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As customizable biomaterials, hydrogels have attracted great promise in several industries, including drug delivery, tissue engineering, biosensing and regenerative medicine. Three-dimensional networks of these hydrophilic polymers exhibit special properties, such as increased water content, soft and flexible texture and biocompatibility, making them excellent candidates to simulate the extracellular matrix and promote cell development and tissue regeneration. In this review paper, we provide a comprehensive overview of hydrogels, focusing on the design concepts, synthesis processes and characterization techniques. Different types of hydrogel materials, including natural polymers, synthetic polymers and hybrid hydrogels, along with their unique properties and applications are discussed. Improvements in hydrogel-based platforms for controlled drug delivery are being investigated. Recent advances in bioprinting processes using hydrogels to create complex tissue constructs with excellent spatial control are also explored. Hydrogel performance is examined across multiple variables, including mechanical properties, degradation behavior and biological interactions, with an emphasis on the importance of tailoring hydrogel qualities for specific applications. This review paper also provides insights into future directions in hydrogel research, including stimuli-sensitive hydrogels, self-healing hydrogels and bioactive hydrogels, which promise promising advances in the field. In general, the aim of this review paper is to provide the reader with a detailed understanding of hydrogels and all of their potential applications, making them a valuable tool for scientists and researchers working on biomaterials and tissue engineering.

We discuss the results of a computer simulation of the biopolymer crystal growth and aggregation based on the 2D lattice Monte Carlo technique and the HP approximation of the biopolymers. As a modeled molecule (growth unit) we comparatively consider the previously studied non-mutant lysozyme protein, Protein Data Bank (PDB) ID: 193L, which forms, under a certain set of thermodynamic-kinetic conditions, the tetragonal crystals, and an amyloidogenic variant of the lysozyme, PDB ID: 1LYY, which is known as fibril-yielding and prone-to-aggregation agent. In our model, the site-dependent attachment, detachment and migration processes are involved. The probability of growth unit motion, attachment and detachment to/from the crystal surface are assumed to be proportional to the orientational factor representing the anisotropy of the molecule. Working within a two-dimensional representation of the truly three-dimensional process, we also argue that the crystal grows in a spiral way, whereby one or more screw dislocations on the crystal surface give rise to a terrace. We interpret the obtained results in terms of known models of crystal growth and aggregation such as B-C-F (Burton-Cabrera-Frank) dislocation driven growth and M-S (Mullins-Sekerka) instability concept, with stochastic aspects supplementing the latter. We discuss the conditions under which crystals vs non-crystalline protein aggregates appear, and how the process depends upon difference in chemical structure of the protein molecule seen as the main building block of the elementary crystal cell.

The results of a computer simulation of the lysozyme crystal growth influenced by monomer and tetramer (aggregate) units are discussed. A very recently introduced computer model of biopolymer crystal growth and aggregation is based on the 2D lattice Monte Carlo technique and the coarse-grained HP approximation of the lysozyme monomeric unit. Acceleration of the lysozyme crystal growth by a factor of 4/3, based on the 2AUB (PDB ID) lysozyme unit, obtained from the Langmuir–Blodgett nanotemplate method, has clearly been confirmed by means of the proposed computer simulation. It is concluded that the aggregates (tetramers) involving 2AUB lysozyme crystal growth can be expected to be slightly accelerated when compared to its monomer-based (PDB ID: 193L) counterpart, which is in excellent accord with very recent experimental findings of the emerging applied science called protein nanocrystallography.

Solubility of tetragonal lysozyme crystal was measured by using two different methods. The solubility measured by using growth rates of the crystal corresponded well to that measured by using change in the concentration of the supernatant of the solution. Our data also corresponded well to the data obtained by Sazaki et al. and Gray et al., while not to those obtained by Howard et al. and Rosenberger et al. The discrepancies are due to the difference in the principles of the methods. We also checked effects of different initial concentrations on the solubility. Contrary to previous reports, the solutions of the different initial concentrations did not reach equilibrium when their concentrations attained to a same value.

The effects of solvents on the structural stability of cross-linked lysozyme crystals were investigated by an immersion test using alkaline (0.1 M ammonia [NH₃] and 0.1 M sodium hydroxide [NaOH]), acidic (0.1 M acetic acid [CH₃COOH] and 0.1 M hydrochloric acid [HCl]) and organic (50% [v/v] and undiluted ethanol, acetone, 2-propanol and dimethyl sulfoxide [DMSO]) solvents. The morphology and lattice constants were monitored by optical microscopy and X-ray crystallography. The cross-linked crystals exhibited good stability against NH₃, CH₃COOH, HCl, ethanol, acetone and 2-propanol. However, samples preserved in DMSO and NaOH were severely degraded.

Macro-sized intrinsically shielded hydrogel beads have been prepared from BSA and CM-dextran grafted with CB using a technique based on freeze-thawing gelation method. The size of the beads lies in around 500 μm. Isothemal titration calorimetry (ITC) showed that the relative binding affinities of the lysozyme for CB, compared with BSA, at pH 3.0 was stronger than that at pH 7.4. They were employed for the affinity separation of lysozyme using chromatography column. Their adsorption capacity for lysozyme at pH 3.0 is higher than that at pH 9. In a binary mixture of lysozyme and ovalbumin, the beads showed very high selectivity toward lysozyme. Lysozyme of very high purity (> 93%) was obtained from a mixture of lysozyme and ovalbumin, and 85% from egg white solution. The results indicate that the macro-sized bead can be used for the separation, purification, and recovery of lysozyme in a chromatograph column.

The bactericidal effect of serum plays a key role in humoral defense against microbial pathogens. Lysozyme - cooperates with the complement system in the bactericidal action of serum. Serotype O48 Salmonella belongs to clinically important bacteria causing diarrhoea in infants and children. Our present results demonstrated that the most efficient killing of Salmonella O48 occurred when all components of normal bovine serum (NBS) cooperated with each other. It is very interesting that elimination of lysozyme from NBS by using bentonite significantly decreased the bactericidal activity of NBS against Salmonella O48 strain. The results of X-ray diffractometric studies suggested that apart from lysozyme, other components of serum were adsorbed on the bentonite particles.