Preparation of Hyaluronic Acid Micro-Hydrogel by Biotin–Avidin-Specific Bonding for Doxorubicin-Targeted Delivery

Effects of Biotin-Avidin Interactions on Hydrogel Swelling

Affinity interactions between the small molecule biotin and the protein avidin have been used extensively to functionalize biomaterials. More recently, researchers have leveraged the changes in biotin-avidin affinity that occur upon biotin conjugation to larger molecules to control the release of biotinylated drugs and proteins. However, the effects of biotin-avidin interactions on hydrogel properties have not been thoroughly investigated. The objective of this study was to evaluate the effect of increasing biotin and avidin concentrations on hydrogel swelling properties, as an indicator of crosslinking. Gelatin, selected as a model hydrogel material, was biotinylated at increasing fold molar excesses of biotin with a PEG linker using N-hydroxysuccinimide chemistry. Afterwards, biotinylated gelatin was formed into hydrogels and stabilized with glutaraldehyde. Swelling properties of the biotinylated hydrogels were investigated by conducting swelling studies in different avidin solutions. Increasing the degree of biotinylation caused significant decreases in swelling ratios of the hydrogels in a dose-dependent manner, suggesting increases in crosslinking of the hydrogels. However, increasing avidin concentrations in excess of biotin content did not significantly affect swelling ratios. Moving hydrogels to phosphate-buffered saline following avidin incorporation resulted in increased swelling ratios for hydrogels prepared with a lower concentration of biotin. However, hydrogels prepared with the highest concentration of biotin did not experience increased swelling ratios, implying that the stability of biotin-avidin-mediated crosslinking depends on the number of biotin molecules available for binding. Collectively, these results demonstrate that biotin-avidin interactions control hydrogel swelling properties, and that the magnitude and stability of the effects depend on the biotin concentration. These results have important implications for affinity-based controlled release of biotinylated drugs or proteins from biotin-avidin-crosslinked hydrogels.

Microgels in biomaterials and nanomedicines

Microgels are colloidal particles with crosslinked polymer networks and dimensions ranging from tens of nanometers to micrometers. Specifically, smart microgels are fascinating capable of responding to biological signals in vivo or remote triggers and making the possible for applications in biomaterials and biomedicines. Therefore, how to fundamentally design microgels is an urgent problem to be solved. In this review, we put forward our important fundamental opinions on how to devise the intelligent microgels for cancer therapy, biosensing and biological lubrication. We focus on the design ideas instead of specific implementation process by employing reverse synthesis analysis to programme the microgels at the original stage. Moreover, special insights will be, for the first time, as far as we know, dedicated to the particles completely composed of DNA or proteins into microgel systems. These are discussed in detail in this review. We expect to give readers a broad overview of the design criteria and practical methodologies of microgels according to the application fields, as well as to propel the further developments of highly interesting concepts and materials.

Recovery and Purity of High Molar Mass Bio-hyaluronic Acid Via Precipitation Strategies Modulated by pH and Sodium Chloride

The effects of ethanol/broth proportions and the number of steps at varying pH in the presence or absence of sodium chloride (NaCl) were studied as precipitation strategies for the recovery and purification of high molar mass bio-hyaluronic acid (Bio-HA). Bio-HA was synthesized by Streptococcus zooepidemicus in a culture medium containing glucose and soy peptones. A single-step precipitation was more attractive than multistep precipitation in terms of recovery and purity as well as decreased use of ethanol. The best conditions in the absence and presence of salt were 2:1 ethanol/broth (v/v) at pH 4 (55.0 ± 0.2% purity and 85.0 ± 0.7% recovery) and 2:1 ethanol/broth (v/v) at pH 7 + 2 mol L^-1 NaCl (59.0 ± 0.9% purity and 82.0 ± 4.3% recovery). Dynamic light scattering (DLS) spectra showed different particle sizes as a consequence of the changes in the molecular structure of HA, mainly with changes in pH. Although slight changes in distribution were observed, the average HA molar mass was not affected by the precipitation strategy, remaining on the order of 10⁵ Da. Therefore, pH and NaCl modulated the precipitation performance of HA. These findings are relevant to further optimizing the precipitation step, thus minimizing costs in the later stages of HA purification.

Avidin Adsorption to Silk Fibroin Films as a Facile Method for Functionalization

Silk fibroin biomaterials are highly versatile in terms of materials formation and functionalization, with applications in tissue engineering and drug delivery, but necessitate modifications for optimized biological activity. Herein, a facile, avidin-based technique is developed to noncovalently functionalize silk materials with bioactive molecules. The ability to adsorb avidin to silk surfaces and subsequently couple biotinylated macromolecules via avidin-biotin interaction is described. This method better preserved functionality than standard covalent coupling techniques using carbodiimide cross-linking chemistry. The controlled release of avidin from the silk surface was demonstrated by altering the adsorption parameters. Application of this technique to culturing human foreskin fibroblasts (hFFs) and human mesenchymal stem cells (hMSCs) on arginine-glycine-aspartic-acid-modified (RGD-modified) silk showed increased cell growth over a seven-day period. This technique provides a facile method for the versatile functionalization of silk materials for biomedical applications including tissue engineering, drug delivery, and biological sensing.

Application of the biotin-labeled toxin mutant for affinity isolation of associated proteins in the mammalian cells

Cholera toxin (CT), one of the AB₅ bacterial toxin families, is produced by Vibrio cholerae, breeches the intestinal epithelial barrier and enters host epithelial cells to cause the massive secretory diarrhea. This study focused on understanding the retro-translocation machinery of the bacterial toxin using biotin-avidin technology to explain toxin trafficking from the endoplasmic reticulum (ER) to the cytosol. Because the association between the A1 chain of CT and other components of the retro-translocation machinery is likely transient or very weak, the successful bioengineering of such a mutant to be trapped as an intermediate in ER is essential for affinity isolation and further analysis. Here, we prepared a mutant toxin that 15 amino acid Biotin Acceptor Peptide (BAP) was fused to the C-terminal of A1 chain of CT. Biotinylation efficiency of the BAP-inserted cholera toxin (BT) was nearly 100%. Moreover, BT was functionally toxic and successfully pulled down by NeutrAvidin in vitro and in vivo. However, NeutrAvidin-bound biotinylated BT was not toxic. These results suggest the possibility of a plug effect of the biotin-NeutrAvidin-BT complex stuck in the ER without retro-translocation to the cytosol. Therefore, this model might identify the interacting proteins with A1 chain of CT in the host cells by holding the moment of retro-translocation of the bacterial toxin. In conclusion, this study established the model using biotin-avidin technology to elucidate the molecular basis for retro-translocation of bacterial toxin from within the lumen of ER to the cytosol.

The principles and applications of avidin-based nanoparticles in drug delivery and diagnosis

Avidin-biotin interaction is one of the strongest non-covalent interactions in the nature. Avidin and its analogues have therefore been extensively utilized as probes and affinity matrices for a wide variety of applications in biochemical assays, diagnosis, affinity purification, and drug delivery. Recently, there has been a growing interest in exploring this non-covalent interaction in nanoscale drug delivery systems for pharmaceutical agents, including small molecules, proteins, vaccines, monoclonal antibodies, and nucleic acids. Particularly, the ease of fabrication without losing the chemical and biological properties of the coupled moieties makes the avidin-biotin system a versatile platform for nanotechnology. In addition, avidin-based nanoparticles have been investigated as diagnostic systems for various tumors and surface antigens. In this review, we will highlight the various fabrication principles and biomedical applications of avidin-based nanoparticles in drug delivery and diagnosis. The structures and biochemical properties of avidin, biotin and their respective analogues will also be discussed.