Polyvinyl acetate-based film coatings

Kollidon® SR: Formulation techniques and drug delivery applications

Kollidon® SR is one of the recent versatile coprocessed excipients in the formulation of modified-release dosage forms. It is prepared by co-spray drying aqueous dispersions of polyvinylacetate and polyvinylpyrrolidone. This article gives a critical review of the physicochemical attributes and technological properties of Kollidon® SR. The current review discusses various technological approaches used in the formulation with Kollidon® SR, from conventional ones like direct compaction and wet granulation to more advanced methodologies such as 3D printing, electrospinning and hot-melt extrusion. The review further elaborates on the influence of the major factors on drug release kinetics from Kollidon® SR-based formulations. Furthermore, this review unravels the potential of Kollidon® SR in the development of site-targeted oral drug delivery systems and focuses on its adaptability to other routes of administration. Further, the review deals with the considerations to be made regarding stability to make sure the formulations based on Kollidon® SR are reliable.

Acetate production from corn stover hydrolysate using recombinant Escherichia coli BL21 (DE3) with an EP-bifido pathway

BACKGROUND

Acetate is an important chemical feedstock widely applied in the food, chemical and textile industries. It is now mainly produced from petrochemical materials through chemical processes. Conversion of lignocellulose biomass to acetate by biotechnological pathways is both environmentally beneficial and cost-effective. However, acetate production from carbohydrate in lignocellulose hydrolysate via glycolytic pathways involving pyruvate decarboxylation often suffers from the carbon loss and results in low acetate yield.

RESULTS

Escherichia coli BL21 (DE3) was confirmed to have high tolerance to acetate in this work. Thus, it was selected from seven laboratory E. coli strains for acetate production from lignocellulose hydrolysate. The byproduct-producing genes frdA, ldhA, and adhE in E. coli BL21 (DE3) were firstly knocked out to decrease the generation of succinate, lactate, and ethanol. Then, the genes pfkA and edd were also deleted and bifunctional phosphoketolase and fructose-1,6-bisphosphatase were overexpressed to construct an EP-bifido pathway in E. coli BL21 (DE3) to increase the generation of acetate from glucose. The obtained strain E. coli 5K/pFF can produce 22.89 g/L acetate from 37.5 g/L glucose with a yield of 0.61 g/g glucose. Finally, the ptsG gene in E. coli 5K/pFF was also deleted to make the engineered strain E. coli 6K/pFF to simultaneously utilize glucose and xylose in lignocellulosic hydrolysates. E. coli 6K/pFF can produce 20.09 g/L acetate from corn stover hydrolysate with a yield of 0.52 g/g sugar.

CONCLUSION

The results presented here provide a promising alternative for acetate production with low cost substrate. Besides acetate production, other biotechnological processes might also be developed for other acetyl-CoA derivatives production with lignocellulose hydrolysate through further metabolic engineering of E. coli 6K/pFF.

Bioadhesive Polymeric Films Containing Rhamnolipids, An Innovative Antimicrobial Topical Formulation

Acne affects most of the world's population, causing an impact on the self-esteem of adolescents and young adults. One of the causes is the presence of the bacteria Cutibacterium acnes which are part of the natural microbiota of the skin. Topical treatments consist of anti-inflammatory and antibiotics, which could select resistant strains. Alternatives to the antibiotic are biocomposites that have antimicrobial activity like biosurfactants which are produced by bacteria. An innovative way of applying these compounds is bioadhesive polymeric films that adhere to the skin and release the active principle topically. Rhamnolipids have great potential to be used in the treatment of acne because they present antimicrobial activity against C. acnes in low and safe concentrations (MIC of 15.62 µg/mL, CBM of 31.25 µg/mL and CC50 of 181.93 µg/mL). Four films with different rhamnolipids concentrations (0.0; 0.1; 0.2; and 0.3%, w/w) were obtained as to visual appearance, mass variation, thickness, density, solubility, pH, water vapor transmission, mechanical properties (folding endurance, bioadhesion strength, tensile strength, elongation at break and Young's modulus), scanning electron microscopy and infrared. The results show that these formulations had a homogeneous appearance; elastic mechanical properties; pH similar to human skin and bioadhesive. The polymeric films containing rhamnolipids were effective against C. acnes, in the in vitro test, at the three concentrations tested, the film with the highest concentration (0.3%, w/w) being the most promising for presenting the highest antimicrobial activity. Thus, the polymeric film containing rhamnolipids has the potential to be used in the treatment of acne.

Genetic Modifications in Bacteria for the Degradation of Synthetic Polymers: A Review

Synthetic polymers, commonly known as plastics, are currently present in all aspects of our lives. Although they are useful, they present the problem of what to do with them after their lifespan. There are currently mechanical and chemical methods to treat plastics, but these are methods that, among other disadvantages, can be expensive in terms of energy or produce polluting gases. A more environmentally friendly alternative is recycling, although this practice is not widespread. Based on the practice of the so-called circular economy, many studies are focused on the biodegradation of these polymers by enzymes. Using enzymes is a harmless method that can also generate substances with high added value. Novel and enhanced plastic-degrading enzymes have been obtained by modifying the amino acid sequence of existing ones, especially on their active site, using a wide variety of genetic approaches. Currently, many studies focus on the common aim of achieving strains with greater hydrolytic activity toward a different range of plastic polymers. Although in most cases the depolymerization rate is improved, more research is required to develop effective biodegradation strategies for plastic recycling or upcycling. This review focuses on a compilation and discussion of the most important research outcomes carried out on microbial biotechnology to degrade and recycle plastics.

Fabrication of 3D-Printed Hydrocortisone Triple Pulsatile Tablet Using Fused Deposition Modelling Technology

Hydrocortisone (HC) is the optimal drug for adolescents diagnosed with congenital adrenal hyperplasia (CAH). Because traditional dosage regimens HC are inconvenient, our study used fused deposition modeling (FDM) three-dimensional (3D) printing technology to solve the problems caused by traditional preparations. First, we designed a core-shell structure tablet with an inner instant release component and an outer delayed release shell. The instant release component was Kollicoat IR: glycerol (GLY): HC = 76.5:13.5:10. Then, we used Affinisol® HPMC 15LV to realize delayed release. Furthermore, we investigated the relationship between the thickness of the delayed release shell and the delayed release time, and an equation was derived through binomial regression analysis. Based on that equation, a novel triple pulsatile tablet with an innovative structure was devised. The tablet was divided into three components, and the drug was released multiple times at different times. The dose and release rate of the tablets can be adjusted by modifying the infill rate of the printing model. The results indicated that the triple pulsatile tablet exhibited desirable release behavior in vitro. Moreover, the physicochemical properties of the drug, excipients, filaments, and tablets were characterized. All these results indicate that the FDM 3D printing method is a convenient technique for producing preparations with intricate structures.

Taste Masking of Steroids for Oral Formulations

Objectives

Oral steroids are commonly prescribed to children. Steroids have a strong bitter taste that limits their oral acceptance in children. The objective of this study was to formulate a pediatric-friendly and palatable oral dosage form of steroids.

Materials and Methods

Solid dispersions of dexamethasone were prepared using polyethylene glycol, pectin, and Eudragit as carrier polymers, and chocolate as a flavoring agent. Taste masking efficiency was evaluated by healthy volunteers to select the best formula. The selected formula was pressed into chewable tablets with varying amounts of sweeteners. Chewable tablets were evaluated for palatability, hardness, and chewing index. The typical application of the taste masking approach was confirmed using prednisolone.

Results

Eudragit-based solid dispersions were effective in dexamethasone taste masking. Using 40% mannitol resulted in palatable tablets with acceptable hardness and chewing difficulty. The effectiveness of the taste masking approach was successfully used to prepare prednisolone chewable tablets. However, an increase in the carrier: drug ratio and a change in the flavor to pineapple were necessary to achieve maximum palatability of prednisolone chewable tablets.

Conclusion

Eudragit solid dispersion is an effective method for the taste masking highly bitter steroids. The solid dispersion was successfully pressed into a palatable, easy-to-chew, and pediatric-friendly chewable tablet dosage form. The carrier: drug ratio and the choice of flavoring agent are crucial factors in improving tablet palatability.

Acetate Production from Syngas Produced from Lignocellulosic Biomass Materials along with Gaseous Fermentation of the Syngas: A Review

Biotransformation of lignocellulose-derived synthetic gas (syngas) into acetic acid is a promising way of creating biochemicals from lignocellulosic waste materials. Acetic acid has a growing market with applications within food, plastics and for upgrading into a wide range of biofuels and bio-products. In this paper, we will review the microbial conversion of syngas to acetic acid. This will include the presentation of acetate-producing bacterial strains and their optimal fermentation conditions, such as pH, temperature, media composition, and syngas composition, to enhance acetate production. The influence of syngas impurities generated from lignocellulose gasification will further be covered along with the means to alleviate impurity problems through gas purification. The problem with mass transfer limitation of gaseous fermentation will further be discussed as well as ways to improve gas uptake during the fermentation.

Effect of polyvinyl acetate (PVAc) based coating on quality characteristics of capsicum during storage

The effect of PVAc (Polyvinyl acetate) coating on various characteristics of capsicum was determined during postharvest storage at room temperature (30 ± 1 °C) and refrigeration temperature (10 ± 1 °C). Food grade PVAc was used to make different coating formulations (2.5, 5, 7.5, 10 and 12.5%) by dissolving alcohol-water mixtures. After coating, the samples were stored at room temperature (30 ± 1 °C) and refrigeration temperature (10 ± 1 °C) for a comparative study. Various physicochemical parameters viz. weight loss, TSS, acidity, chlorophyll, pH, ascorbic acid, and color were analyzed every three days of storage till spoilage. Results revealed that the physicochemical characteristics and the quality of the bell peppers were improved by coating treatments at both the storage conditions. PVAc concentrations of 10 and 12.5% performed better than other PVAc coatings in retaining the chlorophyll and water content, which ultimately increased the shelf life of capsicum without significantly affecting its green color. The coating reduced the weight loss and color change, maintained total soluble solids, titratable acidity, pH over the storage period. About 40-50% less weight loss was observed in case of higher PVAc coating concentrations (10 and 12%). Therefore, the present study results suggested that PVAc coating can maintain postharvest storage quality of capsicum at 30 ± 1 °C and 10 ± 1 °C storage conditions.

Graphical abstract

Bioadhesive Tannic-Acid-Functionalized Zein Coating Achieves Engineered Colonic Delivery of IBD Therapeutics via Reservoir Microdevices

The biggest challenge in oral delivery of anti-inflammatory drugs such as 5-aminosalicylic acid (5-ASA) is to (i) prevent rapid absorption in the small intestine and (ii) achieve localized release at the site of inflammation in the lower gut, i.e., the colon. Here, we present an advanced biopolymeric coating comprising of tannic-acid-functionalized zein protein to provide a sustained, colon-targeted release profile for 5-ASA and enhance the mucoadhesion of the dosage form via a mussel-inspired mechanism. To enable localized delivery and provide high local concentration, 5-ASA is loaded into the microfabricated drug carriers (microcontainers) and sealed with the developed coating. The functionality and drug release profile of the coating are characterized and optimized in vitro, showing great tunability, scalability, and stability toward proteases. Further, ex vivo experiments demonstrate that the tannic acid functionalization can significantly enhance the mucoadhesion of the coating, which is followed up by in vivo investigations on the intestinal retention, and pharmacokinetic evaluation of the 5-ASA delivery system. Results indicate that the developed coating can provide prolonged colonic delivery of 5-ASA. Therefore, the here-developed biodegradable coating can be an eco-friendly substitute to the state-of-the-art commercial counterparts for targeted delivery of 5-ASA and other small molecule drugs.

Influence of redox initiator component ratios on the emulsion copolymerisation of vinyl acetate and neodecanoic acid vinyl ester

Redox initiated emulsion polymerisation of vinyl acetate and neodecanoic acid vinyl ester was investigated at temperatures ranging from -1 °C to 87 °C (initiation temperature between -1 °C and 60 °C), using varying molar ratios of the following redox components: l-ascorbic acid, tert-butyl hydroperoxide and ammonium iron(iii) sulfate dodecahydrate as a catalyst. The high flexibility of redox initiators enables product properties, as well as space-time-yield, to be adjusted as required. Polymers being products by process, it was presumed that modifying the conversion rate would lead to a different product. However, it was shown that the reaction rate is adjustable by varying the catalyst amount without changing the product properties, such as molecular weight, particle size, glass transition temperature and polymer structure, while reducing the overall process time by 40-86% (at equimolar ratios of reducing and oxidising agent). In contrast, variation of the tert-butyl hydroperoxide content resulted in changes of the molecular weight. The influence of the initiation temperature and of the redox system on the reaction rate was determined, enabling control over the reaction rate in the whole temperature range. Meanwhile, overall process times of approximately 2-240 min and high conversions of 90-99% could be achieved. Statistical modelling confirmed the results and facilitated predictions, enabling the conversion rate to be adjusted to the desired properties. The possibility of being able to adjust the conversion rate and product properties independently of each other creates additional degrees of freedom in process design.

In Vitro and In Vivo Evaluations of Berberine-Loaded Microparticles Filled In-House 3D Printed Hollow Capsular Device for Improved Oral Bioavailability

The low oral bioavailability, short biological half-life, high dose, and frequent dosing of berberine (BBR) contribute to its restricted clinical use despite its extensive pharmacological activity. Thus, the objective of this study was to formulate sustained-release microparticles (MPs) using a pH-independent release polymer and to evaluate their potential to improve the oral bioavailability of BBR. BBR loaded MPs were prepared using the emulsion crosslinking method and evaluated for particle size, circularity, morphology, entrapment efficiency, solid-state analysis, swelling index, and in vitro BBR release study fitted with different models of release kinetics. The MPs exhibited desired particle sizes ranges between 11.09-11.62 μm and were almost spherical in shape, as confirmed by the circularity value and micrographic images. A loss of BBR crystallinity was observed after encapsulation in MPs, as evident from various solid-state analyses. The final optimized batch (F3) showed highest % BBR entrapment efficiency value of 81.63% ± 4.9. The in vitro BBR release performance in both acidic and alkaline media showed the desired sustained release behavior from the crosslinked MPs, where the maximum BBR release was observed at alkaline pH, which is in accordance with the swelling study data. In the in vivo study, the oral absorption profiles of BBR from both pristine and MPs formats were investigated using in-house prototyped 3D printed hollow capsules as a unit dose carrier. In vivo data showed sustained and prolonged absorption behavior of BBR from MPs compared to their pristine counterparts, which resulted in a cumulative increment of relative oral bioavailability to mitigate the aforementioned issues related to BBR. Graphical Abstract.

Towards a Better Understanding of Verapamil Release from Kollicoat SR:IR Coated Pellets Using Non-Invasive Analytical Tools

The aim of this study was to gain deeper insight into the mass transport mechanisms controlling drug release from polymer-coated pellets using non-invasive analytical tools. Pellet starter cores loaded with verapamil HCl (10% loading, 45% lactose, 45% microcrystalline cellulose) were prepared by extrusion/spheronization and coated with 5% Kollicoat SR:IR 95:5 or 10% Kollicoat SR:IR 90:10. Drug release was measured from ensembles of pellets as well as from single pellets upon exposure to acetate buffer pH = 3.5 and phosphate buffer pH = 7.4. The swelling of single pellets was observed by optical microscopy, while dynamic changes in the pH in the pellet cores were monitored by fluorescence spectroscopy. Also, mathematical modeling using a mechanistically realistic theory as well as SEM and Raman imaging were applied to elucidate whether drug release mainly occurs by diffusion through the intact film coatings or whether crack formation in the film coatings plays a role. Interestingly, fluorescence spectroscopy revealed that the pH within the pellet cores substantially differed upon exposure to acetate buffer pH = 3.5 and phosphate buffer pH = 7.4, resulting in significant differences in drug solubility (verapamil being a weak base) and faster drug release at lower pH: from ensembles of pellets and single pellets. The monitoring of drug release from and the swelling of single pellets indicated that crack formation in the film coatings likely plays a major role, irrespective of the Kollicoat SR:IR ratio/coating level. This was confirmed by mathematical modeling, SEM and Raman imaging. Importantly, the latter technique allowed also for non-invasive measurements, reducing the risk of artifact creation associated with sample cutting with a scalpel.

Slow release fertilizer prepared with lignin and poly(vinyl acetate) bioblend

Controlled or slow release fertilizers have been recommended to enhance crop yield, while minimizing environmental and economic issues related from current fertilizer applications. However, alternative biodegradable and non-toxic coating material should be suggested to produce biocoated fertilizers. Here we propose the use of lignin and poly(vinyl acetate) (PVAc) as biocoating materials for preparing slow release urea fertilizer. The blend of PVAc and lignin at a mass ratio of 75:25 improved the characteristics of the formed film and increased the nitrogen release time if compared to the pure polymers. The nitrogen release time from urea granules coated with a polymeric layer of 154.3 ± 5.5 μm formed by lignin and PVAc was 36 times greater than from bare urea. The increase in the polymeric coating from 52.6 ± 5.2 to 80.2 ± 6.1 μm decreased the curvature of the nitrogen release data by a factor of at least 1.7, while the curvature was decreased in at least 1.3 with the increase in the polymeric coating from 80.2 ± 6.1 to 158.9 ± 10.6 μm. The adjustment of nitrogen release data to the Peppas-Sahlin model indicated the Fickian diffusion is more predominant than relaxation contributions, since the used polymers did not present considerable swelling. Thus, the blending of PVAc and lignin at 25 wt% of lignin and 75 wt% of PVAc is suggested as a biocoating material for producing slow release fertilizers.

Multi-Analytical Framework to Assess the In Vitro Swallowability of Solid Oral Dosage Forms Targeting Patient Acceptability and Adherence

A lack of effective intervention in addressing patient non-adherence and the acceptability of solid oral dosage forms combined with the clinical consequences of swallowing problems in an ageing world population highlight the need for developing methods to study the swallowability of tablets. Due to the absence of suitable techniques, this study developed various in vitro analytical tools to assess physical properties governing the swallowing process of tablets by mimicking static and dynamic stages of time-independent oral transitioning events. Non-anatomical models with oral mucosa-mimicking surfaces were developed to assess the swallowability of tablets; an SLA 3D printed in vitro oral apparatus derived the coefficient of sliding friction and a friction sledge for a modified tensometer measured the shear adhesion profile. Film coat hydration and in vitro wettability was evaluated using a high-speed recording camera that provided quantitative measurements of micro-thickness changes, simulating static in vivo tablet–mucosa oral processing stages with artificial saliva. In order to ascertain the discriminatory power and validate the multianalytical framework, a range of commonly available tablet coating solutions and new compositions developed in our lab were comparatively evaluated according to a quantitative swallowability index that describes the mathematical relationship between the critical physical forces governing swallowability. This study showed that the absence of a film coat significantly impeded the ease of tablet gliding properties and formed chalky residues caused by immediate tablet surface erosion. Novel gelatin- and λ-carrageenan-based film coats exhibited an enhanced lubricity, lesser resistance to tangential motion, and reduced stickiness than polyvinyl alcohol (PVA)–PEG graft copolymer, hydroxypropyl methylcellulose (HPMC), and PVA-coated tablets; however, Opadry^® EZ possessed the lowest friction–adhesion profile at 1.53 a.u., with the lowest work of adhesion profile at 1.28 J/mm². For the first time, the in vitro analytical framework in this study provides a fast, cost-effective, and repeatable swallowability ranking method to screen the in vitro swallowability of solid oral medicines in an effort to aid formulators and the pharmaceutical industry to develop easy-to-swallow formulations.

Feedforward and Feedback Control of a Pharmaceutical Coating Process

This work demonstrates the use of a combination of feedforward and feedback loops to control the controlled release coating of theophylline granules. Feedforward models are based on the size distribution of incoming granules and are used to set values for the airflow in the fluid bed processor and the target coat weight to be applied to the granules. The target coat weight of the granules is controlled by a feedback loop using NIR spectroscopy to monitor the progress of the process. By combining feedforward and feedback loops, significant variation in the size distributions and ambient conditions were accommodated in the fluid bed coating of the granules and a desired dissolution profile was achieved. The feedforward component of the control system was specifically tested by comparing the performance of the control system with and without this element by Monte Carlo simulation.

Oral Modified Release Multiple-Unit Particulate Systems: Compressed Pellets, Microparticles and Nanoparticles

Oral modified-release multiparticulate dosage forms, which are also referred to as oral multiple-unit particulate systems, are becoming increasingly popular for oral drug delivery applications. The compaction of polymer-coated multiparticulates into tablets to produce a sustained-release dosage form is preferred over hard gelatin capsules. Moreover, multiparticulate tablets are a promising solution to chronic conditions, patients’ adherence, and swallowing difficulties if incorporated into orodispersible matrices. Nonetheless, the compaction of multiparticulates often damages the functional polymer coat, which results in a rapid release of the drug substance and the subsequent loss of sustained-release properties. This review brings to the forefront key formulation variables that are likely to influence the compaction of coated multiparticulates into sustained-release tablets. It focusses on the tabletting of coated drug-loaded pellets, microparticles, and nanoparticles with a designated section on each. Furthermore, it explores the various approaches that are used to evaluate the compaction behaviour of particulate systems.

The Effects of Curing and Casting Methods on the Physicochemical Properties of Polymer Films

Most film coatings in the pharmaceutical industry are prepared using organic solvents or aqueous solvents. Due to different film-formation mechanisms, their properties are significantly different from each other. Curing can alter the microstructure of films by improving the coalescence of polymer particles for aqueous dispersion-based films or accelerating macromolecule relaxation for organic solvent-based films. The aim of this study was to investigate the effects of preparation methods and curing on the physicochemical properties of Kollicoat® SR30D and Kollicoat® MAE100P films. The film's properties, including water diffusion coefficient, mechanical properties, plasticizer loss, swelling behavior, and contact angle, were measured for uncured or cured aqueous dispersion-based or organic solvent-based films. The results indicated that curing decreased water diffusivities in films and increased film's tensile strength. Curing resulted in plasticizer loss from SR30D films but not from MAE100P films due to strong interaction between plasticizer and MAE100P. The surface of organic solvent-based films was more hydrophobic than that of aqueous dispersion-based films. The contact angle of organic solvent-based films was increased after curing possibly because curing decreased roughness of the film surface. Organic solvent-based SR30D films had better mechanical properties than the corresponding aqueous dispersion-based films because of higher degree of polymer-polymer entanglement in the organic solvent-based films. However, contradictory phenomena were observed in MAE100P films possibly due to a "core-shell" structure reserved in the aqueous dispersion-based MAE100P films. In summary, casting methods and curing have significant impact on the film properties due to different film structures, coalescence, or film relaxation, and other concurrent effects including evaporation of residue solvent and plasticizers.

When drugs plasticize film coatings: Unusual formulation effects observed with metoprolol and Eudragit RS

Metoprolol tartrate and metoprolol free base loaded pellet starter cores were coated with Eudragit RS, plasticized with 25% triethyl citrate (TEC). The initial drug loading and coating level were varied from 10 to 40 and 0 to 20%, respectively. Drug release was measured in 0.1 N HCl and phosphate buffer pH 7.4. The water uptake and swelling kinetics, mechanical properties and TEC leaching of/from coated pellets and/or thin, free films of identical composition as the film coatings were monitored. The following unusual tendencies were observed: (i) the relative drug release rate from coated pellets increased with increasing initial drug content, and (ii) drug release from pellets was much faster for metoprolol free base compared to metoprolol tartrate, despite its much lower solubility (factor >70). These phenomena could be explained by plasticizing effects of the drug for the polymeric film coatings. In particular: 1) Metoprolol free base is a much more potent plasticizer for Eudragit RS than the tartrate, leading to higher film permeability and overcompensating the pronounced differences in drug solubility. Also, Raman imaging revealed that substantial amounts of the free base migrated into the film coatings, whereas this was not the case for the tartrate. 2) The plasticizing effects of the drug for the film coating overcompensated potential increasing limited solubility effects when increasing the initial drug loading from 10 to 40%. In summary, this study clearly demonstrates how important the plasticization of polymeric controlled release film coatings by drugs can be, leading to unexpected formulation effects.

Retrospective Quality by Design (rQbD) applied to the optimization of orodispersible films

The study demonstrates the application of QbD based on historical data for a product at a later development stage - retrospective QbD (rQbD). More specifically, it is investigated the root-cause for the observed slower drug release in Orodispersible Films (ODFs) during storage. Risk assessment tools were used to identify parameters affecting ODFs critical quality attributes, namely percent drug release and residual water content. The parameters room temperature, room relative humidity, drying temperature and mixing equipment were used in the statistical modeling of the available data. The estimated models were then used to define the feasible working region. Statistical modeling indicates that initial residual water content of the ODFs is mainly affected by 2nd order interactions of room temperature, room relative humidity and drying temperature, while the stability of drug release profile is mostly influenced by room temperature and an interaction between room relative humidity and drying temperature. Depending on the drying temperature employed the effect of room temperature and room relative humidity change significantly. This work shows that it is possible to apply rQbD to achieve a greater understanding of the manufacturing process of ODFs and to define a proper design space.

Synthesis, characterisation and phase transition behaviour of temperature-responsive physically crosslinked poly (N-vinylcaprolactam) based polymers for biomedical applications

Poly (N-vinylcaprolactam) (PNVCL) is a polymer which offers superior characteristics for various potential medical device applications. In particular it offers unique thermoresponsive capabilities, which fulfils the material technology constraints required in targeted drug delivery applications. PNVCL phase transitions can be tailored in order to suit the requirements of current and next generation devices, by modifying the contents with regard to the material composition and aqueous polymer concentration. In this study, physically crosslinked Poly (N-vinylcaprolactam)-Vinyl acetate (PNVCL-VAc) copolymers were prepared by photopolymerisation. The structure of the polymers was established by Fourier transform infrared spectroscopy, nuclear magnetic resonance and gel permeation chromatography. The polymers were further characterised using differential scanning calorimetry and swelling studies. Determination of the LCST of the polymers in aqueous solution was achieved by employing four techniques; cloud point, UV-spectrometry, differential scanning calorimetry and rheometry. Sol-gel transition was established using tube inversion method and rheological analysis. This study was conducted to determine the characteristics of PNVCL with the addition of VAc, and to establish the effects on the phase transition. The PNVCL based polymers exhibited a decrease in the LCST as the composition of VAc increased. Sol-gel transition could be controlled by altering the monomeric feed ratio and polymer concentration in aqueous milieu. Importantly all copolymers (10wt% in solution) underwent gelation between 33.6 and 35.9°C, and based on this and the other materials properties recorded in this study, these novel copolymers have potential for use as injectable in situ forming drug delivery systems for targeted drug delivery.

Curing mechanism of flexible aqueous polymeric coatings

The objective of this study was to explain curing phenomena for pellets coated with a flexible polymeric coating based on poly(vinyl acetate) (Kollicoat® SR 30D) with regard to the effect of starter cores, thickness of drug layer, adhesion of coating to drug-layered-cores as well as coating properties. In addition, appropriate approaches to eliminate the curing effect were identified. Sugar or MCC cores were layered with the model drugs carbamazepine, theophylline, propranolol HCl, tramadol HCl and metoprolol HCl using HPMC (5 or 25% w/w, based on drug) as a binder. Drug-layered pellets were coated with Kollicoat® SR 30D in a fluidized bed coater using TEC (10% w/w) as plasticizer and talc (35-100% w/w) as anti-tacking agent. Drug release, pellet properties (morphology, water uptake-weight loss and osmolality) and adhesion of the coating to the drug layer were investigated as a function of curing at 60°C or 60°C/75% RH for 24h. The film formation of the aqueous dispersion of Kollicoat® SR 30D was complete, and therefore, a strong curing effect (decrease in drug release) at elevated temperature and humidity (60°C/75% RH) could not be explained by the well-known hydroplasticization and the further gradual coalescence of the colloidal polymer particles. According to the provided mechanistic explanation, the observed curing effect was associated with (1) high flexibility of coating, (2) adhesion between coating and drug layer, (3) water retaining properties of the drug layer, and (4) osmotically active cores. Unwanted curing effects could be minimized/eliminated by the addition of talc or/and pore-forming water soluble polymers in the coating, increasing binder amount or applying an intermediate coating, by increasing the thickness of drug layer or using non-osmotic cores. A new insight into curing phenomena mainly associated with the adhesion between drug layer and coating was provided. Appropriate approaches to avoid unwanted curing effect were identified.

Importance of air bubbles in the core of coated pellets: Synchrotron X-ray microtomography allows for new insights

High-resolution X-ray microtomography was used to get deeper insight into the underlying mass transport mechanisms controlling drug release from coated pellets. Sugar starter cores were layered with propranolol HCl and subsequently coated with Kollicoat SR, plasticized with 10% TEC. Importantly, synchrotron X-ray computed microtomography (SR-μCT) allowed direct, non-invasive monitoring of crack formation in the film coatings upon exposure to the release medium. Propranolol HCl, as well as very small sugar particles from the pellets' core, were expulsed through these cracks into the surrounding bulk fluid. Interestingly, SR-μCT also revealed the existence of numerous tiny, air-filled pores (varying in size and shape) in the pellet cores before exposure to the release medium. Upon water penetration into the system, the contents of the pellet cores became semi-solid/liquid. Consequently, the air-pockets became mobile and fused together. They steadily increased in size (and decreased in number). Importantly, "big" air bubbles were often located in close vicinity of a crack within the film coating. Thus, they play a potentially crucial role for the control of drug release from coated pellets.

Tubular Scaffold with Shape Recovery Effect for Cell Guide Applications

Tubular scaffolds with aligned polylactic acid (PLA) fibres were fabricated for cell guide applications by immersing rolled PLA fibre mats into a polyvinyl acetate (PVAc) solution to bind the mats. The PVAc solution was also mixed with up to 30 wt % β-tricalcium phosphate (β-TCP) content. Cross-sectional images of the scaffold materials obtained via scanning electron microscopy (SEM) revealed the aligned fibre morphology along with a significant number of voids in between the bundles of fibres. The addition of β-TCP into the scaffolds played an important role in increasing the void content from 17.1% to 25.3% for the 30 wt % β-TCP loading, which was measured via micro-CT (µCT) analysis. Furthermore, µCT analyses revealed the distribution of aggregated β-TCP particles in between the various PLA fibre layers of the scaffold. The compressive modulus properties of the scaffolds increased from 66 MPa to 83 MPa and the compressive strength properties decreased from 67 MPa to 41 MPa for the 30 wt % β-TCP content scaffold. The scaffolds produced were observed to change into a soft and flexible form which demonstrated shape recovery properties after immersion in phosphate buffered saline (PBS) media at 37 °C for 24 h. The cytocompatibility studies (using MG-63 human osteosarcoma cell line) revealed preferential cell proliferation along the longitudinal direction of the fibres as compared to the control tissue culture plastic. The manufacturing process highlighted above reveals a simple process for inducing controlled cell alignment and varying porosity features within tubular scaffolds for potential tissue engineering applications.