4.2.7. Other Polymers

Indirectly 3D-printed "stiffness memory" poly(urea-urethane) (PUU)/POSS elastomeric nano-hybrid scaffolds with thermo-responsive mechanical properties that soften at body temperature by inverse self-assembling have been developed. The initial stiffness and subsequent stiffness relaxation (>10 kPa) of the scaffolds directed the proliferation and differentiation of human BMMSCs towards the osteogenic lineages on stiffer scaffolds over 4 weeks, as measured by immunohistochemistry, histology, ELISA, and qPCR, while soft substrates (<1 kPa) promoted MSCs' chondrogenic differentiation [204]. Table 1 lists the key studies investigating the effect of polymeric matrix stiffness on osteogenic differentiation of mesenchymal stem/progenitor cells. *Polymers* **2021**, *13*, x FOR PEER REVIEW 22 of 34 **Table A1.** Key studies on the effect of polymeric matrix stiffness on osteogenic differentiation of mesenchymal **Study Cell Source Polymer Modification Modulus of Elasticity Results**  *Polymers* **2021**, *13*, x FOR PEER REVIEW 22 of 34 **Table A1.** Key studies on the effect of polymeric matrix stiffness on osteogenic differentiation of mesenchymal

**Table 1.** Key studies on the effect of polymeric matrix stiffness on osteogenic differentiation of mesenchymal stem/progenitor cells. **Alginate Study Cell Source Polymer Modification Modulus of Elasticity Results** 


Chemical crosslinking

3D collagen gel culture on the vibrational bioreactor

DHT and EDAC crosslinking

3D collagen gel culture on the vibrational bioreactor

DHT and EDAC crosslinking

gen/alginate nano film 24 and 53 MPa Increase in alkaline

with EDAC and NHS 3.90 −/+ 0.36 kPa

~108 Pa

0.5, 1, and 1.5 kPa

~108 Pa

0.5, 1, and 1.5 kPa

phosphatase activity

Increase in expression of ALP, collagen 1, and Runx2

phosphatase activity

Increase in expression of ALP, collagen 1, and Runx2

Increased expression of Runx2, collagen I, ALP, OPN, OCN, and BMP2.

Osteogenic differentiation with Runx2 expression

Increased expression of Runx2, collagen I, ALP, OPN, OCN, and BMP2.

Osteogenic differentiation with Runx2 expression




