Biodegradable polymeric microspheres and nanospheres for drug delivery in the peritoneum

Thermoresponsive nanogels for prolonged duration local anesthesia

Nanogels based on poly(N-isopropylacrylamide) are attractive vehicles for prolonged duration local anesthesia because of their tunable size, number of functional groups, thermoresponsiveness and anionic charge. Nerve block durations of up to 9h were achieved using acrylic acid-loaded nanogels loaded with bupivacaine. Increasing the anionic charge density of the nanogels or (for more highly acid-functionalized nanogels) decreasing the nanogel size facilitated longer duration of anesthetic release. Small (<300 nm diameter) nanogels formed dense aggregates upon injection in vivo and induced only mild inflammatory responses, while large (>500 nm diameter) nanogels typically remained as liquid-like residues in vivo and induced more severe inflammatory reactions.

Controlled release of bupivacaine HCl through microchannels of biodegradable drug delivery device

Local and prolonged delivery of local analgesics is much desired for post-operative pain management. For delivery of local analgesics at a constant rate over couple of days, a microfluidic device comprised of a drug reservoir and microchannels for drug release was developed using a biodegradable polymer, 85/15 poly(lactic-co-glycolic acid). Unlike conventional methods relying on material property, this device enables convenient modulation of the release speed of drugs by a simple change of the channel geometry such as the length and cross-sectional area. Bupivacaine was selected as our model local analgesic drug and its diffusional transport through microchannels was studied using the microfluidic devices. However, since the salt form of bupivacaine, bupivacaine hydrochloride, has pH-dependent solubility, its precipitation in microchannels had an adverse impact on the release performance of the microfluidic drug delivery devices. Thus, in this investigation, the diffusional transport and precipitation of bupivacaine hydrochloride in microfluidic channels were studied using in vitro release experiments and optical analysis. Furthermore, a concept of co-delivery of bupivacaine hydrochloride together with acidic additives was demonstrated to achieve a zero-order delivery of bupivacaine hydrochloride without the clogging of microchannels by its precipitation.

An in situ cross-linking hybrid hydrogel for controlled release of proteins

There is a clear need for methods to provide a safe controlled release of therapeutic proteins, either to achieve and maintain high local protein concentrations, or for sustained systemic delivery. We have developed a protein delivery system that combines in situ cross-linkable polysaccharide hydrogels with gelatin. This formulation is injectable, easy to apply, and obviates the need for organic solvents or potentially toxic cross-linking agents in the formulation process. The cross-linked polysaccharides themselves (comprising hyaluronic acid, dextran and/or carboxymethylcellulose) provided prolonged release of fluorescently labeled albumin (FITC-albumin). The duration of release was markedly extended by the incorporation of gelatin into the formulation: FITC-albumin and interleukin-2 (IL-2) were released over the course of more than 3 weeks. The IL-2 maintained >70% activity throughout that time. Gelatin also accelerated the gelation time of the hydrogels, and reduced their swelling in phosphate-buffered saline. The composite hydrogel (dextran-carboxymethylcellulose-gelatin) showed minimal cytotoxicity in vitro, and benign tissue reaction after subcutaneous injection in rats.

Long-term stability of quercetin nanocrystals prepared by different methods

OBJECTIVES

This study aimed to examine the long-term physical stability of quercetin nanocrystals produced by three methods.

METHODS

Quercetin nanocrystals were prepared by high pressure homogenization, bead milling and cavi-precipitation. The nanocrystals produced by these methods were compared for particle size, saturation solubility and dissolution of the drug particles, and were subjected to stability testing.

KEY FINDINGS

The X-ray diffraction study and microscopic pictures taken under polarized light indicated the crystalline nature of the nanocrystals produced by the three methods. As the crystalline state is relatively more stable than the amorphous state, a good physical stability was expected from the quercetin nanocrystals prepared. The high-pressure homogenized and bead-milled quercetin nanocrystals showed excellent physical stability when stored under refrigeration (4±2°C) and at room temperature (25±2°C) for 180 days. The dissolution properties were not significantly affected on storage at room temperature. However, increase in the storage temperature to 40±2°C led to physical instability. On the other hand, the cavi-precipitated quercetin nanocrystals exhibited a lower stability than the bead-milled and homogenized formulations and did not show the optimum zeta potential values as well. In the case of cavi-precipitated nanocrystals, recrystallization and agglomeration were responsible for the increasing particle size besides the Ostwald ripening phenomenon. The solvents used during cavi-precipitation might have competed with the surfactant for hydration leading to a partial dehydration of the surfactant, which subsequently affected the stability of the quercetin nanocrystals.

CONCLUSIONS

High-pressure homogenized and bead-milled quercetin nanocrystals showed better physical stability than the cavi-precipitated ones. Freeze drying immediately after nanocrystal production can help to prevent their agglomeration and thus improve physical stability.

PLGA-based nanoparticles: an overview of biomedical applications

Poly(lactic-co-glycolic acid) (PLGA) is one of the most successfully developed biodegradable polymers. Among the different polymers developed to formulate polymeric nanoparticles, PLGA has attracted considerable attention due to its attractive properties: (i) biodegradability and biocompatibility, (ii) FDA and European Medicine Agency approval in drug delivery systems for parenteral administration, (iii) well described formulations and methods of production adapted to various types of drugs e.g. hydrophilic or hydrophobic small molecules or macromolecules, (iv) protection of drug from degradation, (v) possibility of sustained release, (vi) possibility to modify surface properties to provide stealthness and/or better interaction with biological materials and (vii) possibility to target nanoparticles to specific organs or cells. This review presents why PLGA has been chosen to design nanoparticles as drug delivery systems in various biomedical applications such as vaccination, cancer, inflammation and other diseases. This review focuses on the understanding of specific characteristics exploited by PLGA-based nanoparticles to target a specific organ or tissue or specific cells.

Zwitterionic chitosan derivative, a new biocompatible pharmaceutical excipient, prevents endotoxin-mediated cytokine release

Chitosan is a cationic polymer of natural origin and has been widely explored as a pharmaceutical excipient for a broad range of biomedical applications. While generally considered safe and biocompatible, chitosan has the ability to induce inflammatory reactions, which varies with the physical and chemical properties. We hypothesized that the previously reported zwitterionic chitosan (ZWC) derivative had relatively low pro-inflammatory potential because of the aqueous solubility and reduced amine content. To test this, we compared various chitosans with different aqueous solubilities or primary amine contents with respect to the intraperitoneal (i.p.) biocompatibility and the propensity to induce pro-inflammatory cytokine production from macrophages. ZWC was relatively well tolerated in ICR mice after i.p. administration and had no pro-inflammatory effect on naïve macrophages. Comparison with other chitosans indicates that these properties are mainly due to the aqueous solubility at neutral pH and relatively low molecular weight of ZWC. Interestingly, ZWC had a unique ability to suppress cytokine/chemokine production in macrophages challenged with lipopolysaccharide (LPS). This effect is likely due to the strong affinity of ZWC to LPS, which inactivates the pro-inflammatory function of LPS, and appears to be related to the reduced amine content. Our finding warrants further investigation of ZWC as a functional biomaterial.

Novel experimental and clinical therapeutic uses of low-molecular-weight heparin/protamine microparticles

Low-molecular-weight heparin/protamine microparticles (LMW-H/P MPs) were produced as a carrier for heparin-binding growth factors (GFs) and for various adhesive cells. A mixture of low-molecular-weight heparin (MW: approximately 5000 Da, 6.4 mg/mL) and protamine (MW: approximately 3000 Da, 10 mg/mL) at a ratio of 7:3 (vol:vol) yields a dispersion of microparticles (0.5–3 µm in diameter). LMW-H/P MPs immobilize, control the release and protect the activity of GFs. LMW-H/P MPs can also bind to cell surfaces, causing these cells to interact with the LMW-H/P MPs, inducing cells/MPs-aggregate formation and substantially promoting cellular viability. Furthermore, LMW-H/P MPs can efficiently bind to tissue culture plates and retain the binding of important GFs, such as fibroblast growth factor (FGF)-2. The LMW-H/P MPs-coated matrix with various GFs or cytokines may provide novel biomaterials that can control cellular activity such as growth and differentiation. Thus, LMW-H/P MPs are an excellent carrier for GFs and various cells and are an efficient coating matrix for cell cultures.

Nanomedicine as an emerging approach against intracellular pathogens

Diseases such as tuberculosis, hepatitis, and HIV/AIDS are caused by intracellular pathogens and are a major burden to the global medical community. Conventional treatments for these diseases typically consist of long-term therapy with a combination of drugs, which may lead to side effects and contribute to low patient compliance. The pathogens reside within intracellular compartments of the cell, which provide additional barriers to effective treatment. Therefore, there is a need for improved and more effective therapies for such intracellular diseases. This review will summarize, for the first time, the intracellular compartments in which pathogens can reside and discuss how nanomedicine has the potential to improve intracellular disease therapy by offering properties such as targeting, sustained drug release, and drug delivery to the pathogen’s intracellular location. The characteristics of nanomedicine may prove advantageous in developing improved or alternative therapies for intracellular diseases.

Hyaluronic acid-based hydrogel for regional delivery of paclitaxel to intraperitoneal tumors

Intraperitoneal (IP) chemotherapy is an effective way of treating local and regional malignancies confined in the peritoneal cavity such as ovarian cancer. However, a persistent major challenge in IP chemotherapy is the need to provide effective drug concentrations in the peritoneal cavity for an extended period of time. We hypothesized that hyaluronic acid (HA)-based in-situ crosslinkable hydrogel would serve as a carrier of paclitaxel (PTX) particles to improve their IP retention and therapeutic effects. In-vitro gel degradation and release kinetics studies demonstrated that HA gels could entrap microparticulate PTX (>100 μm) and release the drug over 10 days, gradually degraded by hyaluronidase, but had limited effect on retention of Taxol, a 14-nm micelle form of PTX. When administered IP to tumor-bearing nude mice, PTX was best retained in the peritoneal cavity as PTX-gel (microparticulate PTX entrapped in the HA gel), whereas Taxol-gel and other Taxol-based formulations left negligible amount of PTX in the cavity after 14 days. Despite the increase in IP retention of PTX, PTX-gel did not further decrease the tumor burdens than Taxol-based formulations, presumably due to the limited dissolution of PTX. This result indicates that spatial availability of a drug does not necessarily translate to the enhanced anti-tumor effect unless it is accompanied by the temporal availability.

An injectable depot system for sustained intraperitoneal chemotherapy of ovarian cancer results in favorable drug distribution at the whole body, peritoneal and intratumoral levels

The current study characterizes the impact of docetaxel (DTX) distribution on efficacy following sustained intraperitoneal (IP) chemotherapy in murine models of ovarian cancer. A polymer-lipid biodegradable depot (PoLigel) was used to deliver DTX in a sustained manner over 21-days following IP administration. Distribution and efficacy studies were carried out in SCID mice bearing SKOV3 IP solid tumors or C57BL/6 mice with ID8 IP ascites fluid. In addition, a subcutaneous (SC) SKOV3 model was used to determine whether systemic drug levels that result from IP administration of the PoLigel influence antitumor efficacy. Immunostained IP and SC SKOV3 tumor sections were used to study cell death, intratumoral drug distribution and tumor penetration. Sustained concentrations of DTX were observed in plasma, tissue, tumor and ascites over the entire study period. Drug accumulation was several fold greater in tumors and ascites when compared to plasma levels. Sustained chemotherapy resulted in significant reduction in tumor burden and ascites volume. IP tumors showed greater cell death compared to the SC tumors as seen by higher TUNEL and caspase-3 expression. At the intratumoral level, DTX distributed more towards the core of IP tumors compared to the SC tumors. Tumor penetration of drug from nearest blood vessel was 1.5 fold greater in the IP tumors than the SC tumors. Overall, favorable drug distribution at the whole-body, peritoneal and intratumoral levels in combination with local and systemic sustained drug exposure contribute to the high efficacy observed. These results encourage the clinical use of IP sustained chemotherapy for ovarian cancer.

Effective Delivery of PEGylated siRNA-Containing Lipoplexes to Extraperitoneal Tumours following Intraperitoneal Administration

Intraperitoneal (i.p.) administration of small interfering RNA (siRNA) has, to date, shown promise in treating tumours located within the peritoneal cavity. The ability of these siRNA molecules to reach extraperitoneal tumours following i.p. administration is, however, yet to be investigated. Here, we examined the impact of PEGylation on the biodistribution of i.p. administered nucleic acids-containing lipoplexes. We showed that in contrast to non-PEGylated liposomes, PEGylated liposomes can deliver siRNA efficiently to extraperitoneal tumours following i.p. administration, resulting in a 45% reduction in tumour size when the oncogene-targeted siRNA was used. This difference was likely contributed by the decreased uptake of PEGylated lipoplexes in the first-pass organs, and, in particular, we observed a 10-fold decrease in the macrophage uptake of these particles compared to non-PEGylated counterparts. Overall, our results indicated the potential of using PEGylated liposomes to deliver siRNA for the treatment of i.p. localized cancer with coexisting extraperitoneal metastasis.

Intraperitoneal therapy for peritoneal cancer

Cancers originating from organs in the peritoneal cavity (e.g., ovarian, pancreatic, colorectal, gastric and liver) account for approximately 250,000 new cancer cases annually in the USA. Peritoneal metastases are common owing to locoregional spread and distant metastases of extraperitoneal cancers. A logical treatment is intraperitoneal therapy, as multiple studies have shown significant targeting advantage for this treatment, including significant survival benefits in stage III, surgically debulked ovarian cancer patients. However, the clinical use of intraperitoneal therapy has been limited, in part, by toxicity, owing to the use of indwelling catheters or high drug exposure, by inadequate drug penetration into bulky tumors (>1 cm) and by the lack of products specifically designed and approved for intraperitoneal treatments. This article provides an overview on the background of peritoneal metastasis, clinical research on intraperitoneal therapy, the pharmacokinetic basis of drug delivery in intraperitoneal therapy and our development of drug-loaded tumor-penetrating microparticles.

Sterilization of Silver Nanoparticles Using Standard Gamma Irradiation Procedure Affects Particle Integrity and Biocompatibility

Silver nanoparticles are commonly used in a variety of commercial and medical products. Here we investigate the effects of standard sterilization methods, including heat/steam (autoclave) and gamma-irradiation on the structural integrity and biocompatibility of citrate-stabilized silver nanoparticles with nominal sizes of 20, 40, 60 and 80 nm. Particle size, shape and in vitro biocompatibility were studied pre- and post-sterilization. Sterilization by gamma irradiation at dose levels commonly used in medical device industry (15, 25 and 50 kGy) resulted in dramatic changes in particle size and morphology, as monitored by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Exposing the particles to a chemical producer of hydroxyl radicals (N-hydroxy-2-pyridinethione) allowed us to duplicate the sterilization-based changes in size and morphology, implying a free radical mechanism of action. Compared to untreated controls, we also observed a three- to five-fold increase in tendency of sterilized silver nanoparticles to cause platelet aggregation, a sensitive in vitro indicator of thrombogenicity.

Peritoneal adhesions in human and veterinary medicine: from pathogenesis to therapy. A review

Any peritoneal inflammatory process consequent to infections or surgical injuries may induce abdominal adhesion formation. Peritoneal adhesions are connective laciniae that develop among abdomino-pelvic organs that limit physiologic visceral motion. Consequently, fertility may be impaired, and intestinal obstruction and pelvic pain may develop, mainly in subjects that had undergone gynaecological surgery. This review illustrates the pathogenic steps of adhesiogenesis and the therapeutic scenario that evolved over the years to tackle the threat of peritoneal adhesions, both in domestic animals and in women.

Mining the extracellular matrix for tissue engineering applications

Tissue engineering is a rapidly evolving interdisciplinary field that aims to regenerate new tissue to replace damaged tissues or organs. The extracellular matrix (ECM) of animal tissues is a complex mixture of macromolecules that play an essential instructional role in the development of tissues and organs. Therefore, tissue engineering approaches rely on the need to present the correct cues to cells, to guide them to maintain tissue-specific functions. Recent research efforts have allowed us to mine various sequences and motifs, which play key roles in these guidance functions, from the ECM. Small conserved peptide sequences mined from ECM molecules can mimic some of the biological functions of their large parent molecules. In addition, these peptide sequences can be linked to various biomaterial scaffolds that can provide the cells with mechanical support to ensure appropriate cell growth and aid the formation of the correct tissue structure. The tissue engineering field will continue to benefit from the advent of these mined ECM sequences which have two major advantages over recombinant ECM molecules: material consistency and scalability.

Multiresponse strategies to modulate burst degradation and release from nanoparticles

Logic gate nanoparticles, where two chemical transformations take place one after the other, were successfully formulated from a newly synthesized random co-polymer. This polymer, poly([2,2'-(propane-2,2-diylbis(oxy))bis(ethane-2,1-diyl) diacrylate ]-co-[hexane-1,6-diyl diacrylate]-4,4' trimethylene dipiperidine), (poly-β-aminoester ketal-2) contains two pH responsive moieties within its backbone. As nanoparticles they function akin to an AND logic gate. The β-aminoester backbone moiety provides a pH triggered solubility switch, only when this switch is "ON" does the ketal moiety also turn "ON" to undergo rapid acid catalyzed hydrolysis. These AND logic gate polymeric nanoparticles were prepared using an oil in water emulsion method. Their degradation in the pH range of 7.4-5 was monitored by dynamic light scattering and showed excellent stability at pH 7.4 and rapid degradation at pH 5. Our results indicate that the prepared logic gate nanoparticles may prove valuable in delivering therapeutics and diagnostics to cells and diseased tissue.

Zwitterionic chitosan derivatives for pH-sensitive stealth coating

Zwitterionic chitosan, a chitosan derivative with a unique pH-dependent charge profile, was employed to create a stealth coating on the cationic surface of drug carriers. Zwitterionic chitosans were synthesized by amidation of chitosan with succinic anhydride. The succinic anhydride-conjugated chitosan had an isoelectric point, which could be easily tuned from pH 4.9 to 7.1 and showed opposite charges below and above the isoelectric point. The succinic anhydride-conjugated chitosan was able to inhibit the protein adsorption to the cationic surface at physiological pH, compatible with blood components and well tolerated upon intraperitoneal injection. The succinic anhydride-conjugated chitosan has the potential to serve as a coating material to prevent protein adsorption to cationic surfaces, which can be removed in a pH-responsive manner.

Drug delivery systems for intraperitoneal therapy

Disorders associated with the peritoneal cavity include peritoneal adhesions and intraperitoneal (IP) malignancies. To prevent peritoneal adhesions, physical barrier devices are used to prevent organs from contacting other structures in the abdomen and forming adhesions, or pharmacological agents that interfere with adhesion formation are administered intraperitoneally. IP malignancies are other disorders confined to the peritoneal cavity, which are treated by combination of surgical removal and chemotherapy of the residual tumor. IP drug delivery helps in the regional therapy of these disorders by providing relatively high concentration and longer half-life of a drug in the peritoneal cavity. Various studies suggest that IP delivery of anti-neoplastic agents is a promising approach for malignancies in the peritoneal cavity compared to the systemic administration. However, IP drug delivery faces several challenges, such as premature clearance of a small molecular weight drug from the peritoneal cavity, lack of target specificity, and poor drug penetration into the target tissues. Previous studies have proposed the use of micro/nanoparticles and/or hydrogel-based systems for prolonging the drug residence time in the peritoneal cavity. This commentary discusses the currently used IP drug delivery systems either clinically or experimentally and the remaining challenges in IP drug delivery for future development.

Drug delivery systems: Advanced technologies potentially applicable in personalized treatments

Advanced drug delivery systems (DDS) present indubitable benefits for drug administration. Over the past three decades, new approaches have been suggested for the development of novel carriers for drug delivery. In this review, we describe general concepts and emerging research in this field based on multidisciplinary approaches aimed at creating personalized treatment for a broad range of highly prevalent diseases (e.g., cancer and diabetes). This review is composed of two parts. The first part provides an overview on currently available drug delivery technologies including a brief history on the development of these systems and some of the research strategies applied. The second part provides information about the most advanced drug delivery devices using stimuli-responsive polymers. Their synthesis using controlled-living radical polymerization strategy is described. In a near future it is predictable the appearance of new effective tailor-made DDS, resulting from knowledge of different interdisciplinary sciences, in a perspective of creating personalized medical solutions.

RGD modified PLGA/gelatin microspheres as microcarriers for chondrocyte delivery

Poly(lactide-co-glycotide) (PLGA)/gelatin composite microspheres were prepared by an emulsion solvent evaporation technique. RGDS peptides were further immobilized under the catalyzation of water soluble carbodiimide (EDAC). Confocal laser scanning microscopy and transmission electron microscopy revealed that the gelatin was entrapped in the PLGA/gelatin microspheres with a manner of separated domains. The contents of the entrapped gelatin and immobilized RGDS peptides were quantified as 0.9 mg/20 mg and approximately 2.1 microg/20 mg microspheres by hydroxyproline analysis and bicinchoninic acid protein assay, respectively. Moreover, difference in morphology of PLGA, PLGA/gelatin and RGDS modified PLGA/gelatin (PLGA/gelatin-RGDS) microspheres was observed by scanning electron microscopy. The PLGA/gelatin and PLGA/gelatin-RGDS microspheres lost their weight rapidly in PBS, but slowly in DMEM/fetal bovine serum. Rabbit auricular chondrocytes were seeded onto the microspheres in vitro to assess their biological performance and applicability as cell carriers. Results show that amongst the PLGA, PLGA/gelatin and PLGA/gelatin-RGDS microspheres, the latter ones have the best performance in terms of chondrocyte attachment, proliferation, viability and sulfated glycosaminoglycans secretion.

Sparfloxacin-loaded PLGA nanoparticles for sustained ocular drug delivery

Poor ocular bioavailability of drugs (<1%) from conventional eye drops (ie, solution, suspension, and ointments) is mainly due to the physiologic barriers of the eye. In general, ocular efficacy is closely related to ocular drug bioavailability, which may be enhanced by increasing corneal drug penetration and prolonging precorneal drug residence time. In our current work, we develop and evaluate a new colloidal system, that is, poly(dl-lactide-co-glycolide) (PLGA) nanoparticles for sparfloxacin ophthalmic delivery, to improve precorneal residence time and ocular penetration. Nanoparticles were prepared by nanoprecipitation technique and characterized for various properties such as particle size, zeta potential, in vitro drug release, statistical model fitting, stability, and so forth. Microbiological assay was carried out against Pseudomonas aeruginosa using the cup-plate method. Precorneal residence time was studied in albino rabbits by gamma scintigraphy after radiolabeling of sparfloxacin by Tc-99m. Ocular tolerance of the developed nanosuspension was also studied by the Hen Egg Test-Chorioallantoic Membrane (HET-CAM) method. The developed nanosuspension showed a mean particle size in the range of 180 to 190 nm, suitable for ophthalmic application with zeta potential of -22 mV. In vitro release from the developed nanosuspension showed an extended release profile of sparfloxacin according to the Peppas model. Acquired gamma camera images showed good retention over the entire precorneal area for the developed nanosuspension compared with that of a marketed formulation. The marketed drug formulation cleared very rapidly from the corneal region and reached the systemic circulation through the nasolacrimal drainage system, as significant radioactivity was recorded in kidney and bladder after 6 hours of ocular administration, whereas the developed nanosuspension cleared at a very slow rate (P < .05) and remained at the corneal surface for longer duration, as no radioactivity was observed in the systemic circulation. HET-CAM assay with 0 score in 8 hours indicates the nonirritant property of the developed nanosuspension. The developed lyophilized nanosuspension was found to be stable for a longer duration of time than the conventional marketed formulation with a good shelf life.

FROM THE CLINICAL EDITOR

Poor ocular bioavailability of drugs (<1%) from conventional eye drops is mainly due to the eye physiological barriers. In this study, a new colloidal system, PLGA nanoparticle for sparfloxacin ophthalmic delivery was demonstrated to improve precorneal residence time and ocular penetration. The developed lyophilized nanosuspension was found to be stable for longer duration of time than conventional marketed formulations.

One-step electrohydrodynamic production of drug-loaded micro- and nanoparticles

The objective of this work was to produce drug-loaded nanometre- and micrometre-scale particles using a single-step process that provides control over particle size and size distribution. Co-axial electrohydrodynamic processing was used, at ambient temperature and pressure, with poly(lactic-co-glycolic acid) as the polymeric coating material and oestradiol as the encapsulated drug. The particle diameter was varied from less than 120 nm to a few micrometres, by simple methodical adjustments in the processing parameters (polymer concentration and applied voltage). In vitro studies were performed to determine the drug release profile from the particles during unassisted and ultrasound-stimulated degradation in simulated body fluid. An encapsulation efficiency of approximately 70% was achieved and release of the drug was sustained for a period of over 20 days. Exposing the particles to ultrasound (22.5 kHz) increased the rate of release by approximately 8 per cent. This processing method offers several advantages over conventional emulsification techniques for the preparation of drug-loaded particles. Most significantly, process efficiency and the drug's functionality are preserved, as complex multistep processing involving harsh solvents, other additives and elevated temperatures or pressures are avoided. Production rates of 10(12) particles min(-1) can be achieved with a single pair of co-axial needles and the process is amenable to being scaled up by using multiple sets.

Intraperitoneal administration of paclitaxel solubilized with poly(2-methacryloxyethyl phosphorylcholine-co n-butyl methacrylate) for peritoneal dissemination of gastric cancer

Intraperitoneal (i.p.) administration of paclitaxel (PTX) is a hopeful therapeutic strategy for peritoneal malignancy. Intravenously (i.v.) injected nanoparticle anticancer drugs are known to be retained in the blood stream for a long time and favorably extravasated from vessels into the interstitium of tumor tissue. In this study, we evaluated the effect of i.p. injection of PTX (PTX-30W), which was prepared by solubulization with water-soluble amphiphilic polymer composed of PMB-30W, a co-polymer of 2-methacryloxyethyl phosphorylcholine and n-butyl methacrylate, for peritoneal dissemination of gastric cancer. In a peritoneal metastasis model with transfer of MKN45P in nude mice, the effect of i.p. administration of PTX-30W was compared with conventional PTX dissolved in Cremophor EL (PTX-Cre). The drug accumulation in peritoneal nodules was evaluated with intratumor PTX concentration and fluorescence microscopic observation. PTX-30W reduced the number of metastatic nodules and tumor volume significantly more than did conventional PTX dissolved in Cremophor EL (PTX-Cre), and prolonged the survival time (P < 0.05). PTX concentration in disseminated tumors measured by HPLC was higher in the PTX-30W than in the PTX-Cre group up to 24 h after i.p. injection. Oregon green-conjugated PTX-30W, i.p. administered, preferentially accumulated in relatively hypovascular areas in the peripheral part of disseminated nodules, which was significantly greater than the accumulation of PTX-Cre. I.p. administration of PTX-30W may be a promising strategy for peritoneal dissemination, due to its superior characteristics to accumulate in peritoneal lesions.

Effect of liposome size on peritoneal retention and organ distribution after intraperitoneal injection in mice

Peritoneal carcinomatosis is a serious concern when treating digestive or ovarian tumors. Treatment with systemic chemotherapy suffers from poor penetration of cytotoxic agents into the peritoneal cavity and is not quite effective. Local delivery of drugs, especially as controlled-release delivery systems like liposomes, could provide sustained and higher drug levels and reduce systemic toxicity. In order to investigate the effect of liposome size on peritoneal retention, liposomes composed of distearoylphosphatidylcholine and cholesterol (DSPC/CHOL, molar ratio 2:1) were prepared at four sizes of 100, 400, 1000 and 3000 nm. Subsequently, these liposomes were labeled with (99m)Tc complex of hexamethylpropyleneamineoxime ((99m)Tc-HMPAO) and injected into mouse peritoneum. Then, mice were sacrificed at eight different time points and the percentage of injected radiolabel in the peritoneal cavity and the organ distribution in terms of percentage injected dose/gram tissue (%ID/g) were obtained. Results showed that the free label ((99m)Tc-HMPAO) was cleared very rapidly from the cavity so that after 5 min and 7h only 6.89+/-2.51% and 0.91+/-0.51% of the injected dose was recovered, respectively. However, for the liposomal formulations, this recovery value ranged from 8.47+/-1.62% to 29.99+/-12.06% at 7h. Peritoneal retention of the vesicles was increased with their size, and the highest retention rate was obtained with 1000 nm liposomes with an AUC value 15.51 times that of (99m)Tc-HMPAO. In blood, as expected, 100 nm liposomes showed much higher levels because of their greater stability. Their greater blood concentration also caused increased levels in the heart and kidneys, although their organ to blood AUC ratio was the lowest. Overall, among the different sized neutral liposomes investigated, the 1000 nm vesicles seemed to be the most optimal, achieving a greater peritoneal level and retention.

Hydroxyapatite nanoparticles as particulate emulsifier: fabrication of hydroxyapatite-coated biodegradable microspheres

Hydroxyapatite (HAp) nanoparticle-coated micrometer-sized poly(l-lactic acid) (PLLA) microspheres were fabricated via a "Pickering-type" emulsion route in the absence of any molecular surfactants. Stable oil-in-water emulsions were prepared using 40 nm HAp nanoparticles as a particulate emulsifier and a dichloromethane (CH(2)Cl(2)) solution of PLLA as an oil phase. It was clarified that the interaction between carbonyl/carboxylic acid groups of PLLA and the HAp nanoparticles at the CH(2)Cl(2)-water interface played a crucial role to prepare the stable Pickering-type emulsion. The HAp nanoparticle-coated PLLA microspheres were fabricated by the evaporation of CH(2)Cl(2) from the emulsion and characterized in terms of size, particle size distribution, and morphology using scanning/transmission electron microscopes. Scanning electron microscopy study and ultrathin cross section observation using transmission electron microscopy confirmed adsorption of the HAp nanoparticles only at the surface of the PLLA microspheres. Cell-adhesion experiments suggested the HAp nanoparticles on the surface of the PLLA microspheres promoted the cell adhesion and spreading.

Biocompatibility of injectable chitosan-phospholipid implant systems

Injectable biomaterials are desirable therapeutic platforms due to minimal invasiveness and improved patient compliance, and are applicable in such areas as compound delivery and tissue engineering. The present work examined the biocompatibility of injectable blends composed of chitosan, phospholipid and lauric aldehyde (PoLi(gel)-LA) or lauric chloride (PoLi(gel)-LCl). In vitro cytotoxicity was evaluated in L929 and HeLa cell lines. Both blends resulted in acceptable biocompatibility, although greater cell viability was seen with PoLi(gel)-LA. In vivo biocompatibility was investigated in healthy CD-1 mice. Subcutaneous injection of the PoLi(gel)-LA blend caused no local or systemic toxicities over a four-week period while the PoLi(gel)-LCl caused immediate local toxicity. Mice injected intraperitoneally with PoLi(gel)-LA did not show physical or behavioural alterations, and body weight changes did not differ from control animals. Furthermore, histological examination of spleen and liver showed unaltered morphology. Interleukin-6 levels in mice injected with PoLi(gel)-LA did not differ from levels of control animals (6.91+/-3.61 pg/mL versus 6.92+/-5.02 pg/mL, respectively). Biodegradation occurred progressively, with 7.4+/-5.02% of the original injected mass remaining after four weeks. Results obtained herein establish the biocompatibility of PoLi(gel)-LA and indicate its potential for use in various localized therapeutic applications.

Spray-dried lipid-hyaluronan-polymethacrylate microparticles for drug delivery in the peritoneum

Application of controlled release technology to the peritoneum would allow for sustained drug levels. However, some polymeric systems either create adhesions, or rapidly exit the peritoneum; neither result is desirable. Here we have produced particles based on sphyngomyelin, a phospholipid that occurs naturally in the peritoneum, along with hyaluronic acid and the polymethacrylate Eudragit E100 (to modulate drug release). Particles with a low proportion of E100 (5% (w/w); "high SPM") release albumin rapidly over 2 days, then more slowly; increasing the E100 to 20% (w/w; high "E100") slowed drug release markedly. When injected in the murine peritoneum, high SPM particles were disseminated as free particles, without forming collections. There was a mild inflammatory response but no formation of adhesions. High E100 particles formed collections in all animals, with an intense inflammatory response. Even so, there were very few adhesions. These results suggest that microparticulate formulations can be produced that have acceptable drug-releasing properties and are suitable for use in the peritoneum from the standpoint of biocompatibility.

The biocompatibility of mesoporous silicates

Micro- and nano-mesoporous silicate particles are considered potential drug delivery systems because of their ordered pore structures, large surface areas and the ease with which they can be chemically modified. However, few cytotoxicity or biocompatibility studies have been reported, especially when silicates are administered in the quantities necessary to deliver low-potency drugs. The biocompatibility of mesoporous silicates of particle sizes approximately 150 nm, approximately 800 nm and approximately 4 microm and pore sizes of 3 nm, 7 nm and 16 nm, respectively, is examined here. In vitro, mesoporous silicates showed a significant degree of toxicity at high concentrations with mesothelial cells. Following subcutaneous injection of silicates in rats, the amount of residual material decreased progressively over 3 months, with good biocompatibility on histology at all time points. In contrast, intra-peritoneal and intra-venous injections in mice resulted in death or euthanasia. No toxicity was seen with subcutaneous injection of the same particles in mice. Microscopic analysis of the lung tissue of the mice indicated that death may be due to thrombosis. Although local tissue reaction to mesoporous silicates was benign, they caused severe systemic toxicity. This toxicity might be mitigated by modification of the materials.

Tumor-penetrating microparticles for intraperitoneal therapy of ovarian cancer

Intraperitoneal chemotherapy prolongs survival of ovarian cancer patients, but its utility is limited by treatment-related complications and inadequate drug penetration in larger tumors. Previous intraperitoneal therapy used the paclitaxel/Cremophor EL (polyethoxylated castor oil) formulation designed for intravenous use. The present report describes the development of paclitaxel-loaded microparticles designed for intraperitoneal treatment (referred to as tumor-penetrating microparticles or TPM). Evaluation of TPM was performed using intraperitoneal metastatic, human ovarian SKOV3 xenograft tumor models in mice. TPM were retained in the peritoneal cavity and adhered to tumor surface. TPM consisted of two biocompatible and biodegradable polymeric components with different drug release rates; one component released the drug load rapidly to induce tumor priming, whereas the second component provided sustained drug release. Tumor priming, by expanding interstitial space, promoted transport and penetration of particulates in tumors. These combined features resulted in the following advantages over paclitaxel/Cremophor EL: greater tumor targeting (16-times higher and more sustained concentration in omental tumors), lower toxicity to intestinal crypts and less body weight loss, greater therapeutic efficacy (longer survival and higher cure rate), and greater convenience (less frequent dosing). TPM may overcome the toxicities and compliance-related problems that have limited the utility of intraperitoneal therapy.

Polymeric biomaterials in tissue engineering

Polymeric biomaterials are one of the cornerstones of tissue engineering. A wide range of materials has been used. Approaches have shown increasing sophistication over recent years employing drug delivery functionality, micropatterning, microfluidics, and other technologies. Challenges such as producing three-dimensional matrixes and rendering them deliverable through minimally invasive techniques have been addressed. A major recent development is the design of biomaterials for tissue engineering matrices to achieve specific biologic effects on cells, and vice versa. Much remains to be achieved, particularly in integrating other new technologies into the field.

Polymers in the prevention of peritoneal adhesions

Peritoneal adhesions are serious complications of surgery, and can result in pain, infertility, and potentially lethal bowel obstruction. Pharmacotherapy and barrier devices have reduced adhesion formation to varying degrees in preclinical studies or clinical trials; however, complete prevention of adhesions remains to be accomplished. We and others have hypothesized that the limitations of the two approaches could be overcome by combining their strengths in the context of controlled drug delivery. Here we review the role of polymeric systems in the prevention of peritoneal adhesions, with an emphasis on our recent work in developing and applying polymeric drug delivery systems such as nano- or microparticles, hydrogels, and hybrid systems for peritoneal use.

Cross-linked and functionalized polyester materials constructed using ketoxime ether linkages

A modular and simple approach to the graft functionalization and cross-linking of ketone-containing poly(ε-caprolactone)s has been investigated for the preparation of novel gel and nanoparticulate materials. Poly(ε-caprolactone--2-oxepane-1,5-dione) (P(CL--OPD)), was grafted by reaction with 1-aminooxydodecane and cross-linked by reaction with 1,6-bis(aminooxy)hexane, each at room temperature in tetrahydrofuran at 1 and 10 wt% polymer in the absence of an acid catalyst, and at 1, 5 and 10 wt% polymer in the presence of -toluenesulfonic acid. The grafting process served as a model system for the cross-linking reactions, affording products that were fully characterizable and retained the physical properties of (P(CL--OPD)), with a slight increase in measured molecular weight and characteristic spectroscopic signatures for the dodecyl chains and the newly introduced ketoxime functionalities. Early stages of the intermolecular cross-linking were followed by gel permeation chromatography and atomic force microscopy. Ultimately, insoluble, but tetrahydrofuran-swollen gelled products were obtained, which were characterized by infrared spectroscopy, differential scanning calorimetry and thermogravimetric analysis. These materials exhibited interesting melting transition profiles, undergoing melting at lower temperatures and broader temperature ranges than observed for their polymer precursors. This study represents an advance in the development of rapid and efficient chemistry for the preparation of functional and robust hydrolytically-degradable polymer materials with degradable linkages.

Prevention of peritoneal adhesions with an in situ cross-linkable hyaluronan hydrogel delivering budesonide

Peritoneal adhesions are tissue connections that form within the abdominopelvic cavity following surgery or other injuries. They can cause major medical complications. Barrier devices and pharmacological agents have been used to prevent adhesion formation, with mixed success. We hypothesize that an adhesion barrier which also delivers anti-adhesion drugs can address both physical and physiological causes for adhesion formation. Here, we describe an in situ cross-linking hyaluronan hydrogel (barrier device) containing the glucocorticoid receptor agonist budesonide. Budesonide was chosen because of the known role of inflammation in adhesion formation, hyaluronan because of its known biocompatibility in the peritoneum. The system, consisting of two cross-linkable precursor liquids, was applied using a double-barreled syringe, forming a flexible and durable hydrogel in less than 5 s. We applied this formulation or controls to the injured sites after the second injury in a severe repeat sidewall defect-cecum abrasion model of peritoneal adhesion formation in the rabbit. Large adhesions (median area 15.4 cm(2)) developed in all saline-treated animals. Adhesion formation and area were slightly mitigated in animals treated with budesonide in saline (median area 5.0 cm(2)) or the hydrogel without budesonide (median area 4.9 cm(2)). The incidence and area of adhesions were dramatically reduced in animals treated with budesonide in the hydrogel (median area 0.0 cm(2)). In subcutaneous injections in rats, budesonide in hydrogel reduced inflammation compared to hydrogel alone. In summary, budesonide in a hyaluronan hydrogel is easy to use and highly effective in preventing adhesions in our severe repeated injury model. It is a potentially promising system for post-surgical adhesion prevention, and suggests that the effectiveness of barrier devices can be greatly enhanced by concurrent drug delivery.

Microparticles and nanoparticles for drug delivery

Particulate drug delivery systems have become important in experimental pharmaceutics and clinical medicine. The distinction is often made between micro- and nanoparticles, being particles with dimensions best described in micrometers and nanometers respectively. That size difference entails real differences at many levels, from formulation to in vivo usage. Here I will discuss those differences and provide examples of applications, for local and systemic drug delivery. I will outline a number of challenges of interest in particulate drug delivery.