Table 2.

Novel scaffold‐based culture systems used to study the role of ECM stiffness in cancers

	Culture system	Materials	Specialty	Cell type	Ref.
PG scaffold	GG−Silk Spongy‐like Hydrogel	GG and Silk protein	Combining GG with silk protein can fabricate the hydrogel network allowing cell adhesion, and the stiffness can be controlled by modifying the mixing ratio of GG‐Silk.	Osteosarcoma	[ 125 ]
	3D porous chitosan‐CS (C‐CS) scaffolds	Chitosan and CS	Through adding CS to a chitosan scaffold, the biomaterial scaffolds appear to have an effect similar to PG versican, and C‐CS scaffolds are a suitable culture platform in vitro for PCa.	Prostate cancer	[ 126 ]
	3D porous chitosan‐alginate (CA) scaffolds	Chitosan and Alginate	Chitosan is cationic and can interact with anionic polymers to form polyelectrolyte complexes (PECs). PECs can provide the advantages of each polymer in the complex, meanwhile hiding their respective weakness.	Prostate cancer glioma	[ 127 ]
Binding bioactive ingredients	Bioactive peptides modified PEG scaffold	PEG‐PQ PEG‐RGDS	The PEG hydrogels can be modified to render hydrogels bioactive and alter stiffness independently.	Lung cancer	[ 89 ]
	3D PEGDA/GelMA hydrogel matrix	PEGDA and GelMA	Gels incorporating GelMA have an RGD motif in the sequence and the ability to bind cells. Altering the ratio of PEGDA and GelMA permits manipulation of the matrix ligand density and stiffness, respectively, without changing other properties.	Osteosarcoma	[ 41 ]
	PEG‐fibrinogen (PF) hydrogel	PEGDA and Fibrinogen	The Young's modulus of PF hydrogels can be altered by increasing the amount of PEGDA.	Breast cancer	[ 128 ]
	PEG‐heparin‐based 3D model	PEG and Heparin	By coupling cysteine residues within the four‐arm PEG and maleimide‐modified heparin, the mechanical properties can be altered independently without affecting ligand density.	Breast cancer	[ 113 ]
	PEG‐SH scaffold hydrogel	PEG‐disthiol	Linear PEG‐disthiol (PEG‐SH) and MMP‐cleaved sequence (CGPQGIWGQC) are crosslinked and the cell adhesion peptides (CRGDS) can promote cell adhesion.	Brain tumor	[ 129 ]
	Alginate–RGD hydrogels	Alginate	Through coupling the oligopeptide GGGGRGDSP to the alginate to allow cell adhesion.	Osteosarcoma	[ 130 ]
	Modified HA hydrogel	HA	The acrylate HA is crosslinked with an enzymatically degradable peptide and two cysteines, and incorporates adhesion through RGD, forming a modular culture system.	Fibrosarcoma	[ 131 ]
		HA	By using two biorthogonal chemical strategies (oxime ligation and Diels–Alder reaction) within the same HA polymer backbone, the stiffness and bioactivity of the hydrogel can be independently modulated.	Breast cancer	[ 132 ]
Collaborating with other materials	3D bioprinted dECM scaffolds	dECM and GelMA	Liver dECM is combined with GelMA to produce a photocrosslinkable solution, which is printed into hexagonal lobules close to the size of liver lobules using a rapid 3D bioprinting technology based on DLP. Changes in stiffness can easily be controlled by changing the exposure time.	Liver cancer	[ 115 ]
	3D salmon fibrin gel	Thrombin‐activated purified fibrinogen	This mechanistic approach is useful for screening stem‐cell‐like cancer cells independently of stem cell markers.	Melanoma Ovarian cancer Liver cancer Lymphoma	[ 81 , 133 ]
	3D matrices with type I collagen Oligomer (IM)	Col I oligomer and Matrigel	Oligomer can polymerize rapidly to form highly interconnected D‐banded collagen‐fibril networks, which are similar to the networks found in tissues in vivo.	Pancreatic cancer	[ 95 ]
	IPN 3D coculture hydrogel system	Alginate and Matrigel	Allowing alteration of ECM stiffness independently of composition and 3D architecture, the average pore size is similar for all the IPNs, therefore, not affecting diffusion.	Lung cancer Breast cancer	[ 90 , 120 ]
	Collagen‐IV‐coated PA gel	PA and Collagen‐IV	Functionalized a layer of col‐IV to mimic BM‐like properties.	Breast cancer	[ 77 ]
Dynamic stiffness	Thermal induced crosslinking	Alginate	Temperature‐sensitive liposomes using encapsulated gold nanorods will release calcium or chelator when exposed to NIR light, resulting in alginate gelation and crosslinking.	/	[ 134 ]
	Photopolymerization	MeHA	Using dithiothreitol as a cross‐linking agent, the MeHA hydrogel network is further cross‐linked by UV light after cell inoculation to the hydrogel.	Breast cancer	[ 13 , 135 ]
	Enzymatic crosslinking	Thiol‐norbornene and 4‐hydroxyphenylacetic acid‐modified gelatin	In norbornene and 4‐hydroxyphenylacetic acid‐modified gelatin, di‐tyrosine crosslink is then catalyzed by tyrosinase, realizing the on‐demand stiffening.	Pancreatic cancer	[ 96 ]

[Abbreviation] CS: Chondroitin sulfate; dECM: decellularized extracellular matrix; GelMA: Methacrylated gelatin; GG: Gellan gum; MeHA: Methacrylated glycosaminoglycan hyaluronic acid; PA: polyacrylamide; PEG: polyethylene glycol; PEGDA: Poly (ethylene glycol) diacrylate.