The use of SIMS, XPS and in situ AFM to probe the acid catalysed hydrolysis of poly(orthoesters)

Stimulus-cleavable chemistry in the field of controlled drug delivery

This review comprehensively summarises stimulus-cleavable linkers from various research areas and their cleavage mechanisms, thus provides an insightful guideline to extend their potential applications to controlled drug release from nanomaterials.

Tuning the pH sensitivities of orthoester based compounds for drug delivery applications by simple chemical modification

Orthoesters are acid-sensitive moieties that allow substantial structural diversity for biological applications including drug delivery. Here, the pH-sensitivity of a range of novel orthoester based compounds was compared in the range 7.5-4.5 that is characteristic of the increased acidification during endocytosis. We find that simple modifications close to the orthoester had major effects on both the rate and extent of hydrolysis, suggesting this could be exploited for activating drug delivery systems on endocytic pathways.

Characterization of linear and cyclic polylactic acids and their solvolysis products by electrospray ionization mass spectrometry

Linear and cyclic polylactic acids (PLAs) were characterized using electrospray ionization mass spectrometry (ESI-MS) as part of our ongoing investigation of the hydrolysis mechanism of biodegradable polymers. The condensation oligomers of linear polylactic acid (LPLA) were synthesized by thermal dehydration of L-lactic acid. The trimer and tetramer base polymers of cyclic polylactic acid (CPLA) were obtained by cyclization reactions of lactic acid trimers and tetramers, respectively. In the ESI-MS/MS measurement, LPLA yielded three types of product ion series, while CPLA yielded only one type, from which the repeated units of CPLA were removed. The MS/MS spectrum of the NH4+ adduct ion for both cyclic and linear PLA showed loss of one ammonia molecule. The postsource decay (PSD) spectrum of CPLA by matrix-assisted laser desorption ionization (MALDI) mass spectrometry was similar to the ESI-MS/MS spectrum, while that of LPLA was different. In addition, the degradation of cyclic and linear PLAs by solvolysis was investigated. Solvolysis with anhydrous MeOH was quite feasible, but did not readily occur in the presence of even a small amount of water in the MeOH solvent.

Drug release from and hydrolytic degradation of a poly(ethylene glycol) grafted poly(3-hydroxyoctanoate)

Monoacrylate-poly(ethylene glycol)-grafted poly(3-hydroxyoctanoate) (PEGMA-g-PHO) copolymers were synthesized to develop a swelling-controlled release delivery system for ibuprofen as a model drug. The in vitro hydrolytic degradation of and the drug release from a film made of the PEGMA-g-PHO copolymer were carried out in a phosphate buffer saline (pH 7.4) medium. The hydrolytic degradation of the copolymer was strongly dependent on the degree of grafting (DG) of the PEGMA group. The degradation rate of the copolymer films in vitro increased with increasing DG of the PEGMA group on the PHO chain. The copolymer films showed a controlled delivery of ibuprofen to the medium in periods of time that depend on the composition, hydrophilic/hydrophobic characteristics, initial drug loading amount and film thickness of the graft copolymer support. The drug release rate from the grafted copolymer films was faster than the rate of weight loss of the films themselves. In particular, a combination of the low DG of the PEGMA group in the PHO chains with the low ibuprofen solubility in water led to long-term constant release from these matrices in vitro.

Simultaneous time-of-flight secondary ion MS quantitative analysis of drug surface concentration and polymer degradation kinetics in biodegradable poly(L-lactic acid) blends

This paper reports a new quantitative method of analyzing both the earliest stage of degradation of a polymer and the surface concentration of an additive using time-of-flight secondary ion mass spectrometry (TOF-SIMS). The static SIMS spectra of triphenylamine (Ph3N)/poly(L-lactic acid) (PLLA) (20:80 wt %) blend matrixes hydrolyzed in buffered conditions within a short-term (<48 h) period are simultaneously analyzed in the low-mass range for the surface accumulation profile of Ph3N and in the high-mass range to determine the hydrolytic degradation kinetics of PLLA, respectively. The results provide new insight in evaluating the surface concentration of Ph3N (pKb approximately 0) from the blends to see how it relates to the reactions (hydrolytic PLLA degradation) occurring in the surface region in the initial induction period over which negligible loss of polymer weight is observed. The relative PLLA surface degradation at pH 10.0 is approximately 2 times faster than that at pH 7.4. The relative extent of increase in Ph3N surface concentration assayed in pH 10.0 buffer system is 9 times greater than that at pH 7.4. The initial rapid increase in surface concentration of Ph3N is related to but not singularly dependent on the rate of PLLA degradation at the surface of blend matrixes.

Therapeutic applications of viscous and injectable poly(ortho esters)

Poly(ortho esters) (POE) are hydrophobic and bioerodible polymers that have been investigated for pharmaceutical use since the early 1970s. Among the four described generations of POE, the third (POE III) and fourth (POE IV) are promising viscous and injectable materials which have been investigated in numerous biomedical applications. POE III has been extensively studied for ophthalmic drug delivery, it presents an excellent biocompatibility and is currently being investigated as a vehicle for sustained drug delivery to treat diseases of the posterior segment of the eye. POE IV is distinguishable by a highly reproducible and controlled synthesis, a higher hydrophobicity, and an excellent biocompatibility. It is currently under development for a variety of applications, such as ocular delivery, periodontal disease treatment and applications in veterinary medicine. This review will also focus on new perspectives for this promising family of polymers, such as guided tissue regeneration, treatment of osteoarthritis, as well as peptide and protein delivery.