Factors of importance for a successful delivery system for proteins

Role of Polymer Concentration on the Release Rates of Proteins from Single- and Double-Network Hydrogels

Controlled delivery of proteins has immense potential for the treatment of various human diseases, but effective strategies for their delivery are required before this potential can be fully realized. Recent research has identified hydrogels as a promising option for the controlled delivery of therapeutic proteins, owing to their ability to respond to diverse chemical and biological stimuli, as well as their customizable properties that allow for desired delivery rates. This study utilized alginate and chitosan as model polymers to investigate the effects of hydrogel properties on protein release rates. The results demonstrated that polymer properties, concentration, and crosslinking density, as well as their responses to pH, can be tailored to regulate protein release rates. The study also revealed that hydrogels may be combined to create double-network hydrogels to provide an additional metric to control protein release rates. Furthermore, the hydrogel scaffolds were also found to preserve the long-term function and structure of encapsulated proteins before their release from the hydrogels. In conclusion, this research demonstrates the significance of integrating porosity and response to stimuli as orthogonal control parameters when designing hydrogel-based scaffolds for therapeutic protein release.

Protein encapsulation by electrospinning and electrospraying

Given the increasing interest in the use of peptide- and protein-based agents in therapeutic strategies, it is fundamental to develop delivery systems capable of preserving the biological activity of these molecules upon administration, and which can provide tuneable release profiles. Electrohydrodynamic (EHD) techniques, encompassing electrospinning and electrospraying, allow the generation of fibres and particles with high surface area-to-volume ratios, versatile architectures, and highly controllable release profiles. This review is focused on exploring the potential of different EHD methods (including blend, emulsion, and co-/multi-axial electrospinning and electrospraying) for the development of peptide and protein delivery systems. An overview of the principles of each technique is first presented, followed by a survey of the literature on the encapsulation of enzymes, growth factors, antibodies, hormones, and vaccine antigens using EHD approaches. The possibility for localised delivery using stimuli-responsive systems is also explored. Finally, the advantages and challenges with each EHD method are summarised, and the necessary steps for clinical translation and scaled-up production of electrospun and electrosprayed protein delivery systems are discussed.

Optimized Synthesis of Poly(deoxyribose) Isobutyrate, a Viscous Biomaterial for Bone Morphogenetic Protein-2 Delivery

Injectable and phase-transitioning carriers from natural polysaccharides have great potential for the minimally invasive delivery of therapeutic proteins in the field of bone tissue engineering. In this study, a novel and highly viscous drug carrier was synthesized by a sequential process of deoxyribose polycondensation and esterification. The effect of synthesis parameters on the molecular weight, viscosity, and adhesion of the material was studied and correlated to temperature and time of polycondensation ( T_p and t_p), time and temperature of esterification ( T_e and t_e), and the molar ratio of the monomer ( R). The formulations were evaluated for molecular weight and distribution properties using GPC, chemical structures by FTIR and NMR spectra, and rheological properties using a rheometer. Formulations illustrated a wide range of viscosities (0.736 to 2225 Pa s), adhesion (0.896 to 58.45 N), and molecular weights (637 to 4216 Da), where viscosity was significantly reduced in the presence of low amounts of solvents (10-20%). The sustained release of BSA was observed over 42 days in vitro. The biocompatibility of poly(deoxyribose) isobutyrate (PDIB) as well as its potential as a bone morphogenetic protein delivery system was assessed in vivo using a rat ectopic bone model, where bone nodules were observed at 2 weeks. In summary, PDIB is a promising molecule with multiple applications for protein delivery, including for bone tissue engineering.

Room Temperature Consolidation of a Porous Poly(lactic-co-glycolic acid) Matrix by the Addition of Maltose to the Water-in-Oil Emulsion

In composite materials made of polymer matrices and micro-nano dispersed compartments, the morphology of the dispersed phase can strongly affect several features of the final material, including stability, loading efficiency, and kinetic release of the embedded molecules. Such a polymer matrix composite can be obtained through the consolidation of the continuous polymer phase of a water-in-oil (W/O) emulsion. Here, we show that the morphology of the dispersed phase in a poly(lactic-co-glycolic acid, PLGA) matrix can be optimized by combining an effective mild temperature drying process with the addition of maltose as a densifying compound for the water phase of the emulsion. The influence of this addition on final stability and consequent optimal pore distribution was theoretically and experimentally confirmed. Samples were analyzed in terms of morphology on dried flat substrates and in terms of rheology and interfacial tension at the liquid state. While an increase of interfacial tension was found following the addition of maltose, the lower difference in density between the two emulsion phases coming from the addition of maltose allowed us to estimate a reduced creaming tendency confirmed by the experimental observations. Rheological measurements also confirmed an improved elastic behavior for the maltose-containing emulsion.

A method to tune the shape of protein-encapsulated polymeric microspheres

Protein encapsulation technologies of polymeric microspheres currently in use have been optimized to effectively protect their “protein cargo” from inactivation occurring in biological environments, preserving its bioactivity during release up to several weeks. The scenario of protein delivery would greatly benefit by strategies enabling the production of non-spherical particles. Herein we report an easy and effective stamp-based method to produce poly-lactic-glycolic-acid (PLGA) microparticles encapsulating Vascular Endothelial Growth Factor (VEGF) of different shapes. We demonstrate that PLGA microspheres can be deformed at room temperature exploiting solvent/non-solvent plasticization in order to preserve the properties of the starting microspheres. This gentle method allows the production of shaped particles that provide a prolonged release of VEGF in active form, as verified by an angiogenic assay. The retention of the biological activity of an extremely labile molecule, i.e. VEGF, lets us hypothesize that a wide variety of drug and protein encapsulated polymeric microspheres can be processed using this method.

Bioactive factor delivery strategies from engineered polymer hydrogels for therapeutic medicine

Polymer hydrogels have been widely explored as therapeutic delivery matrices because of their ability to present sustained, localized and controlled release of bioactive factors. Bioactive factor delivery from injectable biopolymer hydrogels provides a versatile approach to treat a wide variety of diseases, to direct cell function and to enhance tissue regeneration. The innovative development and modification of both natural-(e.g., alginate (ALG), chitosan, hyaluronic acid (HA), gelatin, heparin (HEP), etc.) and synthetic-(e.g., polyesters, polyethyleneimine (PEI), etc.) based polymers has resulted in a variety of approaches to design drug delivery hydrogel systems from which loaded therapeutics are released. This review presents the state-of-the-art in a wide range of hydrogels that are formed though self-assembly of polymers and peptides, chemical crosslinking, ionic crosslinking and biomolecule recognition. Hydrogel design for bioactive factor delivery is the focus of the first section. The second section then thoroughly discusses release strategies of payloads from hydrogels for therapeutic medicine, such as physical incorporation, covalent tethering, affinity interactions, on demand release and/or use of hybrid polymer scaffolds, with an emphasis on the last 5 years.

Design and processing of nanogels as delivery systems for peptides and proteins

Nanogels, cross-linked networks of >1 μm in size, are attractive drug-delivery systems, as they not only possess the potential advantages of nanoscale formulations, but also the attractive abilities of a hydrogel; high hydrophilicity, high loading capacity and the potential for biocompatibility and controlled release. The focus of this review is to provide an overview of the recent developments within the nanogel field, and how the chemical design of the nanogel polymer has been found to influence the properties of the nanogel system. Novel nanogel systems are discussed with respect to their type of cross-linkage and their suitability as therapeutic delivery systems, as well as their ability to stabilize the protein/peptide drug.

Effect of cryoprotectants on the porosity and stability of insulin-loaded PLGA nanoparticles after freeze-drying

PLGA nanoparticles are useful to protect and deliver proteins in a localized or targeted manner, with a long-term systemic delivery pattern intended to last for a period of time, depending on polymer bioerosion and biodegradability. However, the principal concern regarding these carriers is the hydrolytic instability of polymer in aqueous suspension. Freeze-drying is a commonly used method to stabilize nanoparticles, and cryoprotectants may be also used, to even increase its physical stability. The aim of the present work was to analyze the influence of cryoprotectants on nanoparticle stability and porosity after freeze-drying, which may influence protein release and stability. It was verified that freeze-drying significantly increased the number of pores on PLGA-NP surface, being more evident when cryoprotectants are added. The presence of pores is important in a lyophilizate to facilitate its reconstitution in water, although this may have consequences to protein release and stability. The release profile of insulin encapsulated into PLGA-NP showed an initial burst in the first 2 h and a sustained release up to 48 h. After nanoparticles freeze-drying the insulin release increased about 18% in the first 2 h due to the formation of pores, maintaining a sustained release during time. After freeze-drying with cryoprotectants, the amount of insulin released was higher for trehalose and lower for sucrose, glucose, fructose and sorbitol comparatively to freeze-dried PLGA-NP with no cryoprotectant added. Besides the porosity, the ability of cryoprotectants to be adsorbed on the nanoparticles surface may also play an important role on insulin release and stability.

Fuzzy Logic-based expert system for evaluating cake quality of freeze-dried formulations

Freeze-drying of peptide and protein-based pharmaceuticals is an increasingly important field of research. The diverse nature of these compounds, limited understanding of excipient functionality, and difficult-to-analyze quality attributes together with the increasing importance of the biosimilarity concept complicate the development phase of safe and cost-effective drug products. To streamline the development phase and to make high-throughput formulation screening possible, efficient solutions for analyzing critical quality attributes such as cake quality with minimal material consumption are needed. The aim of this study was to develop a fuzzy logic system based on image analysis (IA) for analyzing cake quality. Freeze-dried samples with different visual quality attributes were prepared in well plates. Imaging solutions together with image analytical routines were developed for extracting critical visual features such as the degree of cake collapse, glassiness, and color uniformity. On the basis of the IA outputs, a fuzzy logic system for analysis of these freeze-dried cakes was constructed. After this development phase, the system was tested with a new screening well plate. The developed fuzzy logic-based system was found to give comparable quality scores with visual evaluation, making high-throughput classification of cake quality possible.

Delivering bioactive molecules as instructive cues to engineered tissues

INTRODUCTION

Growth factors and other bioactive molecules play a crucial role in the creation of functional engineered tissues from dissociated cells.

AREAS COVERED

This review discusses the delivery of bioactive molecules - particularly growth factors - to affect cellular function in the context of tissue engineering. We discuss the primary biological themes that are addressed by delivering bioactives, the types of molecules that are to be delivered, the major materials used in producing scaffolds and/or drug delivery systems, and the principal drug delivery strategies.

EXPERT OPINION

Drug delivery systems have allowed the sustained release of bioactive molecules to engineered tissues, with marked effects on tissue function. Sophisticated drug delivery techniques will allow precise recapitulation of developmental milestones by providing temporally distinct patterns of release of multiple bioactives. High-resolution patterning techniques will allow tissue constructs to be designed with precisely defined areas where bioactives can act. New biological discoveries, just as the development of small molecules with potent effects on cell differentiation, will likely have a marked impact on the field.

Calcium alginate/dextran methacrylate IPN beads as protecting carriers for protein delivery

In the present study, mechanical and protein delivery properties of a system based on the interpenetration of calcium-alginate (Ca-Alg) and dextran-methacrylate (Dex-MA) networks are shown. Interpenetrated hydrogels beads were prepared by means of the alginate chains crosslinking with calcium ions, followed by the exposure to UV light that allows the Dex-MA network formation. Optical microscope analysis showed an average diameter of the IPN beads (Ca-Alg/Dex-MA) of 2 mm. This dimension was smaller than that of Ca-Alg beads because of the Dex-MA presence. Moreover, the strength of the IPN beads, and of their corresponding hydrogels, was influenced by the Dex-MA concentration and the crosslinking time. Model proteins (BSA and HRP) were successfully entrapped into the beads and released at a controlled rate, modulated by changing the Dex-MA concentration. The enzymatic activity of HRP released from the beads was maintained. These novel IPN beads have great potential as protein delivery system.

Supercritical fluid assisted atomization introduced by an enhanced mixer for micronization of lysozyme: Particle morphology, size and protein stability

Supercritical fluid assisted atomization introduced by hydrodynamic cavitation mixer (SAA-HCM) was used to produce lysozyme microparticles with controlled particle size distribution in the range for aerosol drug delivery. The process is based on the atomization effect of carbon dioxide. The solubilization of certain amount of carbon dioxide in the solution plays the key role and the HCM can intensify mass transfer between carbon dioxide and liquid feedstock greatly. Water was used as the solvent to solubilize lysozyme and thus no organic residual was detected. The influences of process parameters on particle formation were investigated including temperature in the precipitator, pressure and temperature in the mixer, concentration of the solution and feed ratio CO(2)/solution. The particles were characterized with respect to their morphologies and particle size: well defined, spherical and separated particles with diameters ranging between 0.2 and 5μm could be always produced at optimum operating conditions. Bio-activity assay showed that good activity maintenance of higher than 85% for lysozyme was usually achieved. Solid state characterizations were further performed to investigate the changes of lysozyme in the process. Fourier transform infrared spectroscopy indicated that no change in secondary structure had occurred for processed lysozyme. X-ray diffraction analysis showed that the lysozyme particles produced remained similarly amorphous as the raw material. Differential scanning calorimetry and thermogravimetry analysis revealed that there was no significant difference in water association but with the increase of water content after processing.

Transdermal delivery of proteins

Transdermal delivery of peptides and proteins avoids the disadvantages associated with the invasive parenteral route of administration and other alternative routes such as the pulmonary and nasal routes. Since proteins have a large size and are hydrophilic in nature, they cannot permeate passively across the skin due to the stratum corneum which allows the transport of only small lipophilic drug molecules. Enhancement techniques such as chemical enhancers, iontophoresis, microneedles, electroporation, sonophoresis, thermal ablation, laser ablation, radiofrequency ablation and noninvasive jet injectors aid in the delivery of proteins by overcoming the skin barrier in different ways. In this review, these enhancement techniques that can enable the transdermal delivery of proteins are discussed, including a discussion of mechanisms, sterility requirements, and commercial development of products. Combination of enhancement techniques may result in a synergistic effect allowing increased protein delivery and these are also discussed.

Research Spotlight: Nanomedicines for delivery of therapeutic proteins and biopharmaceuticals

Biopharmaceuticals are a class of therapeutics including recombinant therapeutic proteins, engineered antibodies and genetic material. They are attractive from a medical point of view, but technologically they face major challenges. The delivery of biopharmaceuticals still prevents them from reaching their maximum pharmacodynamic potential, owing to their physicochemical properties, poor stability, permeability and biodistribution. In our research group we have been involved with inter-related projects that intend to optimize strategies to improve the bioavailability of biopharmaceutical drugs after administration. One of the most employed drugs has been insulin, the oldest therapeutic protein, as well as siRNA and gene silencing genetic material. We are interested in formulating such drugs in polymeric nanoparticles, because they encompass an array of advantages compared with classical dosage forms. We also look for tools to correlate in vitro and in vivo absorption rates of biopharmaceuticals, in a rational chronologic sequence of manufacturing parameters, preclinical assessments and requirements for marketing approval.

Binding mode of Thioflavin T and other molecular probes in the context of amyloid fibrils-current status

Because understanding amyloid fibrillation in molecular detail is essential for development of strategies to control amyloid formation and overcome neurodegenerative disorders, increased understanding of present molecular probes as well as development of new probes are of utmost importance. To date, the binding modes of these molecular probes to amyloid fibrils are by no means adequately described or understood, and the large number of studies on Thioflavin T (ThT) and Congo Red (CR) binding have resulted in models that are incomplete and conflicting. Different types of binding sites are likely to be present in amyloid fibrils with differences in binding modes. ThT may bind in channels running parallel to the long axis of the fibril. In the channels, ThT may bind in either a monomeric or dimeric form of which the molecular conformation is likely to be planar. CR may bind in grooves formed along the β-sheets as a planar molecule in either a monomeric or supramolecular form.

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.

On the design of in situ forming biodegradable parenteral depot systems based on insulin loaded dialkylaminoalkyl-amine-poly(vinyl alcohol)-g-poly(lactide-co-glycolide) nanoparticles

The feasibility to generate in situ forming parenteral depot systems from insulin loaded dialkylaminoalkyl-amine-poly(vinyl alcohol)-g-poly(lactide-co-glycolide) nanoparticles, was investigated. Biodegradable nanoparticles formed polymeric semi-solid depots upon injection into isotonic phosphate buffered saline (PBS) with no additional initiators. Nanoparticles (NP) prepared from the different amine-modified polyesters displayed a pronounced positive zeta-potential of >25 mV. Diethylaminopropyl-amine-poly(vinyl alcohol)-g-poly(lactide-co-glycolide) (DEAPA(68)-PVAL-g-PLGA(1:20)), diethylaminoethyl-amine-poly(vinyl alcohol)-g-poly(lactide-co-glycolide) (DEAEA(33)-PVAL-g-PLGA(1:20)), and dimethylaminopropyl-amine-poly(vinyl alcohol)-g-poly(lactide-co-glycolide) (DMAPA(33)-PVAL-g-PLGA(1:20)), formed in situ depots by an ion-mediated aggregation with subsequent fusion of nanoparticles, related to a decreased glass transition temperature in the presence of PBS. Moreover, two factors, namely, polymer and insulin-nanocomplex concentration, were evaluated using a response surface design with respect to nanoparticles formation and insulin loading. Nanoparticles and implants were investigated by atomic force microscopy (AFM). The in vitro release from implants loaded with 2% insulin was carried out in a flow trough cell and quantified by high performance liquid chromatography (HPLC). The release showed a triphasic profile with an initial burst, pore diffusion and diffusion from the swollen matrix over more than two weeks. Insulin distribution in the implants during the release was followed by confocal laser scanning microscopy (CLSM). These findings combined with the protection of the model peptide against competitive macromolecules and the possibility to get dry powders by lyophilization make these nanoparticles-based depots suitable candidates for the design of controlled release devices for bioactive macromolecules.