Biodegradable and Electroactive TEMPO‐Substituted Acrylamide/Lactide Copolymers

Copolymers composed of PLA and PTAm were prepared by a macromonomer approach. The PLA bearing vinyl group at chain end was copolymerized with 2,2,6,6‐tetrametylpiperidine‐4‐ylacrylamide. The resulted copolymers were oxidized by a peroxide to give PTAm‐g‐PLA. The structures of the copolymers were confirmed by NMR and FTIR spectroscopy. The comparison of ¹H NMR results and SQUID measurements demonstrated that the oxidation of the PTAm fragment proceeded almost to completion. An MTT assay, cell adhesion and spreading evaluation showed that the copolymers exhibited improved cytocompatibility as compared to the PTAm homopolymer due to the introduction of the biocompatible PLA moiety.

     

Effect of the polymer component on biocompatibility and physicochemical properties of porous zirconium ceramics

The dependence of the porosity, mechanical and surface properties of the obtained zirconium ceramics on the content of polylactide as a pore-forming agent was explored. It was shown that modification of ceramics with the polymer material leads to the improvement of mechanical properties and to the decrease in the cytotoxicity of materials.     

Stereocomplexes of Triblock Poly(lactide- PEG2000-lactide) as Carrier of Drugs

Triblock copolymers of poly(lactide)-poly(ethylene-glycol)-poly(lactide) (PLA-PEG₂₀₀₀-PLA) were synthesized by ring-opening polymerization of lactide and PEG₂₀₀₀ diol as co-catalyst. Stereocomplexes with particle sizes ranging from nanometers to microns were obtained by mixing acetonitrile solutions of pairs of enantiomeric homopoly(lactide) and the triblock copolymers. The stereocomplexes exhibited higher crystalline melting temperatures than the optically pure polymers. The ratio of PLA terminals in the copolymers had a significant effect on their stereocomplex degradation and drug release. These stereocomplexes were used for the encapsulation of dexamethasone for controlled release applications. Dexamethasone phosphate loading capacity, in vitro release, degradation and stability of polymers and formulation were investigated for one month. An increase in the dexamethsone phosphate content in the stereocomplex or a decrease in the PLA ratio in the copolymer resulted in a faster release of drug and polymer degradation.     

Catalysts as Key Enablers for the Synthesis of Bioplastics with Sophisticated Architectures

Bioplastics are one of the answers to environmental pollution and linear material flows. The most promising bioplastic polylactide (PLA) is already replacing conventional plastics in a number of applications. The properties of PLA, however, do not fit for all potential application areas, but they can be altered by the introduction of comonomers. The copolymerization of lactide (LA) with other lactones like ϵ-caprolactone (CL) has been established for several years. Nevertheless, controlling copolymerizations remains a challenge due to the high complexity of the system. Copolymerization of LA with other monomer classes is much less investigated, but has the chance to overcome the limitations in material properties that occur when only lactones are used. The crucial factor for all copolymerizations is the catalyst. It dominates the reaction kinetics and determines the resulting microstructure. In this review, copolymerization catalysts for LA are presented divided into catalysts for the synthesis of lactone block copolymers, lactone random copolymers, and multimechanistically synthesized copolymers. The selected catalysts are highlighted either owing to their industrially applicable polymerization conditions or their non-standard mechanism.     

Synthesis of poly(ester-urethane)s from hydroxytelechelic polylactide: Effect of initiators on their physical and degradation properties

A series of poly(l-lactide)-based poly(ester-urethane)s (PEUs) were synthesized by ring-opening polymerization of l-lactide using a variety of diols such as diethylene glycol (DEG), triethylene glycol (TEG), tetraethylene glycol (TetraEG), 1,5-pentanediol (PD), 1,8-octanediol (OD), isopropyl tartrate (TRAⁱPr) and benzyl tartrate (TRABn) in the presence of Sn(Oct)₂, followed by chain extension with hexamethylene diisocyanate (HMDI). The thermal, mechanical, and degradation properties of the resulting PEUs were studied. The crystallinities of the PEUs decreased with increasing diol contents and were also dependent on the kind of the diol unit. The degradabilities of the PEUs with proteinase K were effectively controlled by the kind of diol unit depending on their size and hydrophilicity. The biodegradation of the PEUs in compost also showed strong dependence on the diol units in the PEUs in spite of relatively low diol content (∼3%).     

Mechanical and thermal properties of polylactide/talc microcomposites: before and after accelerated weathering

The purpose of the first part of this study was to investigate effects of micron‐sized talc content on the properties of polylactide (PLA). PLA/talc microcomposites were compounded by melt‐mixing method via twin‐screw extruder, while specimens for testing and analyses were shaped by injection molding. It was observed that, because of the effective stiffening, strengthening, toughening mechanisms of talc, and also their nucleation agent effects for higher crystallinity, many mechanical and thermal properties were improved. In the second part of the study, effects of accelerated weathering on the behavior of PLA microcomposites with 5 wt% talc were investigated by applying ultra violet irradiation and humidity steps according to Cycle‐C of International Organization for Standardization 4892‐3 standards for durations of 100, 200, and 300 hr. Various analyses revealed that, because of the degradation mechanisms of photolysis and hydrolysis during each weathering periods, molecular weight of PLA reduced drastically, that is, mechanical properties almost vanished. Copyright © 2015 John Wiley & Sons, Ltd.     

Polylactide stereocomplex crystallites as nucleating agents for isotactic polylactide

A nucleation efficiency scale for isotactic poly(L ‐lactide) (PLLA) was obtained with self‐nucleation and nonisothermal differential scanning calorimetry experiments. The maximum nucleation efficiency occurred at the highest concentration of self‐nucleating sites, and the minimum efficiency occurred in the absence of these sites (pure PLLA polymer melt). Blends of PLLA and isotactic poly(D ‐lactide) (PDLA) led to the formation of a 1/1 stereocomplex. In comparison with the homopolymer (PLLA), the stereocomplex had a higher melting temperature and crystallized at higher temperatures from the melt. Small stereocomplex crystallites were formed in PLLA/PDLA blends containing low concentrations of PDLA. These crystallites acted as heterogeneous nucleation sites for subsequent PLLA crystallization. Using the PLLA nucleation efficiency scale, we evaluated a series of PLLA/PDLA blends (0.25–15 wt % PDLA). A maximum nucleation efficiency of 66% was observed at 15 wt % PDLA. The nucleation efficiency was largely dependent on the thermal treatment of the sample. The nucleating ability of the stereocomplex was most efficient when it was formed well before PLLA crystallization. According to the efficiency scale, the stereocomplex was far superior to talc, a common nucleating agent for PLLA, in its ability to enhance the rate of PLLA crystallization. In comparison with the PLLA homopolymer, the addition of PDLA led to reduced spherulite sizes and a reduction in the overall extent of PLLA crystallization. The decreased extent of crystallization was attributed to the hindered mobility of the PLLA chains due to tethering by the stereocomplex. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 300–313, 2001     

New Approaches in the Treatment of Critical-Size Segmental Defects in Long Bones

Summary : The treatment of large segmental diaphyseal bone deficiencies presents a formidable challenge. The standard treatment modalities such as cancellous bone grafting, cortical allografts, vascularized bone transfer, or distraction osteogenesis exhibit extremely high complication rates, and can culminate in limb amputation or major functional deficits. Recent efforts to develop new treatment modalities for segmental bone loss have resulted in designing new biodegradable polymeric and metallic mesh implants that can incorporate novel osteogenic, osteoinductive, and/or osteoconductive bone healing augmentation materials. These biologic implant composites are capable of further enhancing the efficacy of the treatment applied. This paper briefly reviews the limitations of the currently applied standard treatment modalities for segmental critical size bone defects, provides insight into the specific treatment challenges, and presents the animal and initial clinical results of new alterative treatment approaches that involve the application of cylindrical mesh implants consisting of biodegradable polylactide membranes or titanium cages as a means of potentiating the efficacy of bone graft.