Heterogeneous pHPMA hydrogel promotes neuronal differentiation of bone marrow derived stromal cellsin vitroandin vivo

Synthetic hydrogels composed of polymer pore frames are commonly used in medicine, from pharmacologically targeted drug delivery to the creation of bioengineering constructions used in implantation surgery. Among various possible materials, the most common are poly-[N(2-hydroxypropyl)methacrylamide] (pHPMA) derivatives. One of the pHPMA derivatives is biocompatible hydrogel, NeuroGel. Upon contact with nervous tissue, the NeuroGel's structure can support the chemical and physiological conditions of the tissue necessary for the growth of native cells. Owing to the different pore diameters in the hydrogel, not only macromolecules, but also cells can migrate. This study evaluated the differentiation of bone marrow stromal cells (BMSCs) into neurons, as well as the effectiveness of using this biofabricated system in spinal cord injuryin vivo. The hydrogel was populated with BMSCs by injection or rehydration. After cultivation, these fragments (hydrogel + BMSCs) were implanted into the injured rat spinal cord. Fragments were immunostained before implantation and seven months after implantation. During cultivation with the hydrogel, both variants (injection/rehydration) of the BMSCs culture retained their viability and demonstrated a significant number of Ki-67-positive cells, indicating the preservation of their proliferative activity. In hydrogel fragments, BMSCs also maintained their viability during the period of cocultivation and were Ki-67-positive, but in significantly fewer numbers than in the cell culture. In addition, in fragments of hydrogel with grafted BMSCs, both by the injection or rehydration versions, we observed a significant number up to 57%-63.5% of NeuN-positive cells. These results suggest that the heterogeneous pHPMA hydrogel promotes neuronal differentiation of bone marrow-derived stromal cells. Furthermore, these data demonstrate the possible use of NeuroGel implants with grafted BMSCs for implantation into damaged areas of the spinal cord, with subsequent nerve fiber germination, nerve cell regeneration, and damaged segment restoration.

Poly(HEMA) hydrogels with controlled pore architecture for tissue regeneration applications

The technique for fabrication of soft porous hydrogels, in which both the size and the orientation of inner pores can be controlled, was developed. Three-dimensional hydrophilic gels based on poly[2-hydroxyethyl methacrylate] are designed as scaffolds for regeneration of soft tissues, e.g., nerve tissue. Anisotropic macropores of the size ranging from 10 to 50 microm were formed (1) by using a porogen-leaching method with a solid organic porogen, (2) by phase-separation during gelation in solvent-nonsolvent mixture, or (3) by combination of solid porogen elimination and phase-separation. As a porogen, poly(L-lactide) fibers were applied and consequently washed away under mild conditions to obtain desired spatial orientation of pores. Highly water-swollen polymer gels were characterized with high pressure (low vacuum) scanning electron microscopy (AquaSEM). The morphology of voids remaining after removing the solid PLLA porogen (the macropores) was clearly shown.

Macroporous Hydrogels Based on 2-Hydroxyethyl Methacrylate. Part 1. Copolymers of 2-Hydroxyethyl Methacrylate with Methacrylic Acid

A series of macroporous crosslinked copolymers of 2-hydroxyethyl methacrylate (HEMA) with methacrylic acid (MA) was prepared in the presence of fractionated particles of sodium chloride. The hydrogels were characterized by the number of pores in unit volume, the pore size, the water content in pores and diffusion parameters. The structure of the hydrogels was followed by confocal and scanning electron microscopy.

Neural tissue formation within porous hydrogels implanted in brain and spinal cord lesions: ultrastructural, immunohistochemical, and diffusion studies

A biocompatible heterogeneous hydrogel of poly [N-(2-hydroxypropyl) methacrylamide] (PHPMA), was evaluated for its ability to promote tissue repair and enhance axonal regrowth across lesion cavities in the brain and spinal cord in adult and juvenile (P17 P21) rats. Incorporation of PHPMA hydrogels into surrounding host tissue was examined at the ultrastructural level and using immunohistochemical techniques. In addition, and in parallel to these studies, diffusion parameters (volume fraction and tortuosity of the gel network) of the PHPMA hydrogels were evaluated pre- to postimplantation using an in vivo real-time iontophoretic method. The polymer hydrogels were able to bridge tissue defects created in the brain or spinal cord, and supported cellular ingrowth, angiogenesis, and axonogenesis within the structure of the polymer network. As a result, a reparative tissue grew within the porous structure of the gel, composed of glial cells, blood vessels, axons and dendrites, and extracellular biological matrices, such as laminin and/or collagen. Consistent with matrix deposition and tissue formation within the porous structure of the PHPMA hydrogels, there were measurable changes in the diffusion characteristics of the polymers. Extracellular space volume decreased and tortuosity increased within implanted hydrogels, attaining values similar to that seen in developing neural tissue. PHPMA polymer hydrogel matrices thus show neuroinductive and neuroconductive properties. They have the potential to repair tissue defects in the central nervous system by replacing lost tissue and by promoting the formation of a histotypic tissue matrix that facilitates and supports regenerative axonal growth. () ()

A laminin and nerve growth factor-laden three-dimensional scaffold for enhanced neurite extension

Agarose hydrogel scaffolds were engineered to stimulate and guide neuronal process extension in three dimensions in vitro. The extracellular matrix (ECM) protein laminin (LN) was covalently coupled to agarose hydrogel using the bifunctional cross-linking reagent 1,19- carbonyldiimidazole (CDI). Compared to unmodified agarose gels, LN-modified agarose gels significantly enhanced neurite extension from three-dimensionally (3D) cultured embryonic day 9 (E9) chick dorsal root ganglia (DRGs), and PC 12 cells. After incubation of DRGs or PC 12 cells with YIGSR peptide or integrin beta1 antibody respectively, the neurite outgrowth promoting effects in LN-modified agarose gels were significantly decreased or abolished. These results indicate that DRG/PC 12 cell neurite outgrowth promoting effect of LN-modified agarose gels involves receptors for YIGSR/integrin beta1 subunits respectively. 1,2-bis(10, 12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DC(8,9)PC)-based lipid microcylinders were loaded with nerve growth factor (NGF), and embedded into agarose hydrogels. The resulting trophic factor gradients stimulated directional neurite extension from DRGs in agarose hydrogels. A PC 12 cell-based bioassay demonstrated that NGF-loaded lipid microcylinders can release physiologically relevant amounts of NGF for at least 7 days in vitro. Agarose hydrogel scaffolds may find application as biosynthetic 3D bridges that promote regeneration across severed nerve gaps.

Heterogeneous PHPMA hydrogels for tissue repair and axonal regeneration in the injured spinal cord

A biocompatible heterogeneous hydrogel of poly[N-(2-hydroxypropyl) methacrylamide] (PHPMA) showing an open porous structure, viscoelastic properties similar to the neural tissue and a large surface area available for cell interaction, was evaluated for its ability to promote tissue repair and axonal regeneration in the transected rat spinal cord. After implantation, the polymer hydrogel could correctly bridge the tissue defect, from a permissive interface with the host tissue to favour cell ingrowth, angiogenesis and axonal growth occurred within the microstructure of the network. Within 3 months the polymer implant was invaded by host derived tissue, glial cells, blood vessels and axons penetrated the hydrogel implant. Such polymer hydrogel matrices which show neuroinductive and neuroconductive properties have the potential to repair tissue defects in the central nervous system by promoting the formation of a tissue matrix and axonal growth by replacing the lost of tissue.

Hydrogels containing peptide or aminosugar sequences implanted into the rat brain: influence on cellular migration and axonal growth

Biocompatible polymer matrices for implantation into lesion sites in the brain were synthesized by incorporating peptide or aminosugar sequences into N-(2-hydroxypropyl)methacrylamide (HPMA) hydrogels. RGD peptide sequences were chemically linked to the hydrogel backbone via a glycylglycine spacer; aminosugars were glucosamine (NHGlc) or N-acetylglucosamine residues. Unmodified or sequence containing HPMA hydrogels were implanted into the lesioned optic tract or cerebral cortex of juvenile (17- to 19-day-old) or adult rat brains, respectively. After 10-12 months host animals were perfused and the brains were processed for immunohistochemistry using antibodies to neurofilaments (RT97), laminin, glial fibrillary acidic protein (GFAP), carbonic anhydrase II (CAII), S100 protein, macrophages (ED1), and myelin basic protein (MBP). Unmodified (control) HPMA hydrogels contained no cellular infiltration or axonal growth. Peptide (RGD)- and aminosugar-modified hydrogels showed increased adhesion properties with host neural tissue, were vascularized, and were infiltrated by host nonneuronal cells. Astrocytes (GFAP+) and macrophages (ED1(+)) were the major cell types seen within modified HPMA hydrogels, the largest numbers being found in RGD-containing polymers. CAII+ oligodendroglia were not seen within any of the hydrogel matrices. RT97(+)/MBP- axons grew into both the RGD and NHGlc hydrogel matrices for small distances. The number of axons was greatest in hydrogels implanted into cerebral cortex but in both cortex and optic tract implants the highest density of axons was seen in polymers containing RGD. The findings of this study are discussed in the context of CNS tissue replacement and the construction of bioactive scaffolds to promote regenerative axonal growth across areas of injury in the brain and spinal cord.

Conjugates of insulin with copolymers of N-(2-hydroxypropyl) methacrylamide: effects on smooth muscle cell proliferation

The hypothesis that an elevated plasma insulin level contributes to an increase in coronary heart disease has led to studies of the mitogenic effect of native insulin and its conjugates on smooth muscle cells (SMC). In this study, insulin was covalently attached to two water-soluble polymers containing N-(2-hydroxypropyl)methacrylamide using the mixed anhydride method. The first polymer was a copolymer of N-(2-hydroxypropyl)methacrylamide and N-methacryloyldiglycine. The second one was a terpolymer of two of the above-given monomers and R-(-)-1-methyl-2-methacryloylamidoethyl 2-acetamido-2-deoxy-beta-D-glucopyranoside. Insulin conjugates were isolated and characterized, and the mitogenic effect on SMC was investigated. The results showed that only conjugates of insulin and terpolymers bearing pendant N-acetyl-glucosamine groups do not have a mitogenic effect on SMC while maintaining the hypoglycemic activity of insulin. This finding suggests that some inter- or intramolecular interactions of coupled insulin with the sugar moiety(ies) attached to the polymer backbone contribute to the observed effects.

Cultured rat neuronal and glial cells entrapped within hydrogel polymer matrices: a potential tool for neural tissue replacement

Cultured Schwann cells, neonatal astrocytes or cells dissociated from embryonic cerebral hemispheres were dispersed within poly-[N-(2-hydroxypropyl)-methacrylamide]-based hydrogel matrices by gel entrapment and maintained in vitro for 1-6 days. Glial cells were pre-labelled with Hoechst 33342. Cell differentiation and viability were studied by immunocytochemistry. Up to 15% of Schwann cells initially entrapped within the polymer matrices were immunopositive for the low affinity nerve growth factor receptor, S100, glial fibrillary acidic protein (GFAP) and laminin; up to 10% of pre-labelled astrocytes were immunopositive for GFAP and laminin. Embryonic neurons displayed immunostaining for neurofilaments. Hydrogels containing entrapped Schwann cells were implanted into the rat neocortex. These polymers supported cellular and axonal ingrowth within parts of the polymer matrix.

Neural tissue engineering: from polymer to biohybrid organs

This investigation reports on the immobilization of neuronal and glial cells (Schwann cells and astrocytes) within N-(2-hydroxypropyl) methacrylamide (HPMA) polymer hydrogels for the production of cell-based polymer hybrid devices. Cells were included within HPMA polymer networks by gel-entrapment, and these biogels were maintained in vitro for up to 6 days. Cell viability and differentiation were studied using immunocytochemical methods and image analysis techniques. The polymer structure and its relationships with cells were examined by scanning electron microscopy. A proportion of the cell population was viable, expressing its own antigenic profile throughout the period of gel incubation, as cells do in conventional culture conditions, and some cells exhibited behaviour such as spreading or process outgrowth and secretion of laminin. The result of the present study allows us to envisage tissue replacement in the central nervous system by means of such cell-based polymer constructs.

Microparticles with neuroactive agents

An overview of biodegradable and biocompatible microcapsules and microspheres loaded with neuroactive substances, or cells producing neuroactive substances, and their role as drug delivery systems (DDS) for drug administration to the central nervous system (CNS) is given. In addition, closely related systems are also summarized.

Hydrogel-based three-dimensional matrix for neural cells

The ability to organize cells in three dimensions (3D) is an important component of tissue engineering. This study sought to develop an extracellular matrix (ECM) equivalent with a physicochemical structure capable of supporting neurite extension from primary neural cells in 3D. Rat embryonic day 14 striatal cells and chick embryonic day 9 dorsal root ganglia extended neurites in 3D in agarose hydrogels in a gel concentration-dependent manner. Primary neural cells did not extend neurites above a threshold agarose gel concentration of 1.25% wt/vol. Gel characterization by hydraulic permeability studies revealed that the average pore radius of a 1.25% agarose gel was 150 mm. Hydraulic permeability studies for calculating average gel pore radius and gel morphology studies by environmental and scanning electron micrography showed that the average agarose gel por size decreased exponentially as the gel concentration increased. It is hypothesized that the average gel porosity plays an important role in determining the ability of agarose gels to support neurite extension. Lamination of alternating nonpermissive, permissive, and nonpermissive gel layers facilitated the creation of 3D neural tracts in vitro. This ability of agarose hydrogels to organize, support, and direct neurite extension from neural cells may be useful for applications such as 3D neural cell culture and nerve regeneration. Agarose hydrogel substrates also offer the possibility of manipulating cells in 3D, and may be used as 3D templates for tissue engineering efforts in vitro and in vivo.