Poly(lactic acid) blends in biomedical applications

Systemic Review of Biodegradable Nanomaterials in Nanomedicine

BACKGROUND

Nanomedicine is a field of science that uses nanoscale materials for the diagnosis and treatment of human disease. It has emerged as an important aspect of the therapeutics, but at the same time, also raises concerns regarding the safety of the nanomaterials involved. Recent applications of functionalized biodegradable nanomaterials have significantly improved the safety profile of nanomedicine.

OBJECTIVE

Our goal is to evaluate different types of biodegradable nanomaterials that have been functionalized for their biomedical applications.

METHOD

In this review, we used PubMed as our literature source and selected recently published studies on biodegradable nanomaterials and their applications in nanomedicine.

RESULTS

We found that biodegradable polymers are commonly functionalized for various purposes. Their property of being naturally degraded under biological conditions allows these biodegradable nanomaterials to be used for many biomedical purposes, including bio-imaging, targeted drug delivery, implantation and tissue engineering. The degradability of these nanoparticles can be utilized to control cargo release, by allowing efficient degradation of the nanomaterials at the target site while maintaining nanoparticle integrity at off-target sites.

CONCLUSION

While each biodegradable nanomaterial has its advantages and disadvantages, with careful design and functionalization, biodegradable nanoparticles hold great future in nanomedicine.

Tailoring synthetic polymeric biomaterials towards nerve tissue engineering: a review

The nervous system is known as a crucial part of the body and derangement in this system can cause potentially lethal consequences or serious side effects. Unfortunately, the nervous system is unable to rehabilitate damaged regions following seriously debilitating disorders such as stroke, spinal cord injury and brain trauma which, in turn, lead to the reduction of quality of life for the patient. Major challenges in restoring the damaged nervous system are low regenerative capacity and the complexity of physiology system. Synthetic polymeric biomaterials with outstanding properties such as excellent biocompatibility and non-immunogenicity find a wide range of applications in biomedical fields especially neural implants and nerve tissue engineering scaffolds. Despite these advancements, tailoring polymeric biomaterials for design of a desired scaffold is fundamental issue that needs tremendous attention to promote the therapeutic benefits and minimize adverse effects. This review aims to (i) describe the nervous system and related injuries. Then, (ii) nerve tissue engineering strategies are discussed and (iii) physiochemical properties of synthetic polymeric biomaterials systematically highlighted. Moreover, tailoring synthetic polymeric biomaterials for nerve tissue engineering is reviewed.

Super tough poly(lactic acid) blends: a comprehensive review

Poly(lactic acid) or poly(lactide) (PLA) is a renewable, bio-based, and biodegradable aliphatic thermoplastic polyester that is considered a promising alternative to petrochemical-derived polymers in a wide range of commodity and engineering applications. However, PLA is inherently brittle, with less than 10% elongation at break and a relatively poor impact strength, which limit its use in some specific areas. Therefore, enhancing the toughness of PLA has been widely explored in academic and industrial fields over the last two decades. This work aims to summarize and organize the current development in super tough PLA fabricated via polymer blending. The miscibility and compatibility of PLA-based blends, and the methods and approaches for compatibilized PLA blends are briefly discussed. Recent advances in PLA modified with various polymers for improving the toughness of PLA are also summarized and elucidated systematically in this review. Various polymers used in toughening PLA are discussed and organized: elastomers, such as petroleum-based traditional polyurethanes (PUs), bio-based elastomers, and biodegradable polyester elastomers; glycidyl ester compatibilizers and their copolymers/elastomers, such as poly(ethylene-co-glycidyl methacrylate) (EGMA), poly(ethylene-n-butylene-acrylate-co-glycidyl methacrylate) (EBA-GMA); rubber; petroleum-based traditional plastics, such as PE and PP; and various biodegradable polymers, such as poly(butylene adipate-co-terephthalate) (PBAT), polycaprolactone (PCL), poly(butylene succinate) (PBS), and natural macromolecules, especially starch. The high tensile toughness and high impact strength of PLA-based blends are briefly outlined, while the super tough PLA-based blends with impact strength exceeding 50 kJ m⁻² are elucidated in detail. The toughening strategies and approaches of PLA based super tough blends are summarized and analyzed. The relationship of the properties of PLA-based blends and their morphological parameters, including particle size, interparticle distance, and phase morphologies, are presented.

PLA is a renewable, bio-based, and biodegradable aliphatic thermoplastic polyester that is considered a promising alternative to petrochemical-derived polymers in a wide range of commodity and engineering applications.

Leucine-activated nanohybrid biofilm for skin regeneration via improving cell affinity and neovascularization capacity

Nanohybrids containing amino acid are doped into biodegradable nanofibrous membranes, which improves the cell affinity, the migration and growth of fibroblasts, and the neovascularization capacity, comprehensively accelerating a rapid wound healing.

Engineered 3D Polymer and Hydrogel Microenvironments for Cell Culture Applications

The realization of biomimetic microenvironments for cell biology applications such as organ-on-chip, in vitro drug screening, and tissue engineering is one of the most fascinating research areas in the field of bioengineering. The continuous evolution of additive manufacturing techniques provides the tools to engineer these architectures at different scales. Moreover, it is now possible to tailor their biomechanical and topological properties while taking inspiration from the characteristics of the extracellular matrix, the three-dimensional scaffold in which cells proliferate, migrate, and differentiate. In such context, there is therefore a continuous quest for synthetic and nature-derived composite materials that must hold biocompatible, biodegradable, bioactive features and also be compatible with the envisioned fabrication strategy. The structure of the current review is intended to provide to both micro-engineers and cell biologists a comparative overview of the characteristics, advantages, and drawbacks of the major 3D printing techniques, the most promising biomaterials candidates, and the trade-offs that must be considered in order to replicate the properties of natural microenvironments.

Bone Healing in the Presence of a Biodegradable PBS-DLA Copolyester and Its Composite Containing Hydroxyapatite

The healing process of the fractured bone in a presence of poly(butylene succinate-butylene dilinoleate) (PBS-DLA) copolymer containing nanosized hydroxyapatite (HAP) particles has been investigated. The PBS-DLA material containing PBS hard segments and DLA soft segments (50:50 wt %) was used to prepare a polymer/ceramic composite with 30 wt % HAP. A new PBS-DLA copolymer showed a high elasticity of 500% and 15 MPa tensile strength. Addition of HAP improved tensile strength up to 25 MPa while high elasticity has been preserved going down only to 300% of elongation at break. A polymer nanocomposite was fabricated into small elastic polymer rods 15 mm long and 1 × 2 mm in cross section and used for tibia bone fixation in rats. Mallory trichrome staining indicated that new biodegradable copolymers and its composite containing HAP have triggered the most advanced bone healing of all tested materials, thus indicating their high potential for bone tissue engineering and repair.

Clinical pilot study to evaluate the neovaginal PACIENA prosthesis® for vaginoplasty without skin grafts in women with vaginal agenesis

Background

To evaluate the feasibility and clinical outcomes of vaginoplasties using a neovaginal polylactic acid prosthesis made with 3-dimensional (3D) printing technology as an intraneovaginal mould.

Methods

This was an interventionist, prospective, and multicentre clinical pilot investigation of a sanitary product (PACIENA prosthesis®) aiming to recruit and operate on 8 patients over 6 months with a follow-up period of 6 months. Only six patients with Rokitansky syndrome and one patient with Morris syndrome (7 patients in total) were operated on in two university hospitals: “La Fe”, Valencia (H1) and “Arrixaca”, Murcia (H2). Interventions: Extensive surgical dissection of a defined space between the urethra and bladder in the front and of the rectum in the back as well as insertion of the PACIENA prosthesis® covered with Interceed® were performed. After 12 days, the prosthesis was changed to the silicone-covered version for daily application.

Results

In the 6 patients with Rokitansky syndrome (86%), the primary endpoint (satisfactory vaginal outcome in terms of appearance, function, and sensation without relevant additional morbidity) was achieved, although only 2 patients (28%) were sexually active at the end of 6 months of follow-up. The patient with Morris syndrome withdrew from the study after 1 month. Patients without bacterial colonization showed positive Schiller tests at 1 month, and subsequent biopsies showed adequate keratinization and epidermization. Epithelization and iodopositivity were delayed in the patients who developed inflammatory granulomas.

Conclusions

Good anatomical and functional results can be achieved with the PACIENA prosthesis® for vaginoplasties without skin grafts. However, adequate patient selection and education, good surgical techniques and haemostasis, postoperative support, and prevention of bacterial colonization are important.

Trial registration

This clinical study was approved by the Ethical Clinical Investigation Committee of San Juan University Hospital on September 27, 2016, to be conducted in the participating centres; it was authorized by the Spanish Agency of Medicines and Health Products (AEMPS) on April 24, 2017 (exp. no. 585/16/EC), to be carried out in that hospitals.

A Perspective on Polylactic Acid-Based Polymers Use for Nanoparticles Synthesis and Applications

Polylactic acid (PLA)-based polymers are ubiquitous in the biomedical field thanks to their combination of attractive peculiarities: biocompatibility (degradation products do not elicit critical responses and are easily metabolized by the body), hydrolytic degradation in situ, tailorable properties, and well-established processing technologies. This led to the development of several applications, such as bone fixation screws, bioresorbable suture threads, and stent coating, just to name a few. Nanomedicine could not be unconcerned by PLA-based materials as well, where their use for the synthesis of nanocarriers for the targeted delivery of hydrophobic drugs emerged as a new promising application. The purpose of the here presented review is two-fold: on one side, it aims at providing a broad overview of PLA-based materials and their properties, which allow them gaining a leading role in the biomedical field; on the other side, it offers a specific focus on their recent use in nanomedicine, highlighting opportunities and perspectives.

Biodegradable atrial septal defect occluders: A current review

Atrial septal defect (ASD) is a common structural congenital heart disease. With the development of interventional closure devices and transcatheter techniques, interventional closure therapy has become the most well-accepted therapeutic alternative worldwide, as it offers a number of advantages over conventional therapies such as improved safety, easier operation, lower complication rates and invasiveness, and shorter anesthetic time and hospitalizations. During the past decades, various types of occluders based on nondegradable shape memory alloys have been used in clinical applications. Considering that the permanent existence of foreign nondegradable materials in vivo can cause many potential complications in the long term, the research and development of biodegradable occluders has emerged as a crucial issue for interventional treatment of ASD. This review aims to summarize partially or fully biodegradable occlusion devices currently reported in the literature from the aspects of design, construction, and evaluation of animal experiments. Furthermore, a comparison is made on the advantages and disadvantages of the materials used in biodegradable ASD occlusion devices, followed by an analysis of the problems and limitations of the occlusion devices. Finally, several strategies are proposed for future development of biodegradable cardiac septal defect occlusion devices. STATEMENT OF SIGNIFICANCE: Although occlusion devices based on nondegradable alloys have been widely used in clinical applications and saved numerouspatients, biodegradable occlusion devices may offer some advantages such as fewer complications, acceptable biocompatibility, and particularly temporary existence, thereby leaving "native" tissue behind, which will certainly become the development trend in the long term. This review summarizes almost all partially or fully biodegradable occlusion devices currently reported in the literature from the aspects of design, construction, and evaluation of animal experiments. Furthermore, a comparison is made on the advantages and disadvantages of the materials used in biodegradable ASD occlusion devices, followed by an analysis of the problems and limitations of the occlusion devices. Finally, several strategies are proposed for future development of biodegradable cardiac septal defect occlusion devices.

Fabrication of topologically anisotropic microparticles and their surface modification with pH responsive polymer brush

This paper describes the fabrication of topologically anisotropic cup shaped polylactide (PLA)/poly[methyl methacrylate‑co‑2‑(2‑bromopropionyloxy) ethyl methacrylate] (poly(MMA-co-BEMA)) (75/25) composite particles of ~6 μm size using electrojetting technique. An attempt was made to understand the mechanism of cup shape formation from the miscible blend by electrojetting. Both the solution parameters and the processing conditions affected the particles' shape which can be varied from cup shaped to discoid type. Surface initiated atom transfer radical polymerization (ATRP) of stimuli responsive DMAEMA (2‑dimethylamino ethyl methacrylate) was subsequently carried out for 1 h onto the surface of cup shaped particles to observe pH responsiveness of the modified anisotropic particles. Interestingly, morphology of the cup shaped particles was changed to elongated cup which did show significant swelling under acidic pH (swelling ratio:~1.6) and enhanced dye adsorption at specific pH as observed by optical microscope and confocal laser scanning microscope implying that DMAEMA polymerization happened onto the surface of the composite microparticles. The Raman microscopy and FTIR spectra obtained from the particles after polymerization further confirmed the immobilization of pH responsive poly(DMAEMA) brushes onto the cup shaped particles which may potentially function as triggered/targeted drug delivery vehicles. Moreover, the brush modified cup shaped particles were found to be two times more efficient in adsorbing dye compared to disc shaped one indicating a clear advantage of using cup shaped particles over other shapes for immobilizing/adsorbing charged species e.g. sensitive biomolecules.

Morphology, molecular interactions and H2O diffusion in a poly(lactic-acid)/graphene composite: A vibrational spectroscopy study

A composite system made of poly(l-lactic acid) (PLLA) and graphene nanoplatelets (GNP) was investigated by Raman and FTIR spectroscopy. Two compositions were prepared and characterized in comparison to the pristine polymer: they contained, respectively, 0.25 and 0.75 wt% of the nanofiller. The study was focused on the morphological properties of the system, and, in particular, on the level of dispersion and the homogeneity obtainable with the adopted preparation protocol. Furthermore, the possible molecular interactions taking place between the nanofiller and the polymer matrix were considered. Both the above issues were investigated by confocal Raman spectroscopy, with the aid of first-principle calculations to strengthen the spectral interpretation. Finally, the effect of the nanofiller on water diffusion was investigated by time-resolved FTIR spectroscopy, which provided accurate equilibrium and kinetic data, as well as molecular level information on the penetrant-to-substrate interactions. It was found that, for a 0.25 wt% composition, the adopted preparation protocol allowed us to achieve a dispersion at the level of single nanoplatelets, while for a 0.75 wt% composition, the GNP's aggregate into a co-continuous phase. PLLA/GNP interactions were detected by Raman spectroscopy, producing a detectable perturbation of the PLLA conformational equilibrium. Both the diffusivities and the equilibrium water uptake were found to decrease significantly by increasing the filler content.

Faster Release of Lumen-Loaded Drugs than Matrix-Loaded Equivalent in Polylactic Acid/Halloysite Nanotubes

Nanocomposite-based drug delivery systems with intrinsic controlled release properties are of great interest in biomedical applications. We report a novel polylactic acid (PLA)/halloysite nanotube (HNT) nanocomposite-based drug delivery system. PLA/HNT nanocomposites have shown immense potential for use in biomedical applications due to their favorable cyto- and hemo-compatibility. The objective of this study was to evaluate the release of active pharmaceutical ingredients (API) from PLA/HNT composites matrix and the effect of preloading the API into the lumen of the HNT on its release profile. Aspirin was used in this study as a model drug as it is a common nonsteroidal anti-inflammatory and antiplatelet agent widely used for various medical conditions. These two types of drug-loaded PLA/HNT nanocomposites were characterised by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR), surface wettability and mechanical testing. Statistical analysis was conducted on numerical data. Drug entrapment and in vitro drug release studies were conducted using UV spectrophotometry. Results indicate that aspirin was successfully loaded into the lumen of HNT, which resulted in the sustained release of aspirin from the nanocomposites. Furthermore, the addition of HNT into the polymer matrix increased the mechanical properties, indicating its suitability as a drug-eluting reinforcing agent.

Effect of Poly(styrene-ran-methyl acrylate) Inclusion on the Compatibility of Polylactide/Polystyrene-b-Polybutadiene-b-Polystyrene Blends Characterized by Morphological, Thermal, Rheological, and Mechanical Measurements

A poly(styrene-ran-methyl acrylate) (S-MA) (75/25 mol/mol), synthesized by surfactant-free emulsion copolymerization, was used as a compatibilizer for polystyrene-b-polybutadiene-b-polystyrene (SBS)-toughened polylactide (PLA) blends. Upon compatibilization, the blends exhibited a refined dispersed-phase morphology, a decreased crystallinity with an increase in their amorphous interphase, improved thermal stability possibly from the thicker, stronger interfaces insusceptible to thermal energy, a convergence of the maximum decomposition-rate temperatures, enhanced magnitude of complex viscosity, dynamic storage and loss moduli, a reduced ramification degree in the high-frequency terminal region of the Han plot, and an increased semicircle radius in the Cole–Cole plot due to the prolonged chain segmental relaxation times from increases in the thickness and chain entanglement degree of the interphase. When increasing the S-MA content from 0 to 3.0 wt %, the tensile properties of the blends improved considerably until 1.0 wt %, above which they then increased insignificantly, whereas the impact strength was maximized at an optimum S-MA content of ~1.0 wt %, hypothetically due to balanced effects of the medium-size SBS particles on the stabilization of preexisting crazes and the initiation of new crazes in the PLA matrix. These observations confirm that S-MA, a random copolymer first synthesized in our laboratory, acted as an effective compatibilizer for the PLA/SBS blends.

Synthesis and Applications of Biopolymer Composites

In recent years, there has been a growing demand for a clean and pollution-free environment and an evident target to minimizing fossil fuel [...].

One step bulk modification of poly(L-lactic acid) composites with functional additives to improve mechanical and biological properties for cardiovascular implant applications

Poly(L-lactic acid) (PLLA) has been widely used as a promising biomaterial in biomedical applications due to its biodegradability and high mechanical strength. However, because of the inherent brittleness, low impact resistance, and weak thermal stability of PLLA, the modification process is usually required to utilize it for biomedical devices. Furthermore, acidic byproducts resulting from the hydrolysis of PLLA after implantation reduce the pH of the surrounding environment and cause inflammatory responses in the implanted area, leading to the failure of their clinical applications. To this end, here, we demonstrate a novel modification process for the PLLA composite with various functional additives, such as cis-aconitic anhydride (AA), triacetin (TA), isosorbide derivative (ISB), and/or Pluronic® F127 (F). The modified PLLA composite with TA and F (PLLA/TF) showed significantly improved elongation at break and Young's modulus and retained tensile strength. Moreover, incorporating magnesium hydroxide (MH) nanoparticles (PLLA/TFMH) significantly reduced acid-induced inflammation responses caused by the acidic degradation products of PLLA. Reduced plasma protein adsorption was observed in the PLLA/TFMH. These results suggest that the one step bulk modification of biodegradable PLLA using TA, F, and MH will have great potential in cardiovascular implant applications.

Application of radially grown ZnO nanowires on poly-l-lactide microfibers complexed with a tumor antigen for cancer immunotherapy

Zinc oxide (ZnO)-based nanocomposites have shown promising potential for various biomedical applications, including vaccine development, owing to their multifunctionality and biocompatibility. Here, we synthesized radially grown ZnO nanowires (NWs) on poly-l-lactic acid (PLLA) microfibers with unique 3-dimensional structure and applied them as therapeutic cancer vaccines. This inorganic-organic hybrid nanocomposite has mild cellular toxicity but efficiently delivers a tumor antigen into dendritic cells, cellular bridges between innate and adaptive immunity, to stimulate them to express inflammatory cytokines and activation surface markers. We also demonstrated that the hybrid nanocomposites successfully induce tumor antigen-specific cellular immunity and significantly inhibit tumor growth in vivo. ZnO NWs on PLLA fibers systemically reduced immune suppressive TReg cells and enhanced the infiltration of T cells into tumor tissues, compared to mice immunized with PLLA fibers coated with the antigen. Our current findings open a new avenue in extending the biomedical application of inorganic metal oxide-inert organic hybrid nanocomposites as a novel vaccine platform.

A Highly Elastic and Autofluorescent Poly(xylitol-dodecanedioic Acid) for Tissue Engineering

In spite of the vast research on developing a highly elastic polymer for tissue regeneration, using a renewable resource and a simple, environment-friendly synthesis route to synthesize an elastic polymer has not been successfully achieved yet. The objective of this study was to use a simple melt condensation polymerization method to develop an elastic polymer for tissue regeneration applications. A nature-derived renewable, nontoxic, and inexpensive monomer, xylitol, and a cross-linking agent, dodecanedioic acid, were used to synthesize the new polymer named poly(xylitol-dodecanedioic acid) (PXDDA). Its physicochemical and biological properties were fully characterized. Fourier transform infrared (FTIR) results confirmed the formation of ester bonding in the polymer structure, and thermal analysis results demonstrated that the polymer was completely amorphous. The polymer is highly elastic. Increasing the molar ratio of dodecanedioic acid resulted in lower elasticity, higher hydrophobicity, and lower glass transition temperature. Further, the polymer degradation rate and in vitro dye release from the polymer also became slower when the amount of dodecanedioic acid in the composite increased. Biocompatibility studies showed that both the polymeric materials and the degraded products of the polymer did not show any toxicity. Instead, this new polymer significantly promoted cell adhesion and proliferation, compared to a widely used polymer, poly(lactic acid), and tissue culture plates. Interestingly, the PXDDA polymer demonstrated autofluorescent properties. Overall, these results suggest that a new, elastic, biodegradable polymer has been successfully synthesized, and it holds great promise for biomedical applications in drug delivery and tissue engineering.

Electrospun Conducting and Biocompatible Uniaxial and Core-Shell Fibers Having Poly(lactic acid), Poly(ethylene glycol), and Polyaniline for Cardiac Tissue Engineering

Electroactive and biocompatible fibrous scaffolds have been prepared and characterized using polyaniline (PAni) doped with dodecylbenzenesulfonic acid (DBSA) combined with poly(lactic acid) (PLA) and PLA/poly(ethylene glycol) (PEG) mixtures. The composition of simple and core-shell fibers, which have been obtained by both uniaxial and coaxial electrospinning, respectively, has been corroborated by Fourier-transform infrared and micro-Raman spectroscopies. Morphological studies suggest that the incorporation of PEG enhances the packing of PLA and PAni chains, allowing the regulation of the thickness of the fibers. PAni and PEG affect the thermal and electrical properties of the fibers, both decreasing the glass transition temperature and increasing the electrical conductivity. Interestingly, the incorporation of PEG improves the PAni-containing paths associated with the conduction properties. Although dose response curves evidence the high cytotoxicity of PAni/DBSA, cell adhesion and cell proliferation studies on PLA/PAni fibers show a reduction of such harmful effects as the conducting polymer is mainly retained inside the fibers through favorable PAni···PLA interactions. The incorporation of PEG into uniaxial fibers resulted in an increment of the cell mortality, which has been attributed to its rapid dissolution into the culture medium and the consequent enhancement of PAni release. In opposition, the delivery of PAni decreases and, therefore, the biocompatibility of the fibers increases when a shell coating the PAni-containing system is incorporated through coaxial electrospinning. Finally, morphological and functional studies using cardiac cells indicated that these fibrous scaffolds are suitable for cardiac tissue engineering applications.

Poly(2-isopropyl-2-oxazoline)-b-poly(lactide) (PiPOx-b-PLA) Nanoparticles in Water: Interblock van der Waals Attraction Opposes Amphiphilic Phase Separation

Poly(2-isopropyl-2-oxazoline)-b-poly(lactide) (PiPOx-b-PLA) diblock copolymers comprise two miscible blocks: the hydrophilic and thermosensitive PiPOx and the hydrophobic PLA, a biocompatible and biodegradable polyester. They self-assemble in water, forming stable dispersions of nanoparticles with hydrodynamic radii (R h) ranging from ∼18 to 60 nm, depending on their molar mass, the relative size of the two blocks, and the configuration of the lactide unit. Evidence from 1H nuclear magnetic resonance spectroscopy, light scattering, small-angle neutron scattering, and cryo-transmission electron microscopy indicates that the nanoparticles do not adopt the typical core-shell morphology. Aqueous nanoparticle dispersions heated from 20 to 80 °C were monitored by turbidimetry and microcalorimetry. Nanoparticles of copolymers containing a poly(dl-lactide) block coagulated irreversibly upon heating to 50 °C, forming particles of various shapes (R h ∼ 200-500 nm). Dispersions of PiPOx-b-poly(l-lactide) coagulated to a lesser extent or remained stable upon heating. From the entire experimental evidence, we conclude that PiPOx-b-PLA nanoparticles consist of a core of PLA/PiPOx chains associated via dipole-dipole interactions of the PLA and PiPOx carbonyl groups. The core is surrounded by tethered PiPOx loops and tails responsible for the colloidal stability of the nanoparticles in water. While the core of all nanoparticles studied contains associated PiPOx and PLA blocks, fine details of the nanoparticles morphology vary predictably with the size and composition of the copolymers, yielding particles of distinctive thermosensitivity in aqueous dispersions.

Hard Tissue Augmentation of Aged Bone by Means of a Tin-Free PLLA-PCL Co-Polymer Exhibiting in vivo Anergy and Long-Term Structural Stability

BACKGROUND

Due to aging, tissue regeneration gradually declines. Contemporary strategies to promote tissue-specific regeneration, in particular in elderly patients, often include synthetic material apt for implantation primarily aiming at upholding body functions and regaining appropriate anatomical and functional integrity.

OBJECTIVE

Biomaterials suitable for complex reconstruction surgical procedures have to exert high physicochemical stability and biocompatibility.

METHOD

A polymer made of poly-L-lactic acid and poly-ε-caprolactone was synthesized by means of a novel tin-free catalytic process. The material was tested in a bioreactor-assisted perfusion culture and implanted in a sheep model for lateral augmentation of the mandible. Histological and volumetric evaluation was performed 3 and 6 months post-implantation.

RESULTS

After synthesis the material could be further refined by cryogrinding and sintering, thus yielding differently porous scaffolds that exhibited a firm and stable appearance. In perfusion culture, no disintegration was observed for extended periods of up to 7 weeks, while mesenchymal stromal cells readily attached to the material, steadily proliferated, and deposited extracellular calcium. The material was tested in vivo together with autologous bone marrow-derived stromal cells. Up to 6 months post-implantation, the material hardly changed in shape with composition also refraining from foreign body reactions.

CONCLUSION

Given the long-term shape stability in vivo, featuring imperceptible degradation and little scarring as well as exerting good compatibility to cells and surrounding tissues, this novel biomaterial is suitable as a space filler in large anatomical defects.

Chitin Nanofibrils in Poly(Lactic Acid) (PLA) Nanocomposites: Dispersion and Thermo-Mechanical Properties

Chitin-nanofibrils are obtained in water suspension at low concentration, as nanoparticles normally are, to avoid their aggregation. The addition of the fibrils in molten PLA during extrusion is thus difficult and disadvantageous. In the present paper, the use of poly(ethylene glycol) (PEG) is proposed to prepare a solid pre-composite by water evaporation. The pre-composite is then added to PLA in the extruder to obtain transparent nanocomposites. The amount of PEG and chitin nanofibrils was varied in the nanocomposites to compare the reinforcement due to nanofibrils and plasticization due to the presence of PEG, as well as for extrapolating, where possible, the properties of reinforcement due to chitin nanofibrils exclusively. Thermal and morphological properties of nanocomposites were also investigated. This study concluded that chitin nanofibrils, added as reinforcing filler up to 12% by weight, do not properties alter the properties of the PLA based material; hence, this additive can be used in bioplastic items mainly exploiting their intrinsic anti-microbial and skin regenerating properties.

Establishment of a pulmonary epithelial barrier on biodegradable poly-L-lactic-acid membranes

Development of biocompatible and functional scaffolds for tissue engineering is a major challenge, especially for development of polarised epithelia that are critical structures in tissue homeostasis. Different in vitro models of the lung epithelial barrier have been characterized using non-degradable polyethylene terephthalate membranes which limits their uses for tissue engineering. Although poly-L-lactic acid (PLLA) membranes are biodegradable, those prepared via conventional Diffusion Induced Phase Separation (DIPS) lack open-porous geometry and show limited permeability compromising their use for epithelial barrier studies. Here we used PLLA membranes prepared via a modification of the standard DIPS protocol to control the membrane surface morphology and permeability. These were bonded to cell culture inserts for use in barrier function studies. Pulmonary epithelial cells (H441) readily attached to the PLLA membranes and formed a confluent cell layer within two days. This was accompanied by a significant increase in trans-epithelial electrical resistance and correlated with the formation of tight junctions and vectorial cytokine secretion in response to TNFα. Our data suggest that a structurally polarized and functional epithelial barrier can be established on PLLA membranes produced via a non-standard DIPS protocol. Therefore, PLLA membranes have potential utility in lung tissue engineering applications requiring bio-absorbable membranes.

Tailoring structural properties of spray-dried methotrexate-loaded poly (lactic acid)/poloxamer microparticle blends

Drug delivery systems can overcome cancer drug resistance, improving the efficacy of chemotherapy agents. Poly (lactic acid) (PLA) microparticles are an interesting alternative because their hydrophobic surface and small particle size could facilitate interactions with cells. In this study, two poloxamers (PLX 407 and 188) were applied to modulate the structural features, the drug release behavior and the cell viability from spray-dried microparticles. Five formulations with different PLA: PLX blend ratio (100:0, 75:25, 50:50, 25:50, and 0:100) were well-characterized by SEM, particle size analysis, FTIR spectroscopy, differential scanning calorimetry (DSC), and X-ray diffraction analysis (XRD). The spray-dried microparticles showed higher drug loading, spherical-shape, and smaller particle size. The type of poloxamer and blend ratio affected their structural and functional properties such as morphology, crystallinity, blend miscibility, drug release rate, and cell viability. The methotrexate (MTX), a model drug, was loaded in amorphous spray-dried microparticles. Moreover, the drug release studies demonstrated that PLX induced a leaching-effect of MTX from PLA: PLX blends, suggesting the formation of MTX/PLX micelles in aqueous medium. This finding was better established by cell viability assays. Therefore, biocompatible PLA: PLX blends showed promising in vitro results, and further in vivo studies will be performed to evaluate the performance of this chemotherapeutic agent.