Water-Insoluble, Thermostable, Crosslinked Gelatin Matrix for Soft Tissue Implant Development.

In this present study, the material science background of crosslinked gelatin (GEL) was investigated. The aim was to assess the optimal reaction parameters for the production of a water-insoluble crosslinked gelatin matrix suitable for heat sterilization. Matrices were subjected to enzymatic degradation assessments, and their ability to withstand heat sterilization was evaluated. The impact of different crosslinkers on matrix properties was analyzed. It was found that matrices crosslinked with butanediol diglycidyl ether (BDDE) and poly(ethylene glycol) diglycidyl ether (PEGDE) were resistant to enzymatic degradation and heat sterilization. Additionally, at 1 v/v % crosslinker concentration, the crosslinked weight was lower than the starting weight, suggesting simultaneous degradation and crosslinking. The crosslinked weight and swelling ratio were optimal in the case of the matrices that were crosslinked with 3% and 5% v/v BDDE and PEGDE. FTIR analysis confirmed crosslinking, and the reduction of free primary amino groups indicated effective crosslinking even at a 1% v/v crosslinker concentration. Moreover, stress-strain and compression characteristics of the 5% v/v BDDE crosslinked matrix were comparable to native gelatin. Based on material science measurements, the crosslinked matrices may be promising candidates for scaffold development, including properties such as resistance to enzymatic degradation and heat sterilization.

Interactions, Structure and Properties of PLA/lignin/PBAT Hybrid Blends.

Poly(butylene adipate-co-terephthalate) (PBAT) was added to poly(lactic acid) (PLA)/lignin blends to decrease the considerable stiffness and brittleness of the blends. Two- and three-component blends were prepared in a wide composition range through homogenization in an internal mixer followed by compression molding. Interactions among the components were estimated by comparing the solubility parameters of the materials used and through thermal analysis. Mechanical properties were characterized by tensile testing. The structure of the blends was studied using scanning electron (SEM) and digital optical (DOM) microscopy. The results showed that the interactions between PBAT and lignin are somewhat stronger than those between PLA and the other two components. The maleic anhydride grafted PLA added as a coupling agent proved completely ineffective; it does not modify the interactions. The structural analysis confirmed the immiscibility of the components; the structure of the blends was heterogeneous at each composition. A dispersed structure formed when the concentration of one of the components was small, while, depending on lignin content, an interpenetrating network-like structure developed and phase inversion took place in the range of 30-60 vol% PBAT content. Lignin was located mainly in the PBAT phase. Properties were determined by the relative amount of PBAT and PLA; the addition of lignin deteriorated properties, mainly the deformability of the blends. Other means, such as reactive processing, must be used to improve compatibility and blend properties. The results contribute considerably to a better understanding of structure-property correlations in lignin-based hybrid blends.

Preparation of Biocomposites with Natural Reinforcements: The Effect of Native Starch and Sugarcane Bagasse Fibers.

Biocomposites were prepared from poly(lactic acid) and two natural reinforcements, a native starch and sugarcane bagasse fibers. The strength of interfacial adhesion was estimated by model calculations, and local deformation processes were followed by acoustic emission testing. The results showed that the two additives influence properties differently. The strength of interfacial adhesion and thus the extent of reinforcement are similar because of similarities in chemical structure, the large number of OH groups in both reinforcements. Relatively strong interfacial adhesion develops between the components, which renders coupling inefficient. Dissimilar particle characteristics influence local deformation processes considerably. The smaller particle size of starch results in larger debonding stress and thus larger composite strength. The fracture of the bagasse fibers leads to larger energy consumption and to increased impact resistance. Although the environmental benefit of the prepared biocomposites is similar, the overall performance of the bagasse fiber reinforced PLA composites is better than that offered by the PLA/starch composites.

Deformation and Failure Mechanism of Particulate Filled and Short Fiber Reinforced Thermoplastics: Detection and Analysis by Acoustic Emission Testing.

Acoustic emission, the detection of signals during deformation, is a frequently used method for the study of local deformation processes occurring in heterogeneous polymer systems. Most of these processes result in the evolution of elastic waves which can be detected by appropriate sensors. The analysis of several parameters characterizing the waves offers valuable information about the possible deformation mechanism. The acoustic emission testing of composites may yield very different number of signals from a few hundred to more than 100,000. This latter was proved to be affected mainly by particle size, interfacial adhesion and composition, but other factors, such as matrix modulus and specimen size, also influence it. Local deformation processes are claimed to have a strong effect on macroscopic properties. Indeed, a close correlation was found between the initiation stress of the dominating particle related process derived from acoustic emission testing and the tensile strength in both polypropylene (PP) and poly(lactic acid) (PLA) composites. However, in polyamide (PA)-based heterogeneous polymer systems, deformations related to the matrix dominated composite properties. Besides forecasting failure, the method makes possible the determination of the inherent strength of lignocellulosic fibers being around 40 MPa as well as the quantitative estimation of adhesion strength for composites in which interactions are created by mechanisms other than secondary forces. The proposed approach based on acoustic emission testing proved that in PP/CaCO3 composites, the strength of adhesion can be increased by ten times from about 100 mJ/m2 to almost 1000 mJ/m2 in the presence of a functionalized polymer.

Poly-ε-Caprolactone/Halloysite Nanotube Composites for Resorbable Scaffolds: Effect of Processing Technology on Homogeneity and Electrospinning.

Polycaprolactone (PCL)/halloysite composites were prepared to compare the effect of homogenization technology on the structure and properties of the composites. Halloysite content changed from 0 to 10 vol% in six steps and homogeneity was characterized by various direct and indirect methods. The results showed that the extent of aggregation depends on technology and on halloysite content; the size and number of aggregates increase with increasing halloysite content. Melt mixing results in more homogeneous composites than the simple compression of the component powders or homogenization in solution and film casting. Homogeneity and the extent of aggregation determines all properties, including functionality. The mechanical properties of the polymer deteriorate with increasing aggregation; even stiffness depends on homogeneity. Strength and deformability decreases drastically as the number and size of aggregates increase. Not only dispersed structure, but also the physical state and crystalline structure of the polymer influence homogeneity and properties. The presence of the filler affects the preparation of electrospun fiber scaffolds as well. A part of the filler is excluded from the fibers while another part forms aggregates that complicates fiber spinning and deteriorates properties. The results indicate that spinning is easier and the quality of the fibers is better if a material homogenized previously by melt mixing is used for the production of the fibers.

Biological and Mechanical Properties of Platelet-Rich Fibrin Membranes after Thermal Manipulation and Preparation in a Single-Syringe Closed System.

Platelet-rich fibrin (PRF) membrane is a three-dimensional biodegradable biopolymer, which consists of platelet derived growth factors enhancing cell adhesion and proliferation. It is widely used in soft and hard tissue regeneration, however, there are unresolved problems with its clinical application. Its preparation needs open handling of the membranes, it degrades easily, and it has a low tensile strength which does not hold a suture blocking wider clinical applications of PRF. Our aim was to produce a sterile, suturable, reproducible PRF membrane suitable for surgical intervention. We compared the biological and mechanical properties of PRF membranes created by the classical glass-tube and those that were created in a single-syringe closed system (hypACT Inject), which allowed aseptic preparation. HypACT Inject device produces a PRF membrane with better handling characteristics without compromising biological properties. Freeze-thawing resulted in significantly higher tensile strength and higher cell adhesion at a lower degradation rate of the membranes. Mesenchymal stem cells seeded onto PRF membranes readily proliferated on the surface of fresh, but even better on freeze/thawed or freeze-dried membranes. These data show that PRF membranes can be made sterile, more uniform and significantly stronger which makes it possible to use them as suturable surgical membranes.