**4. ECM augments therapeutic effects of stem cell therapy**

Many attempts at cell therapy have employed ECM to improve efficacy for the following reasons. First, the major obstacle to the application of stem cells, which is known as the extremely poor survival and engraftment of transplanted stem cells, could be minimized by co-transplantation stem cells with ECM [51,63,64]. Second, engineered ECM mimicking the natural stem-cell microenvironments could provide plenty of subtle and instructive cues to control the fate of both transplanted and endogenous cells, including stem cell self-renewal, differentiation, and migration [7,65,66]. Taken together, the development of engineered matrices is promising for the application of stem cells in regenerative medicine.

#### **4.1. Enhance efficacy of transplanted cells**

For both experimental studies and clinical applications, transplanted stem cells are commonly prepared for transplantation as single cells. During this process, interactions between cells and ECM are lost and adhesion-related survival signals are down-regulated, which could cause a decrease in cell viability and initiated apoptosis [67]. Fortunately, recent research discovered that the down-regulated molecules of detached cells could be regained in the presence of Matrigel [4], which provided a theoretical rationale for using ECM as a protective scaffold to enhance viability and to stimulate self-renewal of the transplanted cells.

In support of this finding, recent study demonstrated that biomimetic scaffold could protect the transplanted stem cells, and further promote functional and structural recovery from acute kidney injury (AKI). Through immobilization of the C-domain of insulin-like growth factor 1 (IGF-1C) to chitosan (CS) hydrogel (CS-IGF-1C), an artificial microenvironment for supporting growth of stem cells was synthesized. The pro-proliferative, anti-apoptotic, and pro-angio‐ genic effects of CS-IGF-1C were demonstrably beneficial for enhancing survival of transplant‐ ed stem cells, which could ameliorate renal function [47] (**Figure 5**).

Extracellular Matrix Enhances Therapeutic Effects of Stem Cells in Regenerative Medicine http://dx.doi.org/10.5772/62229 331

behaviour of stem cells. A preliminary study demonstrated Zyxin played an important role in nanotopographical feature-facilitated changes in stem cells [48]. On 350 nm grating, expression of Zyxin was down-regulated, which was associated with the accelerated speed of migration and the decreased intracellular tension. Likewise, McMurray et al. revealed that modification in surface nanotopography of thermoplastic polycaprolactone (PCL) would influence intra‐ cellular tension, which could maintain the multipotency of stem cells and diminish spontane‐ ous differentiation of MSC [61]. Moreover, his current study further illustrated that nanoscale spatial organization of cell-adhesive ligands bound to ECM could affect lineage commitment of MSCs [62]. By using nanopatterning techniques, arginine-glycine-aspartate (RGD) was covalently linked to the surface of poly (ethyleneglycol) (PEG) hydrogels with different nanospacing. It was interesting to identify that large RGD nanospacing was beneficial for

Many attempts at cell therapy have employed ECM to improve efficacy for the following reasons. First, the major obstacle to the application of stem cells, which is known as the extremely poor survival and engraftment of transplanted stem cells, could be minimized by co-transplantation stem cells with ECM [51,63,64]. Second, engineered ECM mimicking the natural stem-cell microenvironments could provide plenty of subtle and instructive cues to control the fate of both transplanted and endogenous cells, including stem cell self-renewal, differentiation, and migration [7,65,66]. Taken together, the development of engineered

For both experimental studies and clinical applications, transplanted stem cells are commonly prepared for transplantation as single cells. During this process, interactions between cells and ECM are lost and adhesion-related survival signals are down-regulated, which could cause a decrease in cell viability and initiated apoptosis [67]. Fortunately, recent research discovered that the down-regulated molecules of detached cells could be regained in the presence of Matrigel [4], which provided a theoretical rationale for using ECM as a protective scaffold to

In support of this finding, recent study demonstrated that biomimetic scaffold could protect the transplanted stem cells, and further promote functional and structural recovery from acute kidney injury (AKI). Through immobilization of the C-domain of insulin-like growth factor 1 (IGF-1C) to chitosan (CS) hydrogel (CS-IGF-1C), an artificial microenvironment for supporting growth of stem cells was synthesized. The pro-proliferative, anti-apoptotic, and pro-angio‐ genic effects of CS-IGF-1C were demonstrably beneficial for enhancing survival of transplant‐

osteogenesis; small RGD nanospacing was conducive to adipogenesis.

330 Composition and Function of the Extracellular Matrix in the Human Body

**4. ECM augments therapeutic effects of stem cell therapy**

matrices is promising for the application of stem cells in regenerative medicine.

enhance viability and to stimulate self-renewal of the transplanted cells.

ed stem cells, which could ameliorate renal function [47] (**Figure 5**).

**4.1. Enhance efficacy of transplanted cells**

**Figure 5. CS-IGF-1C hydrogel increases ADSCs viability in vivo.** (A) The fate of ADSCs after transplantation was tracked by molecular imaging. Images are from representative animals receiving 1×106 ADSCs alone, with chitosan hy‐ drogel or CS-IGF-1C hydrogel. (B) Quantitative analysis of BLI signals demonstrated that cell survival was improved by chitosan hydrogel and CS-IGF-1C hydrogel application at all time-points. CS-IGF-1C hydrogel group showed sig‐ nificantly better cell survival. Data are expressed as mean ± SEM. (C) Representative photomicrographs displayed the engraftment of ADSCs (GFP, green) within kidneys at day 3 and 14. Proximal tubular epithelial cells were stained by rhodamine-labeled lens culinaris agglutinin (LCA, red). (D) Quantitative analysis data revealed that chitosan hydrogel improved cell engraftment and CS-IGF-1C hydrogel further increased this effect. Data are expressed as mean ± SEM. \*P<0.05 vs. ADSCs, #P<0.05 vs. ADSCs/CS. (E) Representative images showing the proliferation (Ki-67, red) of trans‐ planted ADSCs (GFP, green) in the border regions 3 days after AKI. DyLight 649-labeled LCA staining (cyan) was per‐ formed to reveal renal structure. (F) Quantification of the proliferation index of ADSCs. Data are expressed as mean ± SEM. \*P<0.05 vs. ADSCs, #P<0.05 vs. ADSCs/CS. (47). Reprinted by permission of the publisher.

Besides, we could attribute the efficacy of stem cell therapy partly to the pluripotency of stem cells [68,69]. A morphological study of MSCs in collagen type I (Col I) hydrogel and in interfacial polyelectrolyte complexation (IPC) based hydrogels containing Col I discovered that cells were neatly arranged and closely packed in IPC- Col I hydrogel [70]. This uniform arrangement results in notably enhanced commitment to the chondrogenic lineage of MSC, which could be an attractive source of cartilage equivalents for tissue engineering.

Recently, a variety of studies have demonstrated that decellularized matrix could provide tissue specific cues for cell growth and lineage commitment [71–73]. Decellularized myocardial matrix hydrogel, which keeps the original structure and natural heart ECM, is the most compelling example among these biomaterials. One of the most inspiring finding is that a mouse heart could contract and beat again after removing its own cells and repopulating the decellularized whole-heart ECMs (DC-ECMs) with multipotential cells that could differentiate in response to the signals from the DC-ECMs. Through repopulating decellularized mouse hearts with induced pluripotent stem cell (iPSC)-derived earliest heart progenitors, the recellularized DC-ECMs exhibited myocardium, vessel-like structures, intracellular Ca2+ transients (CaiT), spontaneous heart contractions and significant response to numerous drug interventions [74].

#### **4.2. Support the function of endogenous cells**

MSCs could mobilize into circulating blood and be recruited to the injury site, which was consistent with the evidence that numbers of MSCs were increased considerably in peripheral blood [75]. Several approaches were used in an attempt to investigate this cell recruitment event. It was unexpected to find that ECM was indispensable for the homing of MSCs toward sites of injury [76]. The homing effect could be inhibited through adding inhibitor of serine proteases and leupeptin to ECM, which illustrated the key role of matrix remodelling in MSC migration. In addition, evidence also indicated that exposing MSCs to injury-associated ECM prior to transplantation could augment the efficiency of MSCs' intrinsic tropism for injury [77].

As resident stem cells and progenitor cells could be activated to participate tissue regeneration after injury [78,79], ECM designed for cell seeding should also benefit the growth of host cells and support the function of endogenous cells. Encouragingly, evidence suggested that host cells could respond to ECM in the site of injury in vivo. Firstly, immune responses were elicited in hosts, which was identified by the quickly infiltrated CD68+ cells throughout the entire ECM within 3 days after implantation. Then there were indications of myogenesis in the muscle injury area, which was confirmed by morphology and myosin heavy chain positive staining [80].

Furthermore, accumulating data suggested that human mesenchymal stem cells (hMSCs) could modulate immune system response through their paracrine effect and then create a pro-regenerative environment in situ. Their paracrine effects could be optimized through encapsulating hMSCs into protective ECM [81]. The recruitment of endogenous macrophag‐ es and the M1/M2 polarization were modulated by the trophic factors secreted by hMSCs, which was possibly capable of counteracting the hostile environment and sustaining tissue regeneration. This cell-friendly microenvironment could also be established by administra‐ tion of ECM alone. Increased stem cell tropism, revascularization, and improved cardiac function induced by chitosan-based ECM were observed in ischemic myocardium [82], which may be attributing to the mechanical support provided by ECM and the therapeutic biomolecules enriched by ECM [83–85].
