Edith Mathiowitz

Polyanhydride microspheres as drug carriers. I: Hot-melt microencapsulation

Polyanhydride microspheres containing dyes (acid-orange),p-nitroaniline) or drugs (insulin) were prepared and evaluated for the purpose of creating a bioerodible system with the capability of producing controlled release for molecules of any size, including macromolecules. A “hot melt” microencapsulation method was employed. The model polymer used was poly[bis(p-itcarboxy phenoxy)propane anhydride], copolymerized with sebacic acid (PCPP-SA). The microspheres degrade heterogeneously when low levels of a hydrophilic drug are used; a well-defined degrading zone appears during the degradation process. Insulin-incorporated microspheres implanted into diabetic rats resulted in normoglycemia for a period of 3 to 4 days.

Nanosphere based oral insulin delivery

Zinc insulin is successfully encapsulated in various polyester and polyanhydride nanosphere formulations using Phase Inversion Nanoencapsulation (PIN). The encapsulated insulin maintains its biological activity and is released from the nanospheres over a span of approximately 6 h. A specific formulation, 1.6% zinc insulin in poly(lactide-co-glycolide) (PLGA) with fumaric anhydride oligimer and iron oxide additives has been shown to be active orally. This formulation is shown to have 11.4% of the efficacy of intraperitoneally delivered zinc insulin and is able to control plasma glucose levels when faced with a simultaneously administered glucose challenge. A number of properties of this formulation, including size, release kinetics, bioadhesiveness and ability to traverse the gastrointestinal epithelium, are likely to contribute to its oral efficacy.

Oral insulin delivery1

An oral form of insulin has been the elusive goal for many investigators since the proteins initial discovery by Banting and Best in 1922. This paper will attempt to answer why this is the case by describing the substantial barriers to the development of oral insulin formulations. Following this description, specific strategies to overcome the barriers to oral insulin administration will be discussed. Most notably, the use of permeation enhancers, protease inhibitors, enteric coatings and polymer microsphere formulations will be covered, including commentary on which methods hold more promise towards the successful development of oral insulin.

Sequential release of bioactive IGF-I and TGF-β1 from PLGA microsphere-based scaffolds

Growth factors have become an important component for tissue engineering and regenerative medicine. Insulin-like growth factor-I (IGF-I) and transforming growth factor-beta1 (TGF-beta 1) in particular have great significance in cartilage tissue engineering. Here, we describe sequential release of IGF-I and TGF-beta 1 from modular designed poly(l,d-lactic-co-glycolic acid) (PLGA) scaffolds. Growth factors were encapsulated in PLGA microspheres using spontaneous emulsion, and in vitro release kinetics was characterized by ELISA. Incorporating BSA in the IGF-I formulations decreased the initial burst from 80% to 20%, while using uncapped PLGA rather than capped decreased the initial burst of TGF-beta 1 from 60% to 0% upon hydration. The bioactivity of released IGF-I and TGF-beta 1 was determined using MCF-7 proliferation assay and HT-2 inhibition assay, respectively. Both growth factors were released for up to 70 days in bioactive form. Scaffolds were fabricated by fusing bioactive IGF-I and TGF-beta 1 microspheres with dichloromethane vapor. Three scaffolds with tailored release kinetics were fabricated: IGF-I and TGF-beta 1 released continuously, TGF-beta 1 with IGF-I released sequentially after 10 days, and IGF-I with TGF-beta 1 released sequentially after 7 days. Scaffold swelling and degradation were characterized, indicating a peak swelling ratio of 4 after 7 days of incubation and showing 50% mass loss after 28 days, both consistent with scaffold release kinetics. The ability of these scaffolds to release IGF-I and TGF-beta 1 sequentially makes them very useful for cartilage tissue engineering applications.

Polyanhydrides for controlled release of bioactive agents

This report is a review of the development of a drug delivery system based on biorodible polyanhydrides. With the water labile anhydride linkage, a wide range of matrix degradation and drug release rates can be obtained from these drug-carriers. In addition to monolithic formulations, the feasibility of an injectable system by microencapsulation is demonstrated. The possibility of enhancing the release externally by an ultrasonic source has also been explored. The polymers tested showed good tissue biocompatibility and their breakdown products showed no adverse toxicological effects. Preliminary in vivo results confirmed the efficacy of these devices.

Effect of protein molecular weight on release from micron-sized PLGA microspheres

This study investigates the effect of protein molecular weight on release kinetics from polymeric microspheres (1-3 microm). Proteins were encapsulated at high and low loadings in poly(lactic-co-glycolic acid) (PLGA) by a phase inversion technique. Mechanism of release from this type of microsphere appeared to be dependent on protein molecular weight for microspheres with low loadings (0.5-1.6%), while independent of protein molecular weight for microspheres with high loadings (4.8-6.9%). At low loadings, release of larger proteins was dependent on diffusion through pores for the duration of the study, while smaller proteins seemed to depend on diffusion through pores initially and on degradation at later times. Following an initial diffusion phase from low loaded microspheres, lysozyme and carbonic anhydrase, the two smallest proteins, exhibited lag phases with curtailed protein release followed by a phase of increased protein release between 4 and 8 weeks, a phenomenon not evident for larger proteins. It appears that by 8 weeks, PLGA had degraded enough to allow additional release of smaller proteins which were entrapped efficiently within the microspheres. Higher loaded microspheres, which have more interconnecting channels, did not exhibit the pronounced shift from diffusion-based to polymer degradation-based release seen with the lower loaded microspheres. Interestingly, microspheres encapsulating large proteins maintained sustained release rates for 56 days.

Bioadhesive microspheres: I. A novel electrobalance-based method to study adhesive interactions between individual microspheres and intestinal mucosa

Abstract A simple electrobalance-based method has been developed to measure bioadhesive interactions between individual polymer microspheres and biological tissues. Environmental conditions, such as temperature and pH, are easily controlled to mimic physiological parameters. The technique is unique in that it allows the measurement of many parameters: compressive deformation, peak compressive load, yield point, peak tensile load, deformation to peak load, fracture strength, deformation to failure, compressive work, returned work, and tensile work in a single experiment. The method has been shown to be statistically reproducible and accurate. Using this technique, several hydrophobic, thermoplastic polymers and one hydrogel were studied. Co-polymers of fumaric and sebacic acid, of the polyanhydride family, produced bioadhesive fracture strengths greater than 50 mN/cm 2 with rat small intestinal mucosa, in vitro. We suggest that bioadhesion in these hard, bioerodible materials is not due to chain entanglement, as required by the diffusion theory of bioadhesion, but due to numerous hydrogen bonds generated between hydrophilic functional groups (-COOH) and mucus glycoproteins.

Oral delivery of proteins by biodegradable nanoparticles

Successful administration of therapeutic proteins via the oral route has long eluded the drug delivery community; a variety of factors, both physical and physiological, have hindered the myriad approaches to increasing the bioavailability of orally administered therapeutic proteins, including: 1) pre-systemic degradation by enzymes and 2) poor penetration of the intestinal mucosa and epithelium. Even when bypassing the harsh, acidic environment of the stomach, the intestines pose significant obstacles to systemic uptake. For example, the lining of the gastrointestinal tract comprises a thick wall of epithelial cells covered by a layer of polysaccharides and mucus. In this review, we will discuss the biology underlying intestinal uptake of protein-containing, biodegradable nanoparticles, review insulin delivery as the most accepted model for oral delivery of proteins, and present a variety of new material systems enabling novel approaches to oral protein delivery which we believe will bring to bear the next therapeutic advances in our field.

Novel microcapsules for delivery systems

Abstract Two controlled release systems are described: a photochemical controlled release system, made of polyamide microcapsules, which releases its contents only during exposure to UV light, and an erodible delivery system which is made of polyanhydride microspheres and which was developed in order to release macromolecules.

Correlation of two bioadhesion assays: the everted sac technique and the CAHN microbalance

This contribution correlates two in vitro methods utilized to determine bioadhesion. One method, the everted intestinal sac technique, is a passive test for bioadhesion involving several polymer microspheres and a section of everted intestinal tissue. The other method, the CAHN microbalance, employs a CAHN dynamic contact angle analyzer with modified software to record the tensile forces measured as a single polymer microsphere is pulled from intestinal tissue. This study demonstrates that CAHN and everted sac experiments yield similar results when used to quantify the bioadhesive nature of polymer microsphere systems. A polymer showing high adhesion in one method also demonstrates high bioadhesion in the other method; polymers that exhibit high fracture strength and tensile work measurements with the CAHN microbalance also yield high binding percentages with the everted sac method. The polymers tested and reported here are poly(caprolactone) and different copolymer ratios of poly(fumaric-co-sebacic anhydride). The results of this correlation demonstrate that each method alone is a valuable indicator of bioadhesion.