Fatty acid terminated polyanhydrides

Polyanhydride Chemistry

Polyanhydrides (PAs) are a class of synthetic biodegradable polymers employed as controlled drug delivery vehicles. They can be synthesized and scaled up from low-cost starting materials. The structure of PAs can be manipulated synthetically to meet desirable characteristics. PAs are biocompatible, biodegradable, and generate nontoxic metabolites upon degradation, which are easily eliminated from the body. The rate of water penetrating into the polyanhydride (PA) matrix is slower than the anhydride bond cleavage. This phenomenon sets PAs as "surface-eroding drug delivery carriers." Consequently, a variety of PA-based drug delivery carriers in the form of solid implants, pasty injectable formulations, microspheres, nanoparticles, etc. have been developed for the sustained release of small molecule drugs, and vaccines, peptide drugs, and nucleic acid-based active agents. The rate of drug delivery is often controlled by the polymer erosion rate, which is influenced by the polymer structure and composition, crystallinity, hydrophobicity, pH of the release medium, device size, configuration, etc. Owing to the above-mentioned interesting physicochemical and mechanical properties of PAs, the present review focuses on the advancements made in the domain of synthetic biodegradable biomedical PAs for therapeutic delivery applications. Various classes of PAs, their structures, their unique characteristics, their physicochemical and mechanical properties, and factors influencing surface erosion are discussed in detail. The review also summarizes various methods involved in the synthesis of PAs and their utility in the biomedical domain as drug, vaccine, and peptide delivery carriers in different formulations are reviewed.

Preparation and Characterization of Polyanhydride Terminated with Oleic Acid Extracted from Olive Mills Waste

Valorizing the fatty content of agricultural waste in material synthesis is an interesting topic. This work focused on utilizing oleic acid from the solid waste of olive mills in Saudi Arabia to synthesize biodegradable polyanhydrides based on sebacic acid which terminated with different concentrations of fatty acid (10, 30, 50, and 70 wt%), then characterize the final polymer samples and study the effects of termination on polyanhydrides properties, such as molecular weight and degradation profile. The fatty content of the solid waste was extracted, purified, and analyzed prior to and after separating the saturated and unsaturated fractions by urea crystallization, then the microwave-assisted melt polycondensation technique was used in the synthesis of the final polymers. Molecular weights were determined by gel permeation chromatography (GPC), and the degradation profile of the prepared samples was examined by determining the weight loss percentage of the polymer mass and FT-IR scanning for the anhydride bond before and after sample degradation. Results showed a linear degradation profile for most samples with no significant change in the molecular weights due to termination.

Degradation of Polymer Films on Surfaces: A Model Study with Poly(sebacic anhydride)

There is compelling evidence that the degradation kinetics of thin polymer films differ significantly from those of bulk materials, as interfacial effects become dominant. Therefore, it is crucial to investigate these kinetics separately. Qualitative analytics of thin film degradation exist, e.g. by scanning electron microscopy or atomic force microscopy (AFM), but a quantitative study is so far missing. In this work, poly(sebacic anhydride) (PSA), an aliphatic polyanhydride, is used as a model system for a quantitative degradation study. PSA was spin-coated onto silicon or gold substrates. The degradation of these PSA films was monitored by ellipsometry, surface-plasmon resonance spectroscopy (SPR), and Fourier transform infrared spectroscopy (FTIR). Two kinetic regimes were observed when plotting the relative layer thickness determined by FTIR and SPR against the degradation time. The data obtained by FTIR showed a single process for the rate of ester bond cleavage. Overall, the degradation rate constants of PSA determined by the different methods were consistent. The degradation rate constants of PSA film up to 378 nm thickness were constant. Several thicker free-standing samples studied gravimetrically had a degradation rate constant that was one order of magnitude slower, thus confirming thickness-dependent degradation rate constants.

Biodegradable galactitol based crosslinked polyesters for controlled release and bone tissue engineering

Various classes of biodegradable polymers have been explored towards finding alternates for the existing treatments for bone disorders. In this framework, two families of polyesters using an array of crosslinkers were synthesized. One was based on galactiol/adipic acid and the other based on galactitol/dodecanedioic acid. The structures of the polymers were confirmed by FTIR and further confirmed by ¹H NMR. DSC showed that the polymers were amorphous and the glass transition temperature increased with increase in crosslinking. DMA and contact angle analysis revealed that the modulus and hydrophobicity increased with increase in crosslinking. Swelling studies demonstrated that %swelling decreased with increase in crosslinking. The in vitro hydrolytic degradation studies and dye release studies of all the polymers exhibited that the degradation and release rate decreased with increase in crosslinking, hydrophobicity and modulus. Degradation and release followed first order kinetics and Higuchi kinetics, respectively. The preliminary in vitro cytotoxicity studies proved that this array of polymers was not cytotoxic. Osteogenic differentiation of pre-osteoblasts was observed in three dimensional (3D) porous scaffolds prepared using these polymers. This study demonstrates the ability to modulate the physical properties, degradation and release kinetics of these biodegradable polymers through smart selection of crosslinkers. The findings of these studies have important implications for developing novel biodegradable polymers for drug delivery and tissue engineering applications.

Cisplatin tumor biodistribution and efficacy after intratumoral injection of a biodegradable extended release implant

Local delivery of chemotherapeutic drugs has long been recognized as a potential method for reaching high drug doses at the target site while minimizing systemic exposure. Cisplatin is one of the most effective chemotherapeutic agents for the treatment of various tumors; however, its systemic toxicity remains the primary dose-limiting factor. Here we report that incorporation of cisplatin into a fatty acid-based polymer carrier followed by a local injection into the solid tumor resulted in a successful tumor growth inhibition in heterotopic mouse bladder tumor model in mice. Platinum concentration in the tumor tissue surrounding the injected implant remained above the therapeutic level up to 14 days after the injection, while the plasma levels were several orders of magnitude lower comparing to systemic delivery. The reported delivery system increased the maximum tolerated dose of cisplatin 5 times compared to systemic delivery, thus potentially improving antitumor efficacy of cisplatin in solid tumor model.

Hydroxy fatty acid based polyanhydride as drug delivery system: Synthesis, characterization,in vitro degradation, drug release, and biocompatibility

Low molecular weight hydroxy fatty acid based polyanhydrides were synthesized by one pot method, a variable of typical melt-condensation and characterized by FTIR, NMR, DSC, and GPC. Polymer degrades by both surface and bulk erosion as trailed by weight loss, anhydride loss and surface morphology. Control over drug release was accessed with drugs featuring different aqueous solubility, that is, methotrexate (hydrophobic) and 5-fluorouracil (hydrophilic). Effect of loading, at 5, 10, and 20% w/w of methotrexate on release profiles was also studied and negligible effect was discovered. Biocompatibility of polymers was evaluated in SD rats after SC injection of the polymer. Histopathology revealed initial inflammation of the tissues near the injection site however healed with time. Overall, these polymers were found good to control the release of the entrapped drug and were found biocompatible in preliminary in vivo study. Due to their low melting temperatures they can be injected locally (SC or intratumorally) to from regional in situ depot and have a great potential as a drug carrier for localized delivery of anticancer drugs.

Long acting local anesthetic–polymer formulation to prolong the effect of analgesia

Prolonged postoperative analgesia cannot be achieved using single injections of local anesthetic solutions. The study objective was to evaluate the efficacy and toxicity of a new formulation of bupivacaine loaded in an injectable fatty acid based biodegradable polymer poly(sebacic-co-ricinoleic acid) for producing motor and sensory block when injected near the sciatic nerve. Bupivacaine was dissolved in poly(fatty ester-anhydride) paste and tested for drug release in vitro and in vivo after injection in mice. The efficacy and toxicity of the polymer-drug combination was determined by injecting the polymer formulation near the sciatic nerve of mice and measure the sensory and motor nerve blockade for 48 h, while monitoring the animal general health and the injection site. Seventy percent of the incorporated drug was released during 1 week in vitro. Single injection of 10% bupivacaine in the polymer caused motor and sensory block that lasted 30 h. Microscopic examination of the injection sites revealed only mild infiltration in three of eight examined tissues with no pathological findings for internal organs were found. In conclusion the polymer poly(sebacic-co-ricinoleic acid) is a safe carrier for prolonged activity of bupivacaine.

Bile Acids as Building Blocks of Amphiphilic Polymers. Applications and Comparison with Other Systems

This review deals with the use of bile acids as building blocks of amphiphilic polymers. These natural polyfunctional organic molecules have been employed in the synthesis of macromolecules combining hydrophilic and hydrophobic sequences. The two main synthetic strategies are radical (co)polymerization after attachment of a vinyl group onto the bile acid and molecule grafting of bile acid onto a hydrophilic polymer. The physicochemical properties of the resulting polymers both as bulk materials and in aqueous solution are reviewed and compared with polymers of other structures. Whenever possible, semiquantitative correlations are established and discussed.

Biodegradable Injectable In Situ Depot-Forming Drug Delivery Systems

The scope of drug-delivery systems has expanded significantly in recent years providing new ways to deliver life saving therapeutics to patients. The development of new injectable drug-delivery systems has provided new vistas and opened up unexplored horizons in the field of science, particularly in controlled drug delivery since these systems possess unique advantages over traditional ones, which include ease of application, and localized and prolonged drug delivery. In the past few years, an increasing number of such systems has been reported in the literature for various biomedical applications, including drug delivery, cell encapsulation, and tissue repair. These are injectable fluids that can be introduced into the body in a minimally invasive manner prior to solidifying or gelling within the desired site. For this purpose both natural (chitosan, alginates) as well as synthetic polymers (PEGylated polyesters, ricinoleic acid-based polymers) have been utilized. These systems have been explored widely for the delivery of various therapeutic agents ranging for anti-neoplastic agents like paclitaxel to proteins and peptides such as insulin, almost covering every segment of the pharmaceutical field. This manuscript focuses on the recent advancements in the area of in situ forming biodegradable polymeric drug-delivery systems.

Hydrolytic Degradation and Drug Release of Ricinoleic Acid–Lactic Acid Copolyesters

A systematic study on the degradation and drug release from L-lactic acid and ricinoleic-acid-based copolyesters is reported. These copolyesters were synthesized by ring opening polymerization (ROP), melt condensation (COND) and transesterification (TRANS) of high molecular weight poly(lactic acid) (PLA) with ricinoleic acid (PLA-RA), and repolymerization by condensation to yield random and block copolymers of weight average molecular weights (Mw) between 3000 and 13,000. All polymers showed an almost zero-order weight loss, with a 20-40% loss after 60 days of incubation. Lactic acid release to the degradation solution is proportional to weight loss of the polymer samples. The main decrease in molecular weight was observed during the first 20 days, followed by a slow degradation phase, which kept the number average molecular weight (Mn) at 4000-2000 for another 40 days. Water-soluble 5FU was released from ricinoleic-acid-based polymers faster than slightly water-soluble triamcinolone. Drug release into phosphate-buffered saline (pH 7.4, 0.1 M) at 37 degrees C from P(LA-RA) 60:40 prepared by condensation of the acids was faster than from pasty P(PLA-RA) 60:40 synthesized by transesterification for both drugs.

Poly(sebacic acid-co-ricinoleic acid) biodegradable carrier for paclitaxel—effect of additives

Injectable polymeric formulation for paclitaxel was studied. Poly ricinoleic acid and sebacic acid were synthesized. The effect of additives on the viscosity of polymer, paclitaxel release, and polymer degradation was investigated both in vitro and in vivo. Additives that were used in this study were ricinoleic acid, phospholipid, PEG 400, and PEG 2000. Addition of 20% ricinoleic acid to P(SA:RA)3:7 liquefied the formulation and allowed injection of the formulation containing paclitaxel via a 22-G needle at room temperature with no effect on paclitaxel release rate. Addition of PEG 400, PEG 2000, and phospholipid to the formulation did not affect the paclitaxel release from the formulation. The degradation of modified formulations with paclitaxel and additives was examined in vitro and by subcutaneous injection of liquid formulations to the backspace via a 22-G needle into seven groups of four C3H mice. In vivo formulations with additives (20% ricinoleic acid and PEG or phospholipid) and 5% paclitaxel content degraded faster than the formulation with only 20% ricinoleic acid and the same paclitaxel content: 51% and 54% versus 43%. The slowest degradation (26% in 1 week) was of the formulation containing 10% paclitaxel. The release rate in vivo was affected by the paclitaxel content; the higher the content, the slower was the release. By using additives, we could adjust the physical characteristics of the surgical paste while maintaining a desirable system for sustained paclitaxel release.

Synthesis and characterization of poly(dimer acid-brassylic acid) copolymer and poly(dimer acid-pentadecandioic acid) copolymer

Poly(dimer acid-brassylic acid) [P(DA-BA)] copolymers and poly(dimer acid-pentadecandioic acid) [P(DA-PA)] copolymers were prepared by melt polycondensation of the corresponding mixed anhydride prepolymers. The copolymers were characterized by Fourier transform infrared (FTIR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), wide angle x-ray powder-diffraction, and thermal gravimetric analysis (TGA). In vitro studies show that all the copolymers are degradable in phosphate buffer at 37 degrees C, and leaving an oily dimer acid residue after hydrolysis for the copolymer with high content of dimer acid. The release profiles of hydrophilic model drug, ciprofloxcin hydrochloride, from the copolymers, follow first-order release kinetics. All the preliminary results suggested that the copolymer might be potentially used as drug delivery devices.

Poly(sebacic acid-co-ricinoleic acid) biodegradable carrier for paclitaxel:In vitro release andin vivo toxicity

Polyesteranhydrides synthesized by the transesterification of ricinoleic acid and sebacic acid followed by anhydride polymerization were examined as potential controlled delivery carrier for paclitaxel. Solid and liquid polymers were used. Polymers containing 30% ricinoleic acid are solid whereas polymers containing 70% ricinoleic acid are liquid at body temperature and semisolid at room temperature. It was found that upon addition of the liquid polymer to water it solidifies to form a stable semisolid. Paclitaxel, a potent antitumor agent, was incorporated in the polymers (5-20% w/w) and its release in buffer solution was monitored. Paclitaxel was released for over 100 days while the polymer carrier was being degraded. The release rate was affected by the paclitaxel content; the higher the content, the slower was the release. The toxicity of the polymers and formulations with paclitaxel was examined by subcutaneous injection of liquid polymer samples or implantation of solid polymer specimens to mice for different time periods. Histopathological examination of the tissue surrounding the implant showed minor inflammation 1 week after the injection and no inflammation 3 weeks after implantation. Injection of the polymer without paclitaxel showed no adverse effects.

Nonlinear fatty acid terminated polyanhydrides

A systemic study on the synthesis, characterization, degradation, drug release, and stability of nonlinear fatty acid terminated poly(sebacic anhydride) (PSA) is reported. Ricinoleic acid was transformed into a nonlinear fatty acid by esterification with fatty acid chlorides of C8-C18 chain length in the presence of pyridine. Pure nonlinear fatty acids were obtained by purification of the reaction product using column chromatography. Poly(sebacic acid)s terminated with 30 wt % of various nonlinear fatty acids were synthesized by melt condensation to yield waxy off-white materials with molecular weights in the range of 5000-9000. The terminated polymers are soluble in common organic solvents and melt at temperatures between 70 and 79 degrees C, which allow their fabrication into microspheres and implants. These polymers degrade into their counterparts during a period of a few weeks while constantly releasing an incorporated drug. The incorporation of nonlinear fatty acid terminals to poly(sebacic anhydride) increased the polymer hydrophobicity and decreased polymer crystallinity when compared to PSA or to linear fatty acid terminated PSA. The hydrophobic nonlinear side chains retard water from penetrating into the polymer mass, which resulted in higher stability and surface erosion front mechanism of polymer degradation and drug release.

Polyanhydride degradation and erosion

It was the intention of this paper to give a survey on the degradation and erosion of polyanhydrides. Due to the multitude of polymers that have been synthesized in this class of material in recent years, it was not possible to discuss all polyanhydrides that have gained in significance based on their application. It was rather the intention to provide a broad picture on polyanhydride degradation and erosion based on the knowledge that we have from those polymers that have been intensively investigated. To reach this goal this review contains several sections. First, the foundation for an understanding of the nomenclature are laid by defining degradation and erosion which was deemed necessary because many different definitions exist in the current literature. Next, the properties of major classes of anhydrides are reviewed and the impact of geometry on degradation and erosion is discussed. A complicated issue is the control of drug release from degradable polymers. Therefore, the aspect of erosion-controlled release and drug stability inside polyanhydrides are discussed. Towards the end of the paper models are briefly reviewed that describe the erosion of polyanhydrides. Empirical models as well as Monte-Carlo-based approaches are described. Finally it is outlined how theoretical models can help to answer the question why polyanhydrides are surface eroding. A look at the microstructure and the results from these models lead to the conclusion that polyanhydrides are surface eroding due to their fast degradation. However they switch to bulk erosion once the device dimensions drop below a critical limit.

Polyanhydrides: an overview

Polyanhydrides have been considered to be useful biomaterials as carriers of drugs to various organs of the human body such as brain, bone, blood vessels, and eyes. They can be prepared easily from available, low cost resources and can be manipulated to meet desirable characteristics. Polyanhydrides are biocompatible and degrade in vivo into non-toxic diacid counterparts that are eliminated from the body as metabolites. Owing to their usefulness, this review focuses on the development, synthesis methods, structures and characterization of polyanhydrides, which will provide an overview for the researchers in the field. Their in vitro and in vivo degradability, toxicity, biocompatibility and applications are discussed in the subsequent chapters of this special issue on polyanhydrides and poly(ortho esters).

Stereocomplexes of enantiomeric lactic acid and sebacic acid ester-anhydride triblock copolymers

A systematic study on the synthesis, characterization, degradation, and drug release of d-, l-, and dl-poly(lactic acid) (PLA)-terminated poly(sebacic acid) (PSA) and their stereocomplexes is reported. PLA-terminated sebacic acid polymers were synthesized by melt condensation of the acetate anhydride derivatives of PLA oligomers and sebacic anhydride oligomers to yield ABA triblock copolymers of molecular weights between 3000 and 9000 that melt at temperatures between 35 and 80 degrees C. Pairs of the corresponding enantiomeric ABA copolymers composed of l-PLA-PSA-l-PLA and d-PLA-PSA-d-PLA were solvent mixed to form stereocomplexes. The formed stereocomplexes exhibited higher crystalline melting temperature than the enantiomeric polymers, which indicate stereocomplex formulation. The PLA terminals had a significant effect on the polymer degradation and drug release rate. PSA with up to 20% w/w of PLA terminals degraded and released the incorporated drug for more than 3 weeks as compared with 10 days for PSA homopolymer.

Polymeric controlled drug-delivery systems: perspective issues and opportunities

Although, the drug-delivery system (DDS) concept is not new, great progress has been made recently in the treatment of a variety of diseases. Targeting delivery of drugs to the diseased lesions is one of the most important aspects of DDS. To convey a sufficient dose of drug to the lesion, suitable carriers of drugs are needed. Polymers, which swell and contract in response to external pH levels, are being explored. The research in this area is being carried out all over the world at a great pace. Not only that new developments are emerging in the existing technologies, but also various new technologies are being developed and tested. Consequently, a huge amount of new information is available, which should be compiled and presented in a comprehensive way to benefit large numbers of users in this area as well as to help active research workers in the field. The purpose of this review is to discuss some recent advances and future prospects in controlled drug-delivery technology. The article serves as a useful tool for the beginners as well as for the researchers actively involved in this fascinating area of applied polymer science.