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Bioresorbable poly-L-lactide (PLLA) stents have the potential to fully dissolve after treating injured arteries, leaving nothing behind. However, the manufacturing process for bioresorbable stents (BRS) needs further refinement to eventually replace current permanent stents. This study investigates the effect of radial and biaxial expansion procedures on the microstructure and mechanical properties of PLLA expanded tubes using microfocus wide -angle X-ray scattering (WAXS) and multi-directional tensile tests. A complex microstructure with an orientation gradient across the thickness of the tube wall was observed and linked to the strain history experienced during processing. Correlations between the stretch ratios applied and the mechanical properties of the PLLA tubes were also noted and discussed in relation to stent application.

Poly-L-lactide (PLLA) offers a unique possibility for processing into biocompatible, biodegradable, and implantable piezoelectric structures. With such properties, PLLA has potential to be used as an advanced tool for mimicking biophysical processes that naturally occur during the self-repair of wounds and damaged tissues, including electrostimulated regeneration. The piezoelectricity of PLLA strongly depends on the possibility of controlling its crystallinity and molecular orientation. Here, it is shown that modifying PLLA with a small amount (1 wt%) of crystalline filler particles with a high aspect ratio, which act as nucleating agents during drawing-induced crystallization, promotes the formation of highly crystalline and oriented PLLA structures. This increases their piezoelectricity, and the filler-modified PLLA films provide a 20-fold larger voltage output than nonmodified PLLA during ultrasound (US)-assisted activation. With 99% PLLA content, the ability of the films to produce reactive oxygen species (ROS) and increase the local temperature during interactions with US is shown to be very low. US-assisted piezostimulation of adherent cells directly attach to their surface (such as skin keratinocytes), stimulate cytoskeleton formation, and as a result cells elongate and orient themselves in a specific direction that align with the direction of PLLA film drawing and PLLA dipole orientation., Small, ISSN:1613-6810, ISSN:1613-6829

Experiments are performed to obtain the highest Tm and ΔHm values for poly(l-lactide)s. They also include comparison with literature data and of cyclic and linear species.

In this study, we describe the production of hybrid gelatin-poly-L-lactide electrospun scaffolds whose hydrophilicity was controlled by binding increasing concentrations of hyaluronic acid (HA). We show that cross-linking has advantages over coating when aiming to functionalize the scaffolds with HA. The here described scaffolds structurely mimicked the complexity of the extracellular matrix, and when excited by second harmonic generation, they produced a signal that is typical of collagen-containing biological fibers. Fluorescence lifetime imaging microscopy (FLIM) was used to marker-independently monitor the growth of human dermal fibroblasts on the electrospun scaffolds using reduced (phosphorylated) nicotinamide adenine dinucleotide as target. Benefitting from the different fluorescence lifetimes of the polymer and the endogenous cellular fluorophore, we were able to distinguish and separate the signals produced by the cells from the signals generated by the electrospun scaffolds. FLIM further allowed the detection of metabolic differences in the cells seeded on the HA-functionalized scaffolds compared with cells that were cultured on nonfunctionalized control scaffolds.

In order to obtain the forming regulation and structural evolution of poly(l-lactide)/poly(d-lactide) (PLLA/PDLA) stereocomplexes (sc-PLA), a commercial high molecular weight PLLA was blended with ...

Osteosynthesis systems are used to fixate bone segments in maxillofacial surgery. Titanium osteosynthesis systems are currently the gold standard. However, the disadvantages result in symptomatic removal in up to 40% of cases. Biodegradable osteosynthesis systems, composed of degradable polymers, could reduce the need for removal of osteosynthesis systems while avoiding the aforementioned disadvantages of titanium osteosyntheses. However, disadvantages of biodegradable systems include decreased mechanical properties and possible foreign body reactions. In this review, the literature that focused on the in vitro and in vivo performances of biodegradable and titanium osteosyntheses is discussed. The focus was on factors underlying the favorable clinical outcome of osteosyntheses, including the degradation characteristics of biodegradable osteosyntheses and the host response they elicit. Furthermore, recommendations for clinical usage and future research are given. Based on the available (clinical) evidence, biodegradable copolymeric osteosyntheses are a viable alternative to titanium osteosyntheses when applied to treat maxillofacial trauma, with similar efficacy and significantly lower symptomatic osteosynthesis removal. For orthognathic surgery, biodegradable copolymeric osteosyntheses are a valid alternative to titanium osteosyntheses, but a longer operation time is needed. An osteosynthesis system composed of an amorphous copolymer, preferably using ultrasound welding with well-contoured shapes and sufficient mechanical properties, has the greatest potential as a biocompatible biodegradable copolymeric osteosynthesis system. Future research should focus on surface modifications (e.g., nanogel coatings) and novel biodegradable materials (e.g., magnesium alloys and silk) to address the disadvantages of current osteosynthesis systems.

Osteosynthesis systems are used to fixate bone segments in maxillofacial surgery. Titanium osteosynthesis systems are currently the gold standard. However, the disadvantages result in symptomatic removal in up to 40% of cases. Biodegradable osteosynthesis systems, composed of degradable polymers, could reduce the need for removal of osteosynthesis systems while avoiding the aforementioned disadvantages of titanium osteosyntheses. However, disadvantages of biodegradable systems include decreased mechanical properties and possible foreign body reactions. In this review, the literature that focused on the in vitro and in vivo performances of biodegradable and titanium osteosyntheses is discussed. The focus was on factors underlying the favorable clinical outcome of osteosyntheses, including the degradation characteristics of biodegradable osteosyntheses and the host response they elicit. Furthermore, recommendations for clinical usage and future research are given. Based on the available (clinical) evidence, biodegradable copolymeric osteosyntheses are a viable alternative to titanium osteosyntheses when applied to treat maxillofacial trauma, with similar efficacy and significantly lower symptomatic osteosynthesis removal. For orthognathic surgery, biodegradable copolymeric osteosyntheses are a valid alternative to titanium osteosyntheses, but a longer operation time is needed. An osteosynthesis system composed of an amorphous copolymer, preferably using ultrasound welding with well-contoured shapes and sufficient mechanical properties, has the greatest potential as a biocompatible biodegradable copolymeric osteosynthesis system. Future research should focus on surface modifications (e.g., nanogel coatings) and novel biodegradable materials (e.g., magnesium alloys and silk) to address the disadvantages of current osteosynthesis systems.

In this work, biodegradable Poly(L-lactide) (PLLA) was modified through adding a new organic additive N, N -bis(benzoyl) 1, 4-naphthalenedicarboxylic acid dihydrazide (NABH). A comparison on crystallization of the pure PLLA and PLLA/NABH revealed that the NABH as effective heterogeneous nucleation sites enhanced PLLA𠏋 crystallization, and an increase of NABH loading was able to further accelerate crystallization rate of PLLA; whereas a faster cooling rate was not conducive to PLLA𠏋 crystallization, but the appearance of obvious crystallization peak upon cooling at 30şC/min confirmed the advanced enhancing role of NABH for PLLA crystallization again. The investigation on influence of the final melting temperature on the crystallization behavior of PLLA showed that the 170 şC was optimum final melting temperature for enhancing crystallization, even the onset crystallization temperature of PLLA/NABH were higher than 150şC. The melting processes of PLLA/NABH after different crystallization not only could reflect the previous crystallization, but also depended on crystallization temperature and heating rate. Thermal decomposition results showed that the existence of NABH slightly weakened thermal stability of PLLA, and the maximum difference in onset thermal decomposition temperature was only 9.4şC comparing with the pure PLLA. However, the presence of NABH in PLLA matrix seriously weakened optical property.

A solid microneedle array can be used for “poke and flow” transdermal delivery of a drug, which involves the infusion or diffusion of a drug through pores in the skin that were created by the microneedle array. In this paper, solid microneedle arrays were created out of the polymer RESOMER LG 855 S—poly(l-lactide-co-glycolide) using injection molding. Scanning electron microscopy revealed that the microneedle in the injection-molded four-by-one microneedle array closely matched the dimensions that were used for injection molding. X-ray photoelectron spectroscopy revealed that the carbon bonding in the microneedle material matched that expected for poly(l-lactide-co-glycolide). The reduced elastic modulus of the microneedle material, 6.04 ± 0.17 GPa, was noted to be appropriate for skin penetration applications. The microneedle array was used for the delivery of the model drug methyl blue to surgically discarded human underarm skin. These results suggest that injection molding of RESOMER LG 855 S—poly(l-lactide-co-glycolide) may be an appropriate approach for large-scale manufacturing of solid microneedles.

Among drug delivery systems, polymer microspheres have been proved to be the most promising carriers during the past several years. In this paper we describe the preparation of poly(L-lactide-co-gl...

The use of bioabsorbable threads has become a common minimally invasive technique for the nonsurgical lifting of sagged facial tissues. It entails the passage of barbed threads that form a support structure under the skin of the face and neck to mechanically reposition sagging tissue. Poly(L-lactide-co-ε-caprolactone) has long been used as absorbable sutures and as such has a well-demonstrated efficacy and safety profile. This biomaterial also has a well-defined biocompatibility and degradation profile. All studies reviewed in this paper show that thread lifting with absorbable barbed threads is an effective and well-tolerated procedure for correction of ptosis in facial and neck soft tissue and is associated with minor and reversible adverse effects. Most patients and surgeons consider the procedure satisfactory, with good to excellent results. This publication reviews the literature and clinical data supporting the degradation, absorbability, biocompatibility, safety, and effectiveness of these threads when used for tissue repositioning and facial rejuvenation procedures.

In this work, flexible biocomposites were prepared through melt blending using flexible poly(L-lactide)- b-polyethylene glycol-b-poly(L-lactide) (PLLA-PEG-PLLA) as a matrix and microcrystalline cellulose (MCC) as a filler. The effects of the addition of MCC on the thermal, morphological and mechanical properties of PLLA-PEG-PLLA/MCC biocomposites were investigated compared to PLLA/MCC biocomposites. Thermal stability of both PLLA and PLLA-PEG-PLLA from thermogravimetric analysis (TGA) was improved by MCC blending. Scanning electron microscopy (SEM) of the biocomposites exhibited good phase compatibility between PLLA-PEG-PLLA matrix-MCC filler. From tensile tests, the stress and strain at break of the PLLA/MCC and PLLA-PEG-PLLA/MCC biocomposite films decreased while the Young’s modulus increased as the MCC content increased. The strain at break of PLLA-based and PLLA-PEG-PLLA based biocomposite films containing 20 wt.% MCC were 2% and 162%, respectively. Thus, the PLLA-PEG-PLLA/MCC biocomposites have potential to be used as flexible bioplastics for packaging applications.

Poly(l-lactide) (PLLA) as one of the most well-known biodegradable polyesters has been studied extensively for bone tissue engineering. If being properly programmed, scaffolds from PLLA can also be...

Porous microspheres have interconnecting external and internal pore structure resulting in enormous specific surface area and have drawn attention for drug delivery. In this work, poly(l-lactide-co...

The aim of this study is to develop self-standing, ultrathin film, nanosheets with high magnetic response for use in a medical device that can be migrated to a target location in the body by using an external magnetic field. First, iron oxide nanoparticles are synthesized by either the sol-gel method or thermal decomposition. The resulting magnetic properties of the nanoparticles show that the thermal decomposition method provides a greater saturation magnetization value than the sol-gel method. Next, the nanoparticles obtained by the thermal decomposition method are embedded into nanosheets of poly(L-lactide) at varying concentrations. Embedding of the nanoparticles in the composite nanosheets is achieved by the application of an external magnetic field. The composite nanosheets are then characterized. The thickness of the nanosheet increases, and the nanoparticles are well dispersed, with an increase in poly (L-lactide) concentration. The NP-embedded nanosheets are imaged by transmission electron microscopy, which reveals thin, long aggregates aligned in collinear line features. X-ray diffraction results indicate that the magnetic hard axis of the nanoparticles in the nanosheets is aligned in parallel to the plane of the nanosheet by magnetic field application during nanosheet preparation. In addition, the nanosheets at high poly (L-lactide) concentrations that had been subjected to a magnetic field during preparation show a slightly greater magnetic response compared with both nanosheets without magnetic field exposure and nanosheets prepared at low poly (L-lactide) concentrations.

Designing laboratory-scale degradation experiments for polymer-based biomaterials is crucial for the development of safe and functional implants, in particular regarding high molecular weight polyesters. Within this work, we compared accelerated degradation of solvent cast HMW-PLLA and HMW-P3HB films at 55 °C (16 weeks) with enzyme-associated (proteinase K and lipases) real-time degradation at 37 °C (108 weeks). During real-time degradation, PLLA showed mass loss up to 83%, in contrast to accelerated conditions, where no changes occurred. Moreover, we observed wave-shape development of crystallinity for PLLA and PHB for both degradation conditions applied, whereby PLLA χ value nearly doubled to up to 75%. These results were used to develop a correlation model based on molecular weight decrease and were furthermore discussed in light of a detailed literature review. In summary, real-time in vitro studies could be adapted to accelerated protocols providing the same limiting conditions such as molecular weight and initial crystallinity are given.

Binary and ternary poly (L-lactide) (PLLA) based nanocomposites, containing nanolignin (1% wt.) and different metal oxide nanoparticles (0.5% wt., Ag2O, TiO2, WO3, Fe2O3 and ZnFe2O4) were realized ...

This work was aimed at synthesizing the N, N -isophthalic bis(piperonylic acid) dihydrazide (PAID) to be as a new crystallization accelerator for poly(L-lactide) (PLLA), and a detailed investigations of the non-isothermal crystallization, melting behavior, thermal decomposition behavior and mechanical properties of PLLA nucleated by PAID were performed applying differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and electronic tensile tester. The melt-crystallization proved that the PAID could act as a heterogeneous nucleating agent to significantly promote the crystallization in cooling, even the crystallization was still able to be accelerated upon the fast cooling at 50 oC/min. The final melt temperature was another crucial factor for PLLA�s melt crystallization, and when the final melt temperature was 170 oC, the onset crystallization temperature and melt-crystallization enthalpy was almost up to 150 oC and 56.8 J/g upon cooling of 1 oC/min, respectively. Furthermore, the chemical nucleation was proposed to be the nucleation mechanism of PAID for PLLA via the preliminary theoretical calculation. For the cold-crystallization, the addition of PAID exhibited an inhibition for the crystallization of PLLA, but the total crystallization process depended on the heating rate and PAID concentration. The single melting peak after cooling of 1 oC/min indicated that the crystallization had been thoroughly completed in cooling. Additionally, the single melting peak with different locations after full crystallization resulted from the different crystallization temperatures. A comparison in the onset decomposition temperature implied that the presence of PAID only slightly decreased the thermal stability of PLLA. The mechanical testing showed that, in contrast with the elongation at break, the existence of PAID enhanced the tensile strength of PLLA.

Poly(L-lactide-co-glycolide-co-e-caprolactone) (PLLGC) and 1,4-butanediamine modified maleated poly(D,L-lactide-co-glycolide) (BMPLGA) were both synthesized by ring-opening polymerization with stan...

A comparison of poly(l-lactide) (PLLA) and poly(l-lactide)/hydroxyapatite (PLLA/HAp) biocomposite microspheres fabricated by emulsion solvent evaporation technique designed for laser sintering (LS) applications is presented. Key properties such as thermal and structural as well as geometry, size distribution and powder flowability, which are crucial for this technique, are characterized to validate the applicability of microspheres for LS. The biocomposite microspheres turns out to be more suitable for the LS process than PLLA due to the higher thermal stability, broader sintering window and higher powder flowability.

Fast scanning calorimetry (FSC) is an effective analytical tool to characterize the thermal properties of polymers. Heating rates up to 100 000 K/s allow studies at time scales inaccessible with conventional calorimeters, whose rates are typically less than about 0.5 K/s. Recent studies have successfully demonstrated methods for obtaining quantitative analysis of thermal properties of polymer samples using chip-based FSC. Therefore very small sample sizes, such as particles or nonwovens, can be characterized. In this study, we investigated the thermal properties of poly(L-lactide) PLLA with FSC compared to the results from standard DSC methods. PLLA specimens were fabricated via solution casting and needle electrospinning. The results suggest a significant influence of heating rates on the melting temperature of PLLA. The results show that different fabrication methods lead to changes in crystallinity and that FSC results are not completely comparable with standard DSC measurements.

Poly(l-lactide)-b-polyethylene glycol-b-poly(l-lactide) (PLLA-PEG-PLLA) is found to be more flexible than PLLA due to the flexibility of PEG middle blocks. Melt flow and mechanical properties of PLLA-PEG-PLLA were improved through post melt blending with a chain extender (CE). In this work, in situ chain-extended PLLA-PEG-PLLAs were synthesized by ring-opening polymerization in the presence of Joncryl® CE. The influence of CE content (1.0, 2.0, and 4.0 phr) on the gel content, melt flow index (MFI), thermal properties, and mechanical properties of the obtained in situ chain-extended PLLA-PEG-PLLAs was investigated. The gel content of in situ chain-extended PLLA-PEG-PLLA increased while the MFI and degree of crystallinity significantly decreased with increasing CE content. The in situ chain-extended PLLA-PEG-PLLA with 1.0 phr CE showed the best tensile properties. The extensibility of in situ chain-extended PLLA-PEG-PLLA films decreased when the CE contents were higher than 1.0 phr. These in situ chain-extended PLLA-PEG-PLLA films can be used as highly flexible bioplastics.

Poly( l-lactide-co-ε-caprolactone) is an environment-friendly shape memory polymer. Molecular dynamics method was used to study the shape memory effect and mechanical properties of graphene oxide–reinforced poly( l-lactide-co-ε-caprolactone) to understand the microscopic mechanism. Two models containing dispersed graphene oxide were constructed. It is shown that the addition of graphene oxide causes the glass transition temperature of material to rise because of limitation on polymer activity. The uniaxial tensile properties of the composites were studied. The results exhibited that strength of composites depend on the interface state of the polymer and graphene oxide. The strength of the composite with covalent bond is much higher than that of another without the covalent bond between graphene oxide and poly( l-lactide-co-ε-caprolactone) generated. Stress softening effect was observed in the cross-linked composite in the glass state. Their uniaxial tension thermodynamic cycles were carried out to consider the shape memory effect of the composites. It is shown that graphene oxide–reinforced composites with different interactions exhibit fair shape memory effect in the direction of paralleling graphene oxide surface. In terms of the direction perpendicular to graphene oxide sheet, the fixed ratios of the composites decrease slightly about 1.64%–3.63%, and the recovery ratios of the composites with the covalent bond are higher than others about 3.22%–12.93%.

Poly(L-lactide (PLLA), nano-hydroxyapatite (nHA) and multi-walled carbon nanotube (MWCNTs) biodegradable scaffolds were produced through thermally induced phase separation (TIPS) and ultrasonically...

Nonwoven tubular bioresorbable matrices with an inner diameter of 1.1 mm were obtained by electroforming from solutions of poly (L-lactide) (PLA). Matrices were implanted into the abdominal aorta of rats as a tissue-engineering vascular implant for a period of 2 days to 16 months and showed high biocompatibility, nontoxicity, and pronounced atrombogenic properties. The total implant patency was 93%. Morphometric analysis of the dynamics of population of the matrix with cells showed that, for all observation periods in the outer half of the matrix wall, the number of cells prevails, which indicates the migration of cells from the connective tissue capsule surrounding the matrix. It is shown that two parallel processes occur in the matrix wall: bioresorption of PLA fibers and the formation of connective tissue. Complete bioresorption of matrices with replacement by native tissues, as well as formation of the endothelial and subendothelial layers, took place over the 16 months of the experiment. By this time, all the experimental animals in the reconstruction zone revealed an aneurysmal expansion that did not lead to rupture of the implant. To prevent the development of such complications, it is necessary to develop a method for additional strengthening of the matrix wall.

A biocompatible zinc (II) complex based on a tetradentate N,N,O,O-type salen ligand was synthesized, characterized and used for the solvent-free ring-opening polymerization (ROP) of L-lactide in bu...

In this study, poly(ε-caprolactone) (PCL) has been blended with a more hydrophilic poly(ethylene glycol) (PEG) and with a biocompatible block-co-polymer: poly(L-lactide-co-ε-caprolactone-co-glycolide) (PLCG) in order to improve hydrophilicity, biocompatibility and biodegradability of PCL. PCL and the blend solutions were subjected to electrospinning to produce nanofiber scaffolds by the addition of only 1 wt% of PEG and PLCG either singly or in combination in PCL to retain the mechanical properties of the scaffolds. PCL-PEG-PLCG ternary and two binary (PCL-PEG and PCL-PLCG) blend nanofiber scaffolds have been prepared for comparison. The resulting nanofibers showed a smooth and flaw-free surface and the diameter of the nanofibers displayed a normal distribution. The PCL-PEG nanofiber scaffold showed improved hydrophilicity [water contact angle (WCA) ∼84°] over pristine PCL (WCA ∼127°); while PCL-PLCG and PCL-PEG-PLCG scaffolds exhibited absolute wetting by water, likely due to high porosity.

Recently, we proposed a simple method to derive the size of critical secondary nuclei formed on the growth front of lamellar crystals via the nucleation kinetics of random copolymers and polymer bl...

Despite considerable efforts, however, the exclusive stereocomplex (SC) formation in neat high-molecular-weight (high-MW) poly(l-lactide)/poly(d-lactide) (PLLA/PDLA) blends remains challenging. Thi...

The next‐generation bioresorbable polymeric stents are undergoing continual research and development, especially how to control and optimize their degradation behaviors. The aim of this paper is to study the properties of a poly(l‐lactide) (PLLA) tube over accelerated degradation in vitro. Spherical nanoindentation was particularly adopted to measure the mechanical properties of PLLA tube; while differential scanning calorimetry and gel permeation chromatography were used for crystallinity and molecular weight measurements. Overall, the material degradation was captured by the local stress‐strain response obtained with spherical nanoindentation, and further confirmed with chemical analyses. The results are particularly useful for development of bioresorbable polymeric stents with improved performance.

Polymer blending is an attractive method for producing new polymer materials with excellent properties. In this work the blended polymers were prepared from poly(L-lactide-co-glycolide-co-e-caprola...

Polymeric/ceramic composite scaffolds that are biocompatible and biodegradable are widely used for tissue engineering applications. In this work a series of poly(L-lactide-co-glycolide-co-e-caprola...

The technique of thermally induced phase separation (TIPS) is favorable for the fabrication of a porous scaffold due to a number of advantages. In this work the poly(L-lactide-co-glycolide-co-e-cap...

As cartilage is incapable of self-healing upon severe degeneration because of the lack of blood vessels, cartilage tissue engineering is gaining importance in the treatment of cartilage defects. This study was designed to improve cartilage tissue regeneration by expressing tissue transglutaminase variant 2 (TGM2_v2) in mesenchymal stem cells (MSC) derived from bone marrow of rats. For this purpose, rat MSCs transduced with TGM2_v2 were grown and differentiated on three-dimensional polybutylene succinate (PBSu) and poly-l-lactide (PLLA) blend scaffolds. The transduced cells could not only successfully express the short form transglutaminase-2, but also deposited the protein onto the scaffolds. In addition, they could spontaneously produce cartilage-specific proteins without any chondrogenic induction, suggesting that TGM2_v2 expression provided the cells the ability of chondrogenic differentiation. PBSu:PLLA scaffolds loaded with TGM2_v2 expressing MSCs could be used in repair of articular cartilage defects.

Blending of poly(l-lactide) and poly(d-lactide) (PLLA, PDLA) results in the formation of poly(lactide) stereocomplex crystallites (SC). For the preparation method, numerous reports employed solution mixing and stirring to receive a product with uniform performance. However, the effect of stirring time during solution mixing on the subsequent crystallization behavior did not clear yet, and which is important for solution crystallization, casting and spinning. In this paper, linear PLLA and PDLA with various molecular weights were synthesized. The PLLA and PDLA solutions were mixed together and stirred for different times before casting. Results revealed that the structures of PLA SC and homochiral crystallites (HC) did not vary with change in the stirring time. More amount of content of SC with uniform structure and less amount of content of HC were produced in the specimens stirred for longer time. When the specimens crystallized either from the melt or from the melt-quenching, less amount of content of crystallites (total crystallinity of SC and HC) was produced and the melting temperature of SC and HC depressed in the specimens that were stirred for longer time. With the increase in molecular weights, the effect of stirring time on the crystallization behaviors declined. This investigation provides a route to tailor the crystallization behavior of PLLA/PDLA specimens.

Poly(l-lactide) (PLLA) is a renewable and completely biodegradable material. However, due to its semirigid molecular chain, asymmetric carbon atoms, and poor regularity of the molecular chain, PLLA...