Abstract
Implantable drug delivery systems (IDDSs) offer good patient compliance and allow the controlled delivery of drugs over prolonged times. However, their application is limited due to the scarce material selection and the limited technological possibilities to achieve extended drug release. Porous structures are an alternative strategy that can overcome these shortcomings. The present work focuses on the development of porous IDDS based on hydrophilic (HPL) and hydrophobic (HPB) polyurethanes and chemical pore formers (PFs) manufactured by hot-melt extrusion. Different PF types and concentrations were investigated to gain a sound understanding in terms of extrudate density, porosity, compressive behavior, pore morphology and liquid uptake. Based on the rheological analyses, a stable extrusion process guaranteed porosities of up to 40% using NaHCO3 as PF. The average pore diameter was between 140 and 600 µm and was indirectly proportional to the concentration of PF. The liquid uptake of HPB was determined by the open pores, while for HPL both open and closed pores influenced the uptake. In summary, through the rational selection of the polymer type, the PF type and concentration, porous carrier systems can be produced continuously via extrusion, whose properties can be adapted to the respective application site.
Highlights
Over the last 20 years, the pharmaceutical industry has shown an ever-growing interest in hot-melt extrusion (HME) as a manufacturing technique [1,2]
What has been a golden standard in the polymer industry since the middle of the 20th century [3] has become a topic of rigorous research for the development of novel drug delivery systems [4]
HME has been investigated for the manufacturing of pellets [7,8], tablets [9], gastro retentive systems [10], nanopharmaceuticals [11,12], protein delivery carriers [13,14,15] and shaped drug-delivery systems intended for topical and parenteral applications, such as vaginal films [16], intra-vaginal rings [17,18,19,20] and implantable drug-delivery systems (IDDS) [21,22,23,24,25]
Summary
Over the last 20 years, the pharmaceutical industry has shown an ever-growing interest in hot-melt extrusion (HME) as a manufacturing technique [1,2]. Polyurethane scaffolds and porous systems have been investigated in the field of regenerative medicine [63,64,65] and as drug delivery systems [66,67,68] using, e.g., the solvent-casting particulate leaching method In none of these studies, pores were continuously formed via HME, HME is already well established for the implementation of porous structures in the polymer industry [69,70,71,72]. Claeys et al [61,62] have used water-soluble additives to create porous structures in contact with water and to modify the drug release from TPU-based tablets produced via HME This strategy could be relevant for IDDS applied at sites with sufficient liquid to initiate the formation of pores. By skillful selection of the amount and type of pore formers and TPUs, optimal material and processing parameters were determined to achieve reproducible porous structures
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