Hydrogels from biopolymers are readily synthesized, can possess various characteristics for different applications, and have been widely used in biomedicine to help with patient treatments and outcomes. Polysaccharides, polypeptides, and nucleic acids can be produced into hydrogels, each for unique purposes depending on their qualities. Examples of polypeptide hydrogels include collagen, gelatin, and elastin, and polysaccharide hydrogels include alginate, cellulose, and glycosaminoglycan. Many different theories have been formulated to research hydrogels, which include Flory-Rehner theory, Rubber Elasticity Theory, and the calculation of porosity and pore size. All these theories take into consideration enthalpy, entropy, and other thermodynamic variables so that the structure and pore sizes of hydrogels can be formulated. Hydrogels can be fabricated in a straightforward process using a homogeneous mixture of different chemicals, depending on the intended purpose of the gel. Different types of hydrogels exist which include pH-sensitive gels, thermogels, electro-sensitive gels, and light-sensitive gels and each has its unique biomedical applications including structural capabilities, regenerative repair, or drug delivery. Major biopolymer-based hydrogels used for cell delivery include encapsulated skeletal muscle cells, osteochondral muscle cells, and stem cells being delivered to desired locations for tissue regeneration. Some examples of hydrogels used for drug and biomolecule delivery include insulin encapsulated hydrogels and hydrogels that encompass cancer drugs for desired controlled release. This review summarizes these newly developed biopolymer-based hydrogel materials that have been mainly made since 2015 and have shown to work and present more avenues for advanced medical applications.

This work demonstrates a green method for the encapsulation of a natural phase change material (PCM), lauric acid (LA), in polystyrene (PS) hollow fibers through a solvent-assisted diffusion process inside fiber nanochannels. The obtained LAPS composite fibers had a melting enthalpy of up to 147.8 J/g, which was 82.0% the heat storage capacity of pristine LA (180.2 J/g). This capacity was higher than the values (generally less than 60%) reported in the literature. The LA content in the composite fibers could be controlled by the solution concentration and the solvent. On the contrary, encapsulation time had little effect on the final LA loading beyond 1 h due to the rapid diffusion of the LA solution. The optimal LA loading (82.2%) was achieved in 0.4 g/mL LA ethanol solution for 1 h, which was more than 4 times the weight of PS fibers. Simultaneous TGA−DSC, ATR, Raman, and SEM measurements confirmed the homogeneous distribution of LA inside the fibers across the whole membranes. Further, the LAPS composite fibers showed a long-lasting stability during cycling without storage capacity deterioration, as well as an exceptional structural stability without LA leaking and fiber rupture during 100 heating−cooling cycles. The energy-dense and form-stable LAPS composite fibers have a great potential for various thermal energy storage applications like "temperature-smart" buildings and textiles.