The effects of fixed electrical charge on chondrocyte behavior

Simultaneous usage of sulforaphane nanoemulsion and tannic acid in ternary chitosan/gelatin/PEG hydrogel for knee cartilage tissue engineering: In vitro and in vivo study

The therapeutic potential of tissue engineering in addressing articular cartilage defects has been a focal point of research for numerous years. Despite its promising outlook, a persistent challenge within this domain is the lack of sufficient functional integration between engineered and natural tissues. This study introduces a novel approach that employs a combination of sulforaphane (SFN) nanoemulsion and tannic acid to enhance cartilage tissue engineering and promote tissue integration in a rat knee cartilage defect model. To substantiate our hypothesis, we conducted a series of in vitro and in vivo experiments. The SFN nanoemulsion was characterized using DLS, zeta potential, and TEM analyses. Subsequently, it was incorporated into a ternary polymer hydrogel composed of chitosan, gelatin, and polyethylene glycol. We evaluated the hydrogel with (H-SFN) and without (H) the SFN nanoemulsion through a comprehensive set of physicochemical, mechanical, and biological analyses. For the in vivo study, nine male Wistar rats were divided into three groups: no implant (Ctrl), H, and H-SFN. After inducing a cartilage defect, the affected area was treated with tannic acid and subsequently implanted with the hydrogels. Four weeks post-implantation, the harvested cartilage underwent histological examination employing H&E, safranin O/fast green, alcian blue, and immunohistochemistry staining techniques. Our results revealed that the SFN nanodroplets had an average diameter of 75 nm and a surface charge of -11.58 mV. Moreover, degradation, swelling rates, hydrophilicity, and elasticity features of the hydrogel incorporating SFN were improved. Histopathological analysis indicated a higher production of GAGs and collagen in the H-SFN group. Furthermore, the H-SFN group exhibited superior cartilage regeneration and tissue integration compared to the Ctrl and H groups. In conclusion, the findings of this study suggest the importance of considering cell protective properties in the fabrication of scaffolds for knee cartilage defects, emphasizing the potential significance of the proposed SFN nanoemulsion and tannic acid approach in advancing the field of cartilage tissue engineering.

Three-Dimensional Extrusion Printed Urinary Specific Grafts: Mechanistic Insights into Buildability and Biophysical Properties

The compositional formulations and the optimization of process parameters to fabricate hydrogel scaffolds with urological tissue-mimicking biophysical properties are not yet extensively explored, including a comprehensive assessment of a spectrum of properties, such as mechanical strength, viscoelasticity, antimicrobial property, and cytocompatibility. While addressing this aspect, the present work provides mechanistic insights into process science, to produce shape-fidelity compliant alginate-based biomaterial ink blended with gelatin and synthetic nanocellulose. The composition-dependent pseudoplasticity, viscoelasticity, thixotropy, and gel stability over a longer duration in physiological context have been rationalized in terms of intermolecular hydrogen bonding interactions among the biomaterial ink constituents. By varying the hybrid hydrogel ink composition within a narrow compositional window, the resulting hydrogel closely mimics the natural urological tissue-like properties, including tensile stretchability, compressive strength, and biophysical properties. Based on the printability assessment using a critical analysis of gel strength, we have established the buildability of the acellular hydrogel ink and have been successful in fabricating shape-fidelity compliant urological patches or hollow cylindrical grafts using 3D extrusion printing. Importantly, the new hydrogel formulations with good hydrophilicity, support fibroblast cell proliferation and inhibit the growth of Gram-negative E. coli bacteria. These attributes were rationalized in terms of nanocellulose-induced physicochemical changes on the scaffold surface. Taken together, the present study uncovers the process-science-based understanding of the 3D extrudability of the newly formulated alginate-gelatin-nanocellulose-based hydrogels with urological tissue-specific biophysical, cytocompatibility, and antibacterial properties.

Thermogelling hydrogel charge and lower critical solution temperature influence cellular infiltration and tissue integration in an ex vivo cartilage explant model

Thermogelling hydrogels based on poly(N-isopropyl acrylamide) (p[NiPAAm]) and crosslinked with a peptide-bearing macromer poly(glycolic acid)-poly(ethylene glycol)-poly(glycolic acid)-di(but-2-yne-1,4-dithiol) (PdBT) were fabricated to assess the role of hydrogel charge and lower critical solution temperature (LCST) over time in influencing cellular infiltration and tissue integration in an ex vivo cartilage explant model over 21 days. The p(NiPAAm)-based thermogelling polymer was synthesized to possess 0, 5, and 10 mol% dimethyl-γ-butyrolactone acrylate (DBA) to raise the LCST over time as the lactone rings hydrolyzed. Further, three peptides were designed to impart charge into the hydrogels via conjugation to the PdBT crosslinker. The positively, neutrally, and negatively charged peptides K4 (+), zwitterionic K2E2 (0), and E4 (-), respectively, were conjugated to the modular PdBT crosslinker and the hydrogels were evaluated for their thermogelation behavior in vitro before injection into the cartilage explant models. Samples were collected at days 0 and 21, and tissue integration and cellular infiltration were assessed via mechanical pushout testing and histology. Negatively charged hydrogels whose LCST changed over time (10 mol% DBA) were demonstrated to promote the greatest tissue integration when compared to the positive and neutral gels of the same thermogelling polymer formulation due to increased transport and diffusion across the hydrogel-tissue interface. Indeed, the negatively charged thermogelling polymer groups containing 5 and 10 mol% DBA demonstrated cellular infiltration and cartilage-like matrix deposition via histology. This study demonstrates the important role that material physicochemical properties play in dictating cell and tissue behavior and can inform future cartilage tissue engineering strategies.

An Injectable Hydrogel Scaffold Loaded with Dual-Drug/Sustained-Release PLGA Microspheres for the Regulation of Macrophage Polarization in the Treatment of Intervertebral Disc Degeneration

Due to the unique physical characteristics of intervertebral disc degeneration (IVDD) and the pathological microenvironment that it creates, including inflammation and oxidative stress, effective self-repair is impossible. During the process of intervertebral disc degeneration, there is an increase in the infiltration of M1 macrophages and the secretion of proinflammatory cytokines. Here, we designed a novel injectable composite hydrogel scaffold: an oligo [poly (ethylene glycol) fumarate]/sodium methacrylate (OPF/SMA) hydrogel scaffold loaded with dual-drug/sustained-release PLGA microspheres containing IL-4 (IL-4-PLGA) and kartogenin (KGN-PLGA). This scaffold exhibited good mechanical properties and low immunogenicity while also promoting the sustained release of drugs. By virtue of the PLGA microspheres loaded with IL-4 (IL-4-PLGA), the composite hydrogel scaffold induced macrophages to transition from the M1 phenotype into the M2 phenotype during the early induced phase and simultaneously exhibited a continuous anti-inflammatory effect through the PLGA microspheres loaded with kartogenin (KGN-PLGA). Furthermore, we investigated the mechanisms underlying the immunomodulatory and anti-inflammatory effects of the composite hydrogel scaffold. We found that the scaffold promoted cell proliferation and improved cell viability in vitro. While ensuring mechanical strength, this composite hydrogel scaffold regulated the local inflammatory microenvironment and continuously repaired tissue in the nucleus pulposus via the sequential release of drugs in vivo. When degenerative intervertebral discs in a rat model were injected with the scaffold, there was an increase in the proportion of M2 macrophages in the inflammatory environment and higher expression levels of type II collagen and aggrecan; this was accompanied by reduced levels of MMP13 expression, thus exhibiting long-term anti-inflammatory effects. Our research provides a new strategy for promoting intervertebral disc tissue regeneration and a range of other inflammatory diseases.

Multifunctional Bioactive Scaffolds from ARX-g-(Zn@rGO)-HAp for Bone Tissue Engineering: In Vitro Antibacterial, Antitumor, and Biocompatibility Evaluations

Advanced biomaterials are required with enhanced antibacterial and anticancer activities to obtain desirable biocompatibility during and after scaffold implantation in tissue engineering. Here, we report the development of a nanosystem by the hydrothermal method using different zinc (Zn) amounts and reduced graphene oxide (GO). Arabinoxylan, the nanosystem (Zn@rGO), and nanohydroxyapatite polymeric nanocomposites ARX-g-(Zn@rGO)/HAp were prepared by the free radical polymerization method, and porous bioactive scaffolds were fabricated via the freeze-drying technique. The structural, morphological, and elemental analyses of the bioactive scaffolds were conducted using Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray analysis. The wetting behavior was studied by a water contact meter and swelling in aqueous and phosphate-buffered saline solutions at 37 °C. The degradation was also studied in the phosphate-buffered saline solution at 37 °C. The increase in Zn content increased the pore size, and hydrophobic behavior shifted to hydrophilic (AGZ-1 = 131.40° at 0 s and 120.60° at 10 s to AGZ-1 = 81.30° at 0 s and 69.20° at 10 s) with the increase in contact time. Maximum swelling was observed in deionized water (AGZ-1 = 52.87%, AGZ-4 = 90.20%), followed by phosphate-buffered saline (PBS; AGZ-1 = 44.80%, AGZ-4 = 67.90%) and electrolyte (AGZ-1 = 32.40%, AGZ-4 = 63.47%), and biodegradation in PBS media increased (AGZ-1 = 36.80%, AGZ-4 = 55.92%). Antimicrobial activities against severe infection-causing pathogens and antitumor activity against U87 cell lines showed exceptional results. Cell viability and cell proliferation studies were conducted against preosteoblast cell lines, and increased cell viability and proliferation were observed from AGZ-1 to AGZ-4. Antimicrobial and anticancer activities were enhanced with the increase of Zn content in the Zn@rGO system. The bioactive scaffolds with different formulations could be potential biomaterials to treat and regenerate defected bone tissue.

Wettability, Corrosion Resistance, and Osteoblast Response to Reduced Graphene Oxide on CoCr Functionalized with Hyaluronic Acid

The durability of metal-metal prostheses depends on achieving a higher degree of lubrication. The beneficial effect of hyaluronic acid (HA) on the friction and wear of both natural and artificial joints has been reported. For this purpose, graphene oxide layers have been electrochemically reduced on CoCr surfaces (CoCrErGO) and subsequently functionalized with HA (CoCrErGOHA). These layers have been evaluated from the point of view of wettability and corrosion resistance in a physiological medium containing HA. The wettability was analyzed by contact angle measurements in phosphate buffer saline-hyaluronic acid (PBS-HA) solution. The corrosion behavior of functionalized CoCr surfaces was studied with electrochemical measurements. Biocompatibility, cytotoxicity, and expression of proteins related to wound healing and repair were studied in osteoblast-like MC3T3-E1 cell cultures. All of the reported results suggest that HA-functionalized CoCr surfaces, through ErGO layers in HA-containing media, exhibit higher hydrophilicity and better corrosion resistance. Related to this increase in wettability was the increase in the expressions of vimentin and ICAM-1, which favored the growth and adhesion of osteoblasts. Therefore, it is a promising material for consideration in trauma applications, with improved properties in terms of wettability for promoting the adhesion and growth of osteoblasts, which is desirable in implanted materials used for bone repair.

A bimetallic load-bearing bioceramics of TiO2 @ ZrO2 integrated polycaprolactone fibrous tissue construct exhibits anti bactericidal effect and induces osteogenesis in MC3T3-E1 cells

Bioactive mesoporous binary metal oxide nanoparticles allied with polymeric scaffolds can mimic natural extracellular matrix because of their self-mineralized functional matrix. Herein, we developed fibrous scaffolds of polycaprolactone (PCL) integrating well-dispersed TiO₂@ZrO₂ nanoparticles (NPs) via electrospinning for a tissue engineering approach. The scaffold with 0.1 wt% of bioceramic (TiO₂@ZrO₂) shows synergistic effects on physicochemical and bioactivity suited to stem cell attachment/proliferation. The bioceramics-based scaffold shows excellent antibacterial activity that can prevent implant-associated infections. In addition, the TiO₂@ZrO₂ in scaffold serves as a stem cell microenvironment to accelerate cell-to-cell interactions, including cell growth, morphology/orientation, differentiation, and regeneration. The NPs in PCL exert superior biocompatibility on MC3T3-E1 cells inducing osteogenic differentiation. The ALP activity and ARS staining confirm the upregulation of bone-related proteins and minerals suggesting the scaffolds exhibit osteoinductive abilities and contribute to bone cell regeneration. Based on this result, the bimetallic oxide could become a novel bone ceramic tailor TiO₂@ZrO₂ composite tissue-construct and keep potential nanomaterials-based scaffold for bone tissue engineering strategy.

Functionalized Nanocellulose Drives Neural Stem Cells toward Neuronal Differentiation

Transplantation of differentiated and fully functional neurons may be a better therapeutic option for the cure of neurodegenerative disorders and brain injuries than direct grafting of neural stem cells (NSCs) that are potentially tumorigenic. However, the differentiation of NSCs into a large population of neurons has been a challenge. Nanomaterials have been widely used as substrates to manipulate cell behavior due to their nano-size, excellent physicochemical properties, ease of synthesis, and versatility in surface functionalization. Nanomaterial-based scaffolds and synthetic polymers have been fabricated with topology resembling the micro-environment of the extracellular matrix. Nanocellulose materials are gaining attention because of their availability, biocompatibility, biodegradability and bioactivity, and affordable cost. We evaluated the role of nanocellulose with different linkage and surface features in promoting neuronal differentiation. Nanocellulose coupled with lysine molecules (CNC-Lys) provided positive charges that helped the cells to attach. Embryonic rat NSCs were differentiated on the CNC-Lys surface for up to three weeks. By the end of the three weeks of in vitro culture, 87% of the cells had attached to the CNC-Lys surface and more than half of the NSCs had differentiated into functional neurons, expressing endogenous glutamate, generating electrical activity and action potentials recorded by the multi-electrode array.

Chitosan/Poly Vinyl Alcohol/Graphene Oxide Based pH-Responsive Composite Hydrogel Films: Drug Release, Anti-Microbial and Cell Viability Studies

The composite hydrogels were produced using the solution casting method due to the non-toxic and biocompatible nature of chitosan (CS)/polyvinyl alcohol (PVA). The best composition was chosen and crosslinked with tetraethyl orthosilicate (TEOS), after which different amounts of graphene oxide (GO) were added to develop composite hydrogels. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), atomic force microscopy (AFM) and contact angle was used to analyze the hydrogels. The samples were also evaluated for swelling abilities in various mediums. The drug release profile was studied in phosphate-buffered saline (PBS) at a pH of 7.4. To predict the mechanism of drug release, the data were fitted into kinetic models. Finally, antibacterial activity and cell viability data were obtained. FTIR studies revealed the successful synthesis of CS/PVA hydrogels and GO/CS/PVA in hydrogel composite. SEM showed no phase separation of the polymers, whereas AFM showed a decrease in surface roughness with an increase in GO content. 100 µL of crosslinker was the critical concentration at which the sample displayed excellent swelling and preserved its structure. Both the crosslinked and composite hydrogel showed good swelling. The most acceptable mechanism of drug release is diffusion-controlled, and it obeys Fick's law of diffusion for drug released. The best fitting of the zero-order, Hixson-Crowell and Higuchi models supported our assumption. The GO/CS/PVA hydrogel composite showed better antibacterial and cell viability behaviors. They can be better biomaterials in biomedical applications.

De novo neo-hyaline-cartilage from bovine organoids in viscoelastic hydrogels

Regenerative therapies for articular cartilage are currently clinically available. However, they are associated with several drawbacks that require resolution. Optimizing chondrocyte expansion and their assembly, can reduce the time and costs of these therapies and more importantly increase their clinical success. In this study, cartilage organoids were quickly mass produced from bovine chondrocytes with a new suspension expansion protocol. This new approach led to massive cell proliferation, high viability and the self-assembly of organoids. These organoids were composed of collagen type II, type VI, glycosaminoglycans, with Sox9 positive cells, embedded in a pericellular and interterritorial matrix similarly to hyaline cartilage. With the goal of producing large scale tissues, we then encapsulated these organoids into alginate hydrogels with different viscoelastic properties. Elastic hydrogels constrained the growth and fusion of the organoids inhibiting the formation of a tissue. In contrast, viscoelastic hydrogels allowed the growth and fusion of the organoids into a homogenous tissue that was rich in collagen type II and glycosaminoglycans. The encapsulation of organoids to produce in vitro neocartilage also proved to be superior to the conventional method of encapsulating 2D expanded chondrocytes. This study describes a multimodal approach that involves chondrocyte expansion, organoid formation and their assembly into neohyaline-cartilage which proved to be superior to the current standard approaches used in cartilage tissue engineering. STATEMENT OF SIGNIFICANCE: In this manuscript, we describe a new and simple methodology to quickly mass produce self-assembling cartilage organoids. Due to their matrix content and structure similarities with native cartilage, these organoids on their own have the potential to revolutionize cartilage research and the manner in which we study signaling pathways, disease progression, tissue engineering, drug development, etc. Furthermore, these organoids and their fast mass production were combined with a key relatively ignored hydrogel characteristic, viscoelasticity, to demonstrate their fusion into a neo-tissue. This has the potential to open the door for large scale cartilage regeneration such as for entire joint surfaces.

Defining Spatial Relationships Between Spinal Cord Axons and Blood Vessels in Hydrogel Scaffolds

Positively charged oligo(poly(ethylene glycol) fumarate) (OPF+) hydrogel scaffolds, implanted into a complete transection spinal cord injury (SCI), facilitate a permissive regenerative environment and provide a platform for controlled observation of repair mechanisms. Axonal regeneration after SCI is critically dependent upon nutrients and oxygen from a newly formed blood supply. Our objective was to investigate fundamental characteristics of revascularization in association with the ingrowth of axons into hydrogel scaffolds, thereby defining spatial relationships between axons and the neovasculature. A novel combination of stereologic estimates and precision image analysis techniques quantitate neurovascular regeneration in rats. Multichannel hydrogel scaffolds containing Matrigel-only (MG), Schwann cells (SCs), or SCs with rapamycin-eluting poly(lactic co-glycolic acid) microspheres (RAPA) were implanted for 6 weeks following complete spinal cord transection. Image analysis of 72 scaffold channels identified a total of 2494 myelinated and 4173 unmyelinated axons at 10 μm circumferential intervals centered around 708 individual blood vessel profiles. Blood vessel number, density, volume, diameter, intervessel distances, total vessel surface and cross-sectional areas, and radial diffusion distances were compared. Axon number and density, blood vessel surface area, and vessel cross-sectional areas in the SC group exceeded that in the MG and RAPA groups. Individual axons were concentrated within a concentric radius of 200-250 μm from blood vessel walls, in Gaussian distributions, which identified a peak axonal number (Mean Peak Amplitude) corresponding to defined distances (Mean Peak Distance) from each vessel, the highest concentrations of axons were relatively excluded from a 25-30 μm zone immediately adjacent to the vessel, and from vessel distances >150 μm. Higher axonal densities correlated with smaller vessel cross-sectional areas. A statistical spatial algorithm was used to generate cumulative distribution F- and G-functions of axonal distribution in the reference channel space. Axons located around blood vessels were definitively organized as clusters and were not randomly distributed. A scoring system stratifies 5 direct measurements and 12 derivative parameters influencing regeneration outcomes. By providing methods to quantify the axonal-vessel relationships, these results may refine spinal cord tissue engineering strategies to optimize the regeneration of complete neurovascular bundles in their relevant spatial relationships after SCI. Impact statement Vascular disruption and impaired neovascularization contribute critically to the poor regenerative capacity of the spinal cord after injury. In this study, hydrogel scaffolds provide a detailed model system to investigate the regeneration of spinal cord axons as they directly associate with individual blood vessels, using novel methods to define their spatial relationships and the physiologic implications of that organization. These results refine future tissue engineering strategies for spinal cord repair to optimize the re-development of complete neurovascular bundles in their relevant spatial architectures.

Decreased Sulfate Content and Zeta Potential Distinguish Glycosaminoglycans of the Extracellular Matrix of Osteoarthritis Cartilage

We aimed to determine the characteristics that distinguish glycosaminoglycans (GAGs) from osteoarthritis (OA) and normal cartilage and from men and women. Cartilage samples from 30 patients subjected to total joint arthroplasty secondary to OA or fracture (control) were evaluated, and the GAG content (μg/mg dry cartilage) after proteolysis was determined by densitometry, using agarose-gel electrophoresis. Relative percentages of carbon (C), nitrogen (N), and sulfur (S) in GAGs were determined by elemental microanalysis, as well as the zeta potential. Seventeen samples (56.6%) were from patients >70 years old, with 20 (66.6%) from women, and most [20 (66.6%)] were from the hip. The GAG content was similar regardless of patients being >/≤ 70 years old with 96.5 ± 63.5 and 78.5 ± 38.5 μg/mg (P = 0.1917), respectively. GAG content was higher in women as compared to men, with 89.5 ± 34.3 and 51.8 ± 13.3 μg/mg, respectively (P = 0.0022), as well as in OA than fracture samples, with 98.4 ± 63.5 and 63.6 ± 19.6 μg/mg, respectively (P = 0.0355). The GAG extracted from the cartilage of patients >70 years old had increase in N, and there were no gender differences regarding GAG elemental analysis. GAG from OA had a highly significant (P = 0.0005) decrease in S% (1.79% ± 0.25%), as compared to fracture samples (2.3% ± 0.19%), with an associated and significant (P = 0.0001) reduction of the zeta potential in the OA group. This is the first report of a reduced S content in GAG from OA patients, which is associated with a reduced zeta potential.

Bifunctional hydrogel for potential vascularized bone tissue regeneration

Most of the synthetic polymer-based hydrogels lack the intrinsic properties needed for tissue engineering applications. Here, we describe a biomimetic approach to induce the mineralization and vascularization of poly(ethylene glycol) (PEG)-based hydrogel to template the osteogenic activities. The strategy involves the covalent functionalization of oligo[poly(ethylene glycol) fumarate] (OPF) with phosphate groups and subsequent treatment of phosphorylated-OPF (Pi-OPF) hydrogels with alkaline phosphatase enzyme (ALP) and calcium. Unlike previously reported studies for ALP induced mineralization, in this study, the base polymer itself was modified with the phosphate groups for uniform mineralization of hydrogels. In addition to improvement of mechanical properties, enhancement of MC3T3-E1 cell attachment and proliferation, and promotion of mesenchymal stem cells (MSC) differentiation were observed as the intrinsic benefits of such mineralization. Current bone tissue engineering (BTE) research endeavors are also extensively focused on vascular tissue regeneration due to its inherent advantages in bone regeneration. Taking this into account, we further functionalized the mineralized hydrogels with FG-4592, small hypoxia mimicking molecule. The functionalized hydrogels elicited upregulated in vitro angiogenic activities of human umbilical vein endothelial cells (HUVEC). In addition, when implanted subcutaneously in rats, enhanced early vascularization activities around the implantation site were observed as demonstrated by the immunohistochemistry results. This further leveraged the formation of calcified tissues at the implantation site at later time points evident through X-ray imaging. The overall results here show the perspectives of bifunctional OPF hydrogels for vascularized BTE.

Enhanced proliferation and angiogenic phenotype of endothelial cells via negatively-charged alginate and chondroitin sulfate microsphere hydrogels

Sodium alginate-based hydrogel was the one of the most used polymers for cell delivery. However, the adsorption of extracellular matrix and proteins was inhibited due to the formation of a hydrated surface layer of these hydrogels. In this study, a novel cell delivery system, negatively-charged alginate and chondroitin sulfate microsphere hydrogel (nCACSMH), was fabricated with excellent permeability and biocompatibility in the action of a high voltage direct-current electric field. Negative charge was introduced to the surface of nCACSMH to obtain the expanded network and enhanced permeability. Additionally, the increasing content of chondroitin sulfate in nCACSMH could give rise to the charge density and its asymmetric structure, thus the uneven, plicate and expanded surface of nCACSMH which was favorable to cell proliferation was developed. Moreover, chondroitin sulfate was released with the degradation of nCACSMH, which played a crucial role in maintaining the normal physiological functions of cells. Thus the proliferation of human umbilical vein endothelial cells (HUVECs) was further accelerated and the angiogenesis related genes expression in endothelial cells was continuously and dramatically up-regulated. After 4 d, the proliferation and viability of HUVECs were significantly improved, the cells were distributed evenly in nCACSMH. The novel nCACSMH has the potential to be used as cell delivery, three-dimensional (3D) cell cultures for cell therapy, 3D bioprinting, high-throughput screening for drugs, and disease model for regeneration and constructing of tissue engineering.

Development of Arabinoxylan-Reinforced Apple Pectin/Graphene Oxide/Nano-Hydroxyapatite Based Nanocomposite Scaffolds with Controlled Release of Drug for Bone Tissue Engineering: In-Vitro Evaluation of Biocompatibility and Cytotoxicity against MC3T3-E1

Fabrication of reinforced scaffolds to repair and regenerate defected bone is still a major challenge. Bone tissue engineering is an advanced medical strategy to restore or regenerate damaged bone. The excellent biocompatibility and osteogenesis behavior of porous scaffolds play a critical role in bone regeneration. In current studies, we synthesized polymeric nanocomposite material through free-radical polymerization to fabricate porous nanocomposite scaffolds by freeze drying. Functional group, surface morphology, porosity, pore size, and mechanical strength were examined through Fourier Transform Infrared Spectroscopy (FTIR), Single-Electron Microscopy (SEM), Brunauer-Emmet-Teller (BET), and Universal Testing Machine (UTM), respectively. These nanocomposites exhibit enhanced compressive strength (from 4.1 to 16.90 MPa), Young’s modulus (from 13.27 to 29.65 MPa) with well appropriate porosity and pore size (from 63.72 ± 1.9 to 45.75 ± 6.7 µm), and a foam-like morphology. The increasing amount of graphene oxide (GO) regulates the porosity and mechanical behavior of the nanocomposite scaffolds. The loading and sustained release of silver-sulfadiazine was observed to be 90.6% after 260 min. The in-vitro analysis was performed using mouse pre-osteoblast (MC3T3-E1) cell lines. The developed nanocomposite scaffolds exhibited excellent biocompatibility. Based on the results, we propose these novel nanocomposites can serve as potential future biomaterials to repair defected bone with the load-bearing application, and in bone tissue engineering.

Development and in vitro evaluation of κ-carrageenan based polymeric hybrid nanocomposite scaffolds for bone tissue engineering

The excellent biocompatible and osteogenesis characteristics of porous scaffolds play a vital role in bone regeneration. In this study, we have synthesized polymeric hybrid nanocomposites via free-radical polymerization from carrageenan/acrylic-acid/graphene/hydroxyapatite. Porous hybrid nanocomposite scaffolds were fabricated through a freeze-drying method to mimic the structural and chemical composition of natural bone. Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and water contact-angle studies were carried-out for functional groups, surface morphology and hydrophilicity of the materials, followed by biodegradation and swelling analysis. The cell viability, cell culture and proliferation were evaluated against mouse pre-osteoblast (MC3T3-E1) cell lines using neutral red dye assay. The cell adherence and proliferation studies were determined by SEM. Physical characterization including optimum porosity and pore size (49.75% and 0.41 × 103 μm2), mechanical properties (compression strength 8.87 MPa and elastic modulus 442.63 MPa), swelling (70.20% at 27 °C and 77.21% at 37 °C) and biodegradation (23.8%) were performed. The results indicated CG-g-AAc-3 with a high optical density and better cell viability. Hence, CG-g-AAc-3 was found to be more efficient for bone regeneration with potential applications in fractured bone regeneration.

Graphene Oxide Reinforcement Enhances the Piezoelectric and Mechanical Properties of Poly(3-hydroxybutyrate-co-3-hydroxy valerate)-Based Nanofibrous Scaffolds for Improved Proliferation of Chondrocytes and ECM Production

The discovery of piezoelectricity in natural cartilage has inspired the development of piezoelectric biomaterials for its repair and regeneration using tissue engineering approaches. In the present work, piezoelectric scaffolds composed of poly(3-hydroxybutyrate-co-3-hydroxy valerate) (PB) and graphene oxide (GO) have been successfully fabricated by the electrospinning technology. The fabricated scaffolds were examined for their morphological, physical, chemical, piezoelectric, and biological characterizations. The fiber diameter was found to be in the range of 600-800 nm appropriate for chondrogenic growth. Reinforcement of 1.5% GO enhanced the tensile strength of PB to 2.08 ± 0.33 MPa compared to PB alone (0.59 ± 0.12). Reinforcement of GO significantly enhances the piezoelectric coefficient (d₃₃), and for 0.5, 1, and 1.5% GO in PB, it was found to be 0.12 ± 0.015, 0.57 ± 0.19, and 0.94 ± 0.03 pC/N, respectively, and corresponding voltages of 11.84 ± 1.4, 54.69 ± 18.29, and 100.2 ± 3.2 mV, respectively, were generated. The biological activity of the smart piezo scaffolds was also evaluated on freshly isolated goat chondrocytes. The GO-reinforced scaffold showed higher cell proliferation and cell adhesion as confirmed by alamarBlue assay and field emission scanning electron microscopy imaging. The GO-reinforced scaffold has demonstrated significantly higher extracellular matrix production compared to PB as confirmed by histochemistry and real-time polymerase chain reaction. Hence, the GO-based piezoelectric PB electrospun scaffold can be a better alternative for cell-free and growth factor-free approach for cartilage tissue engineering.

Numerical Simulations as Means for Tailoring Electrically Conductive Hydrogels Towards Cartilage Tissue Engineering by Electrical Stimulation

Cartilage regeneration is a clinical challenge. In recent years, hydrogels have emerged as implantable scaffolds in cartilage tissue engineering. Similarly, electrical stimulation has been employed to improve matrix synthesis of cartilage cells, and thus to foster engineering and regeneration of cartilage tissue. The combination of hydrogels and electrical stimulation may pave the way for new clinical treatment of cartilage lesions. To find the optimal electric properties of hydrogels, theoretical considerations and corresponding numerical simulations are needed to identify well-suited initial parameters for experimental studies. We present the theoretical analysis of a hydrogel in a frequently used electrical stimulation device for cartilage regeneration and tissue engineering. By means of equivalent circuits, finite element analysis, and uncertainty quantification, we elucidate the influence of the geometric and dielectric properties of cell-seeded hydrogels on the capacitive-coupling electrical field stimulation. Moreover, we discuss the possibility of cellular organisation inside the hydrogel due to forces generated by the external electric field. The introduced methodology is easily reusable by other researchers and allows to directly develop novel electrical stimulation study designs. Thus, this study paves the way for the design of future experimental studies using electrically conductive hydrogels and electrical stimulation for tissue engineering.

Interactions at scaffold interfaces: Effect of surface chemistry, structural attributes and bioaffinity

Effective regenerative medicine relies on understanding the interplay between biomaterial implants and the adjoining cells. Scaffolds contribute by presenting sites for cellular adhesion, growth, proliferation, migration, and differentiation which lead to regeneration of tissues over desired periods of time. The fabrication and recruitment of scaffolds often fail to consider the interactions that occur at the interfaces, thereby risking rejection. This lack of knowledge on interfacial microenvironments and related exchanges often causes reduced cellular interactions, poor cell survival and intervention failure. Successful regenerative therapy requires scaffolds with bespoke biocompatibility, optimum pore structure, and cues for cell attachments. These factors determine the development of cellular affinity in scaffolds. For biomedical applications, a detailed understanding of scaffolds and their interfaces is required for better tuning of biomaterials to suit the microenvironments. In this review, we discuss the role of biointerfaces with a focus on surface chemistry, pore structure, scaffold hydro-affinity and their biointeractions. An understanding of the effect of scaffold interfacial properties is crucial for enhancing the progress of tissue engineering towards clinical applications.

Effect of Biomaterial Electrical Charge on Bone Morphogenetic Protein-2-Induced In Vivo Bone Formation

IMPACT STATEMENT

Biomaterials can play a dual role in bone regeneration: they enable local sustained delivery of growth factors, such as bone morphogenetic protein-2 (BMP-2), while they provide structural support as scaffold. By better imitating the properties of native bone tissue, scaffolds may be both osteoconductive and osteoinductive. The latter can be achieved by modifying the electrical charge of the surface. The present work uses tunable oligo[(polyethylene glycol) fumarate] hydrogel and demonstrates that negative charge enhances BMP-2-induced bone formation compared with neutral or positive charge. Altogether, this indicates that tissue-specific surface charge modifications of biomaterials hold great promise in the field of tissue regeneration.

Mammalian Cell Behavior on Hydrophobic Substrates: Influence of Surface Properties

The influence of different surface properties holding to a modification of the substrate towards hydrophobic or superhydrophobic behavior was reviewed in this paper. Cell adhesion, their communication, and proliferation can be strongly manipulated, acting on interfacial relationship involving stiffness, surface charge, surface chemistry, roughness, or wettability. All these features can play mutual roles in determining the final properties of biomedical applications ranging from fabrics to cell biology devices. The focus of this work is the mammalian cell viability in contact with moderate to highly water repellent coatings or materials and also in combination with hydrophilic areas for more specific application. Few case studies illustrate a range of examples in which these surface properties and design can be fruitfully matched to the specific aim.

In Vitro and In Vivo Correlation of Bone Morphogenetic Protein-2 Release Profiles from Complex Delivery Vehicles

Local sustained delivery of bioactive molecules from biomaterials is a promising strategy to enhance bone regeneration. To optimize delivery vehicles for bone formation, the design characteristics are tailored with consequential effect on bone morphogenetic protein-2 (BMP-2) release and bone regeneration. Complying with the 3R principles (Replacement, Reduction, and Refinement), the growth factor release is often investigated in vitro using several buffers to mimic the in vivo physiological environment. However, this remains an unmet need. Therefore, this study investigates the in vitro-in vivo correlation (IVIVC) of BMP-2 release from complex delivery vehicles in several commonly used in vitro buffers: cell culture model, phosphate buffered saline, and a strong desorption buffer. The results from this study showed that the release environment affected the BMP-2 release profiles, creating distinct relationships between release versus time and differences in extent of release. According to the guidance set by the U.S. Food and Drug Administration (FDA), IVIVC resulted in level A internal predictability for individual composites. Since the IVIVC was influenced by the BMP-2 loading method and composite surface chemistry, the external predictive value of the IVIVCs was limited. These results show that the IVIVCs can be used for predicting the release of an individual composite. However, the models cannot be used for predicting in vivo release for different composite formulations since they lack external predictability. Potential confounding effects of drug type, delivery vehicle formulations, and application site should be added to the equation to develop one single IVIVC applicable for complex delivery vehicles. Altogether, these results imply that more sophisticated in vitro systems should be used in bone regeneration to accurately discriminate and predict in vivo BMP-2 release from different complex delivery vehicles.

Fabrication of sulphonated poly(ethylene glycol)-diacrylate hydrogel as a bone grafting scaffold

To improve the biological performance of poly(ethylene glycol)-diacrylate (PEGDA) hydrogel as an injectable bone grafting scaffold, sodium methallyl sulphonate (SMAS) was incorporated into PEGDA hydrogel. The physiochemical properties of the resultant polymers were assessed via Fourier transform infrared spectroscopy (FTIR), swelling ratio, zeta potential, surface morphology, and protein adsorption analysis. MC3T3-E1 cells were seeded on the hydrogel to evaluate the effect of the sulphonated modification on their attachment, proliferation, and differentiation. The results of FTIR and zeta potential evaluations revealed that SMAS was successfully incorporated into PEGDA. With increasing concentrations of SMAS, the swelling ratio of the hydrogels increased in deionized water but stayed constant in phosphate buffered saline. The protein adsorption also increased with increasing concentration of SMAS. Moreover, the sulphonated modification of PEGDA hydrogel not only enhanced the attachment and proliferation of osteoblast-like MC3T3-E1 cells but also up-regulated alkaline phosphatase activity as well as gene expression of osteogenic markers and related growth factors, including collagen type I, osteocalcin, runt related transcription factor 2, bone morphogenetic protein 2, and transforming growth factor beta 1. These findings indicate that the sulphonated modification could significantly improve the biological performance of PEGDA hydrogel. Thus, the sulphonated PEGDA is a promising scaffold candidate for bone grafting.

Phosphate Functional Groups Improve Oligo[(Polyethylene Glycol) Fumarate] Osteoconduction and BMP-2 Osteoinductive Efficacy

Off-the-shelf availability in large quantities, drug delivery functionality, and modifiable chemistry and mechanical properties make synthetic polymers highly suitable candidates for bone grafting. However, most synthetic polymers lack the ability to support cell attachment, proliferation, migration, and differentiation, and ultimately tissue formation. Incorporating anionic peptides into the polymer that mimics acidic proteins, which contribute to biomineralization and cellular attachment, could enhance bone formation. Therefore, this study investigates the effect of a phosphate functional group on osteoconductivity and BMP-2-induced bone formation in an injectable and biodegradable oligo[(polyethylene glycol) fumarate] (OPF) hydrogel. Three types of OPF hydrogels were fabricated using 0%, 20%, or 40% Bis(2-(methacryloyloxy)ethyl) phosphate creating unmodified OPF-noBP and phosphate-modified OPF-BP20 and OPF-BP40, respectively. To account for the osteoinductive effect of various BMP-2 release profiles, two different release profiles (i.e., different ratios of burst and sustained release) were obtained by varying the BMP-2 loading method. To investigate the osteoconductive effect of phosphate modification, unloaded OPF composites were assessed for bone formation in a bone defect model after 3, 6, and 9 weeks. To determine the effect of the hydrogel phosphate modification on BMP-2-induced bone formation, BMP-2 loaded OPF composites with differential BMP-2 release were analyzed after 9 weeks of subcutaneous implantation in rats. The phosphate-modified OPF hydrogels (OPF-BP20 and OPF-BP40) generated significantly more bone in an orthotopic defect compared to the unmodified hydrogel (OPF-noBP). Furthermore, the phosphate functionalized surface-enhanced BMP-2-induced ectopic bone formation regardless of the BMP-2 release profile. In conclusion, this study clearly shows that phosphate functional groups improve the osteoconductive properties of OPF and enhanced BMP-2-induced bone formation. Therefore, functionalizing hydrogels with phosphate groups by crosslinking monomers into the hydrogel matrix could provide a valuable method for improving polymer characteristics and holds great promise for bone tissue engineering.

Modulating cell response on cellulose surfaces; tunable attachment and scaffold mechanics

Combining surface chemical modification of cellulose to introduce positively charged trimethylammonium groups by reaction with glycidyltrimethylammonium chloride (GTMAC) allowed for direct attachment of mammalian MG-63 cells, without addition of protein modifiers, or ligands. Very small increases in the surface charge resulted in significant increases in cell attachment: at a degree of substitution (DS) of only 1.4%, MG-63 cell attachment was > 90% compared to tissue culture plastic, whereas minimal attachment occurred on unmodified cellulose. Cell attachment plateaued above DS of ca. 1.85% reflecting a similar trend in surface charge, as determined from ζ-potential measurements and capacitance coupling (electric force microscopy). Cellulose film stiffness was modulated by cross linking with glyoxal (0.3-2.6% degree of crosslinking) to produce a range of materials with surface shear moduli from 76 to 448 kPa (measured using atomic force microscopy). Cell morphology on these materials could be regulated by tuning the stiffness of the scaffolds. Thus, we report tailored functionalised biomaterials based on cationic cellulose that can be tuned through surface reaction and glyoxal crosslinkin+g, to influence the attachment and morphology of cells. These scaffolds are the first steps towards materials designed to support cells and to regulate cell morphology on implanted biomaterials using only scaffold and cells, i.e. without added adhesion promoters.

Charged Triazole Cross-Linkers for Hyaluronan-Based Hybrid Hydrogels

Polyelectrolyte hydrogels play an important role in tissue engineering and can be produced from natural polymers, such as the glycosaminoglycan hyaluronan. In order to control charge density and mechanical properties of hyaluronan-based hydrogels, we developed cross-linkers with a neutral or positively charged triazole core with different lengths of spacer arms and two terminal maleimide groups. These cross-linkers react with thiolated hyaluronan in a fast, stoichiometric thio-Michael addition. Introducing a positive charge on the core of the cross-linker enabled us to compare hydrogels with the same interconnectivity, but a different charge density. Positively charged cross-linkers form stiffer hydrogels relatively independent of the size of the cross-linker, whereas neutral cross-linkers only form stable hydrogels at small spacer lengths. These novel cross-linkers provide a platform to tune the hydrogel network charge and thus the mechanical properties of the network. In addition, they might offer a wide range of applications especially in bioprinting for precise design of hydrogels.

Investigation of human cell response to covalently attached RADA16-I peptide on silicon surfaces

We described a modification of the ionic (RADARADARADARADA)(1) peptide or RADA16-I with 4-azidophenyl isothiocyanate via a specific and gentle reaction. The azidated peptide was covalently immobilized on an alkyne-terminated monolayer on Si(111) via the Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition reaction. Detailed characterization using Impedance spectroscopy (IS), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy demonstrated high coverage of the RADA 16-I peptide on silicon surfaces. Scanning electron microscopy (SEM) and methyl tetrazole sulfate (MTS) assay were used to characterize the morphology and proliferation ability of human fibroblast cells on surfaces. Cell adhesion assay was performed to examine cell-substrate interactions. Significant differences in fibroblast cell morphology, adhesion, and viability were observed on the RADA16-I peptide modified surfaces compared to the control surfaces. These results may suggest a potential application of RADA16-I peptide modified surfaces in biomedical applications.

Positively Charged Oligo[Poly(Ethylene Glycol) Fumarate] Scaffold Implantation Results in a Permissive Lesion Environment after Spinal Cord Injury in Rat

Positively charged oligo[poly(ethylene glycol) fumarate] (OPF+) scaffolds loaded with Schwann cells bridge spinal cord injury (SCI) lesions and support axonal regeneration in rat. The regeneration achieved is not sufficient for inducing functional recovery. Attempts to increase regeneration would benefit from understanding the effects of the scaffold and transplanted cells on lesion environment. We conducted morphometric and stereological analysis of lesions in rats implanted with OPF+ scaffolds with or without loaded Schwann cells 1, 2, 3, 4, and 8 weeks after thoracic spinal cord transection. No differences were found in collagen scarring, cyst formation, astrocyte reactivity, myelin debris, or chondroitin sulfate proteoglycan (CSPG) accumulation. However, when scaffold-implanted animals were compared with animals with transection injuries only, these barriers to regeneration were significantly reduced, accompanied by increased activated macrophages/microglia. This distinctive and regeneration permissive tissue reaction to scaffold implantation was independent of Schwann cell transplantation. Although the tissue reaction was beneficial in the short term, we observed a chronic fibrotic host response, resulting in scaffolds surrounded by collagen at 8 weeks. This study demonstrates that an appropriate biomaterial scaffold improves the environment for regeneration. Future targeting of the host fibrotic response may allow increased axonal regeneration and functional recovery.

Induction of cell self-organization on weakly positively charged surfaces prepared by the deposition of polyion complex nanoparticles of thermoresponsive, zwitterionic copolymers

We have developed inducible cell self-organization through weakly positively charged culture surfaces. In this study, a thermoresponsive and zwitterionic copolymer comprised of N,N-dimethylaminoethyl methacrylate (DMAEMA) and methacrylic acid (MA) (PDMAEMA-co-PMA; Mn: ∼9.7 × 10⁴ g/mol; PDMAEMA/PMA ratio: 10) was designed for inducing cell self-organization. The copolymer formed single polymer-derived polyion complex (sPIC) nanoparticles following dissolution in an aqueous solution. The sPIC nanoparticles had a positive charge (ca. 25 mV). Self-organization occurred in adipose-derived vascular stromal cell monolayers cultivated on sPIC-deposited surfaces. There were dramatic morphological changes of these cells with the formation of capillary-like networks and single-cell aggregates with little cytotoxicity. This was a significant improvement compared with cells grown on previously developed surfaces deposited with PIC, a mixture of PDMAEMA and plasmid DNA. Thus, sPICs of PDMAEMA-co-PMA may allow for the accurate evaluation of a variety of cell behaviors with less cytotoxicity, and may facilitate additional potential medical applications such as cell-based therapy and drug discovery. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1009-1015, 2017.

Surface charge regulation of osteogenic differentiation of mesenchymal stem cell on polarized ferroelectric crystal substrate

Polarized ferroelectric crystal lithium niobate wafers with different cuts are selected to offer differently charged surfaces. By induction of the mesenchymal stem cells differentiation into osteoblasts on different charged surfaces, the specific osteogenic-associated markers are assessed and the results illustrate that the positively charged wafer surface enhances rBMMSCs osteogenic differentiation.

Hybrid amphiphilic bimodal hydrogels having mechanical and biological recognition characteristics for cardiac tissue engineering

Tissue engineering strategies rely on the favourable microniche scaffolds for 3D cell growth.

Interaction of human osteoblast-like Saos-2 and MG-63 cells with thermally oxidized surfaces of a titanium-niobium alloy

An investigation was made of the adhesion, growth and differentiation of osteoblast-like MG-63 and Saos-2 cells on titanium (Ti) and niobium (Nb) supports and on TiNb alloy with surfaces oxidized at 165°C under hydrothermal conditions and at 600°C in a stream of air. The oxidation mode and the chemical composition of the samples tuned the morphology, topography and distribution of the charge on their surfaces, which enabled us to evaluate the importance of these material characteristics in the interaction of the cells with the sample surface. Numbers of adhered MG-63 and Saos-2 cells correlated with the number of positively-charged (related with the Nb₂O₅ phase) and negatively-charged sites (related with the TiO₂ phase) on the alloy surface. Proliferation of these cells is correlated with the presence of positively-charged (i.e. basic) sites of the Nb₂O₅ alloy phase, while cell differentiation is correlated with negatively-charged (acidic) sites of the TiO₂ alloy phase. The number of charged sites and adhered cells was substantially higher on the alloy sample oxidized at 600°C than on the hydrothermally treated sample at 165°C. The expression values of osteoblast differentiation markers (collagen type I and osteocalcin) were higher for cells grown on the Ti samples than for those grown on the TiNb samples. This was more particularly apparent in the samples treated at 165°C. No considerable immune activation of murine macrophage-like RAW 264.7 cells on the tested samples was found. The secretion of TNF-α by these cells into the cell culture media was much lower than for either cells grown in the presence of bacterial lipopolysaccharide, or untreated control samples. Thus, oxidized Ti and TiNb are both promising materials for bone implantation; TiNb for applications where bone cell proliferation is desirable, and Ti for induction of osteogenic cell differentiation.

Synthesis and characterization of well-defined PAA–PEG multi-responsive hydrogels by ATRP and click chemistry

Well-defined multi-responsive PAA–PEG hydrogels exhibit a unique swelling property at different pH and Ca²⁺ secondary crosslinking, and can potentially be used as stimuli responsive biomaterials.

The effect of electrically charged polyion complex nanoparticle-coated surfaces on adipose-derived stromal progenitor cell behaviour

Surface characteristics of biomaterials such as wettability, rigidity, roughness, and electrical charge affect the fate of transplanted cells such as progenitor cells or stem cells for use in regenerative medicine. Of these, the effects of surface electrical charges on cellular behaviour such as adhesion, proliferation, and differentiation are not well understood. We prepared precisely charged culture surfaces ranging from -28 mV to +21 mV, simply by surface deposition of polyion complex nanoparticles prepared by mixing a positively charged thermoresponsive homopolymer, poly(N,N-dimethylaminoethyl methacrylate), with negatively charged plasmid DNA at various charge ratios. Drastic morphological changes of adipose-derived vascular progenitor cells were generated on the positively charged surface of organized forms at +19 mV. Capillary-like networks or single aggregates of these cells were selectively created depending on cell seeding density. Our findings offer new insights that may aid develop stem cell-processing techniques for use in regenerative medicine.

Bone morphogenetic protein-2 release from composite hydrogels of oligo(poly(ethylene glycol) fumarate) and gelatin

PURPOSE

Hydrogel composites of oligo(poly(ethylene glycol) fumarate) (OPF) and gelatin microparticles (GMs) were investigated as carriers of bone morphogenetic protein-2 (BMP-2) for bone tissue engineering applications.

METHODS

Hydrogel composites with different physical characteristics were prepared by changing the amount and type (acidic vs. basic) of gelatin incorporated in the OPF bulk phase. Composites with differing physical properties (degradation, swelling, and mechanical properties) and differing BMP-2 loading phase were investigated to determine the effect of these factors on BMP-2 release profiles over 28 days.

RESULTS

Overall, higher gelatin amount increased the degradation and swelling of composites, and acidic GMs further increased the degradation and swelling and reduced the compressive modulus of the composites. The most significant factor affecting the release of BMP-2 from composites was the loading phase of the growth factor: GM loading reduced the burst release, increased BMP-2 release during the later phases of the experiment, and increased the cumulative release in faster degrading samples.

CONCLUSIONS

The results indicate that the physical properties and the BMP-2 release kinetics of hydrogel composites can be controlled by adjusting multiple parameters at the time of the hydrogel composite fabrication.

Enhancing biocompatibility of D-oligopeptide hydrogels by negative charges

Oligopeptide hydrogels are emerging as useful matrices for cell culture with commercial products on the market, but L-oligopeptides are labile to proteases. An obvious solution is to create D-oligopeptide hydrogels, which lack enzymatic recognition. However, D-oligopeptide matrices do not support cell growth as well as L-oligopeptide matrices. In addition to chiral interactions, many cellular activities are strongly governed by charge-charge interactions. In this work, the effects of chirality and charge on human mesenchymal stem cell (hMSC) behavior were studied using hydrogels assembled from oppositely charged oligopeptides. It was found that negative charges significantly improved hMSC viability and proliferation in D-oligopeptide gels but had little effect on their interactions with L-oligopeptide gels. This result points to the possibility of using charge and other factors to engineer biomaterials whose chirality is distinct from that of natural biomaterials, but whose performance is close to that of natural biomaterials.

Building biocompatible hydrogels for tissue engineering of the brain and spinal cord

Tissue engineering strategies employing biomaterials have made great progress in the last few decades. However, the tissues of the brain and spinal cord pose unique challenges due to a separate immune system and their nature as soft tissue. Because of this, neural tissue engineering for the brain and spinal cord may require re-establishing biocompatibility and functionality of biomaterials that have previously been successful for tissue engineering in the body. The goal of this review is to briefly describe the distinctive properties of the central nervous system, specifically the neuroimmune response, and to describe the factors which contribute to building polymer hydrogels compatible with this tissue. These factors include polymer chemistry, polymerization and degradation, and the physical and mechanical properties of the hydrogel. By understanding the necessities in making hydrogels biocompatible with tissue of the brain and spinal cord, tissue engineers can then functionalize these materials for repairing and replacing tissue in the central nervous system.

Iterative design of peptide-based hydrogels and the effect of network electrostatics on primary chondrocyte behavior

Iterative peptide design was used to generate two peptide-based hydrogels to study the effect of network electrostatics on primary chondrocyte behavior. MAX8 and HLT2 peptides have formal charge states of +7 and +5 per monomer, respectively. These peptides undergo triggered folding and self-assembly to afford hydrogel networks having similar rheological behavior and local network morphologies, yet different electrostatic character. Each gel can be used to directly encapsulate and syringe-deliver cells. The influence of network electrostatics on cell viability after encapsulation and delivery, extracellular matrix deposition, gene expression, and the bulk mechanical properties of the gel-cell constructs as a function of culture time was assessed. The less electropositive HLT2 gel provides a microenvironment more conducive to chondrocyte encapsulation, delivery, and phenotype maintenance. Cell viability was higher for this gel and although a moderate number of cells dedifferentiated to a fibroblast-like phenotype, many retained their chondrocytic behavior. As a result, gel-cell constructs prepared with HLT2, cultured under static in vitro conditions, contained more GAG and type II collagen resulting in mechanically superior constructs. Chondrocytes delivered in the more electropositive MAX8 gel experienced a greater degree of cell death during encapsulation and delivery and the remaining viable cells were less prone to maintain their phenotype. As a result, MAX8 gel-cell constructs had fewer cells, of which a limited number were capable of laying down cartilage-specific ECM.

Charged nanomatrices as efficient platforms for modulating cell adhesion and shape

In this article, we describe the design and manipulation of charged nanomatrices and their application as efficient platforms for modulating cell behaviors. Using electrospraying technology and well designed biomaterials, poly(ɛ-caprolactone; PCL) and polyethylenimine, the negatively charged PCL nanomatrix (nPCL nanomatrix) and the positively charged PCL nanomatrix (pPCL nanomatrix) were fabricated. It was demonstrated that cell adhesion, affinity, and shape were sensitively modulated in negatively and positively charged nanomatrices. Our results showed that the pPCL nanomatrix promoted adhesion of NIH 3T3 fibroblast cells as compared to the nPCL nanomatrix. When fluid shear stress was applied, cell affinity on the pPCL nanomatrix increased even more. NIH 3T3 fibroblast cells adopted a relatively spherical shape on the pPCL nanomatrix while adopting an aligned, narrow shape on the nPCL nanomatrix. It was also found that charged nanomatrices influenced the cross-sectional cell shape. The cross-sectional cell shape on the pPCL nanomatrix was extremely flattened, whereas the cross-sectional cell shape was relatively round on the nPCL nanomatrix and some of the adhered cells floated. We also showed that the surfaces of the nPCL and pPCL nanomatrices adsorbed the different serum proteins. These results collectively demonstrated a combination of environmental factors including nanoscale structure, electrostatic forces, and absorption of biomolecules on charged substrates affected cell response in terms of cellular adhesion and shape.

Incorporation of phosphate group modulates bone cell attachment and differentiation on oligo(polyethylene glycol) fumarate hydrogel

In this work, we have investigated the development of a synthetic hydrogel that contains a negatively charged phosphate group for use as a substrate for bone cell attachment and differentiation in culture. The photoreactive, phosphate-containing molecule, bis(2-(methacryloyloxy)ethyl)phosphate (BP), was incorporated into oligo(polyethylene glycol) fumarate hydrogel and the mechanical, rheological and thermal properties of the resulting hydrogels were characterized. Our results showed changes in hydrogel compression and storage moduli with incorporation of BP. The modification also resulted in decreased crystallinity as recorded by differential scanning calorimetry. Our data revealed that incorporation of BP improved attachment and differentiation of human fetal osteoblast (hFOB) cells in a dose-dependent manner. A change in surface chemistry and mineralization of the phosphate-containing surfaces verified by scanning electron microscopy and energy dispersive X-ray analysis was found to be important for hFOB cell attachment and differentiation. We also demonstrated that phosphate-containing hydrogels support attachment and differentiation of primary bone marrow stromal cells. These findings suggest that BP-modified hydrogels are capable of sustaining attachment and differentiation of both bone marrow stromal cells and osteoblasts that are critical for bone regeneration.