Controlled delivery systems for proteins using polyanhydride microspheres

Sustained insulin treatment restoring metabolic status, body weight, and cognition in an anorexia nervosa-like animal model in mice

INTRODUCTION

Anorexia Nervosa (AN) is a psycho-socio-biological disease characterized by severe weight loss as result of dieting and hyperactivity. Effective treatments are scarce, despite its significant prevalence and mortality. AN patients show lower basal insulin levels and increased metabolic clearance, leading to weight loss, cognitive deficits, and hormonal imbalances. Low-dose polymer insulin could potentially reverse these effects by restoring brain function, reducing fear of weight gain, encouraging food intake, and restoring fat depots. This study evaluates an insulin delivery system designed for sustained release and AN treatment.

METHODS

AN-like model was established through dietary restriction (DR). On days 1-25, mice were on DR, and on days 26-31 they were on ad libitum regimen. An insulin-loaded delivery system was administered subcutaneously (1% w/w insulin). The impact of insulin treatment on gene expression in the hippocampus (cognition, regulation of stress, neurogenesis) and hypothalamus (eating behavior, mood) was assessed. Behavioral assays were conducted to evaluate motor activity and cognitive function.

RESULTS

The delivery system demonstrated sustained insulin release, maintaining therapeutic plasma levels. Diet restriction mice treated with the insulin delivery system showed body weight restoration. Gene expression analysis revealed enhanced expression of CB1 and CB2 genes associated with improved eating behavior and cognition, while POMC expression was reduced. Insulin-polymer treatment restored cognitive function and decreased hyperactivity in the AN-like model.

CONCLUSION

The PSA-RA-based insulin delivery system effectively restores metabolic balance, body weight, and cognitive function in the AN model. Its ability to steadily release insulin makes it a promising candidate for AN treatment."

Bioplastics for a circular economy

Bioplastics - typically plastics manufactured from bio-based polymers - stand to contribute to more sustainable commercial plastic life cycles as part of a circular economy, in which virgin polymers are made from renewable or recycled raw materials. Carbon-neutral energy is used for production and products are reused or recycled at their end of life (EOL). In this Review, we assess the advantages and challenges of bioplastics in transitioning towards a circular economy. Compared with fossil-based plastics, bio-based plastics can have a lower carbon footprint and exhibit advantageous materials properties; moreover, they can be compatible with existing recycling streams and some offer biodegradation as an EOL scenario if performed in controlled or predictable environments. However, these benefits can have trade-offs, including negative agricultural impacts, competition with food production, unclear EOL management and higher costs. Emerging chemical and biological methods can enable the 'upcycling' of increasing volumes of heterogeneous plastic and bioplastic waste into higher-quality materials. To guide converters and consumers in their purchasing choices, existing (bio)plastic identification standards and life cycle assessment guidelines need revision and homogenization. Furthermore, clear regulation and financial incentives remain essential to scale from niche polymers to large-scale bioplastic market applications with truly sustainable impact.

Zero-order drug delivery: State of the art and future prospects

Pharmaceutical drugs are an important part of the global healthcare system, with some estimates suggesting over 50% of the world's population takes at least one medication per day. Most drugs are delivered as immediate-release formulations that lead to a rapid increase in systemic drug concentration. Although these formulations have historically played an important role, they can be limited by poor patient compliance, adverse side effects, low bioavailability, or undesirable pharmacokinetics. Drug delivery systems featuring first-order release kinetics have been able to improve pharmacokinetics but are not ideal for drugs with short biological half-lives or small therapeutic windows. Zero-order drug delivery systems have the potential to overcome the issues facing immediate-release and first-order systems by releasing drug at a constant rate, thereby maintaining drug concentrations within the therapeutic window for an extended period of time. This release profile can be used to limit adverse side effects, reduce dosing frequency, and potentially improve patient compliance. This review covers strategies being employed to attain zero-order release or alter traditionally first-order release kinetics to achieve more consistent release before discussing opportunities for improving device performance based on emerging materials and fabrication methods.

Development and Application of a Modified Method to Determine the Encapsulation Efficiency of Proteins in Polymer Matrices

A modified method to determine protein encapsulation efficiency in polymer matrices has been developed and applied to two proteins and two polymers to demonstrate its wide range of applicability. This study was pursued due to the wide variation in reported protein encapsulation efficiency of polymer-based microcapsules, even when the protein, the polymer, and the microcapsule manufacturing method were consistent. Hemoglobin (Hb) and bovine serum albumin (BSA) were chosen as model proteins and ethylcellulose and poly(lactic-co-glycolic acid) (PLGA) as model polymers. The polymer of the microcapsule was dissolved in dichloromethane/ethanol or dichloromethane/ethyl acetate for ethylcellulose or PLGA microcapsules, respectively. Liberated proteins were simultaneously precipitated, pelleted by centrifugation, isolated by decanting the polymer solution, redissolved in 10% w/v sodium dodecyl sulfate in 0.8 N sodium hydroxide, and quantified using a modified Lowry assay. Blank microcapsules and exogenously added proteins demonstrated ≥ 93.8% recovery of proteins. The mean encapsulation efficiency of ethylcellulose or PLGA microcapsules was 52.4 or 76.9% for Hb and 86.4 or 74.7% for BSA, respectively. This demonstrates the effective use of centrifugation and the importance of an appropriate cosolvent system in the measure of encapsulation efficiency where one solvent dissolves the polymer while the other solvent quantitatively precipitates the liberated protein. It is evident that an alkaline solution of sodium dodecyl sulfate is efficient at quantitatively dissolving precipitated proteins. Remediation of problems observed with current methods and high reproducibility suggest that this modified method is generally applicable to the measure of protein encapsulation efficiency of polymer microcapsules.

Optimising Hydrogel Release Profiles for Viro-Immunotherapy Using Oncolytic Adenovirus Expressing IL-12 and GM-CSF with Immature Dendritic Cells

Sustained-release delivery systems, such as hydrogels, significantly improve cancer therapies by extending the treatment efficacy and avoiding excess wash-out. Combined virotherapy and immunotherapy (viro-immunotherapy) is naturally improved by these sustained-release systems, as it relies on the continual stimulation of the antitumour immune response. In this article, we consider a previously developed viro-immunotherapy treatment where oncolytic viruses that are genetically engineered to infect and lyse cancer cells are loaded onto hydrogels with immature dendritic cells (DCs). The time-dependent release of virus and immune cells results in a prolonged cancer cell killing from both the virus and activated immune cells. Although effective, a major challenge is optimising the release profile of the virus and immature DCs from the gel so as to obtain a minimum tumour size. Using a system of ordinary differential equations calibrated to experimental results, we undertake a novel numerical investigation of different gel-release profiles to determine the optimal release profile for this viro-immunotherapy. Using a data-calibrated mathematical model, we show that if the virus is released rapidly within the first few days and the DCs are released for two weeks, the tumour burden can be significantly decreased. We then find the true optimal gel-release kinetics using a genetic algorithm and suggest that complex profiles present unnecessary risk and that a simple linear-release model is optimal. In this work, insight is provided into a fundamental problem in the growing field of sustained-delivery systems using mathematical modelling and analysis.

Biodegradable polymers for modern vaccine development

Most traditional vaccines are composed either of a whole pathogen or its parts; these vaccines, however, are not always effective and can even be harmful. As such, additional agents known as adjuvants are necessary to increase vaccine safety and efficacy. This review summarizes the potential of biodegradable materials, including synthetic and natural polymers, for vaccine delivery. These materials are highly biocompatible and have minimal toxicity, and most biomaterial-based vaccines delivering antigens or adjuvants have been shown to improve immune response, compared to formulations consisting of the antigen alone. Therefore, these materials can be applied in modern vaccine development.

pH-Responsive Microencapsulation Systems for the Oral Delivery of Polyanhydride Nanoparticles

Multicompartmental polymer carriers, referred to as Polyanhydride-Releasing Oral MicroParticle Technology (PROMPT), were formed by a pH-triggered antisolvent precipitation technique. Polyanhydride nanoparticles were encapsulated into anionic pH-responsive microparticle gels, allowing for nanoparticle encapsulation in acidic conditions and subsequent release in neutral pH conditions. The effects of varying the nanoparticle composition and feed ratio on the encapsulation efficiency were evaluated. Nanoparticle encapsulation was confirmed by confocal microscopy and infrared spectroscopy. pH-triggered protein delivery from PROMPT was explored using ovalbumin (ova) as a model drug. PROMPT microgels released ova in a pH-controlled manner. Increasing the feed ratio of nanoparticles into the microgels increased the total amount of ova delivered, as well as decreased the observed burst release. The cytocompatibility of the polymer materials were assessed using cells representative of the GI tract. Overall, these results suggest that pH-dependent microencapsulation is a viable platform to achieve targeted intestinal delivery of polyanhydride nanoparticles and their payload(s).

Growth factor sequestration and enzyme-mediated release from genipin-crosslinked gelatin microspheres

Controlled release of growth factors allows the efficient, localized, and temporally-optimized delivery of bioactive molecules to potentiate natural physiological processes. This concept has been applied to treatments for pathological states, including chronic degeneration, wound healing, and tissue regeneration. Peptide microspheres are particularly suited for this application because of their low cost, ease of manufacture, and interaction with natural remodeling processes active during healing. The present study characterizes gelatin microspheres for the entrapment and delivery of growth factors, with a focus on tailored protein affinity, loading capacity, and degradation-mediated release. Genipin crosslinking in PBS and CHES buffers produced average microsphere sizes ranging from 15 to 30 microns with population distributions ranging from about 15 to 60 microns. Microsphere formulations were chosen based on properties important for controlled transient and spatial delivery, including size, consistency, and stability. The microsphere charge affinity was found to be dependent on gelatin type, with type A (GelA) carriers consistently having a lower negative charge than equivalent type B (GelB) carriers. A higher degree of crosslinking, representative of primary amine consumption, resulted in a greater negative net charge. Gelatin type was found to be the strongest determinant of degradation, with GelA carriers degrading at higher rates versus similarly crosslinked GelB carriers. Growth factor release was shown to depend upon microsphere degradation by proteolytic enzymes, while microspheres in inert buffers showed long-term retention of growth factors. These studies illuminate fabrication and processing parameters that can be used to control spatial and temporal release of growth factors from gelatin-based microspheres.

Polyelectrolyte pH-Responsive Protein-Containing Nanoparticles: The Physicochemical Supramolecular Approach

We report on the physicochemical properties and self-assembly behavior of novel efficient pH-sensitive nanocontainers based on the Food and Drug Administration-approved anionic polymer Eudragit L100-55 (poly(methacrylic acid-co-ethyl acrylate) 1:1) and nonionic surfactant Brij98. The features of the interaction between Eudragit L100-55 and Brij98 at different pH values and their optimal ratio for nanoparticle formation were studied using isothermal titration calorimetry. The influence of the polymer-to-surfactant ratio on the size and structure of particles was studied at different pH values using dynamic light scattering and small-angle X-ray scattering methods. It was shown that stable nanoparticles are formed at acidic pH at polymer-to-surfactant molar ratios from 1:43 to 1:139. Trypsin was successfully encapsulated into Eudragit-Brij98 nanoparticles as a model bioactive component. The loading efficiency was determined by labeling trypsin with radioactive iodine-125. Eudragit-Brij98 nanoparticles effectively protected trypsin against pepsin digestion. The results showed that trypsin encapsulated into novel pH-sensitive nanocontainers retained more than 50% of its activity after treatment with pepsin compared with nonencapsulated trypsin. The described concept will contribute both to understanding the principles of and designing next-generation nanocontainers.

Single-injection vaccines: Progress, challenges, and opportunities

Currently, vaccination is the most efficient and cost-effective medical treatment for infectious diseases; however, each year 10 million infants remain underimmunized due to current vaccination schedules that require multiple doses to be administered across months or years. These dosing regimens are especially challenging in the developing world where limited healthcare access poses a major logistical barrier to immunization. Over the past four decades, researchers have attempted to overcome this issue by developing single-administration vaccines based on controlled-release antigen delivery systems. These systems can be administered once, but release antigen over an extended period of time to elicit both primary and secondary immune responses resulting in antigen-specific immunological memory. Unfortunately, unlike controlled release systems for drugs, single-administration vaccines have yet to be commercialized due to poor antigen stability and difficulty in obtaining unconventional release kinetics. This review discusses the current state of single-administration vaccination, challenges delaying the development of these vaccines, and potential strategies for overcoming these challenges.

Fractals in tissue engineering: toward biomimetic cell-culture matrices, microsystems and microstructured implants

Tissue engineering is a rapidly evolving field in which the complexity of biomaterials and biostructures, with typically non-Euclidean or fractal-like geometries, has to be adequately taken into account for the promotion of enhanced and even personalized diagnostic and therapeutic solutions. This study covers the main applications of fractals in the field of tissue engineering, including their advantages for modeling biological processes and cell-culture procedures, but specially focusing on their benefits for describing the complex geometries and structures of biomaterials (both natural and synthetic), many of which have potential uses for the development of cell culture microsystems, scaffolds for tissue repair and implants for tissue repair in general. We also explore the main supporting design, simulation and manufacturing technologies, as well as the most remarkable difficulties and limitations linked to the generalized use of fractals in engineering design, and also detail some current solution proposals and future directions.

Nanocarriers for vascular delivery of antioxidants

Antioxidant enzymes (AOEs) catalase and superoxide dismutase (SOD) detoxify harmful reactive oxygen species, but the therapeutic utility of AOEs is hindered by inadequate delivery. AOE modification by poly-ethylene glycol (PEG) and encapsulation in PEG-coated liposomes increases the AOE bioavailability and enhances protective effects in animal models. Pluronic-based micelles formed with AOEs show even more potent protective effects. Furthermore, polymeric nanocarriers (PNCs) based on PEG-copolymers protect encapsulated AOEs from proteolysis and improve delivery to the target cells, such as the endothelium lining the vascular lumen. Antibodies to endothelial determinants conjugated to AOEs or AOE carriers provide targeting and intracellular delivery. Targeted liposomes, protein conjugates and magnetic nanoparticles deliver AOEs to sites of vascular oxidative stress in the cardiovascular, pulmonary and nervous systems. Further advances in nanodevices for AOE delivery will provide a basis for the translation of this approach in the clinical domain.

Polyanhydride microparticles enhance dendritic cell antigen presentation and activation

The present study was designed to evaluate the adjuvant activity of polyanhydride microparticles prepared in the absence of additional stabilizers, excipients or immune modulators. Microparticles composed of varying ratios of either 1,6-bis(p-carboxyphenoxy)hexane (CPH) and sebacic acid or 1,8-bis(p-carboxyphenoxy)-3,6-dioxaoctane and CPH were added to in vitro cultures of bone marrow-derived dendritic cells (DCs). Microparticles were efficiently and rapidly phagocytosed by DCs in the absence of opsonization and without centrifugation or agitation. Within 2h, internalized particles were rapidly localized to an acidic, phagolysosomal compartment. By 48 h, only a minor reduction in microparticle size was observed in the phagolysosomal compartment, indicating minimal particle erosion consistent with being localized within an intracellular microenvironment favoring particle stability. Polyanhydride microparticles increased DC surface expression of major histocompatability complex class II, the co-stimulatory molecules CD86 and CD40, and the C-type lectin CIRE (murine DC-SIGN; CD209). In addition, microparticle stimulation of DCs also enhanced secretion of the cytokines IL-12p40 and IL-6, a phenomenon found to be dependent on polymer chemistry. DCs cultured with polyanhydride microparticles and ovalbumin induced polymer chemistry-dependent antigen-specific proliferation of both CD4(+) OT-II and CD8(+) OT-I T cells. These data indicate that polyanhydride particles can be tailored to take advantage of the potential plasticity of the immune response, resulting in the ability to induce immune protection against many types of pathogens.

Drug delivery in soft tissue engineering

INTRODUCTION

Tissue defects, sustained through disease or trauma, present enormous challenges in regenerative medicine. Modern tissue engineering (TE) aims at replacing or repairing these defects through a combined approach of biodegradable scaffolds, suitable cell sources and appropriate environmental cues, such as biomolecules presented on scaffold surfaces or sustainably released from within.

AREAS COVERED

This review provides a brief overview of the various drugs and bioactive molecules of interest to TE, as well as a selection of materials that have been proposed for TE scaffolds and matrices in the past. It then proceeds to discuss encapsulation, immobilization and controlled release strategies for bioactive proteins, before discussing recent advances in this area with a special focus on soft TE.

EXPERT OPINION

Overall, minimal clinical success has been achieved so far in using growth factor, morphogen, or adhesion factor modified scaffolds and matrices; only one growth factor delivery system (Regranex Gel), has been approved by the FDA for clinical use, with only a handful of other growth factors being approved for human use so far. However, many more growth factors are currently in clinical Phase I - II or preclinical trials and many delivery systems utilize materials already approved by the FDA for other purposes. With respect to drug delivery in soft TE, a combination of increased research efforts in hydrogel and support material development as well as growth factor development is needed before clinical success is realized.

Polymer-based microparticles in tissue engineering and regenerative medicine

Different types of biomaterials, processed into different shapes, have been proposed as temporary support for cells in tissue engineering (TE) strategies. The manufacturing methods used in the production of particles in drug delivery strategies have been adapted for the development of microparticles in the fields of TE and regenerative medicine (RM). Microparticles have been applied as building blocks and matrices for the delivery of soluble factors, aiming for the construction of TE scaffolds, either by fusion giving rise to porous scaffolds or as injectable systems for in situ scaffold formation, avoiding complicated surgery procedures. More recently, organ printing strategies have been developed by the fusion of hydrogel particles with encapsulated cells, aiming the production of organs in in vitro conditions. Mesoscale self-assembly of hydrogel microblocks and the use of leachable particles in three-dimensional (3D) layer-by-layer (LbL) techniques have been suggested as well in recent works. Along with innovative applications, new perspectives are open for the use of these versatile structures, and different directions can still be followed to use all the potential that such systems can bring. This review focuses on polymeric microparticle processing techniques and overviews several examples and general concepts related to the use of these systems in TE and RE applications. The use of materials in the development of microparticles from research to clinical applications is also discussed.

Sonochemically born proteinaceous micro- and nanocapsules

The use of proteins as a substrate in the fabrication of micro- and nanoparticulate systems has attracted the interest of scientists, manufactures, and consumers. Albumin-derived particles were commercialized as contrast agents or anticancer therapeutics. Food proteins are widely used in formulated dietary products. The potential benefits of proteinaceous micro- and nanoparticles in a wide range of biomedical applications are indisputable. Protein-based particles are highly biocompatible and biodegradable structures that can impart bioadhesive properties or mediate particle uptake by specific interactions with the target cells. Currently, protein microparticles are engineered as vehicles for covalent attachment and/or encapsulation of bioactive compounds, contrast agents for magnetic resonance imaging, thermometric and oximetric imaging, sonography and optical coherence tomography, etc. Ultrasound irradiation is a versatile technique which is widely used in many and different fields as biology, biochemistry, dentistry, geography, geology, medicine, etc. It is generally recognized as an environmental friendly, cost-effective method which is easy to be scaled up. Currently, it is mainly applied for homogenization, drilling, cleaning, etc. in industry, as well for noninvasive scanning of the human body, treatment of muscle strains, dissolution of blood clots, and cancer therapy. Proteinaceous micro- and nanocapsules could be easily produced in a one-step process by applying ultrasound to an aqueous protein solution. The origin of this process is in the chemical changes, for example, sulfhydryl groups oxidation, that takes place as a result of acoustically generated cavitation. Partial denaturation of the protein most probably occurs which makes the hydrophobic interactions dominant and also responsible for the formation of stable capsules. This chapter aims to present the current state-of-the-art in the field of sonochemically produced protein micro- and nanocapsules, paying special attention to the proposed mechanisms for their formation, the factors that influence the capsules characteristics as well to the current applications of these particles. Current challenges in the field are also outlined as, for example, the ultrasound-protein interaction and other possible aspects of the mechanism of their formation.

Salicylic acid-derived poly(anhydride-ester) electrospun fibers designed for regenerating the peripheral nervous system

Continuous biomaterial advances and the regenerating potential of the adult human peripheral nervous system offer great promise for restoring full function to innervated tissue following traumatic injury via synthetic nerve guidance conduits (NGCs). To most effectively facilitate nerve regeneration, a tissue engineering scaffold within a conduit must be similar to the linear microenvironment of the healthy nerve. To mimic the native nerve structure, aligned poly(lactic-co-glycolic acid)/bioactive polyanhydride fibrous substrates were fabricated through optimized electrospinning parameters with diameters of 600 ± 200 nm. Scanning electron microscopy images show fibers with a high degree of alignment. Schwann cells and dissociated rat dorsal root ganglia demonstrated elongated and healthy proliferation in a direction parallel to orientated electrospun fibers with significantly longer Schwann cell process length and neurite outgrowth when compared to randomly orientated fibers. Results suggest that an aligned polyanhydride fiber mat holds tremendous promise as a supplement scaffold for the interior of a degradable polymer NGC. Bioactive salicylic acid-based polyanhydride fibers are not limited to nerve regeneration and offer exciting promise for a wide variety of biomedical applications.

Design of a protective single-dose intranasal nanoparticle-based vaccine platform for respiratory infectious diseases

Despite the successes provided by vaccination, many challenges still exist with respect to controlling new and re-emerging infectious diseases. Innovative vaccine platforms composed of adaptable adjuvants able to appropriately modulate immune responses, induce long-lived immunity in a single dose, and deliver immunogens in a safe and stable manner via multiple routes of administration are needed. This work describes the development of a novel biodegradable polyanhydride nanoparticle-based vaccine platform administered as a single intranasal dose that induced long-lived protective immunity against respiratory disease caused by Yesinia pestis, the causative agent of pneumonic plague. Relative to the responses induced by the recombinant protein F1-V alone and MPLA-adjuvanted F1-V, the nanoparticle-based vaccination regimen induced an immune response that was characterized by high titer and high avidity IgG1 anti-F1-V antibody that persisted for at least 23 weeks post-vaccination. After challenge, no Y. pestis were recovered from the lungs, livers, or spleens of mice vaccinated with the nanoparticle-based formulation and histopathological appearance of lung, liver, and splenic tissues from these mice post-vaccination was remarkably similar to uninfected control mice.

High loading of gentamicin in bioadhesive PVM/MA nanostructured microparticles using compressed carbon-dioxide

PURPOSE

To investigate, for the first time, the viability of compressed antisolvent methodologies for the preparation of drug-loaded particles of the biodegradable and bioadhesive polymer poly (methyl vinyl ether-co-maleic anhydride) (PVM/MA), utilizing gentamicin (Gm) as a model drug.

METHODS

Precipitation with a Compressed Antisolvent (PCA) method was used for the preparation of PVM/MA particles loaded with gentamicin. Before encapsulation, gentamicin was modified into a hydrophobic complex, GmAOT, by exchanging its sulphate ions with an anionic surfactant. GmAOT:PVM/MA composites were fully characterized in terms of size, morphology, composition, drug distribution, phase composition, in vitro activity and drug release.

RESULTS

Homogeneous nanostructured microparticles of PVM/MA loaded with high and uniformly distributed quantities of GmAOT were obtained by PCA. The drug loading factors could be tuned at will, improving up to ten times the loadings obtained by other precipitation techniques. Gentamicin retained its bioactivity after being processed, and, according to its release profiles, after an initial burst it experienced a sustained release over 30 days.

CONCLUSIONS

Compressed antisolvent methods are suitable technologies for the one-step preparation of highly loaded nanostructured PVM/MA matrices with promising application in the delivery of low bioavailable drugs.

Targeted Nanodelivery of Drugs and Diagnostics

Nanomaterials for targeted delivery are uniquely capable of localizing delivery of therapeutics and diagnostics to diseased tissues. The ability to achieve high, local concentrations of drugs or image contrast agents at a target site provides the opportunity for improved system performance and patient outcomes along with reduced systemic dosing. In this review, the design of targeted nanodelivery systems is discussed with an emphasis on in vivo performance, the physicochemical properties that affect localization at the target site, and the incorporation of therapeutic drugs into these systems.

Effect of polymer chemistry and fabrication method on protein release and stability from polyanhydride microspheres

The release kinetics and stability of ovalbumin encapsulated into polyanhydride microspheres with varying chemistries were studied. Polymers based on the anhydride monomers sebacic acid (SA), 1,6-bis(p-carboxyphenoxy)hexane (CPH), and 1,8-bis (p-carboxyphenoxy)-3,6-dioxaoctane (CPTEG) were utilized. Microspheres were fabricated using two non-aqueous methods: a solid/oil/oil double emulsion technique and cryogenic atomization. The studies showed that the two fabrication methods did not significantly affect the release kinetics of ovalbumin, even though the burst release of the protein was a function of the fabrication method and the polymer chemistry. Antigenic stability of ovalbumin released from microspheres prepared by cryogenic atomization was studied by western blot analysis. These studies indicate that the amphiphilic CPTEG:CPH polyanhydrides preserved protein structure and enhanced protein stability by preserving the immunological epitopes of released protein.

High throughput cell-based screening of biodegradable polyanhydride libraries

A parallel screening method has been developed to rapidly evaluate discrete library substrates of biomaterials using cell-based assays. The biomaterials used in these studies were surface-erodible polyanhydrides based on sebacic acid (SA), 1,6-bis(p-carboxyphenoxy)hexane (CPH), and 1,8-bis(p-carboxyphenoxy)-3,6-dioxaoctane (CPTEG) that have been previously studied as carriers for drugs, proteins, and vaccines. Linearly varying compositional libraries of 25 different polyanhydride random copolymers (based on CPH:SA and CPTEG:CPH) were designed, fabricated, and synthesized using discrete (organic solvent-resistant) multi-sample substrates created using a novel rapid prototyping method. The combinatorial libraries were characterized at high throughput using infrared microscopy and validated using 1H NMR and size exclusion chromatography. The discrete libraries were rapidly screened for biocompatibility using standard SP2/0 myeloma, CHO and L929 fibroblasts, and J774 macrophage cell lines. At a concentration of 2.8 mg/mL, there was no appreciable cytotoxic effect on any of the four cell lines evaluated by any of the CPH:SA or CPTEG:CPH compositions. Furthermore, the activation of J774 macrophages was evaluated by incubating the cells with the polyanhydride libraries and quantifying the secreted cytokines (IL-6, IL-10, IL-12, and TNFalpha). The results indicated that copolymer compositions containing at least 50% CPH induced elevated amounts of TNFalpha. In summary, the results indicated that the methodologies described herein are amenable to the high throughput analysis of synthesized biomaterials and will facilitate the rapid and rational design of materials for use in biomedical applications.

Vaccine adjuvants: current challenges and future approaches

For humans, companion animals, and food producing animals, vaccination has been touted as the most successful medical intervention for the prevention of disease in the twentieth century. However, vaccination is not without problems. With the development of new and less reactogenic vaccine antigens, which take advantage of molecular recombinant technologies, also comes the need for more effective adjuvants that will facilitate the induction of adaptive immune responses. Furthermore, current vaccine adjuvants are successful at generating humoral or antibody mediated protection but many diseases currently plaguing humans and animals, such as tuberculosis and malaria, require cell mediated immunity for adequate protection. A comprehensive discussion is presented of current vaccine adjuvants, their effects on the induction of immune responses, and vaccine adjuvants that have shown promise in recent literature.

Polymeric carriers: role of geometry in drug delivery

The unique properties of synthetic nanostructures promise a diverse set of applications as carriers for drug delivery, which are advantageous in terms of biocompatibility, pharmacokinetics, targeting and controlled drug release. Historically, more traditional drug delivery systems have focused on spherical carriers. However, there is a growing interest in pursuing non-spherical carriers, such as elongated or filamentous morphologies, now available due to novel formulation strategies. Unique physiochemical properties of these supramolecular structures offer distinct advantages as drug delivery systems. In particular, results of recent studies in cell cultures and lab animals indicate that rational design of carriers of a given geometry (size and shape) offers an unprecedented control of their longevity in circulation and targeting to selected cellular and subcellular locations. This article reviews drug delivery aspects of non-spherical drug delivery systems, including material selection and formulation, drug loading and release, biocompatibility, circulation behavior, targeting and subcellular addressing.

Polymer chemistry influences monocytic uptake of polyanhydride nanospheres

PURPOSE

To demonstrate that polyanhydride copolymer chemistry affects the uptake and intracellular compartmentalization of nanospheres by THP-1 human monocytic cells.

METHODS

Polyanhydride nanospheres were prepared by an anti-solvent nanoprecipitation technique. Morphology and particle diameter were confirmed via scanning election microscopy and quasi-elastic light scattering, respectively. The effects of varying polymer chemistry on nanosphere and fluorescently labeled protein uptake by THP-1 cells were monitored by laser scanning confocal microscopy.

RESULTS

Polyanhydride nanoparticles composed of poly(sebacic anhydride) (SA), and 20:80 and 50:50 copolymers of 1,6-bis-(p-carboxyphenoxy)hexane (CPH) anhydride and SA were fabricated with similar spherical morphology and particle diameter (200 to 800 nm). Exposure of the nanospheres to THP-1 monocytes showed that poly(SA) and 20:80 CPH:SA nanospheres were readily internalized whereas 50:50 CPH:SA nanospheres had limited uptake. The chemistries also differentially enhanced the uptake of a red fluorescent protein-labeled antigen.

CONCLUSIONS

Nanosphere and antigen uptake by monocytes can be directly correlated to the chemistry of the nanosphere. These results demonstrate the importance of choosing polyanhydride chemistries that facilitate enhanced interactions with antigen presenting cells that are necessary in the initiation of efficacious immune responses.

Influence of the vehicle on the properties and efficacy of microparticles containing amphotericin B

New microparticles containing amphotericin B (AMB) have been developed and manufactured by spray drying. To this end albumin, polylactic-co-glycolic acids (PLGA) and poly(sebacic anhydride) have been employed as drug carriers. The selection of the solvent used to disperse the drug and the vehicle before spray drying was critical on production yields and physical properties of the microparticles. Once particle size, morphology and dispersability in some aqueous media were shown to be acceptable for an intravenous administration, in vivo efficacy was evaluated and compared with the reference medicine Fungizone. Microparticles prepared with albumin, albumin heated at a high temperature, some kinds of PLGA or polyanhydride, as well as Fungizone, were tested in an experimental hamster model of infection with Leishmania infantum, by evaluating the evolution of parasitic burdens in spleen, liver and antibody responses. After the injection of three doses corresponding to 2 mg of AMB per kilogram each, diverse reactions were reported depending on the vehicle. The best dispersability, reduction of parasites and antibody response were achieved when the treatment was performed with AMB in albumin microspheres.

Poly(lactic-co-glycolic acid) nanospheres and microspheres for short- and long-term delivery of bioactive ciliary neurotrophic factor

Ciliary neurotrophic factor (CNTF) has been shown to be neuroprotective in the central nervous system (CNS). However, systemic administration and bolus injections have shown significant side effects and limited efficacy. Sustained, local delivery may lead to effective neuroprotection and avoid or limit adverse side effects, but sustained CNTF delivery has proven difficult to achieve and control. For controlled, sustained delivery, we investigated several processing variables in making poly(DL-lactic-co-glycolic acid) (PLGA) nano- and microspheres to optimize CNTF encapsulation and release. Nano- and microspheres were 314.9 +/- 24.9 nm and 11.69 +/- 8.16 microm in diameter, respectively. CNTF delivery from nanospheres was sustained over 14 days, and delivery from microspheres continued over more than 70 days. To assess protein bioactivity after encapsulation, neural stem cells (NSCs) were treated with CNTF released from nanospheres and compared to those treated with unencapsulated CNTF as a control. NSCs treated with CNTF expressed markers specific to mature cells, notably astrocytes; some increase in oligodendrocytic and neuronal marker expression was also observed. Significantly, cells treated with CNTF released by nanospheres exhibited a similar degree of differentiation when compared to those treated with control CNTF of equivalent concentration, showing that the process of protein encapsulation did not reduce its potency.

Liposomes/chitosan scaffold/human fibrin gel composite systems for delivering hydrophilic drugs--release behaviors of tirofiban in vitro

A new liposomes/chitosan scaffold/human fibrin gel composite system (LCSHFG), as a depot drug delivery system, was developed to deliver low-molecular weight hydrophilic drugs. An antithrombosis drug, Tirofiban, was used as a model drug. Human fibrin gels encapsulated Tirofiban loaded liposomes were formed within chitosan scaffolds to configure the LCSHFG. The in vitro release behaviors of Tirofiban from LCSHFG were studied by characterizing the constituents of LCSHFG. The results show that the release periods of Tirofiban from LCSHFG with 50 microm pores in the chitosan scaffolds are generally 20% or longer more than those with 200 microm pores. The following results were obtained for the system that comprised 50 microm pores. The release periods of Tirofiban from LCSHFG loaded with stearylamine (SA)-liposomes can sustain 20% longer and significantly less burst release (p < 0.01, n = 3) than with liposomes. The release profiles of Tirofiban from LCSHFG change markedly when 0.5 and 2.5% glutaraldehyde is used to cross-link the system. Additionally, for all liposomes, the release periods of Tirofiban from cross-linked LCSHFG with 2.5% glutaraldehyde are 40% or more longer time (e.g., 19 days) with significantly less burst release (p < 0.01, n = 3) than those of noncrosslinked LCSHFG. Notably, the bioactivity of released Tirofiban from LCSHFG that is crosslinked by 2.5% glutaraldehyde effectively inhibits adenosine diphosphate inducing platelet aggregation. The work also suggests that LCSHFG may have potential as a depot drug delivery system for low-molecular-weight hydrophilic drugs.

Sustained release microspheres of diclofenac sodium using PEGylated rosin derivatives

The PEGylated derivatives of rosin-PD-1 and PD-2 synthesized and characterized earlier (Nande et al., 2006) were investigated as potential materials for sustained release microsphere prepared by emulsion solvent evaporation method using diclofenac sodium (DCS) as model drug. All the microspheres exhibited smooth surfaces intercepted by pores; their sizes (d(90)) ranged between 11-24 microm. The entrapment efficiency (< 80%) of the microspheres increased proportionally with derivative concentration. Presence of solvent like isopropyl alcohol or dichloromethane rendered the microspheres with large sizes but with reduced drug entrapment. Microspheres with small size were obtained at an optimum viscosity of liquid paraffin; any change lead to increase in the particle size. Magnesium stearate was found to be most suitable detackifier in the present system. The drug release was directly related to the particle size--small sized microspheres released drug at a faster rate. The dissolution data complied with Higuchi equation while the mechanism of drug release was Fickian diffusion (n approximately 0.5). Controlled inhibition of edema, as tested by hind paw edema method, was observed for 10 h when the microspheres were administered intraperitoneally. The present study found the derivatives as promising materials for preparing microspheres for sustained delivery of DCS.

Controlled drug delivery in tissue engineering

The concept of tissue and cell guidance is rapidly evolving as more information regarding the effect of the microenvironment on cellular function and tissue morphogenesis become available. These disclosures have lead to a tremendous advancement in the design of a new generation of multifunctional biomaterials able to mimic the molecular regulatory characteristics and the three-dimensional architecture of the native extracellular matrix. Micro- and nano-structured scaffolds able to sequester and deliver in a highly specific manner biomolecular moieties have already been proved to be effective in bone repairing, in guiding functional angiogenesis and in controlling stem cell differentiation. Although these platforms represent a first attempt to mimic the complex temporal and spatial microenvironment presented in vivo, an increased symbiosis of material engineering, drug delivery technology and cell and molecular biology may ultimately lead to biomaterials that encode the necessary signals to guide and control developmental process in tissue- and organ-specific differentiation and morphogenesis.

The role of microsphere fabrication methods on the stability and release kinetics of ovalbumin encapsulated in polyanhydride microspheres

The effect of microsphere fabrication methods on the stability and release kinetics of ovalbumin encapsulated in polyanhydride microspheres was investigated. The polyanhydrides used were poly(sebacic anhydride) (poly(SA)) and a 20:80 random copolymer of poly[1,6-bis(p-carboxyphenoxy)hexane] (poly(CPH)) and poly(SA). Microspheres were fabricated using three double emulsion methods (water/oil/water, water/oil/oil and solid/oil/oil) and cryogenic atomization. The encapsulation efficiency was highest for cryogenic atomization and lowest when the w/o/w technique was used. Microspheres fabricated by the s/o/o method had the largest initial burst of released protein. All the methods resulted in zero-order release of the protein after the burst. The release of ovalbumin from poly(SA) and 20:80 (CPH:SA) microspheres lasted approximately 3 and approximately 6 weeks, respectively. For all fabrication methods the primary structure of released ovalbumin was conserved as determined by gel electrophoresis. The secondary structure of ovalbumin encapsulated in 20:80 (CPH:SA) w/o/w microspheres was not conserved.

Macromolecule Release from Monodisperse PLG Microspheres: Control of Release Rates and Investigation of Release Mechanism

Novel macromolecular therapeutics such as peptides, proteins, and DNA are advancing rapidly toward the clinic. Because of typically low oral bioavailability, macromolecule delivery requires invasive methods such as frequently repeated injections. Parenteral depots including biodegradable polymer microspheres offer the possibility of reduced dosing frequency but are limited by the inability to adequately control delivery rates. To control release and investigate release mechanisms, we have encapsulated model macromolecules in monodisperse poly(D,L-lactide-co-glycolide) (PLG) microspheres using a double-emulsion method in combination with the precision particle fabrication technique. We encapsulated fluorescein-dextran (F-Dex) and sulforhodamine B-labeled bovine serum albumin (R-BSA) into PLG microspheres of three different sizes: 31, 44, and 80 microm and 34, 47, and 85 microm diameter for F-Dex and R-BSA, respectively. The in vitro release profiles of both compounds showed negligible initial burst. During degradation and release, the microspheres hollowed and swelled at critical time points dependant upon microsphere size. The rate of these events increased with microsphere size resulting in the largest microspheres exhibiting the fastest overall release rate. Monodisperse microspheres may represent a new delivery system for therapeutic proteins and DNA and provide enhanced control of delivery rates using simple injectable depot formulations.