In vitro, in situ and in vivo models to study microcontainers for improved oral delivery of drugs and probiotics

The oral administration route is preferred by most patients, and, thereby, results in high patient compliance. However, the gastrointestinal (GI) tract presents many obstacles for successful drug delivery, including varying pH values, digestive secretions, enzymes, peristalsis and a protective mucus layer. Recently, oral delivery of live microorganisms with a health benefit to the host, namely probiotics, have shown great promise for treatment of GI diseases such as inflammatory bowel disease. However, oral delivery of viable probiotics is challenged by their sensitivity to factors such as oxygen and low pH values, as well as lack of colonization in the GI tract.
Microfabricated delivery devices, such as microcontainers, have been suggested as carriers to address the challenges related to oral drug delivery. Microcontainers are polymeric devices with a unidirectional compartment for drug loading. They have shown promise for oral drug delivery due to their controlled drug release and spontaneous mucus embedment. When evaluating drug delivery systems, different in vitro, in situ and in vivo models with varying levels of complexity and physiological relevance are traditionally used to access drug release and mucoadhesion.
In this PhD thesis, the potential of microcontainers to improve oral delivery of probiotics is explored by implementing relevant in vitro, in situ and in vivo models. Microcontainers are hypothesized to be beneficial for oral delivery of probiotics due to their protective and mucoadhesive characteristics. Therefore, shape and surface structures were evaluated as factors to improve mucoadhesion in situ and in vivo, to provide a competitive advantage for the delivered probiotics. In an in situ perfusion model in the rat colon, the mucoadhesion of cylindrical, cubic and triangular microcontainers with the same outer surface area was assessed. Additionally, the absorption of amoxicillin loaded into the devices was measured. These studies revealed significantly better colonic mucoadhesion of cubic than cylindrical microcontainers. Based on these promising results, cubic microcontainers were further evaluated in vivo. Here, the retention of 3D printed cubic microcontainers with different surface structures was investigated using planar X-ray imaging. However, it was found that the cubic 3D printed microcontainers did not result in a different GI retention than previously published for cylindrical SU-8 microcontainers.
To enable co-delivery of antibiotics and probiotics and, hereby, provide a competitive advantage for the delivered probiotics, dual-compartment microcontainers (DCMCs) were fabricated with two separate compartments. As a proof-of-concept, they were loaded with two model drugs (furosemide and propranolol), coated with the pH-sensitive polymers Eudragit® L100 and S100, and evaluated in vitro and in vivo. With this delivery system, we showed a sequential release of the two drugs in vitro, and a difference in absorption profile of the two drugs in vivo.
Finally, the viability and release of robust model probiotics loaded into microcontainers was evaluated in vitro and in vivo. To evaluate probiotic delivery using microcontainers in vitro, an anaerobic and temperature-controlled in vitro model was developed and characterized to study release rate and viability. The developed model was successfully applied to measure the release and survival of Lactobacillus rhamnosus GG (LGG) in biorelevant media, as well as the release of a small-molecule drug (Mesalazine (5-ASA)) in the presence of viable anaerobic bacteria (Bifidobacterium thermophilum (B. thermophilum)). In vivo, microcontainers with different polymeric lids were used for delivery of LGG and Escherichia coli (E. coli) Nissle to rats and mice. Based on these studies, we showed that microcontainers can be used for successful delivery of viable probiotics. However, delivery in microcontainers did not significantly improve the colonization of these probiotics.
Conclusively, this thesis highlights the potential for microcontainers as a future strategy in oral delivery of probiotics – especially if the presented design modifications are exploited to achieve improved mucoadhesion and separate co-delivery of probiotics and antibiotics. However, future studies should include delivery of more sensitive probiotics, which may benefit more from delivery in microcontainers due to their sensitivity towards low pH and oxygen. Additionally, more active mucoadhesion features might be needed to achieve notable mucoadhesion in vivo, which could improve bacterial colonization in the GI tract.