Degradation Rate Of Hydrogels Research Articles

A smart aminoglycoside hydrogel with tunable gel degradation, on-demand drug release, and high antibacterial activity

Aminoglycosides are a family of critically important antibiotics for the treatment of serious infections including multidrug-resistant pathogens. However, clinical use of aminoglycoside antibiotics is compromised by bacterial biofilm formation at subinhibitory concentrations or adverse side effects such as ototoxicity and nephrotoxicity at high antibiotic doses. Preparation of aminoglycoside formulation that allows on-demand drug delivery is a solution to this sticky issue. Here, we designed a new type of aminoglycoside hydrogels by cross-linking oxidized polysaccharides such as dextran, carboxymethyl cellulose, alginate, and chondroitin using aminoglycosides as cross-linkers. The hydrogel modulus, degradation rate and release kinetics can be precisely modulated by tailoring the aminoglycoside dose during gel formation. The aminoglycoside hydrogel showed fast gelation, self-healing and on-demand drug release behaviors, and high antibacterial activities in vitro and in vivo against both Gram-positive and Gram-negative bacteria. This study provides a facile and promising strategy to develop smart hydrogels for topical administration of aminoglycoside antibiotics.

Degradation prediction model and stem cell growth of gelatin-PEG composite hydrogel.

Gelatin hydrogel has great potential in regenerative medicine. The degradation of gelatin hydrogel is important to control the release profile of encapsulated biomolecules and regulate in vivo tissue repair process. As a plasticizer, PEG can significantly improve the mechanical property of gelatin hydrogel. However, how preparation parameters affect the degradation rate of gelatin-PEG composite hydrogel is still not clear. In this study, the significant effect factor, glutaraldehyde (GA) concentration, was confirmed by means of Plackett-Burman method. Then a mathematical model was built to predict the degradation rate of composite hydrogels under different preparation conditions using the response surface method (RSM), which was helpful to prepare the certain composite hydrogel with desired degradation rate. In addition, it was found that gelatin-PEG composite hydrogel surface well supported the adhesion and growth of human mesenchymal stem cells (MSCs). Moreover, PEG concentration not only could adjust hydrogel degradation more subtly, but also might increase the cross-linking degree and affect the cell migration. Therefore, these results would be useful to optimize the preparation of gelatin-PEG composite hydrogel for drug delivery or tissue engineering. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 3149-3156, 2016.

Graphene oxide–enriched double network hydrogel with tunable physico-mechanical properties and performance

An emerging approach to obtain polymeric hydrogels with superior properties is integrating carbon-based nanomaterials within their network structure. On the other hand, hydrogels with tailored physical and mechanical characteristics are desirable class of materials which have extensive application in drug delivery and tissue engineering. This study presents a strategy to achieve graphene oxide (GO)-enriched hydrogels with modulated physico-mechanical properties and performance. GO/poly acrylic acid (PAA)/gelatin hydrogels are fabricated via in situ polymerization method followed by chemical crosslinking of gelatin molecules. N,N′-Methylenebisacrylamide (BIS) in a various concentrations is used within the prepolymer composition as cross-linking agent to prepare a set of nanocomposite hydrogels. Fourier transform infrared (FTIR), X-ray diffraction (XRD), and atomic force microscopy (AFM) are utilized to characterize the fabricated hydrogel samples. The microstructure of samples is analyzed with scanning electron microscopy (SEM). The mechanical properties of the specimens are evaluated by rheometry. The swelling behavior, degradation kinetic and porosity of the hydrogels as well as their in vitro cytotoxicity are also assessed. The results show successful synthesis of nano GO sheets and polymer composites. The increase of cross-linker concentration is decreased the swelling ratio and increased the porosity of hydrogel samples. A wide range of pore diameters (70–300μm) and mechanical stiffness (storage modulus of 2000–25,000Pa) is obtained. Through manipulation of cross-linking density the degradation rate of nanocomposite hydrogels is controlled. Finally, no toxicity is detected by exposure of the hydrogel extracts to osteoblast osteosarcoma cells. The optimized hydrogel samples having appropriate range of physical characteristics and functionality suggest the application of the 3D structures as scaffold material for hard tissue construction.

Insight into the Unexpectedly Rapid Degradation of Dihydroxyacetone-Based Hydrogels

Biodegradable hydrogels are an important class of biomaterials with a diverse range of applications. In some cases, a rapid hydrogel degradation rate is advantageous. Polycarbonate hydrogels based on dihydroxyacetone (DHA), a natural metabolite, have been reported to undergo surprisingly fast hydrolytic degradation. In the present work, insight into the key features of DHA that contribute to the observed degradation rates is gained. In vitro degradation (mass loss) of three different chemically cross-linked polycarbonate hydrogels is investigated to shed light on the role of the ketone functional group, as well as the carbon-chain length between the ketone and carbonate bonds. The ketone is found to be the major cause of rapid degradation. Also, mass loss is accelerated by increased temperature and pH, offering insight into potential tuning parameters and storage conditions. The results show that DHA is a promising monomeric unit for the design of rapidly degrading, biocompatible, and functional biomaterials.

Tissue engineering cell-based bioelectronics

Event Abstract Back to Event Tissue engineering cell-based bioelectronics Ulises Aregueta Robles1, Khoon S. Lim2, Penny J. Martens1, Nigel H. Lovell1, Laura A. Poole-Warren1 and Rylie A. Green1 1 University of NSW, Graduate School of Biomedical Engineering, Australia 2 University of Otago, Department of Orthopaedic Surgery & Musculoskeletal Medicine, New Zealand Tissue engineered electrodes aim to deliver a living cellular layer to interface bionic devices with target tissue by establishing synaptic connections between the electrode and target nerve. A significant challenge in developing this technology is to engineer a hydrogel carrier that can support growth and function of complex neuronal networks. To provide an appropriate neural cell niche, it is desirable to have not only neural cells, but supporting glia within the hydrogel carrier. It has been hypothesized that a hydrogel tailored to support glial cell survival and function will be able to support neuronal development. Poly(vinyl alcohol) functionalized with tyramine (PVA-Tyr) is a hydrogel system that supports covalent incorporation of non-modified tyrosine rich proteins, mimicking the biological environment and enabling 3D cell encapsulation[1]. PVA-Tyr has been co-polymerized with gelatin and sericin and the resulting gel supported glial cell growth. However, development of an appropriate system for use at the neural interface requires tailoring of the hydrogel properties such that (i) the mechanical stiffness is similar to that of neural tissues, and (ii) the hydrogel degradation rate is matched to cell maturation and development of extracellular matrix (ECM). Since physical and mechanical properties of PVA relate to the percent polymer[2], the aim of this research was to investigate the impact of varying the hydrogel macromer percentage on the mechanical stiffness and physical degradation of PVA-Tyr/sericin/gelatin (PVA-T/S/G), and the subsequent impact on glial cell survival and development. Two variants of PVA-T/S/G, 10 wt% and 5 wt%, were developed and used to encapsulate peripheral glia (Schwann cells). PVA-Tyr (8 or 3 wt%) hydrogel was crosslinked with gelatin (1 wt%) and sericin (1 wt%) as previously described[1]. Schwann cells (SC, SCL4.1/F7) were encapsulated at 107 cells/mL. Cellular viability was tracked by live/dead staining. Hydrogel stiffness was measured by compression tests (50 N load cell, 0.5 mm/min, 5 - 15% strain). Cells were immunostained for S100 (mature SC marker), laminin and collagen-IV (ECM deposition) and bisbenzimide (nuclei). Hydrogel degradation was tracked to the point of reverse gelation. All the tests were performed at 0, 1, 5 and 10 days. Cells remained viable at all the time points. Compression tests showed that PVA-T/S/G at 10 wt% had a mean compressive modulus of 41.5 kPa at Day 0, which reduced to 0.5 kPa by Day 10. The corresponding compressive modulus for the 5 wt% hydrogel was 6.1 kPa at Day 0 and 0.6 kPa at Day 10. SCs interact preferably with substrates having a stiffness from 1 - 10 kPa[3], where they adopt bipolar morphologies that support nerve guidance and repair in vivo[4]. In both systems at 5 days post-encapsulation bipolar morphologies were evident (see Figure 1), but were more prolific in the 5 wt% hydrogels. Presence of laminin and collagen-IV was also observed by immunostaining. Expression of these molecules is an indication of mature and functional SCs[5]. Both systems were shown to be completely degraded at 15 ± 3 days. While these different hydrogels provide similar support to SCs the ability to vary the hydrogel stiffness is expected to be key to the development of a complex living electrode with both glia and neuronal cell types, as previously proposed[6]. Figure 1. SC embedded in 10% (left) and 5%(right) PVA-T/S/G hydrogel at 5 days in culture. Nuclei (blue). Collagen-IV (green). Scale bar = 50 μm SCs were able to adopt bipolar morphologies and express ECM required for neuronal development with 5 and 10 wt% hydrogels. These outcomes suggest that the PVA-T/S/G hydrogels provide physical and biochemical support for SC survival and maturation. Future studies will assess the capacity of SCs to support neuronal survival within PVA-T/S/G. Australian Research Council (ARC) through its Special Research Initiative (SRI) in Bionic Vision Science and Technology grant to Bionic Vision Australia (BVA)

Modulating In Vivo Degradation Rate of Injectable Extracellular Matrix Hydrogels.

Extracellular matrix (ECM) derived hydrogels are increasingly used as scaffolds to stimulate endogenous repair. However, few studies have examined how altering the degradation rates of these materials affect cellular interaction in vivo. This study sought to examine how crosslinking or matrix metalloproteinase (MMP) inhibition by doxycycline could be employed to modulate the degradation rate of an injectable hydrogel derived from decellularized porcine ventricular myocardium. While both approaches were effective in reducing degradation in vitro, only doxycycline significantly prolonged hydrogel degradation in vivo without affecting material biocompatibility. In addition, unlike crosslinking, incorporation of doxycycline into the hydrogel did not affect mechanical properties. Lastly, the results of this study highlighted the need for development of novel crosslinkers for in situ modification of injectable ECM-derived hydrogels, as none of the crosslinking agents investigated in this study were both biocompatible and effective.

Glycosaminoglycan-based hydrogels with tunable sulfation and degradation for anti-inflammatory small molecule delivery

Event Abstract Back to Event Glycosaminoglycan-based hydrogels with tunable sulfation and degradation for anti-inflammatory small molecule delivery Liane Tellier1*, Yifeng Peng1* and Johnna S. Temenoff1, 2* 1 Georgia Institute of Technology and Emory University, Coulter Department of Biomedical Engineering, United States 2 Georgia Institute of Technology, Parker H. Petit Institute for Bioengineering and Bioscience, United States Introduction: Crystal violet (CV) is a small molecule shown to have anti-bacterial, anti-fungal & more recently, anti-inflammatory properties in part by acting as a Nox & angiopoietin-2 (ang-2) inhibitor[1]. Though treatment for many inflammatory conditions would ideally be delivered with zero order release kinetics, this remains particularly challenging for small molecule drugs such as CV. Therefore, to tune CV release kinetics we have developed a CV-loaded glycosaminoglycan (GAG)-based hydrogel system with heparin (a highly sulfated GAG) of varying sulfation levels (affects CV affinity) & with varying amounts of degradable crosslinker (affects hydrogel degradation). It is hypothesized that more sulfated heparin hydrogels will release bioactive CV over a longer period than more desulfated heparin hydrogels & that varying hydrogel degradation will allow us to further tune the rate of CV release. Methods: Hydrogels were prepared via free radical polymerization with 90 wt% water, 9 wt% PEG diacrylate (PEGDA), 1 wt% heparin, & 0, 30, or 42 mol% hydrolytically degradable crosslinker (DTT) for non-, slow-, & fast-degrading hydrogels, respectively. N-desulfated (Hep-N), 6O,N-desulfated (Hep-N,-6O) & fully desulfated (Hep-) heparin were prepared & functionalized with methacrylamide groups. CV was preloaded (20mg) into the hydrogel precursor prior to crosslinking. To quantify CV release, hydrogel supernatant was removed & the amount of CV was measured with a plate reader (absorption at 590nm) every 2 days. CV bioactivity was assessed by incubating hydrogel supernatant diluted to ~20μM with bEnd.3 cells & quantifying bEnd.3 ang-2 gene expression via PCR. Results: CV release kinetics were dependent on heparin sulfation level, whereby more sulfated heparin hydrogels (Hep&Hep-N) exhibited a linear release profile, whereas more desulfated hydrogels (Hep-N,-6O&Hep-) released significantly more CV at Day 1, followed by more plateaued release over 9-15 days (Fig1). Moreover, slow-degrading hydrogels required at least 2 additional days to release an equivalent amount of CV as fast-degrading hydrogels with the same heparin derivative. Finally, after incubating hydrogel releasate with bEnd.3 cells, bEnd.3 ang-2 gene expression was significantly lower than the no treatment control & was not significantly different from the 20μM soluble CV, indicating that CV maintained its bioactivity after release from hydrogels (Fig2). Conclusion: We have fabricated GAG-based hydrogels with heparin derivatives of varying sulfation levels (alters CV release kinetics) & with varying concentrations of DTT (alters hydrogel degradation & CV release rate). In this way, we have developed a highly tailorable hydrogel platform & have achieved near zero-order release of bioactive CV in particular formulations. Thus, in the future, this system can be utilized in vivo with the unique advantage of releasing small molecule anti-inflammatories such as CV in a sustained manner over a period of weeks. We would like to acknowledge NIH R01 AR063692.

Enzymatically-responsive poly(ethylene glycol) hydrogels for the controlled delivery of therapeutic peptides

Therapeutic angiogenesis holds great potential for treatment of ischemic tissues and in tissue engineering, where insufficient vascularization limits construct size, complexity, and anastomosis with host vasculature. However, no FDA approved treatments exist to robustly enhance vascularization within ischemic tissue. Many proangiogenic approaches have been developed, often via delivery of angiogenic proteins or peptides. Peptides typically mimic the bioactivity of larger proteins or growth factors, and offer advantages over traditional protein delivery, including more versatile synthesis methods and increased stability in vivo. However, both proteins and peptides suffer from rapid clearance and poor pharmacokinetics when delivered systemically, motivating the development of controlled release systems. Enzymatically-responsive systems where delivery of protein drugs is controlled by the local tissue microenvironment have shown improved tissue healing over bolus protein delivery. Therefore, a hydrogel-based platform technology was developed to control and sustain peptide drug release via matrix metalloproteinase (MMP) activity. Poly(ethylene glycol) (PEG) hydrogels were formed by crosslinking norbornene functionalized multi-arm PEG with peptide drugs flanked by MMP substrates and terminal cysteine residues. In vitro bioactivity testing identified three peptides (Qk (from Vascular Endothelial Growth Factor), SPARC113, and SPARC118 (from Secreted Protein Acidic and Rich in Cysteine)) that retained bioactivity in their expected released forms (e.g., with residual amino acids left by MMP substrates after cleavage). Incorporation of these peptides into hydrogels flanked by MMPdegradable substrates successfully produced hydrogels with enzymatically-responsive hydrogel degradation and peptide release behaviors. Hydrogels degraded via bulk degradation, and peptide release was in close agreement with mass loss. Qk, SPARC113, and SPARC118-releasing hydrogels were confirmed to release bioactive components in vitro after MMP-mediated degradation. Further investigation revealed key peptide drug properties, specifically size and hydrophobicity, control the rate of hydrogel degradation and peptide release. When implanted subcutaneously, SPARC113 and SPARC118-releasing hydrogels both significantly increased vascular ingrowth compared to controls one week after implantation without significantly affecting vessel size. As the longitudinal availability of VEGF has been shown critical for bioactivity, alternate hydrogels were formed to provide temporal control over enzymatically-responsive release of the VEGF peptide mimic, Qk. MMP-degradable linkers with a variety of cleavage kinetics were used to tether Qk to hydrogels formed with non-degradable peptide crosslinks. Hydrogel degradation was successfully uncoupled from peptide release, and three of the linkers provided temporal control over enzymatically-responsive peptide release kinetics in vitro and in vivo. Qk was confirmed to be bioactive as released,…

Calcium carbonate hydrogel construct with cynnamaldehyde incorporated to control inflammation during surgical procedure

The incorporation of CaCO3 hydrogel has been proven to enhance the bone biological activity of Plaster of Paris (POP) and to decrease its degradability. However, the installation of this bone substitute in a bone defect will still be associated with an inflammatory response. In this study, the influence of cinnamaldehyde as anti-inflammatory agent, was investigated. In addition, it is known that aldehyde chains of cinnamaldehyde may also act as crosslinking agent and function as a plastisizer to the CaCO3 hydrogel construct. Therefore, different concentrations of cinnamaldehyde were added to CaCO3 hydrogel and the effect on the diametral tensile strength, age swelling, gel fractination, cinnamaldehyde release, antimicrobial effect, and cell cytotoxycity were investigated. The incorporation of cinnamaldehyde was found to decrease the age swelling and degradation rate of CaCO3 hydrogel and to have no toxic effect to human gingival fibroblast cells. Moreover, the incorporation of cinnamaldehyde essential oil into the CaCO3 hydrogel was beneficial and acted as an antiinflammatory agent. Further research in vivo is warranted to determine the final favorable effect of cinnamaldehyde incorporated CaCO3 hydrogel in POP to provide a bone substitute. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 768-774, 2016.

Poly(ethylene glycol) hydrogels with cell cleavable groups for autonomous cell delivery

Cell-responsive hydrogels hold tremendous potential as cell delivery devices in regenerative medicine. In this study, we developed a hydrogel-based cell delivery vehicle, in which the encapsulated cell cargo control its own release from the vehicle in a protease-independent manner. Specifically, we have synthesized a modified poly(ethylene glycol) (PEG) hydrogel that undergoes degradation responding to cell-secreted molecules by incorporating disulfide moieties onto the backbone of the hydrogel precursor. Our results show the disulfide-modified PEG hydrogels disintegrate seamlessly into solution in presence of cells without any external stimuli. The rate of hydrogel degradation, which ranges from hours to months, is found to be dependent upon the type of encapsulated cells, cell number, and fraction of disulfide moieties present in the hydrogel backbone. The differentiation potential of human mesenchymal stem cells released from the hydrogels is maintained in vitro. The in vivo analysis of these cell-laden hydrogels, through a dorsal window chamber and intramuscular implantation, demonstrated autonomous release of cells to the host environment. The hydrogel-mediated implantation of cells resulted in higher cell retention within the host tissue when compared to that without a biomaterial support. Biomaterials that function as a shield to protect cell cargos and assist their delivery in response to signals from the encapsulated cells could have a wide utility in cell transplantation and could improve the therapeutic outcomes of cell-based therapies.

Systemic modulation of the stability of pluronic hydrogel by a small amount of graphene oxide

Thermo-sensitive and injectable hydrogels have been widely investigated for drug delivery, tissue engineering, and other biomedical applications. Pluronic copolymers can form thermo-sensitive physical gel state, thus applicable for injectable hydrogels. However, they are not stable in vivo, showing a very fast dissolution, which limits their applications. We propose a novel Pluronic-based physical hydrogel with enhanced stability by simply adding a small quantity of graphene oxide (GO) which has a large surface area and can make strong interactions with Pluronic. Further carboxylated GO could act as a more efficient additive. The addition of GO increased the moduli of hydrogels, but more importantly, it enhanced the stability of Pluronic gel dramatically. The in vitro dissolution rate of Pluronic hydrogel could be systematically modulated by increasing GO content. Upon subcutaneous injection at a sol state, GO-containing hydrogel induced a stable gel state, and was maintained over several weeks whereas very fast degradation was observed without the addition of GO. Furthermore, histological analyses demonstrated that the GO-containing Pluronic hydrogel was biocompatible and showed no severe inflammatory response. Similarly, GO-containing hydrogel resulting from the packing of Pluronic-based nanogel also showed the more enhanced stability by the addition of GO both in vitro and in vivo. In both systems, hydrogels with remarkably enhanced stability by the addition of GO were also effective for the sustained release of loaded protein, and the release rates were mainly determined by the degradation rates of hydrogels. Thus, these GO-containing Pluronic systems can be used as a thermo-sensitive injectable system with a sufficient stability in vivo.

Development and in vitro assessment of enzymatically-responsive poly(ethylene glycol) hydrogels for the delivery of therapeutic peptides

Despite the recent expansion of peptide drugs, delivery remains a challenge due to poor localization and rapid clearance. Therefore, a hydrogel-based platform technology was developed to control and sustain peptide drug release via matrix metalloproteinase (MMP) activity. Specifically, hydrogels were composed of poly(ethylene glycol) and peptide drugs flanked by MMP substrates and terminal cysteine residues as crosslinkers. First, peptide drug bioactivity was investigated in expected released forms (e.g., with MMP substrate residues) in vitro prior to incorporation into hydrogels. Three peptides (Qk (from Vascular Endothelial Growth Factor), SPARC113, and SPARC118 (from Secreted Protein Acidic and Rich in Cysteine)) retained bioactivity and were used as hydrogel crosslinkers in full MMP degradable forms. Upon treatment with MMP2, hydrogels containing Qk, SPARC113, and SPARC118 degraded in 6.7, 6, and 1 days, and released 5, 8, and, 19% of peptide, respectively. Further investigation revealed peptide drug size controlled hydrogel swelling and degradation rate, while hydrophobicity impacted peptide release. Additionally, Qk, SPARC113, and SPARC118 releasing hydrogels increased endothelial cell tube formation 3.1, 1.7, and 2.8-fold, respectively. While pro-angiogenic peptides were the focus of this study, the design parameters detailed allow for adaptation of hydrogels to control peptide release for a variety of therapeutic applications.

Modulating hydrogel crosslink density and degradation to control bone morphogenetic protein delivery and in vivo bone formation

Bone morphogenetic proteins (BMPs) show promise in therapies for improving bone formation after injury; however, the high supraphysiological concentrations required for desired osteoinductive effects, off-target concerns, costs, and patient variability have limited the use of BMP-based therapeutics. To better understand the role of biomaterial design in BMP delivery, a matrix metalloprotease (MMP)-sensitive hyaluronic acid (HA)-based hydrogel was used for BMP-2 delivery to evaluate the influence of hydrogel degradation rate on bone repair in vivo. Specifically, maleimide-modified HA (MaHA) macromers were crosslinked with difunctional MMP-sensitive peptides to permit protease-mediated hydrogel degradation and growth factor release. The compressive, rheological, and degradation properties of MaHA hydrogels were characterized as a function of crosslink density, which was varied through either MaHA concentration (1–5wt.%) or maleimide functionalization (10–40%f). Generally, the compressive moduli increased, the time to gelation decreased, and the degradation rate decreased with increasing crosslink density. Furthermore, BMP-2 release increased with either a decrease in the initial crosslink density or an increase in collagenase concentration (non-specific MMP degradation). Lastly, two hydrogel formulations with distinct BMP-2 release profiles were evaluated in a critical-sized calvarial defect model in rats. After six weeks, minimal evidence of bone repair was observed within defects left empty or filled with hydrogels alone. For hydrogels that contained BMP-2, similar volumes of new bone tissue were formed; however, the faster degrading hydrogel exhibited improved cellular invasion, bone volume to total volume ratio, and overall defect filling. These results illustrate the importance of coordinating hydrogel degradation with the rate of new tissue formation.

Biodestruction of strongly swelling polymer hydrogels and its effect on the water retention capacity of soils

The biodestruction of strongly swelling polymer hydrogels (water adsorbing soil conditioners of the new generation) has been studied at the quantitative level using original mathematical models. In laboratory experiments, a relationship between the hydrogel degradation rate and the temperature has been obtained, and the effect of the biodestruction on the water retention curve of soil compositions with hydrogels (used as an index of their water retention capacity) has been assessed. From the automatic monitoring data of the temperature regime of soils, the potential biodestruction of hydrogels has been predicted for different climatic conditions. The loss of hydrogels during three months of the vegetation period because of destruction can exceed 30% of their initial content in irrigated agriculture under arid climatic conditions and more than 10% under humid climatic conditions. Thus, the biodestruction of hydrogels is one of the most important factors decreasing their efficiency under actual soil conditions.

Cartilage regeneration using biodegradable oxidized alginate/hyaluronate hydrogels

Despite the widespread use of alginate (AL) hydrogels in many biomedical applications, including tissue engineering, AL is inherently non-degradable under physiological conditions. We hypothesized that degradable alginate (dAL) would be useful for cartilage regeneration when combined with hyaluronate (HA). We prepared dAL by partial oxidation of AL using sodium periodate, and the degradation rate of AL hydrogel was able to be regulated by control of sodium periodate concentration. The degradable oxidized AL/HA gels were formed in the presence of cells and their characteristics were investigated. dAL/HA gels with primary chondrocytes were injected subcutaneously into mice. Effective cartilage regeneration was observed after 6 weeks of transplantation based on histological analysis. Moreover, substantial secretion of sulfated glycosaminoglycans and expression of chondrogenic marker genes were also observed compared with non-dAL/HA gels. These results indicate that dAL/HA hydrogels may be useful in cartilage regeneration, and in many tissue engineering applications.

Real-time and non-invasive fluorescence tracking of in vivo degradation of the thermosensitive PEGlyated polyester hydrogel

The real-time monitoring of materials degradation is crucial to determine the in vivo retention time and the design or screening of degradable biomaterials. However, in vivo performance cannot always be predicted through the traditional determination of in vitro erosion and current standard methods sacrifice samples or animals, preventing the sequential measurement of the same specimen. Herein, a non-invasive fluorescence imaging method was developed to sequentially follow in vivo loss of fluorescence signal to simultaneously characterize the hydrolytic and enzymatic degradation of PEGlyated polyester hydrogel. Rhodamine B was conjugated to thermosensitive amphiphilic triblock copolymer based on cyclic ether modified PCL and PEG (abbreviated as PECT) and no obvious influence on gelation time or gel strength was observed with the conjugation content under 0.121% (w/w). Both in vitro and in vivo degradation profiles followed linear fittings while in vivo and in vitro hydrogel degradation rates correlated in an exponential mathematical model, enabling the general prediction of in vivo erosion trends of new biomaterial formulations from in vitro data. This methodology possibly enabled rational design and rapid in vitro screening of degradable materials, and might be potentially extended to simultaneously determine the material erosion and speculate the drug release from a drug-incorporated scaffold, or the cell growth profile in tissue-engineering formulations.

Effects of bound versus soluble pentosan polysulphate in PEG/HA-based hydrogels tailored for intervertebral disc regeneration

Previous reports in the literature investigating chondrogenesis in mesenchymal progenitor cell (MPC) cultures have confirmed the chondro-inductive potential of pentosan polysulphate (PPS), a highly sulphated semi-synthetic polysaccharide, when added as a soluble component to culture media under standard aggregate-assay conditions or to poly(ethylene glycol)/hyaluronic acid (PEG/HA)-based hydrogels, even in the absence of inductive factors (e.g. TGFβ). In this present study, we aimed to assess whether a ‘bound’ PPS would have greater activity and availability over a soluble PPS, as a media additive or when incorporated into PEG/HA-based hydrogels. We achieved this by covalently pre-binding the PPS to the HA component of the gel (forming a new molecule, HA-PPS). We firstly investigated the activity of HA-PPS compared to free PPS, when added as a soluble factor to culture media. Cell proliferation, as determined by CCK8 and EdU assay, was decreased in the presence of either bound or free PPS whilst chondrogenic differentiation, as determined by DMMB assay and histology, was enhanced. In all cases, the effect of the bound PPS (HA-PPS) was more potent than that of the unbound form. These results alone suggest wider applications for this new molecule, either as a culture supplement or as a coating for scaffolds targeted at chondrogenic differentiation or maturation. We then investigated the incorporation of HA-PPS into a PEG/HA-based hydrogel system, by simply substituting some of the HA for HA-PPS. Rheological testing confirmed that incorporation of either HA-PPS or PPS did not significantly affect gelation kinetics, final hydrogel modulus or degradation rate but had a small, but significant, effect on swelling. When encapsulated in the hydrogels, MPCs retained good viability and rapidly adopted a rounded morphology. Histological analysis of both GAG and collagen deposition after 21 days showed that the incorporation of the bound-PPS into the hydrogel resulted in increased matrix formation when compared to the addition of soluble PPS to the hydrogel, or the hydrogel alone. We believe that this new generation injectable, degradable hydrogel, incorporating now a covalently bound-PPS, when combined with MPCs, has the potential to assist cartilage regeneration in a multitude of therapeutic targets, including for intervertebral disc (IVD) degeneration.

Sustained release of avastin® from polysaccharides cross-linked hydrogels for ocular drug delivery

Avastin® was the first choice drug for the treatment of age related macular degeneration (AMD) and proliferative diabetic retinopathy in clinic. Due to its short half-time in intraocular, it was required repeat administration. In this paper, an in situ injectable polysaccharides cross-linked hydrogel was developed for potential ocular drug delivery of avastin. The polysaccharide cross-linked hydrogel was first synthesized by simple mixing of glycol chitosan and oxidized alginate aqueous solution, and then characterized by scanning electron microscopy (SEM) and rheometer. In vitro degradation test indicated that the degradation rate of hydrogels could be controlled by the varying the content of oxidized alginate in hydrogels. In vitro release study showed that the encapsulated avastin had an initial burst release at early stage (within 4h) followed by a sustained release manner in period of 3 days. With the increase of oxidized alginate concentration in the hydrogel, the release rate of avastin from hydrogels declined accordingly. Meanwhile, the structure stability of avastin released from hydrogels at specific time intervals did not show apparent changes as compared with native avastin based on the analysis of SDS-polyacrylamide gel electrophoresis (SDS-PAEG). As a result, the developed in situ injectable polysaccharides cross-linked hydrogel with controllable degradation rate and drug release might be a versatile carrier for avastin to apply in ocular drug delivery.

Designing degradable hydrogels for orthogonal control of cell microenvironments.

Degradable and cell-compatible hydrogels can be designed to mimic the physical and biochemical characteristics of native extracellular matrices and provide tunability of degradation rates and related properties under physiological conditions. Hence, such hydrogels are finding widespread application in many bioengineering fields, including controlled bioactive molecule delivery, cell encapsulation for controlled three-dimensional culture, and tissue engineering. Cellular processes, such as adhesion, proliferation, spreading, migration, and differentiation, can be controlled within degradable, cell-compatible hydrogels with temporal tuning of biochemical or biophysical cues, such as growth factor presentation or hydrogel stiffness. However, thoughtful selection of hydrogel base materials, formation chemistries, and degradable moieties is necessary to achieve the appropriate level of property control and desired cellular response. In this review, hydrogel design considerations and materials for hydrogel preparation, ranging from natural polymers to synthetic polymers, are overviewed. Recent advances in chemical and physical methods to crosslink hydrogels are highlighted, as well as recent developments in controlling hydrogel degradation rates and modes of degradation. Special attention is given to spatial or temporal presentation of various biochemical and biophysical cues to modulate cell response in static (i.e., non-degradable) or dynamic (i.e., degradable) microenvironments. This review provides insight into the design of new cell-compatible, degradable hydrogels to understand and modulate cellular processes for various biomedical applications.

Three-dimensional porous HPMA-co-DMAEM hydrogels for biomedical application

The aim of this work is to develop a novel biocompatible drug delivery carrier and tissue engineering scaffold with the ability of controlled drug release and also tissue regeneration. We have synthesized N-(2-hydroxypropyl)methacrylamide and 2-(dimethylamino)ethyl methacrylate copolymer-based hydrogels loaded with doxorubicin and tested in vitro. The manifestation of temperature sensitivity is noted with a sharp decrease or increase in hydrogel optical transparency that happens with the temperature exceeding a critical transition value. The drug release profile exhibited pH-sensitive behavior of the hydrogel. The hydrolytic degradation of gel and in vitro studies of polymer–doxorubicin conjugate and doxorubicin release from hydrogel matrix indicated that hydrogels were stable under acidic conditions (in buffers at pH 4.64 and 6.65). In both drug forms, polymer–doxorubicin conjugate and free doxorubicin could be released from the hydrogel scaffold at a rate depending directly on either the rate of drug diffusion from the hydrogel or rate of hydrogel degradation or at rate controlled by a combination of the both processes. In vitro analysis showed homogenous cell attachment and proliferation on synthesized hydrogel matrix. In vivo implantation demonstrated integration of the gel with the surrounding tissue of mice within 2 weeks and prominent neo-angiogenesis observed in the following weeks. This multifunctional hydrogels can easily overcome biological hurdles in the in vivo conditions where the pH range changes drastically and could attain higher site-specific drug delivery improving the efficacy of the treatment in various therapeutical applications, especially in cancer therapy, and could also be used as tissue engineering scaffold due to its porous interconnected and biocompatible behavior.