Sodium bicarbonate-gelled chitosan beads as mechanically stable carriers for the covalent immobilization of enzymes

Trends in sustainable chitosan-based hydrogel technology for circular biomedical engineering: A review

Eco-friendly materials have emerged in biomedical engineering, driving major advances in chitosan-based hydrogels. These hydrogels offer a promising green alternative to conventional polymers due to their non-toxicity, biodegradability, biocompatibility, environmental friendliness, affordability, and easy accessibility. Known for their remarkable properties such as drug encapsulation, delivery capabilities, biosensing, functional scaffolding, and antimicrobial behavior, chitosan hydrogels are at the forefront of biomedical research. This paper explores the fabrication and modification methods of chitosan hydrogels for diverse applications, highlighting their role in advancing climate-neutral healthcare technologies. It reviews significant scientific advancements and trends chitosan hydrogels focusing on cancer diagnosis, drug delivery, and wound care. Additionally, it addresses current challenges and green synthesis practices that support a circular economy, enhancing biomedical sustainability. By providing an in-depth analysis of the latest evidence on climate-neutral management, this review aims to facilitate informed decision-making and foster the development of sustainable strategies leveraging chitosan hydrogel technology. The insights from this comprehensive examination are pivotal for steering future research and applications in sustainable biomedical solutions.

In Situ Hydrogel Formulation for Advanced Wound Dressing: Influence of Co-Solvents and Functional Excipient on Tailored Alginate-Pectin-Chitosan Blend Gelation Kinetics, Adhesiveness, and Performance

Chronic skin wounds affect more than 40 million patients worldwide, representing a huge problem for healthcare systems. This study elucidates the optimization of an in situ gelling polymer blend powder for biomedical applications through the use of co-solvents and functional excipients, underlining the possibility of tailoring microparticulate powder properties to generate, in situ, hydrogels with advanced properties that are able to improve wound management and patient well-being. The blend was composed of alginate, pectin, and chitosan (APC). Various co-solvents (ethanol, isopropanol, and acetone), and salt excipients (sodium bicarbonate and ammonium carbonate) were used to modulate the gelation kinetics, rheology, adhesiveness, and water vapor transmission rate of the gels. The use of co-solvents significantly influenced particle size (mean diameter ranging from 2.91 to 5.05 µm), depending on the solvent removal rate. Hydrogels obtained using ethanol were able to absorb over 15 times their weight in simulated wound fluid within just 5 min, whereas when sodium bicarbonate was used, complete gelation was achieved in less than 30 s. Such improvement was related to the internal microporous network typical of the particle matrix obtained with the use of co-solvents, whereas sodium bicarbonate was able to promote the formation of allowed particles. Specific formulations demonstrated an optimal water vapor transmission rate, enhanced viscoelastic properties, gel stiffness, and adhesiveness (7.7 to 9.9 kPa), facilitating an atraumatic removal post-use with minimized risk of unintended removal. Microscopic analysis unveiled that porous inner structures were influencing fluid uptake, gel formation, and transpiration. In summary, this study provided valuable insights for optimizing tailored APC hydrogels as advanced wound dressings for chronic wounds, including vascular ulcers, pressure ulcers, and partial and full-thickness wounds, characterized by a high production of exudate.

Increasing Chemotherapeutic Efficacy Using pH-Modulating and Doxorubicin-Releasing Injectable Chitosan-Poly(ethylene glycol) Hydrogels

Modulation of pH is crucial to maintaining the chemical homeostasis of biological environments. The irregular metabolic pathways exhibited by cancer cells result in the production of acidic byproducts that are excreted and accumulate in the extracellular tumor microenvironment, reducing the pH. As a consequence of the lower pH in tumors, cancer cells increase the expression of metastatic phenotypes and chemotherapeutic resistance. A significant limitation in current cancer therapies is the inability to locally deliver chemotherapeutics, leading to significant damage to healthy cells in systemic administration. To overcome these challenges, we present an injectable chitosan-poly(ethylene glycol) hydrogel that is dual-loaded with doxorubicin and sodium bicarbonate providing alkaline buffering of extracellular acidity and simultaneous chemotherapeutic delivery to increase chemotherapeutic efficacy. We conducted in vitro studies of weak base chemotherapeutic and alkaline buffer release from the hydrogel. The release of doxorubicin from hydrogels increased in a low-pH environment and was dependent on the encapsulated sodium bicarbonate concentration. We investigated the influence of pH on the doxorubicin efficacy and viability of MCF-7 and MDA-MB-231 breast cancer cell lines. The results show a 2- to 3-fold increase in IC50 values from neutral pH to low pH, showing decreased cancer cell viability at neutral pH as compared to acidic pH. The IC50 results were shown to correlate with a decrease in intracellular uptake of doxorubicin at low pH. The proposed hydrogels were confirmed to be nontoxic to healthy MCF-10A mammary epithelial cells. Rheological studies were performed to verify that the dual-loaded hydrogels were injectable. The mechanical and release properties of the hydrogels were maintained after extended storage. The chemotherapeutic activity of doxorubicin was evaluated in the presence of the proposed pH-regulating hydrogels. The findings suggest a promising nontoxic, biodegradable hydrogel buffer delivery system that can achieve two simultaneous important goals of local acidosis neutralization and chemotherapeutic release.

Glutaraldehyde-pea protein grafted polysaccharide matrices for functioning as covalent immobilizers

Three polysaccharide matrices (κ-Carrageenan (Carr), gellan gum, and agar) were grafted via glutaraldehyde (GA) and pea protein (PP). The grafted matrices covalently immobilized β-D-galactosidase (β-GL). Nonetheless, grafted Carr acquired the topmost amount of immobilized β-GL (iβ-GL). Thus, its grafting process was honed via Box-Behnken design and was further characterized via FTIR, EDX, and SEM. The optimal GA-PP-Carr grafting comprised processing Carr beads with 10% PP dispersion of pH 1 and 25% GA solution. The optimal GA-PP-Carr beads acquired 11.44 Ug^-1 iβ-GL with 45.49% immobilization efficiency. Both free and GA-PP-Carr iβ-GLs manifested their topmost activity at the selfsame temperature and pH. Nonetheless, the β-GL K_m and V_max values were reduced following immobilization. The GA-PP-Carr iβ-GL manifested good operational stability. Moreover, its storage stability was incremented where 91.74% activity was offered after 35 storage days. The GA-PP-Carr iβ-GL was utilized to degrade lactose in whey permeate with 81.90% lactose degradation efficiency.

Boosting the stability of β-galactosidase immobilized onto soy-protein isolate-glutaraldehyde-functionalized carrageenan beads

Uncontrolled enzyme-immobilizer interactions were evident after immobilizing β-galactosidase onto soy-protein isolate-glutaraldehyde-functionalized carrageenan beads. Such interactions triggered shortcomings in the immobilized β-galactosidase (iβGL) thermal and storage stabilities. The thermal stability of the iβGL was somewhat lesser than that of the free βGL. Moreover, the iβGL suffered an initial sharp fall-off in its activity after storing it. Thus, approaches were adopted to prevent the occurrence of such uncontrolled enzyme-immobilizer interactions, and accordingly, boost the stability of the iβGL. These approaches involved neutralizing the covalently reactive GA entities via glycine and also altering the functionalizing GA concentrations. Nonetheless, no improvement was recorded in the iβGL thermal stability and this indicated that the uncontrolled enzyme-immobilizer interactions were not mediated via GA. Another approach was then attempted which involved treating the iβGL with lactose. The lactose-treated iβGL (LT-iβGL) presented superior thermal stability as was verified from its smaller k _d and bigger t _1/2 and D-values. The LT-iβGL t _1/2 values were 5.60 and 3.53 fold higher than those presented by the free βGL at 62 and 65 °C, respectively. Moreover, the LT- iβGL presented loftier ΔG than did the free βGL. The storage stability of the LT- iβGL was also superior as it offered 100.41% of its commencing activity on its 43rd storage day. Thus, it could be concluded that lactose prevented the uncontrolled enzyme-immobilizer interactions. Finally, advantageous galacto-oligosaccharides (GOS) were prepared via the iβGL. The GOS were then analyzed with mass spectrometry, and it was shown that their degree of polymerization reached up to 7.

Green method for improving performance attributes of wool fibres using immobilized proteolytic thermozyme

Wool has the tendency to turn into felt during agitation in washing machines. Thus, a benign non-polluting method for the production of machine-washable wool was developed herein. Initially, a proteolytic bacteria was isolated from hot region soil. The bacterial isolate was identified as Bacillus safensis FO-36bMZ836779 according to the 16S rRNA gene sequencing. Afterwards, the extracellular protease produced by this isolate was covalently immobilized in order to enhance its stability under non-ambient conditions which are usually adopted in industrial sectors like textile industries. Sericin, which is usually discharged into degumming effluent of natural silk, was utilized to prepare the immobilization carrier. Box–Behnken design was adopted in order to hone the preparation of the sericin–polyethylene–imine–glutaraldehyde activated agar carrier. The pH and temperature profiles of the free and immobilized proteases were compared. Later, wool fibres were bio-treated with both the free and the immobilized enzymes. The effect of process conditions on the resistance of the bio-finished wool to felting was investigated. The alteration in the fibre morphology was monitored using SEM. Amino acid analysis and alkali solubility tests were adopted to assign any change in the chemical structure of the bio-treated wool. The influence of bio-treatment of wool on its inherent properties was assigned. Results revealed that bio-treatment of wool with the said enzyme led to production of machine-washable wool without severe deterioration in the fibres’ properties. In an energy- and water-consuming process, the hot solution from bio-treatment bath was used successfully in dyeing of wool.

Amphiphilic chitosan-g-poly(trimethylene carbonate) - A new approach for biomaterials design

The paper presents the synthesis and characterization of poly(trimethylene carbonate) grafted chitosan as a new water soluble biopolymer suitable for in vivo applications. The synthesis was performed via ring-opening polymerization of 1,3-dioxan-2-one (trimethylene carbonate) (TMC) monomer, initiated by the functional groups of chitosan in the presence of toluene as solvent/swelling agent. By varying the molar ratio between the glucosamine units of chitosan and TMC, a series of chitosan derivatives with different content of poly(trimethylene carbonate) chains was synthetized. The structural characterization of the polymers was realized by FTIR and ¹H NMR spectroscopy and their solubility was assessed in water and in organic solvents as well. The biocompatibility was investigated by MTS assay on Normal Human Dermal Fibroblasts, and the biodegradability was evaluated in lysozyme buffer solution. Further, the surface properties of the polymer films were analyzed by polarized optical microscopy, atomic force microscopy and water-to-air contact angle measurements. It was established that, by 5% substitution of chitosan with poly(trimethylene carbonate) chains having an average polymerization degree of 7, a water soluble polymer can be attained. Compared to the pristine chitosan, it has improved biocompatibility in solution and moderate wettability and higher biodegradability rate in solid state, pointing its suitability for in vivo applications.

Enhancement of the mechanical properties of chitosan

Chitosan (CS) has been investigated for copious applications in the biomedical, industrial and environmental fields owing to its diverse advantageous traits. Nevertheless, CS exhibits debilitated mechanical stability. This debilitated mechanical stability constitutes an obstacle to nearly all of CS's applications. Hence, in this review we discussed different approaches that could be adopted in order to escalate the mechanical properties of CS. Chemical cross-linking was among these approaches where CS was chemically cross-linked with various agents, such as glutaraldehyde, vanillin, and genipin. Different plasticizers were also incorporated with CS. Moreover, nano-materials were added to CS so as to form nano-composites of enhanced mechanical properties. Porogens were also employed to increase the surface area available for the CS's physical and chemical cross-linking processes. Other reports attempted to modify the fabrication conditions and gelling system of CS as a means of producing mechanically stable CS gels.

Chitosan-based (Nano)materials for Novel Biomedical Applications

Chitosan-based nanomaterials have attracted significant attention in the biomedical field because of their unique biodegradable, biocompatible, non-toxic, and antimicrobial nature. Multiple perspectives of the proposed antibacterial effect and mode of action of chitosan-based nanomaterials are reviewed. Chitosan is presented as an ideal biomaterial for antimicrobial wound dressings that can either be fabricated alone in its native form or upgraded and incorporated with antibiotics, metallic antimicrobial particles, natural compounds and extracts in order to increase the antimicrobial effect. Since chitosan and its derivatives can enhance drug permeability across the blood-brain barrier, they can be also used as effective brain drug delivery carriers. Some of the recent chitosan formulations for brain uptake of various drugs are presented. The use of chitosan and its derivatives in other biomedical applications is also briefly discussed.

Supramolecular Strategy Effects on Chitosan Bead Stability in Acidic Media: A Comparative Study

Chitosan beads attract interest in diverse applications, including drug delivery, biocatalysis and water treatment. They can be formed through several supramolecular pathways, ranging from phase inversion in alkaline solutions, to the ionic crosslinking of chitosan with multivalent anions, to polyelectrolyte or surfactant/polyelectrolyte complexation. Many chitosan bead uses require control over their stability to dissolution. To help elucidate how this stability depends on the choice of supramolecular gelation chemistry, we present a comparative study of chitosan bead stability in acidic aqueous media using three common classes of supramolecular chitosan beads: (1) alkaline solution-derived beads, prepared through simple precipitation in NaOH solution; (2) ionically-crosslinked beads, prepared using tripolyphosphate (TPP); and (3) surfactant-crosslinked beads prepared via surfactant/polyelectrolyte complexation using sodium salts of dodecyl sulfate (SDS), caprate (NaC10) and laurate (NaC12). Highly variable bead stabilities with dissimilar sensitivities to pH were achieved using these methods. At low pH levels (e.g., pH 1.2), chitosan/SDS beads were the most stable, requiring roughly 2 days to dissolve. In weakly acidic media (at pH 3.0⁻5.0), however, chitosan/TPP beads exhibited the highest stability, remaining intact throughout the entire experiment. Beads prepared using only NaOH solution (i.e., without ionic crosslinking or surfactant complexation) were the least stable, except at pH 5.0, where the NaC10 and NaC12-derived beads dissolved slightly faster. Collectively, these findings provide further guidelines for tailoring supramolecular chitosan bead stability in acidic media.