Effect of Composition and Size on Surface Properties of Anti-Cancer Nanoparticles.

Liposomal formulations offer significant advantages as anticancer drug carriers for targeted drug delivery; however, due to their complexity, clinical translation has been challenging. In addition, liposomal product manufacturing has been interrupted in the past, as was the case for Doxil® (doxorubicin hydrochloride liposome injection). Here, interfacial tension (IFT) measurements were investigated as a potential physicochemical characterization tool to aid in liposomal product characterization during development and manufacturing. A pendant drop method using an optical tensiometer was used to measure the interfacial tension of various analogues of Doxil® liposomal suspensions in air and in dodecane. The effect of liposome concentration, formulation (PEG and cholesterol content), presence of encapsulated drug, as well as average particle size was analyzed. It was observed that Doxil® analog liposomes demonstrate surfactant-like behavior with a sigmoidal-shape interfacial tension vs. concentration curve. This behavior was heavily dependent on PEG content, with a complete loss of surfactant-like behavior when PEG was removed from the formulation. In addition to interfacial tension, three data analyses were identified as able to distinguish between formulations with variations in PEG, cholesterol, and particle size: (i) polar and non-polar contribution to interfacial tension, (ii) liposomal concentration at which the polar and non-polar components were equal, and (iii) rate of interfacial tension decay after droplet formation, which is indicative of how quickly liposomes migrate from the bulk of the solution to the surface. We demonstrate for the first time that interfacial tension can be used to detect certain liposomal formulation changes, such as PEG content, encapsulated drug presence, and size variability, and may make a useful addition to physicochemical characterization during development and manufacturing of liposomal products.

Novel Method to Obtain Contact Angles of Tumor Biopsies.

Characterizing the strength of a solid-liquid interface can be done by depositing a single drop of liquid on a planar solid surface and measuring the angle of the formed semicircle, called the contact angle. The contact angle of pure water is indicative of a surface's hydrophobicity and is a useful metric in biomedical applications such as tissue scaffolding and drug/tissue interactions. However, the roughness and inhomogeneity of most biological surfaces make obtaining accurate contact angles of such materials challenging. Here, we developed an instrument and methodology to obtain contact angles of tissue sections. Breast cancer tumor and nearby healthy tissue sections were used as the model biological surface. The custom instrument was built on existing equipment by improving drop dispensing accuracy in the nanoliter range, an XYZ stage, additional side view cameras, and microscope-based sample visualization. The method takes into account the inherent surface inhomogeneity and topology of tissue and the required method of illumination for contact angle acquisition. As such, the system uses an inverted microscope with a high sensitivity camera, an XYZ stage for accurate droplet placement on tissue, and multiple cameras to obtain contact angles around the entire perimeter of the drop. We tested the system with breast cancer biopsies and adjacent normal tissue from 75 patients and report here a trend of tumor exhibiting higher water contact angles, and thus higher hydrophobicity, compared to their respective normal adjacent tissue. The system described here can be used to characterize any type of biological tissue, which can be sectioned, with any liquid including water or solutions with dissolved or suspended therapeutic molecules and particles.

Novel adapter method for in vitro release testing of in situ forming implants.

In situ forming implants are injectable liquid formulations which form solid or semisolid depots following injection. This allows for minimally invasive administration, localized drug delivery, and extended drug release. Unfortunately, this drug delivery strategy lacks standardized in vitro dissolution methods due to the difficulties in recreating implant formation in vitro that is biomimicry and with reproducible and controllable shape and dimensions. In the present study, an innovative, adapter-based in vitro release testing method was developed to solve this problem. Two distinctively different in situ forming implants (a risperidone formulation (suspension) consisting of PLGA dissolved in N-methyl pyrrolidone (NMP), where risperidone powder was suspended to form a drug suspension, and a naproxen formulation (solution) consisting of PLGA dissolved in NMP, where naproxen was completely dissolved to form a solution), were used as model in situ-forming implants. The results revealed that the implants formed in the custom-designed adapter with a water-dissolvable polyvinyl alcohol (PVA) film were bio-mimicking and reproducible in both shape and burst release of drug according to rabbit data. For both the suspension and solution formulations, this adapter-based in vitro release testing method resulted in consistent release data. Compared with a direct injection in vitro release testing method, the release profiles generated using the adapter-based method were capable of distinguishing the different release phases (initial release within 24 h, diffusion-facilitated release, and degradation-controlled release). In addition, the adapter-based method could discriminate formulation and dissolution apparatus changes and could be utilized to develop accelerated release testing methods. This adapter-based method has the promise of wide use in release testing of in situ forming implant formulations and has the potential to be used in the development of in vivo-predictive in vitro release methods.

Sterilization of Drug-Loaded Composite Coatings for Implantable Glucose Biosensors.

BACKGROUND: An anti-inflammatory drug-loaded composite coating (dexamethasone-loaded poly (lactic-co-glycolic acid) [PLGA] microspheres/polyvinyl alcohol [PVA] hydrogel) was previously developed to counter the foreign body reaction to a fully implantable continuous glucose monitoring biosensor. The long-term sensor functionality was ensured in the presence of the drug-loaded composite coating thus facilitating better diabetes control and management. In order to advance such a drug-device combination product toward clinical testing, addressing sterilization remains a key step due to the heterogeneity of the product components. The main objective of this research was to investigate the effect of two terminal sterilization techniques: gamma radiation and ethylene oxide (EO) on the stability of the anti-inflammatory coatings as well as retention of the glucose sensing ability of the implantable sensor. METHOD: The composite coatings, their individual components, and the glucose-sensing elements of the biosensor were subjected to low-temperature gamma radiation and EO cycles. Detailed characterization was conducted on all components before and after sterilization. RESULTS: Exposure to gamma radiation affected dexamethasone crystallinity and glucose response linearity of the sensing element, whereas physical aging of microspheres in composite coatings was observed poststerilization with EO. Despite these effects, dexamethasone drug release from coatings was not significantly affected by either technique. CONCLUSION: The research findings indicate that both sterilization techniques are feasible for the sterilization of the dexamethasone-loaded PLGA microspheres/PVA hydrogel composite coatings, while EO was preferred for the sterilization of the glucose-sensing element of the biosensor.

Effect of implant formation on drug release kinetics of in situ forming implants.

In situ forming implants are attractive long-acting implant dosage forms due to their: i) ability to control drug release; ii) simple manufacturing process; and iii) minimally invasive administration. In situ forming implants are typically made of a drug, solvent, and a biocompatible polymer that controls drug release. Once injected in the subcutaneous tissue, they form solid depots through solvent/non-solvent exchange and phase separation of the biodegradable polymer (such as poly (lactic-co-glycolic acid), PLGA and poly (lactic acid), PLA). However, the mechanism of implant formation and the changes in their microstructure that determine drug release behavior are not fully understood. Furthermore, there is no standardized in vitro release testing method for in situ forming implants due to limitations in recreating bio-relevant and reproducible implant formation in vitro with controllable implant shape, dimensions and surface-to-volume ratio. In the present study, bio-relevant implant formation was recreated in vitro by testing five different methods to determine their effect on drug release kinetics, reproducibility, and internal microstructure formation. The leuprolide acetate formulation Eligard® was used as a model in situ-forming implant, consisting of lyophilized leuprolide acetate, and PLGA dissolved in N-methyl pyrrolidone. The results revealed that the in vitro implant formation method is a crucial step in the dissolution testing process that significantly impacts the release profile of in situ forming implants. An implant formation method that utilizes dissolvable polyvinyl alcohol (PVA) films allowed for initial drug burst release control by modulating implant dimensions (i.e. surface area) and resulted in reproducible in vitro release profiles. In addition, implant formation was shown to affect the internal microstructure of in situ forming implant and was the main factor controlling the release profile which consisted of an initial release phase followed by a release plateau (lag phase) and then a second erosion-controlled release phase.

l-DOPA as a small molecule surrogate to promote angiogenesis and prevent dexamethasone-induced ischemia.

The foreign body response to implantable biosensors has been successfully countered through the use of corticosteroids, such as dexamethasone. However, while controlling inflammation, dexamethasone also decreases angiogenesis, which may lead to delayed analyte readings. The concurrent application of VEGF with dexamethasone increases angiogenesis, but VEGF has physical stability issues and is not cost-effective. The use of l-DOPA, a small molecule drug shown to up-regulate VEGF in the Parkinsonian brain, can potentially resolve these issues by substituting for VEGF. In this work, l-DOPA was used for the first time as a pro-angiogenic agent to counteract dexamethasone-induced ischemia. Angiogenesis was modeled using the CAM assay and changes in blood vessel formation were recorded with both manual and digital techniques. As expected, dexamethasone reduced blood vessel formation in the CAM. Application of l-DOPA, on the other hand, increased blood vessel formation when dexamethasone and l-DOPA were administered simultaneously. This novel finding suggests the utility of l-DOPA in the field of implantable medical devices, such as biosensors, as well as tissue engineering applications where both a vascularized tissue environment and control of tissue response is desired.

Foreign Body Reaction to Subcutaneous Implants.

Subcutaneously implanted materials trigger the host's innate immune system, resulting in the foreign body reaction. This reaction consists of protein adsorption on the implant surface, inflammatory cell infiltration, macrophage fusion into foreign body giant cells, fibroblast activation and ultimately fibrous encapsulation. This series of events may affect the function of subcutaneous implants, such as inhibition of drug diffusion from long-acting drug delivery depots and medical device failure. The foreign body reaction is a complex phenomenon and is not yet fully understood; ongoing research studies aim to elucidate the cellular and molecular dynamics involved. Recent studies have revealed information about the specific role of macrophages and their differential activation towards pro- and anti-inflammatory states, as well as species differences in the timing of collagen deposition and fibrosis. Understanding of the diverse processes involved in the foreign body reaction has led to multiple approaches towards its negation. Delivery of tissue response modifiers, such as corticosteroids, NSAIDs, antifibrotic agents, and siRNAs, has been used to prevent or minimize fibrosis. Of these, delivery of dexamethasone throughout the implantation period is the most common method to prevent inflammation and fibrosis. More recent approaches employ surface modifications to minimize protein adsorption to 'ultra-low' levels and reduce fibrosis. However, the diverse nature of the processes involved in the foreign body reaction favor the use of corticosteroids due to their wide spectrum action compared to other approaches. To date, combination approaches, such as hydrophilic coatings that reduce protein adsorption combined with delivery of dexamethasone are the most effective.

Drug Distribution in Microspheres Enhances Their Anti-Inflammatory Properties in the Gottingen Minipig.

The foreign body reaction (FBR), one of the body's defense mechanisms against foreign materials, results in loss of implant biocompatibility. A popular strategy to prevent FBR is the constant release of dexamethasone in the tissue surrounding the implant. However, FBR prevention has not been sufficiently studied in large animal models, which offer a better representation of the human subcutaneous tissue physiology. Accordingly, a long-term strategy to prevent FBR to subcutaneous implants in a large animal model is necessary to translate the existing research for clinical applications. Here, a poly(lactic-co-glycolic) (PLGA) microsphere/poly(vinyl alcohol) (PVA) hydrogel composite coating for one-month prevention of FBR in Gottingen minipigs was developed. A modified PLGA microsphere formulation process is presented, that utilizes coprecipitation of dexamethasone and PLGA. Traditional methods result in heterogeneous distribution of large drug crystals in the microsphere matrix, which in turn results in low drug loading since the drug crystal size is close to that of the microspheres. The modified microsphere preparation method showed homogeneous distribution of dexamethasone, which in turn gave rise to increased drug loading, low burst release, and minimal lag phase. Elimination of the lag phase was dictated from previous work that compared FBR between rats and minipigs. The ability of the coatings to improve implant biocompatibility was successfully tested in vivo via histological examination of explanted tissue from the area surrounding the implants. The biocompatible coatings presented here are suitable for miniaturized implantable devices, such as biosensors, that require constant communication with the local microenvironment.

Multiple tissue response modifiers to promote angiogenesis and prevent the foreign body reaction around subcutaneous implants.

Dexamethasone-releasing PLGA poly(lactic-co-glycolic acid) microsphere/PVA (polyvinyl alcohol) hydrogel composite coatings have been shown to prevent the foreign body reaction (FBR) to subcutaneous implants in small and large animal models. Such coatings were developed to extend the lifetime of implantable biosensors. However, long-term exposure of tissue to low levels of dexamethasone results in a reduction in blood vessel density due to the anti-angiogenic effect of dexamethasone. This mild effect, while not threatening to the subject's health, may interfere with analyte detection and the sensor response time over the long-term. The present work is focused on the development of coatings that deliver combinations of three tissue response modifiers (TRMs): dexamethasone, VEGF (vascular endothelial growth factor) and PDGF (platelet derived growth factor). Dexamethasone, VEGF and PDGF prevent the FBR, increase angiogenesis and promote blood vessel maturation (which increases blood flow), respectively. To minimize any potential interference among these three TRMs (for example, PDGF increases fibrosis), the relative doses of dexamethasone, VEGF and PDGF were adjusted. It was determined that: a) all three TRMs are required for maximum promotion of angiogenesis, blood vessel maturation and prevention of the FBR; b) VEGF has to be administered at higher doses than PDGF; c) an increase in dexamethasone dosing must be accompanied by a proportional increase in growth factor dosing; and d) modification of the TRM ratio can achieve a constant capillary density throughout the implantation period which is important for applications such as biosensors to maintain sensitivity and a stable sensor baseline. Moreover, an osmosis-driven process for encapsulation of proteins in PLGA microspheres that showed low burst release was developed.

Continuous metabolic monitoring based on multi-analyte biomarkers to predict exhaustion.

This work introduces the concept of multi-analyte biomarkers for continuous metabolic monitoring. The importance of using more than one marker lies in the ability to obtain a holistic understanding of the metabolism. This is showcased for the detection and prediction of exhaustion during intense physical exercise. The findings presented here indicate that when glucose and lactate changes over time are combined into multi-analyte biomarkers, their monitoring trends are more sensitive in the subcutaneous tissue, an implantation-friendly peripheral tissue, compared to the blood. This unexpected observation was confirmed in normal as well as type 1 diabetic rats. This study was designed to be of direct value to continuous monitoring biosensor research, where single analytes are typically monitored. These findings can be implemented in new multi-analyte continuous monitoring technologies for more accurate insulin dosing, as well as for exhaustion prediction studies based on objective data rather than the subject's perception.

Prevention of foreign body reaction in a pre-clinical large animal model.

In this work, the foreign body reaction (FBR) to small subcutaneous implants was compared between small (rodent) and large (swine) animal species for the first time. Dexamethasone-releasing poly(lactic-co-glycolic acid) microspheres/polyvinyl alcohol hydrogel composite coatings were adapted to prevent FBR to small, subcutaneous implants in a large animal model (Goettingen minipigs). The implants consisted of small silicon chips (used to mimic small medical devices) that were coated with the composite formulations. The stages of the FBR were compared with previous studies in rats (that used the same-sized implants); the onset and severity of chronic inflammation (collagen deposition) was identified as a key difference between the two species. In the absence of inflammation control, fibrosis was observed from day 7 post-implantation in minipigs, whereas in rats this did not occur until day 14. This is significant as swine skin is the most commonly used model for preclinical testing of dermal formulations. It was determined that for long-term prevention of the FBR (longer than 24h), a lag phase in dexamethasone release between days 1 and 10 did not affect the anti-FBR properties of the implant in rats. However, continuous release of dexamethasone, with no lag phase, was necessary to prevent inflammation in minipigs (effective dexamethasone dose was 100µg delivered immediately after implantation and 10µg/day delivered continuously thereafter). This study offers significant insight into the translation of anti-FBR strategies across species, and showcases the importance of tailoring the controlled release kinetics of the formulation to the host response.

Haemocompatibility improvement of metallic surfaces by covalent immobilization of heparin-liposomes.

Stainless steel surfaces were processed by means of plasma enhanced chemical vapor deposition (PE-CVD) fed with acrylic acid vapors in order to functionalize them with carboxyl groups, which were subsequently activated for covalent immobilization of heparin-loaded (HEP) NH(2) group-functionalized (Fun) nanoliposomes (NLs). Empty Fun or HEP non-functionalized (control) NLs were used as controls. NLs were characterized for mean diameter, surface charge and heparin encapsulation/release. Different lipid compositions were used for NL construction; PC/Chol (2:1mol/mol) or PC/Chol (4:1mol/mol) (fluid type vesicles) [which allow gradual release of heparin] and DSPC/Chol (2:1mol/mol) (rigid type vesicles). Surface haemocompatibility was tested by measuring blood clotting time. Platelet adhesion on surfaces was evaluated morphologically by SEM and CLSM. The haemocompatibility of plasma-processed surfaces was improved (compared to untreated surfaces); Fun-HEP NL-coated surfaces demonstrated highest coagulation times. For short surface/blood incubation periods, surfaces coated with Fun-HEP NLs consisting of PC/Chol (2:1) had higher coagulation times (compared to DSPC/Chol NLs) due to faster release of heparin. Heparin release rate from the various NL types and surface platelet adhesion results were in agreement with the corresponding blood coagulation times. Concluding, covalent immobilization of drug entrapping NLs on plasma processed surfaces is a potential method for preparation of controlled-rate drug-eluting metallic stents or devices.