Hydrogel Implants Research Articles

Ex vivo model unravelling cell distribution effect in hydrogels for cartilage repair

SummaryThe implantation of chondrocyte-laden hydrogels is a promising cartilage repair strategy. Chondrocytes can be spatially positioned in hydrogels and thus in defects, while current clinical cell therapies introduce chondrocytes in the defect depth. The main aim of this study was to evaluate the effect of spatial chondrocyte distribution on the reparative process. To reduce animal experiments, an ex vivo osteochondral plug model was used and evaluated. The role of the delivered and endogenous cells in the repair process was investigated.Full thickness cartilage defects were created in equine osteochondral plugs. Defects were filled with (A) chondrocytes at the bottom of the defect, covered with a cell-free hydrogel, (B) chondrocytes homogeneously encapsulated in a hydrogel, and (C, D) combinations of A and B with different cell densities. Plugs were cultured for up to 57 days, after which the cartilage and repair tissues were characterized and compared to baseline samples. Additionally, at day 21, the origin of cells in the repair tissue was evaluated.Best outcomes were obtained with conditions C and D, which resulted in well-integrated cartilage-like tissue that completely filled the defect, regardless of the initial cell density. A critical role of the spatial chondrocyte distribution in the repair process was observed. Moreover, the osteochondral plugs stimulated cartilage formation in the hydrogels when cultured in the defects. The resulting repair tissue originated from the delivered cells.These findings confirm the potential of the osteochondral plug model for the optimization of the composition of cartilage implants and for studying repair mechanisms.

The degradation and local tissue effects of collagen hydrogel and sponge implants in muscle

Collagen products will degrade and evoke certain local tissue reaction after being implanted. ISO 10993.6 is the international standard to evaluate local tissue reaction for biomaterials. However, even in the present version, it does not define the specific view fields for scoring local tissue reaction in the sections, which may influence the fair evaluation for the degradable polymer, such as collagen. In this study, 4 kinds of collagens and 2 kinds of bio-inert products were implanted into the rabbit muscle for 26 weeks, and two different scoring methods (uniform distribution scoring method and area locating scoring method) were applied to evaluate the local tissue reaction for each implant. The results showed that the tissue reaction on the interface was active, but the various scores in the implant and surrounding areas could help us to understand the differences of the degradation process. An area locating scoring method which selected the fields in the implant, interface and surroundings respectively showed a higher total score and offered more detailed information compared to the uniform distribution scoring method. Since the degradation and tissue reaction degree in the different areas are ever changing for the degradable implants, this area locating scoring method is sensitive, effective and applicable for the semi-quantitative evaluating system of ISO 10993.6.

Implantation of Brain-Derived Extracellular Matrix Enhances Neurological Recovery after Traumatic Brain Injury

Scaffolds composed of extracellular matrix (ECM) are being investigated for their ability to facilitate brain tissue remodeling and repair following injury. The present study tested the hypothesis that the implantation of brain-derived ECM would attenuate experimental traumatic brain injury (TBI) and explored potential underlying mechanisms. TBI was induced in mice by a controlled cortical impact (CCI). ECM was isolated from normal porcine brain tissue by decellularization methods, prepared as a hydrogel, and injected into the ipsilesional corpus callosum and striatum 1 h after CCI. Lesion volume and neurological function were evaluated up to 35 d after TBI. Immunohistochemistry was performed to assess post-TBI white matter integrity, reactive astrogliosis, and microglial activation. We found that ECM treatment reduced lesion volume and improved neurobehavioral function. ECM-treated mice showed less post-TBI neurodegeneration in the hippocampus and less white matter injury than control, vehicle-treated mice. Furthermore, ECM ameliorated TBI-induced gliosis and microglial pro-inflammatory responses, thereby providing a favorable microenvironment for tissue repair. Our study indicates that brain ECM hydrogel implantation improved the brain microenvironment that facilitates post-TBI tissue recovery. Brain ECM offers excellent biocompatibility and holds potential as a therapeutic agent for TBI, alone or in combination with other treatments.

Nanoscale Silk-Hydroxyapatite Hydrogels for Injectable Bone Biomaterials.

Injectable hydrogel systems are important bone substitutes for regeneration because of their handling properties and the ability to fill irregular defects. Silk-hydroxyapatite composite materials with silk nanofibers in hydrogels were prepared and used as biomaterials for osteogenesis. These thixotropic silk nanofiber hydrogels and water-dispersible silk-HA nanoparticles were blended to form injectable nanoscale systems with a homogeneous distribution of a high HA content [60% (w/w)] to imitate bone niche. A modulus of ∼21 kPa was also achieved following the addition of HA in the systems, providing physical cues to induce osteodifferentiation. The composite hydrogels supported improved osteogenesis compared to that with silk nanofiber hydrogels. The newly formed bone tissue and bone defect healing were detected after implantation of the silk-HA composite hydrogels, suggesting utility for the regeneration of irregular bone defects.

Novel model of orthotopic U-87 MG glioblastoma resection in athymic nude mice

In vitro and in vivo models of experimental glioma are useful tools to gain a better understanding of glioblastoma (GBM) and to investigate novel treatment strategies. However, the majority of preclinical models focus on treating solid intracranial tumours, despite surgical resection being the mainstay in the standard care of patients with GBM today. The lack of resection and recurrence models therefore has undermined efforts in finding a treatment for this disease. Here we present a novel orthotopic tumour resection and recurrence model that has potential for the investigation of local delivery strategies in the treatment of GBM. The model presented is simple to achieve through the use of a biopsy punch, is reproducible, does not require specific or expensive equipment, and results in a resection cavity suitable for local drug delivery systems, such as the implantation or injection of hydrogels. We show that tumour resection is well tolerated, does not induce deleterious neurological deficits, and significantly prolongs survival of mice bearing U-87 MG GBM tumours. In addition, the resulting cavity could accommodate adequate amounts of hydrogels for local delivery of chemotherapeutic agents to eliminate residual tumour cells that can induce tumour recurrence.

Evisceration With Injectable Hydrogel Implant in a Rabbit Model.

To determine the safety, durability, and biocompatibility of 2.5% polyacrylamide hydrogel (Aquamid, Specialty European Pharma, Ltd., London, UK) as an injectable viscoelastic implant following evisceration in a rabbit model. The protocol was reviewed and approved by the Wake Forest Institutional Animal Care and Use Committee. Adult New Zealand rabbits underwent cornea-sparing evisceration of the right eye with injection of 2.5% polyacrylamide hydrogel implant. The rabbits were sacrificed after 2 weeks (n = 1), 5 weeks (n = 2), 12 weeks (n = 3), 25 weeks (n = 3), and 1 year (n = 3) to evaluate the implant volume and host reaction to the implant. Both eyes were enucleated and their diameters were measured. The eviscerated eyes were fixed in formalin and processed using routine histopathologic methods to assess inflammatory reaction and vascularization. The implant material was well tolerated with a moderate giant cell reaction seen at 6 weeks that improved over time. Extensive vascularization of the implant was noted starting at 6 weeks. There was excellent maintenance of globe volume that did not diminish over time. The relative diameters of the eviscerated eyes compared with control were 89 ± 6% (mean% ± SD) at 12 weeks (n = 3), 94 ± 2% at 25 weeks (n = 3), and 93 ± 4% at 1 year (n = 3). With further study, injectable 2.5% polyacrylamide hydrogel may provide an excellent alternative to solid orbital implants. The implant material was universally well tolerated and maintained appropriate volume in the orbit for the study period of 1 year. Extensive vascularization of the implant was noted indicating biointegration.

A Dual-Bonded Approach for Improving Hydrogel Implant Stability in Cartilage Defects.

Integration and stability of hydrogels and surrounding cartilage/bone tissue is crucial for both immediate functionality and long-term performance of the tissue. In this work, chondroitin sulphate (CS) a polysaccharide found in cartilage and other tissues was used to synthesize a tough hydrogel that was chemically functionalized with methacrylate and aldehyde groups, bonding to surrounding tissue via a dual-bonded approach. The hydrogel can not only chemically anchor onto implanted titanium at the subchondral bone, but also on cartilage tissue via the Schiff-base reaction. In vitro experiments confirmed that the strategy improved hydrogel implant stability with cartilage tissue, was favorable for chondrocyte attachment, and has the potential to quickly and effectively repair cartilage defects and maintain joint functionality for a long time.

Keratin Hydrogel Enhances In Vivo Skeletal Muscle Function in a Rat Model of Volumetric Muscle Loss.

Volumetric muscle loss (VML) injuries exceed the considerable intrinsic regenerative capacity of skeletal muscle, resulting in permanent functional and cosmetic deficits. VML and VML-like injuries occur in military and civilian populations, due to trauma and surgery as well as due to a host of congenital and acquired diseases/syndromes. Current therapeutic options are limited, and new approaches are needed for a more complete functional regeneration of muscle. A potential solution is human hair-derived keratin (KN) biomaterials that may have significant potential for regenerative therapy. The goal of these studies was to evaluate the utility of keratin hydrogel formulations as a cell and/or growth factor delivery vehicle for functional muscle regeneration in a surgically created VML injury in the rat tibialis anterior (TA) muscle. VML injuries were treated with KN hydrogels in the absence and presence of skeletal muscle progenitor cells (MPCs), and/or insulin-like growth factor 1 (IGF-1), and/or basic fibroblast growth factor (bFGF). Controls included VML injuries with no repair (NR), and implantation of bladder acellular matrix (BAM, without cells). Initial studies conducted 8 weeks post-VML injury indicated that application of keratin hydrogels with growth factors (KN, KN+IGF-1, KN+bFGF, and KN+IGF-1+bFGF, n = 8 each) enabled a significantly greater functional recovery than NR (n = 7), BAM (n = 8), or the addition of MPCs to the keratin hydrogel (KN+MPC, KN+MPC+IGF-1, KN+MPC+bFGF, and KN+MPC+IGF-1+bFGF, n = 8 each) (p < 0.05). A second series of studies examined functional recovery for as many as 12 weeks post-VML injury after application of keratin hydrogels in the absence of cells. A significant time-dependent increase in functional recovery of the KN, KN+bFGF, and KN+IGF+bFGF groups was observed, relative to NR and BAM implantation, achieving as much as 90% of the maximum possible functional recovery. Histological findings from harvested tissue at 12 weeks post-VML injury documented significant increases in neo-muscle tissue formation in all keratin treatment groups as well as diminished fibrosis, in comparison to both BAM and NR. In conclusion, keratin hydrogel implantation promoted statistically significant and physiologically relevant improvements in functional outcomes post-VML injury to the rodent TA muscle.

Photocrosslinked tyramine-substituted hyaluronate hydrogels with tunable mechanical properties improve immediate tissue-hydrogel interfacial strength in articular cartilage

Articular cartilage lacks the ability to self-repair and a permanent solution for cartilage repair remains elusive. Hydrogel implantation is a promising technique for cartilage repair; however for the technique to be successful hydrogels must interface with the surrounding tissue. The objective of this study was to investigate the tunability of mechanical properties in a hydrogel system using a phenol-substituted polymer, tyramine-substituted hyaluronate (TA-HA), and to determine if the hydrogels could form an interface with cartilage. We hypothesized that tyramine moieties on hyaluronate could crosslink to aromatic amino acids in the cartilage extracellular matrix. Ultraviolet (UV) light and a riboflavin photosensitizer were used to create a hydrogel by tyramine self-crosslinking. The gel mechanical properties were tuned by varying riboflavin concentration, TA-HA concentration, and UV exposure time. Hydrogels formed with a minimum of 2.5 min of UV exposure. The compressive modulus varied from 5 to 16 kPa. Fluorescence spectroscopy analysis found differences in dityramine content. Cyanine-3 labelled tyramide reactivity at the surface of cartilage was dependent on the presence of riboflavin and UV exposure time. Hydrogels fabricated within articular cartilage defects had increasing peak interfacial shear stress at the cartilage-hydrogel interface with increasing UV exposure time, reaching a maximum shear stress 3.5× greater than a press-fit control. Our results found that phenol-substituted polymer/riboflavin systems can be used to fabricate hydrogels with tunable mechanical properties and can interface with the surface tissue, such as articular cartilage.

Preferred M2 Polarization by ASC-Based Hydrogel Accelerated Angiogenesis and Myogenesis in Volumetric Muscle Loss Rats.

Volumetric muscle loss (VML) injury resulted from massive muscle defects and diseases for which there are still no effective therapeutic treatments. This study aimed to investigate the effects of rat adipose-derived mesenchymal stem cells (rASCs) and rASCs-conditioned medium- (CM-) based type I collagen hydrogel on macrophage (MP) transition, myogenesis, and vascularization in the rat VML model. Laser Doppler results demonstrated much higher blood flow in the rASC- and CM-based hydrogel groups. qRT-PCR, hematoxylin and eosin, immunofluorescence, and Sirius Red staining manifested that both rASCs and CM-based hydrogel implantation accelerated muscle repair with upregulated angiogenesis and myogenesis, attenuated inflammation while facilitating M2 transition, and decreased the collagen deposition compared with the hydrogel group. In vitro experiments indicated that factors secreted from polarized M2 MPs could accelerate the migration and tube formation capacities of HUVECs. These results suggested that rASCs exerted immunomodulatory effects on MPs which further enhanced the proangiogenic potential on ECs to promote myogenesis and angiogenesis during muscle repair. These fundamental results support further clinical applications of ASCs for muscle loss injury.

Neovascularization Induced by the Hyaluronic Acid-Based Spongy-Like Hydrogels Degradation Products.

Neovascularization has been a major challenge in many tissue regeneration strategies. Hyaluronic acid (HA) of 3-25 disaccharides is known to be angiogenic due to its interaction with endothelial cell receptors. This effect has been explored with HA-based structures but a transitory response is observed due to HA burst biodegradation. Herein we developed gellan gum (GG)-HA spongy-like hydrogels from semi-interpenetrating network hydrogels with different HA amounts. Enzymatic degradation was more evident in the GG-HA with high HA amount due to their lower mechanical stability, also resulting from the degradation itself, which facilitated the access of the enzyme to the HA in the bulk. GG-HA spongy-like hydrogels hyaluronidase-mediated degradation lead to the release of HA oligosaccharides of different amounts and sizes in a HA content-dependent manner which promoted in vitro proliferation of human umbilical cord vein endothelial cells (HUVECs) but not their migration. Although no effect was observed in human dermal microvascular endothelial cells (hDMECs) in vitro, the implantation of GG-HA spongy-like hydrogels in an ischemic hind limb mice model promoted neovascularization in a material-dependent manner, consistent with the in vitro degradation profile. Overall, GG-HA spongy-like hydrogels with a sustained release of HA oligomers are valuable options to improve tissue vascularization, a critical issue in several applications in the tissue engineering and regenerative medicine field.

Diamagnetic chemical exchange saturation transfer (diaCEST) affords magnetic resonance imaging of extracellular matrix hydrogel implantation in a rat model of stroke.

Extracellular matrix (ECM) is widely used as an inductive biological scaffold to repair soft tissue after injury by promoting functional site-appropriate remodeling of the implanted material. However, there is a lack of non-invasive analysis methods to monitor the remodeling characteristics of the ECM material after implantation and its biodegradation over time. We describe the use of diamagnetic chemical exchange saturation transfer (CEST) magnetic resonance imaging to monitor the distribution of an ECM hydrogel after intracerebral implantation into a stroke cavity. Invitro imaging indicated a robust concentration-dependent detection of the ECM precursor and hydrogel at 1.8 and 3.6ppm, which broadly corresponded to chondroitin sulfate and fibronectin. This detection was robust to changes in pH and improved at 37°C. Invivo implantation of ECM hydrogel into the stroke cavity in a rat model corresponded macroscopically to the distribution of biomaterial as indicated by histology, but mismatches were also evident. Indeed, CEST imaging detected an endogenous "increased deposition". To account for this endogenous activity, pre-implantation images were subtracted from post-implantation images to yield a selective visualization of hydrogel distribution in the stroke cavity and its evolution over 7 days. The CEST detection of ECM returned to baseline within 3 days due to a decrease in fibronectin and chondroitin sulfate in the hydrogel. The distribution of ECM hydrogel within the stroke cavity is hence feasible invivo, but further advances are required to warrant a selective long-term monitoring in the context of biodegradation.

Safety and tolerability of silk fibroin hydrogels implanted into the mouse brain.

The increasingly use of sophisticated biomaterials to encapsulate stem cells has changed the comprehensive overview of potential strategies for repairing the nervous system. Silk fibroin (SF) meets with most of the standards of a biomaterial suitable to enhance stem cell survival and function. However, a proof-of-principle of the in vivo safety and tolerability of SF implanted into the brain tissue is needed. In this study we have examined the tissue bioresponse and brain function after implantation of SF hydrogels. We have demonstrated the benign coexistence of silk with the complex neuronal circuitry that governs sensorimotor coordination and mechanisms such as learning and memory. Our results have repercussion in the development of advances strategies using this biomaterial in regenerative neuroscience.

&lt;i&gt;In situ&lt;/i&gt; epicatechin-loaded hydrogel implants for local drug delivery to spinal column for effective management of post-traumatic spinal injuries

Purpose: To prepare hydrogels loaded with epicatechin, a strong antioxidant, anti-inflammatory, and neuroprotective tea flavonoid, and characterise them in situ as a vehicle for prolonged and safer drug delivery in patients with post-traumatic spinal cord injury.Methods: Five in situ gel formulations were prepared using chitosan and evaluated in terms of their visual appearance, clarity, pH, viscosity, and in vitro drug release. In vivo anti-inflammatory activity was determined and compared with 2 % piroxicam gel as standard. Motor function activity in a rat model of spinal injury was examined comparatively with i.v. methylprednisolone as standard.Results: The N-methyl pyrrolidone solution (containing 1 % w/w epicatechin with 2 to 10 % w/w chitosan) of the in situ gel formulation had a uniform pH in the range of 4.01 ± 0.12 to 4.27 ± 0.02. High and uniform drug loading, ranging from 94.48 ± 1.28 to 98.08 ± 1.24 %, and good in vitro drug release (79.48 ± 2.84 to 96.48 ± 1.02 % after 7 days) were achieved. The in situ gel prepared from 1 % epicatechin and 2 % chitosan (E5) showed the greatest in vivo anti-inflammatory activity (60.58 % inhibition of paw oedema in standard carrageenan-induced hind rat paw oedema model, compared with 48.08 % for the standard). The gels showed significant therapeutic effectiveness against post-traumainduced spinal injury in rats. E5 elicited maximum motor activity (horizontal bar test) in the spinal injuryrat model; the rats that received E5 treatment produced an activity score of 3.62 ± 0.02 at the end of 7 days, compared with 5.0 ± 0.20 following treatment with the standard.Conclusion: In situ epicatechin-loaded gel exhibits significant neuroprotective and anti-inflammatory effects, and therefore can potentially be used for prolonged and safe drug delivery in patients with traumatic spinal cord injury.Keywords: Epicatechin, In situ gel, Chitosan, Spinal injury, Post-traumatic, Motor activity, Antiinflammatory

Abstract 216: Intra-myocardial Injection of a Novel Thermosensitive Hydrogel Inhibits Post-infarct Heart Failure in Rats

Intra-myocardial injection of hydrogel after myocardial infarction (MI) has been confirmed for preventing post-infarct ventricular remodeling (VR) in numerous studies. Meanwhile, VR or existed heart failure (HF) symptoms of patients with MI was improved after intra-myocardial injection of hydrogels in recent clinical trials. However, whether the injection of hydrogel immediately after MI can prevent post-infarct HF in a long follow-up period is unclear. In present study, MI was induced by permanent coronary artery ligation in SD rats. Immediately, 100μl Dex-PCL-HEMA/ PNIPAAm (DPHP) hydrogel solution was injected into the infarct border myocardium of experimental rats, while phosphate-buffered saline (PBS) was employed in control group. Twelve weeks later, compared with PBS group (n=11), echocardiography and hemodynamics showed left ventricle dilatation was attenuated (end-diastolic diameter 9.30±0.73 mm vs 10.74±0.57 mm, p &lt;0.01) and cardiac function was improved (+dp/dt 12351±1158 mmHg/s vs 9488±695 mmHg/s, p &lt;0.01) in hydrogel group (n=11). Serum brain natriuretic peptide (107.74±18.21 pg/ml vs 132.17±20.62 pg/ml, p &lt;0.05) and cardiac aldosterone production of hydrogel group was suppressed, and so did pulmonary congestion. Histological analysis indicated thicker scar, smaller infarct size, diminished cardiac fibrosis (collagen volume fraction 21.74±3.13% vs 33.38±3.08%, p &lt;0.01) and hypertrophy in hydrogel group. Higher Col3α1 mRNA (27.32±0.71 vs 14.29±1.37, p &lt;0.01) in infarct zone but lower Col3α1 mRNA (0.97±0.12 vs 9.06±1.04, p &lt;0.01) and ANP mRNA (10.03±1.49 vs 24.74±2.40, p &lt;0.01) in non-infarct zone (NIZ) were detected by RT-PCR in hydrogel group. These data proves that the intra-myocardial injection of DPHP hydrogel immediately after MI can improve cardiac function including diastolic function, decrease infarct size, and enhance fibrotic healing in the infarct area. On the other hand, this treatment suppresses reactive fibrosis and hypertrophy in NIZ and thus delays post-infarct VR and prevents HF. DPHP hydrogel implantation immediately after MI is an effective strategy to prevent abnormal cardiac remodeling and have a long term beneficial effect even after it has been biodegraded.

In Vivo Neural Tissue Engineering: Cylindrical Biocompatible Hydrogels That Create New Neural Tracts in the Adult Mammalian Brain.

Individuals with neurodegenerative disorders or brain injury have few treatment options and it has been proposed that endogenous adult neural stem cells can be harnessed to repopulate dysfunctional nonneurogenic regions of the brain. We have accomplished this through the development of rationally designed hydrogel implants that recruit endogenous cells from the adult subventricular zone to create new relatively long tracts of neuroblasts. These implants are biocompatible and biodegradable cylindrical hydrogels consisting of fibrin and immobilized neurotrophic factors. When implanted into rat brain such that the cylinder intersected the migratory path of endogenous neural progenitors (the rostral migratory stream) and led into the nonneurogenic striatum, we observed a robust neurogenic response in the form of migrating neuroblasts with long (>100 μm) complex neurites. The location of these new neural cells in the striatum was directly coincident with the original track of the fibrin implant, which itself had completely degraded, and covered a significant area and distance (>2.5 mm). We also observed a significant number of neuroblasts in the striatal region between the implant track and the lateral ventricle. When these fibrin cylinders were implanted into hemiparkinson rats, correction of parkinsonian behavior was observed. There were no obvious behavioral, inflammatory or tumorigenic sequelae as a consequence of the implants. In conclusion, we have successfully engineered neural tissue in vivo, using neurogenic biomaterials cast into a unique cylindrical architecture. These results represent a novel approach to efficiently induce neurogenesis in a controlled and targeted manner, which may lead toward a new therapeutic modality for neurological disorders.

Effect of moderate treadmill exercise together with modified hydroxyapatite chitosan composite hydrogel implantation on repair of full-thickness defects of articular cartilage in rats

Objective To investigate the effect of moderate treadmill exercise together with modified hydroxyapatite chitosan composite hydrogel(CS/HA-g-CS)implantation on repair of full-thickness defects of articular cartilage in rats. Methods Full-thickness cartilage defects were drilled in the patellar groove of bilateral femoral condyles in a total of 24 male SD rats before they were randomly assigned into 4 groups. The control group(BC group)was subjected to no exercise or CS/HA-g-CS implantation; the chitosan group(CHI group)to CS/HA-g-CS implantation without exercise; the moderate treadmill exercise group(MIR group)to exercise 4 weeks after modeling without CS/HA-g-CS implantation; the CHI + MIR group to moderate treadmill exercise plus CS/HA-g-CS implantation 4 weeks after modeling. Half of the animals were sacrificed at week 8 and half at week 16 after operation. Femoral condyles were harvested for gross observation and his-tochemical measurement by O’ Driscoll scoring system. mRNA expressions of glycosaminoglycan, collagen typeⅡ and BMP-2 were detected by RT-PCR. Results Gross observation revealed: at 8 weeks after modeling, the CHI + MIR group was significantly better than the other 3 groups, with the BC group in the poorest(P 0. 05). O' Driscoll scoring revealed: at both 8and 16 weeks after modeling, the CHI + MIR group was significantly better than the other 2 groups and the BC group significantly poorer than the other 3 groups(P 0. 05). The expressions of collagen type Ⅱ, glycosaminoglycan and BMP-2 were significantly higher in the CHI + MIR group than in the other 3 groups(P< 0. 05)and significantly lower in the BC group than in the other 3 groups(P< 0. 05). Conclusions Moderate treadmill exercise together with CS/HA-g-CS implantation has significant positive effects on repair of full-thickness defects of articular cartilage in rats than merely moderate treadmill exercise or CS/HA-g-CS implantation alone. The defective cartilage repaired by moderate treadmill exercise together with CS/HA-g-CS implantation contains more collagen type II and glycosaminoglycan and shows morphology of nearly normal cartilage. Key words: Exercise; Cartilage, articuler; Injuries; Hydroxyapatite chitosan composite hydrogel

Physical Cross-Linking Starch-Based Zwitterionic Hydrogel Exhibiting Excellent Biocompatibility, Protein Resistance, and Biodegradability

In this work, a novel starch-based zwitterionic copolymer, starch-graft-poly(sulfobetaine methacrylate) (ST-g-PSBMA), was synthesized via Atom Transfer Radical Polymerization. Starch, which formed the main chain, can be degraded completely in vivo, and the pendent segments of PSBMA endowed the copolymer with excellent protein resistance properties. This ST-g-PSBMA copolymer could self-assemble into a physical hydrogel in normal saline, and studies of the formation mechanism indicated that the generation of the physical hydrogel was driven by electrostatic interactions between PSBMA segments. The obtained hydrogels were subjected to detailed analysis by scanning electron microscopy, swelling ratio, protein resistance, and rheology tests. Toxicity and hemolysis analysis demonstrated that the ST-g-PSBMA hydrogels possess excellent biocompatibility and hemocompatibility. Moreover, the cytokine secretion assays (IL-6, TNF-α, and NO) confirmed that ST-g-PSBMA hydrogels had low potential to trigger the activation of macrophages and were suitable for in vivo biomedical applications. On the basis of these in vitro results, the ST-g-PSBMA hydrogels were implanted in SD rats. The tissue responses to hydrogel implantation and the hydrogel degradation in vivo were determined by histological analysis (Hematoxylin and eosin, Van Gieson, and Masson's Trichrome stains). The results presented in this study demonstrate that the physical cross-linking, starch-based zwitterionic hydrogels possess excellent protein resistance, low macrophage-activation properties, and good biocompatibility, and they are a promising candidate for an in vivo biomedical application platform.

A photopolymerized composite hydrogel and surgical implanting tool for a nucleus pulposus replacement

Nucleus pulposus replacements have been subjected to highly controversial discussions over the last 40 years. Their use has not yet resulted in a positive outcome to treat herniated disc or degenerated disc disease. The main reason is that not a single implant or tissue replacement was able to withstand the loads within an intervertebral disc. Here, we report on the development of a photo-polymerizable poly(ethylene glycol)dimethacrylate nano-fibrillated cellulose composite hydrogel which was tuned according to native tissue properties. Using a customized minimally-invasive medical device to inject and photopolymerize the hydrogel insitu, samples were implanted through an incision of 1 mm into an intervertebral disc of a bovine organ model to evaluate their long-term performance. When implanted into the bovine disc model, the composite hydrogel implant was able to significantly re-establish disc height after surgery (p < 0.0025). The height was maintained after 0.5 million loading cycles (p < 0.025). The mechanical resistance of the novel composite hydrogel material combined with the minimally invasive implantation procedure into a bovine disc resulted in a promising functional orthopedic implant for the replacement of the nucleus pulposus.

Robust and bioadhesive supramolecular hydrogel stabilized by pre-assembled host-guest complexation for in situ tissue regeneration

Event Abstract Back to Event Robust and bioadhesive supramolecular hydrogel stabilized by pre-assembled host-guest complexation for in situ tissue regeneration Qian Feng1, 2, Kongchang Wei1, 2 and Liming Bian1, 2 1 The Chinese University of Hong Kong, Biomedical Engineering Division, Hong Kong, SAR China 2 The Chinese University of Hong Kong, Department of Mechanical & Automation Engineering, Hong Kong, SAR China Introduction: Hydrogels made of biopolymers are promising for biomedical applications due to their good biocompatibility and intrinsic bioactivities1. Most of these biopolymer-based hydrogels are covalently crosslinked and are stable and stiff. However, these hydrogels are brittle and lack self-healing capability[1],[2]. Alternatively, supramolecular hydrogels stabilized by physical crosslinking, possess unique physical properties[3],[4]. However, to form these supramolecular hydrogels, chemical modifications of the biopolymers are still usually required, which may alter the properties of the biopolymers[5]. Herein, we show the formation of supramolecular hydrogels, free from chemical modifications and direct crosslinking of the biopolymers, via a novel “Host-Guest Macromer” (HGM) approach. This simple but effective strategy opens up a new route to develop biopolymeric supramolecular hydrogels with enhanced physical and biological functionalities as drug and/or cell carriers for regenerative medicine. Materials and Methods: Gelatin HGM supramolecular hydrogels were prepared by pre-assembling acrylated host (β-cyclodextrin) monomer and gelatin (bearing guest aromatic groups) before radical chain polymerization. Stromal cell-derived factor (SDF-1α) was used for migration test. Hydrogels were soaked in dexamethasone (Dex) solutions to measure the percentage of Dex loaded into the hydrogels and then were incubated in PBS to measure the Dex releasing. Human mesenchymal stem cells (hMSCs) laden hydrogels were cultured in osteogenic media for in vitro study. Rat calvarial defect model was used for in vivo study. Results and Discussion: The HGM gelatin hydrogels show outstanding tensile and compression properties (Fig. 1a, b). Moreover, our HGM hydrogels can be drawn into a syringe and injected into a mold of a different shape and recover to self-standing hydrogels (Fig. 1c). Furthermore, the HGM hydrogels bond the two pieces of bone tightly (Fig. 1d) even in the aqueous environment. Besides, HGM hydrogels facilitate the migration of hMSCs inside the hydrogels (Fig. 1e). This property can support the recruitment of endogenous cells to participate in the healing process. Compared to chemical crosslinking methacrylated gelatin (MeGel) hydrogesl, the HGM hydrogels hold more hydrophobic small molecular drug (Dex) and release it continuously for a longer time. For in vitro, our HGM hydrogels can support the growth and osteogenic differentiation of hMSCs (Fig. 2a-c). Finally, the implantation of the HGM gelatin hydrogels without any growth factors and cells in rat calvarial bone defects shows that our HGM hydrogels have the potential to modulate macrophage polarization and to support in situ tissue regeneration without using exogenous cells (Figure 2 d-e), thereby greatly simplifying the regenerative therapy. Conclusion: Collectively, Our work provides an original “host-guest macromer” approach to prepare supramolecular hydrogels. The HGM hydrogels are ideal biomaterial to assist the repair and regeneration of injured tissues such as bone. Figure 1. The unique features of (a) strechability, (b) compressibility, (c) injectability, (d) moldability, (e) tissue adhesion, (e) cell migration and drug loading (f) / realsing (g) of the HGM hydrogels. **p < 0.001. Figure 2. (a) Cell viability staining of the hMSC-laden MeGel and HGM hydrogels. (b) Selected osteogenic gene expression. (c) H&E staining, Von Kossa staining, and type I collagen immunohistochemical staining of hMSC-laden HGM and MeGel hydrogels after 14 days of osteogenic culture. (d) representative mCT reconstitution for blank group (without hydrogel), and Dex-loaded MeGel (left) and HGM (right) hydrogel. (e) H&E staining, Col I, osteocalcin (OCN), CD68, and CD163 immunohistochemical staining of the MeGel and HGM hydrogel groups after 10 weeks of implantation (black narrow: the calvarial defect boundary). Scale bars: 100 m (a), 50 m (c, and 100 m (inserts), 50 m (e, except the leftmost column of H&E staining, 500 m). **p < 0.001. Research Grants Council of Hong Kong (Project No. 439913); National Natural Science Foundation of China (Project No. 31300796); Shun Hing Institute of Advanced Engineering (Project No. BME-8115043)