Development of smart injectable and biodegradable sodium alginate hydrogels for biomedical applications
Loading...
Date
2025-06-06
Authors
Σαραβάνου, Σοφία Φαλιά
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Biomedicine has made significant progress driven by continuous innovation and research in healthcare. During the last few decades, functional improved natural polysaccharides have gained great attention for hydrogel development for biological purposes. These materials derived from natural sources are attractive choices for biomedical applications due to their similarities with the extracellular matrix, biocompatibility and negligible toxicity. Therefore, chemical modifications could maximize their potential. As so, modification of natural polysaccharides into “smart” systems by chemical and physical alterations to respond and to adapt to external stimuli, such as temperature and pH, enables their use in a wide range of biomedical applications. These hydrogel systems are continuously being designed and developed and present great potential in bioapplications such as drug delivery and tissue regeneration. Therefore, the aim of this work is to design and investigate the utilization of multi-responsive hydrogels using the natural polysaccharide sodium alginate as the main backbone material in potential bioapplications such as injectable drug delivery systems or as 3D printable bioink cell carrier. First, Chapter 2 highlights the development of a dual crosslinked network based on sodium alginate-based graft copolymers by combining the hydrophobic association of the thermosensitive P(NIPAM-co-NtBAM) grafted chains with a second ionic association through the addition of Ca2+ cations. Oscillatory rheology revealed a two-step synergistic gelation of 5 wt.% NaALG-g-P(NIPAMco-NtBAM)/Ca2+ hydrogels: 1. at room temperature a soft 3D network is formed via the “egg-box model” i.e., ionic interaction between the calcium ions and the carboxyl groups on sodium alginate monomer unit groups and 2. the heating process triggers the hydrophobic association of the thermoresponsive P(NIPAMco-NtBAM) side chains, expanding the network. Surprisingly, the dual crosslinking mechanism resulted in a five-to-eight-fold increase in the storage modulus of the developed hydrogel due to reinforced hydrophobic crosslinkers above the critical gelation temperature, which was further boosted by the ionic bonding of the alginate backbone. Furthermore, the co-existence of the two bonding interactions is crucial for the morphology, injectability and 3D printability of the gels, as they exhibit a shear thinning effect under applied shear stress. Therefore, the proposed copolymer can form arbitrary domains under mild 3D printing conditions indicating its further use as a bioprinting ink. The 3D printed scaffold can promote human periosteum derived cells (hPDCs) growth and their capacity to develop 3D spheroids. Furthermore, as the bioink can behave as a sol-to-gel and gel-to-sol during heating or cooling, the thermoresponsive crosslinking mechanism of the polymer network can be further utilized for the facile recovery of the cell spheroids. As a result, the proposed system presents selfhealing and shear thinning properties under mild conditions and it can host and promote cell spheroid formation. The aforementioned properties enable the utilization of biomaterials in various biomedical applications such as cell spheroid encapsulants for drug screening, injectable therapeutics or 3D in vitro modeling. Moreover, a sodium alginate-based copolymer grafted by pure PNIPAM chains was used as a second gelator combined with methylcellulose as a gelation thickener (NaALG-co-PNIPAM/MC). The gelation properties of the networks were further enhanced through the addition of calcium cations. Once more, the crosslinking mechanism of the proposed network is regulated by the secondary ionic interactions by the addition of calcium ions and by hydrophobic associations due to the thermoresponsive PNIPAM chains. Interestingly, methylcellulose was found to increase the dynamic moduli of the developed hydrogels, rendering them suitable for 3D printing in biomedical applications. The fidelity of the 3D printed scaffolds remained as high as 94% after one week. Furthermore, pre osteoblastic cells adhered to the proposed 3D printed scaffolds showed 80% viability compared to tissue culture polystyrene controls and the sodium alginatebased materials were found to promote significant osteogenic potential, as indicated by increased alkaline phosphatase activity, calcium and collagen production. The proposed materials were found to demonstrate great potential in bone tissue engineering. In addition, in Chapter 3 emphasis is given to a single chain polymer gelator comprising an alginate dually grafted backbone with thermoresponsive P(NIPAM-co-NtBAM) polymer grafting chains and diols/pH sensitive 3aminophenylboronic acid moieties. The resulting material can form robust polymer networks by three cooperative crosslinking mechanisms: 1. the hydrophobic association of the thermo-sensitive polymer grafts above gelation temperature at 24 oC, 2. the boronate esters formation between the boronic acid and the diols of the sodium alginate at physiological pH and 3. the ionic interactions of the alginate carboxylate moieties with calcium ions. The developed polymer presents excellent tunability of the mechanical properties guided by combinations of temperature, pH and glucose stimuli. Also, the graft polymer is found to be non-toxic and could form simple 3D printing structures that can undergo multi-stimuli responsive erosion profiles based on the variation of temperature, pH or glucose and it could be utilized as a drug delivery system for Type I diabetes. Finally, in Chapter 4 the design of a semi-interpenetrated polymer network is presented. The development of the network is based on the intramolecular combination of alginate-based backbones grafted either with the diols/pHsensitive 3-aminophenylboronic acid moieties, i.e., NaALG-g-BA or with the thermoresponsive P(NIPAM-co-NtBAM) polymer, i.e., NaALG-g-P(NIPAM-coNtBAM). The gelation behavior of the resulting networks is determined by the blending ratio of the two alginate-based materials. In this chapter the crosslinking mechanisms are the hydrophobic association due to the thermoresponsive PNIPAM-based chains above 24 oC and the formation of dynamic covalent boronate esters at physiological pH. At a blending ratio 70/30 wt.% of the thermo/diols-responsive copolymers, the hybrid network enhanced the arrangement of cell spheroids with average diameter approximately 60 μm after one day as the boronic acids can spontaneously form boronate esters with the cellular glycocalyx. The network can be dissociated by the enrichment of glucose solution, an antagonistic molecule to the ester blocks. The blending matrix is found to be non-toxic, injectable and 3D printable by forming 3D geometries rendering it promising for use in drug screening and in microtissue formation engineering.
Description
Keywords
Sodium alginate, Smart hydrogels, Drug delivery, 3d bioprinting