Development of Biodegradable Polymer Blends Based on Chitosan and Polylactide and Study of Their Properties

Composite materials of various compositions based on chitosan and polylactide were obtained in the form of films or porous bulk samples. Preliminarily, poly-d,l-lactide was synthesized by ring-opening polymerization of lactide in the presence of Ti(OⁱPr)₄. Polylactide obtained at components molar ratio [lactide]:[Ti(OⁱPr)₄] = 3:1 had the best molecular weight characteristics at a high product yield. Film composition with the weight ratio chitosan-polylactide 50:50 wt. % was characterized by high mechanical properties. The value of the tensile strength of the film was 72 MPa with a deformation of 10% and an elastic modulus of 40 GPa, which is higher than the tensile strength of native chitosan by ~three times. The observed effect is a consequence of the fact that the chitosan-polylactide composite has an amorphous structure in contrast to the native chitosan, which is proved by X-ray phase analysis. An increase in the elastic modulus of the composite in the range of 20–60 °C in contrast to polylactide was found by dynamic mechanical analysis. The observed effect is apparently caused by the formation of hydrogen bonds between functional groups of chitosan and polylactide which is possible through an increase in polylactide segments mobility when its glass transition temperature is reached. The composite material is biocompatible and characterized by high cellular adhesion of fibroblasts (line hTERT BJ-5ta). Their growth on the composite surface was 2.4 times more active than on native chitosan. Bulk porous samples of the composition with the weight ratio chitosan-polylactide 50:50 wt. % were synthesized by original method in ammonium bicarbonate presence. Samples were characterized by a porosity of 82.4% and an average pore size of 100 microns. The biodegradability of such material and absence of inflammatory processes were proven in vivo by the blood parameters of experimental animals. Thus, materials with the weight ratio chitosan-polylactide 50:50 wt. % are promising for potential use in regenerative medicine.     

Modern Biodegradable Plastics—Processing and Properties Part II

Four different plastics were tested: potato starch based plastic (TPS-P)–BIOPLAST GF 106/02; corn starch based plastic (TPS-C)–BioComp BF 01HP; polylactic acid (polylactide) plastic (PLA)—BioComp BF 7210 and low density polyethylene, trade name Malen E FABS 23-D022; as a petrochemical reference sample. Using the blown film extrusion method and various screw rotational speeds, films were obtained and tested, as a result of which the following were determined: breaking stress, strain at break, static and dynamic friction coefficient of film in longitudinal and transverse direction, puncture resistance and strain at break, color, brightness and gloss of film, surface roughness, barrier properties and microstructure. The biodegradable plastics tested are characterized by comparable or even better mechanical strength than petrochemical polyethylene for the range of film blowing processing parameters used here. The effect of the screw rotational speed on the mechanical characteristics of the films obtained was also demonstrated. With the increase in the screw rotational speed, the decrease of barrier properties was also observed. No correlation between roughness and permeability of gases and water vapor was shown. It was indicated that biodegradable plastics might be competitive for conventional petrochemical materials used in film blowing niche applications where cost, recyclability, optical and water vapor barrier properties are not critical.     

Gelation Behavior of Bioabsorbable Hydrogels Consisting of Enantiomeric Mixtures of A–B–A Tri‐block Copolymers of Polylactides (A) and Poly(ethylene glycol) (B)

A–B–A tri‐block copolymers of poly(L ‐lactide) (PLLA: A) and poly(ethylene glycol) (PEG: B) and those of poly(D ‐lactide) (PDLA: A) and PEG (B) were prepared and suspended in saline. Mixing suspensions consisting of the enantiomeric copolymers with identical block compositions induced a temperature‐dependent sol‐to‐gel transition. It was found that the composition window of the copolymers that allowed the spontaneous sol–gel transition around body temperature was considerably narrow, being affected by how easily the PLLA and PDLA blocks of the copolymers can form the stereocomplex in the mixed suspensions. The gelation rate and gel strength also depended on the copolymer composition and concentration at a constant gelation temperature of 37 °C.     

The Influence of Sub-Zero Conditions on the Mechanical Properties of Polylactide-Based Composites

Polylactide-based composites filled with waste fillers due to their sustainability are a subject of many current papers, in which their structural, mechanical, and thermal properties are evaluated. However, few studies focus on their behavior in low temperatures. In this paper, dynamic and quasi-static mechanical properties of polylactide-based composites filled with 10 wt% of linseed cake (a by-product of mechanical oil extraction from linseed) were evaluated at room temperature and at −40 °C by means of dynamic mechanical analysis (DMA), Charpy’s impact strength test and uniaxial tensile test. It was found that the effect of plasticization provided by the oil contained in the filler at room temperature is significantly reduced in sub-zero conditions due to solidification of the oil around −18 °C, as it was shown by differential scanning calorimetry (DSC) and DMA, but the overall mechanical performance of the polylactide-based composites was sufficient to enable their use in low-temperature applications.     

Tissue engineered extracellular matrices (ECMs) in urology: Evolution and future directions

Autologous gastrointestinal tissue has remained the gold-standard reconstructive biomaterial in urology for >100 years. Mucus-secreting epithelium is associated with lifelong metabolic and neuromechanical complications when implanted into the urinary tract. Therefore, the availability of biocompatible tissue-engineered biomaterials such as extracellular matrix (ECM) scaffolds may provide an attractive alternative for urologists. ECMs are decellularised, biodegradable membranes that have shown promise for repairing defective urinary tract segments in vitro and in vivo by inducing a host-derived tissue remodelling response after implantation. In urology, porcine small intestinal submucosa (SIS) and porcine urinary bladder matrix (UBM) are commonly selected as ECMs for tissue regeneration. Both ECMs support ingrowth of native tissue and differentiation of multi-layered urothelial and smooth muscle cells layers while providing mechanical support in vivo. In their native acellular state, ECM scaffolds can repair small urinary tract defects. Larger urinary tract segments can be repaired when ECMs are manipulated by seeding them with various cell types prior to in vivo implantation. In the present review, we evaluate and summarise the clinical potential of tissue engineered ECMs in reconstructive urology with emphasis on their long-term outcomes in urological clinical trials.     

Articular cartilage repair with recombinant human type II collagen/polylactide scaffold in a preliminary porcine study

The purpose of this study was to investigate the potential of a novel recombinant human type II collagen/polylactide scaffold (rhCo‐PLA) in the repair of full‐thickness cartilage lesions with autologous chondrocyte implantation technique (ACI). The forming repair tissue was compared to spontaneous healing (spontaneous) and repair with a commercial porcine type I/III collagen membrane (pCo). Domestic pigs (4‐month‐old, n = 20) were randomized into three study groups and a circular full‐thickness chondral lesion with a diameter of 8 mm was created in the right medial femoral condyle. After 3 weeks, the chondral lesions were repaired with either rhCo‐PLA or pCo together with autologous chondrocytes, or the lesion was only debrided and left untreated for spontaneous repair. The repair tissue was evaluated 4 months after the second operation. Hyaline cartilage formed most frequently in the rhCo‐PLA treatment group. Biomechanically, there was a trend that both treatment groups resulted in better repair tissue than spontaneous healing. Adverse subchondral bone reactions developed less frequently in the spontaneous group (40%) and the rhCo‐PLA treated group (50%) than in the pCo control group (100%). However, no statistically significant differences were found between the groups. The novel rhCo‐PLA biomaterial showed promising results in this proof‐of‐concept study, but further studies will be needed in order to determine its effectiveness in articular cartilage repair. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:745–753, 2016.     

聚乳酸基形状记忆材料对兔输卵管黏膜的影响

目的:探讨聚乳酸基形状记忆输卵管避孕材料的安全性。方法:雌性大白兔15只随机分为实验组、自身对照组及空白组,分别于术后1、4、8周,取输卵管制作标本,以光镜及透射电镜观察黏膜变化。结果:实验组及自身对照组手术侧,肉眼可见材料植入体内后变短粗,后期逐渐变细小,光镜下初期可见输卵管皱襞被压缩,后皱襞内逐渐有纤维增生。电镜下上皮细胞内有异物颗粒,后期肌细胞间可见大量胶原。结论:聚乳酸基形状记忆材料植入兔输卵管后能刺激输卵管纤维组织增生,材料可降解,对机体无危害。     

Functional repair after dorsal root rhizotomy using nerve conduits and neurotrophic molecules

Functional recovery after large excision of dorsal roots is absent because of both the limited regeneration capacity of the transected root, and the inability of regenerating sensory fibers to traverse the dorsal root entry zone. In this study, bioresorbable guidance conduits were used to repair 6-mm dorsal root lesion gaps in rats, while neurotrophin-encoding adenoviruses were used to elicit regeneration into the spinal cord. Polyester conduits with or without microfilament bundles were implanted between the transected ends of lumbar dorsal roots. Four weeks later, adenoviruses encoding NGF or GFP were injected into the spinal cord along the entry zone of the damaged dorsal roots. Eight weeks after injury, nerve regeneration was observed through both types of implants, but those containing microfilaments supported more robust regeneration of calcitonin gene-related peptide (CGRP)-positive nociceptive axons. NGF overexpression induced extensive regeneration of CGRP(+) fibers into the spinal cord from implants showing nerve repair. Animals that received conduits containing microfilaments combined with spinal NGF virus injections showed the greatest recovery in nociceptive function, approaching a normal level by 7-8 weeks. This recovery was reversed by recutting the dorsal root through the centre of the conduit, demonstrating that regeneration through the implant, and not sprouting of intact spinal fibers, restored sensory function. This study demonstrates that a combination of PNS guidance conduits and CNS neurotrophin therapy can promote regeneration and restoration of sensory function after severe dorsal root injury.     

Evaluation of a bioabsorable polylactide film in a large animal model for the reduction of retrosternal adhesions

Objectives

An adult pig model of retrosternal adhesion formation via an inferior hemisternotomy was used to evaluate the formation and development of pericardial and retrosternal adhesions, as well as adhesion reduction using two thicknesses of a bioabsorbable polylactide film.

Materials and methods

Twenty-five adult female pigs (70 kg) were allocated to either a control group or four different treatments using two thicknesses (0.02 or 0.05 mm) of a polylactide film. In each animal, the film was placed either inside the pericardium or inside and outside the pericardium.

Results

All animals demonstrated adhesions between the posterior and lateral surfaces of the heart and pericardium. Thick fibrous retrosternal adhesions and pericardial adhesions were noted in the control animals with complete obliteration of the anatomical plane. The polylactide films preserved the anatomical planes and reduced the adhesion response.

Conclusions

A reproducible animal model was used to examine the formation and reduction of retrosternal and pericardial adhesions. A polylactide film placed inside the pericardium or between the heart and sternum was able to limit adhesion formation and maintain the anatomical planes, which would facilitate reentry.