Cellular and multicellular form and function

Abstract

Engineering artificial tissue constructs requires the appropriate spatial arrangement of cells within scaffolds. The introduction of microengineering tools to the biological community has provided a valuable set of techniques to manipulate the cellular environment, and to examine how cell structure affects cellular function. Using micropatterning techniques, investigators have found that the geometric presentation of cell-matrix adhesions are important regulators of various cell behaviors including cell growth, proliferation, differentiation, polarity and migration. Furthermore, the presence of neighboring cells in multicellular aggregates has a significant impact on the proliferative and differentiated state of cells. Using microengineering tools, it will now be possible to manipulate the various environmental factors for practical applications such as engineering tissue constructs with greater control over the physical structure and spatial arrangement of cells within their surrounding microenvironment.

Figure 1. Microfabrication methods to control cell-ECM and cell-cell adhesion

(A) Microcontact printing is used to pattern adhesive islands. Various sized islands are used to control cell-ECM adhesion and cell shape or spreading [5]. (B) Agarose microwells allow the control of both cell-ECM adhesion and cell-cell adhesion. Cells form cadherin-mediated cell-cell contacts across the center of the bowtie [42]. (C) Electroactive substrates dynamically activate inert surfaces to render them adhesive to cells. Patterned cells that are exposed to a newly adhesive surface form new adhesions and migrate away from the initial patterns [9]. (D) Microfabricated silicon combs dynamically control adhesion of cells to neighboring cells by changing from a contacting to separated configuration [10].

Figure 2. Cell shape regulates proliferation and differentiation

(A) Cells seeded on increasingly larger islands exhibit progressively higher rates of proliferation and lower rates of apoptosis [5]. (B) Mesenchymal stem cells seeded on large islands tend to differentiate into bone, while cells seeded on small islands differentiate into fat [18].

Figure 3. Micropatterning techniques demonstrate the role of ECM geometry in regulating cell function

(A) Cells patterned onto a teardrop shape polarize and form lamellepodia at the blunt end of the drop [20]. (B) Cells patterned to form squares with an asymmetric underlying ECM pattern exhibit a polarized axis of division [21].

Figure 4. RhoA and cytoskeletal tension are involved in transducing extracellular signals

(A) Cells patterned on microfabricated post arrays exhibit higher contractility at higher levels of spreading. RhoA activation increases contractility further [24]. (B) Mesenchymal stem cells seeded on soft substrates tend to be less well spread and differentiate into neurons, while cells on stiffer matrices exhibited myogenesis, and cells even stiffer matrices exhibited osteogenesis [25].

Figure 5. Multicellular structure regulates cell function

(A) Endothelial cells contacting a single neighboring cell exhibit a VE-cadherin dependent increase in proliferation when compared to single cells that are spread to the same extent [36]. (B) Groups of cells seeded on larger islands have higher levels of proliferation at the periphery compared to cells located at the interior [38]. (C) Chondrocytes patterned within three-dimensional PEG gels exhibit cluster-size dependent biosynthesis (filled circles). Unpatterned control cells did not exhibit changes in biosynthesis (open circles) [41].