Injectable in situ forming drug delivery system based on poly(ε-caprolactone fumarate) for tamoxifen citrate delivery: Gelation characteristics,in vitro drug release and anti-cancer evaluation

The present study deals with the preparation and characterization of an injectable and in situ forming drug delivery system based on photocrosslinked poly(ε-caprolactone fumarate) (PCLF) networks loaded with tamoxifen citrate (TC). Networks were made of PCLF macromers, a photoinitiation system (comprising initiator and accelerator) and the active ingredient N-vinyl-2-pyrrolidone (NVP) as a crosslinker and reactive diluent. Shrinkage behavior, equilibrium swelling and sol fraction ratios of photocrosslinked PCLF gels were determined as functions of NVP content. It was shown that the crosslinking is facilitated up to a certain concentration of NVP and most of NVP remained unreacted above this value. In vitro drug release, biocompatibility evaluation and activity against MCF-7 breast cancer cell line were also investigated. Accurate but simple bipartite expressions were also derived that enable rapid determination of effective diffusion coefficients of TC in photocrosslinked PCLF/NVP disks. Cytotoxicity assay showed that while the photocrosslinked PCLF network with optimum NVP content exhibits no significant cytotoxicity against MCF-7 and L929 cell lines, 40–60% of the MCF-7 cells were killed after incubation with TC-loaded devices.     

Hydroxyapatite scaffolds infiltrated with thermally crosslinked polycaprolactone fumarate and polycaprolactone itaconate

In this work, two unsaturated derivatives of polycaprolactone (PCL), polycaprolactone fumarate (PCLF), and polycaprolactone itaconate (PCLI), have been synthesized and used as an infiltrating polymer to improve the mechanical properties of brittle hydroxyapatite (HA) scaffolds. PCLF and PCLI were first synthesized through polyesterification of the low molecular weight PCL diols with fumaryl chloride and itaconyl chloride respectively, and then characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, gel permeation chromatography, and differential scanning calorimetry analysis. HA scaffolds were sintered using a foam replication technique, with porosity of about 60%. Polymer-HA composites were obtained by infiltrating the HA scaffolds with PCLF and PCLI solution (12.5 and 30 w/v in dichloromethane) followed by thermal crosslinking. The polymer infiltrated HA scaffolds were characterized by scanning electron microscopy, porosimetry, and gravimetrical analysis. The polyesterification reaction of PCL diols with fumarate chloride was more efficient than itaconyl chloride and dependent upon the molecular weight of the initial PCL precursor; the resultant PCLF demonstrated a degree of substitution of 1.2, 4.2, and 2.7 times higher than PCLIs. Polymer infiltration improved the compressive strength of the HA scaffolds, and based upon the type of macromer (PCLF or PCLI) and also their concentration in infiltrating solution (12.5 or 30 w/v %) compressive strength increased about 14-328%. In all studied samples, the reinforcement effect of PCLF infiltration was higher than PCLI. The macromers and their corresponding infiltrated HA scaffolds did not show any significant cytotoxicity toward human primary osteogenic sarcoma cell (G92 cell lines), in vitro.     

Biodegradable and photocrosslinkable polyphosphoester hydrogel

A new biodegradable, photocrosslinkable and multifunctional macromer, poly(6-aminohexyl propylene phosphate) (PPE-HA)-ACRL, was synthesized by conjugation of acrylate groups to the side chains of PPE-HA. By controlling the synthetic conditions, different weight fractions of acrylate in the macromers were achieved as confirmed by 1H NMR. The hydrogels obtained from PPE-HA-ACRL through photocrosslinking were dominantly elastic. With increasing acrylate contents in the macromers, the hydrogels exhibited a lower swelling ratio and higher mechanical strength. The hydrogels with different crosslinking densities lost between 4.3% and 37.4% of their mass in 84 days when incubated in phosphate-buffered saline at 37 degrees C. No significant cytotoxicity of the macromers against bone marrow-derived mesenchymal stem cells from goat (GMSC) was observed at a concentration up to 10mg/ml. Finally, GMSCs encapsulated in the photopolymerized gel maintained their viability when cultured in osteogenic medium for three weeks. Clear mineralization in the hydrogel scaffold was revealed by Von Kossa staining. This study suggests the potential of these biodegradable and photocrosslinkable as injectable tissue engineering scaffolds.     

Influence of the power density on the kinetics of photopolymerization and properties of dental composites

Polymer shrinkage during photopolymerization of dimethacrylate monomers, used for many years to produce materials for dental restoration, can induce either the formation of tooth-restoration gaps or the production of residual stress depending on the quality of adhesion between tooth and dental composites. In this work, the effect of the power density, used to photopolymerize three commercial dental composites (Fill Magic, Supra Fill, and Z100), on the kinetics of the reaction was investigated to determine processing conditions in which the generation of residual stress would be reduced by allowing polymer chains and macromers to flow before freezing during gelation of the polymer network. The kinetics of photopolymerization of the dental composites was monitored by real-time infrared (FTIR) spectroscopy. Polymer shrinkage and mechanical properties were also investigated by using, respectively, density and microhardness measurements. Results showed that the final conversion (after 200 s), volumetric shrinkage, and microhardness values were not affected by different power densities, mainly because the amount of energy used during photopolymerization was set constant by using different irradiation times. Lower power densities were able to reduce the maximum polymerization rate and delay the formation of a rigid network. Conversion before the formation of the rigid network was also enhanced by using a lower power density. Considering that too premature gelation can lead to residual stress during shrinkage, the results of this work indicated that the use of a lower power density can be effective in terms of delaying the onset of the formation of a rigid network, providing then conditions for macromolecules to flow and relieve stress during shrinkage.     

VUV‐Induced Photopolymerization of Acrylates

Acrylates and methacrylates are photopolymerized without photoinitiator by exposure to 172 nm radiation. The kinetics of the polymerization is studied using real‐time Fourier‐transform infrared attenuated total reflectance (FTIR‐ATR) spectroscopy. It is shown that layers with a thickness of ≈500 nm can be polymerized very rapidly. The effect of structure, viscosity, functionality, and absorption of the acrylates as well as the influence of temperature and oxygen concentration on the reactivity are studied. A strong conversion gradient is observed in layers up to ≈2 μm thickness, which reflects the intensity gradient within the layer. However, the penetration of the polymerization into the layer exceeds the initial penetration depth of the VUV radiation, which indicates strong bleaching of the acrylates during irradiation.     

Residual monomers and degree of conversion of partially bioresorbable fiber-reinforced composite

The aim of this study was to evaluate the total quantity of residual monomer (bis-phenyl glycidyl dimethacrylate, i.e. Bis-GMA, and triethylene glycol dimethacrylate, i.e. TEGDMA), residual monomer release into water and the degree of monomer conversion (DC%) of glass fiber-reinforced composites (FRC) with a partially bioresorbable polymer matrix. Another aim was to find out whether the curing mode affects the quantity of residual monomer and degree of conversion. Glass fibers were preimpregnated with a bioresorbable poly(hydroxyproline) amide and non-resorbable Bis-GMA-TEGDMA resin system. Specimens were immersed in water for 1, 3 or 7 days (37 degrees C) to determine the quantity of leached residual monomers, or in the solvent tetrahydrofuran for 3 days to determine the total quantity of residual monomers by high performance liquid chromatography. DC% was measured by Fourier transform infrared spectroscopy. The quantity of residual monomer of the specimens decreased when the specimens contained glass fibers, and/or poly(hydroxyproline) amide, and/or when it was post-cured. The majority of the residual monomers were leached out during the first 24 h of immersion in water. The DC% of the specimens increased when post-cured. Also glass fibers in the composite increased the DC% in contrast to Bis-GMA-TEGDMA resin only. In conclusion, use of poly(hydroxyproline) amide as a sizing of the glass fibers in FRC does not increase the quantity of residual monomers. These results suggest that this new kind of partially bioresorbable FRC has potential for biomedical applications.     

Spatially resolved photopolymerization kinetics and oxygen inhibition in dental adhesives

A comparative study of three commercial dental adhesives was performed by (1)H nuclear magnetic resonance spectroscopy and Stray-Field magnetic resonance imaging. Spectroscopic evidence was found for the presence of solvent and unreacted methacrylate groups in photopolymerized adhesives. Spatially resolved photopolymerization kinetics and volumetric contraction (solvent evaporation and polymerization shrinkage) were obtained without solvent removal and in the presence of oxygen from the atmosphere. The oxygen and solvent inhibitor effects in the photopolymerization were found to be higher for water/ethanol based adhesives. However, was one of these adhesives that exhibited less spatially dependent irradiation time to start vitrification, higher concentration and a more uniform spatial distribution of rigid domains at the end of the photopolymerization.     

Synthesis,Evaluation and Preliminary Antibacterial Testing of Hybrid Composites Based on Urethane Oligodimethacrylates and Ag Nanoparticles

A series of urethane dimethacrylates differing structurally by the nature of the spacer (PTHF, PCL, PEG) and the presence or absence of the carboxylic acid groups was synthesized via an isocyanate route frequently encountered in ionomer chemistry. ¹H-NMR and FT-IR spectroscopy confirmed the structure of the macromers. Subsequently, the progress of photo-polymerization of all dimethacrylates under UV irradiation was investigated by FT-IR spectroscopy and photo-DSC with respect to conversion and polymerization rate using Irgacure as an initiator. The results of spectroscopic analysis suggested the lower reactivity of some non-carboxylic analogues during the formation of cross-linked polymers, the degree of conversion depending on the structure and viscosity. Photo-polymerization may provide many advantages for incorporating silver nanoparticles (2.5 wt%) into macromers in order to obtain hybrid nanocomposite films with controllable thickness and hydrophobicity. Combined analyses of UV spectroscopy and transmission electron microscopy confirmed the existence of nanosized silver (mean diameter 12 ± 0.7 nm) uniformly distributed in the polymer matrix. Preliminary results concerning the antibacterial activity of some composite films (thickness approx. 24 μm) showed that the obtained nanomaterial could have an excellent bactericidal effect and effectiveness in reducing bacterial growth (Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25923).     

Free radical polymerization of poly(ethylene glycol) diacrylate macromers: impact of macromer hydrophobicity and initiator chemistry on polymerization efficiency

A series of poly(ethylene glycol)-co-poly(lactide) diacrylate macromers was synthesized with variable PEG molecular weights (10 or 20 kDa) and lactate contents (0 or 6 lactates per end group). These macromers were polymerized to form hydrogels by free radical polymerization using either redox or photochemical initiators. The extent of polymerization was determined by monitoring the compressive modulus of the resulting hydrogels and by quantitative determination of unreacted acrylate after exhaustive hydrolysis of the gel. Polymerization efficiency was found to depend on the lactate content of the macromer, with higher lactate macromers giving more efficient polymerization. For redox-initiated polymerization using ferrous gluconate/t-butyl hydroperoxide initiator, macromers containing approximately six lactate repeats per end group required lower concentrations of initiator to reach high conversion than lactate-free macromers. Photochemical polymerization with α,α-dimethoxy-α-phenylacetophenone (Irgacure 651(?)) was found to be less efficient than redox polymerization, requiring the addition of N-vinyl-2- pyrrolidone (NVP) as a co-monomer to achieve conversions comparable with redox polymerization. When conditions were optimized to provide near complete conversion for all gels, the presence of lactate repeat units in the hydrogel was generally found to reduce swelling and increase the compressive modulus. Calculated values of molecular weight between cross-links (M(c)) and mesh size using Flory-Rehner theory showed that macromer molecular weight had the greatest impact on the network structure of the gel.     

Combinatorial investigation of the structure-properties characterization of photopolymerized dimethacrylate networks

The effects of co-monomer composition and irradiation time in a model two-component dimethacrylate dental resin blend were evaluated using combinatorial methods to determine the degree of methacrylate conversion and resulting mechanical properties. 2-Dimensional gradient samples varying in monomer composition and light exposure time were fabricated. The conversion was measured using near infrared spectroscopy (NIR) and the mechanical properties (i.e., hardness and elastic modulus) were determined using nanoindentation via the continuous stiffness method. An excellent correlation was observed between the reaction conversion and mechanical properties for the cross-linked networks. The methacrylate conversion ranged from 40% to 85% and the mechanical properties increased over two orders of magnitude over this conversion range. The ultimate reaction conversion and mechanical properties depended on both the co-monomer composition and cure time.     

Change of properties during storage of a UDMA/TEGDMA dental resin

The aim of this study was to evaluate the changes in viscoelastic properties of a UDMA-based dental resin as a function of time after initial light exposure. Specimens of a UDMA/TEGDMA (70:30 wt%) resin were irradiated by a visible-light-curing unit. Immediately after the irradiation, the light-cured specimen was stored in the dark for different times from 1 to 120 h at 37 degrees C, and characterized by means of DMA, DSC, and FTIR spectroscopy. The irradiated specimen exhibited a bimodal shape in the form of two rapid declines in log E' corresponding to glass transition with a plateau between the two declines. Two distinct peaks were seen in tan delta versus temperature. The thermal reaction of the incompletely cured sample with residual groups trapped by the fast reaction during irradiation is responsible for the plateau. After storage, significant changes were observed in dynamic mechanical parameters, DSC exotherm, and degree of conversion. Storage modulus continued to increase during the 4 h of storage and leveled off thereafter. Peak heights of tan delta versus temperature were also influenced by storage. Degree of conversion increased from 75 +/- 2% immediately after irradiation to 87 +/- 3% after 120 h storage. The changes of the properties of this dental resin system when stored at 37 degrees C after irradiation are clinically important in terms of stability, durability, and performance after initial polymerization.     

Nanofibrillated cellulose composite hydrogel for the replacement of the nucleus pulposus

The swelling and compressive mechanical behavior as well as the morphology and biocompatibility of composite hydrogels based on Tween? 20 trimethacrylate (T3), N-vinyl-2-pyrrolidone (NVP) and nanofibrillated cellulose (NFC) were assessed in the present study. The chemical structure of T3 was verified by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance, and the degree of substitution was found to be around 3. Swelling ratios of neat hydrogels composed of different concentrations of T3 and NVP were found to range from 1.5 to 5.7 with decreasing concentration of T3. Various concentrations of cellulose nanofibrils (0.2-1.6wt.%) were then used to produce composite hydrogels that showed lower swelling ratios than neat ones for a given T3 concentration. Neat and composite hydrogels exhibited a typical nonlinear response under compression. All composite hydrogels showed an increase in elastic modulus compared to neat hydrogel of about 3- to 8-fold, reaching 18kPa at 0% strain and 62kPa at 20% strain for the hydrogel with the highest NFC content. All hydrogels presented a porous and homogeneous structure, with interconnected pore cells of around 100nm in diameter. The hydrogels are biocompatible. The results of this study demonstrate that composite hydrogels reinforced with NFC may be viable as nucleus pulposus implants due to their adequate swelling ratio, which may restore the annulus fibrosus loading, and their increased mechanical properties, which could possibly restore the height of the intervertebral discs.     

Photocrosslinking of functionalized rubbers, 7. Styrene-butadiene block copolymers

The photocrosslinking of polystyrene-block-polybutadiene-block-polystyrene (SBS) was studied by means of infrared spectroscopy, by monitoring the disappearance of the pendent vinyl double bonds, which was shown to proceed within a few seconds upon UV exposure in the presence of an acylphosphine oxide photoinitiator. Complete insolubilization requires the reaction of 17 double bonds per polymer chain for an SBS sample containing 8% vinyl groups. An increase of the vinyl content has little effect on the crosslinking process, because it enhances mainly intramolecular reactions. A paraffinic oil proved to be an effective plasticizer for the photocrosslinked elastomer. The addition of a telechelic acrylate oligomer causes a substantial increase of both the reaction rate and the final degree of conversion of the SBS double bonds. The light-induced copolymerization of the vinyl and butene double bonds with the acrylate double bonds leads to the formation of a hard and flexible polymer material within a fraction of a second.     

Stabilization of collagen tissues by photocrosslinking

Photocrosslinking, using 2 mM Ru(II)(bpy)(3)Cl(2) and various concentrations of sodium persulfate with irradiation by blue light, ～455 nm, has been shown to be a rapid and effective method for crosslinking various tissues: tendon, amnion membrane, pericardium, and heart valve leaflet. The presence of new crosslinking was demonstrated by the increase in the shrinkage temperature of these tissues. In all the cases, increase in the shrinkage temperatures were seen, although at higher sodium persulfate concentrations, for example, 100 mM, both with and without the Ru(II)(bpy)(3)Cl(2) catalyst, some degradation of the collagenous tissues was found. The effectiveness of this photocrosslinking method when used with tissues was also shown through the increase in the break strength of tissues after crosslinking, and by the reduction of protein that could be extracted by urea. In solution studies, dityrosine has been shown to be formed during photocrosslinking. With tissues, Western blotting showed the presence of new dityrosine crosslinked proteins.     

New Fluorescent Probes for Monitoring Polymerization Reactions: Photocuring of Acrylic Adhesives, 2

The results of following the fluorescence of selected probes during the entire range of curing of acrylic‐based adhesives are presented in this work. The change of fluorescence parameters has been continuously measured during the photocrosslinking reactions of acrylic adhesive systems under UV‐irradiation. Real‐time FT‐IR (RT‐FT‐IR) has been used to measure the conversion reached at different irradiation times. Intensity ratio, maximum emission wavelength and the first moment of fluorescence have been used as parameters to correlate with the double bond conversion degree. Two‐slope plots have been obtained during UV‐curing, which correspond to the different stages of the crosslinking reaction. Also, the size of fluorescent probe appears to be a parameter that influences the sensing time in which the probe can detect the changes in viscosity/polarity occurring along the UV‐curing process. The results are compared with those of commercial probes such as dansylamide and prodan. The use of the fluorescence technique allowed us to understand the mechanism taking place and the role of the binder matrix, depending on the photoinitiator used. This information is not obtained when the reaction is followed by the conventional RT‐FT‐IR technique.     

Porous crosslinked poly(ε-caprolactone fumarate)/nanohydroxyapatite composites for bone tissue engineering

Porous nanocomposites based on poly(ε-caprolactone fumarate) (PCLF) resin matrix; N-vinyl pyrrolidone (NVP) as a reactive diluents and nanohydroxyapatite (nHA) filler were developed for bone tissue engineering applications. Nanocomposite scaffolds with three different contents of nHA [5, 10, and 20 (w/w %)] were prepared by thermal crosslinking of PCLF followed by particulate leaching and characterized in terms of mechanical properties (cyclic loading) and in vitro cell-material interaction by MTT assay and alkaline phosphatase activity measurements. Five osteoblastic cell lines were used to investigate the ability of the nanocomposites to support cell attachment, spreading, and proliferation after 3, 7, and 14 days. By adding the nHA filler phase, elastic modulus of the nanocomposites increased significantly. Scaffolds showed comparable biocompatibility to neat nHA particles, commercial bone graft (Bio-Oss) and tissue culture polystyrene as control groups. According to the results it can be concluded that these scaffolds are potential candidates for bone substitution because of their mechanical strength and bioactivity.     

Grafting of maleic anhydride onto poly(tetrahydrofuran)

A well-defined modification of poly(tetrahydrofuran)s was realized by grafting with maleic anhydride. The grafted products were investigated by Fourier-transform infrared (FTIR) spectroscopy and ¹³C nuclear magnetic resonance (NMR) spectroscopy. FTIR spectroscopy evidenced a characteristic shift of the carbonyl valence vibrations of cyclic anhydrides to higher wave numbers due to grafting. The grafting of maleic anhydride, which occurred mainly onto poly(tetrahydrofuran) carbons in α-position, was proved by means of ¹³C NMR spectroscopy. Furthermore, it was found that approximately 10% of all graftings took place onto poly(tetrahydrofuran) carbons in β-position. All the grafted units were monosubstituted succinic anhydride units. Indications for the formation of poly(maleic anhydride) graft units were not found. The quantitative determination of grafted anhydride units was carried out by titration after hydrolysis to the acid form. Remarkably high values of percentage grafting up to 20 wt.-% of maleic anhydride were obtained using an initiator concentration of only 2.5 mol-% related to maleic anhydride. The high values of percentage grafting at an initail maleic anhydride concentration of 20 wt.-% were due to a nearly complete conversion of the maleic anhydride. If the initial amount of maleic anhydride was higher than 20 wt.-% phase separation took place during the reaction. This phase separation prevented complete conversion of the maleic anhydride.     

The micro-Raman spectroscopy, a useful tool to determine the degree of conversion of light-activated composite resins.

Light-activated composites are now among the most popular dental restorative materials. Nevertheless, concerns exist about the so-called depth of cure. Infrared spectroscopy (FTIR) has traditionally been used to quantify this problem by evaluating the degree of conversion of dental resins. However, Raman scattering provides an alternate method. This article describes the advantages and the limitations of micro-Raman spectroscopy, as compared to FTIR and other techniques, for calculating the local degree of conversion and the depth of cure of light-cured composites.     

Photosensitive polymers with pendent p-dialkylaminobenzylideneacetophenone residues as photoinduced radical polymerization initiators

Polymers with pendent p-dialkylaminobenzylideneracetophenone (PABA) groups were prepared by copolymerization of 4-(4-dimethylaminobenzylidenemethylcarbonyl)phenyl methacrylate ( 1 ) with alkyl methacrylates and by the substitution reaction of poly(chloromethylstyrene-co-methyl methacrylate) with sodium 4-(4-dimethylaminobenzylidenemethylcarbonyl)phenolate ( 3 ). The polymers having PABA groups become insoluble upon photodimerization of PABA. Furthermore, the photosensitivity of the polymers increases considerably when mixed with vinyl monomers and diphenyliodonium hexafluorophosphate (DPI) during irradiation. The photocrosslinking may involve graft polymerization initiated by PABA which sensitizes the decomposition of DPI to form radicals. Introduction of unsaturated groups like maleate or crotonyl groups into the PABA polymer depresses the shrinkage of the photocured polymer film when the polymer was mixed with DPI. Sensitivity characteristics of PABA polymers toward Ar laser emitting 488 nm light are mentioned.     

新型生物可降解交联N-乙烯基吡咯烷酮(NVP)材料的制备

用甘油和丙交酯在辛酸亚锡的催化下合成了可降解的三羟基中间体 ,在三乙胺存在的条件下 ,末端用丙烯酰氯进行功能化 ,合成了可降解的三乙烯基交联剂 ,并且对中间体和交联剂进行了FTIR ,1H—NMR ,GPC分析表征。这种交联剂与乙烯基吡咯烷酮 (NVP)用偶氮二异丁氰 (AIBN)为引发剂自由基引发聚合制备了组织工程支架材料 ,并且对材料的基本性能(吸水率和接触角 )进行了分析表征。