Table 1 The injectable hydrogel systems and their crosslinking reactions/interactions and applications

Agar

 Agar/MBP

PC, HB/

Delivery of TD (DOX), chemotherapy for colon cancer, photothermal treatment by MBP

Temperature-sensitive release, temperature changed by MBP (a photoabsorbent)

[37]

Alginate

 Alginate-Ca

PC, EI/

Delivery of TD (MX) and TPs (SDF-1α and pDNA), breast cancer therapy

Self-healing, the release and therapeutic efficacy regulated by pulsatile ultrasound

[38]

 OAlg/CMCS with GMs-TH

CC, SBR/

Bacterial infection therapy

Antibacterial and biodegradable properties

[52]

Chitosan

 Chitosan/gelatin/polydopamine

PC, EI/ MR, SBR,

Parkinson’s disease therapy, TD delivery (MT)

Mechanical strength improved via EI

[20]

 Chitosan/gelatin/NDs

PC, EI, HB, VDWF/HB, DDI, HP

Scaffold for TE (embedded cell: VEGF)

Thermosensitive gelation, mechanical features improved by NDs, sustained release

[30]

 Chitosan-polyaniline/oxidized dextran

CC, SBR/

Delivery of TDs (Amoxicillin and ibuprofen)

pH- and electric field- responsive, antibacterial activity

[33]

 CEC/OSA

CC, MR/

TAD

Self-assembling, self-healing

[49]

 GC/poly(EO-co-Gly)-CHO

CC, SBR/

Scaffold for TE (embedded cell: chondrocyte), cartilage repair

Mechanical properties and morphology controlled by poly(EO-co-Gly)-CHO

[51]

Chondroitin Sulfate (ChS)

 Pluronic F127-ChS/PEG

CC, DACR/

Scaffold for TE (embedded cell: BMP-4), bone defect repair

Gelation of Pluronic F127-ChS at 37 ^oC, dual crosslinked Pluronic F127-ChS/PEG hydrogels

[44]

Collagen

 Collagen/Au

PC, EI/

PTT, PDT, TAD (TMPyP), breast cancer therapy

Shear-thinning, self-healing, antitumor efficacy affected by light irradiation

[21]

 Collagen

PC, EI/

Scaffold for TE (embedded cell: osteoblast (OB)), bone repair

Successful bone tissue regeneration by OB and LIPUS

[39]

Dextrin

 CD/PEG-phospholipid/Fe₃O₄

PC, HI/

Hyperthermia cancer therapy, chemotherapy for preventing breast cancer recurrence, delivery of TDs (PTX, DOX)

PTX and DOX Released by ACMF induced heat

[34]

Gelatin

 Gelatin MPs

PC, EI/

Scaffold for TE (embedded TPs: VEGF and BMP2)

Release controlled by hydrogel degradation induced by CLSPA collagenase

[40]

 Gelatin-tetrazine fg/Gelatin- norbornene fg

CC, DACR/

Scaffold for TE

Cell-compatible and enzymatically degradable properties

[43]

Hyaluronic acid (HA)

 HA-CD/ HA-AD, and HA-CD-MA/HA-AD-MA

PC, HGI, CC/

Delivery of TP (EPC), vascular regeneration

Shear-thinning, self-healing

[28]

 HA-HMDA-cytosine/HA-HMDA-guanosine

PC, HB/

Delivery of TP (BSA), scaffold for TE

pH-sensitive and self-healing, gelation only at pH 6-8

[32]

 HAMC

PC, EI, HB/

Delivery of TPs (RSCs, NSCs), retina and brain tissue therapy, scaffold for TE

Biodegradable and light-sensitive, HAMC-CD44 interaction

[35]

 HA-Heparin (HA-HP)

CC, PIC/

Delivery of TP (AFS), wound healing

Crosslinking by UV light

[56]

 HA-Tyr

CC, EMCR, OCR/

Scaffold for TE (embedded cell: hESC)

Highest hESC proliferation at HA-Tyr hydrogels with modulus of 350 Pa

[59]

Peptide/protein

 P1

PC, PI, HP/

Delivery of TDs (vitamin B12 and vancomycin, an antibiotic)

Thixotropic behavior at physiological condition

[23]

 ^FG_d/Ag

PC, PI/

Antimicrobial treatment with Ag

Mechanical stability for six months, high antimicrobial activity

[24]

 PA

PC, HI, HB, EI/

Chemotherapy, delivery of TD (DOX)

PA concentration-dependent release behavior

[25]

 Peptide/catalase/glucose oxidase

PC, EI/

Diabetic therapy, delivery of TP (insulin)

pH- and glucose-sensitive, self-assembling

[31]

 Multi-domain peptides (MDPs) nanofiber/liposome NPs

PS, HB, HI/

Delivery of TPs (EGF, PlGF-1, MCP-1), Scaffold for TE

Release regulated via the hydrogel degradation by enzyme-mediation and the physical gelation by self-assembly

[41]

 Protein and Protein-GOX-CAT (PGT)

CC, EMCR/

Scaffold for TE

Reversible self-healing, enzyme (glucose) mediated crosslinking by dynamic covalent interaction, 100% recovery PGT

[58]

PCL

 PEG-PCL-PEG

PC, HI/

Chemotherapy including diabetic treatment, delivery of TP (insulin)

Sol-gel transition at 37 ^oC, lower viscosity than Pluronic®, Fickian release

[26]

PEG

 Polyamine-PEG-polyamine

PC, CC, EI, HB, PI/

Delivery of TPs (insulin, BSA, glucose, avidin, neutravidin, or IL-12)

Self-assembling at 30 ^oC

[19]

 PLga-PEG-PLga -chol fg/ PLga-CD fg

PC, HGI/

Scaffold for TE

Self-healing, self-assembling, properties regulated by the ratio of CD/Chol, high storage modulus

[27]

 PCLA-PEG-PCLA/heparin

PC, HI, CC, MR/EI

Delivery of TP (lysozyme), immunotherapy

Thermosensitive gelation at BT, sustained release

[29]

 PEG- aryl thiol fg/PEG-maleimide fg (or heparin-maleimide fg)

CC, MR/RLI

Delivery of TPs (FGF-2, cytokines, and immunomodulatory agents)

Light-and reducing environment- sensitive release

[36]

 PEG/TMV_Cyss and PEG/wt-TMV

CC, MR and PC/

Scaffold for TE

TMV with multi-functionality, storage moduli improved by adding TMV_Cyss. No effect of wt-TMV on storage moduli

[48]

 PEG/PPLL

CC, SBR/

Delivery of TDs (ME and 5FC), colon cancer therapy

Degradation and release controlled by pHs

[53]

Polyoxamine

 Polyoxamine-maleimide fg/ Polyoxamine-furyl fg

PC, CC, HI, DACR/

Delivery of TP (bevacizumab, an antibody), colon, lung, and breast cancer therapy

Physical and chemical crosslinking, triphasic release controlled by two polyoxamines

[45]

PVA

 PVA-Tyr and PVA-Tyr-sericin-gelatin (PVA-SG)

CC, PIC/

Scaffold for TE (embedded TP: Schwann)

Crosslinking by visible light, PVA-Tyr: no cell adhesion, PVA-SG: cell adhesion

[55]

PNIPAAm

 PNIPAAm/CNC

PC, VDWF, HB/

Delivery of TD (MT), wound dressing

Volume transition at 36-39 ^oC, Mechanical strength increased by CNC

[22]