Modulating rheological and degradation properties of temperature-responsive gelling systems composed of blends of PCLA-PEG-PCLA triblock copolymers and their fully hexanoyl-capped derivatives

Dynamic hydrazone crosslinked salecan/chondroitin sulfate hydrogel platform as a promising wound healing Strategy: A comparative study on antibiotic and probiotic delivery

Natural polysaccharide-based active-ingredient carriers have been a source of great concern for a long time. In order to explore potential antibiotics and probiotics carriers, a novel injectable chondroitin sulfate/salecan (CS) hydrogel was constructed by forming dynamic hydrazone bonds. Scanning electron microscope (SEM), proton nuclear magnetic resonance (1H NMR), Fourier transform infrared spectroscopy (FTIR), bacteriostatic test, and rheological experiments were used to investigate the chemical structure, inherent morphology, and enzymatic corruption of the hydrogel in vitro. The resulting hydrogels exhibited ideal probiotics loading capacity, drug release behavior, excellent antimicrobial activity and variable properties. Crucially, owing to its exceptional biocompatibility and reversible crosslinking network, this hydrogel can function as a three-dimensional extracellular matrix for cells, enabling cells to maintain high vitality and proliferation, and promote wound healing. The aforementioned findings indicated that this novel hydrogel can be a promising candidate as an active-ingredient carrier and scaffold material for tissue engineering.

Precisely Programmable Degradation and Drug Release Profiles in Triblock Copolyether Hydrogels with Cleavable Acetal Pendants

Hydrogels hold significant promise as drug delivery systems due to their distinct advantage of sustained localized drug release. However, the challenge of regulating the initial burst release while achieving precise control over degradation and drug-release kinetics persists. Herein, we present an ABA-type triblock copolymer-based hydrogel system with precisely programmable degradation and release kinetics. The resulting hydrogels were designed with a hydrophilic poly(ethylene oxide) midblock and a hydrophobic end-block composed of polyethers with varying ratios of ethoxyethyl glycidyl ether and tetrahydropyranyl glycidyl ether acetal pendant possessing different hydrolysis kinetics. This unique side-chain strategy enabled us to achieve a broad spectrum of precise degradation and drug-release profiles under mildly acidic conditions while maintaining the cross-linking density and viscoelastic modulus, which is unlike the conventional polyester-based backbone degradation system. Furthermore, programmable degradation of the hydrogels and release of active therapeutic agent paclitaxel loaded therein are demonstrated in an in vivo mouse model by suppressing tumor recurrence following surgical resection. Tuning of the fraction of two acetal pendants in the end-block provided delicate tailoring of hydrogel degradation and the drug release capability to achieve the desired therapeutic efficacy. This study not only affords a facile means to design hydrogels with precisely programmable degradation and release profiles but also highlights the critical importance of aligning the drug release profile with the target disease.

Hydrolysis-Driven Viscoelastic Transition in Triblock Copolyether Hydrogels with Acetal Pendants

While the hydrolytic cleavage of ester groups is widely exploited in degradable hydrogels, the scission in the midst of chain backbones can bring dramatic changes in the mechanical properties of the hydrogels. However, the predictive design of the mechanical profile of the hydrogels is a complex task, mainly due to the randomness of the location of chain scission. To overcome this challenge, we herein present degradable ABA triblock poly(ethylene oxide)-based hydrogels containing an A-block bearing acetal pendant, which provides systematically tunable mechano-temporal properties of the hydrogels. In particular, hydrophobic endocyclic tetrahydropyranyl or exocyclic 1-(cyclohexyloxy)ethyl acetal pendants are gradually cleaved by acidic hydrolysis, leading to the gel-to-sol transition at room temperature. Most importantly, a series of dynamic mechanical analyses coupled with ex situ NMR spectroscopy revealed that the hydrolysis rate can be orthogonally and precisely tuned by changing the chemical structure and hydrophobicity of acetal pendants. This study provides a platform for the development of versatile degradable hydrogels in a highly controllable manner.

PEG-based thermosensitive and biodegradable hydrogels

Injectable thermosensitive hydrogels are free-flowing polymer solutions at low or room temperature, making them easy to encapsulate the therapeutic payload or cells via simply mixing. Upon injection into the body, in situ forming hydrogels triggered by body temperature can act as drug-releasing reservoirs or cell-growing scaffolds. Finally, the hydrogels are eliminated from the administration sites after they accomplish their missions as depots or scaffolds. This review outlines the recent progress of poly(ethylene glycol) (PEG)-based biodegradable thermosensitive hydrogels, especially those composed of PEG-polyester copolymers, PEG-polypeptide copolymers and poly(organophosphazene)s. The material design, performance regulation, thermogelation and degradation mechanisms, and corresponding applications in the biomedical field are summarized and discussed. A perspective on the future thermosensitive hydrogels is also highlighted. STATEMENT OF SIGNIFICANCE: Thermosensitive hydrogels undergoing reversible sol-to-gel phase transitions in response to temperature variations are a class of promising biomaterials that can serve as minimally invasive injectable systems for various biomedical applications. Hydrophilic PEG is a main component in the design and fabrication of thermoresponsive hydrogels due to its excellent biocompatibility. By incorporating hydrophobic segments, such as polyesters and polypeptides, into PEG-based systems, biodegradable and thermosensitive hydrogels with adjustable properties in vitro and in vivo have been developed and have recently become a research hotspot of biomaterials. The summary and discussion on molecular design, performance regulation, thermogelation and degradation mechanisms, and biomedical applications of PEG-based thermosensitive hydrogels may offer a demonstration of blueprint for designing new thermogelling systems and expanding their application scope.

Injectable and thermosensitive hydrogels mediating a universal macromolecular contrast agent with radiopacity for noninvasive imaging of deep tissues

It is very challenging to visualize implantable medical devices made of biodegradable polymers in deep tissues. Herein, we designed a novel macromolecular contrast agent with ultrahigh radiopacity (iodinate content > 50%) via polymerizing an iodinated trimethylene carbonate monomer into the two ends of poly(ethylene glycol) (PEG). A set of thermosensitive and biodegradable polyester-PEG-polyester triblock copolymers with varied polyester compositions synthesized by us, which were soluble in water at room temperature and could spontaneously form hydrogels at body temperature, were selected as the demonstration materials. The addition of macromolecular contrast agent did not obviously compromise the injectability and thermogelation properties of polymeric hydrogels, but conferred them with excellent X-ray opacity, enabling visualization of the hydrogels at clinically relevant depths through X-ray fluoroscopy or Micro-CT. In a mouse model, the 3D morphology of the radiopaque hydrogels after injection into different target sites was visible using Micro-CT imaging, and their injection volume could be accurately obtained. Furthermore, the subcutaneous degradation process of a radiopaque hydrogel could be non-invasively monitored in a real-time and quantitative manner. In particular, the corrected degradation curve based on Micro-CT imaging well matched with the degradation profile of virgin polymer hydrogel determined by the gravimetric method. These findings indicate that the macromolecular contrast agent has good universality for the construction of various radiopaque polymer hydrogels, and can nondestructively trace and quantify their degradation in vivo. Meanwhile, the present methodology developed by us affords a platform technology for deep tissue imaging of polymeric materials.

Biocompatible copolymer formulations to treat glioblastoma multiforme

The treatment for glioblastoma multiforme (GBM) has not changed for more than 20 years while the prognosis for the patients is still poor and most of them survive less than 1 year after diagnosis. The standard of care for GBM is comprised of surgical resection followed by radiotherapy and oral chemotherapy with temozolomide. The placement of carmustine wafers in the brain after tumour removal is added in cases of recurrent glioma. Significant research is underway to improve the GBM therapy outcome and patient quality of life. Biomaterials are in the front line of the research focus for new treatment options. Specially, biocompatible polymers have been proposed in hydrogel-based formulations aiming at injectable and localized therapies. These formulations can comprise many different pharmacological agents such as chemotherapeutic drugs, nanoparticles, cells, nucleic acids, and diagnostic agents. In this manuscript, we review the most recent formulations developed and tested both in vitro and in vivo using different types of hydrogels. Firstly, we describe three common types of thermo-responsive polymers addressing the advantages and drawbacks of their formulations. Then, we focus on formulations specifically developed for GBM treatment.

Localized controlled release of bevacizumab and doxorubicin by thermo-sensitive hydrogel for normalization of tumor vasculature and to enhance the efficacy of chemotherapy

In a malignant tumor, overexpression of pro-angiogenic factors like vascular endothelial growth factor (VEGF) provokes the production of pathologic vascular networks characterized by leaky, chaotically organized, immature, thin-walled, and ill-perfused. As a result, hostile tumor environment would be developed and profoundly hinders anti-cancer drug activities and fuels tumor progression. In this study, we develop a strategy of sequential sustain release of anti-angiogenic drug, Bevacizumab (BVZ), and anti-cancer drug, Doxorubicin (DOX), using poly (d, l-Lactide)- Poly (ethylene glycol) -Poly (d, l-Lactide) (PDLLA-PEG-PDLLA) hydrogel as a local delivery system. The release profiles of the drugs from the hydrogel were investigated in vitro which confirmed that relatively rapid release of BVZ (73.56 ± 1.39%) followed by Dox (61.21 ± 0.62%) at pH 6.5 for prolonged period. The in vitro cytotoxicity test revealed that the copolymer exhibited negligible cytotoxicity up to 2.5 mg ml^-1 concentration on HaCaT and HeLa cells. Likeways, the in vitro degradation of the copolymer showed 41.63 ± 2.62% and 73.25 ± 4.36% weight loss within 6 weeks at pH 7.4 and 6.5, respectively. After a single intratumoral injection of the drug-encapsulated hydrogel on Hela xenograft nude, hydrogel co-loaded with BVZ and Dox displayed the highest tumor suppression efficacy for up to 36 days with no noticeable damage on vital organs. Therefore, localized co-delivery of anti-angiogenic drug and anti-cancer drug by hydrogel system may be a promising approach for enhanced chemotherapeutic efficacy in cancer treatment.

Sustained Release of Vascular Endothelial Growth Factor from Poly(ε-caprolactone-PEG-ε-caprolactone)-b-Poly(l-lactide) Multiblock Copolymer Microspheres

Vascular endothelial growth factor (VEGF) is the major regulating factor for the formation of new blood vessels, also known as angiogenesis. VEGF is often incorporated in synthetic scaffolds to promote vascularization and to enhance the survival of cells that have been seeded in these devices. Such applications require sustained local delivery of VEGF of around 4 weeks for stable blood vessel formation. Most delivery systems for VEGF only provide short-term release for a couple of days, followed by a release phase with very low VEGF release. We now have developed VEGF-loaded polymeric microspheres that provide sustained release of bioactive VEGF for 4 weeks. Blends of two swellable poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone)-b-poly(l-lactide) ([PCL-PEG-PCL]-b-[PLLA])-based multiblock copolymers with different PEG content and PEG molecular weight were used to prepare the microspheres. Loading of the microspheres was established by a solvent evaporation-based membrane emulsification method. The resulting VEGF-loaded microspheres had average sizes of 40-50 μm and a narrow size distribution. Optimized formulations of a 50:50 blend of the two multiblock copolymers had an average VEGF loading of 0.79 ± 0.09%, representing a high average VEGF loading efficiency of 78 ± 16%. These microspheres released VEGF continuously over 4 weeks in phosphate-buffered saline pH 7.4 at 37 °C. This release profile was preserved after repeated and long-term storage at -20 °C for up to 9 months, thereby demonstrating excellent storage stability. VEGF release was governed by diffusion through the water-filled polymer matrix, depending on PEG molecular weight and PEG content of the polymers. The bioactivity of the released VEGF was retained within the experimental error in the 4-week release window, as demonstrated using a human umbilical vein endothelial cells proliferation assay. Thus, the microspheres prepared in this study are suitable for embedment in polymeric scaffolds with the aim of promoting their functional vascularization.

Diselenide linkage containing triblock copolymer nanoparticles based on Bi(methoxyl poly(ethylene glycol))-poly(ε-carprolactone): Selective intracellular drug delivery in cancer cells

Redox-responsive diselenide bond containing triblock copolymer Bi(mPEG-SeSe)-PCL,Bi(mPEG-SeSe)-PCL was developed for specific drug release in cancer cells. Initially, ditosylated polycaprolactone was prepared via the reaction between polycaprolactone diol (PCL-diol) and tosyl chloride (TsCl). Next, Bi(mPEG-SeSe)-PCL was synthesized via the reaction between ditosylated polycaprolactone and sodium diselenide initiated poly (ethylene glycol) methyl ether tosylate. The synthesized amphiphilic triblock copolymer could self-assemble into uniform nanoparticles in aqueous medium and disassemble upon redox stimuli. The Bi(mPEG-SeSe)-PCL nanoparticles showed a DOX loading content of 5.1 wt% and a loading efficiency of 49%. In vitro drug release studies showed that about 62.4% and 56% of DOX was released from the nanoparticles during 72 h at 37 °C in PBS containing 2 mg/mL (6 mM) GSH and 0.1% H2O2, respectively, whereas only about 30% of DOX was released in PBS under the same conditions. The cell viability (MTT assays) results showed that the synthesized material was biocompatible with above 90% cell viability, and that the DOX-loaded Bi(mPEG-SeSe)-PCL nanoparticles had a high antitumor activity against HeLa cells and low antitumor activity against HaCaT cells, following a 24-h incubation period. Three-dimensional (3D) spheroids of HeLa cells were established for the evaluation of localization of the DOX-loaded nanoparticles into spheroids cells and the successfully inhibition of 3D tumor spheroid growth. The results indicated that the synthesized material Bi(mPEG-SeSe)-PCL was biocompatible and it could be a potential candidate for anticancer drug delivery system.

Non-Anticoagulant Heparin Prodrug Loaded Biodegradable and Injectable Thermoresponsive Hydrogels for Enhanced Anti-Metastasis Therapy

Metastasis is a pathogenic spread of cancer cells from the primary site to surrounding tissues and distant organs, making it one of the primary challenges for effective cancer treatment and the major cause of cancer mortality. Heparin-based biomaterials exhibit significant inhibition of cancer cell metastasis. In this study, a non-anticoagulate heparin prodrug is developed for metastasis treatment with a localized treatment system using temperature sensitive, injectable, and biodegradable (poly-(ε-caprolactone-co-lactide)-b-poly(ethylene glycol)-b-poly(ε-caprolactone-co-lactide) polymeric hydrogel. The drug molecule (heparin) is conjugated with the polymer via esterification, and its sustained release is ensured by hydrolysis and polymeric biodegradation. An aqueous solution of the polymer could be used as an injectable solution at below 25 °C and it achieves gel formation at 37 °C. The anti-metastasis effect of the hydrogels is investigated both in vitro and in vivo. The results demonstrated that local administration of injectable heparin-loaded hydrogels effectively promote an inhibitory effect on cancer metastasis.

In vivo pharmacokinetics of celecoxib loaded endcapped PCLA-PEG-PCLA thermogels in rats after subcutaneous administration

Injectable thermogels based on poly(ε-caprolactone-co-lactide)-b-poly(ethylene glycol)-b-poly(ε-caprolactone-co-lactide) (PCLA-PEG-PCLA) containing an acetyl- or propyl endcap and loaded with celecoxib were developed for local drug release. The aim of this study was to determine the effects of the composition of the celecoxib/PCLA-PEG-PCLA formulation on their in vivo drug release characteristics. Furthermore, we want to obtain insight into the in vitro-in vivo correlation. Different formulations were injected subcutaneously in rats and blood samples were taken for a period of 8 weeks. Celecoxib half-life in blood increased from 5 h for the bolus injection of celecoxib to more than 10 days for the slowest releasing gel formulation. Sustained release of celecoxib was obtained for at least 8 weeks after subcutaneous administration. The release period was prolonged from 3 to 6-8 weeks by increasing the injected volume from 100 to 500 µL, which also led to higher serum concentrations in time. Propyl endcapping of the polymer also led to a prolonged release compared to the acetyl endcapped polymer (49 versus 21 days) and at equal injected dose of the drug in lower serum concentrations. Increasing the celecoxib loading from 10 mg/mL to 50 mg/mL surprisingly led to prolonged release (28 versus 56 days) as well as higher serum concentrations per time point, even when corrected for the higher dose applied. The in vivo release was about twice as fast compared to the in vitro release for all formulations. Imaging of organs of mice, harvested 15 weeks after subcutaneous injection with polymer solution loaded with infrared-780 labelled dye showed no accumulation in any of these harvested organs except for traces in the kidneys, indicating renal clearance. Due to its simplicity and versatility, this drug delivery system has great potential for designing an injectable to locally treat osteoarthritis, and to enable tuning the gel to meet patient-specific needs.

Effects of the multilayer structures on Exenatide release and bioactivity in microsphere/thermosensitive hydrogel system

Traditional polypeptide-loaded PLGA microspheres (PM) using emulsion electrospray techniques often exhibit unsteady release and limited bioactivity. To solve these two problems, an Exenatide (EXT)-loaded multilayer system composed ofPM and thermosensitive hydrogel was prepared by the emulsion electrospray technique in this study. Hydrogel mixture were loaded in PLGA microspheres as Depot-hydrogel to prepare Gel/PM. The PM/Gel and Gel/PM/Gel systems were obtained by dispersion of PM and Gel/PM into hydrogel mixture, respectively. EXT in Gel/PM/Gel showed a constantly in vitro release for 30 days, which was significantly enhanced in comparison of those in the PM/Gel and the Gel/PM. PM/Gel and Gel/PM/Gel showed diminished burst release and no platform period compared with PM and Gel/PM. And these could be because the introduced Matrix-hydrogel outside, as a buffer layer, inhibited burst releases and exhibited a sustained manner. The inner Depot-hydrogelstructure slowed the PLGA degradation rate and drug release rate. As well, more than 15-day blood glucose levels in KKAy mice were greatly maintained at 7.50-9.50 mmol/L after a single subcutaneous injection of Gel/PM/Gel (4.95 μg/kg). Spatial stability and further bioactivity of released EXT were well protected by EXT-hydrogel complexes, and undesirable uptake of EXT and microspheres via phagocytes were also decreased by PEG shell. Thus, the long-acting microspheres/hydrogel multilayer system prepared by emulsion electrospray technique showed promising potentials for loading hydrophilic polypeptides and proteins.

Structural and Rheological Properties of Temperature-Responsive Amphiphilic Triblock Copolymers in Aqueous Media

Thermoresponsive amphiphilic biodegradable block copolymers of the type poly(ε-caprolactone-co-lactide)-poly(ethylene glycol)-poly(ε-caprolactone-co-lactide) (PCLA-PEG_m-PCLA) have great potential for various biomedical applications. In the present study, we have surveyed the effects of PEG spacer length (m = 1000 and 1500), temperature, and polymer concentration on the self-assembling process to form supramolecular structures in aqueous solutions of the PCLA-PEG_m-PCLA copolymer. This copolymer has a lower critical solution temperature, and the cloud point depends on both concentration and PEG length. Thermoreversible hydrogels are formed in the semidilute regime; the gel windows in the phase diagrams can be tuned by the concentration and length of the PEG spacer. The rheological properties of both dilute and semidilute samples were characterized; especially the sol-to-gel transition was examined. Small-angle neutron scattering (SANS) experiments reveal fundamental structural differences between the two copolymers for both dilute and semidilute samples. The intensity profiles for the copolymer with the long PEG spacer could be described by a spherical core-shell model over a broad temperature domain, whereas the copolymer with the short hydrophilic spacer forms rod-like species over an extended temperature range. This finding is supported by cryo-TEM images. At temperatures approaching macroscopic phase separation, both copolymers seem to assume extended rod-like structures.

Efficacy of Poly(D,L-Lactic Acid-co-Glycolic acid)-Poly(Ethylene Glycol)-Poly(D,L-Lactic Acid-co-Glycolic Acid) Thermogel As a Barrier to Prevent Spinal Epidural Fibrosis in a Postlaminectomy Rat Model

STUDY DESIGN

Experimental animal study.

OBJECTIVE

The authors conducted a study to determine the efficacy and safety of the poly(D,L-lactic acid-co-glycolic acid)-poly(ethylene glycol)-poly(D,L-lactic acid-co-glycolic acid) (PLGA-PEG-PLGA) thermogel to prevent peridural fibrosis in an adult rat laminectomy model.

SUMMARY OF BACKGROUND DATA

Peridural fibrosis often occurs after spinal laminectomy. It might cause persistent back and/or leg pain postoperatively and make a reoperation more difficult and dangerous. Various materials have been used to prevent epidural fibrosis, but only limited success has been achieved.

MATERIALS AND METHODS

The PLGA-PEG-PLGA thermogel was synthesized by us. Total L3 laminectomies were performed on 24 rats. The PLGA-PEG-PLGA thermogel or chitosan (CHS) gel (a positive control group) was applied to the operative sites in a blinded manner. In the control group, the L3 laminectomy was performed and the defect was irrigated with the NS solution 3 times. All the rats were killed 4 weeks after the surgery.

RESULTS

The cytotoxicity of this thermogel was evaluated in vitro and the result demonstrated that no evidence of cytotoxicity was observed. The extent of epidural fibrosis, the area of epidural fibrosis, and the density of the fibroblasts and blood vessel were evaluated histologically. There were statistical differences among the PLGA-PEG-PLGA thermogel or CHS gel group compared with the control group. Although there was no difference between the PLGA-PEG-PLGA thermogel and CHS gel, the efficiency of the PLGA-PEG-PLGA thermogel was shown to be slightly improved compared with the CHS gel.

CONCLUSIONS

The biocompatibility of the PLGA-PEG-PLGA thermogel was proven well. The application of this thermogel effectively reduced epidural scarring and prevented the subsequent adhesion to the dura mater. No side effects were noted in the rats.

Positional isomeric effects of coupling agents on the temperature-induced gelation of triblock copolymer aqueous solutions

The linking angles of positional isomers in the middle of thermogelling mPEG-PLGA-mPEG polymers were found to affect their microscopic conformations and macroscopic properties.

A novel sulfamethazine-based pH-sensitive copolymer for injectable radiopaque embolic hydrogels with potential application in hepatocellular carcinoma therapy

After transcatheter delivery through hepatic artery, a hydrogel can be formed within tumor vasculature by the decrease of environmental pH, block the blood vessel and control the release of loaded anticancer drugs.

Multi-Functional Macromers for Hydrogel Design in Biomedical Engineering and Regenerative Medicine

Contemporary biomaterials are expected to provide tailored mechanical, biological and structural cues to encapsulated or invading cells in regenerative applications. In addition, the degradative properties of the material also have to be adjustable to the desired application. Oligo- or polymeric building blocks that can be further cross-linked into hydrogel networks, here addressed as macromers, appear as the prime option to assemble gels with the necessary degrees of freedom in the adjustment of the mentioned key parameters. Recent developments in the design of multi-functional macromers with two or more chemically different types of functionalities are summarized and discussed in this review illustrating recent trends in the development of advanced hydrogel building blocks for regenerative applications.

An injectable thermogel with high radiopacity

An injectable thermogel with high X-ray opacity was designed and synthesized for the first time and such a system shows great potential in non-invasive diagnosis and therapy.

Comparative studies of thermogels in preventing post-operative adhesions and corresponding mechanisms

Post-surgical peritoneal adhesions constitute a classic problem in surgery, and thus anti-adhesion materials are much required. In this study, a series of polyester-PEG-polyester triblock copolymers with different biodegradable polyester compositions were synthesized, their properties were examined, and the in vivo efficacies as anti-adhesion biomaterials were evaluated in a comparative way for the first time. These samples not only exhibited various morphologies in the bulk state, but also possessed different stabilities in the sol state. All the polymer aqueous solutions with appropriate compositions and concentrations underwent sol-gel transitions with increase of temperature and formed semi-solid hydrogels at body temperature. The efficacy of PEG/polyester thermogels (25 wt%) for preventing post-operative abdominal adhesions was investigated and compared in a rabbit model of sidewall defect-bowel abrasion. Different efficacies of anti-adhesion were observed, possible mechanisms were discussed, and the importance of viscoelasticity was suggested for the first time. These results illustrated that appropriate properties of PEG/polyester thermogels including viscoelastic matrix, hydrophilic surface and moderate in vivo persistence played crucial roles in enabling an effective device to prevent post-surgical peritoneal adhesions.

Biomimetic fibrin–hyaluronan hydrogels for nucleus pulposus regeneration

Aim: To develop a biomimetic polymeric injectable hydrogel that can support nucleus pulposus (NP) regeneration. Materials & methods: Natural polymer-based hydrogels were synthesized using fibrinogen (FBG) and hyaluronic acid (HA), conjugated by a novel two-step procedure. Bovine NP cells were cultured in FBG–HA conjugate-based 3D beads in vitro and in a nucleotomized organ culture model. Results: FBG–HA conjugate-based hydrogels prepared with 235 KDa HA at a FBG/HA w/w ratio of 17:1 showed superior gel stability and mechanical properties and markedly increased glycosaminoglycan synthesis compared with a FBG/HA mixture-based hydrogels or fibrin gels. Gene-expression levels of NP markers were maintained in vitro. In organ culture, NP cells seeded in FBG–HA conjugate-based hydrogels showed better integration with native NP tissue compared with fibrin gels. Moreover, FBG–HA conjugate-based hydrogels restored compressive stiffness and disc height after nucleotomy under dynamic load. Conclusion: Specific FBG–HA conjugate-based hydrogels may be suitable as injectable materials for minimally invasive, biological NP regeneration.

Effects of l-lactide and d,l-lactide in poly(lactide-co-glycolide)-poly(ethylene glycol)-poly(lactide-co-glycolide) on the bulk states of triblock copolymers, and their thermogellation and biodegradation in water

In this study, the effects of l-lactide and d,l-lactide on the thermogelling and biodegradation behaviors of PLGA-PEG-PLGA copolymers were revealed.

pH-sensitive micelles self-assembled from multi-arm star triblock co-polymers poly(ε-caprolactone)-b-poly(2-(diethylamino)ethyl methacrylate)-b-poly(poly(ethylene glycol) methyl ether methacrylate) for controlled anticancer drug delivery

A series of amphiphilic 4- and 6-armed star triblock co-polymers poly(ε-caprolactone)-b-poly(2-(diethylamino)ethyl methacrylate)-b-poly(poly(ethylene glycol) methyl ether methacrylate) (4/6AS-PCL-b-PDEAEMA-b-PPEGMA) were developed by a combination of ring opening polymerization and continuous activators regenerated by electron transfer atom transfer radical polymerization. The critical micelle concentration values of the star co-polymers in aqueous solution were extremely low (2.2-4.0mgl(-1)), depending on the architecture of the co-polymers. The self-assembled blank and doxorubicin (DOX)-loaded three layer micelles were spherical in shape with an average size of 60-220nm determined by scanning electron microscopy and dynamic light scattering. The in vitro release behavior of DOX from the three layer micelles exhibited pH-dependent properties. The DOX release rate was significantly accelerated by decreasing the pH from 7.4 to 5.0, due to swelling of the micelles at lower pH values caused by the protonation of tertiary amine groups in DEAEMA in the middle layer of the micelles. The in vitro cytotoxicity of DOX-loaded micelles to HepG2 cells suggested that the 4/6AS-PCL-b-PDEAEMA-b-PPEGMA micelles could provide equivalent or even enhanced anticancer activity and bioavailability of DOX and thus a lower dosage is sufficient for the same therapeutic efficacy. The results demonstrate that the pH-sensitive multilayer micelles could have great potential application in delivering hydrophobic anticancer drugs for improved cancer therapy.