Biodegradation and tumorigenicity of implanted plates made from a copolymer of epsilon-caprolactone and L-lactide in rat

Establishment of a bioluminescence model for microenvironmentally induced oral carcinogenesis with implications for screening bioengineered scaffolds

Background

Microenvironmental cues play a major role in head and neck cancer. Biodegradable scaffolds used for bone regeneration might also act as stimulative cues for head and neck cancer. The purpose of this study was to establish an experimental model for precise and noninvasive evaluation of tumorigenic potential of microenvironmental cues in head and neck cancer.

Methods

Bioluminescence was chosen to image tumor formation. Early neoplastic oral keratinocyte (DOK) cells were luciferase‐transduced (DOK^Luc), then tested in nonobese diabetic severe combined immunodeficient IL2rγnull mice either orthotopically (tongue) or subcutaneously for their potential as “screening sensors” for diverse microenvironmental cues.

Results

Tumors formed after inoculation of DOK^Luc were monitored easier by bioluminescence, and bioluminescence was more sensitive in detecting differences between various microenvironmental cues when compared to manual measurements. Development of tumors from DOK^Luc grown on scaffolds was also successfully monitored noninvasively by bioluminescence.

Conclusion

The model presented here is a noninvasive and sensitive model for monitoring the impact of various microenvironmental cues on head and neck cancer in vivo. © 2015 The Authors Head & Neck Published by Wiley Periodicals, Inc. Head Neck38: E1177–E1187, 2016

Bridging a 30 mm defect in the canine ulnar nerve using vessel-containing conduits with implantation of bone marrow stromal cells

Previously, we showed that undifferentiated bone marrow stromal cell (uBMSC) implantation and vessel insertion into a nerve conduit facilitated peripheral nerve regeneration in a rodent model. In this study, we investigated the efficacy of the uBMSC-laden vessel-containing conduit in repair of segmental nerve defects, using a canine model. Eight beagle dogs were used in this study. Thirty-millimeter ulnar nerve defects were repaired with the conduits (right forelimbs, n = 8) or autografts (left forelimbs, n = 7). In the conduit group, the ulnar artery was inserted into the l-lactide/ε-caprolactone tube, which was filled with autologous uBMSCs obtained from the ilium. In the autograft group, the reversed nerve segments were sutured in situ. At 8 weeks, one dog with only nerve repair with the conduit was sacrificed and the regenerated nerve in the conduit underwent immunohistochemistry for investigation of the differentiation capability of the implanted uBMSCs. In the remaining seven dogs, the repaired nerves underwent electrophysiological examination at 12 and 24 weeks and morphometric measurements at 24 weeks. The wet weight of hypothenar muscles was measured at 24 weeks. At 8 weeks, almost 35% of the implanted uBMSCs expressed glial markers. At 12 weeks, amplitude (0.4 ± 0.4mV) and conduction velocity (18.9 ± 14.3m/s) were significantly lower in the conduit group than in the autograft group (3.2 ± 2.5 mV, 34.9 ± 12.1 m/s, P < 0.05). Although the nerve regeneration in the conduit group was inferior when compared with the autograft group at 24 weeks, there were no significant differences between both groups, regarding amplitude (10.9 ± 7.3 vs. 25.3 ± 20.1 mV; P = 0.11), conduction velocity (23.5 ± 8.7 vs 31.6 ± 20.0m/s; P = 0.35), myelinated axon number (7032 ± 4188 vs 7165 ± 1814; P = 0.94), diameter (1.73 ± 0.31 vs 2.09 ± 0.39μm; P = 0.09), or muscle weight (1.02 ± 0.40 vs 1.19 ± 0.26g; P = 0.36). In conclusion, this study showed that vessel-containing tubes with uBMSC implantation may be an option for treatment of peripheral nerve injuries. However, further investigations are needed. © 2015 Wiley Periodicals, Inc. Microsurgery 36:316-324, 2016.

The influence of chain microstructure of biodegradable copolyesters obtained with low-toxic zirconium initiator to in vitro biocompatibility

Because of the wide use of biodegradable materials in tissue engineering, it is necessary to obtain biocompatible polymers with different mechanical and physical properties as well as degradation ratio. Novel co- and terpolymers of various composition and chain microstructure have been developed and applied for cell culture. The aim of this study was to evaluate the adhesion and proliferation of human chondrocytes to four biodegradable copolymers: lactide-coglycolide, lactide-co-ε-caprolactone, lactide-co-trimethylene carbonate, glycolide-co-ε-caprolactone, and one terpolymer glycolide-colactide-co-ε-caprolactone synthesized with the use of zirconium acetylacetonate as a nontoxic initiator. Chain microstructure of the copolymers was analyzed by means of ¹H and ¹³C NMR spectroscopy and surface properties by AFM technique. Cell adhesion and proliferation were determined by CyQUANT Cell Proliferation Assay Kit. After 4 h the chondrocyte adhesion on the surface of studied materials was comparable to standard TCPS. Cell proliferation occurred on all the substrates; however, among the studied polymers poly(L-lactide-coglycolide) 85 : 15 that characterized the most blocky structure best supported cell growth. Chondrocytes retained the cell membrane integrity evaluated by the LDH release assay. As can be summarized from the results of the study, all the studied polymers are well tolerated by the cells that make them appropriate for human chondrocytes growth.

Preparation of Cross-Linked Poly[(ɛ-caprolactone)-co-lactide] and Biocompatibility Studies for Tissue Engineering Materials

In this study, cross-linked materials were prepared using the branched macromonomer with different CL/LA molar ratios, and feasibility studies for tissue engineering were carried out. The thermal and mechanical properties of these materials depended on the CL/LA compositions; however, there was no change in the wettability of each material. The HeLa cells adhesion and growth on the CL-LA7030c were equal to that on the commercially available polystyrene dish. The protein absorption experiment using the FBS proteins revealed that the materials with well-grown cells showed better adhesion of the proteins. [photo: see text]

Membranas de poli (ácido lático-co-ácido glicólico) como curativos para pele: degradação in vitro e in vivo

O poli (ácido lático-co-ácido glicólico) é um copolímero biodegradável e bioreabsorvível. Suas propriedades físico-químicas têm sido estudadas com o intuito de modular sua suscetibilidade à degradação e suas interações com células e fluidos biológicos para aplicações na área médica e odontológica. Neste trabalho, membranas de poli (ácido lático-co-ácido glicólico) com e sem plastificante foram preparadas pela técnica de evaporação do solvente e caracterizadas in vitro e in vivo. Os resultados in vitro mostraram que a adição de plastificante diminui a temperatura de transição vítrea (Tg) das membranas e, conseqüentemente, aumenta a flexibilidade das mesmas. Com o avanço da degradação, verifica-se o aparecimento de regiões cristalinas e de poros. Os estudos in vivo mostraram que o polímero degradou rapidamente em contato com a pele sem causar inflamações sérias e protegeu a área ulcerada da ação de agentes externos. Além disso, a cicatrização das feridas foi mais rápida na presença das membranas mostrando que as mesmas podem ser potencialmente utilizadas como curativos para pele.

Manufacture of elastic biodegradable PLCL scaffolds for mechano-active vascular tissue engineering

A soft and very elastic poly(lactide-co-epsilon-caprolactone) (PLCL)(50:50, Mn 185 x 10(3)) was synthesized. Tubular scaffolds were prepared by an extrusion-particulate leaching method for mechano-active vascular tissue engineering. The copolymer was very flexible but completely rubber-like elastic. Even the high porous PLCL scaffolds (90% salt wt) exhibited 200% elongation, but recovery over 85% in a tensile test. Moreover, the PLCL scaffolds maintained their high elasticity also in culture media under cyclic mechanical strain conditions. The highly porous scaffold (90% salt wt) withstood for an initial 1 week without any deformation and sustained for 2 weeks in culture media under cyclic stress of 10% amplitude and at 1 Hz frequency which are similar to the natural vascular conditions. Vascular smooth muscle cells (VSMCs) were seeded on to the PLCL scaffolds. The cell adhesion and proliferation on the scaffolds of various pore-size were increased with increasing pore size. For the pore sizes of 50-100 microm, 100-150 microm, 150-200 microm and 200-250 microm, the ratios of cell numbers were about 1:1.2:1.9:2.2, respectively, at both 12 h and 5 days. Similarly, the higher porous scaffolds exhibited more cell adhesion and proliferation compared to lower porous one, where the effect was more pronounced in the longer proliferation period. SMC-seeded scaffolds were implanted subcutaneously in athymic nude mice to confirm the biocompatibility. Such a high elastic property and proper biocompatibility to SMCs of PLCL scaffolds prepared in this study will be very useful to engineer SM-containing tissues such as blood vessels under mechanically dynamic environments (mechano-active tissue engineering).

In vitro degradation and biocompatibility of poly(DL-lactide-epsilon-caprolactone) nerve guides

Bridging nerve gaps by means of autologous nerve grafts involves donor nerve graft harvesting. Recent studies have focused on the use of alternative methods, and one of these is the use of biodegradable nerve guides. After serving their function, nerve guides should degrade to avoid a chronic foreign body reaction. The in vitro degradation, in vitro cytotoxicity, hemocompatibility, and short-term in vivo foreign body reaction of poly((65)/(35) ((85)/(15) (L)/(D)) lactide-epsilon-caprolactone) nerve guides was studied. The in vitro degradation characteristics of poly(DLLA-epsilon-CL) nerve guides were monitored at 2-week time intervals during a period of 22 weeks. Weight loss, degree of swelling of the tube wall, mechanical strength, thermal properties, and the intrinsic viscosity of the nerve guides were determined. Cytotoxicity was studied by measuring the cell proliferation inhibition index (CPII) on mouse fibroblasts in vitro. Cell growth was evaluated by cell counting, while morphology was assessed by light microscopy. Hemocompatibility was evaluated using a thrombin generation assay and a complement convertase assay. The foreign body reaction against poly(DLLA-epsilon-CL) nerve guides was investigated by examining toluidine blue stained sections. The in vitro degradation data showed that poly(DLLA-epsilon-CL) nerve guides do not swell, maintain their mechanical strength and flexibility for a period of about 8-10 weeks, and start to lose mass after about 10 weeks. Poly(DLLA-epsilon-CL) nerve guides were classified as noncytotoxic, as cytotoxicity tests demonstrated that cell morphology was not affected (CPII 0%). The thrombin generation assay and complement convertase assay indicated that the material is highly hemocompatible. The foreign body reaction against the biomaterial was mild with a light priming of the immunesystem. The results presented in this study demonstrate that poly((65)/(35) ((85)/(15) (L)/(D)) lactide-epsilon-caprolactone) nerve guides are biocompatible, and show good in vitro degradation characteristics, making these biodegradable nerve guides promising candidates for bridging peripheral nerve defects up to several centimeters.

Fibroblast culture on surface-modified poly(glycolide-co-epsilon-caprolactone) scaffold for soft tissue regeneration

Novel porous matrices made of a copolymer of glycolide (G) and epsilon-caprolactone (CL) (51 : 49, Mw 103000) was prepared for tissue engineering using a solvent-casting particulate leaching method. Poly(glycolide-co-epsilon-caprolactone) (PGCL) copolymer showed a rubber-like elastic characteristic, in addition to an amorphous property and fast biodegradability. In order to investigate the effect on the fibroblast culture, PGCL scaffolds of varying porosity and pore size, in addition to surface-hydrolysis or collagen coating, were studied. The large pore-sized scaffold (pore size >150 microm) demonstrated a much greater cell adhesion and proliferation than the small pore-sized one. In addition, the higher porosity, the better the cell adhesion and proliferation. The surface-hydrolyzed PGCL scaffold showed enhanced cell adhesion and proliferation compared with the unmodified one. Type I collagen coating revealed a more pronounced contribution for increased cell interactions than the surface-hydrolyzed one. These results demonstrate that surface-modified PGCL scaffold can provide a suitable substrate for fibroblast culture, especially in the case of soft tissue regenerations.

Long-term implantation test and tumorigenicity of polyvinyl alcohol hydrogel plates

Two types of flat plates made from a polyvinyl alcohol (PVA) hydrogel with a water content of 80 and 20 (PVA-H80, PVA-H20), 20 x 10 x 1 mm in size, were subcutaneously implanted into each of 50 young, male Wistar rats. As a control, a sham operation was done on another set of 50 rats (Sham Op group). The shape and transparency of the PVA hydrogel were unchanged for up to 24 months. Tumors arose in 14 rats from the PVA-H80 group. In the PVA-H20 group, tumors appeared in 15 rats. The average tumor latency was 598 +/- 109 days in the PVA-H80 and 637 +/- 94 days in the PVA-H20. There was no difference in tumor incidence between the PVA-H20 and PVA-H80 groups (p < 0.05). In the Sham Op group, no malignant tumors appeared. Histopathologically, the tumors induced by hydrogel plates were malignant tumors resembling fibrosarcoma or malignant fibrous histiocytoma. This indicates that PVA hydrogel implants also induce solid state carcinogenesis at a similarly high rate to medical grade hydrophobic material reported in a previous study.

Evaluation of the capacity of the SCGE assay to assess the genotoxicity of biomaterials

The comet test or SCGE assay, which is already widely used in other areas, has never been used to evaluate the mutagenic potential of medical biomaterials in the final form. The purpose of our study was thus to assess the comet test as a means of assessing the genotoxic potential of finished medical biomaterials. We used silicone elastomers with increasing concentrations of 4-nitroquinoline oxide, a genotoxic agent. Hydrogen peroxide was used as the positive control, and tissue culture polystyrene as the negative control. In our study, the comet test did not detect a significant difference in genotoxicity between the pure elastomer and the same elastomer containing 0.01 mg/ml 4-nitroquinoline oxide, but did detect a significant difference between two elastomers containing 0.01 and 0.3 mg/ml of 4-nitroquinoline oxide, respectively. Since, the surface properties of the samples were identical, only the chemical composition may have caused significant differences in mutagenicity. Whatever the cause of the genotoxicity detected by the SCGE assay, testing finished biomaterials using the comet assay makes it possible to evaluate interactions between biomaterials and living tissues that are much closer to actual application conditions.

Evaluation of biological responses to polymeric biomaterials by RT-PCR analysis IV: study of c-myc, c-fos and p53 mRNA expression

In order to investigate how cells recognize biomaterials, mRNA that was expressed in attached human fibroblasts on various substrates was evaluated. The expressed oncogenes (c-fos and c-myc) and tumor suppressor gene (p53) mRNA were then isolated and detected using the RT-PCR method. As a result, c-fos and c-myc mRNA expression varied with respect to differences in the hydrophilicity-hydrophobicity of the substrates. Both c-fos and c-myc mRNA expression were low in the fibroblasts that had adhered to hydrophilic surfaces. The tendency of c-fos mRNA expression was similar to the adhesion curve of the cells. c-myc mRNA was largely induced in fibroblasts that had adhered to hydrophobic surfaces. p53 mRNA were largely induced in fibroblasts that had adhered to hydrophilic surfaces, while in the cells that had adhered to hydrophobic surfaces, p53 mRNA expression was low. We concluded that the expression of oncogenes and p53 mRNA is a powerful method for studying cell-polymer interactions or the evaluation of the carcinogenic activity of biomaterials.