BSA Release Research Articles

In vitro degradation and protein release of semi‐IPN hydrogels consisted of poly(acrylic acid‐acrylamide‐methacrylate) and amylose

AbstractThe enzymatic degradation mechanism of semi‐interpenetrating network (semi‐IPN) hydrogel of poly (acrylic acid‐acrylamide‐methacrylate) crosslinked by azocompound and amylose in vitro was investigated in the presence of Fungamyl 800L (α‐amylase) and rat cecum content (cecum bacteria). The degradation mechanism involves degradable competition, i.e., reduction of azo crosslinkage is dominant in the earlier period of degradation. Subsequently, the degradation of gels is continued by combination of reduction of azo crosslinkage and hydrolysis of amylose. The cumulative release ratios of Bovine serum albumin (BSA, as a model drug) loaded semi‐IPN gels are 25% in pH 2.2 buffer solutions and 74% in pH 7.4 buffer solutions within 48 h. Moreover, the release behavior of BSA from the semi‐IPN gels indicates that it follows Fickian diffusion mechanism in pH 2.2 media and non‐Fickian diffusion and polymer chains relaxation mechanism in pH 7.4 media. The results indicate that the release of BSA from the semi‐IPN gels was controlled via a combined mechanism of pH dependent swelling and specificity to enzymatic degradation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

In Vitro and in Vivo Release of Albumin Using a Biodegradable MPEG-PCL Diblock Copolymer as an in Situ Gel-Forming Carrier

An MPEG-PCL diblock copolymer was synthesized as an in situ gel carrier, and its phase transition behavior in aqueous solutions was examined. For comparison, aqueous solutions of Pluronic F-127, a widely used injectable gel-forming solution, were also studied. Both MPEG-PCL copolymer and Pluronic aqueous solutions were sols at room temperature. As the temperature was increased above room temperature, the diblock copolymer and Pluronic solutions underwent a sol-to-gel phase transition, which manifested as an increase in viscosity indicative of the formation of a gel. All of the copolymer solutions became gels at body temperature, although the gel viscosity increased with the increasing concentration of the MPEG-PCL diblock copolymer in the solution. In in vitro experiments, in which the gels were exposed to PBS, the MPEG-PCL gels maintained their structural integrity for more than 28 days, whereas the Pluronic gel disappeared within 2 days. The same results were observed when the polymer solutions were subcutaneously injected into rats. The MPEG-PCL gels maintained their structural integrity longer than 30 days, while the Pluronic gel could not be observed after 2 days. The ability of the gels as drug carriers was studied by measuring the release of fluorescein isothiocyanate-labeled bovine serum albumin (BSA-FITC) from MPEG-PCL diblock copolymer gels in vitro as well as in vivo. In vitro, BSA release was sustained above 20 days, with a greater release at lower diblock copolymer concentration; by contrast, Pluronic gels exhibited almost complete release of BSA-FITC within 1 day. When the BSA-FITC-loaded diblock copolymer and Pluronic solutions were subcutaneously injected into rats, they immediately transformed into a gel. In vivo, sustained release of BSA-FITC over 30 days was observed from the MPEG-PCL gel, whereas BSA-FITC release from the Pluronic gel ceased within 3 days. Collectively, the present findings show that MPEG-PCL diblock copolymer solutions are thermo-responsive and maintain their structural integrity under physiological conditions, indicating that they are suitable for use as injectable drug carriers.

Long acting porous microparticle for pulmonary protein delivery

This study investigated the porous-microparticle (PM) with low mass density and large size for pulmonary drug delivery. PM was prepared by the water-in-oil-in-water (W(1)/O/W(2)) multi-emulsion method with cyclodextrin derivative as a porogen and a stabilizer of peptide drugs. Herein, sucrose ethyl acetate (SAIB) was incorporated in PM for long acting protein release. In vitro release studies, the rapid release rate of proteins from PM was reduced due to the high viscosity of the added SAIB. As a result, BSA release from PM continued up to 7 days. This result suggests that PM having sustained release characteristics may be successfully applied for long-term pulmonary administration of protein or peptide drug. In addition, it is expected that these particles arrive at a deep lung epithelium due to low density (high porosity) and limit macrophage recognition because of big particle size (more than 5 microm).

Encapsulation of proteins in biodegradable polymeric microparticles using electrospray in the Taylor cone‐jet mode

Solvent extraction (or evaporation from a W(1)/O/W(2)-dispersion), coacervation, and spray drying methods are commonly employed to encapsulate protein drugs in polymeric microparticles for sustained delivery applications. To overcome the limitations of these methods, a novel electrospray method was developed to encapsulate a model protein drug-bovine serum albumin (BSA) in biodegradable polymeric microparticles and examine the feasibility of the process in not denaturing the protein. Microparticles of approximately 20 microm diameter with corrugated surfaces and smooth surfaces were observed by scanning electron microscope. Confocal laser scanning microscope images showed that BSA was distributed evenly in microparticles. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was employed to investigate the protein integrity of BSA released from the polymer matrix after 38 days. No protein degradation was observed during the 38 days release. The secondary structure of released BSA was characterized by Fourier transform infrared (FTIR) and circular dichroism (CD), which suggested that the released BSA was almost identical to native BSA. The encapsulation efficiency could reach 76% by adjusting the amount of the additive Pluronic F127 and processing parameters. The release profile could be tailored by the fabrication process and the sustained release of BSA could endure for more than 1 month. More than 80% of the bioactivity of BSA (evaluated by BSA ELISA kit) could be maintained after releasing from polymer matrix. Findings of the present study demonstrate that this novel electrospray method is a promising approach to encapsulate bioactive materials such as proteins, enzymes, antibiotics, and DNA fragments in biodegradable polymeric particles.

Production of BSA-loaded alginate microcapsules: Influence of spray dryer parameters on the microcapsule characteristics and BSA release

The aim of this study was to optimize the production of BSA-loaded alginate microcapsules by spray drying and to study the release of bovine serum albumin fraction V (BSA) under gastric simulated conditions. Microcapsule yield, BSA release, microcapsule size and size distribution were characterized following the application of different production parameters including inlet air temperature, inlet air pressure and liquid feed rate. The microcapsules were incubated in 0.1 N HCl and BSA release was quantified over time. The yields were higher with the pressure of 3 bar compared to 4 bar and with a feed rate of 0.45 vs. 0.2 ml s−1. A high feed rate (0.45 vs. 0.2 ml s−1) allows one to obtain microcapsules with a low BSA release (p = 0.0327). The increase of the atomizer inlet temperature leads to microcapsules with a higher BSA release (p = 0.0230). A higher air pressure of 4 bar compared to 3 bar resulted in a lower microcapsule size (2.55 vs. 2.80 µm) and led to a narrower size distribution (0.92 vs. 1.07). In conclusion, the spray dryer parameters influenced the alginate microcapsule characteristics as well as subsequent protein release into a simulated gastric medium.

Production of BSA-loaded alginate microcapsules: Influence of spray dryer parameters on the microcapsule characteristics and BSA release

The aim of this study was to optimize the production of BSA-loaded alginate microcapsules by spray drying and to study the release of bovine serum albumin fraction V (BSA) under gastric simulated conditions. Microcapsule yield, BSA release, microcapsule size and size distribution were characterized following the application of different production parameters including inlet air temperature, inlet air pressure and liquid feed rate. The microcapsules were incubated in 0.1 N HCl and BSA release was quantified over time. The yields were higher with the pressure of 3 bar compared to 4 bar and with a feed rate of 0.45 vs. 0.2 ml s−1. A high feed rate (0.45 vs. 0.2 ml s−1) allows one to obtain microcapsules with a low BSA release (p = 0.0327). The increase of the atomizer inlet temperature leads to microcapsules with a higher BSA release (p = 0.0230). A higher air pressure of 4 bar compared to 3 bar resulted in a lower microcapsule size (2.55 vs. 2.80 µm) and led to a narrower size distribution (0.92 vs. 1.07). In conclusion, the spray dryer parameters influenced the alginate microcapsule characteristics as well as subsequent protein release into a simulated gastric medium.

Modulation of protein delivery from modular polymer scaffolds

Growth factors are increasingly employed to promote tissue regeneration with various biomaterial scaffolds. In vitro release kinetics of protein growth factors from tissue engineering scaffolds are often investigated in aqueous environment, which is significantly different from in vivo environment. This study investigates the release of model proteins with net-positive (histone) and net-negative charge (bovine serum albumin, BSA) from various scaffolding surfaces and from encapsulated microspheres in the presence of ions, proteins, and cells. The release kinetics of proteins in media with varying concentrations of ions (NaCl) suggests stronger electrostatic interaction between the positively charged histone with the negatively charged substrates. While both proteins released slowly from hydrophobic PCL surfaces, plasma etching resulted in rapid release of BSA, but not histone. Interestingly, although negatively charged BSA released readily from negatively charged collagen (col), BSA released slowly from col-coated PCL scaffolds. Such electrostatic interaction effects were abolished in the presence of serum proteins and cells as evidenced by the rapid release of proteins from col-coated scaffolds. To achieve sustained release in the complex environment of serum proteins and cells, the model proteins were encapsulated into poly( d, l-lactic- co-glycolic acid) (PLGA) microspheres, which were embedded within col-coated PCL scaffolds. Protein release from microspheres was modulated by changing the lactide-to-glycolide ratio of PLGA polymer. BSA adsorbed to col released faster than histone encapsulated in microspheres in the presence of serum and cells. Collectively, the data suggest that growth factor release is highly influenced by scaffold surface and the presence of ions, proteins, and cells in the media. Strategies to deliver multiple growth factors and studies which investigate their release should consider these important variables.

Calcium‐carboxymethyl chitosan hydrogel beads for protein drug delivery system

AbstractIn this study, carboxymethyl chitosan (CMC) hydrogel beads were prepared by crosslinking with Ca2+. The pH‐sensitive characteristics of the beads were investigated by simulating gastrointestinal pH conditions. As a potential protein drug delivery system, the beads were loaded with a model protein (bovine serum albumin, BSA). To improve the entrapment efficiency of BSA, the beads were further coated with a chitosan/CMC polyelectrolyte complex (PEC) membrane by extruding a CMC/BSA solution into a CaCl2/chitosan gelation medium. Finally, the release studies of BSA‐loaded beads were conducted. We found that, the maximum swelling ratios of the beads at pH 7.4 (17–21) were much higher than those at pH 1.2 (2–2.5). Higher entrapment efficiency (73.2%) was achieved in the chitosan‐coated calcium‐CMC beads, compared with that (44.4%) in the bare calcium‐CMC beads. The PEC membrane limited the BSA release, while the final disintegration of beads at pH 7.4 still leaded to a full BSA release. Therefore, the chitosan‐coated calcium‐CMC hydrogel beads with higher entrapment efficiency and proper protein release properties were a promising protein drug carrier for the site‐specific release in the intestine. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3164–3168, 2007

Evaluation and modification of N-trimethyl chitosan chloride nanoparticles as protein carriers

N-Trimethyl chitosan chloride (TMC) nanoparticles were prepared by ionic crosslinking of TMC with tripolyphosphate (TPP). Two model proteins with different p I value s, bovine serum albumin (BSA, p I = 4.8) and bovine hemoglobin (BHb, p I = 6.8), were used to investigate the loading and release features of the TMC nanoparticles. TMC samples with different degrees of quaternization were synthesized to evaluate its influence on the physicochemical properties and release profiles of the nanoparticles. Sodium alginate was used to modify the TMC nanoparticles to reduce burst release. The results indicated that the TMC nanoparticles had a high loading efficiency (95%) for BSA but a low one (30%) for BHb. The particle size and zeta potential were significantly affected by the BSA concentration but not by the BHb concentration. Nanoparticles of TMC with a lower degree of quaternization showed an increase in particle size, a decrease in zeta potential and a slower drug-release profile. As for the alginate-modified nanoparticles, a smaller size and lower zeta potential were observed and the burst release of BSA was reduced. These studies demonstrated that TMC nanoparticles are potential protein carriers, and that their physicochemical properties and release profile could be optimized by means of various modifications.

Synthesis and characterizations of amphiphilic poly( l-lactide)-grafted chondroitin sulfate copolymer and its application as drug carrier

In this investigation, new biodegradable brush-like amphiphilic copolymers were synthesized by ring opening polymerization. Poly( l-lactide) (PLLA) was grafted onto chondroitin sulfate (CS), which is one of the physiologically significant specific glycosaminoglycans (GAGs), using a tin octanoate [Sn(Oct) 2] catalyst in DMSO. The hydroxyl groups of the chondroitin sulfate were used as initiating groups. These functional groups enable specific mucoadhesion or receptor recognition. The degree of substitution (DS), the degree of polymerization (DP) and the chondroitin sulfate content (from 1.1 to 15.4%) were analyzed by 1H NMR. The characteristics of these grafted copolymers, including the structure, the thermal properties and biodegradability, etc., were examined with respect to CS content. Meanwhile, the amphiphilic core (PLLA)–corona (CS) nanoparticles, with size smaller than 200 nm, was examined by dynamic light scattering (DLS). Zeta potential analysis exhibited the value in the range −18.3 to −49.4 mV. The morphologies of the nanoparticles were observed by field-emission scanning electron microscopy (FE-SEM). The nanoparticles with lower cytotoxicity were examined by MTT assay. Furthermore, the in vitro BSA release kinetics of those CS n –PLLA nanoparticles was also determined in this study.

Synthesis, characterization of biodegradable dextran–allyl isocyanate–ethylamine/polyethylene glycol–diacrylate hydrogels and their in vitro release of albumin

Based on dextran–allyl isocyanate–ethylamine (Dex-AE) and polyethylene glycol–diacrylate (PEGDA), a pH sensitive biodegradable hydrogel with improved protein release was prepared through UV photo-crosslinking. The Dex-AE precursor was prepared through a two-step chemical modification and characterized by FT-IR and 1H NMR. The effects of reaction conditions on the synthesis of Dex-AE were studied. The interior morphology data by scanning electron microscopy (SEM) revealed that an increase in Dex-AE content led to an initial decrease in pore size of the microstructure of the Dex-AE/PEGDA hydrogels, but a further increase in Dex-AE content resulted in a relatively looser network structure. The swelling data indicated that the swelling ratio depended on the precursor feed ratio and was correlated to the morphology of the microporous network structure. The pH sensitive property of the Dex-AE/PEGDA hydrogels was studied in different pH buffer solutions and was found that these hydrogels were pH sensitive due to the presence of ample pendant amino groups. The ionic strength data demonstrated that the Dex-AE/PEGDA hydrogels exhibit the highest swelling ratio in pure water, but the swelling ratio became lower as the ionic strength of the media increased. The in vitro albumin release from these hydrogels was examined in different pH (3.0, 7.4) buffer solutions. Both the protein loading and release data indicated that the Dex-AE/PEGDA hydrogels had more protein loading and sustained release capability than pure PEGDA hydrogel, and this ability increased as the Dex-AE composition increased; the Dex-AE/PEGDA hydrogel also showed a faster BSA release in a lower pH than a higher pH medium.

A novel method for the preparation of biodegradable microspheres for protein drug delivery

Microspheres are potential candidates for the protein drug delivery. In this work, we prepared polymer-coated starch/bovine serum albumin (BSA) microspheres using co-axial electrohydrodynamic atomization (CEHDA). First, starch solution in dimethyl sulphoxide (DMSO) was prepared and then an aqueous solution of BSA was added to it to make a starch-BSA solution. Subsequently, this solution was made to flow through the inner capillary, while the polymer, polydimethylsiloxane (PDMS), flowed through the outer capillary. On collection, filtration and subsequent drying, near-monodisperse microspheres of 5-6microm in size were obtained. The microspheres were characterized by Fourier-transform infrared (FT-IR) spectroscopy and scanning electron microscopy. Cumulative BSA release was investigated by UV spectroscopy. BSA structure and activity was preserved in the microspheres and its release in 0.01M phosphate buffered saline (PBS) was studied over a period of 8 days. There was an initial burst with 32wt% of total BSA released in 2h. Overall 75wt% of BSA was released over a 7 day period.

Controlled release of bovine serum albumin using MPEG–PCL diblock copolymers as implantable protein carriers

MPEG–PCL diblock copolymers consisting of methoxy polyethylene glycol (MPEG) and poly(ϵ-caprolactone) (PCL) as drug carriers were synthesized by ring-opening polymerization. It is possible to control the balance between hydrophilic and hydrophobic by changing the MPEG and the ratio of ϵ-CL to MPEG. Implantable wafers were easily fabricated by the direct compression method after physical mixing of diblock copolymers and bovine serum albumin–fluorescein isothiocyanate (BSA-FITC) as a model protein drug. The BSA release from wafers prepared by MPEG–PCL diblock copolymers were higher than that from PCL with the physical blending of MPEG. The wafers prepared by a variety of MPEG–PCL diblock copolymers exhibited the controlled BSA release profiles with a dependence on MPEG–PCL diblock copolymer compositions. In addition, the changing of MPEG and PCL molecular weights within MPEG–PCL diblock copolymer controlled the initial burst of BSA. We confirmed that the diblock copolymers could be served as protein delivery carrier in implantable wafer form. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:1561–1567, 2006

Light-Triggered Association of Bovine Serum Albumin and Azobenzene-Modified Poly(acrylic acid) in Dilute and Semidilute Solutions

Reversible photoswitch of viscosity and photoresponsive binding of protein has been achieved in water solution of azobenzene-modified polyacrylate. We synthesized polymers with a few mol % hydrophobic side groups, including azobenzene groups with different spacers between the photochrome and the backbone. The binding of the protein (BSA) onto the polymers was investigated by capillary electrophoresis in dilute solution and rheology (viscosity, dynamic moduli, and stress relaxation) in semidilute solution of polymer. In the dilute regime, BSA/polymer complexes are formed in equilibrium with unbound BSA. Both the length of the hydrophobic spacer on the azobenzene side group and the presence of additional n-alkyl side groups significantly affect the affinity of BSA for the polymer. In the semidilute regime, viscosity enhancement by several decades is obtained upon addition of BSA in polymer solutions and ascribed to physical cross-linking involving BSA. In the two regimes, light was shown to modify the binding properties. Reversible release of BSA (by up to 80% of the protein) was obtained by exposure to UV. Reversible viscosity swings by up to 40-fold were cycled for hours by alternative exposure to UV/vis light. Light-induced cis−trans isomerization of the azobenzene together with low concentration of photochrome in the samples made it possible to obtain rapid responses (half-time ∼20 s) in solutions or in gels having thickness of the order of centimeters. An unprecedented degree of sensitivity is achieved thanks to the amplification provided by properties of optimal modified polymers. These properties are analyzed in term of the response of cross-links density, chain dynamics, and binding affinity.

Sustained release of bovine serum albumin using implantable wafers prepared by MPEG–PLGA diblock copolymers

MPEG–PLGA diblock copolymers, consisting of methoxy polyethylene glycol (MPEG) and poly( l-lactic- co-glycolic acid) (PLGA), were synthesized by ring-opening polymerization of l-lactide and glycolide in the presence of MPEG as an initiator. Implantable wafers, using diblock copolymers as a drug carrier, were fabricated by direct compression method after freeze milling of the diblock copolymers and bovine serum albumin–fluorescein isothiocyanate (BSA–FITC) as a model protein drug. The wafers prepared with MPEG–PLGA diblock copolymers exhibited initial burst in the release of BSA. The BSA release profiles from the wafers depended on MPEG–PLGA diblock copolymer compositions. The in vitro release of the BSA also correlated with the degradation rate of the PLGA part in the diblock polymers. The wafers prepared from diblock copolymers with an increased MPEG segment showed the more structural metamorphosis of crack form due to higher water absorption of MPEG inside the wafer, and induced faster BSA release. The wafers prepared by using MPEG–PLGA diblock copolymers in the presence of small intestinal submucosa (SIS) as a drug carrier additive exhibited controlled BSA release profiles, although the wafers exhibited release patterns with a lag time at the initial stage as the MPEG segment in diblock copolymer compositions increased. Thus, we confirmed that the MPEG–PLGA diblock copolymers could be used as a protein delivery carrier in implantable wafer form.

Optimizing double emulsion process to decrease the burst release of protein from biodegradable polymer microspheres

The process parameters such as the compositions of inner and outer aqueous phase and emulsification technique of the primary emulsion were optimized to decrease the burst release of BSA from biodegradable polymer microspheres in double emulsion method. It was found that diminished burst release of –14% was achieved for the microspheres produced by formulations, where no phosphate was present in the inner water phase (non-buffered system). Primary emulsion made by probe sonication rather than homogenization or mechanical stirring led to microspheres with insignificant burst effect. Microspheres obtained using 0.1% aqueous Tween 80® solution as the outer aqueous phase, frequently exhibit reduced burst effect of 2.7%. Low microsphere yield (52.1%), however, was observed. Microsphere yield was, therefore, enhanced by addition of additive such as sodium chloride, glucose or mannitol into the outer aqueous phase. Decrease in BSA entrapment was observed in the presence of sodium chloride, but reduction in entrapment efficiency was observed in the case of glucose. Burst release increased from 2.7% to 9.5% or 3.4% as 2.5% sodium chloride or 7.5% glucose was added into the outer aqueous phase respectively. Marked burst release (>20%) was observed in the presence of additive of higher concentration independent of sodium chloride or glucose. As far as surfactant type was concerned, diminished burst was found when PVP or Tween 80® rather than PVA was utilized as the surfactant during microsphere preparation. In addition to PLGA, the copolymers of L-lactide (LLA) and dimethyl trimethylene carbonate (DTC) or trimethylene carbonate (TMC) were also evaluated. Insignificant burst effect was found for the microspheres composed of DTC or TMC copolymers.

PH-sensitive behavior of two-component hydrogels composed of N,O-carboxymethyl chitosan and alginate

A two-component pH-sensitive hydrogel system composed of a water-soluble chitosan derivative (N,O-carboxymethyl chitosan, NOCC) and alginate cross-linked by genipin, glutaraldehyde or Ca2+ was investigated. Preparation and structures of these hydrogels and their swelling characteristics and release profiles of a model protein drug (bovine serum albumin, BSA) in simulated gastrointestinal media are reported. At pH 1.2, the swelling ratios of the hydrogels cross-linked by distinct methods were limited. Of note is that the lowest swelling ratios of test hydrogels were found at pH 4.0. At pH 7.4, the carboxylic acid groups on test hydrogels became progressively ionized and led to a significant swelling. There was barely any BSA released from the glutaraldehyde-cross-linked hydrogel throughout the entire course of the study. The amounts of BSA released at pH 1.2 from the genipin- and Ca2+-cross-linked hydrogels were relatively low (approx. 20%). At pH 4.0, there was still significant BSA release from the Ca2+-cross-linked hydrogel, while the cumulative BSA released from the genipin-cross-linked hydrogel was limited due to its shrinking behavior. At pH 7.4, the amount of BSA released from the genipin- and Ca2+-cross-linked hydrogels increased significantly (approx. 80%) because the swelling of both test hydrogels increased considerably. The aforementioned results indicated that the swelling behaviors and drug-release profiles of these test hydrogels are significantly different due to their distinct cross-linking structures.

Temperature-Sensitive Poly(N-Isopropylacrylamide)/Poly(Ethylene Glycol) Diacrylate Hydrogel Microspheres

To develop and characterize a new class of temperature-sensitive hydrogel microspheres composed of poly(N-isopropylacrylamide)/poly(ethylene glycol) diacrylate (PNIPAAm/PEG-DA). The PNIPAAm/PEG-DA hydrogel microspheres were fabricated in two aqueous systems as a result of polymer/polymer immiscibility. Both PNIPAAm and PEG-DA were used as the precursors; the PEG-DA was also used as a cross-linker for the formation of the hydrogel microspheres. Bovine serum albumin was used as the model protein drug to examine the effects of the thermo-responsive properties of the hydrogel microspheres on the release of a protein at two different temperatures (22°C and 37°C). The hydrated PNIPAAm/PEG-DA hydrogel microspheres exhibited a swollen diameter of 50µm, with a narrow particle-size distribution. Scanning electron microscopy and environmental scanning electron microscopy observations revealed that, upon swelling, the resulting hydrogel microspheres had a regular spherical and rough surface morphology. The lower critical solution temperature (LCST) of the PNIPAAm/PEG-DA hydrogel microspheres was around 29.1°C, based on differential scanning calorimetric data. The release of BSA from the hydrogel microspheres at 37°C was slower than that at 22°C because of the thermo-responsive nature of PNIPAAm at temperatures above its LCST. We believe that these kinds of PNIPAAm/PEG-DA hydrogel microspheres may have wide applications as promising drug delivery systems, because of their intelligent nature upon external temperature change.

Evaluating proteins release from, and their interactions with, thermosensitive poly ( N-isopropylacrylamide) hydrogels

Poly ( N-isopropylacrylamide) (PNIPAAm) hydrogels possess a lower critical solution temperature (LCST) at around 32 °C. When the external temperature is raised above the LCST, the hydrogels experience abrupt and drastic shrinkage. This unique property makes them very useful for biomedical applications such as on–off switches for modulated drug delivery and tissue engineering. The aim of this work was to study the potential of using PNIPAAm hydrogels for protein delivery, and to obtain basic understandings of the protein–gel interactions as well as their effect on protein loading and release. PNIPAAm gels were synthesized with different crosslinker contents. The effects of crosslinker content, in vitro release temperature, protein loading level and molecular size as well as temperature cycling on protein release from PNIPAAm gels were examined. Greater amount of BSA was loaded using gels fabricated with lower crosslinker contents and loading solution with higher concentrations of BSA. An incomplete release of encapsulated BSA from the gels was observed in all cases. Enhanced mass transfer created by oscillating swelling–deswelling in response to temperature cycling across the LCST and lowering in vitro release temperature did not promote BSA release because of strong BSA–gel interactions. Evidence for the residual BSA in the gels after in vitro release was provided by dyeing the gels with protein determination reagent and shift in the LCST of the gels. In contrast, insulin release was much faster and more complete when compared to BSA because of its smaller size. The protein–gel interactions were analysed by investigating the LCST of, and state of water in, the blank and protein-loaded hydrogels.

Some basic parameters of microspheres fabricated from a branched oligoester by a rapid procedure

Microspheres were prepared from a branched copolymer of DL-lactic acid with mannitol containing native albumin and albumin labelled with fluorescein isothiocyanate, using a rapid method of distribution of methylformate as the solvent of the copolymer from the intermediate phase of the multiple w/o/w emulsion. The primary w/o emulsion was prepared by the method of homogenization with a turbine or, alternatively, by the method of dispersion with ultrasound in modified vessels. Different additives in the external aqueous phase, such as polyvinyl alcohol or the gelatin hydrolyzate as emulsifiers were tested. Ammonium sulphate, methylformate or ethyl acetate were used as moderators of solidification of microspheres. The effect of these selected formulation parameters on the size, encapsulation efficiency, yield of microspheres and on the course of the BSA and FITC-BSA release in vitro conditions were examined.