16.4 Assembly-Time Molecular Encapsulation

Assembly-Time Molecular Encapsulation describes the incorporation of molecular cargo into a synthetic cell compartment that occurs as a direct consequence of the boundary closing around cargo already present in the surrounding medium, rather than through any deliberate loading step applied after the compartment has already formed. This route relies on passive entrapment during closure and is inherently statistical in nature, since the amount of cargo captured depends on what happened to be present in the immediate vicinity of the boundary at the moment of closure.

The Basic Mechanism

Cargo Presence during Compartment Formation

Cargo presence during compartment formation refers to the simple requirement that intended cargo molecules be dissolved or dispersed in the medium at the time and location where boundary closure is occurring, since assembly-time encapsulation cannot capture cargo that is not already present in the relevant region.

Passive Molecular Entrapment

Passive molecular entrapment is the core mechanism of assembly-time encapsulation, in which cargo molecules become enclosed within the forming compartment simply because they happen to be located within the volume the closing boundary comes to surround, without any active transport process directing them inward.

Bulk Solution Sampling

Bulk solution sampling describes the way in which the enclosed volume, at the moment of closure, effectively captures a small sample of whatever composition was present in the surrounding bulk solution, meaning the internal cargo composition initially mirrors the external bulk composition at the point of closure.

Concurrent Incorporation Across Cargo

Concurrent Compartment Cargo Incorporation

Concurrent compartment cargo incorporation refers to the fact that, when multiple cargo species are present in the surrounding medium during closure, all of them are subject to passive entrapment simultaneously, meaning assembly-time encapsulation naturally supports multi-cargo encapsulation without requiring separate incorporation events for each cargo type.

Distribution Behavior During Closure

Assembly-Time Cargo Concentration

Assembly-time cargo concentration refers to the amount of a given cargo per unit volume present in the medium at the moment of closure, which directly determines the expected amount of that cargo captured within the resulting enclosed volume.

This relationship expresses the expected number of cargo molecules captured as the product of the bulk cargo concentration and the compartment's enclosed internal volume, forming the statistical basis for predicting assembly-time encapsulation outcomes.

Assembly-Time Cargo Partitioning

Assembly-time cargo partitioning refers to any tendency of a cargo molecule to distribute unevenly between the region immediately enclosed by the closing boundary and the surrounding bulk medium, deviating from simple uniform sampling due to the cargo's own chemical partitioning behavior.

Assembly-Time Cargo Exclusion

Assembly-time cargo exclusion refers to the active repulsion of a cargo molecule away from the region the boundary is closing around, resulting in captured cargo levels below what bulk concentration alone would predict.

Assembly-Time Cargo Adsorption

Assembly-time cargo adsorption refers to a cargo molecule's tendency to associate specifically with the forming boundary surface during closure, which can elevate the effective cargo captured relative to what uniform bulk sampling alone would predict.

Boundary Closure and Cargo Fate

Boundary Closure around Cargo

Boundary closure around cargo is the specific moment at which the compartment boundary completes its closure while enclosing whatever cargo molecules were present within its bounded region, fixing the initial internal cargo composition at that instant.

Assembly-Time Cargo Dilution

Assembly-time cargo dilution refers to a reduction in effective internal cargo concentration that can occur if the bulk medium concentration used during assembly is itself relatively low, since assembly-time encapsulation cannot concentrate cargo beyond what was present in the surrounding bulk solution.

Assembly-Time Cargo Loss

Assembly-time cargo loss refers to cargo that was present in the bulk medium but failed to become captured within any closed compartment, either remaining in the external medium after closure or being lost through incomplete closure or other assembly defects.

Assembly-Induced Cargo Damage

Assembly-induced cargo damage refers to structural or functional harm suffered by cargo molecules as a result of exposure to the specific conditions present during the assembly process itself, representing the encapsulation-specific instance of the general assembly-induced component damage risk relevant to cargo co-assembly.

Completion of the Process

Passive Encapsulation Completion

Passive encapsulation completion is the point at which boundary closure around cargo has finished and no further passive entrapment can occur, marking the end of the assembly-time encapsulation window and the beginning of the compartment's subsequent existence as an independently sealed structure with whatever cargo composition it captured.