Hyaluronidase-Responsive Bactericidal Cryogel for Promoting Healing of Infected Wounds: Inflammatory Attenuation, ROS Scavenging, and Immune Regulation

Wounds infected with multidrug-resistant (MDR) bacteria are increasingly threatening public health and challenging clinical treatments because of intensive bacterial colonization, excessive inflammatory responses, and superabundant oxidative stress. To overcome this malignant burden and promote wound healing, a multifunctional cryogel (HA/TA2/KR2) composed of hyaluronic acid (HA), tannic acid (TA), and KR-12 peptides is designed. The cryogel exhibited excellent shape-memory properties, strong absorption performance, and hemostatic capacity. In vitro experiments demonstrated that KR-12 in the cryogel can be responsively released by stimulation with hyaluronidase produced by bacteria, reaching robust antibacterial activity against Escherichia coli (E. coli), MDR Pseudomonas aeruginosa (MDR-PA), and methicillin-resistant Staphylococcus aureus (MRSA) by disrupting bacterial cell membranes. Furthermore, the synergetic effect of KR-12 and TA can efficiently scavenge ROS and decrease expression of pro-inflammatory cytokines (tumor necrosis factor (TNF)-α & interleukin (IL)-6), as well as modulate the macrophage phenotype toward the M2 type. In vivo animal tests indicated that the cryogel can effectively destroy bacteria in the wound and promote healing process via accelerating angiogenesis and re-epithelialization. Proteomic analysis revealed the underlying mechanism by which the cryogel mainly reshaped the infected wound microenvironment by inhibiting the Nuclear factor kappa B (NF-κB) signaling pathway and activating the Janus kinase-Signal transducer and activator of transcription (JAK-STAT6) signaling pathway. Therefore, the HA/TA2/KR2 cryogel is a promising dressing candidate for MDR bacteria-infected wound healing.

Preparation and assessment of agar/TEMPO-oxidized bacterial cellulose cryogels for hemostatic applications

In this work, we have demonstrated agar and oxidized bacterial cellulose cryogels as a potential hemostatic dressing material. TEMPO-oxidized bacterial cellulose (OBC) was incorporated into the agar matrix, improving its mechanical and hemostatic properties. The oxidation of bacterial cellulose (BC) was evidenced by chemical characterization studies, confirming the presence of carboxyl groups. The in vitro blood clotting test conducted on agar/OBC composite cryogels demonstrated complete blood clotting within 90 seconds, indicating their excellent hemostatic efficacy. The cryogels exhibited superabsorbent properties with a swelling degree of 4200%, enabling them to absorb large amounts of blood. Moreover, the compressive strength of the composite cryogels was appreciably improved compared to pure agar, resulting in a more stable physical structure. The platelet adhesion test proved the significant ability of the composite cryogels to adhere to and aggregate platelets. Hemocompatibility and cytocompatibility tests have verified the safety of these cryogels for hemostatic applications. Finally, the material exhibited remarkable in vivo hemostatic performance, achieving clotting times of 64 seconds and 35 seconds when tested in the rat tail amputation model and the liver puncture model, respectively. The experiment results were compared with those of commercial hemostat, Axiostat, and Surgispon, affirming the potential of agar/OBC composite cryogel as a hemostatic dressing material.

Cellulose nanocrystals-reinforced dual crosslinked double network GelMA/hyaluronic acid injectable nanocomposite cryogels with improved mechanical properties for cartilage tissue regeneration

Improvement of mechanical properties of injectable tissue engineering scaffolds is a current challenge. The objective of the current study is to produce a highly porous injectable scaffold with improved mechanical properties. For this aim, cellulose nanocrystals-reinforced dual crosslinked porous nanocomposite cryogels were prepared using chemically crosslinked methacrylated gelatin (GelMA) and ionically crosslinked hyaluronic acid (HA) through the cryogelation process. The resulting nanocomposites showed highly porous structures with interconnected porosity (>90%) and mean pore size in the range of 130-296 μm. The prepared nanocomposite containing 3%w/v of GelMA, 20 w/w% of HA, and 1%w/v of CNC showed the highest Young's modulus (10 kPa) and excellent reversibility after 90% compression and could regain its initial shape after injection by a 16-gauge needle in the aqueous media. The in vitro results demonstrated acceptable viability (>90%) and migration of the human chondrocyte cell line (C28/I2), and chondrogenic differentiation of human adipose stem cells. A two-month in vivo assay on a rabbit's ear model confirmed that the regeneration potential of the prepared cryogel is comparable to the natural autologous cartilage graft, suggesting it is a promising alternative for autografts in the treatment of cartilage defects.

Gelatin Methacryloyl Based Injectable Cryogels with Tunable Degradability for Cell Delivery

Scaffold-based cell delivery can improve therapeutic effects of transplanted cells in cell therapy. Biomaterial scaffolds serveas niche for cell growth and proliferation which improves cell survival and overall function post cell delivery. In this study, gelatin methacryloyl based injectable scaffolds made using poly(ethylene)glycol as a sacrificial polymer and cryogelation as a technique, are demonstrated to have tunable degradability and porosity that is required for cell and drug delivery applications. The pore size (10-142 µm) of these gels makes them suitable for loading different cell types as per the application. In vitro studies using mammalian cells confirm that these cryogels are cytocompatible. These cell-laden scaffolds are injectable and have a cell retention ability of up to 90% after injection. Rheology is done to evaluate stiffness and shape recovery property, and it is found that these gels can maintain their original shape even after applying 7 cycles of strain from 0.1% to 20%. Furthermore, their degradability can be modulated between 6 and 10 days by changing the overall polymer composition. Thus, injectability and degradability of these cryogels can circumvent invasive surgical procedures, thereby making them useful for a variety of applications including delivery of cells and bioactive factors.

Biomaterial-assisted local oxygenation safeguards the prostimulatory phenotype and functions of human dendritic cells in hypoxia

Dendritic cells (DCs), professional antigen-presenting cells, function as sentinels of the immune system. DCs initiate and fine-tune adaptive immune responses by presenting antigenic peptides to B and T lymphocytes to mount an effective immune response against cancer and pathogens. However, hypoxia, a condition characterized by low oxygen (O2) tension in different tissues, significantly impacts DC functions, including antigen uptake, activation and maturation, migration, as well as T-cell priming and proliferation. In this study, we employed O2-releasing biomaterials (O2-cryogels) to study the effect of localized O2 supply on human DC phenotype and functions. Our results indicate that O2-cryogels effectively mitigate DC exposure to hypoxia under hypoxic conditions. Additionally, O2-cryogels counteract hypoxia-induced inhibition of antigen uptake and migratory activity in DCs through O2 release and hyaluronic acid (HA) mediated mechanisms. Furthermore, O2-cryogels preserve and restore DC maturation and co-stimulation markers, including HLA-DR, CD86, and CD40, along with the secretion of proinflammatory cytokines in hypoxic conditions. Finally, our findings demonstrate that the supplemental O2 released from the cryogels preserves DC-mediated T-cell priming, ultimately leading to the activation and proliferation of allogeneic CD3+ T cells. This work emphasizes the potential of local oxygenation as a powerful immunomodulatory agent to improve DC activation and functions in hypoxia, offering new approaches for cancer and infectious disease treatments.

Bioactive Glasses-Based Nanozymes Composite Macroporous Cryogel with Antioxidative, Antibacterial, and Pro-Healing Properties for Diabetic Infected Wound Repair

The treatment for diabetic ulcers still remains a big clinic challenge owing to the adverse repair microenvironment. Bioactive glasses (BGs) play an important role in the late stages of healing due to their ability to promote vascularization and collagen fiber deposition, but fail to improve infection and oxidative stress in the early stage.Therefore, it is critical to develop a material involved in regulating the whole healing phases. In this work, BGs-based nanozymes (MnO2 @PDA-BGs) with antioxidation, antibacterial and pro-healing abilities are synthesized by the redox deposition of MnO2 on mesoporous BGs. Afterward, cryogel with the interconnected macropore structure is fabricated by the polymerization of methacrylate anhydride gelatin (GelMA) at -20 °C. MnO2 @PDA-BGs are loaded into the cryogel to obtain nanocomposite cryogel (MnO2 @PDA-BGs/Gel) with multiple enzymes-like- activities to eliminate reactive oxygen species (ROS). Besides, MnO2 @PDA-BGs/Gel has intensive peroxidase-like activity under acidic condition and near infrared photothermal responsiveness to achieve excellent antibacterial performance. Cells experiments demonstrate that MnO2 @PDA-BGs/Gel recruits L929s and promotes their proliferation. Furthermore, MnO2 @PDA-BGs/Gel eliminates intracellular overexpressed ROS and maintains the viability of L929s. Animal experiments confirm that MnO2 @PDA-BGs/Gel promotes wound healing and avoided scarring by killing bacteria, reversing inflammation, promoting vascularization, and improving the deposition of collagen III.

Chitosan versus Carboxymethyl Chitosan Cryogels: Bacterial Colonization, Human Embryonic Kidney 293T Cell Culturing and Co-Culturing

The potential of chitosan and carboxymethyl chitosan (CMC) cryogels cross-linked with diglycidyl ether of 1,4-butandiol (BDDGE) and poly(ethylene glycol) (PEGDGE) have been compared in terms of 3D culturing HEK-293T cell line and preventing the bacterial colonization of the scaffolds. The first attempts to apply cryogels for the 3D co-culturing of bacteria and human cells have been undertaken toward the development of new models of host-pathogen interactions and bioimplant-associated infections. Using a combination of scanning electron microscopy, confocal laser scanning microscopy, and flow cytometry, we have demonstrated that CMC cryogels provided microenvironment stimulating cell-cell interactions and the growth of tightly packed multicellular spheroids, while cell-substrate interactions dominated in both chitosan cryogels, despite a significant difference in swelling capacities and Young's modulus of BDDGE- and PEGDGE-cross-linked scaffolds. Chitosan cryogels demonstrated only mild antimicrobial properties against Pseudomonas fluorescence, and could not prevent the formation of Staphylococcus aureus biofilm in DMEM media. CMC cryogels were more efficient in preventing the adhesion and colonization of both P. fluorescence and S. aureus on the surface, demonstrating antifouling properties rather than the ability to kill bacteria. The application of CMC cryogels to 3D co-culture HEK-293T spheroids with P. fluorescence revealed a higher resistance of human cells to bacterial toxins than in the 2D co-culture.

An Integrated Strategy for Rapid Hemostasis during Tumor Resection and Prevention of Postoperative Tumor Recurrence of Hepatocellular Carcinoma by Antibacterial Shape Memory Cryogel

The inevitable bleeding during tumor resection greatly increases the risk of tumor recurrence caused by metastasis of cancer cells with blood, and hemostasis and prevention of post-operation tumor recurrence is still a challenge. However, a biomaterials approach for rapid hemostasis during tumor resection and simultaneous prevention of tumor recurrence is rarely reported. Here, zeolitic imidazolate framework (ZIF-8) nanoparticle-enhanced multinetwork cryogels are proposed which provide an integrated treatment regimen for rapid hemostasis through intraoperative blood trigger shape recovery and enhanced coagulation, and prevention of postoperative cancer recurrence via sonodynamic anticancer in a hepatocellular carcinoma model. A series of antibacterial shape memory multifunctional cryogels are synthesized based on glycidyl methacrylate-functionalized quaternized chitosan (QCSG), dopamine-modified hyaluronic acid (HA-DA), and hematoporphyrin monomethyl ether (HMME)-loaded dopamine-modified ZIF-8 (ZDH). Blood loss in different bleeding models confirms good hemostasis of ZIF-8 loading cryogels. Besides, in vitro tests confirm that QCSG/HA-DA/ZDH (QH/ZDH) cryogels significantly killed cancer cells by generating reactive oxygen species under ultrasound. Finally, significantly reduced tumor recurrence after the resection of ectopic hepatocellular carcinoma further confirms the good effect of QH/ZDH cryogels in preventing recurrence by a coordinated strategy of intraoperative hemostasis and postoperative sonodynamic therapy by pH-responsive HMME release, showing great potential in clinical application.

Metcalf Lecture Award: Applying niche biology to engineer T-cell regenerative therapies

The processes generating cells of adaptive immunity render them less amenable to the single cytokine signals used so effectively to regenerate myeloid cells. T-cell neogenesis begins in the bone marrow, where specific sets of late osteolineage cells govern the specification of hematopoietic cells capable of migrating to the thymus where differentiation is completed. Osteocalcin-expressing bone marrow stromal cells producing Dll4 serve as a progenitor niche enabling this T-competent cell production. Biocompatible alginate-based cryogels containing bone morphogenetic proteins (BMP-2) and the Notch ligand Dll4 were engineered to recapitulate the endogenous niche. These cryogels are highly pliable and can be injected under the skin of animals undergoing bone marrow transplantation. The result in mice is an ectopic niche fostering T-competent progenitor generation that results in improved T-cell numbers and receptor diversity. The recipients can generate neoantigen vaccine responses while having improved tolerance manifest by reduced graft-versus-host disease upon allogeneic transplant. Through emerging details of niches in the bone marrow, therapeutics more complex than those necessary for myeloid reconstitution are possible. Niche biology-guided bioengineered design offers the possibility of regenerative therapies for T lymphoid cells.

Cryogel scaffolds for regionally constrained delivery of lysophosphatidylcholine to central nervous system slice cultures: A model of focal demyelination for multiple sclerosis research

The pathology of multiple sclerosis (MS) is typified by focal demyelinated areas of the brain and spinal cord, which results in axonal degeneration and atrophy. Although the field has made much progress in developing immunomodulatory therapies to reduce the occurrence of these focal lesions, there is a conspicuous lack of licensed effective therapies to reduce axonal degeneration or promote repair. Remyelination, carried out by oligodendrocytes, does occur in MS, and is protective against axonal degeneration. Unfortunately, remyelination is not very efficient, and ultimately fails and so there is a research focus to generate new therapeutics to enhance remyelination leading to neuroprotection. To develop these therapies, we need preclinical models that well reflect remyelination in MS. We have previously characterized an ex vivo model that uses lysophosphatidylcholine (LPC) to cause acute and global demyelination of tissue slices, followed by spontaneous remyelination, which has been widely used as a surrogate for in vivo rodent models of demyelination. However, this ex vivo model lacks the focal demyelinated lesions seen in MS, surrounded by normal tissue from which the repairing oligodendrocytes are derived. Therefore, to improve the model, we have developed and characterized small macroporous cryogel scaffolds for controlled/regional delivery of LPC with diameters of either 0.5, 1 or 2 mm. Placement of LPC loaded scaffolds adjacent to ex vivo cultured mouse brain and spinal cord slices induced focal areas of demyelination in proximity to the scaffold. To the best of our knowledge, this is the first such report of spatial mimicry of the in vivo condition in ex vivo tissue culture. This will allow not only the investigation into focal lesions, but also provides a better platform technology with which to test remyelination-promoting therapeutics. STATEMENT OF SIGNIFICANCE: This manuscript is the first report of using macroporous hydrogels (cryogels) as a research tool for lysophosphatidylcholine (LPC) delivery, in order to create an ex vivo model of focal demyelination in the brain and spinal cord, which is of great relevance to multiple sclerosis research. Here, we transform an existing ex vivo model of demyelination by delivering LPC to focal regions of brain and spinal cord slice cultures. We have developed an easy-to-handle cylindrical and macroporous PEG-based sponge-like scaffold material (cryogel) that can deliver LPC only to a small area of the slice. Such cryogels are ideal as a delivery system in this culture model as they exhibit a soft but robust nature, with high mechanical deformability in their dry and swollen state, with no need to stay permanently hydrated. In addition, the synthesis of these cryogels is simple and easy to reproduce via photochemical cryopolymerisation using a PEG-diacrylate monomer and a photoinitiator, which are both commercially available. This more accurate model of demyelination will not only allow researchers to gain a better understanding of the CNS remyelination process in diseases such as MS, but also provides a platform technology, which could be utilized to screen and test pro-remyelination compounds which may help to find new therapeutics for progressive MS.

Mussel-inspired cryogels for promoting wound regeneration through photobiostimulation, modulating inflammatory responses and suppressing bacterial invasion

Wound healing is a complex and dynamic process, and involves a series of events, which create a unique microenvironment at the wound sites. It is highly desirable to develop multi-functional skin substitutes which can play their roles in the whole healing processes to enhance the final healing efficiency. Herein, we fabricated a mussel-inspired chitosan/silk fibroin cryogel functionalized with near-infrared light-responsive polydopamine nanoparticles (PDA-NPs), as a multifunctional platform to regulate the wound microenvironment and enhance efficient wound healing. The cryogel has an extracellular matrix-like macroporous structure, mimicking the natural tissue environment, which allows cell attachment and tissue ingrowth. The cryogel shows high anti-oxidative activity to eliminate overproduced reactive oxygen species during inflammatory responses. Furthermore, the cryogel exhibits photothermally assisted antibacterial activity to prevent bacterial invasion. Thus, by combining the photobiostimulation of infrared light, the cryogel realizes bio-chemo-photothermal synergistic therapy for accelerating the complete skin-thickness wound healing by simultaneously suppressing adverse events due to its antibacterial activity and anti-oxidative ability, and promoting cell activities and tissue regeneration. Our work therefore presents the great promise shown by this multifunctional biopolymer cryogel as a flexible wound dressing with combinatory therapy for accelerating wound healing.

A collagen based cryogel bioscaffold coated with nanostructured polydopamine as a platform for mesenchymal stem cell therapy

Cryo-hydrogels (cryogels) are polymer hydrogels formed at sub-zero temperatures. Bioscaffolds created from cryogels have interconnected macropores which allow for cell migration, tissue-ingrowth, unhindered diffusion of solutes and mass transport of therapeutics. In this study, we developed collagen based cryogel bioscaffolds and coated them with polydopamine using a simple two-step technique. Cryogel bioscaffolds were synthesized by collagen crosslinking at -20°C and exhibited a macroporous interconnected architecture with 75% ± 3% porosity. Two groups of pore sizes were observed: 300 ± 50 µm and 30 ± 10 µm in diameter. The addition of a polydopamine coating to cryogel bioscaffolds was confirmed using composition analysis. This resulted in a 41% ± 5% decrease in water uptake, 81% ± 10% decrease in swelling rate and 12% ± 3% decrease in their degree of dissolution (p < 0.05), with a 48% ± 2% increase in stiffness and 57% ± 5% increase in compressive strength (p < 0.05). Seeding adipose tissue-derived mesenchymal stem cells (AD-MSCs) into polydopamine coated-cryogel bioscaffolds resulted in cells demonstrating a 52% ± 4% increase in viability and 33% ± 3% increase in proliferation when compared to AD-MSCs seeded into uncoated-cryogel bioscaffolds (p < 0.05). In summary, our novel polydopamine coated-cryogel bioscaffold represents an efficient and low-cost bioscaffold platform to support MSC therapies. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 2213-2228, 2018.

Injectable antibacterial conductive nanocomposite cryogels with rapid shape recovery for noncompressible hemorrhage and wound healing

Developing injectable antibacterial and conductive shape memory hemostatic with high blood absorption and fast recovery for irregularly shaped and noncompressible hemorrhage remains a challenge. Here we report injectable antibacterial conductive cryogels based on carbon nanotube (CNT) and glycidyl methacrylate functionalized quaternized chitosan for lethal noncompressible hemorrhage hemostasis and wound healing. These cryogels present robust mechanical strength, rapid blood-triggered shape recovery and absorption speed, and high blood uptake capacity. Moreover, cryogels show better blood-clotting ability, higher blood cell and platelet adhesion and activation than gelatin sponge and gauze. Cryogel with 4 mg/mL CNT (QCSG/CNT4) shows better hemostatic capability than gauze and gelatin hemostatic sponge in mouse-liver injury model and mouse-tail amputation model, and better wound healing performance than Tegaderm™ film. Importantly, QCSG/CNT4 presents excellent hemostatic performance in rabbit liver defect lethal noncompressible hemorrhage model and even better hemostatic ability than Combat Gauze in standardized circular liver bleeding model.

Alleviating liver failure conditions using an integrated hybrid cryogel based cellular bioreactor as a bioartificial liver support

Conventionally, some bioartificial liver devices are used with separate plasmapheresis unit to separate out plasma from whole blood and adsorbent column to detoxify plasma before it passes through a hepatocytes-laden bioreactor. We aim to develop a hybrid bioreactor that integrates the separate modules in one compact design improving the efficacy of the cryogel based bioreactor as a bioartificial liver support. A plasma separation membrane and an activated carbon cloth are placed over a HepG2-loaded cryogel scaffold in a three-chambered bioreactor design. This bioreactor is consequently connected extracorporeally to a rat model of acute liver failure for 3 h and major biochemical parameters studied. Bilirubin and aspartate transaminase showed a percentage decrease of 20-60% in the integrated bioreactor as opposed to 5-15% in the conventional setup. Urea and ammonia levels which showed negligible change in the conventional setup increase (40%) and decrease (18%), respectively in the integrated system. Also, an overall increase of 5% in human albumin in rat plasma indicated bioreactor functionality in terms of synthetic functions. These results were corroborated by offline evaluation of patient plasma. Hence, integrating the plasmapheresis and adsorbent units with the bioreactor module in one compact design improves the efficacy of the bioartificial liver device.

Dual Function of Glucosamine in Gelatin/Hyaluronic Acid Cryogel to Modulate Scaffold Mechanical Properties and to Maintain Chondrogenic Phenotype for Cartilage Tissue Engineering

Glucosamine (GlcN) fulfills many of the requirements as an ideal component in scaffolds used in cartilage tissue engineering. The incorporation of GlcN in a gelatin/hyaluronic acid (GH) cryogel scaffold could provide biological cues in maintaining the phenotype of chondrocytes. Nonetheless, substituting gelatin with GlcN may also decrease the crosslinking density and modulate the mechanical properties of the cryogel scaffold, which may be beneficial as physical cues for chondrocytes in the scaffold. Thus, we prepared cryogel scaffolds containing 9% GlcN (GH-GlcN9) and 16% GlcN (GH-GlcN16) by carbodiimide-mediated crosslinking reactions at -16 °C. The crosslinking density and the mechanical properties of the cryogel matrix could be tuned by adjusting the content of GlcN used during cryogel preparation. In general, incorporation of GlcN did not influence scaffold pore size and ultimate compressive strain but increased porosity. The GH-GlcN16 cryogel showed the highest swelling ratio and degradation rate in hyaluronidase and collagenase solutions. On the contrary, the Young's modulus, storage modulus, ultimate compressive stress, energy dissipation level, and rate of stress relaxation decreased by increasing the GlcN content in the cryogel. The release of GlcN from the scaffolds in the culture medium of chondrocytes could be sustained for 21 days for GH-GlcN16 in contrast to only 7 days for GH-GlcN9. In vitro cell culture experiments using rabbit articular chondrocytes revealed that GlcN incorporation affected cell proliferation, morphology, and maintenance of chondrogenic phenotype. Overall, GH-GlcN16 showed the best performance in maintaining chondrogenic phenotype with reduced cell proliferation rate but enhanced glycosaminoglycans (GAGs) and type II collagen (COL II) secretion. Quantitative real-time polymerase chain reaction also showed time-dependent up-regulation of cartilage-specific marker genes (COL II, aggrecan and Sox9) for GH-GlcN16. Implantation of chondrocytes/GH-GlcN16 constructs into full-thickness articular cartilage defects of rabbits could regenerate neocartilage with positive staining for GAGs and COL II. The GH-GlcN16 cryogel will be suitable as a scaffold for the treatment of articular cartilage defects.

Bilayer Cryogel Wound Dressing and Skin Regeneration Grafts for the Treatment of Acute Skin Wounds

In this study, the potential of cryogel bilayer wound dressing and skin regenerating graft for the treatment of surgically created full thickness wounds was evaluated. The top layer was composed of polyvinylpyrrolidone-iodine (PVP-I) cryogel and served as the antiseptic layer, while the bottom regenerative layer was made using gelatin cryogel. Both components of the bilayer showed typical features of a cryogel interconnected macropore network, rapid swelling, high water uptake capacity of about 90%. Both PVP and gelatin cryogel showed high tensile strength of 45 and 10 kPa, respectively. Gelatin cryogel sheets were essentially elastic and could be stretched without any visible deformation. The antiseptic PVP-I layer cryogel sheet showed sustained iodine release and suppressed microbial growth when tested with skin pathogens (zone of inhibition ∼2 cm for sheet of 0.9 cm diameter). The gelatin cryogel sheet degraded in vitro in weeks. The gelatin cryogel sheet supported cell infiltration, attachment, and proliferation of fibroblasts and keratinocytes. Microparticles loaded with bioactive molecules (mannose-6-phosphate and human fibrinogen) were also incorporated in the gelatin cryogel sheets for their role in enhancing skin regeneration and scar free wound healing. In vivo evaluation of healing capacity of the bilayer cryogel was checked in rabbits by creating full thickness wound defect (diameter 2 cm). Macroscopic and microscopic observation at regular time intervals for 4 weeks demonstrated better and faster skin regeneration in the wound treated with cryogel bilayer as compared to untreated defect and the repair was comparable to commercial skin regeneration scaffold Neuskin-F. Complete skin regeneration was observed after 4 weeks of implantation with no sign of inflammatory response. Defects implanted with cryogel having mannose-6-phosphate showed no scar formation, while the wound treated with bilayer incorporated with human fibrinogen microparticles showed early signs of skin regeneration; epidermis formation occurred at 2 weeks after implantation.

Combined Effect of Cryogel Matrix and Temperature-Reversible Soluble-Insoluble Polymer for the Development of in Vitro Human Liver Tissue

Hepatic cell culture on a three-dimensional (3D) matrix or as a hepatosphere appears to be a promising in vitro biomimetic system for liver tissue engineering applications. In this study, we have combined the concept of a 3D scaffold and a spheroid culture to develop an in vitro model to engineer liver tissue for drug screening. We have evaluated the potential of poly(ethylene glycol)-alginate-gelatin (PAG) cryogel matrix for in vitro culture of human liver cell lines. The synthesized cryogel matrix has a flow rate of 7 mL/min and water uptake capacity of 94% that enables easy nutrient transportation in the in vitro cell culture. Young's modulus of 2.4 kPa and viscoelastic property determine the soft and elastic nature of synthesized cryogel. Biocompatibility of PAG cryogel was evaluated through MTT assay of HepG2 and Huh-7 cells on matrices. The proliferation and functionality of the liver cells were enhanced by culturing hepatic cells as spheroids (hepatospheres) on the PAG cryogel using temperature-reversible soluble-insoluble polymer, poly(N-isopropylacrylamide) (PNIPAAm). Pore size of the cryogel above 100 μm modulated spheroid size that can prevent hypoxia condition within the spheroid culture. Both the hepatic cells have shown a significant difference (P < 0.05) in terms of cell number and functionality when cultured with PNIPAAm. After 10 days of culture using 0.05% PNIPAAm, the cell number increased by 11- and 7-fold in case of HepG2 and Huh-7 cells, respectively. Similarly, after 10 days of hepatic spheroids culture on PAG cryogel, the albumin production, urea secretion, and CYP450 activity were significantly higher in case of culture with PNIPAAm. The developed tissue mass on the PAG cryogel in the presence of PNIPAAm possess polarity, which was confirmed using F-actin staining and by presence of intercellular bile canalicular lumen. The developed cryogel matrix supports liver cells proliferation and functionality and therefore can be used for in vitro and in vivo drug testing.

Tackling Cell Transplantation Anoikis: An Injectable, Shape Memory Cryogel Microcarrier Platform Material for Stem Cell and Neuronal Cell Growth

Highly macroporous semisynthetic cryogel microcarriers can be synthesized for culturing stem cells and neuronal type cells. Growth factors loaded to heparin-containing microcarriers show near zero-order release kinetics and cell-loaded microcarriers can be injected through a fine gauge cannula without negative effect on the cells. These carriers can be applied for cell transplantation applications.

Osteocompatibility and osteoinductive potential of supermacroporous polyvinyl alcohol-TEOS-agarose-CaCl2 (PTAgC) biocomposite cryogels

Bone tissue engineering majorly focuses on the development of biomaterials which have the capability to mimic bone as well as the ability to induce bone formation. To this direction, we have prepared supermacroporous polyvinyl alcohol-TEOS-Agarose-CaCl2 (PTAgC) biocomposite cryogels having a uniform porous structure with an interconnected porosity of 77 ± 0.16 % and pore size of 190 ± 0.78 μm, as determined by scanning electron microscopic and micro-computed tomographic analyses. These biocomposite cryogels show an osteocompatible response towards Saos-2 human osteoblasts as analyzed via MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay, alkaline phosphatase (ALP) assay and cell adhesion behaviour showing a flattened morphology of the cells on the cryogel surface. The property of bioactivity was also observed on the surface of these biomaterials. Further, we also explored the osteoinductive potential of these biocomposite cryogels by the analysis of osteogenic differentiation of C2C12 myoblasts after seeding onto these biocomposite cryogels. The results indicate that these biocomposite cryogels indeed show an osteoinductive potential as we could observe the presence of respective markers for different stages during osteoblast maturation. During early timepoints, higher alkaline phosphatase production via ALP assay and BCIP/NBT staining was observed in the case of biocomposite cryogel seeded cells suggesting the osteoblastic differentiation of C2C12 cells. Whereas, during later timepoints, formation of calcium-phosphate like crystals was confirmed by von-kossa staining, further indicating towards the onset of mineralization phase during osteoblast maturation. Therefore, these results suggest that PTAgC biocomposite cryogels can form an important part of bone tissue engineered biomaterials due to their osteocompatible behaviour and osteoinductive potential.

A case of successful interaction between cells derived from human ovarian follicular liquid and gelatin cryogel for biotech and medical applications

Significant research efforts have been undertaken in the last decade to develop specific cell-based therapies and, in particular, adult multipotent mesenchymal stem cells (MSCs) hold great promise toward such regenerative strategies. Bio-materials have been widely used in reconstructive bone surgery to heal critical-size bone defects due to trauma, tumor resection, and tissue degeneration. In particular, gelatin cryogel scaffolds are promising new biomaterials owing to their biocompatibility. There is an increasing demand for MSC-based regenerative approaches in the musculoskeletal system. Combining stem cells with biomaterial scaffolds provides a promising strategy for tissue engineering. Our previous studies showed the possibility to obtain MSCs from the human ovarian follicular liquid (FL) that is usually wasted during in vitro fertilization (IVF). In this study, we tested the ability of these FL cells to grow on gelatin cryogel in comparison with MSCs derived from human bone marrow. Samples and controls were analyzed with confocal and scanning electron microscopes. Results demonstrated that FL cells could grow on the biomaterial not only on the top but also in the layers below till 60 µm of deepness. Data suggested that the observed cells were mesenchymal since positive for vimentin and CD-44, typical MSC markers. Successful growth of putative MSCs derived from follicular liquid on 3D gelatin cryogel opens potential developments in biotech and medical applications.

Ultrasound stimulus to enhance the bone regeneration capability of gelatin cryogels

In the present study, gelatin-based cryogels have been seeded with human SAOS-2 osteoblasts. In order to overcome the drawbacks associated with in vitro culture systems, such as limited diffusion and inhomogeneous cell-matrix distribution, this work describes the application of ultrasounds (average power, 149 mW; frequency, 1.5 MHz) to physically enhance the cell culture in vitro. The results indicate that the physical stimulation of cell-seeded gelatin-based cryogels upregulates the bone matrix production.

Conducting cryogel scaffold as a potential biomaterial for cell stimulation and proliferation

The aim of the study was to demonstrate the potential of the cryogelation technique for the synthesis of the conducting cryogel scaffolds which would encompass the advantages of the cryogel matrix, like the mechanical strength and interconnected porous network as well as the conductive properties of the incorporated conducting polymeric material, polypyrrole. The cryogels were synthesized using different combinations of oxidizing agents and surfactants like, sodium dodecyl sulfate (SDS)/ammonium persulfate (APS), SDS/iron chloride (FeCl(3)), cetyl trimethyl ammonium bromide (CTAB)/APS, and CTAB/FeCl(3). The synthesized gels were characterized by scanning electron microscopic analysis for morphology, Fourier transform infrared spectroscopy for analyzing the presence of the polypyrrole (0.5-4 %) as nano-fillers in the gel. It was observed that the presence of these nano-fillers increased the swelling ratio by approximately 50 %. The synthesized conducting cryogels displayed high stress bearing capacity without being deformed as analysed by rheological measurements. The degradation studies showed 12-15 % degradation in 4 weeks time. In vitro studies with conducting and non-conducting cryogel scaffold were carried out to optimize the stimulation conditions for the two cell lines, neuro2a and cardiac muscle C2C12. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay showed approximately 25 and 15 % increase in the cell proliferation rate for neuro2a and C2C12 cell line, respectively. This was observed at a specific voltage of 100 mV and 2 V, for a specified duration of 2 h and 1 min, respectively for the conducting scaffold as compared to the control. This can play an important role in tissue engineering applications for cell lines where acquiring a high cell number and functionality is desired.