Novel modulation of drug delivery using binary zinc-alginate-pectinate polyspheres for zero-order kinetics over several days: experimental design strategy to elucidate the crosslinking mechanism

Evaluation of Extended-Release of Piroxicam Loaded Pectin-Zein Hydrogel Microspheres: In Vitro, Ex Vivo, and In Vivo Studies

OBJECTIVE

This study evaluated drug delivery systems based on Pectin (P) and Zein (Z) hydrogel microspheres. Piroxicam (Px) loaded P/Z hydrogel microspheres (P/Z HM) were developed, and their extended-release pharmacokinetic properties were evaluated.

METHODS

Experiments were executed under three different conditions: in vitro, ex vivo, and in vivo. Then, the in vitro-in vivo correlations (IVIVC) and ex vivo - in vivo correlations (EVIVC) were examined.

RESULTS

Analysis of drug release mechanisms were evaluated by fitting the in vitro data into the Ritger-Peppas equation, showing the contribution of both polymers' relaxation and drug diffusion from the hydrogel microspheres. The fraction absorbed in vivo was determined by the deconvolution of plasma concentration data using the Loo-Riegelman method. After oral single-dose administration of the two formulations, their basic independent model parameters were calculated.

CONCLUSION

P/Z HM had different drug release behaviors in in vitro and in vivo conditions. However, the ex vivo and in vivo characteristics were similar (R² = 0.99). This seemed reasonable to use the ex vivo method to predict the in vivo drug absorption behavior during the polymeric drug delivery system developmental studies. The P/Z HM formulation maintained the drug dose at the colon site for a long duration and could be applied for delivery of active pharmaceutical and food ingredients to the colon site.

Metal alginates for polyphenol delivery systems: Studies on crosslinking ions and easy-to-use patches for release of protective flavonoids in skin

Incorporation of bioactive natural compounds like polyphenols is an attractive approach for enhanced functionalities of biomaterials. In particular flavonoids have important pharmacological activities, and controlled release systems may be instrumental to realize the full potential of these phytochemicals. Alginate presents interesting attributes for dermal and other biomaterial applications, and studies were carried here to support the development of polyphenol-loaded alginate systems. Studies of capillary viscosity indicated that ionic medium is an effective strategy to modulate the polyelectrolyte effect and viscosity properties of alginates. On gelation, considerable differences were observed between alginate gels produced with Ca2+, Ba2+, Cu2+, Fe2+, Fe3+ and Zn2+ as crosslinkers, especially concerning shrinkage and morphological regularity. Stability assays with different polyphenols in the presence of alginate-gelling cations pointed to the choice of calcium, barium and zinc as safer crosslinkers. Alginate-based films loaded with epicatechin were prepared and the kinetics of release of the flavonoid investigated. The results with calcium, barium and zinc alginate matrices indicated that the release dynamics is dependent on film thicknesses, but also on the crosslinking metal used. On these grounds, an alginate-based system of convenient use was devised, so that flavonoids can be easily loaded at simple point-of-care conditions before dermal application. This epicatechin-loaded patch was tested on an ex-vivo skin model and demonstrated capacity to deliver therapeutically relevant concentrations on skin surface. Moreover, the flavonoid released was not modified and retained full antioxidant bioactivity. The alginate-based system proposed offers a multifunctional approach for flavonoid controllable delivery and protection of skin injured or under risk.

Biomaterials for the Delivery of Growth Factors and Other Therapeutic Agents in Tissue Engineering Approaches to Bone Regeneration

Bone fracture followed by delayed or non-union typically requires bone graft intervention. Autologous bone grafts remain the clinical "gold standard". Recently, synthetic bone grafts such as Medtronic's Infuse Bone Graft have opened the possibility to pharmacological and tissue engineering strategies to bone repair following fracture. This clinically-available strategy uses an absorbable collagen sponge as a carrier material for recombinant human bone morphogenetic protein 2 (rhBMP-2) and a similar strategy has been employed by Stryker with BMP-7, also known as osteogenic protein-1 (OP-1). A key advantage to this approach is its "off-the-shelf" nature, but there are clear drawbacks to these products such as edema, inflammation, and ectopic bone growth. While there are clinical challenges associated with a lack of controlled release of rhBMP-2 and OP-1, these are among the first clinical examples to wed understanding of biological principles with biochemical production of proteins and pharmacological principles to promote tissue regeneration (known as regenerative pharmacology). After considering the clinical challenges with such synthetic bone grafts, this review considers the various biomaterial carriers under investigation to promote bone regeneration. This is followed by a survey of the literature where various pharmacological approaches and molecular targets are considered as future strategies to promote more rapid and mature bone regeneration. From the review, it should be clear that pharmacological understanding is a key aspect to developing these strategies.

Development of Functional or Medical Foods for Oral Administration of Insulin for Diabetes Treatment: Gastroprotective Edible Microgels

Insulin and an antacid [Mg(OH)₂] were co-encapsulated inside calcium alginate microgels (diameter = 280 μm) using a vibrating nozzle injector. Confocal microscopy indicated that insulin was successfully encapsulated inside the microgels and remained inside them after they were exposed to simulated gastric conditions. Localized fluorescence intensity measurements indicated that the internal pH of the antacid-loaded microgels was around pH 7.4 after incubation in acidic gastric fluids but below the limit of detection (pH < 4) in the antacid-free microgels. After incubation in small intestine conditions, around 30% of the insulin was released from the antacid-loaded microgels over a 2 h period. Encapsulation of insulin within the antacid-loaded microgels increased its biological activity after exposure to simulated gastric conditions. In particular, the encapsulated insulin significantly increased Akt phosphorylation at both Thr308 and Ser473 in L6 myotubes when compared to free insulin.

Crosslinker effects on functional properties of alginate/N-succinylchitosan based hydrogels

In this paper, physico-chemical, mechanical and antimicrobial properties of hydrogels based on alginate/N-succinylchitosan blends crosslinked by calcium or zinc ions containing cellulose microfibers were investigated and discussed. With respect to plain alginate hydrogels, the addition of N-succinylchitosan significantly improved properties such as swelling degree and stability in saline solution. The water vapour transmission rate confirmed that all the hydrogels were able to assure a moist wound environment. Morphological analysis showed a good embedding of fibres within the zinc crosslinked hydrogels. In addition, zinc-crosslinked hydrogels evidenced antimicrobial activity against two common skin pathogenic bacteria, Staphylococcus aureus and Escherichia coli. Cytotoxicity assays proved that the amount of zinc released is slightly over the toxic level. Overall, the characteristics of the zinc-crosslinked hydrogels showed their potential interest as materials for wound dressing.

Biomaterial delivery of morphogens to mimic the natural healing cascade in bone

Complications in treatment of large bone defects using bone grafting still remain. Our understanding of the endogenous bone regeneration cascade has inspired the exploration of a wide variety of growth factors (GFs) in an effort to mimic the natural signaling that controls bone healing. Biomaterial-based delivery of single exogenous GFs has shown therapeutic efficacy, and this likely relates to its ability to recruit and promote replication of cells involved in tissue development and the healing process. However, as the natural bone healing cascade involves the action of multiple factors, each acting in a specific spatiotemporal pattern, strategies aiming to mimic the critical aspects of this process will likely benefit from the usage of multiple therapeutic agents. This article reviews the current status of approaches to deliver single GFs, as well as ongoing efforts to develop sophisticated delivery platforms to deliver multiple lineage-directing morphogens (multiple GFs) during bone healing.

Localized delivery of growth factors for periodontal tissue regeneration: role, strategies, and perspectives

Difficulties associated with achieving predictable periodontal regeneration, means that novel techniques need to be developed in order to regenerate the extensive soft and hard tissue destruction that results from periodontitis. Localized delivery of growth factors to the periodontium is an emerging and versatile therapeutic approach, with the potential to become a powerful tool in future regenerative periodontal therapy. Optimized delivery regimes and well-defined release kinetics appear to be logical prerequisites for safe and efficacious clinical application of growth factors and to avoid unwanted side effects and toxicity. While adequate concentrations of growth factor(s) need to be appropriately localized, delivery vehicles are also expected to possess properties such as protein protection, precision in controlled release, biocompatibility and biodegradability, self-regulated therapeutic activity, potential for multiple delivery, and good cell/tissue penetration. Here, current knowledge, recent advances, and future possibilities of growth factor delivery strategies are outlined for periodontal regeneration. First, the role of those growth factors that have been implicated in the periodontal healing/regeneration process, general requirements for their delivery, and the different material types available are described. A detailed discussion follows of current strategies for the selection of devices for localized growth factor delivery, with particular emphasis placed upon their advantages and disadvantages and future prospects for ongoing studies in reconstructing the tooth supporting apparatus.

Controlled delivery of VEGF via modulation of alginate microparticle ionic crosslinking

Clinical application of therapeutic angiogenesis is hampered by a lack of viable systems that demonstrate controlled, sustained release of vascular endothelial growth factor (VEGF). Alginate has emerged as a popular material for VEGF delivery; however most alginate-based systems offer limited means to control the rate of VEGF release beyond reducing the VEGF:alginate ratio to suboptimal efficiency. This study describes methods to control the release of VEGF from small (<10 microm mean diameter) alginate microparticles via the use of different ionic crosslinkers. Crosslinking with Zn(2+) versus Ca(2+) reduced VEGF diffusional release and the combination of discrete populations of either Zn(2+)- or Ca(2+)-crosslinked particles allowed for control over the sustained release profiles for VEGF. The particle preparations were non-toxic and VEGF was bioactive after release. These results demonstrate that ionic modulation of alginate crosslinking is a viable strategy for controlling release of VEGF while retaining the high protein:polymer ratio that makes alginate an attractive carrier for delivery of protein therapeutics.

Indentation test for free-flowable powder excipients

Indentation of a sphere into nonconsolidated powder excipients is a suitable complementary method for the evaluation of flow properties of the free-flowable noncohesive powders. To use the standard penetrometry method to indentation of nonconsolidated powder layer by a glass sphere of 16 mm in diameter, the suitable geometry of the measurement container is required to prevent undesirable moving in a direction opposite to that in which the indenting sphere moves. Thus, the powder indentation by a sphere seems to be similar to indentation by the Brinell hardness tester. In this work, the depth of indentation was measured for five pharmaceutical powder excipients: sodium chloride, sodium citrate, potassium citrate, sorbitol, and boric acid with the three size fractions in the range of 0.315-0.630 mm. To express powder flowability, the uniform mass and/or volume flow rate from the 10-mm cylindrical outlet of the cylindrical testing hopper was used. The relationships between the powder flow rate and its bulk density and/or the different characteristics of indentation were modeled by using linear regression. Out of the indentation characteristics, the mass of indentation calculated as the multiple of the volume of indentation and the powder bulk density could be recommended to estimate the powder mass flow rate due to the linear regression with the coefficient of determination equal to 0.973 and the accuracy of 4.3%. In conclusion, the indentation by the sphere could be recommended as a quick simple method for the comparison of flow properties of the nonconsolidated, noncohesive powder excipients.

Ex vivo mucoadhesion of different zinc-pectinate hydrogel beads

The objective of this study was to investigate the mucoadhesive properties of pre-swelled hydrogel beads made of six types of pectin from three manufacturers. The types of pectin differed mainly in the degree of methoxylation and degree of amidation. Zinc ions were used as cross-linking agent. The mucoadhesive properties were tested on an inverted fresh porcine small intestine attached to a rotating cylinder. Beads made of pectin with a high degree of methoxylation (70%) showed superior mucoadhesive results compared to the other formulations, which could be correlated to the lower amount of zinc in this formulation, subsequently leading to a lower amount of cross-linking and higher mobility of the polymer chains of these beads. This study therefore also indicated the importance of doing mucoadhesive measurements on relevant formulations, and not basing the understanding solely on investigating polymer solutions. Samples from different manufacturers produced the same results.

Design and development of a novel controlled release PLGA alginate-pectinate polyspheric drug delivery system

A 23 full factorial design was employed to evaluate and optimize the drug entrapment efficiency and in vitro drug release from PLGA microparticles encapsulated in a complex crosslinked alginate-pectinate matrix (polysphere). The independent formulation variables included the volume of internal and external phases, and concentration of PLGA. Surface morphology and internal structure of PLGA microparticles and polyspheres were examined by scanning electron microscopy which revealed spherical PLGA microparticles with highly porous surfaces that accounted for the rapid burst effect of this system. Texture analysis was used to profile the matrix resilience, tolerance, and energy absorbed. In vitro drug release was assessed in buffer media on PLGA microparticles and polyspheres. Polyspheres exhibited ideal zero-order release while PLGA microparticles had a burst effect followed by lag phase. Kinetic modeling of in vitro drug release data indicated that formulations were not highly dependent on polymeric erosion as a mechanism for drug release but rather diffusion. A close correlation existed between the matrix tolerance and energy absorbed. Formulations with decreased tolerance absorbed less energy, thus led to rapid surface erosion, lower matrix integrity and hence a burst effect. The converse was true for an increased matrix tolerance, which led to zero-order release supported by superior matrix integrity and a significantly reduced burst effect. The rat subcutaneous model validated in vitro release data and demonstrated that the polyspheres provided flexible yet superior rate-modulated drug delivery.

Insulin encapsulation in reinforced alginate microspheres prepared by internal gelation

Insulin-loaded alginate microspheres prepared by emulsification/internal gelation were reinforced by blending with polyanionic additive polymers and/or chitosan-coating in order to increase the protection of insulin at simulated gastric pH and obtain a sustained release at simulated intestinal pH. Polyanionic additive polymers blended with alginate were cellulose acetate phtalate (CAP), Eudragit L100 (EL100), sodium carboxymethylcellulose (CMC), polyphosphate (PP), dextran sulfate (DS) and cellulose sulfate (CS). Chitosan-coating was applied by using a one-stage procedure. The influence of additive polymers and chitosan-coating on the size distribution of microspheres, encapsulation efficiency and release profile of insulin in simulated gastrointestinal pH conditions was studied. The mean diameter of blended microspheres ranged from 65 to 106 microm and encapsulation efficiency of insulin varied from 14 to 100%, reaching a maximum value when CS and DS were incorporated in the alginate matrix. Insulin release, at pH 1.2, was almost prevented by the incorporation of PP, DS and CS. When uncoated microspheres were transferred to pH 6.8, a fast dissolution occurred, independently of the additive polymer blended with alginate, and insulin was completely released. Increasing the additive polymer concentration in the alginate matrix and/or chitosan-coating the blended alginate microspheres did not promote a sustained release of insulin from microspheres at pH 6.8.