Table 2.

Physically cross-linked injectable hydrogels

	Polymer	Mechanism of gelation	Cross-linker agent	Chemical factors	Biological factor	Year	Ref.
1	Alginate	Ionic gelation	Calcium chloride		β-TCP MSC	2008	Matsuno et al. (2008)
2	Core–shell structured collagen–alginate hydrogel	Ionic gelation	Ca2+		MSCs	2014	Perez et al. (2014)
3	Alginate/GDL (GMs)	Ionic gelation	CaCO3		Tetracycline hydrochloride HAp	2016	Yan et al. (2016a, b)
4	Chitosan biguanidine and carboxymethylcellulose	Ionic gelation			BMP-2 and VEGF	2021	Divband et al. (2021)
5	Gellan xanthan gels along with chitosan nanoparticles	Ionic and chemical and thermogelation	DMEM(Ca2+)		bFGF BMP7	2012	Dyondi et al. (2012)
6	ADA-GEL	Covalently cross-linking and Ionic gelation	(CaCl2)		(nBG) MSCs	2014	Rottensteiner et al. (2014)
7	SMO-PCLA-PEG-PCLA-SMO block copolymer	pH and thermogelation			hMSCs rhBMP-2	2009	Kim et al. (2008)
8	Chitosan, ad heparin	pH and thermogelation			HAp	2020	Kocak et al. (2020)
9	Poly(propylene fumarate) (PPF)	Thermogelation				2006	Shi et al. (2006)
10	PNIPAM−PAA(PEA)−PNIPAM	Thermogelation				2013	Lin et al. (2013)
11	PEGePCLePEG	Thermogelation			ABM	2014	Ni et al. (2014)
12	MPEG-PCL	Thermogelation			hTMSCs	2014	Kwon et al. (2014)
13	Copolymers (PLGA-PEG-PLGA)	Thermogelation			Simvastatin	2015	Yan et al. (2015)
14	Xylan/chitosan	Thermogelation				2016	Bush et al. (2016)
15	Poly propylene fumerate (PPF), Pluronic F127 and PEG-PCL-PEG	Thermogelation		PEG as an initiator and Sn(Oct)2 as a catalyst	Simvastatin	2017	Kondiah et al. (2017)
16	CS/CSn-GP	Thermogelation			pDNA BMP2	2017	Li et al. (2017)
17	CS/GP(CS/CMCS NPs)	Thermogelation			SDF-1α	2017	Mi et al. (2017)
18	PLGA–PEG–PLGA	Thermogelation			nHAp P-15 peptide b	2017	Gohil and Kumar (2017)
19	Chitosan and κ-carrageenan and poly(NIPAM)	Thermogelation			Au nanoparticles and MG-63	2019	Pourjavadi et al. (2019)
20	Chitosan	Thermogelation		NaHCO3/α-MEM	HAp	2018	Ressler et al. (2018)
21	HA	Thermogelation		Ag NPs and	β-TCP	2020	Makvandi et al. (2020)
22	Methylcellulose	Thermogelation	Trisodium citrate	Bassorin and halloysite nanotubes		2021	Varshosaz et al. (2021)
23	Methoxy polyethylene glycol–polycaprolactone (MP) and RGD-conjugated MP	Thermogelation				2020	Kim et al. (2020)
24	Chitosan	Thermogelation	Sodium-β-glycerol phosphate pentahydrate	Halloysite nanoclay		2021	Kazemi-Aghdam et al. (2021)
25	DA-PF 127	Photopolymerization and thermogelation		Irgacure 2959 as an initiator		2007	Lee and Tae (2007)
26	Gellan gum, PEGMA, and (2-methacrylamidoethyl dihydrogen phosphate)	Thermogelation and photopolymerization	PEG-DA, and photoinitiator I2959			2020	Li et al. (2020)
27	Chitosan, and polygalacturonic acid	Thermogelation and self-assembling	Sodium-β-glycerol phosphate pentahydrate		HAp	2020	Wasupalli and Verma (2020)
28	Zn-CS	Chemical and thermogelation			β-GP	2013	Niranjan et al. (2013)
29	PNiPAAm containing pendant epoxy rings	Chemical and thermogelation	PAMAM		MSCs encapsulated with GMPs	2014	Tzouanas et al. (2014)
30	NiPAAm-co-AAm-co-MAEP	Chemical and thermogelation		APS and TEMED as an initiators		2014	Watson et al. (2014)
31	NiPAAm-AAm-MAEP	Chemical and thermogelation			MSCs	2015	Watson et al. (2015)
32	P(NiPAAm-co-GMA-co-DBA-co-AA) TGM	Chemical and thermogelation	PAMAM			2015	Vo et al. (2015)
33	Poly(phosphazene)	Chemical and thermogelation			BMP-2	2017	Seo et al. (2017)
34	P(NiPAAm-co-GMA-co-DBA-co-AA)	Chemical and thermogelation	PAMAM	AIBN as an initiator		2017	Vo et al. (2017)
35	P(NiPAAm-co-GMA-co-DBA-co-AA) TGM	Chemical and thermogelation	PAMAM			2017	Vo et al. (2017)
36	F127@ChS and PEG-AMI	DA click chemistry and thermogelation			BMP-4	2017	Bai et al. (2017)
37	MeGel,Ac-b-CDs	Host–guest interactions and photo-cross-linking				2017	Feng et al. (2017)
38	(β-CD)-modified HA and adamantane-modified HA	Host − guest interactions			MSCs	2020	Jeong et al. (2020)
39	b-CD-g-PNIPAM/ G2.5 PAMAM-Ad	Noncovalent host–guest interaction and Diels–Alder (DA) chemical cross-linking	PEG2K–AMI			2016	Bai et al. (2016)
40	Squid pen chitosan/glycerol phosphate	Electrostatic cross-linking			HA/b-TCP	2016	Shavandi et al. (2016)
41	Methacrylate gelatin	Electrostatic and van der waal cross-linking and photopolymerization	Silicate nanoplatelets (Laponite)		Stromal cell-derived factor 1 alpha	2020	Shi et al. (2020)
42	PSAGE/PPF resins		CaCO3 and citric acid	BPO as an initiator and DMPT as an activator		2017	Śmiga-Matuszowicz et al. (2017)
43	HA-HAp	Physically cross-linking (colloidal gel)			DCC or DBM as ECM VEGF as growth factor	2017	Townsend et al. (2017)
44	Collagen type II and activated chondroitin sulfate	Chemical cross-linking between Col II and CS-sNHS and physical self-assembly of Col II			Chondrocytes	2018	Gao et al. (2018a, b)
45	Collagen type I and activated chondroitin sulfate	Physical and chemical cross-linking			Chondrocytes	2018	Gao et al. (2018a, b)