Table 3.

Porous materials based on cellulose nanofibrils (CNF) and applied in regenerative medicine.

Material	Fabrication Method	Cell type	Application	Experimental conditions	Observations	Ref.
CNFa TOCNF Acetylated CNF	3D printing	H9c2 cardiomyoblast	Cell culturing scaffolds	Nozzle diameter of 410 μm, 630 μm, and 840 μm, extrusion pressure of 35–55 kPa, print speed 5–12 mm/s	High biocompatibility with cardio myoblasts and induced cell proliferation for 21 days	[218]
CNF-alginate- lignin particles	3D printing	HepG2 Hepatocellular carcinoma cell line	Soft tissue engineering	Nozzle diameter of 410 μm (22 G), print speed 11.5 mm/min. The scaffolds were crosslinked in 90 mM CaCl2, stored at ambient conditions for 2 h, or in 1 × DPBS + solution for 1 week at 4 °C	The shear-thinning behavior of CNF did not alter due to addition of up to 25% LPs. Good cell viability regardless of the lignin content (LP/CNF ratio 0–25 w/w %)	[242]
PGS-PPy-TOCNF	3D printing	H9c2 cardiomyoblast	Treatment of cardiovascular diseases	Nozzle diameter of 840 μm (18G). After 3D printing, the samples were frozen overnight at −18 °C followed by freeze-drying for 48 h, at −49 °C and 0.05 mbar. Then, the sample was cured for 48 h in a vacuum oven at 120 °C	Porosity of 78 ± 2%, electrical conductivity of 34 ± 2.7 mS cm−1, Young’s Modulus 0.6 ± 0.16 MPa, high biocompatibility with cardiomyoblasts and induced cell proliferation for 28 days	[114]
CNF-CNT	3D printing	HPACC, human neuroblastoma	Neural guidelines	Nozzle diameter of 300 μm, printing pressure 65 kPa, print speed 10 mm/s	Viability, proliferation, and attachment of cells to the guidelines with less than 1 mm diameter and 3.8 × 10−1 S cm−1 conductivity	[231]
Cross-linked TOCNF-alginate	3D printing	–	Bone tissue engineering	Nozzle diameter of 500 μm, printing pressure of 50 kPa, printing speed 16 mm/s. The structures were post-crosslinked in 0.5 M CaCl2 for 20 min.	Successful ex vivo mineralization of HA up to 20% in the scaffold made from an equal ratio of CNF and alginate. The compressive strength and elastic modulus ranged from 87 to 455 MPa, and 135–1511 MPa, respectively.	[233]
CNF	3D printing	–	Tissue engineering	Nozzle diameter 200–510 μm	4D shape-morphing mesoscale structures that are initiated upon hydration. Young’s Modulus in longitudinal and Transverse direction 1267 ± 201 and 1011 ± 39, respectively.	[121]
polyurethane-CNF	3D printing	NIH 3T3 mouse skin fibroblasts and human fibroblasts	Tissue engineering	Nozzle diameter 160 μm, Printing pressure 50–200 kPa, printing speed 7–10 mm/s	Waterborne PU and CNF developed high fidelity structures with high cell proliferation. The compression storage modulus decreased from 1.57 MPa at day 0–0.91 MPa at day 28.	[243]
Cross-linked CNF	3D printing	Mouse embryonic fibroblast	Cell culture scaffold		The smallest tested concentration of CaCl2 (0.22 wt%) was better for the cells. The higher stability of the structures by cooling and crosslinking steps that favor cell viability.	[220]
Cross-linked CNF-alginate	3D printing	Human nasoseptal chondrocytes	Cartilage tissue engineering	Nozzle diameter 300 μm, Printing pressure 20–60 kPa, printing speed 10–20 mm/s	Shapes resembling an ear and a meniscus with high fidelity and stability were successfully printed. Viability of 73% and 86% after 1 and 7 days of 3D culture.	[112]
CNF-alginate	3D printing	human nasal chondrocytes, human bone marrow-derived mesenchymal stem	Cartilage tissue engineering	Cell density 10 million/mL	Effective cartilage synthesis occurred in cell-laden 3D constructs with promising mechanical properties hand high fidelity.	[236]
CNF-alginate	3D printing	human nasal chondrocytes	Cartilage tissue engineering	Cell density 20 million/mL, nozzle diameter 150 μm	Excellent stability of shape and size that supports the redifferentiation of cells.	[235]
TOCNF- Aloe vera	3D printing	–	Tissue engineering	Nozzle diameter 630 μm	Development of fully bio-based hydrogels with high stability and excellent viscoelastic properties. Porosity higher than 80–95% and a high-water uptake capacity of up to 46 g/g. Tensile modulus of 4.95–73.44 kPa	[244]
CNF–CaCO3	3D printing	–	Controlled drug release	Nozzle diameter 1.21 mm	Achieving controlled drug release that mimicked the colons condition	[245]
CNF-alginate	3D printing	L929 mouse fibroblast	Wound healing	Nozzle diameter 580 μm, printing speed 3 mm/s	CNF from sugarcane bagasse residue has efficient biocompatibility	[237]
Cross-linked CNF-GelMA	3D printing	3T3 fibroblast	Wound healing	Precision tips (25G, and 30G), printing pressure 65–80 kPa, printing speed 16–32 mm/s	A facile approach to obtain high cell compatibility and proliferation. Mechanical strength in the range of 2.5–5 kPa	[246]
Cross-linked TOCNF	3D printing	Human dermal fibroblasts	Wound healing	Nozzle diameter 200 μm, printing pressure 50 kPa, printing speed 8 mm/s	Higher rigidity of the scaffold improves cell proliferation. Mechanical strength in the range of 3–8 kPa	[219]
CNF- Peptide	3D printing	–	Wound healing	Nozzle diameter 410–840 μm, printing pressure 100–350 kPa, printing speed 10 mm/s	Obtaining structures with programmable actuation and texture with controlled mechanical and antimicrobial properties	[247]
CNF- bioactive glass	Freeze casting	MC3T3-E1 cells	Bone tissue engineering		Light-weight bio-active cryogels that promote ion release (Si, Ca, P, Na). Cryogel compression strength range 11 ± 1 to 24 ± 1 kPa	[225]
Cross-linked gelatin-CNF	Freeze casting	Human bone marrow mesenchymal stem	Bone tissue engineering	The samples were frozen at −20 °C followed by freeze-drying for 24 h	Different crosslinking methods did not have an adverse biological effect on cells, and the composite promoted cell differentiation	[238]
CNF-PEGDA	Freeze casting	NIH 3T3 mouse embryonic fibroblast	Cartilage tissue engineering	The samples were frozen at −80 °C for 24 h followed by freeze-drying at −68 °C for 48 h	Structure with about 90% porosity and 1–3 MPa mechanical strength.	[239]
CNF-PVA	Freeze casting	Fibroblast cells and keratinocytes	Skin tissue engineering		A novel, integrated skin mimics bilayer structures (mimicking Epidermis and Dermis). Elongation at break range of 52 ± 7 to 91 ± 1. Young’s modulus range of 0.04–8.3 ± 1.8 kPa and porosity of 77 ± 7.3%	[240]
TOCNF	Freeze casting	U937 cell	Tissue engineering	The structures were frozen at −20 °C for 24 h and then freeze-dried for 24 h	Production of considerably less inflammatory cytokines than gelatin according to in vivo test	[249]
Cross-linked CNF/organosilanes and chitosan	Freeze casting	Human skin fibroblasts	Hemostatic dressing	The hydrophilic layer was frozen at −80 °C, and after permeation of the hydrophobic layer, the Combination structure was freeze-dried for 36 h at −50 °C.	Effective bleeding control with nearly 50% less blood loss	[234]
CNC/CNF-alginate	Freeze casting	L929-fibroblast	Tissue repair and wound healing	The samples were frozen in liquid nitrogen (−196 °C) for 5 min, followed by a freeze-drying step at −50 °C for 48 h. The dried materials were then added to a bath of CaCl2 at 2 wt % for 24 h. Then, the gels were washed with distilled water and were frozen with liquid nitrogen and freeze-dried again.	ECM biomimetic structure with promising mechanical properties, bioadhesion, cytocompatibility	[207]
CNC/CNF-chitosan	Freeze casting	–	Tissue regeneration	The slurry was poured in a polytetrafluoroethylene tube and was sealed with a copper mold (bottom section). The mold was then placed on liquid nitrogen. The molds were equilibrated to 4 °C for 10 min before a cooling rate of either 10 or 1 °C/min was applied until the mold reached a temperature of −150 °C. The frozen slurries for 72 h at 0.008 mbar and a coil temperature of −85 °C.	Obtaining structures with high porosity and surface area with controllable pore alignment	[192]
Crosslinked CNF/CNC-alginate	Casting	Human naso-septal chondrocytes	Cartilage tissue engineering	Crosslinking was performed at room temperature using 0.1 M, 0.5 M or 1.0 M calcium chloride (CaCl2).	Different crosslinking and sterilization conditions had a considerable impact on the microstructure architecture.	[194]
PLA-PBS- CNF	Electrospinning	Dermal fibroblasts	Vascular tissue engineering	The operating voltage of 20 kV, flow rate 0.5 mL/h and the distance between the electrodes was 12 cm.	ECM mimic microstructure with excellent cell proliferation and attachment on the composites	[241]
CNF–CNC	Electro-spinning	Human dental follicle	Artificial organ	The operating voltage of 20 kV, flow rate 0.03 mL/min, A steel rotating collector (6 cm in diameter) wrapped with aluminum foil was placed 10 cm away. The tangential velocity of the collector was set at 300 m/min	All cellulose nanocomposite with high fiber alignment and indentation modulus of 2492 ± 61.6 MPa	[197]
Cellulose acetate	Electro-spinning**	Osteoblast	Bone tissue engineering	The operating voltage of 17 kV, flow rate 1.0 mL/h and the distance between the electrodes was 15 cm. Then, the fabricated mats were dried at 40 °C for 24 h.	Biomimetic mineralization, enhanced cell proliferation, and attachment. The apparent density of 0.26 g/mL	[152]
Cellulose acetate	Electro-spinning	–	Bone tissue engineering		Formation of HA covering the nanofibers. Specific surface areas of the composite were 51.08 m2/g. The CelluNF/HAp composites had mesopores in a range of 2–18 nm, and large amount of micropores in a range of 1.03–2.0 nm	[151]

^aCNF: Cellulose nanofibrils; TOCNF: TEMPO-oxidized cellulose nanofibrils; PGS: Poly (glycerol sebacate); PPy: Polypyrrole; CNT: Carbon nanotube; GelMA: Gelatin meth acryloyl; PEGDA: Poly(ethylene glycol)diacrylate; PVA: Polyvinyl alcohol; PLA: Polylactic acid; PBS: Polybutylene succinate; ECM: extracellular matrix.