Adhesion Subsystem

The adhesion subsystem of a synthetic cell is responsible for attaching the cell to other synthetic cells or to surfaces in its environment. Adhesion defines the physical topology of a multi-cellular synthetic cell assembly — which cells are neighbors, what signals can be exchanged locally, and what mechanical forces are transmitted across cell boundaries. It is therefore a prerequisite for the coordinated multi-cellular behaviors described on the Multi-cellular Synthetic Cells page.

Role in Synthetic Cell Design

Unlike living cells, synthetic cells cannot use growth or replication to establish physical contact with neighbors. Adhesion must instead be explicitly engineered as a defined subsystem with programmable specificity. Key design requirements include:

• Selectivity: adhesion should occur between intended cell types and not others, enabling structured assemblies with defined connectivity rather than random aggregation.

• Reversibility: depending on the application, adhesion bonds may need to be formed and broken in a controlled way, for example in response to a chemical signal or change in environmental conditions.

• Compatibility with the synthetic cell membrane: adhesion proteins or molecules must be displayable on a lipid bilayer or polymersome surface without disrupting membrane integrity or interfering with transport and sensing functions.

• Mechanical strength: the adhesion interaction must be strong enough to maintain the intended topology under the mechanical forces the assembly will experience, including osmotic stress and fluid shear.

State of the Art

Programmable adhesion has been demonstrated in living cell systems. A notable example is the helixCAM platform, which enables selective cell–cell and cell–surface interactions through programmable coiled-coil binding domains displayed on the cell surface. By decoupling adhesion specificity from native regulatory machinery, helixCAM provides a conceptual template for adhesion modules that could be adapted to synthetic cell membranes.

Adapting such approaches to synthetic cells remains an open engineering challenge. Surface display of proteins on lipid vesicles or polymersomes requires either membrane anchoring via lipid conjugation or transmembrane insertion, and the density and orientation of displayed proteins must be controlled to achieve reliable adhesion without aggregation.

Open Challenges

Programmable adhesion in synthetic cell systems is largely unrealized and represents an important near-term target. Specific open problems include:

• Demonstrating selective adhesion between distinct synthetic cell populations using orthogonal binding pairs.
• Integrating adhesion display with the synthetic cell assembly process, so that surface protein composition is set at fabrication time.
• Coupling adhesion state to internal gene expression, so that physical contact between cells can trigger a downstream response (contact-dependent signaling).