. 2021 Mar 26;14(7):1631. doi: 10.3390/ma14071631

Table 2.

Gels applied to bone regeneration.

Authors	Materials	Process	Advantages	Disadvantages
Takeshita et al. [17]	CS	Air-drying; Freeze-drying; SC-CO₂ drying	Presence of a suitable nanostructure during SC-CO₂ drying	Structural degradation during freeze-drying and air-drying; Smooth pores surface for freeze-drying and SC-CO₂ drying
Conzatti et al. [18]	CS/ALG	Air-drying; Freeze-drying; SC-CO₂ drying	Mesoporosity was obtained by freeze-drying and SC-CO₂ drying	Not presence of porosity after air-drying
Gupta and Nayak [23]	KRT/ALG	Freeze-drying	High level of porosity	Time-consuming process; Polydisperse macropores size distribution
Baldino et al. [27]	ALG/GLT	SC-CO₂ drying	Possible modulation of morphology and mechanical properties of polymeric blends; Presence of nanopores and homogenous structure; Good polymer dispersion	Long time process to completely remove GTA traces
Baldino et al. [54]	CS	SC-CO₂ drying	Removal of GTA during the process; Presence of nanoporous structure; Good definition of cells three-dimensional scaffolds orientation	Absence of microporosity
Kazimierczak et al. [77]	CS/AGR/HAp	Gas foaming + Freeze-drying	Good value of porosity	Presence of closed pores; Complex process
Baldino et al. [79]	CS/GLT	SC-CO₂ drying	Possibility to obtain different levels of microporosity and nanoporosity changing polymeric blend compositions; Good mechanical properties	Possible phenomena of separation between the two biopolymers increasing the relative concentrations
Tohamy et al. [93]	SALG/Hydroxyethylcellulose/HAp	Freeze-drying + Cross-linking with Ca²⁺	Improved good mechanical properties	Disomogenous macroporosity and absence of nanoporous structure for cell attachment
Purohit et al. [94]	GO/GLT/ALG	Freeze-drying	Suitable swelling profile	Morphology mainly represented by closed pores
Afshar and Ghaee [95]	CS/ALG/HNT	Freeze-drying + Amination reaction	Homogenous porous structure; Good biochemical characteristics	Complex and time-consuming process
Martins et al. [96]	CAALG/STR	SC-CO₂ drying using three different depressurization rates	Good biocompatibility; Good bioactivity	Not presence of nanoporous structure
Tsiourvas et al. [99]	Nano-HAp/CS	Freeze-drying	Open interconnected highly porous structure; Improved mechanical properties of CS	Disomogenous macroporosity; HA microparticles were not homogenously dispersed
Serra et al. [100]	CS/GLT/β-TCP	Ionic cross-linking + Freeze-drying	Improved mechanical properties of CS after the addition of GLT and β-TCP; Good level of biomineralization	Drastic decrease in porosity after TCP addition
Nath et al. [102]	BMP-2/CS/HA/Genipin	Freeze-drying	Cross-linking of CS-HA improved the PEC stability in aqueous solution	Burst effect was detected for all samples
Adhikari et al. [103]	CS/CMC/MgG	Freeze-drying	MgG decreased water adsorption of CS scaffolds; Presence of macroporosity and smaller inner pores	Time-consuming process; Burst effect during MgG release
Liu et al. [104]	ALG/CS	Freeze-drying	Good bioactivity of the scaffolds	Samples collapse after processing
Shi et al. [105]	ALG–DA/QCS templated HAp	Iterative layering freeze-drying + Crosslinking by Ca²⁺	Presence of a layered microstructure	Complex process; Uncontrolled degradation profile; Burst effect during levofloxacin release
Kolanthai et al. [106]	SALG/CS/CLG	Freeze-drying	Controlled swelling profile; Improvement of mechanical properties; Good support for cells growth and osteogenic differentiation	The use of a chemical cross-linker resulted in a loss of interconnectivity and in a loss of nanofibrous structure
Yilmaz et al. [108]	CS/GO/HAp	SC-CO₂ drying	Improved tensile strength of CS scaffolds	Possible residues of GTA; Limitation in GO wt.% used because it can be cytotoxic for living cells; Not presence of nanopores
Baldino et al. [109]	CS	SFEP	Possible modulation of morphology; Uniform structure; High interconnectivity; Presence of micropores and nanopores	Time-consuming process
Ozdemir et al. [110]	CS	Freeze-drying; SC-CO₂ drying	Smaller and more uniform structure after SC-CO₂ drying	Not uniform structure during freeze-drying
Luo et al. [116]	NG/HAp/AGR	Hydrothermal + Cross-linking + Freeze-drying	Good mechanical properties	Large pores with irregular shape
Sivashankari and Prabaharan [117]	AGR/CS	Freeze-drying	Good swelling properties; Good mechanical properties; Good bioactivity	The effect of GO on the porosity did not show a precise trend