Novel method to characterize the hydrolytic decomposition of biopolymer surfaces

Factors Controlling Degradation of Biologically Relevant Synthetic Polymers in Solution and Solid State

The field of biodegradable synthetic polymers, which is central for regenerative engineering and drug delivery applications, encompasses a multitude of hydrolytically sensitive macromolecular structures and diverse processing approaches. The ideal degradation behavior for a specific life science application must comply with a set of requirements, which include a clinically relevant kinetic profile, adequate biocompatibility, benign degradation products, and controlled structural evolution. Although significant advances have been made in tailoring materials characteristics to satisfy these requirements, the impacts of autocatalytic reactions and microenvironments are often overlooked resulting in uncontrollable and unpredictable outcomes. Therefore, roles of surface versus bulk erosion, in situ microenvironment, and autocatalytic mechanisms should be understood to enable rational design of degradable systems. In an attempt to individually evaluate the physical state and form factors influencing autocatalytic hydrolysis of degradable polymers, this Review follows a hierarchical analysis that starts with hydrolytic degradation of water-soluble polymers before building up to 2D-like materials, such as ultrathin coatings and capsules, and then to solid-state degradation. We argue that chemical reactivity largely governs solution degradation while diffusivity and geometry control the degradation of bulk materials, with thin "2D" materials remaining largely unexplored. Following this classification, this Review explores techniques to analyze degradation in vitro and in vivo and summarizes recent advances toward understanding degradation behavior for traditional and innovative polymer systems. Finally, we highlight challenges encountered in analytical methodology and standardization of results and provide perspective on the future trends in the development of biodegradable polymers.

Tuning morphology of Pickering emulsions stabilised by biodegradable PLGA nanoparticles: How PLGA characteristics influence emulsion properties

In this study, we proved that the stabilisation of Pickering emulsions by polymer nanoparticles (NPs) heavily depends on polymer characteristics. We prepared NPs with four poly(lactide-co-glycolide) polymers (PLGA), of different molar masses (14,000 and 32,000 g/mol) and end groups (acid or alkylester). NPs were either bare (without stabilising polymer) or covered by polyvinyl alcohol (PVA). Pickering emulsions were prepared by mixing NP aqueous suspensions with various amounts of oil (Miglyol 812 N). First, NP wettability was directly affected by PLGA end group: ester-ending PLGA led to more hydrophobic NPs, compared to acid-ending PLGA. This effect of the end group could be slightly enhanced with smaller molar mass. Thus, bare PLGA NPs stabilised different types of emulsions (W/O/W and W/O), following Finkle's rule. However, the effect of PLGA characteristics was masked when NPs were covered by PVA, as PVA drove the stabilisation of O/W emulsions. Secondly, PLGA molar mass and end group also influenced its glass transition temperature (T_g), with spectacular consequences on emulsion formation. Indeed, the shortest ester-ending PLGA exhibited a T_g close to room temperature, when measured in the emulsion. This T_g, easily exceeded during emulsification process, led to a soft solid emulsion, stabilised by a network of NP debris.

Effect of Hydrolysis Pretreatment on the Formation of Bone-like Apatite on Poly(L-lactide) by Mineralization in Simulated Body Fluids

A bone-like apatite-coated surface that mediates a positive interaction between materials and bone is key to the development of desirable bone substitute materials. To incorporate apatite-coating on poly(L-lactide) (PLLA) surfaces, the effect of the hydrolysis of PLLA surfaces on the formation ability of bone-like apatite was investigated in this study.PLLA films and porous PLLA scaffolds were hydrolyzed for different time periods in alkaline solution and the hydrolyzed PLLA surfaces were characterized with X-ray photoelectron spectroscopy, atomic force microscopy, contact angle, and the measurement of carboxyl density. An apatite coating was formed by mineralizing the hydrolyzed PLLA in simulated body fluids (SBF) for 3 weeks and characterized. The hydrolyzed PLLA surfaces were rich in COOH and OH; the hydrophilicity, surface roughness, and carboxyl density increased with the hydrolysis time. After the incubation in SBF, a bone-like apatite layer with different morphology and composition was formed on the PLLA surfaces. The apatite formation on PLLA surfaces was promoted by the hydrolysis pretreatment and this increases with hydrolysis time. In addition, the compression module of the apatite-coated PLLA scaffolds increased compared with the pure PLLA scaffolds and increased with the hydrolysis time. The hydrolysis pretreatment was important in functionalizing the PLLA surfaces, facilitating subsequent apatite nucleation and apatite growth.

Synthesis and characterization of hydrolytically degradable copolyester biomaterials based on glycolic acid, sebacic acid and ethylene glycol

Copolyesters of glycolic acid (G) combined with sebacic acid (S) and ethylene glycol were synthesized in different molar ratios (G: 0-100% and S: 100-0%) and their hydrolytic degradation was studied and correlated with their structures. Based on the FTIR spectra of the homopolyesters and copolyesters and the normalized peak intensity of the I(2918), I(2848) and I(1087) for the corresponding wavenumbers, it is concluded that the I(2918) and the I(2848) are in accordance with the mean number degree of polymerization of ethylene sebacate units and the I(1087) is in accordance with the mean number degree of polymerization of glycolate units. Based on the XRD diffractograms, poly(ethylene sebacate) and poly(glycolic acid) belong to the monoclinic and the orthorhombic crystal system, respectively and both have higher crystallinity than the copolyesters. The experimental data of the hydrolytic degradation were fitted with exponential rise to maximum type functions using two-parameter model and four-parameter model. Three regions can been distinguished for the hydrolytic degradation by decreasing the molar feed ratio of sebacic acid, which are correlated with the changes of crystallinity. Two copolyesters are proposed: first the copolyester with high amount of glycolate units (S10G90) having higher hydrolytic degradation than G100 and second the copolyester with equal amount of glycolate and ethylene sebacate units (S50G50), having lower hydrolytic degradation than G100. These hydrolytically degradable copolyesters are soluble in common organic solvents, opposite to poly(glycolic acid) and could have perspectives for biomedical applications.

Correlation of hydrolytic degradation with structure for copolyesters produced from glycolic and adipic acids

Copolyesters based on glycolic acid (G) combined with adipic acid (A) and ethylene glycol (E) were synthesized in different percentage of molar ratios (A: 100-50% and G: 100%) and their hydrolytic degradation was studied and correlated with their structures. According to the DSC, the production of polyesters leads to the formation of copolyesters and not to mixtures of homopolyesters. The crystallites in the copolyesters mainly consist of continuous sequences of ethylene adipate structural units. The hydrolytic degradation of the polyesters was followed by their weight loss during hydrolysis and by the FTIR spectra of the initial polyesters compared with that of the degraded polyesters at equilibrium. The region between 1142 and 800 cm(-1) can be utilized to evaluate the extent of degradation of polyesters after their hydrolysis. The absorption bands at 1142, 1077 and 850 cm(-1) due to the amorphous region decrease after hydrolysis, whereas those at 972, 901 and 806 cm(-1) due to the crystalline region increase. The experimental data of the hydrolytic degradation were fitted with exponential rise to maximum type functions using two-parameter model, which describes very well mainly the initial part of the degradation, and four-parameter model (containing two exponential terms), which is appropriate for fitting the hydrolytic degradation on the entire time period (including the equilibrium). Furthermore, the kinetics of the hydrolytic degradation of the polyesters for the initial time period based on both models results to similar values of the rate constant, k. The synthesized copolyesters of glycolic acid combined with adipic acid and ethylene glycol are soluble in many common organic solvents opposite to PGA, leading to modified biodegradable polyesters and therefore they can be easily processed.

An approach to the design of a particulate system for oral protein delivery. I. In vitro stability of various poly (alpha-hydroxy acids)-microspheres in simulated gastrointestinal fluids

The stability of various biodegradable polyester polymers with different molecular weights and lactic/glycolic acids ratios were evaluated in simulated gastrointestinal fluids as an approach to apply microparticles for oral protein delivery on the basis of particle uptake mechanism. A common w/o/w emulsion solvent evaporation technique using dichloromethane for dissolving the polymer and polyvinyl alcohol as the stabilizer was used for encapsulation. Microspheres were incubated at 37 degrees C in USP simulated fluids with a concentration of 20 mg mL(-1) and also in the literature, which suggested fed or fasted simulated intestinal fluids for different times up to 24 h, while shaking at 75 rpm. The stability assessment was done by detecting pH alterations of the media, enzymatic assay of L-lactic acid, performing differential scanning calorimetric studies and observing the size and morphology of particles. Results showed that the three polymers, namely Resomers R207, RG756 and RG505, could be suitable for the preparation of protein-loaded microspheres.

Surface modification of poly( L ‐lactic acid) by entrapment of chitosan and its derivatives to promote osteoblasts‐like compatibility

Surface modification of biomaterials has been adopted over the years to improve their biocompatibility. In this study, aiming to promote hydrophilicity and to introduce natural recognition sites onto poly(L-lactic acid) (PLLA) films, chitosan and its derivatives, carboxymethyl chitosan (CMC) and N-methylene phosphonic chitosan (NPC), were used to modify the surface of PLLA films by an entrapment method. The surface properties of original and modified PLLA films were measured by using water contact angle measurement and X-ray photoelectron spectroscopy (XPS). Subsequently, the cytocompatibility of these PLLA films was investigated by testing osteoblasts-like cytocompatibility, cell attachment, cell proliferation, alkaline phosphatase activity, and cell cycle. Experimental results indicated that the hydrophilicity of the modified films was improved and the surface of the modified PLLA films became enriched with chitosan and its derivatives. Moreover, the surface modification with chitosan and its derivatives significantly promoted osteoblasts-like compatibility of PLLA films. This surface modification, combining the individual advantages of PLLA with good mechanical property and chitosan as well as its derivatives with good cytocompatibility, is a promising method to prepare desirable biomaterials.

Importance of Surface Tension Characterization for Food, Pharmaceutical and Packaging Products: A Review

This article reviews the various theoretical approaches that have been developed for determination of the surface tension of solids, and the applications to food industrial products. The surface tension of a solid is a characteristic of surface properties and interfacial interactions such as adsorption, wetting or adhesion. The knowledge of surface tension is thus of great interest for every domain involved in understanding these mechanisms, which recover a lot of industrial investigations. Indeed, it is the case for the packaging industry, the food materials science, the biomedical applications and the pharmaceutical products, cleaning, adhesive technology, painting, coating and more generally all fields in relation with wettability of their systems. There is however no direct method for measurements of surface tension of solids, except the contact angle measurements combined with an appropriate theoretical approach are indirect methods for estimation of surface tension of solids. Moreover, since the publication by Young (1805) who developed the basis of the theory of contact angle some two hundred years ago, measurements and interpretations are still discussed in scientific literature, pointing out the need to better understand the fundamental mechanisms of solid-liquid interfacial interactions. Applications of surface tension characterization in the field of food materials science are detailed, especially for packaging and coating applications, which recover different actual orientations in order to improve process and quality.

Substrate chemistry influences the morphology and biological function of adsorbed extracellular matrix assemblies

In addition to mediating cell signalling events, native extracellular matrix (ECM) assemblies interact with other ECM components, act as reservoirs for soluble signalling molecules and perform structural roles. The potential of native ECM assemblies in the manufacture of biomimetic materials has not been fully exploited due, in part, to the effects of substrate interactions on their morphology. We have previously demonstrated that the ECM components, fibrillin and type VI collagen microfibrils, exhibit substrate dependent morphologies on chemically and topographically variable heterogeneous surfaces. Using both cleaning and coating approaches on silicon wafers and glass coverslips we have produced chemically homogeneous, topographically similar substrates which cover a large amphiphilic range. Extremes of substrate amphiphilicity induced morphological changes in periodicity, curvature and lateral spreading which may mask binding sites or disrupt domain structure. Biological functionality, as assayed by the ability to support cell spreading, was significantly reduced for fibrillin microfibrils adsorbed on highly hydrophilic substrates (contact angle 20.7 degrees) compared with less hydrophilic (contact angle 38.3 degrees) and hydrophobic (contact angle 92.8 degrees) substrates. With an appropriate choice of surface chemistry, multifunctional ECM assemblies retain their native morphology and biological functionality.