Strategies for endogenous spinal cord repair: HPMA hydrogel to recruit migrating endogenous stem cells.

Injury to the spinal cord disrupts ascending and descending axonal pathways and causes tissue damage with a subsequent limited cellular regeneration. Successful treatment would encompass the restoration of the cytoarchitecture, homeostasis and function all in dear need. Transplantation-based treatments using exogenous cells are the most favoured approach.

Development of a sialic acid-containing hydrogel of poly[N-(2-hydroxypropyl) methacrylamide]: characterization and implantation study.

This study describes the preparation and the characterization of poly[ N-(2-hydroxypropyl methacrylamide)] hydrogel with bulk-modified saccharidic portion of ganglioside GM 3 (Neu5Ac-alpha2,3-Gal-beta1,4-Glc). The 3'-sialyllactose is a bioactive epitope recognized by many cell surface receptors on viruses, bacteria, and human cells such as growth factor receptors. Acrylated 3'-sialyllactose was synthesized and incorporated into the macromolecular network of hydrogels by free radical cross-linking copolymerization.

Expression of heat shock protein (HSP)-25 and HSP-32 in the rat spinal cord reconstructed with Neurogel.

We recently showed a successful reconstruction of the cat spinal cord using NeuroGel a polymer hydrogel bridge between the two spinal stumps. The polymer graft supports axonal elongation, myelination and angiogenesis up to 21 months, Wallerian degeneration was diminished and gliotic scarring was prevented. In the present study, we report the expression patterns of two stress proteins, (HSPs) HSP-25 and HSP-32 after spinal cord hemisection with and without reparative surgery with NeuroGel.

Prevention of gliotic scar formation by NeuroGel allows partial endogenous repair of transected cat spinal cord.

Spinal cords of adult cats were transected and subsequently reconnected with the biocompatible porous poly (N-[2-hydroxypropyl] methacrylamide) hydrogel, NeuroGel. Tissue repair was examined at various time points from 6-21 months post reconstructive surgery. We examined two typical phenomena, astrogliosis and scar formation, in spines reconstructed with the gel and compared them to those from transected non-reconstructed spines.

Polymeric hydrogels placed into a fimbria-fornix lesion cavity promote fiber (re)growth: a morphological study in the rat.

To examine the regeneration capacity of dorsal septohippocampal neurons in the presence of an artificial growth-promoting substrate, biocompatible polymeric hydrogels were implanted between the septum and the hippocampus in a fimbria-fornix lesion cavity. Unmodified (control) or aminosugar-containing (glucosamines or N-acetyl-glucosamines) hydrogels were implanted immediately or ten days after the lesions. Six months later, brain sections were processed for cresyl-violet, acetylcholinesterase, and immunocytochemical (glial fibrillary acidic protein, protein S100, neurofilaments, laminin, fibronectin) staining.

Homotopic septal grafts combined with a hydrogel bridge promote functional recovery in rats with fimbria-fornix lesions: A unit recording study.

Fimbria-fornix lesions abolish the hippocampal electrophysiological activity time-locked to the theta rhythm and alter some functional characteristics of place cells. The present experiment investigated whether homotopic grafts of fetal septal cells can alleviate some of these alter-ations when combined with a polymeric hydrogel bridging a fimbria-fornix lesion-cavity. Eleven months after grafting surgery, unit recordings were obtained from hippocampal neurons of seven rats [two sham-operated (S), two lesion-only (L) and three grafted (G)] while they explored a radial maze.

Polymer hydrogels usable for nervous tissue repair.

The implantation of non-resorbable biocompatible polymer hydrogels into defects in the central nervous system can reduce glial scar formation, bridge the lesion and lead to tissue regeneration within the hydrogel. We implanted hydrogels based on crosslinked poly hydroxyethyl-methacrylate (pHEMA) and poly N-(2-hydroxypropyl)-methacrylamide (pHPMA) into the rat cortex and evaluated the cellular invasion into the hydrogels by means of immunohistochemical methods and tetramethylammonium diffusion measurements. Astrocytes and NF160-positive axons grew similarly into both types of hydrogels.

Spinal cord reconstruction using NeuroGel implants and functional recovery after chronic injury.

There is currently a lack of effective ways to achieve functional tissue repair of the chronically injured spinal cord. We investigated the potential of using NeuroGel, a biocompatible polymer hydrogel, to induce a reconstruction of the rat spinal cord after chronic compression-produced injury. NeuroGel was inserted 3 months after a severe injury into the post-traumatic lesion cavity.

Natural and artificial substrates for retinal pigment epithelial monolayer transplantation.

The aim of this study was to culture retinal pigment epithelial (RPE) cells on natural and synthetic substrates for future use in RPE monolayer transplantation in the eye. The extracellular capsules surrounding the human lens and a hydrogel biomaterial were used as substrates for monolayer culture. All materials were seeded with either pig or human retinal pigment epithelial cells and were maintained in tissue culture conditions.

Homotopic grafts of septal neurons combined to polymeric hydrogels placed into a fimbria-fornix lesion cavity attenuate locomotor hyperactivity but not mnemonic dysfunctions in rats.

Purpose: We studied the behavioral effects of an intracavitary implantation of poly[N-(2-hydroxypropyl)-methacrylamidel (PHPMA) hydrogels combined to intraseptal grafts of fetal septal cell suspensions in adult female rats subjected to aspirative fimbria-fornix lesions. The hydrogels were used as substrates for bridging the lesion cavity between the septum and the hippocampus.

Methods: Control groups included sham-operated or lesion-only rats, as well as lesioned rats with only the hydrogel bridge in the lesion cavity, only the graft in the septum, or an intrahippocampal graft of a septal cell suspension as a control for the standardly used ectopic transplantation strategy.

The regrowth of axons within tissue defects in the CNS is promoted by implanted hydrogel matrices that contain BDNF and CNTF producing fibroblasts.

In this study we demonstrate the potential for combining biocompatible polymers with genetically engineered cells to elicit axon regrowth across tissue defects in the injured CNS. Eighteen- to 21-day-old rats received implants of poly N-(2-hydroxypropyl)-methacrylamide (HPMA) hydrogels containing RGD peptide sequences that had been infiltrated with control (untransfected) fibroblasts (n = 8), fibroblasts engineered to express brain-derived neurotrophic factor (BDNF) (n = 5), ciliary neurotrophic factor (CNTF) (n = 5), or a mixture of BDNF and CNTF expressing fibroblasts (n = 11). Fibroblasts were prelabeled with Hoechst 33342.

Spinal cord repair with PHPMA hydrogel containing RGD peptides (NeuroGel).

A biocompatible hydrogel of poly[N-(2-hydroxypropyl)methacrylamide] (PHPMA) which includes the cell-adhesive region of fibronectin Arg-Gly-Asp was synthesized and its structure, rheological and dielectric properties were characterized. The ability of a PHPMA-RGD hydrogel to promote tissue regeneration and support axonal outgrowth in the injured adult and developing rat spinal cord was evaluated. The structure of the PHPMA-RGD hydrogel displayed an interconnected porous structure, with viscoelastic properties similar to those of the neural tissue, and conductivity properties due to a peptide group.

Reconstruction of the transected cat spinal cord following NeuroGel implantation: axonal tracing, immunohistochemical and ultrastructural studies.

This study examined the ability of NeuroGel, a biocompatible porous poly [N-(2-hydroxypropyl) methacrylamide] hydrogel, to establish a permissive environment across a 3 mm gap in the cat spinal cord in order to promote tissue reconstitution and axonal regeneration across the lesion. Animals with NeuroGel implants were compared to transection-only controls and observed for 21 months. The hydrogel formed a stable bridge between the cord segments.

In vivo magnetic resonance imaging and relaxometry study of a porous hydrogel implanted in the trapezius muscle of rabbits.

In vivo magnetic resonance imaging (MRI) and relaxometry were performed to assess noninvasively the tissue reaction and the biological integration of hydrogels made of poly[N-(2-hydroxypropyl) methacrylamide] (PHPMA) after implantation in the trapezius muscle of rabbits. The benefits of incorporating RGD peptide sequences in the polymer backbone were also investigated. The histological status of each implant was probed by the trend of their transversal relaxation times, T(2), while their biocompatibility was evaluated by analyzing the host tissue response through the evolution of the relaxation times of the adjacent muscle tissue.

Restorative surgery of the central nervous system by means of tissue engineering using NeuroGel implants.

A novel approach aimed at restoring tissue structure and function and enhancing axonal recovery in damaged parts of the central nervous system is described. In contrast to contemporary neurotransplantation technologies which focus on tissue reconstruction of neural parenchyma by cell replacement, this approach is based on repair by tissue engineering. The technique involves the implantation of a 3-dimensional polymer hydrogel into the site of injury.

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.

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.

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.

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.

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.

Intracerebral implantation of hydrogel-coupled adhesion peptides: tissue reaction.

Arg-Gly-Asp peptides (RGD) were synthesized and chemically coupled to the bulk of N-(2-hydroxypropyl) methacrylamide-based polymer hydrogels. Fourier Transform Infrared Spectroscopy (FTIR) and amino acid analysis confirmed the peptide coupling to the polymer. Activated and control (unmodified) polymer matrices were stereotaxically implanted in the striata of rat brains, and two months later the brains were processed for immunohistochemistry using antibodies for glial acidic fibrillary protein (GFAP), laminin and neurofilaments.

Hydrogels for neural tissue reconstruction and transplantation.

Since the first use of hydrogels as biomaterials, interest in synthetic hydrogels in medicine has increased considerably and the range of biomedical applications has expanded. This paper discusses a novel application of the use of synthetic hydrogels that are processed to serve as artificial matrices for neural tissue reconstruction, the delivery of cells and the promotion of axonal regeneration required for successful neurotransplantation. The possibility to create hydrogels with bioactive characteristics for neural cell adhesion and growth is also presented.

SYNTHETIC POLYMER MATRICES FOR NEURAL CELL TRANSPLANTATION.

This study proposes a strategy to promote the integration of a neural graft into the host brain tissue. It involves the attachment of donor cells to a polymeric matrix, and the implantation of this cell-polymer matrix. We have synthesized hydrogels based on N-(2-hydroxypropyl)-methacrylamide (HPMA) to produce highly porous matrices.

Synthetic polymer derivatives as substrata for neuronal adhesion and growth.

The adhesion and viability of dissociated neurons of rat cerebral hemispheres onto methacrylate and methacrylamide hydrogels, either unmodified or containing collagen, basement membrane proteins, and glucosamine, were measured in vitro. The degree of cell adhesion was affected by properties of the polymers such as hydrophilicity, hydrophobicity, presence of reactive chemical groups, and incorporation of biological molecules. Adhesion was promoted by attachment of glucosamine to the polymer backbone.