RESUMO
Supramolecular hydrogels derived from the self-assembly of α-cyclodextrin with pluronic F127 were found to be built up with polypseudorotaxane nanosheets with a thickness of 30-40 nm and possessed flower-like hierarchically assembled structures. The findings in this work could provide critical guidance for material design for biomedical purposes.
RESUMO
A syndiotactic-rich PHEMA oligomer ( rr = 74%, DP = 29, PDI = 1.19) was synthesized and subsequently subjected to self-assembly with a varying amount of γ-CDs in its aqueous solution to create mismatched overfit polypseudorotaxanes (PPRs). The inclusion complexation proceeded in an obvious mismatched manner between the cavity of γ-CDs and the cross-sectional area of an incoming PHEMA chain. The 2D-NOESY NMR analysis provided direct evidence indicating that two adjacent pendant hydroxyethyl groups in PHEMA preferably adopt a curled conformation to pass through the cavity of γ-CDs, giving the PPRs characteristics of a mismatched overfit instead of a matched tight-fit crystal structure. The results suggested that the mutual adaption of pendant side chains of HEMA units with the cavity geometry of γ-CDs would play a dominant role in this unfavorable overfit inclusion complexation besides the size of γ-CDs and the stereoregularity of the PHEMA chain.
RESUMO
Both chiral OFm monosubstituted cyclo(l-Glu-l-Glu) and cyclo(d-Glu-d-Glu) display a robust gelation ability in a variety of organic solvents and water. In contrast to an individual enantiomer, their racemate can form rapidly recoverable thixotropic hydrogels with a remarkably shorter thixotropic recovery time. This unexpected thixotropic behavior is induced by the random arrangement of d- and l-enantiomers in the cell units, leading to the formation of "pseudoracemate", noncrystalline self-assemblies in the resulting 3D fibrous network.
RESUMO
Four cyclo(l-Lys-l-Glu) derivatives (3-6) were synthesized from the coupling reaction of protecting l-lysine with l-glutamic acid followed by the cyclization, deprotection, and protection reactions. They can efficiently gelate a wide variety of organic solvents or water. Interestingly, a spontaneous chemical reaction proceeded in the organogel obtained from 3 in acetone exhibiting not only visual color alteration but also increasing mechanical strength with the progress of time due to the formation of Schiff base. Moreover, 6 bearing a carboxylic acid and Fmoc group displayed a robust hydrogelation capability in PBS solution. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) revealed the characteristic gelation morphologies of 3D fibrous network structures in the resulting organo- and hydrogels. FT-IR and fluorescence analyses indicated that the hydrogen bonding and π-π stacking play as major driving forces for the self-assembly of these cyclic dipeptides as low-molecular-weight gelators. X-ray diffraction (XRD) measurements and computer modeling provided information on the molecular packing model in the hydrogelation state of 6. A spontaneous chemical reaction proceeded in the organogel obtained from 3 in acetone exhibiting visual color alteration and increasing mechanical strength. 6 bearing an optimized balance of hydrophilicity to lipophilicity gave rise to a hydrogel in PBS with MGC at 1 mg/mL.
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Studies on three-dimensional tissue engineered graft (3DTEG) have attracted great interest among researchers as they present a means to meet the pressing clinical demand for tissue engineering scaffolds. To explore the feasibility of 3DTEG, high porosity poly-ε-caprolactone (PCL) was obtained via the co-electrospinning of polyethylene glycol and PCL, and used to construct small-diameter poly-ε-caprolactone-lysine (PCL-LYS-H) scaffolds, whereby heparin was anchored to the scaffold surface by lysine groups. A variety of small-diameter 3DTEG models were constructed with different PCL layers and the mechanical properties of the resulting constructs were evaluated in order to select the best model for 3DTEGs. Bone marrow mononuclear cells were induced and differentiated to endothelial cells (ECs) and smooth muscle cells (SMCs). A 3DTEG (labeled '10-4%') was successfully produced by the dynamic co-culture of ECs on the PCL-LYS-H scaffolds and SMCs on PCL. The fluorescently labeled cells on the 3DTEG were subsequently observed by laser confocal microscopy, which showed that the ECs and SMCs were embedded in the 3DTEG. Nitric oxide and endothelial nitric oxide synthase assays showed that the ECs behaved normally in the 3DTEG. This study consequently provides a new thread to produce small-diameter tissue engineered grafts, with excellent mechanical properties, that are perfusable to vasculature and functional cells.
Assuntos
Células Endoteliais/citologia , Leucócitos Mononucleares/citologia , Miócitos de Músculo Liso/citologia , Poliésteres/química , Engenharia Tecidual/instrumentação , Alicerces Teciduais , Animais , Materiais Biocompatíveis/síntese química , Diferenciação Celular/fisiologia , Proliferação de Células/fisiologia , Sobrevivência Celular/fisiologia , Células Cultivadas , Força Compressiva , Cães , Módulo de Elasticidade , Galvanoplastia/métodos , Células Endoteliais/fisiologia , Desenho de Equipamento , Análise de Falha de Equipamento , Estudos de Viabilidade , Leucócitos Mononucleares/fisiologia , Teste de Materiais , Miócitos de Músculo Liso/fisiologia , Estresse Mecânico , Propriedades de Superfície , Resistência à TraçãoRESUMO
Pentablock copolymers PMA-PPO-PEO-PPO-PMA synthesized via atom transfer radical polymerization (ATRP) were self-assembled with varying amounts of γ-CDs to prepare poly(pseudorotaxanes) (PPRs). When the concentration of γ-CDs was lower, the central PEO segment served as a shell of the micelles and was preferentially bent to pass through the γ-CD cavity to construct double-chain-stranded tight-fit PPRs characterized by a channel-like crystal structure. With an increase in the amount of γ-CDs added, they began to accommodate the poly(methyl acrylate) (PMA) segments dissociated from the core of the micelles. When more γ-CDs were threaded and slipped over the segments, the γ-CDs were randomly distributed along the pentablock copolymer chain to generate single-chain-stranded loose-fit PPRs and showed no characteristic channel-like crystal structure. All the self-assembly processes of the pentablock copolymers resulted in the formation of hydrogels. After endcapping via in situ ATRP of 2-methacryloyloxyethyl phosphorylcholine (MPC), these single-chain-stranded loose-fit PPRs were transformed into conformational identical polyrotaxanes (PRs). The structures of the PPRs and PRs were characterized by means of (1)H NMR, GPC, (13)C CP/MAS NMR, 2D (1)H NOESY NMR, FTIR, WXRD, TGA and DSC analyses.
RESUMO
A pentablock copolymer was prepared via the atom transfer radical polymerization of 2-hydroxyethyl methacrylate (HEMA) initiated by 2-bromoisobutyryl end-capped PPO-PEO-PPO as a macroinitiator in DMF. Attaching PHEMA blocks altered the self-assembly process of the pentablock copolymer with γ-CDs in aqueous solution. Before attaching the PHEMA, the macroinitiator was preferentially bent to pass through the inner cavity of γ-CDs to give rise to tight-fit double-chain stranded polypseudorotaxanes (PPRs). After attaching the PHEMA, the resulting pentablock copolymer was single-chain stranded into the interior of γ-CDs to form more stable, loose-fit PPRs. The results of (1)H NMR, WXRD, DSC, TGA, (13)C CP/MAS NMR and FTIR analyses indicated that γ-CDs can accommodate and slip over PHEMA blocks to randomly distribute along the entire pentablock copolymer chain. This results in unique, single-chain stranded PPRs showing no characteristic channel-type crystal structure.
RESUMO
In our previous study, the pristine bilayer small-diameterin situtissue engineered vascular grafts (pTEVGs) were electrospun from a heparinized polycaprolactone (PCL45k) as an inner layer and a non-heparinized PCL80k as an outer layer in the thickness of about 131 µm and 202 µm, respectively. However, the hydrophilic enhancement of inner layer stemmed from the heparinization accelerated the degradation of grafts leading to the early formation of arterial aneurysms in a period of 3 months, severely hindering the perennial observation of the neo-tissue regeneration, host cell infiltration and graft remodeling in those implanted pTEVGs. Herein to address this drawback, the thickness of the outer layers was increased with PCL80k to around 268 µm, while the inner layer remained unchangeable. The thickened TEVGs named as tTEVGs were evaluated in six rabbits via a carotid artery interpositional model for a period of 9 months. All the animals kept alive and the grafts remained patent until explantation except for one whose one side of arterial blood vessels was occluded after an aneurysm occurred at 6 months. Although a significant degradation was observed in the implanted grafts at 9 month, the occurrence of aneurysms was obviously delayed compared to pTEVGs. The tissue stainings indicated that the endothelial cell remodeling was substantially completed by 3 months, while the regeneration of elastin and collagen remained smaller and unevenly distributed in comparison to autologous vessels. Additionally, the proliferation of macrophages and smooth muscle cells reached the maximum by 3 months. These tTEVGs possessing a heparinized inner layer and a thickened outer layer exhibited good patency and significantly delayed onset time of aneurysms.
Assuntos
Aneurisma , Poliésteres , Engenharia Tecidual , Animais , Coelhos , Prótese Vascular , Artérias CarótidasRESUMO
With the development of modern material science, life science and medical science, implantation materials are widely employed in clinical fields. In recent years, these materials have also evolved from inert supports or functional substitutes to bioactive materials able to trigger or promote the regenerative potential of tissues. Reasonable biological evaluation of implantation materials is the premise to make sure their safe application in clinical practice. With the continual development of implantation materials and the emergence of new implantation materials, new challenges to biological evaluation have been presented. In this paper, the research progress of implantation materials, the progress of biological evaluation methods, and also the characteristics of biocompatibility evaluation for novel implantation materials, like animal-derived implantation materials, nerve contact implantation materials, nanomaterials and tissue-engineered medical products were reviewed in order to provide references for the rational biological evaluation of implantable materials.
Assuntos
Nanoestruturas , Animais , Engenharia TecidualRESUMO
A polypseudorotaxane (PPR) comprising γ-cyclodextrin (γ-CD) as host molecules and poly(N-isopropylacrylamide) (PNIPAM) as a guest polymer is prepared via self-assembly in aqueous solution. Due to the bulky pendant isopropylamide group, PNIPAM exhibits size-selectivity toward self-assembly with α-, ß-, and γ-CDs. It can fit into the cavity of γ-CD to give rise to a PPR, but cannot pass through α-CD and ß-CD under the same conditions. The ratio of the number of γ-CD molecules to entrapped NIPAM repeat units is kept at 1:2.2 or 1:2.4, determined by (1) H NMR spectroscopy and TGA analysis, respectively, indicating that there are more than 2 but less than 3 NIPAM repeat units included by one γ-CD molecule. This finding opens new avenues to PPR-based supramolecular polymers to be used as solid, stimuli-responsive materials.
Assuntos
Acrilamidas/química , Polímeros/síntese química , Rotaxanos/química , gama-Ciclodextrinas/química , Resinas Acrílicas , Estrutura Molecular , Polimerização , Polímeros/química , beta-Ciclodextrinas/químicaRESUMO
As thermoplastic polyurethane (TPU) elastomers possess good biocompatibility and mechanical properties similar to those of native vascular tissues, they were intended to be co-electrospun with poly(ε-caprolactone) (PCL) onto the outer surface of PCL electrospun small-diameter single-layer vascular grafts (SLVGs) in this study, combining with surface heparinization. In this work, a kind of structurally reinforced TPU+PCL/PCL small-diameter bilayer vascular graft (BLVG) was fabricated via layer-by-layer electrospinning followed by the heparinization of PCL via EDC/NHS chemistry. The resulting (TPU+PCL/PCL)-Hep BLVGs presented excellent mechanical strength and higher compliance, and sustainably released heparin exhibited enhanced anti-coagulation activity. During 6-month implantation in 18 rat abdominal aortas, these vascular prostheses induced the remodeling and regeneration of neovascular tissues, and promoted ECM deposition. Compared to heparinized PCL (PCL-Hep) SLVGs, the formation of aneurysm was completely inhibited and the onset of calcification was significantly delayed in (TPU+PCL/PCL)-Hep BLVGs. Not only vascular cell makers co-expressed by CD206+ cells were identified, but also a high content of elastin was evidenced due to the improvement of mechanical strength and compliance. These results indicated the feasibility and efficacy of inhibiting the aneurysm formation and boosting the vascular remodeling by incorporating TPU into PCL-Hep small-diameter artificial vascular grafts.
Assuntos
Prótese Vascular , Poliuretanos , Animais , Aorta Abdominal/cirurgia , Poliésteres/química , Poliuretanos/química , Ratos , Alicerces Teciduais/químicaRESUMO
Increasingly growing problems in vascular access for long-term hemodialysis lead to a considerable demand for synthetic small diameter vascular prostheses, which usually suffer from some drawbacks and are associated to high failure rates. Incorporating the concept of in situ tissue engineering (TE) into synthetic small diameter blood vessels, for example, thermoplastic poly(ether urethane) (TPU) ones, could provide an alternative approach for vascular access that profits from the advantages of excellent mechanical properties of synthetic polymer materials (early cannulation) and unique biointegration regeneration of autologous neovascular tissues (long-term fistulae). In this study, a kind of heparinized small diameter (d = 2.5 mm) TPU/poly(ε-caprolactone) (TPU/PCL-Hep) bi-layered blood vessels was electrospun with an inner layer of PCL and an outer layer of TPU. Afterward, the inner surface heparinization was conducted by coupling H2N-PEG-NH2 to the corroded PCL layer and then heparin to the attached H2N-PEG-NH2 via the EDCI/NHS chemistry. Herein a heparinized PCL inner layer could not only inhibit thrombosis, but also provide sufficient space for the neotissue regeneration via biodegradation with time. Meanwhile, a TPU outer layer could confer the vascular access the good mechanical properties, such as flexibility, viability and fitness of elasticity between the grafts and host blood vessels as evidenced by the adequate mechanical properties, such as compliance (4.43 ± 0.07%/ 100 mmHg), burst pressure (1447 ± 127 mmHg) and suture retention strength (1.26 ± 0.07 N) without blood seepage after implantation. Furthermore, a rabbit carotid aortic replacement model for 5 months was demonstrated 100% animal survival and 86% graft patency. Puncture assay also revealed the puncture resistance and self-sealing (hemostatic time < 2 min). Histological analysis highlighted neotissue regeneration, host cell infiltration and graft remodeling in terms of extracellular matrix turnover. Altogether, these results showed promising aspects of small diameter TPU/PCL-Hep bi-layered grafts for hemodialytic vascular access applications.
Assuntos
Substitutos Sanguíneos , Alicerces Teciduais , Animais , Artérias Carótidas/cirurgia , Poliésteres/química , Coelhos , Engenharia Tecidual/métodos , Alicerces Teciduais/químicaRESUMO
Rapid endothelialization is crucial for in situ tissue engineering vascular grafts to prevent graft failure in the long-term. Gelatin is a promising nature material that can promote endothelial cells (ECs) adhesion, proliferation, and migration. In this study, the internal surface of electrospun polycaprolactone (PCL) vascular grafts was coated with gelatin. Endothelialization and vascular wall remolding were investigated by imaging and histological studies in the rat abdominal aorta replacement model. The endothelialization of heparinized gelatin-coated PCL (GP-H) vascular grafts was more rapid and complete than heparinized PCL (P-H) grafts. Intimal hyperplasia was milder in the GP-H vascular grafts than the P-H vascular grafts in the long-term. Meanwhile, smooth muscle cells (SMCs) and extracellular matrix (ECM) regeneration were better in the GP-H vascular grafts. By comparison, an aneurysm was observed in the P-H group in 6 months. Calcification was observed in both groups. All vascular grafts were patient after implantation in both groups. Our results showed that gelatin coating on the internal surface of PCL grafts is a simple and effective way to promote endothelialization. A more rapid endothelialization and complete endothelium can inhibit intimal hyperplasia in the long-term.
Assuntos
Células Endoteliais , Gelatina , Animais , Prótese Vascular , Humanos , Poliésteres , RatosRESUMO
Hydrogel complex scaffolds (hydrogel scaffolds) are prepared by coating precursor solutions onto heparin-modified poly(ε-caprolactone) (PCLH) scaffolds followed by subsequent in situ gelation. Here, we show that hydrogel complexation can significantly strengthen the scaffold and slow its degradation. The hydrogel scaffold was implanted into the abdominal aorta of a rat model, and the aneurysm incidence rate of the hydrogel scaffolds sharply decreased compared with that of the hydrogel-free scaffolds. Histological and immunohistological analyses showed that the implanted grafts had good vascular regeneration. The absence of calcification and occurrence of contractile smooth muscle cells (SMCs) at the first month was found in the hydrogel-free PCLH scaffold due to the presence of surface-modified heparin, whereas the hydrogel scaffold exhibited mild calcification and later occurrence of contractile SMCs as the complexed hydrogel covered the fibers and blocked the interaction between heparin and cells. Heparin was further physically encapsulated into the hydrogel before gelation, and its sustainable release was demonstrated by an in vitro release test. A pilot implantation in a rabbit carotid model showed that the encapsulated heparin modulated the scaffold characteristics including anticoagulation, anticalcification, and the early occurrence of contractile SMCs in vivo. Consequently, hydrogel complexation can significantly improve the in vivo regeneration property of the scaffold due to its multiple beneficial characteristics.
Assuntos
Aorta Abdominal/efeitos dos fármacos , Materiais Biocompatíveis/farmacologia , Hidrogéis/farmacologia , Miócitos de Músculo Liso/efeitos dos fármacos , Engenharia Tecidual , Animais , Aorta Abdominal/patologia , Materiais Biocompatíveis/síntese química , Materiais Biocompatíveis/química , Feminino , Hidrogéis/síntese química , Hidrogéis/química , Masculino , Teste de Materiais , Miócitos de Músculo Liso/patologia , Tamanho da Partícula , Ratos , Ratos Wistar , Alicerces Teciduais/químicaRESUMO
Decellularization is a promising approach in tissue engineering to generate small-diameter blood vessels. However, some challenges still exist. We performed two decellularization phases to develop an optimal decellularized scaffold and analyze the relationship between the extracellular matrix (ECM) composition and mechanical properties. In decellularization phase I, we tested sodium dodecylsulfate (SDS), Triton X-100 (TX100) and trypsin at different concentrations and exposure times. In decellularization phase II, we systematically compared five combined decellularization protocols based on the results of phase I to identify the optimal method. These protocols tested cell removal, ECM preservation, mechanical properties, and residual cytotoxicity. We further immobilized heparin to optimal decellularized scaffolds and determined its anticoagulant activity and mechanical properties. The combined decellularization protocol comprising treatment with 0.5% SDS followed by 1% TX100 could completely remove the cellular contents and preserve the mechanical properties and ECM architecture better. In addition, the heparinized decellularized scaffolds not only had sustained anticoagulant activity, but also similar mechanical properties to native vessels. In conclusion, heparinized decellularized scaffolds represent a promising direction for small-diameter vascular grafts, although further in vivo studies are needed.
Assuntos
Heparina/metabolismo , Fenômenos Mecânicos , Alicerces Teciduais/química , Animais , Matriz Extracelular/metabolismo , Octoxinol/química , Dodecilsulfato de Sódio/química , Tripsina/químicaRESUMO
AIM: Recent studies have demonstrated that mesenchymal stem cells (MSCs) can differentiate into endothelial cells. The effect of shear stress on MSC differentiation is incompletely understood, and most studies have been based on two-dimensional systems. We used a model of tissue-engineered vascular grafts (TEVGs) to investigate the effects of shear stress on MSC differentiation. METHODS: MSCs were isolated from canine bone marrow. The TEVG was constructed by seeding MSCs onto poly-epsilon-caprolactone and lactic acid (PCLA) scaffolds and subjecting them to shear stress provided by a pulsatile bioreactor for four days (two days at 1 dyne/cm(2) to 15 dyne/cm(2) and two days at 15 dyne/cm(2)). RESULTS: Shear stress significantly increased the expression of endothelial cell markers, such as platelet-endothelial cell adhesion molecule-1 (PECAM-1), VE-cadherin, and CD34, at both the mRNA and protein levels as compared with static control cells. Protein levels of alpha-smooth muscle actin (alpha-SMA) and calponin were substantially reduced in shear stress-cultured cells. There was no significant change in the expression of alpha-SMA, smooth muscle myosin heavy chain (SMMHC) or calponin at the mRNA level. CONCLUSION: Shear stress upregulated the expression of endothelial cell-related markers and downregulated smooth muscle-related markers in canine MSCs. This study may serve as a basis for further investigation of the effects of shear stress on MSC differentiation in TEVGs.
Assuntos
Prótese Vascular , Transplante de Medula Óssea , Diferenciação Celular , Células-Tronco Mesenquimais , Estresse Mecânico , Engenharia Tecidual , Actinas/metabolismo , Animais , Antígenos CD34/metabolismo , Biomarcadores/análise , Proteínas de Ligação ao Cálcio/metabolismo , Células Cultivadas , Cães , Receptores de Hialuronatos/metabolismo , Células-Tronco Mesenquimais/metabolismo , Proteínas dos Microfilamentos/metabolismo , Modelos Anatômicos , RNA/metabolismo , Alicerces Teciduais , CalponinasRESUMO
Compared with polypseudorotaxanes (PPRs) formed from the self-assembly of ß-cyclodextrins (ß-CDs) with poly(propylene glycol) (PPG) and γ-CDs with poly( N-isopropylacrylamide) (PNIPAAm), the ratio of the inner cavity size of ß-CD to the cross-sectional area of PNIPAAm appears not appropriate for their self-assembly. For a better understanding of the possibility of ß-CDs including PNIPAAm and the crystal structure of PPRs formed therefrom, the PNIPAAm homo- and copolymers were subjected to self-assembly with ß-CDs in an aqueous solution at room temperature. The results revealed that when ß-CDs meet thicker PNIPAAms, the self-assembly takes place, not only giving rise to PPRs by a manner of main-chain inclusion complexation but also presenting the PPRs a matched over-fit crystal structure different from those of either a matched tight-fit ß-CD-PPG PPR or a mismatched over-fit γ-CD-PNIPAAm PPR. This is most likely due to the thicker PNIPAAm adapting its unfavorable main-chain cross-sectional area to fit into the cavity of ß-CDs by changing the side-chain conformations. Based on the X-ray diffraction patterns, a monoclinic crystal system was created from these PPRs and the unit cell parameters calculated were as follows: a = 15.3 Å, b = 10.3 Å, and c = 21.2 Å; ß = 110.3°; and space group P2. It suggested that this matched over-fit crystal structure would possess a Mosaic crystal structure rather than a typical channel-like one.
RESUMO
Aiming to construct small diameter (ID <6 mm) off-the-shelf tissue-engineered vascular grafts, the end-group heparinizd poly(ε-caprolactone) (PCL) is synthesized by a three-step process and then electrospun into an inner layer of double-layer vascular scaffolds (DLVSs) showing a hierarchical double distribution of nano- and microfibers. Afterward, PCL without the end-group heparinization is electrospun into an outer layer. A steady release of grafted heparin and the existence of a glycocalyx structure give the grafts anticoagulation activity and the conjugation of heparin also improves hydrophilicity and accelerates degradation of the scaffolds. The DLVSs are evaluated in six rabbits via a carotid artery interpositional model for a period of three months. All the grafts are patent until explantation, and meanwhile smooth endothelialization and fine revascularization are observed in the grafts. The composition of the outer layer of scaffolds exhibits a significant effect on the aneurysm dilation after implantation. Only one aneurysm dilation is detected at two months and no calcification is formed in the follow-up term. How to prevent aneurysms remains a challenging topic.
Assuntos
Implantes Absorvíveis , Prótese Vascular , Heparina/farmacologia , Neovascularização Fisiológica , Poliésteres/química , Engenharia Tecidual/métodos , Animais , Artérias Carótidas/cirurgia , Proliferação de Células/efeitos dos fármacos , Técnicas Eletroquímicas , Células Endoteliais/citologia , Células Endoteliais/efeitos dos fármacos , Células Endoteliais/fisiologia , Heparina/química , Nanofibras/química , Coelhos , Alicerces TeciduaisRESUMO
Four l-Lysine(Lys)-l-glutamic acid(Glu) dipeptide derivatives (1-4) and their precursor-a single fluorenyl-9-methoxycarbonyl(Fmoc)-l-Lys(Fmoc)-OH amino acid (5) were demonstrated as gelators to gelate a variety of alcohols and aromatic solvents under the sonication conditions. Compared to the routine heating-cooling protocol, the ultrasound substantially brought down the minimum gelation concentrations (MGCs) of the resulting organogels. The Fourier transform infrared spectroscopy (FT-IR) and fluorescence studies revealed that the π-π stacking and hydrogen bonding act as major driving forces for the self-assembly of these lysine-based gelators into supramolecular fibrous three dimensional (3D) network, where the more the Fmoc protecting groups, the gelators are more responsive to ultrasound-stimulus and more conducive to an ordered molecular arrangement reinforcing the intermolecular forces. Moreover, the ultrasound-triggered organogels of 5 exhibited the thixotropic property. Upon imposing a mechanical shear, its gels with the fibrous 3D network structure were unraveled into sols. However, after standing quiescently over time, these sols returned to the gels showing a more ordered lamella-like packing structure as evidenced by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses.
Assuntos
Dipeptídeos/química , Fluorenos/química , Géis/química , Lisina/análogos & derivados , Ligação de Hidrogênio , Modelos Moleculares , Sonicação , Espectroscopia de Infravermelho com Transformada de Fourier , Difração de Raios XRESUMO
A kind of novel three-dimensional crosslinked networks based on the self-assemly of α-CDs with thiolated four-arm PEG was prepared by thiol-disulfide interchange reaction using a three-step oxidation. The supramolecular structure of the resulting hydrogels was characterized FTIR, H NMR, XRD, DSC and TGA measurements. The results demonstrated that the channel-type crystalline structure of inclusion complexes is still maintained after the multi-step oxidation. According to the swelling and degradation tests, the swelling behaviors and degradation properties can be readily regulated by tuning the feed compositions of α-CDs and PEG-thiolated prepolymer. Furthermore, the threading α-CDs clearly protects disulfide bonds from an attack of a reduced form of glutathione as a result of prolonging the degradation time of the hydrogels in water.