-cooling the suspension to 4 degrees C. Gradual release of approximately 80% of the GS content occurred over 11 weeks in PBS at 37 degrees C and low amounts of antibiotic were measured up to 20 weeks. The kinetics of release could be described effectively by the Higuchi model with the diffusion rate constant (D) increasing from of 1.7 to 5.1 microg/mg matrix/day(0.5) as the drug loading increased from 1.4% to 8.3% w/w. GS-loaded PCL matrices retained anti-bacterial activity after immersion in PBS at 37 degrees C over 14 days as demonstrated by inhibition of growth of S. epidermidis in culture. These findings recommend further investigation of precipitation-cast PCL matrices for delivery of hydrophilic molecules such as anti-bacterial agents from implanted, inserted or topical devices.

Microwave-assisted synthesis of poly(epsilon-caprolactone)-poly(ethylene glycol)-poly(epsilon-caprolactone) tri-block co-polymers and use as matrices for sustained delivery of ibuprofen taken as model drug

Poly(epsilon-caprolactone)-poly(ethylene glycol)-poly(epsilon-caprolactone) triblock co-polymers with number-average molar mass (Mn) over 20000 g/mol were prepared by ring-opening polymerization of epsilon-caprolactone initiated by poly(ethylene glycol) under microwave irradiation. This method was proposed as a means to improve in vivo compatibility as no harmful chemicals were involved in the polymerization except epsilon-caprolactone and poly(ethylene glycol). The resulting tri-block co-polymers were characterized by FT-IR, H-NMR, GPC and WAXD. Their Mn and their composition was controlled by the amount and the chain length of the poly(ethylene glycol) macromers involved in the feed. The ability of poly(epsilon-caprolactone)-poly(ethylene glycol)-poly(epsilon-caprolactone) co-polymers to entrap and deliver drugs was investigated with ibuprofen as a model drug. The release of ibuprofen was significantly influenced by the co-polymer composition and the extent of loading. The in vitro release of ibuprofen was sustained from 3 to 15 days for 10% loading, depending on the ratio of epsilon-caprolactone to ethylene glycol-derived subunits in co-polymer chains. This ratio ranged from 0.97 to 9.78. In the case of the co-polymer whose epsilon-caprolactone molar ratio to ethylene glycol-derived subunits was 2.49, the ibuprofen release was sustained for 2 to 24 days for ibuprofen loads going from 5 to 20 wt%.

Evaluation of biodegradable synthetic scaffold coated on arterial prostheses implanted in rat subcutaneous tissue

Polyester arterial prostheses impregnated with various synthetic biodegradable materials and with gelatin were implanted subcutaneously in rats for 3-180 days. The inflammation was assessed by quantifying the activity of alkaline phosphatase and by histology. The degradation of the scaffold materials was determined by scanning electron microscopy (SEM), size exclusion chromatography (SEC), and differential scanning calorimetry (DSC). The alkaline phosphatase activity induced by the polymer-impregnated grafts was similar to that induced by the non-impregnated controls during most of the post-implantation periods. Histological studies revealed that the acute inflammatory response was moderate to mild and was similar for all types of specimens, except for the gelatin-impregnated grafts that induced a severe acute inflammation during the first 2 weeks post-implantation. At 4 and 6 months, significant disintegration of the scaffold was observed, accompanied by enhanced tissue infiltration and a reactivation of the acute inflammatory phase. Linear and exponential degradation rates of the synthetic polymers were described. The relative degradation rates of the biodegradable polymers were ranked as following: PLLACL > PDLLA > PLLA > PCEL. In conclusion, biodegradable polymers may provide an option as sealant/scaffolding materials for vascular prosthesis. It is suggested that the degradation rate of the polymer scaffolding materials should be higher to achieve early healing while without inducing strong inflammation.