| 1. |
- Fager, Cecilia, 1990, et al.
(författare)
-
3D high spatial resolution visualisation and quantification of interconnectivity in polymer films
- 2020
-
Ingår i: International Journal of Pharmaceutics. - : Elsevier B.V.. - 0378-5173 .- 1873-3476. ; 587
-
Tidskriftsartikel (refereegranskat)abstract
- A porous network acts as transport paths for drugs through films for controlled drug release. The interconnectivity of the network strongly influences the transport properties. It is therefore important to quantify the interconnectivity and correlate it to transport properties for control and design of new films. This work presents a novel method for 3D visualisation and analysis of interconnectivity. High spatial resolution 3D data on porous polymer films for controlled drug release has been acquired using a focused ion beam (FIB) combined with a scanning electron microscope (SEM). The data analysis method enables visualisation of pore paths starting at a chosen inlet pore, dividing them into groups by length, enabling a more detailed quantification and visualisation. The method also enables identification of central features of the porous network by quantification of channels where pore paths coincide. The method was applied to FIB-SEM data of three leached ethyl cellulose (EC)/hydroxypropyl cellulose (HPC) films with different weight percentages. The results from the analysis were consistent with the experimentally measured release properties of the films. The interconnectivity and porosity increase with increasing amount of HPC. The bottleneck effect was strong in the leached film with lowest porosity.
|
|
| 2. |
- Eriksson Barman, Sandra, 1985, et al.
(författare)
-
A three-dimensional statistical model for imaged microstructures of porous polymer films
- 2018
-
Ingår i: Journal of Microscopy. - : Wiley. - 0022-2720 .- 1365-2818. ; 269:3, s. 247-258
-
Tidskriftsartikel (refereegranskat)abstract
- A thresholded Gaussian random field model is developed for the microstructure of porous materials. Defining the random field as a solution to stochastic partial differential equation allows for flexible modelling of nonstationarities in the material and facilitates computationally efficient methods for simulation and model fitting. A Markov Chain Monte Carlo algorithm is developed and used to fit the model to three-dimensional confocal laser scanning microscopy images. The methods are applied to study a porous ethylcellulose/hydroxypropylcellulose polymer blend that is used as a coating to control drug release from pharmaceutical tablets. The aim is to investigate how mass transport through the material depends on the microstructure. We derive a number of goodness-of-fit measures based on numerically calculated diffusion through the material. These are used in combination with measures that characterize the geometry of the pore structure to assess model fit. The model is found to fit stationary parts of the material well. Lay description We develop a stochastic model for the pore structure of a polymer material which is used as coatings to control drug release from pharmaceutical tablets. The pore geometries of the coatings determine how quickly the drug is released. For instance, the drug transport through a coating with many bottlenecks will be slower compared to the transport through a coating with a lower number of bottlenecks. The model will in future work be used to analyze how the rate of transport of the drug through the coating depends on the distribution of bottlenecks and other characteristics of the pore geometry. In this article we present the model. Each stochastic simulation from the model gives a different pore structure, but with similar pore geometries. This randomness in the model captures that each coating is different. We develop an efficient mathematical algorithm to fit the model to microscopy images of the material. The algorithm uses the information in the microscopy images to find the parameters of the model that make the pore geometry of the microscopy images as similar as possible to the pore geometries of stochastic simulations from the model. To determine how similar the geometries are we use measures that summarize different properties of the pore geometries. We also derive a new measure which compares the results of numerically calculated transport through the pore structures. These measures show that the stochastic simulations from the model are similar to the microscopy images, and we conclude that the model fits the data well.
|
|
| 3. |
- Eriksson Barman, Sandra, 1985
(författare)
-
Gaussian random field based models for the porous structure of pharmaceutical film coatings
- 2015
-
Ingår i: Acta Stereologica. - 0351-580X.
-
Konferensbidrag (refereegranskat)abstract
- Drug release from oral tablets can be controlled using polymer film coatings, and is determined by the porous structure of the coatings. Our aim is to analyze the transport properties of ethylcellulose/hydroxypropylcellulose (EC/HPC) polymer films using Gaussian random field based models.
|
|
| 4. |
- Eriksson Barman, Sandra, 1985, et al.
(författare)
-
Modeling and solving vehicle routing problems with many available vehicle types
- 2015
-
Ingår i: Springer Proceedings in Mathematics & Statistics. - Cham : Springer International Publishing. - 2194-1009 .- 2194-1017. - 9783319185668
-
Konferensbidrag (refereegranskat)abstract
- Vehicle routing problems (VRP) involving the selection of vehicles from a large set of vehicle types are hitherto not well-studied in the literature. Such problems arise at Volvo Group Trucks Technology, who faces an immense set of possible vehicle configurations, of which an optimal set needs to be chosen for each specific combination of transport missions. Another property of real-world VRP’s that is often neglected in the literature is that the fuel resources required to drive a vehicle along a route is highly dependent on the actual load of the vehicle. We define the fleet size and mix VRP with many available vehicle types, called many-FSMVRP, and suggest an extended set-partitioning model of this computationally demanding combinatorial optimization problem. To solve the extended model, we have developed a method based on Benders’ decomposition, the subproblems of which are solved using column generation, and the column generation subproblems being solved using dynamic programming; the method is implemented with a so-called projection-of-routes procedure. The resulting method is compared with a column generation approach for the standard set-partitioning model. Our method for the extended model performs on par with column generation applied to the standard model for instances such that the two models are equivalent. In addition, the utility of the extended model for instances with very many available vehicle types is demonstrated. Our method is also shown to efficiently handle cases in which the costs are dependent on the load of the vehicle. Computational tests on a set of extended standard test instances show that our method, based on Benders’ algorithm, is able to determine combinations of vehicles and routes that are optimal to a relaxation (w.r.t. the route decision variables) of the extended model. Our exact implementation of Benders’ algorithm appears, however, too slow when the number of customers grows. To improve its performance, we suggest that relaxed versions of the column generation subproblems are solved, and that the set-partitioning model is replaced by a set-covering model.
|
|
| 5. |
- Eriksson Barman, Sandra, 1985, et al.
(författare)
-
New characterization measures of pore shape and connectivity applied to coatings used for controlled drug release
- 2021
-
Ingår i: Journal of Pharmaceutical Sciences. - : Elsevier BV. - 1520-6017 .- 0022-3549. ; 110:7, s. 2753-2764
-
Tidskriftsartikel (refereegranskat)abstract
- Pore geometry characterization-methods are important tools for understanding how pore structure influences properties such as transport through a porous material. Bottlenecks can have a large influence on transport and related properties. However, existing methods only catch certain types of bottleneck effects caused by variations in pore size. We here introduce a new measure, geodesic channel strength, which captures a different type of bottleneck effect caused by many paths coinciding in the same pore. We further develop new variants of pore size measures and propose a new way of visualizing 3-D characterization results using layered images. The new measures together with existing measures were used to characterize and visualize properties of 3-D FIB-SEM images of three leached ethyl-cellulose/hydroxypropyl-cellulose films. All films were shown to be anisotropic, and the strongest anisotropy was found in the film with lowest porosity. This film had very tortuous paths and strong geodesic channel-bottlenecks, while the paths through the other two films were relatively straight with well-connected pore networks. The geodesic channel strength was shown to give important new visual and quantitative insights about connectivity, and the new pore size measures provided useful information about anisotropies and inhomogeneities in the pore structures. The methods have been implemented in the freely available software MIST.
|
|
| 6. |
- Eriksson Barman, Sandra, 1985, et al.
(författare)
-
Prediction of diffusive transport through polymer films from characteristics of the pore geometry
- 2019
-
Ingår i: Aiche Journal. - : Wiley. - 0001-1541 .- 1547-5905. ; 65:1, s. 446-457
-
Tidskriftsartikel (refereegranskat)abstract
- Diffusive transport through porous materials is to a large extent determined by the microstructure of the material. To design materials with controlled transport properties, it is hence important to connect properties of the pore geometry to diffusive transport rates. Different kinds of microstructures from a stochastic model are generated and multiplicative regression is used to find relationships between geometric measures of the microstructures and numerically simulated diffusive transport. The main results are that the geodesic tortuosity explains a large part of the transport variation, and that the standard deviations we introduce further improves prediction. It was found that it is best to compute the tortuosity using the whole pore space, instead of using only the inlet, as is commonly done. The effects of calculating the measures using small samples of the pore structure were investigated, and a method for minimizing errors resulting from boundary effects was proposed.
|
|
| 7. |
- Eriksson Barman, Sandra, 1985
(författare)
-
The pore geometry of pharmaceutical coatings: statistical modelling, characterization methods and transport prediction
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis contains new methods for bridging the gap between the pore geometry of porous materials and experimentally measured functional properties. The focus has been on diffusive transport in pharmaceutical coatings used in controlled drug delivery systems, but the methods are general and can be applied to other porous materials and functional properties. Relatively large datasets are needed to train realistic models connecting the pore geometry and diffusive transport properties of porous materials. 3-D statistical pore models based on microscopy images of the coating material were in this thesis used to generate large sets of pore structures, in which diffusive transport was computed numerically. Characterization measures capturing important features of the pore geometry were developed and used as predictors of diffusive transport rates in multiplicative regression models. The characterization measures have been implemented in a freely available software, MIST. In Paper I, a Gaussian random field based pore model was developed and fitted to microscopy images of the coating material. Due to the large size of the data, the model was formulated using a Gaussian Markov random field approximation, which allows for efficient inference. A new method for solving linear equations with Kronecker matrices which reduced the complexity of the model fitting algorithm considerably was developed. The pore model was found to fit the microscopy images well. In Paper II, characterization measures that have been shown to provide good regression models for diffusive transport rates were developed further and implemented. Multiplicative regression models were fitted to pore structures from the model from Paper I, and the new methods were shown to give improved results. In Papers III and V characterization measures that capture a type of bottleneck effect which was observed in another set of microscopy images of the coating material (Papers III and IV), but which is not captured by existing methods, were invented. Pore structures with this type of bottleneck were generated using 3-D statistical pore models, and the new type of bottleneck was found to be an important determinant of diffusive transport rates when the regression models were fitted to simple pore structures (Paper V).
|
|
