The effect of particle size on the sublimation behavior of butylhydroxytoluene as antioxidant in tablets during storage and coating.

The effect of particle size on the sublimation behavior of butylhydroxytoluene (BHT) was investigated when BHT was included as antioxidant in tablets. Sublimation of pure BHT was found to be independent of its particle size, with pore formation on the surface of all tablets after storage at room temperature and above. Moreover, a higher residual BHT content after storage was detected in tablets containing a larger size fraction. X-ray µCT scans revealed the formation of peripherally larger pores at higher BHT particle sizes, implying a slower sublimation rate in the tablet core. A stability study indicated an increase in the extent of BHT sublimation at higher temperature and longer exposure time for all size fractions. The influence of BHT particle size was more pronounced when the tablets were stored at higher temperature, but the effect receded with longer exposure time. Similar trends were seen in film-coated tablets. Due to the short exposure time to elevated temperatures, a gradient in pore size was also observed at smaller particle sizes, with peripheral pores being larger in uncoated tablets. Superficial pores disappeared when a film coating was deposited onto the tablets. After storage of the film-coated tablets, less BHT had sublimated compared to the uncoated tablet. The coating layer did not prevent sublimation, but the process was slowed down.

Development of a new age-appropriate, chewable tablet of mebendazole 500 mg for preventive chemotherapy of soil-transmitted helminth infections in pre-school and school-age children.

The aim of this study was to develop an age-appropriate tablet of mebendazole 500 mg to be used in large donation programs by the World Health Organization (WHO) for preventive chemotherapy of soil-transmitted helminth (STH) infections in pre-school and school-age children living in tropical and subtropical endemic areas. To that end, a new oral tablet formulation was developed that can be either chewed or given to young (≥1 year old) children by spoon after rapid disintegration to a soft mass with the addition of a small amount of water directly on the spoon. Although the tablet was manufactured using conventional fluid bed granulation, screening, blending, and compression processes, one of the main challenges was to combine properties of a chewable, dispersible, and regular (solid) immediate release tablet to meet the predefined requirements. The tablet disintegration time was below 120 s, allowing for administration by the "spoon method". The tablet hardness was higher (160-220 N) than normally applicable for chewable tablets, permitting shipment along a lengthy supply chain in a primary 200-tablet count bottle packaging. In addition, the resulting tablets are stable for 48 months in all climatic zones (I-IV). In this article, several aspects of the development of this unique tablet are described, including formulation, process development, stability, clinical acceptability testing, and regulatory filing.

Protein macromonomers containing reduction-sensitive linkers for covalent immobilization and glutathione triggered release from dextran hydrogels.

We report an efficient strategy to conjugate methacrylamide moieties to the lysine units of lysozyme for co-polymerization and subsequent triggered release from hydrogels. Two novel linker molecules, containing an ester bond and/or a disulfide bond for temporary immobilization, were synthesized and conjugated to lysozyme. Lysozyme was successfully modified with on average 2.5 linker molecules per protein molecule, as evidenced by MALDI-TOF and by titration of the free amine groups, while spectral analysis verified the preservation of the protein structure. Next, methacrylated dextran (Dex-MA) was polymerized in presence of native or modified lysozyme to yield hydrogels. The release of native and modified lysozyme from Dex-MA hydrogels was studied in acetate buffer (pH 5, in absence of any trigger) and only a minor fraction (~15%) of the modified lysozyme was released, whereas ~74% of the native lysozyme was released. This indicates successful immobilization of the majority of the modified lysozyme in the hydrogel network. Upon hydrolysis of the ester bonds or incubation with glutathione to reduce disulfide bonds of the linker molecules that conjugate the lysozyme to the gel network, the modified lysozyme was mobilized and released from the hydrogel to the same extent as native lysozyme. These data were confirmed by fluorescence recovery after photobleaching experiments. This approach appeared to be highly interesting for temporary immobilization and subsequent glutathione triggered intracellular delivery of proteins from hydrogels.

Challenges for the effective molecular imprinting of proteins.

Molecular imprinting is a technique that is used to create artificial receptors by the formation of a polymer network around a template molecule. This technique has proven to be particularly effective for molecules with low molecular weight (<1500 Da), and during the past five years the number of research articles on the imprinting of larger (bio)templates is increasing considerably. However, expanding the methodology toward imprinted materials for selective recognition of proteins, DNA, viruses and bacteria appears to be extremely challenging. This paper presents a critical analysis of data presented by several authors and our own experiments, showing that the molecular imprinting of proteins still faces some fundamental challenges. The main topics of concern are proper monomer selection, washing method/template removal, quantification of the rebinding and reproducibility. Use of charged monomers can lead to strong electrostatic interactions between monomers and template but also to undesired high aspecific binding. Up till now, it has not been convincingly shown that electrostatic interactions lead to better imprinting results. The combination of a detergent (SDS) and AcOH, commonly used for template removal, can lead to experimental artifacts, and should ideally be avoided. In many cases template rebinding is unreliably quantified, results are not evaluated critically and lack statistical analysis. Therefore, it can be argued that presently, in numerous publications the scientific evidence of molecular imprinting of proteins is not convincing.

Anionic and cationic dextran hydrogels for post-loading and release of proteins.

In this study, post-loading of proteins in and release from chemically crosslinked dextran hydrogels exploiting reversible electrostatic interactions was investigated. Methacrylated dextran (Dex-MA) was co-polymerized with methacrylic acid (MA) or dimethylaminoethyl methacrylate (DMAEMA) to form negatively and positively charged hydrogels, respectively. Incubation of negatively charged hydrogels in a low ionic strength (10 mM HEPES, pH 7.4) solution of cytochrome C (isoelectric point (pI) 10.2) led to quantitative absorption of the protein in the hydrogel. BSA (pI 4.8) and myoglobin (pI 7.2) were post-loaded into positively charged gels at neutral pH and negatively charged gels at pH 5, respectively. Loading efficiency and protein distribution in the gels were dependent on network charge (maximum loading efficiency at 100-150 µmol charged monomer/g gel) and crosslink density (higher and more homogenous loading at lower crosslink density) and on the ionic strength during loading (lower but more homogenous loading at higher ionic strength). Diffusion controlled release of the loaded protein was triggered by incubation of the hydrogel in HEPES buffered saline (HBS) pH 7.4. The amount of released cytochrome C in HBS varied from 94% to 70% from gels containing 60 and 150 MA/g, respectively. Importantly, quantitative release was obtained in 1 M NaCl, indicating that post-loading led to neither the formation of insoluble protein aggregates nor irreversible immobilization of the protein in the matrix. ESI-MS analysis of the released cytochrome C revealed that post-loading did not result in oxidation of the protein, as opposed to loading during preparation of the gels. In conclusion, this paper shows that post-loading of proteins in dextran hydrogels and release exploiting reversible charge interactions can be applied for efficient loading of proteins that are negative, positive or neutral at physiological pH. Importantly, our data demonstrate that using this loading method no chemical modification to the protein occurred.

Conjugation of methacrylamide groups to a model protein via a reducible linker for immobilization and subsequent triggered release from hydrogels.

An efficient strategy is reported to introduce methacrylamide groups on the lysine residues of a model protein (lysozyme) for immobilization and triggered release from a hydrogel network. A novel spacer unit was designed, containing a disulfide bond, such that the release of the protein can be triggered by reduction. The modified proteins were characterized by MALDI-TOF MS, titration of free NH(2) residues and spectral analysis. The modification reaction is well controlled, and the number of introduced functions can be tailored by changing the reaction conditions. Gel electrophoresis experiments showed that the methacrylamide modified protein can be immobilized in a polyacrylamide hydrogel and subsequently released by reduction of the spacer by which the protein was grafted to the polymeric network.