Preparation and Characterization of Oxidized Starch Polymer Microgels for Encapsulation and Controlled Release of Functional Ingredients

Optimizing anthocyanin Oral delivery: Effects of food biomacromolecule types on Nanocarrier performance for enhanced bioavailability

Wall material types influence the efficacy of nanocarriers in oral delivery systems. We utilized three food biomacromolecules (whey protein isolate, oxidized starch, lipids) to prepare three types of nanocarriers. Our aim was to investigate their performance in digestion, cellular absorption, mucus penetration, intestinal retention, and bioavailability of the encapsulated anthocyanins (Ant). The release rate of protein nanocarriers (Pro-NCs) was twice that of starch nanocarriers (Sta-NCs) and four times that of lipid nanocarriers (Lip-NCs) in simulated gastrointestinal fluid. Additionally, Pro-NCs demonstrated superior transmembrane transport capacity and over three times cellular internalization efficiency than Sta-NCs and Lip-NCs. Sta-NCs exhibited the highest mucus-penetrating capacity, while Pro-NCs displayed the strongest mucoadhesion, resulting in extended gastrointestinal retention time for Pro-NCs. Sta-NCs significantly enhanced the in vivo bioavailability of Ant, nearly twice that of free Ant. Our results demonstrate the critical role of wall material types in optimizing nanocarriers for the specific delivery of bioactive compounds.

Preparation and characterization of particle-filled microgels by chemical cross-linking based on zein and carboxymethyl starch for delivering the quercetin

This work aimed to develop novel particle-filled microgels based on zein and carboxymethyl starch for delivering quercetin (Que). The anti-solvent precipitation and chemical cross-linking methods were combined to produce the zein-carboxymethyl starch particle-filled microgels (SM-Z). The critical finding of the study was that adding zein nanoparticles significantly improved the strength, water holding capacity, and thermal stability of carboxymethyl starch microgel (SM). Besides, SM-Z had good biodegradability, and the particle size was about 44-61 μm. SM-Z successfully encapsulated Que with a high encapsulation efficiency of 86.7 %. Que-loaded SM-Z (Q/SM-Z) significantly enhanced 30 d storage and UV light stability (up to 89.4 % retention rate) of Que than the Que-loaded SM (Q/SM). Q/SM-Z exhibited pH-responsive swelling behavior, and the swelling was greatest in the simulated intestinal fluid (pH = 7). Besides, the Q/SM-Z showed good stability in simulated gastric fluids and sustained release of Que in simulated intestinal fluids, 72.5 % Que was released at 8 h. During Que transport in Caco-2 cell monolayers, Q/SM (5.8 %) and Q/SM-Z (9.7 %) were significantly higher than free Que (1.93 %). Therefore, as an oral delivery system for hydrophobic active substances, SM-Z possesses good biodegradability and pH-responsive intestinal-targeted delivery capability, providing a new strategy for designing starch-based encapsulation materials.

Starch-based materials for drug delivery in the gastrointestinal tract-A review

Starch is a natural copolymer with unique physicochemical characteristics. Historically, it has been physically, chemically, or enzymatically modified to obtain ad-hoc functional properties for its use in different applications. In this context, the use of starch-based materials in drug delivery systems (DDSs) has gained great attention mainly because it is cheap, biodegradable, biocompatible, and renewable. This paper reviews the state of the art in starch-based materials design for their use in drug-controlled release with internal stimulus responsiveness; i.e., pH, temperature, colonic microbiota, or enzymes; specifically, those orally administered for its release in the gastrointestinal tract (GIT). Physical-chemical principles in the design of these materials taking into account their response to a particular stimulus are discussed. The relationship between the type of DDSs structure, starch modification routes, and the corresponding drug release profiles are systematically analyzed. Furthermore, the challenges and prospects of starch-based materials for their use in stimulus-responsive DDSs are also debated.

Ion-Induced Reassembly between Protein Nanotubes and Nanospheres

Proteins used as building blocks to template nanostructures with manifold morphologies have been widely reported. Understanding their self-assembly and reassembly mechanism is important for designing functional biomaterials. Herein, we show that enzyme-hydrolyzed α-lactalbumin (α-lac) can self-assemble into either nanotubes in the presence of Ca2+ ions or nanospheres in the absence of Ca2+ in solution. Remarkably, such assembled α-lac nanotubes can be elongated by adding preassembled α-lac nanospheres and Ca2+ solution, which suggests that the self-assembled α-lac nanospheres undergo disassembly and reassembly processes into existing nanotube nuclei. By performing atomic force microscopy (AFM), transmission electron microscopy (TEM), and confocal laser scanning microscopy (CLSM), it indicates that there is an equilibrium among nanotubes, nanospheres, hydrolyzed α-lac, and Ca2+ in solution. The structural transition between nanotubes and nanospheres is driven from a less stable structure into a more stable structure determined by the conditions. During the transition from nanospheres into nanotubes, the hydrolyzed α-lac in nanospheres transfers into helical ribbon form at both nanotube extremities. Then helical ribbons close into mature nanotubes, extending the length of the initial nuclei. Besides, by dilution or adding ethylene glycol bis(2-aminoethyl ether) tetraacetic acid (EGTA), the decreased Ca2+ concentration in solution drives the Ca2+ dissociating from nanotubes into solution, leading to the transitions from nanotubes into nanospheres. The reversible transformation between nanotubes and nanospheres is achieved by adjusting the pH value from 7.5 to 5.0 and back to 7.5. This is because the stability of nanotubes decreases from pH 7.5 to 5 but increases from 5 to 7.5. Significantly, this approach can be used for the fabrication of various responsive nanomaterials from the same starting material.

Effect of High Temperature and UV Radiation on the Insecticidal Capacity of a Spodoptera frugiperda Nucleopolyhedrovirus Microencapsulated in a Matrix Based on Oxidized Corn Starch

A multiple nucleopolyhedrovirus native isolate (SfCH32) of Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) was encapsulated by spray-drying in a matrix based on oxidized corn starch without and with a fluorescent brightener. The microcapsules were exposed to UV radiation (365 nm) for 0, 2, 4, and 8 h at 25 °C or temperatures of 35, 40, and 45 °C for 8 h. The data obtained with temperatures 35, 40, and 45 °C were contrasted with those obtained at 25 °C. The microcapsules were evaluated for size, shape, and insecticidal capacity against third instar S. frugiperda larvae under laboratory conditions. The 82-84.2% of the encapsulating matrix, in a dry-weight basis, was recovered as NPV microcapsules of heterogeneous shape and size. The exposure to UV radiation and temperatures reduced significantly the insecticidal capacity of tested viruses; however, such capacity was higher for microencapsulated than for non-microencapsulated viruses. The non-encapsulated virus that had been exposed to 45 °C or maintained at UV radiation for 8 h showed the lowest insecticidal activity at 5th day post-inoculation, with a larvae mortality of 25.3 and 16%, respectively. The fluorescent brightener increased significantly the insecticidal capacity of encapsulated and non-encapsulated viruses, causing a mortality of 100% at that time point, and decreased the median lethal time independently of the incubation temperature and exposure time to radiation. The findings suggested that an encapsulating matrix based on oxidized corn starch might protect the insecticidal capacity of NPV under field conditions.

On demand regulation of blood glucose level by biocompatible oxidized starch-Con A nanogels for glucose-responsive release of exenatide

Diabetes mellitus is a long-term chronic disease characterized by abnormal high level blood glucose (BG). An artificial closed-loop system that mimics pancreatic β-cells and releases insulin on demand has potential to improve the therapeutic efficiency of diabetes. Herein, a lectin Concanavalin A modified oxidized starch nanogel was designed to regulate glucose dynamically according to different glucose concentrations. The nanogels were formed by double cross-linking the Concanavalin A and glucose units on oxidized starch via specific binding and amide bonds to achieve the high drug loading and glucose responsiveness. The results showed that oxidized starch nanogels prolonged the half-life of antidiabetic peptide drug exenatide and released it in response to high BG concentrations. It could absorb BG at a high level and maintain glucose homeostasis. Besides, the oxidized starch nanogels performed well in recovering regular BG level from hyperglycemia state and maintaining in euglycemia state that fitted in a biological rhythm. In addition, the nanogels showed high biocompatibility in vivo and could improve plasma half-life and therapeutic efficacy of exenatide. Overall, the nanogels protected peptide drugs from degradation in plasma as a glucose-responsive platform showing a high potential for peptide drugs delivery and antidiabetic therapy.

Structural and mechanistic insights into starch microgel/anthocyanin complex assembly and controlled release performance

We report a self-assembly method for the fabrication of multilayer-starch-based microgels used for anthocyanin encapsulation. Alcohol-heating treatment and ionization reactions were employed to reduce the crystallinity of starch and introduce ionic groups on the molecule to further cross-link it with sodium trimetaphosphate and produce a starch microgel. The molecular interactions between the starch and the anthocyanins facilitated the anthocyanin encapsulation and the starch-microgel/anthocyanin complexes with one, two, and three self-assembled layers were obtained. The Lay-1 microgel exhibited an encapsulation efficiency of 50.1% when the anthocyanin concentration, cross-linking starch concentration, contact time, and temperature were 0.25 mg/mL, 1.5 mg/mL, 3 h, and 40 °C, respectively. An increase in the number of layers resulted in a more compact microgel structure with the zeta potential presenting variations upon structural changes. Furthermore, the encapsulated anthocyanins presented a slow release from Lay-1, while the multilayered microgels (Lay-2 and Lay-3) displayed outstanding encapsulation stability. This study gives an insight on the encapsulation and release of anthocyanins by starch microgels, and provides a novel strategy for the design of starch-based encapsulation materials presenting great stability.

The effect of reduction on the properties of the regioselectively oxidized starch granules prepared by bromide-free oxidation system

Development of intact oxidized starch granules by regioselective oxidation technology is of interest and provides a new research direction for oxidized starch. In this study, new sodium tetrahydridoborate (NaBH₄)-treated oxidized starch (OS-BH₄) granules were prepared by a one-pot method, where native corn starch (NS) granules were oxidized by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)/sodium hypochlorite (NaClO) system followed by reduction with NaBH₄. Oxidized starch (OS) granules without NaBH₄ reduction were also prepared to investigate the effect of C6 aldehyde groups remained after TEMPO-mediated oxidation on properties of the granules. When degrees of oxidation were controlled to be not higher than 12%, both the OS and OS-BH₄ granules had similar morphology to the NS granules with envelopes. Compared to the OS granules, except for lower pasting temperatures and dextrose equivalents, the OS-BH₄ granules had higher molecular weights, degrees of polymerization (DP), peak viscosities, final viscosities, and swelling power. Difference of the properties was considered related to (1) repulsive forces formed between the C6 carboxylate groups, (2) C6 aldehyde groups with lower hydrophilicity than the C6 hydroxyl groups, and (3) some hemiacetal linkages formed between the C6 aldehyde groups and the hydroxyl groups. Furthermore, pregelatinized OS-BH₄ granules were preliminarily prepared, which showed good swelling behavior with intact granular morphology in alkaline environment.

Drug-Induced Phase Separation in Polyelectrolyte Microgels

Polyelectrolyte microgels may undergo volume phase transition upon loading and the release of amphiphilic molecules, a process important in drug delivery. The new phase is “born” in the outermost gel layers, whereby it grows inward as a shell with a sharp boundary to the “mother” phase (core). The swelling and collapse transitions have previously been studied with microgels in large solution volumes, where they go to completion. Our hypothesis is that the boundary between core and shell is stabilized by thermodynamic factors, and thus that collapsed and swollen phases should be able to also coexist at equilibrium. We investigated the interaction between sodium polyacrylate (PA) microgel networks (diameter: 400–850 µm) and the amphiphilic drug amitriptyline hydrochloride (AMT) in the presence of NaCl/phosphate buffer of ionic strength (I) 10 and 155 mM. We used a specially constructed microscopy cell and micromanipulators to study the size and internal morphology of single microgels equilibrated in small liquid volumes of AMT solution. To probe the distribution of AMT micelles we used the fluorescent probe rhodamine B. The amount of AMT in the microgel was determined by a spectrophotometric technique. In separate experiments we studied the binding of AMT and the distribution between different microgels in a suspension. We found that collapsed, AMT-rich, and swollen AMT-lean phases coexisted in equilibrium or as long-lived metastable states at intermediate drug loading levels. In single microgels at I = 10 mM, the collapsed phase formed after loading deviated from the core-shell configuration by forming either discrete domains near the gel boundary or a calotte shaped domain. At I = 155 mM, single microgels, initially fully collapsed, displayed a swollen shell and a collapsed core after partial release of the AMT load. Suspensions displayed a bimodal distribution of swollen and collapsed microgels. The results support the hypothesis that the boundary between collapsed and swollen phases in the same microgel is stabilized by thermodynamic factors.

Impact of calcium ions and degree of oxidation on the structural, physicochemical, and in-vitro release properties of resveratrol-loaded oxidized gellan gum hydrogel beads

Oxidized gellan gum (OGG) hydrogel beads as delivery systems for resveratrol were fabricated by ionic cross-linking with calcium chloride (CaCl₂). The degree of oxidation (DO) and CaCl₂ concentration had significant influences on the formation and functional properties of hydrogel beads. The resveratrol encapsulation efficiency (66.43%-79.84%) and loading capacity (4.15%-5.05%) of OGG hydrogel beads were enhanced as DO increased. The hydrogel beads exhibited a uniform spherical shape as observed by scanning electron microscope. Fourier transform infrared spectroscopy analysis confirmed that hydrogen bonds and ionic interaction participated in the formation of hydrogel beads. X-ray diffraction analysis revealed that the physical state of resveratrol was changed from crystalline to amorphous form after encapsulation. Furthermore, the physical stability and antioxidant capacity evaluation demonstrated that the hydrogel bead fabricated with DO80 OGG and CaCl₂ concentration of 1.0 M could provide high protection for resveratrol against degradation by environmental stresses and maintain its antioxidant capacity. The DO and CaCl₂ concentrations could modulate the in-vitro release behaviors of hydrogel beads and obtain a good small intestinal-targeted release of resveratrol at high DO and medium CaCl₂ concentration. These findings suggested that a promising delivery system for encapsulating bioactive ingredients can be fabricated by rational design.

Masking the Perceived Astringency of Proanthocyanidins in Beverages Using Oxidized Starch Hydrogel Microencapsulation

Proanthocyanidins (PAs) are responsible for several health benefits of many fruits, but they could cause a generally disliked sensation of astringency. Traditional deastringency methods remove bioactive ingredients, resulting in the loss of valuable nutrients and associated health benefits. This work aimed to microencapsulate PAs from grape seeds using oxidized starch hydrogel (OSH) and mask its perceived astringency in beverages while maintaining its bioavailability. The maximum PA uptake capabilities of OSH, as well as the binding site and primary binding force between these two components, were determined. The resulting PA-OSH complex was stable under in vitro digestion, with only 1.6% of PA being released in the salivary digestion, and it has an intestine-specific release property. The reaction of PA with α-amylase in artificial saliva was substantially reduced by OSH microencapsulation, leading to 41.5% less precipitation of the salivary proteins. The sensory evaluation results showed that the microencapsulation was able to mask the astringency of PA-fortified water, as the perceived threshold of astringency increased by 3.85 times. These results proved that OSH could be used as a novel food additive to reduce the astringency of beverage products due to its hydrogel properties and ability to encapsulate phenolic compounds.

The hepatic-targeted, resveratrol loaded nanoparticles for relief of high fat diet-induced nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is the early stage of many metabolic syndromes. The intervention of NAFLD can prevent its further development into severe metabolic syndromes. Given the inefficiency and side effects of chemical drugs for treating NAFLD, the hepatic-targeted nanocarriers loaded with bioactive compounds may offer a more effective and acceptable strategy for eliminating NAFLD. Here we developed hepatic-targeted oxidized starch-lysozyme (OSL) nanocarriers to specifically deliver resveratrol (Res) to liver tissue in order to maximize its therapeutic efficiency. The hepatic targeting was achieved using covalently conjugated galactose (Gal), which is recognized by the asialoglycoprotein receptors specifically expressed in hepatocytes. In steatotic HepG2 cell model, treatment with hepatic-targeted Gal-OSL/Res nanocarriers enhanced the cellular Res uptake and anti-lipogenesis capabilities, and effectively decreased triglyceride accumulation by modulating AMP-activated protein kinase (AMPK)/silent information regulation 2 homolog 1(SIRT1)/fatty acid synthase (FAS)/sterol regulatory element-binding protein-1c (SREBP1c) signaling pathway. In mice, Gal-OSL increased Res delivery into liver tissues and increased their hepatic effective concentration in liver. Most importantly, Gal-OSL/Res nanocarriers effectively reversed NAFLD and recovered hepatic insulin sensitivity of NAFLD mice to the healthy state. Furthermore, Gal-OSL/Res efficiently ameliorated lipid deposition and insulin resistance by modulating AMPK/SIRT1/FAS/SREBP1c signaling pathway and downregulated insulin receptor substrate-1 (IRS-1) phosphorylation at serine 307 in liver. These findings suggested that the hepatic-targeted Gal-OSL nanocarriers delivering Res could potentially serve as a safe and promising platform for NAFLD and other liver related diseases.

Effect of poly-methyltriethoxysilane on the waterproof property of starch/fiber composites with open cell structures

Novel starch/fiber composites with open cell structures were proposed through thermo-cavity molding. To overcome the disadvantage of the water sensitivity of the resulting composites, poly-methyltriethoxysilane (PTS) was added as a waterproofing agent. The results showed that the addition of PTS improved the waterproof property of the composites. The composites with 15 g PTS (PTS-15) exhibited an optimal waterproof property. The water contact angle and drop absorption of the PTS-15 composites improved by 59.9% and 223.5%, respectively, compared with the values for those without PTS. Moreover, the addition of PTS could effectively prevent the degradation of the mechanical properties of the composites after water absorption. The rate of tensile property degradation for the PTS-15 composites reached 5.3%, whereas that for the PTS-0 composites totaled 56.6%. The chemical bonds and micro-structure of the composites were investigated to reveal the inherent mechanism of property changes. Fourier transform infrared spectra revealed the formation of new hydrogen bonds between starch and PTS. Hydrophobic groups, including Si-O-Si, Si-C, and Si-OH, were found in the resulting composites, thereby explaining the waterproof property changes. Scanning electron microscopy images showed that the open cell structure of the composites initially became denser and then loosened with the increase in the PTS content, resulting in the initial enhancement and the subsequent weakening of their mechanical properties.

Inhibition of oil digestion in Pickering emulsions stabilized by oxidized cellulose nanofibrils for low-calorie food design

Celluloses are renewable and biodegradable natural resources. The application of celluloses as oil-in-water Pickering emulsifiers is still quite limited. In this paper, cellulose nanofibrils (CNFs) with oxidation degrees (DOs) of 52.8% and 92.7% (DO50 and DO90) were obtained from TEMPO-mediate oxidation for microcrystalline cellulose (MC). The production of carboxyl groups of CNFs were confirmed by FT-IR and 13C solid-NMR. CNF-stabilized O/W Pickering emulsion showed excellent colloidal stability compared with un-oxidized cellulose by Turbiscan stability analysis. Additionally, CNF-stabilized Pickering emulsions showed stable colloidal properties in simulated intestinal fluid (SIF). Most importantly, in vitro fatty acid release kinetics under SIF showed that CNFs have strong inhibitory lipid digestion behavior. Our results suggest that the oxidation modification not only improves their emulsification activity but also promotes their application in oil digestion inhibition, providing inspiration for designing and developing low-calorie food products.

The delivery of sensitive food bioactive ingredients: Absorption mechanisms, influencing factors, encapsulation techniques and evaluation models

Food-sourced bioactive compounds have drawn much attention due to their health benefits such as anti-oxidant, anti-cancer, anti-diabetes and cardiovascular disease-preventing functions. However, the poor solubility, low stability and limited bioavailability of sensitive bioactive compounds greatly limited their application in food industry. Therefore, numbers of carriers were developed for improving their dispersibility, stability and bioavailability. This review addresses the digestion and absorption mechanisms of bioactive compounds in epithelial cells based on several well-known in vitro and in vivo models. Factors such as environmental stimuli, stomach conditions and mucus barrier influencing the utilization efficacy of the bioactive compounds are discussed. Delivery systems with enhanced utilization efficacy, such as complex coacervates, cross-linked polysaccharides, self-assembled micro-/nano-particles and Pickering emulsions are compared. It is a comprehensive multidisciplinary review which provides useful guidelines for application of bioactive compounds in food industry.

Shear-thinning hyaluronan-based fluid hydrogels to modulate viscoelastic properties of osteoarthritis synovial fluids

Hyaluronan-based injectable fluid hydrogel was prepared and used as an artificial synovial fluid for the treatment of osteoarthritis.

TEMPO-oxidized starch nanoassemblies of negligible toxicity compared with polyacrylic acids for high performance anti-cancer therapy

There is an urgent need for developing nanocarrier of excellent biocompatibility which can selectively release drugs at desired locations that can increase intratumoral drug concentration and reduce side effects. Herein, we developed a highly biocompatible nanocarrier made of oxidized starch in delivering doxorubicin (DOX) for enhanced anti-cancer therapy. The 30% oxidized starch can spontaneously self-assemble into 30-50 nm spherical nanoassemblies under physiological concentrations. DO30 nanoassemblies possessed negligible toxicity in several cell lines and ICR mice, in contrast to severe toxicity of synthetic polyacrylic acid (PAA), both of which are carboxyl-abundant polymers. The biocompatible DO30 was further decorated with cyclic RGD (Arg-Gly-Asp-Phe-Cys) peptides via PEG linker to target αvβ3 integrin overexpressed on HepG2 cells. RGD-PEG-DO30/DOX demonstrated an enhanced tumor-targeting ability and anti-cancer property in vitro and in vivo. In general, RGD-oxidized starch nanoassemblies showed a great potential as a new type of safe and effective nanocarrier for anti-cancer therapy.

Microfluidic fabrication of polyethylene glycol microgel capsules with tailored properties for the delivery of biomolecules

Microfluidic encapsulation platforms have great potential not only in pharmaceutical applications but also in the consumer products industry. Droplet-based microfluidics is increasingly used for the production of monodisperse polymer microcapsules for biomedical applications. In this work, a microfluidic technique is developed for the fabrication of monodisperse double emulsion droplets, where the shell is crosslinked into microgel capsules. A six-armed acrylated star-shaped poly(ethylene oxide-stat-propylene oxide) pre-polymer is used to form the microgel shell after a photo-initiated crosslinking reaction. The synthesized microgel capsules are hollow, enabling direct encapsulation of large amounts of multiple biomolecules with the inner aqueous phase completely engulfed inside the double emulsion droplets. The shell thickness and overall microgel sizes can be controlled via the flow rates. The morphology and size of the shells are characterized by cryo-SEM. The encapsulation and retention of 10 kDa FITC-dextran and its microgel degradation mediated release are monitored by fluorescence microscopy.

TEMPO-mediated oxidation of polysaccharides: An ongoing story

The oxidation of natural polysaccharides by TEMPO has become by now an "old chemical reaction" which led to numerous studies mainly conducted on cellulose. This regioselective oxidation of primary alcohol groups of neutral polysaccharides has generated a new class of polyuronides not identified before in nature, even if the discovery of enzymes promoting an analogous oxidation has been more recently reported. Around the same time, the scientific community discovered the surprising biological and techno-functional properties of these anionic macromolecules with a high potential of application in numerous industrial fields. The objective of this review is to establish the state of the art of TEMPO chemistry applied to polysaccharide oxidation, its history, the resulting products, their applications and the associated modifying enzymes.

Co-loading and intestine-specific delivery of multiple antioxidants in pH-responsive microspheres based on TEMPO-oxidized polysaccharides

In this study, pH-responsive microspheres loaded with multiple antioxidants were developed for intestine-specific delivery and exhibited synergistic activity. They consist of chitosan (CS)-coated microspheres made of TEMPO-oxidized Konjac glucomannan (OKGM) polymers, of which the carboxyl (COO^-) groups are cross-linked via ferric ions (Fe³⁺), allowing the hydrophobic (β-carotene) and hydrophilic (anthocyanins) antioxidants to be simultaneously incorporated. CLSM images showed successful co-encapsulation of β-carotene and anthocyanins. The in vitro release kinetics of co-loaded CS-OKGM microspheres in simulated GI fluids indicated that the microspheres retain the dual antioxidants in an acidic gastric environment and release them at intestinal pH. Free radical scavenging experiments demonstrated that multiple antioxidants loaded into OKGM system had synergistic activity with enhanced stability against heat. The multi-functional CS-OKGM microspheres showed great potential for multiple antioxidants and intestine-specific delivery with enhanced stability.

Intestine-Specific Delivery of Hydrophobic Bioactives from Oxidized Starch Microspheres with an Enhanced Stability

An intestine-specific delivery system for hydrophobic bioactives with improved stability was developed. It consists of oxidized potato starch polymers, where the carboxyl groups were physically cross-linked via ferric ions. The model hydrophobic ingredients (β-carotene) were incorporated inside the starch microspheres via a double-emulsion method. Confocal laser scanning microscopy images showed that β-carotene were distributed homogeneously in the inner oil phase of the starch microspheres. The negative value of the ζ-potential of microspheres increased with increasing pH and decreasing ionic strength. In vitro release experiments showed that the microspheres were stable at acidic stomach conditions (pH < 2), whereas at neutral intestinal conditions (pH 7.0), they rupture to release the loaded β-carotene. The 1,1-diphenyl-2-picrylhydrazyl radical, 2,2-diphenyl-1-(2,4,6-trinitriphenyl), scavenging activity results suggested that microsphere-encapsulated β-carotene had an improved activity after thermal treatment at 80 °C. The storage stability of encapsulated β-carotene at room temperature was also enhanced. The starch microspheres showed potential as intestine-specific carriers with an enhanced stability.

Synthesis of pH- and ionic strength-responsive microgels and their interactions with lysozyme

Microgels composed of carboxymethyl cellulose (CMC) polymers via chemical crosslinking with sodium trimetaphosphate were synthesized and characterized using thermogravimetric analysis (TGA), swelling, and rheological analysis. The effects of pH, ionic strength, and crosslinking density on lysozyme loading in microgels were also studied. The microgel particle size ranged primarily from 10 to 20 μm. TGA revealed that the crosslinking increased the thermal stability of CMC. The swelling degree increased as pH increased from 3 to 5, and remained almost constant from pH 5 to 8. However, the swelling degree decreased with increasing ionic strength. The rheological analysis was in good agreement with the results of swelling degree. The protein uptake decreased with increasing ionic strength and crosslinking density. The pH 6 was the optimal pH for lysozyme absorption at ionic strength 0.05 M. The lysozyme-microgel complex was identified by confocal laser scanning microscopy, and the lysozyme distribution in the microgel was observed to be rather homogeneous.

Preparation and characterization of carboxymethyl starch microgel with different crosslinking densities

Microgels synthesized with different crosslinking densities were characterized by Fourier transform infrared (FT-IR) spectroscopy, thermogravimetry analysis (TGA), swelling, and rheological analyses. The lysozyme uptake capacity of these microgels was evaluated through the effects of lysozyme concentration, pH, and ionic strength. The microgel particle size mostly ranged within 25μm to 45μm. FT-IR analysis results suggested that sodium trimetaphosphate reacted with the hydroxyl groups of carboxymethyl starch (CMS), thereby forming ester linkages. TGA data indicated that crosslinking increased the thermal stability of CMS. Swelling degree increased with increasing pH before pH 5, and then remained almost constant. However, swelling degree decreased with increasing ionic strength and crosslinking density. The microgels behaved as viscoelastic solids because the storage modulus was higher than the loss modulus over the entire frequency range of dispersions with polymer concentrations of 3% (W/W) at 25°C. The data for the uptake of lysozyme by microgels demonstrated that the protein uptake increased with increasing pH and lysozyme concentration, as well as with decreasing ionic strength and crosslinking density. The lysozyme-microgels complex was identified by CLSM, and the distribution of lysozyme in microgels with low crosslinking density was rather homogeneous.

Controlled uptake and release of lysozyme from glycerol diglycidyl ether cross-linked oxidized starch microgel

A biodegradable microgel system based on glycerol-1,3-diglycidyl ether (GDGE) cross-linked TEMPO-oxidized potato starch polymers was developed for controlled uptake and release of proteins. A series of microgels were prepared with a wide range of charge density and cross-link density. We found both swelling capacity (SWw) and lysozyme uptake at saturation (Γsat) increased with increasing degree of oxidation (DO) and decreasing cross-link density. Microgel of DO100% with a low cross-link density (RGDGE/polymer (w/w) of 0.025) was selected to be the optimum gel type for lysozyme absorption; Γsat increased with increasing pH and decreasing ionic strength. It suggests that the binding strength was the strongest at high pH and low ionic strength, which was recognized as the optimum absorption conditions. The lysozyme release was promoted at low pH and high ionic strength, which were considered to be the most suitable conditions for triggering protein release. These results may provide useful information for the controlled uptake and release of proteins by oxidized starch microgels.

Characterization of different substituted carboxymethyl starch microgels and their interactions with lysozyme

A carboxymethyl starch (CMS) microgel system was prepared for the control of uptaking and releasing proteins (lysozyme). The physicochemical properties of microgels in various degrees of substitution (DS) were determined by thermal gravimetric analysis (TGA), swelling degree, and rheological analysis. The microgel particle size mostly ranged from 25 µm to 45 µm. The result obtained from the TGA studies indicated that carboxymethylation decreased the thermal stability of starch, but crosslinking increased the thermal stability of CMS. The CMS microgels showed typical pH sensitivity, and the swelling degree of microgel increased with the increasing of DS and pH, because of the large amounts of carboxyl group ionization. The samples (2.25%) could behave as viscoelastic solids since the storage modulus was larger than the loss modulus over the entire frequency range. The protein uptake increased with increasing pH and DS at low salt concentration. The optimal pH shifted to lower pH with increasing ionic strength. The saturated protein uptake decreased with increasing ionic strength at each pH. The protein was easily released from the microgel with high pH and high salt concentration.

A study of controlled uptake and release of anthocyanins by oxidized starch microgels

Anthocyanins are well-known antioxidants, but they are sensitive to environmental conditions. Herein we used oxidized starch microgel to prevent their early degradation and deliver them to the target place. The aim of this study was to investigate the uptake and the release ability of anthocyanins by the oxidized starch microgels and measure their in vitro gastrointestinal release. The gels were made of oxidized potato starch polymers, which were chemically cross-linked by sodium trimetaphosphate (STMP). In this study, the uptake and release behaviors of anthocyanins by starch microgel were investigated under various pH and salt concentrations. The microgel of high degree of oxidation and high cross-link density had a high uptake capacity for anthocyanins at low pH and salt concentration; 62 mg anthocyanins had been absorbed per gram of dry DO100% (degree of oxidation 100%) microgel at pH 3 with ionic strength 0.05M. The in vitro study of the release was investigated under stimulated gastrointestinal fluid. The anthocyanins were identified and quantified by UV/vis detection. The results indicated that the oxidized starch microgels had a potential for being a carrier system for protecting anthocyanins from degradation in the upper gastric tract and for delivering them to the intestine. This paper provides a good reference for an intestinal-targeted delivery system of vulnerable functional ingredients by oxidized starch microgel.

Stabilization of protein-loaded starch microgel by polyelectrolytes

The interaction of biocompatible polyelectrolytes (chargeable poly(amino acids)) with oxidized starch microgel particles has been studied. The aim was to form a polyelectrolyte complex layer around the outer shell of microgel particles filled with functional ingredients to slow down the release of the ingredients from the gel and make this process less sensitive to salt. First, the distribution of positively charged poly(l-lysine) (PLL) of two different molecular weights ("small", 15-30 kDa, and "large", 30-70 kDa) in the negatively charged gel particles was measured. The small PLL distributes homogeneously throughout the gel particles, but the large PLL forms a shell; i.e., its concentration at the outer layer of the particles was found to be much higher than in their core. This shell formation does not occur at a relatively high salt concentration (0.07 M). The large PLL was selected for further study. It was found that upon addition of PLL to lysozyme-loaded gel particles the protein is exchanged by PLL. The exchange rate increases with increasing pH, in line with the increasing electrostatic attraction between the gel and the polyelectrolyte. Therefore, it was decided to use also a negatively charged poly(amino acid), poly(L-glutamic acid) (PGA), to form together with PLL a stable polyelectrolyte complex shell around the gel particles. This approach turned out to be successful, and the PLL/PGA complex layer effectively slows down the release of lysozyme from the microgel particles at 0.05 M salt. In addition, it was found that the PLL/PGA layer protects the gel particle from degradation by α-amylase.

Microgels and microcapsules in peptide and protein drug delivery

The present review focuses on the interaction of microgels and microcapsules with biological macromolecules, particularly peptides and proteins, as well as drug delivery applications of such systems. Results from recent studies on factors affecting peptide/protein binding to, and release from, microgels and related systems are discussed, including effects of network properties, as well as protein aggregation, peptide length, hydrophobicity and charge (distributions), secondary structure, and cyclization. Effects of ambient conditions (pH, ionic strength, temperature, etc.) are also discussed, all with focus on factors of importance for the performance of microgel and microcapsule delivery systems for biomacromolecular drugs.