1. Platform Overview
AdaptDelivery is a polymer informatics platform that integrates
molecular modeling, molecular dynamics simulations, machine learning and interactive
web technologies to support the rapid prediction and visualization of polymer
structural properties.
The platform was developed to reduce the computational effort associated with
conventional molecular dynamics workflows. Instead of performing a new simulation
for every polymer system and chain length, users can obtain machine learning-based
predictions directly through a standard web browser.
The current version focuses on two key structural descriptors:
radius of gyration (Rg) and
solvent-accessible surface area (SASA). These properties provide
information about polymer dimensions, compactness, conformational behavior,
solvent exposure, hydration, and possible aggregation tendencies.
In addition to numerical predictions, AdaptDelivery provides interactive
property-versus-chain-length graphs and browser-based three-dimensional visualization
of generated polymer structures, allowing users to inspect both predicted values and
the corresponding molecular representation within the same interface.
Platform objective:
to provide fast, accessible, and reproducible polymer property predictions
through a unified online environment for real-time prediction and interactive
visualization.
2. Computational Workflow
The AdaptDelivery workflow integrates molecular modeling, molecular dynamics
simulations, structural descriptor extraction, machine learning model development,
and web-based deployment within a unified computational framework.
Representative synthetic and natural polymer systems are first constructed and
solvated in water. Molecular dynamics simulations are then performed to capture
polymer conformational behavior and polymer–solvent interactions over time.
The resulting molecular trajectories are analyzed to calculate two key structural
descriptors: the radius of gyration (Rg) and the
solvent-accessible surface area (SASA). These values are used to
generate the datasets required for training and evaluating the artificial neural
network models.
After training and validation, the predictive models are integrated into the
AdaptDelivery online platform. Users can select a polymer and chain length to obtain
real-time property predictions, interactive graphs, and a browser-based
three-dimensional representation of the generated polymer structure.
Workflow:
Polymer construction
→ Molecular dynamics simulation
→ Structural descriptor extraction
→ ANN training and validation
→ Real-time prediction
→ 2D and 3D visualization
3. Supported Polymer Systems
The AdaptDelivery scientific framework includes both synthetic and natural polymer
systems. Polymers are organized through a hierarchical selection structure based on
Polymer Class: Polymer Type, and
Polymer Name.
Synthetic polymers
The synthetic polymer dataset includes representative systems from several chemical
families, including acrylamides, amines, amides, imines, ketones, olefins, oxides,
and vinyl-based polymers.
The polymers investigated in the AdaptDelivery framework include:
Polyethylene (PE),
Polyethylene oxide (PEO),
Polyethyleneimine (PEI),
Polyacrylamide (PAM),
Poly(allyamine), isotactic R configuration (PAAMR),
Poly(N-isopropylacrylamide), isotactic R configuration (PNIPAAMR),
and
Poly(vinyl methyl ketone), isotactic R configuration (PVMKR).
Natural polymers
The natural polymer dataset currently includes representative lignin-based units:
the Guaiacyl unit (GUAI),
the p-Hydroxyphenyl unit (PHP), and
the Syringyl unit (SYR).
Polymer selection hierarchy:
Polymer Class
→ Polymer Type
→ Polymer Name
Availability note:
the polymer systems accessible through the online interface may represent a curated
subset of the complete scientific dataset, depending on the current platform version.
4. Molecular Dynamics Simulations
Molecular dynamics simulations are used to investigate the conformational behavior
of polymer chains in aqueous environments and to generate the reference data required
for machine learning model development.
The molecular topology and parameter files for each polymer are generated using
CHARMM-GUI. The resulting polymer systems are subsequently
simulated with NAMD 3.0 using the CHARMM36 all-atom force field.
Each polymer system is first equilibrated for 3 ns, followed by a
200 ns production simulation using a 2 fs integration
timestep. The simulations are performed at a temperature of
300 K and a pressure of 1 atm.
Temperature is controlled using a Langevin thermostat with a damping coefficient
of 1 ps−1, while pressure is maintained using a
Langevin piston. Bonds involving hydrogen atoms are constrained with the SHAKE
algorithm. Long-range electrostatic interactions are treated using the Particle
Mesh Ewald method with a grid spacing of 1 Å and a cutoff
distance of 12 Å.
Periodic boundary conditions are applied to mimic an infinite system. During the
simulations, the energy and temperature of each system are monitored to ensure
stability and support the generation of high-quality, reproducible data.
Simulation protocol:
CHARMM-GUI preparation
→ NAMD 3.0
→ CHARMM36 all-atom force field
→ 3 ns equilibration
→ 200 ns production run
→ 2 fs timestep
→ 300 K
→ 1 atm
5. Radius of Gyration
The radius of gyration, denoted by Rg, is a fundamental
descriptor of polymer size and conformational organization. It quantifies the spatial
distribution of the polymer atoms around the center of mass and is commonly used to
characterize the compactness and spatial extent of a polymer chain in solution:
\[
R_g =
\sqrt{
\frac{1}{N}
\sum_{i=1}^{N}
\left\|\mathbf{r}_i-\mathbf{r}_{\mathrm{cm}}\right\|^2
}.
\]
Here, N is the number of selected polymer atoms,
ri is the position vector of atom i, and
rcm is the position vector of the polymer center of mass:
\[
\mathbf{r}_{\mathrm{cm}} =
\frac{
\sum_{i=1}^{N} m_i\mathbf{r}_i
}{
\sum_{i=1}^{N} m_i
}.
\]
For each molecular dynamics trajectory frame, the center of mass is calculated using
atomic masses, after which the radius of gyration is evaluated as the root-mean-square
distance of the selected atoms from that center.
Calculating Rg independently for every trajectory frame makes it possible
to analyze conformational fluctuations and the temporal evolution of polymer size.
In general, lower Rg values correspond to more compact conformations,
whereas higher values indicate a more spatially extended polymer chain.
Platform interpretation:
AdaptDelivery predicts the radius of gyration as a function of the selected polymer
system and monomer number.
6. Solvent-Accessible Surface Area
The solvent-accessible surface area, denoted by SASA, quantifies
the extent of the polymer surface that is accessible to solvent molecules, typically
water. It is an important structural descriptor for characterizing polymer–solvent
interactions, hydration, folding, conformational changes, and aggregation behavior:
\[
A_{\mathrm{SASA}} = \sum_i A_i.
\]
Here, Ai represents the solvent-accessible surface area
contribution associated with atom i.
SASA is calculated by rolling a spherical solvent probe over the molecular surface.
In the AdaptDelivery molecular dynamics workflow, a probe radius of
1.4 Å is used to represent a water molecule:
\[
r_{\mathrm{probe}} = 1.4\ \text{Å}.
\]
The calculation is performed independently for each frame of the molecular dynamics
trajectory using the selected polymer atoms while excluding the surrounding solvent.
The accessible surface contributions of all selected atoms are then summed to obtain
the total SASA value.
This frame-by-frame analysis makes it possible to monitor changes in solvent exposure
and polymer conformation over time. In general, larger SASA values indicate greater
exposure of the polymer surface to the surrounding solvent.
Platform interpretation:
AdaptDelivery predicts the solvent-accessible surface area as a function of the
selected polymer system and monomer number.
7. Structural Dataset Generation
Reference values for the radius of gyration and solvent-accessible surface area
were calculated from molecular dynamics simulations for representative polymer
chain lengths:
\[
n \in \left\{5,\,8,\,10,\,12,\,16,\,25,\,50,\,100,\,150,\,200\right\}.
\]
To construct a continuous relationship between monomer number and polymer property,
the tabulated molecular dynamics values were fitted using a power-law function:
\[
f(x;a,b)=a\,x^b.
\]
Here, x represents the monomer number, while a and
b are fitting parameters determined through nonlinear least-squares
fitting using the curve_fit function from the SciPy computational
library.
The fitted power-law relationship was evaluated for monomer numbers up to 1000
and used to generate 20,000 pairs consisting of a monomer number
and the corresponding polymer property value.
Dataset generation workflow:
Molecular dynamics reference values
→ Power-law fitting
→ Evaluation up to 1000 monomers
→ 20,000 property pairs
→ Training, validation and test datasets
8. Machine Learning Models
AdaptDelivery uses artificial neural networks to learn the relationship between
polymer chain length and structural properties derived from molecular dynamics
simulations. Once trained, the models can generate predictions on a substantially
shorter timescale than running a new molecular dynamics simulation for each input.
The monomer number is used as the input variable, while the output of the neural
network is the predicted polymer property:
\[
x \xrightarrow{\mathrm{ANN}} \widehat{P}(x).
\]
Separate models are used for the prediction of
radius of gyration (Rg) and
solvent-accessible surface area (SASA), because these properties lie on different numerical scales.
Radius of gyration model
For the Rg prediction model, the study reports an architecture containing an input
layer, one fully connected hidden layer with a channel size of
16, and an output layer that returns the predicted radius of
gyration. Several alternative architectures were also investigated.
Solvent-accessible surface area model
The SASA prediction model uses a deeper fully connected architecture with three
hidden layers containing 64, 32, and
16 channels, respectively.
Nonlinearity is introduced through the rectified linear unit activation function:
\[
\operatorname{ReLU}(z)=\max(0,z).
\]
Here, z represents the linear activation of a neuron, obtained from the
weighted input values and the corresponding bias term. The ReLU activation allows
the network to approximate nonlinear relationships between polymer chain length and
the predicted structural property.
Current modeling strategy:
Separate property-specific ANN models
→ Rg prediction
→ SASA prediction
→ Real-time deployment within AdaptDelivery
9. Training Procedure
The artificial neural networks are trained using supervised learning. For each
input monomer number, the corresponding reference value of the polymer property
is known from the generated dataset and is used as the target value during
model optimization.
Before training, the complete dataset is randomly shuffled and divided into
three subsets:
Dataset partition:
80% training set
→ 10% validation set
→ 10% test set
The training set is used to optimize the neural-network parameters. The validation
set is evaluated after each training cycle to monitor model performance and detect
possible overfitting, while the test set is reserved for the final evaluation of
the fully trained model.
Training samples are processed in mini-batches of 128. For each
mini-batch, the difference between the predicted property values and the
corresponding reference values is calculated using the mean absolute error:
\[
E_1 =
\frac{1}{m}
\sum_{i=1}^{m}
\left|
P_i^{\mathrm{predicted}}
-
P_i^{\mathrm{label}}
\right|.
\]
Here, m = 128 is the mini-batch size,
Pipredicted is the property value returned by
the neural network, and
Pilabel is the corresponding reference value.
The objective of the training process is to minimize this error with respect to
the network parameters. Optimization is performed using the
Adam algorithm, which applies stochastic gradient-based updates.
The error gradient is propagated backward through the network, and the model
parameters are updated iteratively.
Training cycle:
Mini-batch input
→ Forward propagation
→ Property prediction
→ Error calculation
→ Backpropagation
→ Parameter update
12. Current Limitations
The current machine learning models support polymer chain lengths from
1 to 1000 monomers. This restriction corresponds to the interval
covered by the generated training, validation, and test datasets. Predictions are
therefore restricted to the same range used for model training and evaluation.
The current version of AdaptDelivery predicts two structural descriptors:
radius of gyration (Rg) and
solvent-accessible surface area (SASA). Separate property-specific
neural networks are used for these outputs.
The three-dimensional structure displayed in the browser is a dynamically generated,
strictly linear polymer chain in PDB format. It should not be interpreted as the
equilibrated molecular conformation obtained from the molecular dynamics trajectory.
Predictions are available only for polymer systems that have already been included
in the scientific workflow. Adding a new polymer requires the generation of molecular
dynamics data, extraction of structural descriptors, construction of the corresponding
dataset, model training and validation, and integration into the platform backend.
Current scope:
Supported polymer systems
→ 1–1000 monomers
→ Rg and SASA prediction
→ Linear PDB visualization
→ Property-specific ANN models
13. Citation and Availability
AdaptDelivery was developed as an online polymer informatics platform for the
real-time prediction and visualization of structural polymer properties. The
platform integrates molecular dynamics simulations, data-driven modeling,
artificial neural networks, and interactive web technologies within a unified
computational environment.
The scientific work associated with the AdaptDelivery platform is cited below.
Researchers who use AdaptDelivery in scientific studies, presentations, teaching
materials, or publications are encouraged to cite this work.
Recommended citation:
Parajdi, L. G.; Toth, I.; Farcas, A.-A.; Balint, Z.; Kiraly, A.; Farcas, A.
AdaptDelivery: A Polymer Informatics Platform for Predicting Structural
Properties of Polymers via Machine Learning.
According to the associated study, all data generated or analyzed during the
research are included in the paper mentioned above.