Summary: The use of ionizing radiation for the preparation of polymeric biomaterials is one of the examples of the application of atomic energy for the benefit of humanity. Radiation processing is based on the use of high energy ionizing radiation to induce chemical and biological changes in irradiated systems. High energy electron (EB) under 10 keV and gamma irradiation are the most frequently used of ionizing radiation for synthesis, modification of polymers, and sterilization of medical devices. Potential biomedical and pharmaceutical applications of these polymers are implants, topical dressings, injectable formulations, drug delivery devices, diagnostic assays, and immobilized enzyme. Through radiation crosslinking or degradation processes, polymers with specific characteristics can be prepared. The advantages of radiation processing include the absent of any chemical residues (since no chemical additives are requires to initiate the reactions), can be used at all temperatures, can be limited to the surface only and in certain cases, the synthesis/modification of materials can be combined with sterilization.

Bacterial cellulose membrane synthesized by Acetobacter xylinum in coconut water medium has potential application for Guided bone Regeneration. However, this membrane may not meet some application requirements due to its low biodegradation properties. In this paper, incorporation of gamma irradiation into the membrane is a developed strategy to increase its biodegradability properties. The in-vitro degradation study in synthetic body fluid (SBF) of the irradiated membrane has been analyzed during periods of 6 months by means of weight loss, mechanical properties and scanning electron microscopy observation compared to that the un-irradiated one. The result showed that weight loss of irradiated membrane with 25 kGy and 50 kGy and immersed in SBF solution for 6 months reached 18% and 25% respectively. While un-irradiated membrane did not give significant weight loss. Tensile strength of membranes decreases with increasing of irradiation dose and further decreases in tensile strength is observed when irradiated membrane was followed by immersion in SBF solution. Microscope electron image of cellulose membranes shows that un-irradiated bacterial cellulose membrane consists of dense ultrafine fibril network structures, while irradiation result in cleavage of fibrils network of cellulose. The fibrils network become loosely after irradiated membrane immersed in SBF solution due to released of small molecular weight carbohydrates formed during by irradiation from the structure.

Reproducing the features of the extracellular matrix is important for fabricating three-dimensional (3D) scaffolds for tissue regeneration. A collagen-like polypeptide, poly(Pro-Hyp-Gly), is a promising material for 3D scaffolds because of its excellent physical properties, biocompatibility, and biodegradability. In this paper, we present a novel photocrosslinked poly(Pro-Hyp-Gly) hydrogel as a 3D scaffold for simultaneous rat bone marrow stromal cell (rBMSC) encapsulation. The hydrogels were fabricated using visible-light photocrosslinking at various concentrations of methacrylated poly(Pro-Hyp-Gly) (20-50 mg/ml) and irradiation times (3 or 5 min). The results show that the rBMSCs encapsulated in the hydrogels survived 7 days of incubation. Calcium deposition on the encapsulated rBMSCs was assessed with scanning electron microscope observation, Alizarin Red S, and von Kossa staining. The most strongly stained area was observed in the hydrogel formed with 30 mg/ml of methacrylated poly(Pro-Hyp-Gly) with 5-min irradiation. These findings demonstrate that poly(Pro-Hyp-Gly) hydrogels support rBMSC viability and differentiation, as well as demonstrating the feasibility of using poly(Pro-Hyp-Gly) hydrogels as a cytocompatible, biodegradable 3D scaffold for tissue regeneration.

Polyion complex (PIC) gel of poly(Pro-Hyp-Gly) was successfully fabricated by simply mixing polyanion and polycation derivatives of poly(Pro-Hyp-Gly), a collagen-like polypeptide. The polyanion, succinylated poly(Pro-Hyp-Gly), and the polycation, arginylated poly(Pro-Hyp-Gly), contain carboxy (pK = 5.2) and guanidinium (pK = 12.4) groups, respectively. Mixing the polyanion and the polycation at physiological pH (pH = 7.4) resulted in PIC gel. The hydrogel formation was optimum at an equimolar ratio of carboxy to guanidinium groups, suggesting that ionic interaction is the main determinant for the hydrogel formation. The hydrogel was successfully used for simultaneous rat bone marrow stromal cell encapsulation. The encapsulated cells survived and proliferated within the hydrogel. In addition, the cells exhibited different morphology in the hydrogel compared with cells cultured on a tissue culture dish as a two-dimensional (2D) control. At day one, a round morphology and homogeneous single cell distribution were observed in the hydrogel. In contrast, the cells spread and formed a fibroblast-like morphology on the 2D control. After three days, the cells in the hydrogel maintained their morphology and some of them formed multicellular aggregates, which is similar to cell morphology in an in vivo microenvironment. These results suggest that the PIC gel of poly(Pro-Hyp-Gly) can serve as a cytocompatible three-dimensional scaffold for stem cell encapsulation, supporting their viability, proliferation, and in vivo-like behavior.

Incorporation of bone-like hydroxyapatite into bacterial cellulose (BC) is an attractive approach for the fabrication of a bioactive three-dimensional (3D) scaffold for bone tissue regeneration. This study investigates the influence of the succinylation of BC on its ability to incorporate bone-like hydroxyapatite. A biomimetic process using a 1.5 × Simulated Body Fluid (SBF) was used to deposit the hydroxyapatite into the succinylated-BC. After soaking the succinylated-BC in the 1.5 × SBF for six days, Scanning Electron Microscope (SEM) images were taken and the composition of the succinylated-BC was analyzed by energy dispersive X-ray spectrometry. The biocompatibility of the scaffolds was tested in vitro using rat Bone Marrow Stromal Cells (rBMSCs). The SEM images and Fourier Transform Infrared Spectroscopy (FTIR) spectra showed that carbonated hydroxyapatite was deposited on the succinylated-BC. In contrast, only a small amount of carbonated hydroxyapatite deposition was observed on unmodified BC, indicating that the succinyl group in the BC is effective for inducing hydroxyapatite deposition. In vitro studies using rBMSCs revealed the biocompatibility of the scaffold. Combining with the ability of the cells to differentiate into bone cells, the succinylated-BC scaffold is a promising 3D scaffold for bone tissue regeneration.