Jordi Puiggalí

Epitaxial crystallization and crystalline polymorphism of polylactides

Abstract Two crystal phases of poly( l -lactide) and that of the racemate of poly( l -lactide) and poly( d -lactide) can be grown epitaxially on one and the same crystalline substrate, hexamethylbenzene (HMB), which had been shown by Zwiers et al. [Polymer 1983;24:167] to form a eutectic with these polymers. The stable α-crystal modification of the optically active polymer, based on a 103 helix conformation (for PDLA; 107 for PLLA), is obtained for Tc near 155°C. A new crystal modification is produced by epitaxial crystallization at slightly lower Tc (≈140°C). The crystal structure of this new form is established by electron diffraction and packing energy analysis. Two antiparallel helices are packed in an orthorhombic unit-cell of parameters a=9.95 A , b=6.25 A and c=8.8 A . The racemate of poly( l -lactide) and poly( d -lactide) also crystallize epitaxially (at ≈165°C) on HMB, which appears to be a very versatile substrate.

The frustrated structure of poly(L-lactide)

Abstract The crystal structure formed upon stretching or stroking of poly( l -lactide) is determined by electron diffraction and conformational energy analysis. It rests on a frustrated packing of three three-fold helices in a trigonal unit-cell of parameters a=b=1.052 nm, c=0.88 nm, space group P32. The frustrated packing is of the type described as North–South–South (NSS). This structure appears to be formed to accommodate the random up–down orientation of neighbor chains associated with rapid crystallization conditions. This randomness introduces structural disorder (c-axis shifts and azimuthal setting of neighbor helices). The resultant streaking of the diffraction pattern is modeled. Frustrated packings observed in polymeric systems that depart from three-fold symmetry, and in pseudo-racemates of low molecular weight compounds are discussed.

Synthesis and characterization of a family of biodegradable poly(ester amide)s derived from glycine

A series of aliphatic poly(ester amide)s derived from 1,6-hexanediol, glycine, and diacids with a variable number of methylenes (from 2 to 8) have been synthesized and characterized. Infrared spectroscopy shows that the studied polymers present a unique kind of hydrogen bond that is established between their amide groups. Thermal properties as melting, glass transition, and decomposition temperatures are reported. The data indicate that all the polymers are highly crystalline. Thus, different kinds of spherulites (positive and/or negative) were obtained depending on the preparation conditions and on the polymer samples. Moreover, all the polymers crystallized from dilute diol solutions as ribbonlike crystals where a regular folding habit and a single hydrogen bond direction could be deduced. A test of enzymatic hydrolysis was employed to assess the potential biodegradability of these polymers.

Studies on the biodegradation and biocompatibility of a new poly(ester amide) derived from L-alanine

A new poly(ester amide) derived from L-alanine has been synthesized and characterized. The polymer has good fiber- and film-forming properties, as well as other characteristics like thermal stability and solubility in chloroform, which enhance its processing facilities. Degradation studies show that both pH and temperature influence in the hydrolisis rate that takes mainly place through the ester linkages. Degradation was also studied by using different enzymes. Results indicated that papain was the most efficient of these, and that the hydrolysis to water-soluble products could be attained in a few days. Basal cytotoxicity was assayed using a mouse L929 fibroblast permanent cell line. The MTT viability test was performed with liquid extract of the material (50 days, 37°C). An attachment and proliferation screening study with intact material was also carried out. No cytotoxic responses were detected, in either assay, after a 24- and 48-h incubation period with the cells. After 72 h a slight cytotoxicity was detected in the polymer material, while a more significant one was detected in the material extract.

Synthesis, Properties and Applications of Biodegradable Polymers Derived from Diols and Dicarboxylic Acids: From Polyesters to Poly(ester amide)s

Poly(alkylene dicarboxylate)s constitute a family of biodegradable polymers with increasing interest for both commodity and speciality applications. Most of these polymers can be prepared from biobased diols and dicarboxylic acids such as 1,4-butanediol, succinic acid and carbohydrates. This review provides a current status report concerning synthesis, biodegradation and applications of a series of polymers that cover a wide range of properties, namely, materials from elastomeric to rigid characteristics that are suitable for applications such as hydrogels, soft tissue engineering, drug delivery systems and liquid crystals. Finally, the incorporation of aromatic units and α-amino acids is considered since stiffness of molecular chains and intermolecular interactions can be drastically changed. In fact, poly(ester amide)s derived from naturally occurring amino acids offer great possibilities as biodegradable materials for biomedical applications which are also extensively discussed.

Study on the degradability of poly(ester amide)s derived from the α-amino acids glycine, and l-alanine containing a variable amide/ester ratio

Abstract Two series of poly(ester amide)s prepared from sebacic acid and different ratios of 1,12-dodecanediamine and a diamine that contains both α-amino acid residues and ester groups have been synthesized and characterized. In order to maintain hydrogen bonding interactions, two diamines with the same number of main chain atoms were selected. The series differ on the nature of the α-amino acid residue: glycine or l -alanine. The calorimetric analysis shows that melting temperatures increase as the amide/ester ratio does. Polymers derived from l -alanine show lower crystallinities and melting temperatures than those constituted by glycine units. Hydrolytic and enzymatic degradabilities of both series of poly(ester amide)s have also been studied. The ratio and nature of α-amino acid residues in the chemical repeat unit greatly affect the degradation rate.

Biocompatibility and drug release behavior of scaffolds prepared by coaxial electrospinning of poly(butylene succinate) and polyethylene glycol.

Scaffolds constituted by electrospun microfibers of poly(ethylene glycol) (PEG) and poly(butylene succinate) (PBS) were studied. Specifically, coaxial microfibers having different core-shell distributions and compositions were considered as well as uniaxial micro/nanofibers prepared from mixtures of both polymers. Processing conditions were optimized for all geometries and compositions and resulting morphologies (i.e. diameter and surface texture) characterized by scanning electron microscopy. Chemical composition, molecular interactions and thermal properties were evaluated by FTIR, NMR, XPS and differential scanning calorimetry. The PEG component of electrospun fibers could be solubilized by immersion of scaffolds in aqueous medium, giving rise to high porosity and hydrophobic samples. Nevertheless, a small amount of PEG was retained in the PBS matrix, suggesting some degree of mixing. Solubilization was slightly dependent on fiber structure; specifically, the distribution of PEG in the core or shell of coaxial fibers led to higher or lower retention levels, respectively. Scaffolds could be effectively loaded with hydrophobic drugs having antibacterial and anticarcinogenic activities like triclosan and curcumin, respectively. Their release was highly dependent on their chemical structure and medium composition. Thus, low and high release rates were observed in phosphate buffer saline (SS) and SS/ethanol (30:70 v/v), respectively. Slight differences in the release of triclosan were found depending on fiber distribution and composition. Antibacterial activity and biocompatibility were evaluated for both loaded and unloaded scaffolds.

Comparative studies on the degradability of poly(ester amide)s derived from L‐ and L,D‐alanine

The hydrolytic degradation of two poly(ester amide)s derived from sebacic acid, dodecanediol, and alanine in both the quiral L configuration and the racemic L,D mixture has been studied. The degradation was monitored by following the changes in intrinsic viscosity, mass loss, chemical constitution, and mechanical properties. The results show that these poly(ester amide)s degrade slowly at 37°C through the ester linkage. Little changes in the Youngs modulus of both samples were found at the beginning of the degradation process. Biodegradation has also been studied by using different enzymes. Papain was the most effective one, although the degradation rate was dependent on the stereochemical composition of the polymer.

Studies on the degradability of a poly(ester amide) derived from L-alanine, 1,12-dodecanediol and 1,12-dodecanedioic acid

Abstract A new aliphatic poly(ester amide) derived from l -alanine has been synthesized and characterized. Degradability in different media has been studied and compared with BIOPOL, a well-known biodegradable polymer. The new poly(ester amide) shows a hydrolytic degradation that takes place through the ester linkage and an enzymatic degradation that strongly depends on the type of enzyme. Thus, proteolytic enzymes such as papain and proteinase K are the most effective ones. Biodegradation by microorganisms from soils and activated sludges has also been evaluated. Results indicate that BIOPOL degrades faster with microorganisms than the new polymer does.

Effects of ultrasonic vibration on the micro-molding processing of polylactide

A new ultrasonic micro-molding system was used to process polylactide (PLA) and fabricate reduced dimension specimens. Plasticization and molding of PLA were achieved by applying ultrasonic waves after feeding the polymer into a plasticizing chamber. Chemical and physical characteristics of processed PLA varied depending on the processing window (i.e. changes in ultrasonic wave amplitude between 14.2 and 48.1 μm and molding pressure between 0.5 in 6 bars). In terms of chemical effects, the application of ultrasound can lead to lower molecular weights (e.g. decreases of more than 45% in the weight average molecular weight), revealing partial degradation of the material. Also, the processed materials exhibited slightly higher thermal degradability than pure PLA because ultrasonic vibrations break molecular linkages and worsen the polymer structure. Finally, the processing conditions for the preparation of PLA specimens could be optimized without causing degradation and preserving structural characteristics and mechanical properties. Specifically, the use of an amplitude of 48.1 μm and a pressure of 3 bars gave samples with the same molecular weight as the raw material (i.e. 117,500 g/mol as opposed to 117,300 g/mol for Mw).