Collagen Functional Hydrogel

While the ECM is composed of around 300 proteins, proteoglycans (heparan sulfate), glycoproteins (laminin and fibronectin), and collagen are the most common components1. The collagen superfamily consists of 28 different isoforms in vertebrates8. Collagens consist of three polypeptide chains, referred to as α chains8. Different α chains are subcategorized and given a numerical value. Moreover, many collagen isoforms are proteolytically cleavable, which can lead to the production of fragments with exposed, bioactive, cryptic binding sites11. Collagen I is the most abundantly expressed ECM protein and is regularly used in cell studies12. Cells readily bind to collagen matrices and are shown to survive at high rates. Collagen promotes attachment of cells from multiple tissues, including cancer13, skin14, eye15, and muscle16. Collagens bind different receptor families, including integrins, receptor tyrosine kinases, leukocyte receptor complex, and mannose receptor family43. Integrin receptors are highly expressed adhesion receptors that, upon ECM binding, recruit a variety of adhesion scaffold, signaling, and stretch gated proteins to initiate and stabilize adhesion complexes44, 45. Integrin based adhesions regulate intracellular signaling, cell morphology, and migration, and may be important for cell survival. Integrin receptors are heterodimers consisting of α (18 in humans) and ß (8 in humans) subunits46. Collagen has been shown to bind four different integrin heterodimers (α1β1, α2β1, α10β1, and α11β1)43. Among these, collagen I binds α1β1 and α2β1, with a particular affinity for α2β143. The bioactive motif underlying collagen I and α2β1 interaction was discovered by Knight and colleagues to be GFOGER, and has subsequently been used in a variety of studies7. Being that this motif underlies cell-collagen matrices binding, hydrogels modified with covalently bound GFOGER, VitroGel COL, have been developed for cell culture studies.

The field of cancer biology has perhaps most significantly utilized 3D collagen matrices. Collagen gels give cancer researchers a great cell culture system to study cancer cell clustering, invasion, and migration. Upon attachment, collagen matrices support the proliferation of many different cancer cell lines13,17,18. This process is dependent upon the ability of cells to spread and change morphology. Cell spreading has been observed in collagen matrices with different cancer types, including breast cancer. Specifically, MCF-7 cells, a breast cancer cell line, were shown to have spread morphologies in 3D collagen gels, which ultimately lead to increased proliferation, likely due to increased expression of matrix metalloproteases (MMPs)17. In vivo, cancer cells, and cancer-associated fibroblasts, release MMPs, and ECM molecules, to remodel the local environment. Due to the fibril structure of collagen, cancer facilitated remodeling can create fibril “tracks” upon which cancer cells can migrate1. Also, MMP release can breakdown ECM barriers, allowing metastatic cancer cells to invade and disseminate. This phenomenon has also been observed and investigated in 3D collagen. Specifically, cancer cell lines have been shown to upregulate MMPs in collagen17–20, leading to increased invasion18–22 and migration19,22,23, likely due to ECM remodeling. While studies have illustrated the importance of MMP activity in promoting cancer cell growth and metastasis, few studies have examined the effect of both collagen binding and ECM remodeling using modifiable hydrogels. However, using a modified hydrogel containing GFOGER, as an adhesive peptide, and MMP target substrates, Mhanna et. al. (2014) found human mesenchymal stem cells spread and were highly proliferative relative to non-degradable hydrogels. Thus, these effects can be further studied in other cell types, such as cancer cells, using a combination of VitroGel COL and VitroGel GFOGER. Overall, studies utilizing 3D collagen gels have expanded how we can examine cancer progression.

In addition to cancer biology, 3D collagen gels are powerful tools to study tissue development. Using collagen gels allows scientists to examine the mechanisms of development from studying individual cell morphological changes to tissue engineering. Individual cell morphological changes, such as cell spreading, may be investigated in real-time in collagen matrices. Collagen induces cell spreading of different cell types, such as fibroblasts24, lung fibroblasts16, corneal endothelial cells15, hepatocytes25, myoblasts16, and aortic endothelial cells24,26. Moreover, cell spreading and integrin-mediated signaling have been shown to control cell differentiation27–31, which has been extensively studied in 3D collagen. For instance, osteogenic differentiation of human32 and mouse33 bone marrow-derived mesenchymal stem cells was observed in 3D collagen gels. Differentiation was also detected with muscle cells, where collagen matrices induced mature myoblast differentiation and the subsequent formation of myotubes34,35. Collagen also supports the differentiation of embryonic stem cells into mature neurons36, further illustrating the many different cell types that may be examined using collagen gels.

Similar molecular processes are conserved during cell migration and neurite outgrowth, including integrin-mediated adhesions. Consequently, collagen matrices are a robust cell culture system used to study cell mobility and neurite extension. In fact, cells migrate rapidly on collagen19,22,23.Additionally, neurite extension in 3D collagen gels has been shown with human37, chick38,39, and rat40–42 neurons. Furthermore, the mechanical properties of collagen strongly control neurite extension, as cortical and peripheral neurites often extend more rapidly in soft collagen relative to rigid37–39. Conversely, Nichol and colleagues found human motor neurons extend longer neurites in more rigid collagen gels37.Taken together, these data further demonstrate the advantages of collagen gels in studying different developmental processes in a variety of tissue.

As stated above, GFOGER can act as a functionalized ligand for cells expressing integrin receptors to bind and undergo subsequent morphological changes and migration. Similar to other ECM derived small peptides, e.g. RGD, YIGSR, or IKVAV, GFOGER is most extensively used as an adhesive ligand to test cellular processes and promote tissue engineering for healthy and disease cells48. GFOGER has most widely been used in 3D hydrogels to examine osteogenic differentiation and bone regeneration49–56, as well as cancer cell behavior57–61. In multiple studies, the employment of 3D hydrogels containing GFOGER has been shown to drive differentiation of bone marrow stromal or mesenchymal cells into mature osteogenic cells51,52,55,62–64 with the ability to remodel the ECM53. More importantly, the effects of GFOGER on osteogenic differentiation have enabled researchers to utilize GFOGER incorporated hydrogels to repair bone in vivo. Injectable GFOGER hydrogels, in conjunction with bone morphogenic protein 2, were found to drive greater bone repair in mouse bone defects than hydrogels containing RGD62. In another study, GFOGER was immobilized onto polycaprolactone scaffolds and implanted into rats with bone injuries50. Implanted GFOGER coated polycaprolactone scaffolds promoted bone regeneration as measured by an increase in bone mass. The bone regenerative effects of GFOGER have been additionally observed in vivo with other materials, including titanium51, poly(ethylene glycol) (PEG)54, and hydroxyapatite55. Besides osteogenesis, GFOGER supports the development of many other tissue types. For example, GFOGER may be used as an adhesive substratum for liver65, muscle58, neural66, and vascular67 cells. In addition, similar to RGD, GFOGER has been utilized to support adhesion, proliferation, and differentiation of stem cells68. Encapsulating stem cells proliferated and differentiated into chondrogenic cells that secreted cartilage-specific ECM. Overall, these studies demonstrate the use of GFOGER modified biomaterials as a promising tool to study cell adhesion, differentiation, and regeneration, among other phenomena.

As stated above, ECM and specifically collagen, remodeling is a critical step in cancer progression. Therefore, VitroGel COL, which contains GFOGER provides a robust platform to study myriad cancer cell behaviors, including adhesion, proliferation and cell cluster growth, invasion, and migration. Similar to RGD and native collagen, GFOGER has been shown to act as an effective adhesive substratum for different types of cancer cells, such as breast57, fibrosarcoma58,59, glioma60, and prostate61. The GFOGER mediated effects on cancer cell adhesion were shown to be integrin-dependent58,60. Furthermore, adhesion allows for cancer cell aggregation and cluster growth, a cell culture model for tumor growth. Sawicki and colleagues demonstrated GFOGER dependent adhesion and subsequent cluster growth of two independent breast cancer cell lines, MDA-MB-231 and T47D57. Likewise, GFOGER incorporated hydrogels promoted an invasive morphology, migration, and clustering of PC3 cells, a metastatic prostate cancer cell line61. These data further illustrate the ability of GFOGER to act similarly to native collagen and promote cell behaviors.

Cell Type Behavior Reference Table for VitroGel COL

Bone
Cell TypeBehavior
Bovine bone marrow stromal cellsIncreased cell spreading and osteocalcin expression
Human boneIncreased cell spreading, proliferation, and collagen II production
marrow mesenchymal stem cells
Rat bone marrow stromal cellsIncreased cell adhesion and osteoblast differentiation
Human bone marrow-derived mesenchymal stem cellsPromoted calcium deposition and chondrogenic/
osteogenic differentiation
Mouse bone marrow stromal cellsSupports osteogenesis
Breast
Cell TypeBehavior
Mouse mammary epitheliumPromoted transient cell invasion and dissemination
Cancer/Tumor
Cell TypeBehavior
Breast MDA-MB-231Increased cell cluster size and spreading
Breast T47DIncreased cell cluster size
Breast T47D Promoted force dependent tubule formation
Breast MCF-7Increased cell proliferation, morphological changes, MMP expression, and angiogenesis
Co-culture of liver carcinoma HepG2 and stromal fibroblasts 3T3-J2Increased cell viability, growth, and drug resistance
Fibrosarcoma HT1080Support cell infiltration and growth
Fibrosarcoma HT1080Promoted integrin dependent cell adhesion
Fibrosarcoma HT1080Promoted cell adhesion
Glioma RuGliPromoted integrin dependent cell adhesion
Glioma U87-MGCell migration dependent on mechanical force
Prostate PC3Increased cell invasion, migration, and spheroid metabolic activity
Human primary breastPromoted cell invasion, migration, and dissemination
Melanoma B16F10Increased cell migration, invasion, and MMP release
Ovarian OVCA429MMP dependent cell invasion
Prostate LNCaPSupported cell proliferation and increased prostate-specific antigen release
Prostate PC3Supported cell proliferation and reduced MMP release
Connect Tissues
Cell TypeBehavior
Co-culture human dermal fibroblasts and epidermal keratinocytesPromoted cell viability
Fibroblast NIH3T3Increased cell spreading on rigid
Eye
Cell TypeBehavior
Corneal endothelial B4G12Increased cell attachment and spreading
Xenopus retinal ganglion cellsPromoted neurite outgrowth
Liver
Cell TypeBehavior
Human Hep3BPromoted cell attachment
Rat hepatocytesPromote albumin secretion
Swine hepatocytesPromoted cell spreading and albumin section
Lung
Cell TypeBehavior
Lung fibroblasts HFL1 (CCL153)Promoted cell proliferation and spindle morphology
Human lung cancer associated fibroblastsIncreased smooth muscle actin and substrata contractility
Lung fibroblasts MCR-5Promoted NGF-mediated substrata contraction
Muscle
Cell TypeBehavior
Human myoblastsPromoted cell adhesion, alignment along fiber, and myotube formation
Mouse myoblast C2C12Promote integrin dependent cell adhesion
Myoblasts C2C12Promoted formation of myotubes and myotendinous
Myoblasts C2C12Promote cell proliferation, differentiation, and myotube formation
Myoblasts C25Cl48Promote cell proliferation, differentiation, and myotube formation
Neural
Cell TypeBehavior
Human neural stem/progenitor cellsPromoted cell attachment
Chick dorsal root ganglion*Increased neurite length on soft
Chick dorsal root ganglion*Increased neurite outgrowth toward soft
Human motor neurons*Increased neurite length on rigid
Human forebrain neurons*Increased neurite length on soft
Neural PC12Increased neurite length
Rat cortical neuronsIncreased neuronal viability and neurite length
Rat dorsal root ganglionPromoted axon outgrowth
Rat dorsal root ganglionPromoted neurite outgrowth
Rat spinal cord sectionPromoted neurite outgrowth
Stem Cells
Cell TypeBehavior
Human mesenchymal stem cellsPromoted cell adhesion, spreading, viability, and osteoblast differentiation
Human mesenchymal stem cellsPromoted chondrogenic differentiation
Human mesenchymal stem cellsIncreased cell migration, proliferation, and osteogenic differentiation
Human mesenchymal stem cellsPromoted cell attachment and tenogenic differentiation
Human mesenchymal stem cellsPromoted cell proliferation
Mouse embryonic stem cellsSupported neuronal differentiation and neurite outgrowth
Vascular/Cardiac
Cell TypeBehavior
Bovine aortic endothelial cellsPromoted cell spreading along fiber
Bovine aortic endothelial cellsIncreased cell spreading on rigid
Bovine capillary endothelial cellsFormation of capillary like networks
Human umbilical vein endothelial cellsIncreased VEGF dependent vascularization
Human umbilical vein endothelial cellsPromoted cell adhesion, spreading and supported increased VEGF dependent migration

Reference

Reference

[1]C. Bonnans, J. Chou, and Z. Werb, “Remodelling the extracellular matrix in development and disease,” Nature Reviews Molecular Cell Biology. 2014, doi: 10.1038/nrm3904.
[2]T. Rozario and D. W. DeSimone, “The extracellular matrix in development and morphogenesis: A dynamic view,” Developmental Biology. 2010, doi: 10.1016/j.ydbio.2009.10.026.
[3]H. Sonbol, “Extracellular matrix remodeling in human disease,” J. Microsc. Ultrastruct., 2018, doi: 10.4103/jmau.jmau_4_18.
[4]A. D. Doyle, N. Carvajal, A. Jin, K. Matsumoto, and K. M. Yamada, “Local 3D matrix microenvironment regulates cell migration through spatiotemporal dynamics of contractility-dependent adhesions,” Nat. Commun., 2015, doi: 10.1038/ncomms9720.
[5]C. B. Raub et al., “Noninvasive assessment of collagen gel microstructure and mechanics using multiphoton microscopy,” Biophys. J., 2007, doi: 10.1529/biophysj.106.097998.
[6]B. R. Williams, R. A. Gelman, D. C. Poppke, and K. Piez, “Collagen fibril formation. Optimal in vitro conditions and preliminary kinetic results,” J. Biol. Chem., 1978.
[7]K. Wolf et al., “Collagen-based cell migration models in vitro and in vivo,” Seminars in Cell and Developmental Biology. 2009, doi: 10.1016/j.semcdb.2009.08.005.
[8]S. Ricard-Blum, “The Collagen Family,” Cold Spring Harb. Perspect. Biol., 2011, doi: 10.1101/cshperspect.a004978.
[9]M. Durbeej, “Laminins,” Cell and Tissue Research. 2010, doi: 10.1007/s00441-009-0838-2.
[10]R. Pankov and K. M. Yamada, “Fibronectin at a glance,” J. Cell Sci., 2002, doi: 10.1242/jcs.00059.
[11]S. Ricard-Blum and L. Ballut, “Matricryptins derived from collagens and proteoglycans,” Front. Biosci., 2011, doi: 10.2741/3712.
[12]J. Glowacki and S. Mizuno, “Collagen scaffolds for tissue engineering,” Biopolymers, 2008, doi: 10.1002/bip.20871.
[13]D. Yip and C. H. Cho, “A multicellular 3D heterospheroid model of liver tumor and stromal cells in collagen gel for anti-cancer drug testing,” Biochem. Biophys. Res. Commun., 2013, doi: 10.1016/j.bbrc.2013.03.008.
[14]W. Lee et al., “Multi-layered culture of human skin fibroblasts and keratinocytes through three-dimensional freeform fabrication,” Biomaterials, 2009, doi: 10.1016/j.biomaterials.2008.12.009.
[15]P. W. Madden, J. N. X. Lai, K. A. George, T. Giovenco, D. G. Harkin, and T. V. Chirila, “Human corneal endothelial cell growth on a silk fibroin membrane,” Biomaterials, 2011, doi: 10.1016/j.biomaterials.2010.12.034.
[16]W. F. Daamen et al., “Preparation and evaluation of molecularly-defined collagen-elastin-glycosaminoglycan scaffolds for tissue engineering,” Biomaterials, 2003, doi: 10.1016/S0142-9612(03)00273-4.
[17]L. Chen et al., “The enhancement of cancer stem cell properties of MCF-7 cells in 3D collagen scaffolds for modeling of cancer and anti-cancer drugs,” Biomaterials, 2012, doi: 10.1016/j.biomaterials.2011.10.056.
[18]K. A. Fitzgerald et al., “The use of collagen-based scaffolds to simulate prostate cancer bone metastases with potential for evaluating delivery of nanoparticulate gene therapeutics,” Biomaterials, 2015, doi: 10.1016/j.biomaterials.2015.07.019.
[19]W. Zhao et al., “Migration and metalloproteinases determine the invasive potential of mouse melanoma cells, but not melanin and telomerase,” Cancer Lett., 2001, doi: 10.1016/S0304-3835(00)00656-X.
[20]K. L. Sodek, T. J. Brown, and M. J. Ringuette, “Collagen I but not Matrigel matrices provide an MMP-dependent barrier to ovarian cancer cell penetration,” BMC Cancer, 2008, doi: 10.1186/1471-2407-8-223.
[21]C. N. Grover, R. E. Cameron, and S. M. Best, “Investigating the morphological, mechanical and degradation properties of scaffolds comprising collagen, gelatin and elastin for use in soft tissue engineering,” J. Mech. Behav. Biomed. Mater., 2012, doi: 10.1016/j.jmbbm.2012.02.028.
[22]K. V. Nguyen-Ngoc et al., “ECM microenvironment regulates collective migration and local dissemination in normal and malignant mammary epithelium,” Proc. Natl. Acad. Sci. U. S. A., 2012, doi: 10.1073/pnas.1212834109.
[23]P. Kaphle, Y. Li, and L. Yao, “The mechanical and pharmacological regulation of glioblastoma cell migration in 3D matrices,” J. Cell. Physiol., 2019, doi: 10.1002/jcp.27209.
[24]T. Yeung et al., “Effects of substrate stiffness on cell morphology, cytoskeletal structure, and adhesion,” Cell Motil. Cytoskeleton, 2005, doi: 10.1002/cm.20041.
[25]Y. J. Wang, H. L. Liu, H. T. Guo, H. W. Wen, and J. Liu, “Primary hepatocyte culture in collagen gel mixture and collagen sandwich,” World J. Gastroenterol., 2004, doi: 10.3748/wjg.v10.i5.699.
[26]P. Lee, R. Lin, J. Moon, and L. P. Lee, “Microfluidic alignment of collagen fibers for in vitro cell culture,” Biomed. Microdevices, 2006, doi: 10.1007/s10544-006-6380-z.
[27]Y. Yang et al., “Influence of Cell Spreading Area on the Osteogenic Commitment and Phenotype Maintenance of Mesenchymal Stem Cells,” Sci. Rep., 2019, doi: 10.1038/s41598-019-43362-9.
[28]G. Vertelov, E. Gutierrez, S. A. Lee, E. Ronan, A. Groisman, and E. Tkachenko, “Rigidity of silicone substrates controls cell spreading and stem cell differentiation,” Sci. Rep., 2016, doi: 10.1038/srep33411.
[29]G. Chen, W. Song, and N. Kawazoe, “Dependence of spreading and differentiation of mesenchymal stem cells on micropatterned surface area,” J. Nanomater., 2011, doi: 10.1155/2011/265251.
[30]S. M. C. Bruekers et al., “Fibrin-fiber architecture influences cell spreading and differentiation,” Cell Adhesion and Migration. 2016, doi: 10.1080/19336918.2016.1151607.
[31]H. Wang, X. Luo, and J. Leighton, “Extracellular Matrix and Integrins in Embryonic Stem Cell Differentiation,” Biochem. Insights, 2015, doi: 10.4137/bci.s30377.
[32]L. Meinel et al., “Bone tissue engineering using human mesenchymal stem cells: Effects of scaffold material and medium flow,” Ann. Biomed. Eng., 2004, doi: 10.1023/B:ABME.0000007796.48329.b4.
[33]M. M. Villa, L. Wang, J. Huang, D. W. Rowe, and M. Wei, “Bone tissue engineering with a collagen-hydroxyapatite scaffold and culture expanded bone marrow stromal cells,” J. Biomed. Mater. Res. – Part B Appl. Biomater., 2015, doi: 10.1002/jbm.b.33225.
[34]J. Prüller, I. Mannhardt, T. Eschenhagen, P. S. Zammit, and N. Figeac, “Satellite cells delivered in their niche efficiently generate functional myotubes in three-dimensional cell culture,” PLoS One, 2018, doi: 10.1371/journal.pone.0202574.
[35]C. Rhim et al., “Morphology and ultrastructure of differentiating three-dimensional mammalian skeletal muscle in a collagen gel,” Muscle and Nerve, 2007, doi: 10.1002/mus.20788.
[36]C. R. Kothapalli and R. D. Kamm, “3D matrix microenvironment for targeted differentiation of embryonic stem cells into neural and glial lineages,” Biomaterials, 2013, doi: 10.1016/j.biomaterials.2013.04.042.
[37]R. H. Nichol, T. S. Catlett, M. M. Onesto, D. Hollender, and T. M. Gómez, “Environmental Elasticity Regulates Cell-type Specific RHOA Signaling and Neuritogenesis of Human Neurons,” Stem cell reports, 2019, doi: 10.1016/j.stemcr.2019.10.008.
[38]R. K. Willits and S. L. Skornia, “Effect of collagen gel stiffness on neurite extension,” J. Biomater. Sci. Polym. Ed., 2004, doi: 10.1163/1568562042459698.
[39]H. G. Sundararaghavan, G. A. Monteiro, B. L. Firestein, and D. I. Shreiber, “Neurite growth in 3D collagen gels with gradients of mechanical properties,” Biotechnol. Bioeng., 2009, doi: 10.1002/bit.22074.
[40]P. W. Lin, C. C. Wu, C. H. Chen, H. O. Ho, Y. C. Chen, and M. T. Sheu, “Characterization of cortical neuron outgrowth in two- and three-dimensional culture systems,” J. Biomed. Mater. Res. – Part B Appl. Biomater., 2005, doi: 10.1002/jbm.b.30276.
[41]D. Kacy Cullen et al., “Microtissue engineered constructs with living axons for targeted nervous system reconstruction,” Tissue Eng. – Part A, 2012, doi: 10.1089/ten.tea.2011.0534.
[42]I. Allodi, M. S. Guzmán-Lenis, J. Hernàndez, X. Navarro, and E. Udina, “In vitro comparison of motor and sensory neuron outgrowth in a 3D collagen matrix,” J. Neurosci. Methods, 2011, doi: 10.1016/j.jneumeth.2011.03.006.
[43]I. Boraschi-Diaz, J. Wang, J. S. Mort, and S. V. Komarova, “Collagen type i as a ligand for receptor-mediated signaling,” Frontiers in Physics. 2017, doi: 10.3389/fphy.2017.00012.
[44]A. Huttenlocher and A. R. Horwitz, “Integrins in cell migration,” Cold Spring Harb. Perspect. Biol., 2011, doi: 10.1101/cshperspect.a005074.
[45]S. Huveneers and E. H. J. Danen, “Adhesion signaling – Crosstalk between integrins, Src and Rho,” Journal of Cell Science. 2009, doi: 10.1242/jcs.039446.
[46]D. V. Iwamoto and D. A. Calderwood, “Regulation of integrin-mediated adhesions,” Current Opinion in Cell Biology. 2015, doi: 10.1016/j.ceb.2015.06.009.
[47]C. G. Knight, L. F. Morton, A. R. Peachey, D. S. Tuckwell, R. W. Farndale, and M. J. Barnes, “The collagen-binding a-domains of integrins α1/β1 and α2/β1 recognize the same specific amino acid sequence, GFOGER, in native (triple- helical) collagens,” J. Biol. Chem., 2000, doi: 10.1074/jbc.275.1.35.
[48]N. Huettner, T. R. Dargaville, and A. Forget, “Discovering Cell-Adhesion Peptides in Tissue Engineering: Beyond RGD,” Trends in Biotechnology. 2018, doi: 10.1016/j.tibtech.2018.01.008.
[49]S. A. et al., “Bone regeneration using an alpha 2 beta 1 integrin-specific hydrogel as a BMP-2 delivery vehicle,” Biomaterials. 2014.
[50]A. M. Wojtowicz et al., “Coating of biomaterial scaffolds with the collagen-mimetic peptide GFOGER for bone defect repair,” Biomaterials, 2010, doi: 10.1016/j.biomaterials.2009.12.008.
[51]C. D. Reyes, T. A. Petrie, K. L. Burns, Z. Schwartz, and A. J. García, “Biomolecular surface coating to enhance orthopaedic tissue healing and integration,” Biomaterials, 2007, doi: 10.1016/j.biomaterials.2007.04.003.
[52]J. T. Connelly, T. A. Petrie, A. J. García, and M. E. Levenston, “Fibronectin-and collagen-mimetic ligands regulate bone marrow stromal cell chondrogenesis in three-dimensional hydrogels,” Eur. Cells Mater., 2011, doi: 10.22203/ecm.v022a13.
[53]R. Mhanna, E. Öztürk, Q. Vallmajo-Martin, C. Millan, M. Müller, and M. Zenobi-Wong, “GFOGER-modified MMP-sensitive polyethylene glycol hydrogels induce chondrogenic differentiation of human mesenchymal stem cells,” Tissue Eng. – Part A, 2014, doi: 10.1089/ten.tea.2013.0519.
[54]J. R. García, A. Y. Clark, and A. J. García, “Integrin-specific hydrogels functionalized with VEGF for vascularization and bone regeneration of critical-size bone defects,” J. Biomed. Mater. Res. – Part A, 2016, doi: 10.1002/jbm.a.35626.
[55]K. M. Hennessy et al., “The effect of collagen I mimetic peptides on mesenchymal stem cell adhesion and differentiation, and on bone formation at hydroxyapatite surfaces,” Biomaterials, 2009, doi: 10.1016/j.biomaterials.2008.12.053.
[56]A. Y. Clark et al., “Integrin-specific hydrogels modulate transplanted human bone marrow-derived mesenchymal stem cell survival, engraftment, and reparative activities,” Nat. Commun., 2020, doi: 10.1038/s41467-019-14000-9.
[57]L. A. Sawicki et al., “Tunable synthetic extracellular matrices to investigate breast cancer response to biophysical and biochemical cues,” APL Bioeng., 2019, doi: 10.1063/1.5064596.
[58]N. Davidenko et al., “Selecting the correct cellular model for assessing of the biological response of collagen-based biomaterials,” Acta Biomater., 2018, doi: 10.1016/j.actbio.2017.10.035.
[59]C. D. Reyes and A. J. García, “Engineering integrin-specific surfaces with a triple-helical collagen-mimetic peptide,” J. Biomed. Mater. Res. – Part A, 2003, doi: 10.1002/jbm.a.10550.
[60]J. D. Malcor et al., “The synthesis and coupling of photoreactive collagen-based peptides to restore integrin reactivity to an inert substrate, chemically-crosslinked collagen,” Biomaterials, 2016, doi: 10.1016/j.biomaterials.2016.01.044.
[61]A. V. Taubenberger et al., “3D extracellular matrix interactions modulate tumour cell growth, invasion and angiogenesis in engineered tumour microenvironments,” Acta Biomater., 2016, doi: 10.1016/j.actbio.2016.03.017.
[62]A. Shekaran et al., “Bone regeneration using an alpha 2 beta 1 integrin-specific hydrogel as a BMP-2 delivery vehicle,” Biomaterials, 2014, doi: 10.1016/j.biomaterials.2014.03.055.
[63]C. D. Reyes and A. J. García, “α2β1 integrin-specific collagen-mimetic surfaces supporting osteoblastic differentiation,” in Journal of Biomedical Materials Research – Part A, 2004, doi: 10.1002/jbm.a.30034.
[64]J. Sun, Y. Zhang, B. Li, Y. Gu, and L. Chen, “Controlled release of BMP-2 from a collagen-mimetic peptide-modified silk fibroin-nanohydroxyapatite scaffold for bone regeneration,” J. Mater. Chem. B, 2017, doi: 10.1039/c7tb02043k.
[65]S. T. Khew, X. H. Zhu, and Y. W. Tong, “An integrin-specific collagen-mimetic peptide approach for optimizing Hep3B liver cell adhesion, proliferation, and cellular functions,” Tissue Eng., 2007, doi: 10.1089/ten.2007.0063.
[66]R. A. Que, J. Arulmoli, N. A. Da Silva, L. A. Flanagan, and S. W. Wang, “Recombinant collagen scaffolds as substrates for human neural stem/progenitor cells,” J. Biomed. Mater. Res. – Part A, 2018, doi: 10.1002/jbm.a.36343.
[67]F. Roche et al., “Histidine-rich glycoprotein blocks collagen-binding integrins and adhesion of endothelial cells through low-affinity interaction with α2 integrin,” Matrix Biol., 2015, doi: 10.1016/j.matbio.2015.06.002.
[68]S. Q. Liu, Q. Tian, J. L. Hedrick, J. H. Po Hui, P. L. Rachel Ee, and Y. Y. Yang, “Biomimetic hydrogels for chondrogenic differentiation of human mesenchymal stem cells to neocartilage,” Biomaterials, 2010, doi: 10.1016/j.biomaterials.2010.06.001.