The return of a forgotten polymer—Polycaprolactone in the 21st century

Utilization of polymers as biomaterials has greatly impacted the advancement of modern medicine. Specifically, polymeric biomaterials that are biodegradable provide the significant advantage of being able to be broken down and removed after they have served their function. Applications are wide ranging with degradable polymers being used clinically as surgical sutures and implants. In order to fit functional demand, materials with desired physical, chemical, biological, biomechanical and degradation properties must be selected. Fortunately, a wide range of natural and synthetic degradable polymers has been investigated for biomedical applications with novel materials constantly being developed to meet new challenges. This review summarizes the most recent advances in the field over the past 4 years, specifically highlighting new and interesting discoveries in tissue engineering and drug delivery applications.

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Biomedical Applications of Biodegradable Polymers

Preservatives in eyedrops: The good, the bad and the ugly ☆

During the resorbable-polymer-boom of the 1970s and 1980s, polycaprolactone (PCL) was used in the biomaterials field and a number of drug-delivery devices. Its popularity was soon superseded by faster resorbable polymers which had fewer perceived disadvantages associated with long term degradation (up to 3-4 years) and intracellular resorption pathways; consequently, PCL was almost forgotten for most of two decades. Recently, a resurgence of interest has propelled PCL back into the biomaterials-arena. The superior rheological and viscoelastic properties over many of its aliphatic polyester counterparts renders PCL easy to manufacture and manipulate into a large range of implants and devices. Coupled with relatively inexpensive production routes and FDA approval, this provides a promising platform for the production of longer-term degradable implants which may be manipulated physically, chemically and biologically to possess tailorable degradation kinetics to suit a specific anatomical site. This review will discuss the application of PCL as a biomaterial over the last two decades focusing on the advantages which have propagated its return into the spotlight with a particular focus on medical devices, drug delivery and tissue engineering.

The return of a forgotten polymer : Polycaprolactone in the 21st century

Nitrogen-containing heterocyclic compounds and their derivatives have historically been invaluable as a source of therapeutic agents. Pyrazole, which has two nitrogen atoms and aromatic character, provides diverse functionality and stereochemical complexity in a five-membered ring structure. In the past decade, studies have reported a growing body of data on different pyrazole derivatives and their innumerable physiological and pharmacological activities. In part, such studies attempted to reveal the wide range of drug-like properties of pyrazole derivatives along with their structure–activity relationships in order to create opportunities to harness the full potentials of these compounds. Here, we summarize strategies to synthesize pyrazole derivatives and demonstrate that this class of compounds can be targeted for the discovery of new drugs and can be readily prepared owing to recent advances in synthetic medicinal chemistry.

Review: biologically active pyrazole derivatives

Sixteen 1-(2-naphthyloxyacetyl)-4-substituted-3-thiosemicarbazide, 2-(2-naphthyloxymethyl)-5-substitutedamino-1,3,4-oxadiazole, 2-(2-naphthyloxymethyl)-5-substitutedamino-1,3,4-thiadiazole and 5-(2-naphthyloxymethyl)-4-substituted-1,2,4-triazole-3thione derivatives have been prepared and evaluated as orally active anti-inflammatory agents with reduced side-effects. The structures of the compounds were confirmed by IR and 1H NMR spectral data and microanalysis. The anti-inflammatory and ulcerogenic activities of the compounds were compared with naproxen, indomethacin and phenylbutazone. In carrageenan-induced foot pad edema assay, 2-(2-naphthyloxymethyl)-5-methylamino-1,3,4-oxadiazole, 5-(2-naphthyloxymethyl)-4-methyl-1,2,4-triazole-3-thione and 5-(2-naphthyloxymethyl)-4-ethyl-1,2,4-triazole-3-thione showed an interesting anti-inflammatory activity. In the air-pouch test, 1,3,4-oxadiazole and 1,2,4-triazole-3-thione derivatives reduced total number of leukocytes of the exudate that indicates excellent inhibition of prostaglandin production. Side effects of the compounds were examined on gastric mucosa, liver and stomach and none of the compounds showed significant side effects compared with reference nonsteroidal anti-inflammatory drugs (NSAIDs).

Synthesis and anti-inflammatory activity of 1-acylthiosemicarbazides, 1,3,4-oxadiazoles, 1,3,4-thiadiazoles and 1,2,4-triazole-3-thiones.

Synthesis and antidepressant activities of some 3,5-diphenyl-2-pyrazolines.

Six new 5-(1-/2-naphthyloxymethyl)-1,3,4-oxadiazole-2(3 H )-thione, 2-amino-5-(1-/2-naphthyloxymethyl)-1,3,4-oxadiazole, 5-(1-/2-naphthyloxymethyl)-1,3,4-oxadiazole-2(3 H )-one derivatives have been synthesized from 1-and/or 2-naphthol. The structures of the compounds were confirmed by IR and 1 H NMR spectral data and microanalysis. The antimicrobial properties of the compounds were investigated against Staphylococcus aureus , Escherichia coli and Pseudomonas aeruginosa , Candida albicans , C . krusei and C. parapsilosis using microbroth dilution method. 2-Amino-5-(2-naphthyloxymethyl)-1,3,4-oxadiazole and 5-(2-naphthyloxymethyl)-1,3,4-oxadiazole-2(3 H )-one show significantly (32 μg/ml), compounds 5-(1-/2-naphthyloxymethyl)-1,3,4-oxadiazole-2(3 H )-thione, 2-amino-5-(1-naphthyloxymethyl)-1,3,4-oxadiazole and 5-(1-naphthyloxymethyl)-1,3,4-oxadiazole-2(3 H )-one moderately (64 μg/ml) active against C. krusei. All the compounds were active against S. aureus , E. coli , P. aeruginosa , C. albicans , and C. parapsilosis at 64–256 μg/ml concentration.

Synthesis and antimicrobial activity of some 1,3,4-oxadiazole derivatives

Hyaluronic acid coated poly-epsilon-caprolactone nanospheres deliver high concentrations of cyclosporine A into the cornea.

Several 1-thiocarbamoyl-3,5-diphenyl-2-pyrazoline derivatives have been synthesized by reacting 1,3-diphenyl-2-propen-1-one (chalcones) with thiosemicarbazide, or hydrazine hydrate and then with various isothiocyanates. Their chemical structures have been proven by UV, IR, 1H-NMR and elemental analysis. Antidepressant activities were investigated by "Porsolt's Behavioural Despair Test". 1-Thiocarbamoyl-3-(phenyl and 4-chlorophenyl-5-(4-methyl and 4-methoxyphenyl-2-pyrazoline (compounds III, IV, VII, VIII) and 3-(4-methylphenyl)-5-(4-methoxyphenyl)-2-pyrazoline (compound XII) showed equivalent or higher activity than pargyline hydrochloride and tranylcypromine sulfate.

Erhan Palaska

Papers

Synthesis and anti-inflammatory activity of 1-acylthiosemicarbazides, 1,3,4-oxadiazoles, 1,3,4-thiadiazoles and 1,2,4-triazole-3-thiones.

Synthesis and antidepressant activities of some 3,5-diphenyl-2-pyrazolines.

Synthesis and antimicrobial activity of some 1,3,4-oxadiazole derivatives

Hyaluronic acid coated poly-epsilon-caprolactone nanospheres deliver high concentrations of cyclosporine A into the cornea.

Studies on the synthesis and antidepressant activity of some 1-thiocarbamoyl-3,5-diphenyl-2-pyrazolines.