Crystallization study and comparative in vitro-in vivo hydrolysis of PLA reinforcement ligament

Segmental mobility in sustainable copolymers based on poly(lactic acid) blocks built onto poly(butylene succinate) in situ

Two series of newly synthesized sustainable block copolymers based on poly(butylene succinate) (PBSu) and polylactide (PLA) were studied. The copolymers were synthesized by a ring-opening polymerization of PLA in the presence of two initial PBSu of low molar mass. We focused on the effects of the PBSu/PLA ratio (1/99 up to 15/85), chain length and initial PBSu length on the final thermal transitions in the copolymers with an emphasis on molecular mobility/dynamics and subsequently on crystallization. Both aspects are considered relevant to the final materials performance, as well as facilitation of polymer renewability. Calorimetry and dielectric spectroscopy were the main investigation tools. In the amorphous state (i.e., in which the direct effects of copolymer structure are assessable), the segmental mobility of neat PLA was significantly faster in the copolymers. Segmental mobility was monitored via the decrease in the calorimetric and dielectric (α relaxation) glass-transition temperatures, Tg and Tg,diel, respectively. The effect was systematic with an increase in the PBSu/PLA ratio, and was rationalized through the plasticizing role of PBSu (low-Tg component) and facilitated also by the simultaneous lowering of the chain length in the copolymers. Dielectric spectroscopy allowed evaluation of the dynamical fragility (cooperativity) of chains, which was strongly suppressed in the copolymers. This finding suggested an increase in free volume or a gradual increase of interchain distances. This phenomenon could favor the natural enzymatic degradation of the systems (compostability), which is limited in neat PLA. We recorded enhancement of nucleation and the crystalline fraction in the copolymers that was likely connected with faster chain diffusion. Further lowering of the Tg with the implementation of crystallization was noted (which seemed a controversial effect) but which indicated crystallization-induced phase separation.

Biodegradation Behavior Control for Shape Memory Polyester Poly(Glycerol-Dodecanoate): An In Vivo and In Vitro Study

Poly(glycerol-dodecanoate) (PGD) has garnered increasing attention in biomedical engineering for its degradability, shape memory, and rubber-like mechanical properties. Adjustable degradation is important for biodegradable implants and is affected by various aspects, including material properties, mechanical environments, temperature, pH, and enzyme catalysis. The crosslinking and chain length characteristics of poly(lactic acid) and poly(caprolactone) have been widely used to adjust the in vivo degradation rate. The PGD degradation rate is affected by its crosslink density in in vitro hydrolysis; however, there is no difference in vivo. We believe that this phenomenon is caused by the differences in enzymatic conditions in vitro and in vivo. In this study, it is found that the degradation products of PGD with different molar ratios of hydroxyl and carboxyl (MR_H/C) exhibit varied pH values, affecting the enzyme activity and thus achieving different degradation rates. The in vivo degradation of PGD is characterized by surface erosion, and its mass decreases linearly with degradation duration. The degradation duration of PGD is linearly extrapolated from 9-18 weeks when MR_H/C is in the range of 2.00-0.75, providing a protocol for adjusting the degradation durations of subsequent implants made by PGD.

Recent Advances in the Investigation of Poly(lactic acid) (PLA) Nanocomposites: Incorporation of Various Nanofillers and their Properties and Applications

Poly(lactic acid) (PLA) is considered the most promising biobased substitute for fossil-derived polymers due to its compostability, biocompatibility, renewability, and good thermomechanical properties. However, PLA suffers from several shortcomings, such as low heat distortion temperature, thermal resistance, and rate of crystallization, whereas some other specific properties, i.e., flame retardancy, anti-UV, antibacterial or barrier properties, antistatic to conductive electrical characteristics, etc., are required by different end-use sectors. The addition of different nanofillers represents an attractive way to develop and enhance the properties of neat PLA. Numerous nanofillers with different architectures and properties have been investigated, with satisfactory achievements, in the design of PLA nanocomposites. This review paper overviews the current advances in the synthetic routes of PLA nanocomposites, the imparted properties of each nano-additive, as well as the numerous applications of PLA nanocomposites in various industrial fields.

Effect of Micro- and Nano-Lignin on the Thermal, Mechanical, and Antioxidant Properties of Biobased PLA-Lignin Composite Films

Bio-based poly(lactic acid) (PLA) composite films were produced using unmodified soda micro- or nano-lignin as a green filler at four different contents, between 0.5 wt% and 5 wt%. The PLA-lignin composite polymers were synthesized by solvent casting to prepare a masterbatch, followed by melt mixing. The composites were then converted into films, to evaluate the effect of lignin content and size on their physicochemical and mechanical properties. Differential scanning calorimetry (DSC), supported by polarized light microscopy (PLM), infrared spectroscopy (FTIR-ATR), X-ray diffraction (XRD), and transmission electron microscopy (TEM) were employed to investigate the PLA crystallization and the interactions with Lignin (L) and Nanolignin (NL). The presence of both fillers (L and NL) had a negligible effect on the glass transition temperature (chain diffusion). However, it resulted in suppression of the corresponding change in heat capacity. This was indicative of a partial immobilization of the PLA chains on the lignin entities, due to interfacial interactions, which was slightly stronger in the case of NL. Lignin was also found to facilitate crystallization, in terms of nucleation; whereas, this was not clear in the crystalline fraction. The addition of L and NL led to systematically larger crystallites compared with neat PLA, which, combined with the higher melting temperature, provided indications of a denser crystal structure in the composites. The mechanical, optical, antioxidant, and surface properties of the composite films were also investigated. The tensile strength and Young's modulus were improved by the addition of L and especially NL. The UV-blocking and antioxidant properties of the composite films were also enhanced, especially at higher filler contents. Importantly, the PLA-NL composite films constantly outperformed their PLA-L counterparts, due to the finer dispersion of NL in the PLA matrix, as verified by the TEM micrographs. These results suggest that bio-based and biodegradable PLA films filled with L, and particularly NL, can be employed as competitive and green alternatives in the food packaging industry.

Revisiting Non-Conventional Crystallinity-Induced Effects on Molecular Mobility in Sustainable Diblock Copolymers of Poly(propylene adipate) and Polylactide

This work deals with molecular mobility in renewable block copolymers based on polylactide (PLA) and poly(propylene adipate) (PPAd). In particular, we assess non-trivial effects on the mobility arising from the implementation of crystallization. Differential scanning calorimetry, polarized light microscopy and broadband dielectric spectroscopy were employed in combination for this study. The materials were subjected to various thermal treatments aiming at the manipulation of crystallization, namely, fast and slow cooling, isothermal melt- and cold-crystallization. Subsequently, we evaluated the changes recorded in the overall thermal behavior, semicrystalline morphology and molecular mobility (segmental and local). The molecular dynamics map for neat PPAd is presented here for the first time. Unexpectedly, the glass transition temperature, T_g, in the amorphous state drops upon crystallization by 8–50 K. The drop becomes stronger with the increase in the PPAd fraction. Compared to the amorphous state, crystallization leads to significantly faster segmental dynamics with severely suppressed cooperativity. For the PLA/PPAd copolymers, the effects are systematically stronger in the cold- as compared to the melt-crystallization, whereas the opposite happens for neat PLA. The local β_PLA relaxation of PLA was, interestingly, recorded to almost vanish upon crystallization. This suggests that the corresponding molecular groups (carbonyl) are strongly involved and immobilized within the semicrystalline regions. The overall results suggest the involvement of either spatial nanoconfinement imposed on the mobile chains within the inter-crystal amorphous areas and/or a crystallization-driven effect of nanophase separation. The latter phase separation seems to be at the origins of the significant discrepancy recorded between the calorimetric and dielectric recordings on T_g in the copolymers. Once again, compared to more conventional techniques such as calorimetry, dielectric spectroscopy was proved a powerful and quite sensitive tool in recording such effects as well as in providing indirect indications for the polymer chains’ topology.

Poly(Lactic Acid) Block Copolymers with Poly(Hexylene Succinate) as Microparticles for Long-Acting Injectables of Risperidone Drug

In the present work, Risperidone microparticles from poly(lactic acid)/poly(hexylene succinate) (PLA-b-PHSu) block copolymers in different ratios, 95/05, 90/10 and 80/20 w/w, were examined as long-acting injectable formulations. Nuclear magnetic resonance (NMR) was used to verify the successful synthesis of copolymers. Enzymatic hydrolysis showed an increase in weight loss as the content of PHSu increased, while the cytotoxicity studies confirmed the biocompatibility of the copolymers. The polyesters were further used to encapsulate Risperidone by spray drying. The drug-loaded microparticles were studied by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray diffraction (XRD). SEM microphotographs confirmed that spherically shaped microparticles were prepared with sizes about 5-12 μm, while XRD and differential scanning calorimetry (DSC) studies evidenced that Risperidone was encapsulated in amorphous form. The drug loading and the entrapment efficiency of Risperidone were studied as well as the in vitro release from the prepared microparticles. As the content of PHSu increased, a higher release of Risperidone was observed, with PLA-b-PHSu 80/20 w/w succeeding to release 100% of RIS within 12 days. According to theoretical modeling, the kinetics of RIS release from PLA-b-PHSu microparticles is complex, governed by both diffusion and polymer erosion.

Imaging moiety-directed co-assembly for biodegradation control with synchronous four-modal biotracking

The complexity of existing methods for biodegradation control limits the multi-functionality of biomedical materials. It is urgent to develop simple and straightforward strategies to control the biodegradation rate with precise tracking of various parameters in real-time. Here, we show an imaging moiety-directed co-assembly strategy, in which different imaging moieties bearing non-covalent interaction sites are covalently introduced into the poly (D,l-lactic acid) (PDLLA) chain as end groups, followed by alternate non-covalent interactions with polymer chains upon compression molding. This strategy takes advantage of a variety of bonding types (including CH-π, CH-F, etc.) to firmly integrate the PDLLA chains and strongly control the biodegradation rate, making the amorphous prototype degraded much slower than higher-molecular-weight counterparts, and the local inflammatory response is insignificant. On this basis, a synchronous four-modal (X-ray computed tomography + fluorescence + photoacoustics + ultrasound) imaging was achieved on the single entity in vivo, even within a millimeter-scale thick-skin tissue. These imaging signals can precisely correlate the multi parameter variation trend of material mass, volume and molecular weight, signifying that co-assembly can be utilized to develop advanced theranostic systems. SINGLE SENTENCE SUMMARY: We developed an imaging moiety-directed co-assembly strategy to control the biodegradation rate and achieve the synchronization of real-time four-modal imaging in vivo. These imaging signals can precisely correlate the multi-parameter variation trend of material mass, volume and molecular weight, which provided comprehensive biomedical information accessing both qualitatively and quantitatively.

Direct and indirect effects on molecular mobility in renewable polylactide-poly(propylene adipate) block copolymers as studied via dielectric spectroscopy and calorimetry

In this work, we study a series of sustainable block copolymers based on polylactide, PLA, and poly(propylene adipate), PPAd, both polymers being prepared from renewable resources. Envisaging a wide range of future applications in the frame of a green and circular economy, e.g., packaging materials replacing conventional petrochemicals, the employment of PPAd aims at lowering the glass transition and melting temperatures of PLA and, finally, facilitation of the enzymatic degradation and compostability. The copolymers have been synthesized via ring opening polymerization of lactides in the presence of propylene adipate oligomers (5, 15 and 25%). The direct effects on the molecular mobility by the structure/composition are assessed in the amorphous state employing broadband dielectric spectroscopy (BDS) and calorimetry. BDS allowed the recording of local PLA and PPAd dynamics in all cases. The effects on local relaxations suggest favoring of interchain interactions, both PLA-PPAd and PPAd-PPAd. Regarding the more important segmental dynamics, the presence of PPAd leads to faster polymer chain diffusion, as monitored by the significant lowering of the dielectric and calorimetric glass transition temperature, T_g. This suggests the plasticizing role of PPAd on PLA (majority) in combination with the lowering of the average molar mass, M_n, in the copolymers from ∼75 to ∼30 kg mol^-1, which is the actual scope for the synthesis of these materials. Interestingly, a strong suppression in fragility (chain cooperativity) is additionally recorded. In contrast to calorimetry and due to the high resolving power of BDS, for the higher PPAd fraction, the weak segmental relaxation of PPAd was additionally recorded. Overall, the recordings suggest a strong increase in free volume and two individual dynamic states, one for 0 and 5% PPAd and another for 15 and 25% PPAd. Within the latter, we gained indications for partial phase nano-separation of PPAd. Regarding indirect effects, these were followed via crystallization. Independent of the method of crystallization, namely, melt or cold, the presence of PPAd led to the systematic lowering of crystallization and melting temperatures and enthalpies. The effects reflect the decrease of crystalline nuclei, which is confirmed by optical microscopy as in the copolymers fewer although larger crystals are formed.

Melt-Spun, Cross-Section Modified Polycaprolactone Fibers for Use in Tendon and Ligament Tissue Engineering

Tissue Engineering is considered a promising route to address existing deficits of autografts and permanent synthetic prostheses for tendons and ligaments. However, the requirements placed on the scaffold material are manifold and include mechanical, biological and degradation-related aspects. In addition, scalable processes and FDA-approved materials should be applied to ensure the transfer into clinical practice. To accommodate these aspects, this work focuses on the high-scale fabrication of high-strength and highly oriented polycaprolactone (PCL) fibers with adjustable cross-sectional geometry and degradation kinetics applying melt spinning technology. Four different fiber cross-sections were investigated to account for potential functionalization and cell growth guidance. Mechanical properties and crystallinity were studied for a 24-week exposure to phosphate-buffered saline (PBS) at 37 °C. PCL fibers were further processed into scaffolds using multistage circular braiding with three different hierarchical structures. One structure was selected based on its morphology and scaled up in thickness to match the requirements for a human anterior cruciate ligament (ACL) replacement. Applying a broad range of draw ratios (up to DR9.25), high-strength PCL fibers with excellent tensile strength (up to 69 cN/tex) could be readily fabricated. The strength retention after 24 weeks in PBS at 37 °C was 83–93%. The following braiding procedure did not affect the scaffolds’ mechanical properties as long as the number of filaments and the braiding angle remained constant. Up-scaled PCL scaffolds resisted loads of up to 4353.88 ± 37.30 N, whilst matching the stiffness of the human ACL (111–396 N/mm). In conclusion, this work demonstrates the fabrication of highly oriented PCL fibers with excellent mechanical properties. The created fibers represent a promising building block that can be further processed into versatile textile implants for tissue engineering and regenerative medicine.

Special Features of Polyester-Based Materials for Medical Applications

This article presents current possibilities of using polyester-based materials in hard and soft tissue engineering, wound dressings, surgical implants, vascular reconstructive surgery, ophthalmology, and other medical applications. The review summarizes the recent literature on the key features of processing methods and potential suitable combinations of polyester-based materials with improved physicochemical and biological properties that meet the specific requirements for selected medical fields. The polyester materials used in multiresistant infection prevention, including during the COVID-19 pandemic, as well as aspects covering environmental concerns, current risks and limitations, and potential future directions are also addressed. Depending on the different features of polyester types, as well as their specific medical applications, it can be generally estimated that 25–50% polyesters are used in the medical field, while an increase of at least 20% has been achieved since the COVID-19 pandemic started. The remaining percentage is provided by other types of natural or synthetic polymers; i.e., 25% polyolefins in personal protection equipment (PPE).

Poly(Lactic Acid)-Based Microparticles for Drug Delivery Applications: An Overview of Recent Advances

The sustained release of pharmaceutical substances remains the most convenient way of drug delivery. Hence, a great variety of reports can be traced in the open literature associated with drug delivery systems (DDS). Specifically, the use of microparticle systems has received special attention during the past two decades. Polymeric microparticles (MPs) are acknowledged as very prevalent carriers toward an enhanced bio-distribution and bioavailability of both hydrophilic and lipophilic drug substances. Poly(lactic acid) (PLA), poly(lactic-co-glycolic acid) (PLGA), and their copolymers are among the most frequently used biodegradable polymers for encapsulated drugs. This review describes the current state-of-the-art research in the study of poly(lactic acid)/poly(lactic-co-glycolic acid) microparticles and PLA-copolymers with other aliphatic acids as drug delivery devices for increasing the efficiency of drug delivery, enhancing the release profile, and drug targeting of active pharmaceutical ingredients (API). Potential advances in generics and the constant discovery of therapeutic peptides will hopefully promote the success of microsphere technology.

3D Printing of Temporary Prostheses for Controlled-Release of Drugs: Design, Physical Characterization and Preliminary Studies

In recent years, the use of 3D printing technologies in orthopedic surgery has markedly increased, as they offer the possibility of printing personalized prostheses. The work presented in this article is a preliminary study of a research project which aims to manufacture customized spacers containing antibiotics for use in joint replacement surgery. The objective of this work was to design and print different 3D constructs to evaluate the use of different materials, their properties after the process of 3D printing, such as resistance, and the release kinetics of drugs from the constructs. Different designs and different materials were analyzed to obtain a 3D construct with suitable properties. Our design takes advantage of the micropores created between the layers of the 3D printed filaments to release the contained drug. Using polylactic acid (PLA) we were able to print cylindrical structures with interconnected micropores and a hollow chamber capable of releasing methylene blue, which was selected as a model drug. The final PLA 3D construct was printed with a 10% infill. The physical and technological characteristics, morphological changes at body temperature and interaction with water were considered to be acceptable. The PLA 3D printed constructs were found to have sufficient strength to withstand a force of 500 kg. The results obtained allow to continue research in this project, with the aim of manufacturing prostheses containing a reservoir of antibiotics or other drugs in their interior for their subsequent controlled release.

An experimental investigation into the physical, thermal and mechanical degradation of a polymeric bioresorbable scaffold

This study presents a comprehensive evaluation of the mechanical, micro-mechanical and physical properties of Reva Medical Fantom Encore Bioresorbable Scaffolds (BRS) subjected to a thermally-accelerated degradation protocol. The Fantom Encore BRS were immersed in phosphate buffered saline solution at 50 °C for 112 days with radial compression testing, nanoindentation, differential scanning calorimetry, gel permeation chromatography and mass loss characterisation performed at consecutive time points. In the initial stages of degradation (Days 0-21), the Fantom Encore BRS showed increases in radial strength and stiffness, despite a substantial reduction in in molecular weight, with a slight increase in the melt temperature also observed. In the second phase (Days 35-54), the radial strength of the BRS samples were maintained despite a continued loss in molecular weight. However, during this phase, the ductility of the stent showed a reduction, with stent fracture occurring earlier in the crimp process and with lower amounts of plastic deformation evident under visual examination post-fracture. In the final phase (Days 63-112), the load-bearing capacity of the Fantom Encore BRS showed continued reduction, with decreases in radial stiffness and strength, and drastic reduction in the work-to-fracture of the devices. Throughout each phase, there was a steady increase in the relative crystallinity, with limited mass loss until day 112 and only minor changes in glass transition and melt temperatures. Limited changes were observed in nano-mechanical properties, with measured local elastic moduli and hardness values remaining largely similar throughout degradation. Given that the thermally-accelerated in vitro conditions represented a four-fold acceleration of physiological conditions, these results suggest that the BRS scaffolds could exhibit substantially brittle behaviour after ∼ one year of implantation.

Poly(lactic Acid): A Versatile Biobased Polymer for the Future with Multifunctional Properties-From Monomer Synthesis, Polymerization Techniques and Molecular Weight Increase to PLA Applications

Environmental problems, such as global warming and plastic pollution have forced researchers to investigate alternatives for conventional plastics. Poly(lactic acid) (PLA), one of the well-known eco-friendly biodegradables and biobased polyesters, has been studied extensively and is considered to be a promising substitute to petroleum-based polymers. This review gives an inclusive overview of the current research of lactic acid and lactide dimer techniques along with the production of PLA from its monomers. Melt polycondensation as well as ring opening polymerization techniques are discussed, and the effect of various catalysts and polymerization conditions is thoroughly presented. Reaction mechanisms are also reviewed. However, due to the competitive decomposition reactions, in the most cases low or medium molecular weight (MW) of PLA, not exceeding 20,000-50,000 g/mol, are prepared. For this reason, additional procedures such as solid state polycondensation (SSP) and chain extension (CE) reaching MW ranging from 80,000 up to 250,000 g/mol are extensively investigated here. Lastly, numerous practical applications of PLA in various fields of industry, technical challenges and limitations of PLA use as well as its future perspectives are also reported in this review.

Block copolymers based on poly(butylene adipate) and poly(L-lactic acid) for biomedical applications: synthesis, structure and thermodynamical studies

This work describes the synthesis of poly(butylene adipate) (PBAd), by melt polycondensation, poly(l-lactic acid) (PLLA), by ring opening polymerization, and the new block copolymer PLLA/PBAd in ratios 90/10, 95/5, 75/25 and 50/50. Due to the biocompatibility and low toxicity of neat PBAd and PLLA, these copolymers are suitable to be used in biomedical applications. The 1H and 13C nuclear magnetic resonance spectroscopy techniques were employed for structural characterization. The thermal transitions, with an emphasis on crystallization, were assessed by differential scanning calorimetry, supplemented by X-ray diffraction and polarized optical microscopy. Molecular mobility studies were conducted using two advanced techniques, broadband dielectric spectroscopy and thermally stimulated depolarization currents. The results from the structural techniques, in combination with each other, provided proof of the presence of PLLA and PBAd blocks and, moreover, the successful copolymer synthesis. The overall data showed that the different co-polymer compositions result directly in severe changes in the polymer crystal distribution and, indirectly, the formation of PBAd micro/nano domains surrounded by PLLA. Furthermore, it was demonstrated that both the continuity of the two polymers throughout the copolymer volume and the semicrystalline morphology can be tuned to a wide extent. The latter makes these systems quite promising envisaging biomedical applications, including the encapsulation of small molecules, e.g. drug solutions. The molecular mobility map was constructed for these systems for the first time, revealing the local (short scale) and segmental (larger nm scale) mobility of PBAd and PLLA, as well as intermediate behaviors of the copolymers.

Microneedles with dual release pattern for improved immunological efficacy of Hepatitis B vaccine

In this study, dissolving microneedles (DMNs) with dual-release pattern, capable of both bolus release and slow release, were prepared. These DMNs were used with a hepatitis B vaccine that requires multiple shots to achieve immunological efficacy comparable to that obtained when two separate shots are administered. Dissolving microneedles with HBsAg in PLA tips and CMC coating formulation together (HBsAg-PLA/CMC-DMNs) consist of polylactic acid (PLA) tips for slow release, a carboxy-methyl cellulose (CMC) coating formulation for bolus release, and a dissolving base of polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP) for dissolution in the skin. The in vitro release pattern of HBsAg from the CMC coating formulation and PLA tips was observed. Through an in vivo test, 1) the delivery efficiency of HBsAg-PLA/CMC-DMNs was observed, and 2) the immunological efficacy of this method was compared with the efficacy of two shots delivered by conventional intramuscular (IM) administration and two shots delivered by HBsAg-coated microneedle (CMNs) administration. HBsAg-PLA/CMC-DMNs punctured the skin successfully. The PVA/PVP base was completely dissolved within 10 min of insertion, resulting in the delivery of all microneedle tips into the skin. In the in vitro release experiment, all of the HBsAg in the CMC coating formulation was released within 20 min, and the HBsAg present in the PLA tips was gradually released over more than 55 days. The antibody titer of one shot of HBsAg-PLA/CMC-DMNs was the same as or higher than two shots delivered by conventional IM and CMN methods. DMNs with dual-release pattern can deliver two formulations simultaneously with a single shot, resulting in improved immunological efficacy of HBsAg that requires multiple doses. In addition, this dual-release MN system can be used for the delivery of other drugs that require multiple administrations.

Current status of in vivo bioanalysis of nano drug delivery systems

The development of nano drug delivery systems (NDDSs) provides new approaches to fighting against diseases. The NDDSs are specially designed to serve as carriers for the delivery of active pharmaceutical ingredients (APIs) to their target sites, which would certainly extend the benefit of their unique physicochemical characteristics, such as prolonged circulation time, improved targeting and avoiding of drug-resistance. Despite the remarkable progress achieved over the last three decades, the understanding of the relationships between the in vivo pharmacokinetics of NDDSs and their safety profiles is insufficient. Analysis of NDDSs is far more complicated than the monitoring of small molecular drugs in terms of structure, composition and aggregation state, whereby almost all of the conventional techniques are inadequate for accurate profiling their pharmacokinetic behavior in vivo. Herein, the advanced bioanalysis for tracing the in vivo fate of NDDSs is summarized, including liquid chromatography tandem-mass spectrometry (LC-MS/MS), Förster resonance energy transfer (FRET), aggregation-caused quenching (ACQ) fluorophore, aggregation-induced emission (AIE) fluorophores, enzyme-linked immunosorbent assay (ELISA), magnetic resonance imaging (MRI), radiolabeling, fluorescence spectroscopy, laser ablation inductively coupled plasma MS (LA-ICP-MS), and size-exclusion chromatography (SEC). Based on these technologies, a comprehensive survey of monitoring the dynamic changes of NDDSs in structure, composition and existing form in system (i.e. carrier polymers, released and encapsulated drug) with recent progress is provided. We hope that this review will be helpful in appropriate application methodology for investigating the pharmacokinetics and evaluating the efficacy and safety profiles of NDDSs.

New Biodegradable Poly(l-lactide)-Block-Poly(propylene adipate) Copolymer Microparticles for Long-Acting Injectables of Naltrexone Drug

In the present study, novel block copolymers of poly(l-lactide)-block-poly(propylene adipate) (PLLA-b-PPAd) were synthesized in two ratios, 90/10 and 75/25 w/w and were further investigated as long-acting injectable (LAI) polymeric matrices in naltrexone base microparticle formulations. The synthesized polymers were characterized by 1H-NMR, 13C-NMR, FTIR, XRD, TGA and DSC. NMR and FTIR spectroscopies confirmed the successful synthesis of copolymers while DSC showed that these are block copolymers with well-defined and separated blocks. Microparticles were prepared by single emulsification method and were further characterized. Nanoparticles in the range of 0.4-4.5 μm were prepared as indicated by SEM, with copolymers giving the lowest particle size. By XRD and DSC it was found that naltrexone was present in the amorphous state in its microparticles. Dissolution study showed a drug release extending over seven days, indicating that these novel PLLA-b-PPAd copolymers could be promising matrices for naltrexone's LAI formulations. It was evidenced that drug release depended on the copolymer composition. Model release studies showed that drug release is controlled by diffusion.

One Year Evaluation of Material Properties Changes of Polylactide Parts in Various Hydrolytic Degradation Conditions

Biodegradable biocompatible materials are widely used in medical applications. Determining the possibility of using biodegradable materials depends on determining the changes in their parameters over time due to degradation. The current scientific research on biodegradable materials has presented results based on research methods characterized by the different geometry and cross-section size of the specimen, type of degradation medium, or different pH value of the medium or maximum degradation time. This paper presents the results of a one-year study on the influence of the type of degradation medium on the changes in mechanical behavior and the uptake of the degradation medium by biodegradable specimens with large cross-sections. In addition, a prototype of a test stand was created, which allowed for the specimens to be stored vertically to ensure regular medium exposure and eliminate the interaction of the surface of the tested specimens with the sides of the container. The obtained results allowed the statistical significance of differences in the mechanical parameters determined in the uniaxial tensile test after 2, 4, 6, 12, 26, 39, and 52 weeks of degradation to be indicated depending on the type of degradation medium. It was proven that the changes in mechanical behavior depend on the percentage change in the mass of the specimens during degradation. The percentage change in mass depends on the type of degradation medium. Based on the results of this research, it was noted that in long-term degradation above 12 weeks, buffered sodium chloride solution is the optimal choice for the degradation medium. However, distilled water or physiological saline solution can be used as an alternative during the degradation period for up to 12 weeks.

Absorption, distribution, metabolism and excretion of the biomaterials used in Nanocarrier drug delivery systems

Nanocarriers (NCs) are a type of drug delivery system commonly used to regulate the pharmacokinetic and pharmacodynamic properties of drugs. Although a wide variety of NCs has been developed, relatively few have been registered for clinical trials and even fewer are clinically approved. Overt or potential toxicity, indistinct mechanisms of drug release and unsatisfactory pharmacokinetic behavior all contribute to their high failure rate during preclinical and clinical testing. These negative characteristics are not only due to the NCs themselves but also to the materials of the drug nanocarrier system (MDNS) that are released in vivo. In this article, we review the main analytical techniques used for bioassay of NCs and MDNS and their pharmacokinetics after administration by various routes. We anticipate our review will serve to improve the understanding of MDNS pharmacokinetics and facilitate the development of NC drug delivery systems.

Non-invasive characterization of hybrid gelatin:poly-l-lactide electrospun scaffolds using second harmonic generation and multiphoton imaging

Hybrid scaffolds composed of synthetic polymers and naturally occurring components have become more relevant in the field of tissue engineering and regenerative medicine. Synthetic polymers are responsible for scaffold durability, strength and structural integrity; however, often do not provide biological signals. Introducing a biological component leads to more advanced and biocompatible scaffolds. In order to use these scaffolds as implants, a deeper knowledge of material characteristics and the impact of the biological component on the scaffold mechanical properties are required. Furthermore, it is necessary to implement fast, easy and non-invasive methods to determine material characteristics. In this work, we aimed to generate gelatin-poly-l-lactide (PLA) hybrids via electrospinning with defined, controllable and tunable scaffold characteristics. Using Raman microspectroscopy, we demonstrated the effectiveness of the cross-linking reaction and evaluated the increasing PLA content in the hybrid scaffolds with a non-invasive approach. Using multiphoton microscopy, we showed that gelatin fibers electrospun from a fluorinated solvent exhibit a second harmonic generation (SHG) signal typical for collagen-like structures. Compared to pure gelatin, where the SHG signal vanishes after cross-linking, the signal could be preserved in the hybrid scaffolds even after cross-linking. Furthermore, we non-invasively imaged cellular growth of human dermal fibroblasts on the hybrid electrospun scaffolds and performed fluorescence lifetime imaging microscopy on the cell-seeded hybrids, where we were able to discriminate between cells and scaffolds. Here, we successfully employed non-invasive methods to evaluate scaffold characteristics and investigate cell-material interactions.

Risperidone Controlled Release Microspheres Based on Poly(Lactic Acid)-Poly(Propylene Adipate) Novel Polymer Blends Appropriate for Long Acting Injectable Formulations

The present study evaluates the preparation of risperidone controlled release microspheres as appropriate long-acting injectable formulations based on a series of novel biodegradable and biocompatible poly(lactic acid)⁻poly(propylene adipate) (PLA/PPAd) polymer blends. Initially, PPAd was synthesized using a two-stage melt polycondensation method (esterification and polycondensation) and characterized by 1H-NMR, differential scanning calorimetry (DSC), and powder X-ray diffraction (XRD) analyses. DSC and XRD results for PLA/PPAd blends (prepared by the solvent evaporation method) showed that these are immiscible, while enzymatic hydrolysis studies performed at 37 °C showed increased mass loss for PPAd compared to PLA. Risperidone-polyester microparticles prepared by the oil⁻water emulsification/solvent evaporation method showed smooth spherical surface with particle sizes from 1 to 15 μm. DSC, XRD, and Fourier-transformed infrared (FTIR) analyses showed that the active pharmaceutical ingredient (API) was dispersed in the amorphous phase within the polymer matrices, whereas in vitro drug release studies showed risperidone controlled release rates in all PLA/PPAd blend formulations. Finally, statistical moment analysis showed that polyester hydrolysis had a major impact on API release kinetics, while in PLA/PPAd blends with high PLA content, drug release was mainly controlled by diffusion.

Complex poly(lactic acid)-based biomaterial for urinary catheters: II. Biocompatibility

The present paper is focused on the surface and bulk characterization of poly(lactic acid) (PLA)-based composites that contain hydrolyzed collagen as a biological polymer, silver nanoparticles and vitamin E and epoxidized soybean oil as a plasticizer. The bionanocomposites were obtained by melt processing and evaluated for structural and surface characteristics, biocompatibility, functional properties such as antimicrobial and antioxidant activity and hydrolytic degradation behavior. It has been established that the optimal composition to impart functional properties to the PLA matrix is a formulation containing 15% epoxidized soybean oil, 15% hydrolyzed collagen, 5% Pluronic, 5% vitamin E and 0·3% silver nanoparticles. This bionanocomposite inhibits the growth of both Gram-positive bacteria, Escherichia coli and Salmonella typhimurium, and Gram-negative bacteria, Listeria monocytogenes, and reaches 100% radical-scavenging activity. The PLA-based biomaterials obtained in this study are stable in biological media in the short and medium terms and therefore are recommended as multifunctional biomaterials for the manufacture of medical devices, such as urinary catheters.

Degradation mechanisms of bioresorbable polyesters. Part 1. Effects of random scission, end scission and autocatalysis

A mathematical model was developed to relate the degradation trend of bioresorbable polymers to different underlying hydrolysis mechanisms, including noncatalytic random scission, autocatalytic random scission, noncatalytic end scission or autocatalytic end scission. The effect of each mechanism on molecular weight degradation and potential mass loss was analysed. A simple scheme was developed to identify the most likely hydrolysis mechanism based on experimental data. The scheme was first demonstrated using case studies, then used to evaluate data collected from 31 publications in the literature to identify the dominant hydrolysis mechanisms for typical biodegradable polymers. The analysis showed that most of the experimental data indicates autocatalytic hydrolysis, as expected. However, the study shows that the existing understanding on whether random or end scission controls degradation is inappropriate. It was revealed that pure end scission cannot explain the observed trend in molecular weight reduction because end scission would be too slow to reduce the average molecular weight. On the other hand, pure random scission cannot explain the observed trend in mass loss because too few oligomers would be available to diffuse out of a device. It is concluded that the chain ends are more susceptible to cleavage, which produces most of the oligomers leading to mass loss. However, it is random scission that dominates the reduction in molecular weight.