Associative and segregative phase separations of poly(N-tert-butylacrylamide)/poly(acrylic acid) mixtures. Effect of solvent

Superhydrophilic and topography-regulatable surface grafting on PEEK to improve cellular affinity

Polyetheretherketone (PEEK) has been widely used in the preparation of orthopedic implants due to its biological inertness and similar mechanical modulus to natural bone. However, the affinity between biological tissue (bone and soft tissue) and PEEK surface is weak, leading to low osseointegration and an increased risk of inflammation. The situation could be improved by modifying PEEK surface. Surfaces with good hydrophilicity and proper microtopography would promote cellular adhesion and proliferation. This work presented a two-step surface modification method to achieve the effect. Polyacrylic acid (PAA) chains were grafted on PEEK surface by UV irradiation. Then, ethylenediamine (EDA) was added to introduce amino groups and promote the cross-linking of PAA chains. Furthermore, a mathematical model was built to describe and regulate the surface topography growth process semi-quantitatively. The model fits experimental data quite well (adjusted R² = 0.779). Results showed that the modified PEEK surface obtained superhydrophilicity. It significantly improved the adhesion and proliferation of BMSCs and MFBs by activating the FAK pathway and Rho family GTPase. The cellular affinity performed better when the surface topography was in network structure with holes in about 25 μm depth and 20-50 μm diameter. Good hydrophilicity seems necessary for the FAK pathway activation, but simply improving surface hydrophilicity might not be enough for cellular affinity improvement. Surface topography at micron scale should be a more important cue. This simple surface modification method could be contributed to further study of cell-microtopography interaction and have potential applications in clinical PEEK orthopedic implants.

Bioaccessibility and antioxidant activity of phenolic acids, flavonoids, and anthocyanins of encapsulated Thai rice bran extracts during in vitro gastrointestinal digestion

Encapsulation technique was applied to improve the stability of bioactive compounds in bran extracts from Thai rice cultivars (Khao Dawk Mali 105, Kiaw Ngu, Hom Nil, and Leum Pua), using three carriers including gelatin, gum Arabic, and the mixture of gelatin and gum Arabic. The microcapsules obtained using gelatin provided a higher production yield of 76.08, 85.63, 85.63 and 85.59%, respectively. A greater encapsulation efficiency was also observed in the extracts encapsulated with gelatin (93.45, 95.91, 91.19 and 95.09%, respectively). After simulated gastric and intestinal digestion, the microcapsules formed by using gelatin exhibited the higher release of bioactive compounds and antioxidant activity than unencapsulated extracts. However, the extracts encapsulated using gelatin and gum Arabic complex yielded the lowest release of bioactive compounds and their antioxidant activity after simulated digestion. The overall results showed that gelatin was an appropriate carrier that could protect bioactive compounds from the digestion conditions.

Interpolymer complexation between copovidone and carbopol and its effect on drug release from matrix tablets

The interaction between copovidone and Carbopol 907 is pH dependent. When the pH of an aqueous solution fell below pH 4.5, a water-insoluble complex began to form and precipitate. This complex resulted from a hydrogen-bond-induced interaction between the carboxylic groups in Carbopol 907 and the carbonyl groups of N-vinylpyrrolidone repeat units in copovidone. Consisting of these two polymers at an approximate 1:1 weight ratio, the complex was an amorphous material with a glass transition temperature of 157 °C. The interpolymer complexation in situ was applied to modify drug release properties of Carbopol 907-based theophylline matrix tablets. The effect of copovidone on drug release was dependent on the pH of the dissolution medium. In a 0.1 N hydrochloride acid solution at pH 1.2 and 50 mM acetate buffer at pH 4.0, an insoluble tablet matrix was formed as a result of the in situ interpolymer complexation, and theophylline was released therefore via Fickian diffusion. In a 50 mM phosphate buffer at pH 6.8, drug release from the matrix tablets was still impacted by the in situ interpolymer complexation because of the low-pH microenvironment induced by Carbopol 907. As a result, drug release rate of the matrix tablet containing both polymers at pH 6.8 was slower than that of the matrix tablets containing individual polymers. We observed similar drug release rates at both pH 1.2 and pH 6.8 between tablets containing the physical blend of these two polymers and tablets containing preformed interpolymer complexes.