Glycosaminoglycans compositional analysis of Urodele axolotl (Ambystoma mexicanum) and Porcine Retina.

Retinal degenerative diseases, such as age-related macular degeneration (AMD) and retinitis pigmentosa (RP), are major causes of blindness worldwide. Humans cannot regenerate retina, however, axolotl (Ambystoma mexicanum), a laboratory-bred salamander, can regenerate retinal tissue throughout adulthood. Classic signaling pathways, including fibroblast growth factor (FGF), are involved in axolotl regeneration. Glycosaminoglycan (GAG) interaction with FGF is required for signal transduction in this pathway. GAGs are anionic polysaccharides in extracellular matrix (ECM) that have been implicated in limb and lens regeneration of amphibians, however, GAGs have not been investigated in the context of retinal regeneration. GAG composition is characterized native and decellularized axolotl and porcine retina using liquid chromatography mass spectrometry. Pig was used as a mammalian vertebrate model without the ability to regenerate retina. Chondroitin sulfate (CS) was the main retinal GAG, followed by heparan sulfate (HS), hyaluronic acid, and keratan sulfate in both native and decellularized axolotl and porcine retina. Axolotl retina exhibited a distinctive GAG composition pattern in comparison with porcine retina, including a higher content of hyaluronic acid. In CS, higher levels of 4- and 6- O-sulfation were observed in axolotl retina. The HS composition was greater in decellularized tissues in both axolotl and porcine retina by 7.1% and 15.4%, respectively, and different sulfation patterns were detected in axolotl. Our findings suggest a distinctive GAG composition profile of the axolotl retina set foundation for role of GAGs in homeostatic and regenerative conditions of the axolotl retina and may further our understanding of retinal regenerative models.

Biopolymeric nanoparticles.

This review on nanoparticles highlights the various biopolymers (proteins and polysaccharides) which have recently revolutionized the world of biocompatible and degradable natural biological materials. The methods of their fabrication, including emulsification, desolvation, coacervation and electrospray drying are described. The characterization of different parameters for a given nanoparticle, such as particle size, surface charge, morphology, stability, structure, cellular uptake, cytotoxicity, drug loading and drug release, is outlined together with the relevant measurement techniques. Applications in the fields of medicine and biotechnology are discussed along with a promising future scope.

Mulberry non-engineered silk gland protein vis-à-vis silk cocoon protein engineered by silkworms as biomaterial matrices.

Silk fibroin from silk gland of Bombyx mori 5th instar larvae was utilized to fabricate films, which may find possible applications as two-dimensional matrices for tissue engineering. Bombyx mori cocoon fibroin is well characterized as potential biomaterial by virtue of its good mechanical strength, water stability, thermal properties, surface roughness and biocompatibility. The present study aims to characterize the biophysical, thermal, mechanical, rheological, swelling properties along with spectroscopic analysis, surface morphology and biocompatibility of the silk gland fibroin films compared with cocoon fibroin. Fibroin solutions showed increased turbidity and shear thinning at higher concentration. The films after methanol treatment swelled moderately and were less hydrophilic compared to the untreated. The spectroscopic analysis of the films illustrated the presence of various amide peaks and conformational transition from random coil to beta sheet on methanol treatment. X-ray diffraction studies also confirmed the secondary structure. Thermogravimetric analysis showed distinct weight loss of the films. The films were mechanically stronger and AFM studies showed surfaces were rougher on methanol treatment. The matrices were biocompatible and supported L929 mouse fibroblast cell growth and proliferation. The results substantiate the silk gland fibroin films as potential biomaterial matrices.

Interphotoreceptor matrix based biomaterial: Impact on human retinal progenitor cell attachment and differentiation.

While cell transplantation therapies show great promise as treatments for retinal degeneration, the challenge of low cell survival upon transplantation motivates exploration of materials that may serve as cell delivery vehicles and promote survival and differentiation. In this study, we explored the native matrix that surrounds the outer segments of photoreceptors and promotes their homeostasis, interphotoreceptor matrix (IPM), as a substrate for human retinal progenitor cells (hRPCs). Bovine IPM was characterized to determine its structure and biochemical composition, and processed to develop substrates for cells. Cell viability, morphology, proliferation and expression of photoreceptors marker genes were studied on IPM-based substrates in vitro. We explored different preparations of IPM as a scaffold. Lectin staining revealed that a distinct honeycomb structure of native IPM is lost during centrifugation to prepare a more concentrated suspension of matrix. Biochemical analysis of bovine IPM indicated presence of glycosaminoglycans and proteins. IPM mediated hRPC attachment and spreading with no signs of cytotoxicity. Cells proliferated more on native IPM substrates compared to IPM that was centrifuged to create a concentrated suspension. Cells cultured on IPM substrates expressed markers of photoreceptors: rhodopsin, NRL and ROM1. Together this data supports further exploration of IPM as a tool for retinal tissue engineering. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 891-899, 2018.

Decellularized retinal matrix: Natural platforms for human retinal progenitor cell culture.

Tissue decellularization strategies have enabled engineering of scaffolds that preserve native extracellular matrix (ECM) structure and composition. In this study, we developed decellularized retina (decell-retina) thin films. We hypothesized that these films, mimicking the retina niche, would promote human retinal progenitor cell (hRPC) attachment, proliferation and differentiation. Retinas isolated from bovine eyes were decellularized using 1% w/v sodium dodecyl sulfate (SDS) and pepsin digested. The resulting decell-retina was biochemically assayed for composition and cast dried to develop thin films. Attachment, viability, morphology, proliferation and gene expression of hRPC cultured on the films were studied in vitro. Biochemical analyses of decell-retina compared to native retina indicated the bulk of DNA (94%) was removed, while the majority of sulfated GAGs (55%), collagen (83%), hyaluronic acid (87%), and key growth factors were retained. The decell-retina films supported hRPC attachment and growth, with cell number increasing 1.5-fold over a week. RT-PCR analysis revealed hRPC expression of rhodopsin, rod outer membrane, neural retina-specific leucine zipper neural and cone-rod homeobox gene on decell-retina films, indicating photoreceptor development. In conclusion, novel decell-retina films show promise as potential substrates for culture and/or transplantation of retinal progenitor cells to treat retinal degenerative disorders. STATEMENT OF SIGNIFICANCE: In this study, we report the development of a novel biomaterial, based on decellularized retina (decell-retina) that mimics the retina niche and promotes human retinal progenitor cell (hRPC) attachment, proliferation and differentiation. We estimated, for the first time, the amounts of collagen I, GAGs and HA present in native retina, as well as the decell-retina. We demonstrated that retinas can be decellularized using ionic detergents and can be processed into mechanically stable thin films, which can act as substrates for culturing hRPCs. Rhodopsin, ROM1, NRL and CRX gene expression on the decell-retina films indicated photoreceptor development from RPCs. These results support the potential of decell-retina as a cell delivery platform to treat and manage retinal degenerative disease like AMD.

Non-Mulberry and Mulberry Silk Protein Sericins as Potential Media Supplement for Animal Cell Culture.

Silk protein sericins, in the recent years, find application in cosmetics and pharmaceuticals and as biomaterials. We investigate the potential of sericin, extracted from both mulberry Bombyx mori and different non-mulberry sources, namely, tropical tasar, Antheraea mylitta; muga, Antheraea assama; and eri, Samia ricini, as growth supplement in serum-free culture medium. Sericin supplemented media containing different concentrations of sericins from the different species are examined for attachment, growth, proliferation, and morphology of fibrosarcoma cells. The optimum sericin supplementation seems to vary with the source of sericins. The results indicate that all the sericins promote the growth of L929 cells in serum-free culture media; however, S. ricini sericin seems to promote better growth of cells amongst other non-mulberry sericins.

An additive manufacturing-based PCL-alginate-chondrocyte bioprinted scaffold for cartilage tissue engineering.

Regenerative medicine is targeted to improve, restore or replace damaged tissues or organs using a combination of cells, materials and growth factors. Both tissue engineering and developmental biology currently deal with the process of tissue self-assembly and extracellular matrix (ECM) deposition. In this investigation, additive manufacturing (AM) with a multihead deposition system (MHDS) was used to fabricate three-dimensional (3D) cell-printed scaffolds using layer-by-layer (LBL) deposition of polycaprolactone (PCL) and chondrocyte cell-encapsulated alginate hydrogel. Appropriate cell dispensing conditions and optimum alginate concentrations for maintaining cell viability were determined. In vitro cell-based biochemical assays were performed to determine glycosaminoglycans (GAGs), DNA and total collagen contents from different PCL-alginate gel constructs. PCL-alginate gels containing transforming growth factor-ß (TGFß) showed higher ECM formation. The 3D cell-printed scaffolds of PCL-alginate gel were implanted in the dorsal subcutaneous spaces of female nude mice. Histochemical [Alcian blue and haematoxylin and eosin (H&E) staining] and immunohistochemical (type II collagen) analyses of the retrieved implants after 4 weeks revealed enhanced cartilage tissue and type II collagen fibril formation in the PCL-alginate gel (+TGFß) hybrid scaffold. In conclusion, we present an innovative cell-printed scaffold for cartilage regeneration fabricated by an advanced bioprinting technology.

Interphotoreceptor matrix-poly(ϵ-caprolactone) composite scaffolds for human photoreceptor differentiation.

Tissue engineering has been widely applied in different areas of regenerative medicine, including retinal regeneration. Typically, artificial biopolymers require additional surface modification (e.g. with arginine-glycine-aspartate-containing peptides or adsorption of protein, such as fibronectin), before cell seeding. Here, we describe an alternative approach for scaffold design: the manufacture of hybrid interphotoreceptor matrix-poly (ϵ-caprolactone) scaffolds, in which the insoluble extracellular matrix of the retina is incorporated into a biodegradable polymer well suited for transplantation. The incorporation of interphotoreceptor matrix did not change the topography of polycaprolactone film, although it led to a slight increase in hydrophilic properties (water contact angle measurements). This hybrid scaffold provided sufficient stimuli for human retinal progenitor cell adhesion and inhibited proliferation, leading to differentiation toward photoreceptor cells (expression of Crx, Nrl, rhodopsin, ROM1). This scaffold may be used for transplantation of retinal progenitor cells and their progeny to treat retinal degenerative disorders.

Approaches to cell delivery: substrates and scaffolds for cell therapy.

Retinal degeneration, associated with loss of photoreceptors, is the primary cause of permanent vision impairment, impacting millions of people worldwide. Age-related macular degeneration and retinitis pigmentosa are two common retinal diseases resulting in photoreceptor loss and vision impairment or blindness. Presently, available treatments can only delay the progress of retinal degeneration, and there are no treatments that can restore permanent vision loss. Research is underway to develop methods of regenerating the impaired retina by delivering photoreceptor precursor cells and retinal pigment epithelium to the subretinal space. Challenges to cell transplantation include limited survival upon implantation and the formation of abnormal cell architectures in vivo. Retinal tissue engineering shows immense promise and potential in treatment of retinal degeneration by employing scaffold-based delivery systems of retinal progenitor cells to the subretinal space. Scaffold delivery strategy has been shown to enhance the cell survival and direct cell differentiation in a variety of retinal degenerative models. In this chapter, we summarize the research findings on different scaffold- or substrate-based transplantation techniques used to deliver retinal progenitor/photoreceptor precursors and retinal pigment epithelial cells to the subretinal space.

Effects of alginate hydrogel cross-linking density on mechanical and biological behaviors for tissue engineering.

An effective cross-linking of alginate gel was made through reaction with calcium carbonate (CaCO3). We used human chondrocytes as a model cell to study the effects of cross-linking density. Three different pore size ranges of cross-linked alginate hydrogels were fabricated. The morphological, mechanical, and rheological properties of various alginate hydrogels were characterized and responses of biosynthesis of cells encapsulated in each gel to the variation in cross-linking density were investigated. Desired outer shape of structure was maintained when the alginate solution was cross-linked with the applied method. The properties of alginate hydrogel could be tailored through applying various concentrations of CaCO3. The rate of synthesized GAGs and collagens was significantly higher in human chondrocytes encapsulated in the smaller pore structure than that in the larger pore structure. The expression of chondrogenic markers, including collagen type II and aggrecan, was enhanced in the smaller pore structure. It was found that proper structural morphology is a critical factor to enhance the performance and tissue regeneration.

Three-dimensional printing of rhBMP-2-loaded scaffolds with long-term delivery for enhanced bone regeneration in a rabbit diaphyseal defect.

In this study, recombinant human bone morphogenetic protein-2 (rhBMP-2) delivery system with slow mode was successfully developed in three-dimensional (3D) printing-based polycaprolactone (PCL)/poly(lactic-co-glycolic acid) (PLGA) scaffolds for bone formation of critical-sized rabbit segmental diaphyseal defect. To control the delivery of the rhBMP-2, collagen (for long-term delivery up to 28 days) and gelatin (for shor-term delivery within a week) solutions encapsulating rhBMP-2 were dispensed into a hollow cylinderical type of PCL/PLGA scaffold. An effective dose of 5µg/mL was determined by measuring the alkaline phosphatase and osteocalcin gene expression levels of human nasal inferior turbinate-derived mesenchymal stromal cells (hTMSCs) seeded on the PCL/PLGA/collagen scaffold in vitro. However, it was found that a burst release of rhBMP-2 from the PCL/PLGA/gelatin scaffold did not induce the osteogenic differentiation of hTMSCs in vitro at an equivalent dose. In the in vivo animal experiements, microcomputed tomography and histological analyses confirmed that PCL/PLGA/collagen/rhBMP-2 scaffolds (long-term delivery mode) showed the best bone healing quality at both weeks 4 and 8 after implantation without inflammatory response. On the other hand, a large number of macrophages indicating severe inflammation provoked by burst release of rhBMP-2 were observed in the vicinity of PCL/PLGA/gelatin/rhBMP-2 (short-term delivery mode) at week 4.

In vitro and in vivo evaluation of bone formation using solid freeform fabrication-based bone morphogenic protein-2 releasing PCL/PLGA scaffolds.

The aim of this study was to develop novel polycaprolactone/poly(lactic-co-glycolic acid) (PCL/PLGA) scaffolds with a heparin-dopamine (Hep-DOPA) conjugate for controlled release of bone morphogenic protein-2 (BMP-2) to enhance osteoblast activity in vitro and also bone formation in vivo. PCL/PLGA scaffolds were prepared by a solid freeform fabrication method. The PCL/PLGA scaffolds were functionalized with Hep-DOPA and then BMP-2 was sequentially coated onto the Hep-DOPA/PCL/PLGA scaffolds. The characterization and surface elemental composition of all scaffolds were evaluated by scanning electron microscope and x-ray photoelectron spectroscopy. The osteoblast activities on all scaffolds were assessed by cell proliferation, alkaline phosphatase (ALP) activity and calcium deposition in vitro. To demonstrate bone formation in vivo, plain radiograph, micro-computed tomography (micro-CT) evaluation and histological studies were performed after the implantation of all scaffolds on a rat femur defect. Hep-DOPA/PCL/PLGA had more controlled release of BMP-2, which was quantified by enzyme-linked immunosorbent assay, compared with Hep/PCL/PLGA. The in vitro results showed that osteoblast-like cells (MG-63 cells) grown on BMP-2/Hep-DOPA/PCL/PLGA had significantly enhanced ALP activity and calcium deposition compared with those on BMP-2/Hep/PCL/PLGA and PCL/PLGA. In addition, the plain radiograph, micro-CT evaluation and histological studies demonstrated that the implanted BMP-2/Hep-DOPA/PCL/PLGA on rat femur had more bone formation than BMP-2/Hep/PCL/PLGA and PCL/PLGA in vivo.

An emerging functional natural silk biomaterial from the only domesticated non-mulberry silkworm Samia ricini.

Mulberry silk fibroin is a widely used biomaterial and recent work on non-mulberry silk fibroin also suggests it may have similar uses. We expect silk fibroin from the only domesticated non-mulberry eri silkworm, Samia ricini, to possess useful properties as a biomaterial. Eri silk gland fibroin is a heterodimeric protein of approximately 450 kDa. Cytocompatibility evaluation with fibroblasts and osteoblast-like cells shows good cell attachment, viability and proliferation. The matrices, which have high thermal stability and good swellability, are also haemocompatible. Eri silk production is cost effective as no agronomic practices are required for their host plant cultivation. This fibroin provide new opportunities as an alternative natural functional biomaterial in various biomedical applications.

Silk fibroin/poly(vinyl alcohol) photocrosslinked hydrogels for delivery of macromolecular drugs.

Hydrogels are three-dimensional polymer networks widely used in biomedical applications as drug delivery and tissue engineered scaffolds to effectively repair or replace damaged tissue. In this paper we demonstrate a newly synthesized cytocompatible and drug releasing photo-crosslinked hydrogel based on poly(vinyl alcohol) methacrylate and silk fibroin which possesses tailorable structural and biological properties. The initial silk fibroin content was 0%, 10%, 20%, 30%, 40% and 50% with respect to the weight of poly(vinyl alcohol) methacrylate. The prepared hydrogels were characterized with respect to morphology, crystallinity, stability, swelling, mass loss and cytotoxicity. FITC-dextrans of different molecular weights were chosen as model drugs molecules for release studies from the hydrogels. The hydrogels containing different silk fibroin percentages showed differences in pore size and distribution. X-ray diffraction analysis revealed that amorphous silk fibroin in poly(vinyl alcohol) methacrylate is crystallized to ß-sheet secondary structure upon gelation. The sol fraction increased with increasing fibroin concentration in the co-polymer gel (from 18% to 45%), although the hydrogel extracts were non-cytotoxic. Similarly, the addition of silk fibroin increased water uptake by the gels (from 7% to 21%). FITC-dextran release from the hydrogels was dependent on the silk fibroin content and the molecular weight of encapsulated molecules. The study outlines a newer type of photo-crosslinked interpenetrating polymer network hydrogel that possess immense potential in drug delivery applications.

The influence of silkworm species on cellular interactions with novel PVA/silk sericin hydrogels.

Sericin peptides and PVA are chemically modified with methacrylate groups to produce a covalent PVA/sericin hydrogel. Preservation of the sericin bioactivity following methacrylation is confirmed, and PVA/sericin hydrogels are fabricated for both B. mori and A. mylitta sericin. Cell adhesion studies confirm the preservation of sericin bioactivity post incorporation in PVA gels. PVA/A. mylitta gels are observed to facilitate cell adhesion to a significantly greater degree than PVA/B. mori gels. Overall, the incorporation of sericin does not alter the physical properties of the PVA hydrogels but does result in significantly improved cellular interaction, particularly from A. mylitta gels.

Invited review nonmulberry silk biopolymers.

The silk produced by silkworms are biopolymers and can be classified into two types--mulberry and nonmulberry. Mulberry silk of silkworm Bombyx mori has been extensively explored and used for century old textiles and sutures. But for the last few decades it is being extensively exploited for biomedical applications. However, the transformation of nonmulberry silk from being a textile commodity to biomaterials is relatively new. Within a very short period of time, the combination of load bearing capability and tensile strength of nonmulberry silk has been equally envisioned for bone, cartilage, adipose, and other tissue regeneration. Adding to its advantage is its diverse morphology, including macro to nano architectures with controllable degradation and biocompatibility yields novel natural material systems in vitro. Its follow on applications involve sustained release of model compounds and anticancer drugs. Its 3D cancer models provide compatible microenvironment systems for better understanding of the cancer progression mechanism and screening of anticancer compounds. Diversely designed nonmulberry matrices thus provide an array of new cutting age technologies, which is unattainable with the current synthetic materials that lack biodegradability and biocompatibility. Scientific exploration of nonmulberry silk in tissue engineering, regenerative medicine, and biotechnological applications promises advancement of sericulture industries in India and China, largest nonmulberry silk producers of the world. This review discusses the prospective biomedical applications of nonmulberry silk proteins as natural biomaterials.

Silk fibroin/sodium carboxymethylcellulose blended films for biotechnological applications.

The potential of silk protein is increased because of its importance as natural biopolymer for biotechnological and biomedical applications. The main disadvantage of silk fibroin films is their high brittleness. Thus, we studied blends of fibroin with other polymers to improve the film properties. Considering the possible applications of films in biomedical applications, we used a natural and biodegradable polymer as the second component. This study reports the fabrication and characterization of mulberry silk protein fibroin and sodium carboxymethylcellulose (NaCMC) blended films as potential substrates for in vitro cell culture. The blended films are investigated of their chemical interactions, morphologies, thermal, mechanical properties in addition to its swelling properties and biocompatibility. The addition of NaCMC improves the elasticity of fibroin films and its thermal properties. The change of morphology, swelling behavior and increase of surface roughness of the films were also observed in the blended films. The films become insoluble on alcohol treatment and are stable for longer duration in hydrolytic medium. The blended films are cytocompatible and supported adhesion and growth of mouse fibroblast cells. The results suggest that NaCMC blended silk fibroin films are found to be potential substratum for supporting cell adhesion and proliferation.

Silk fibroin nanoparticles for cellular uptake and control release.

Silk nanoparticles were prepared from silk fibroin solutions of domesticated Bombyx mori and tropical tasar silkworm Antheraea mylitta and investigated in respect to its particle size, surface charge, stability and morphology along with its cellular uptake and release of growth factors. The nanoparticles were stable, spherical, negatively charged, 150-170nm in average diameter and exhibited mostly Silk II (beta-sheet) structure and did not impose any overt toxicity. Cellular uptake studies showed the accumulation of fluorescence isothiocyanate conjugated silk nanoparticles in the cytosol of murine squamous cell carcinoma cells. In vitro VEGF release from the nanoparticles showed a significantly sustained release over 3 weeks, signifying the potential application as a growth factor delivery system.