Introduction: For tissue replacement in wound healing applications biomaterials should form a beneficial micro-milieu that provides key functions of the natural extra-cellular environment supporting adhesion, proliferation and differentiation of dFb. Here, hydrogels are of particular interest since they can mimic several physical properties of the skin and easily adapt to the size and shape of the wound due to their tuneable physical properties and high water content. Furthermore, chemical modifications enable these hydrogels to become an instructive biomaterial to a variety of cell types. Their functionality can be adjusted further by reversible binding of endogenous and recombinant mediator proteins.
Human dermal fibroblasts play a pivotal role during wound healing, especially for the synthesis of novel dermal tissue replacing the primary fibrin clot. Thus, the control of growth and differentiation of dermal fibroblasts (dFb) is important to modulate wound healing. Therefore, cell-instructive hydrogels enabling the independent control of physical cues, cell adhesion and the delivery of growth factors may be beneficial to control dFb cell fate and therefore modulate wound healing (Fig.1). Especially, the administration of TGFß from hydrogel matrices displaying a high cytokine binding and releasing capacity could be advantageous for myofibroblast activation, matrix deposition and wound closure.
Materials and Methods: A previously established modular hydrogel material based on star-shaped poly(ethylene glycol) (starPEG) and heparin [1] was investigated as an adaptable material to support growth and differentiation of human dermal fibroblasts. starPEG-heparin hydrogels may be adjusted towards their mechanical properties at constant heparin concentration [2], enabling cell responsiveness (via MMP-sensitive linkers [3]), adhesiveness (e.g. by incorporation of fibronectin derived adhesion peptides such as RGD) and cytokine presentation [4] independent of the network characteristics (stiffness, mesh size, hydration). Attachment and proliferation of fibroblasts on starPEG-heparin hydrogels of differing stiffness, density of pro-adhesive RGD peptides and MMP cleavable peptide linkers were tested. Binding and release of human TGFβ1 as well as biological effect of the pre-adsorbed growth factor on fibroblast gene expression and myofibroblast differentiation were investigated.
Results and Discussion: starPEG-heparin hydrogels supplemented with RGD peptides supported fibroblast attachment, spreading, proliferation, matrix deposition and remodeling compared to starPEG-heparin hydrogels without any modifications. Reversibly conjugated TGFβ1 was demonstrated to be constantly released from starPEG-heparin hydrogels for several days and biologically active in inducing myofibroblast differentiation of human dFb as determined by induction of collagen type I, ED-A-Fibronectin gene expression and incorporation of alpha smooth muscle actin and palladin proteins into F-actin stress fibers.
Conclusion: Taken together, customized starPEG-heparin hydrogels could be of value to promote dermal wound healing by stimulating growth and differentiation of human dermal fibroblasts [5].
Authors gratefully acknowledge the financial support of the Deutsche Forschungsgemeinschaft (TRR 67 collaborative research group (Projects B4 to UA, A10 to UF and CW, B3 to JS). AW received a TRR67 scholarship award.
References:
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