Zhongyong Fan

Degradation and osteogenic potential of a novel poly(lactic acid)/nano-sized β-tricalcium phosphate scaffold

The purpose of this study was to investigate the influence of nano-sized β-tricalcium phosphate (β-TCP) on the biological performance of poly (lactic acid) (PLA) composite scaffolds by using in vitro degradation and an in vivo model of heterotopic bone formation. Nano-sized β-TCP (nβ-TCP) was prepared with a wet grinding method from micro-sized β-TCP (mβ-TCP), and composite scaffolds containing 0, 10, 30, or 50 wt% nβ-TCP or 30 wt% mβ-TCP were generated using a freeze-drying method. Degradation was assessed by monitoring changes in microstructure, pH, weight, and compressive strength over a 26-week period of hydrolysis. Composite scaffolds were processed into blocks, and implanted into muscular pockets of rabbits after loading with recombinant human bone morphogenetic protein-2 (rhBMP-2). New bone formation was evaluated based on histological and immunohistochemical analysis 2, 4, and 8 weeks after implantation. The in vitro results indicated that the buffering effect of nβ-TCP was stronger than mβ-TCP, which was positively correlated with the content of nβ-TCP. The in vivo findings demonstrated that nβ-TCP enhanced the osteoconductivity of the scaffolds. Although composite scaffolds containing 30% nβ-TCP exhibited similar osteoconductivity to 50% nβ-TCP, they had better mechanical properties than the 50% nβ-TCP scaffolds. This study supports the potential application of a composite scaffold containing 30% nβ-TCP as a promising scaffold for bone regeneration.

In vitro biocompatibility evaluation of bioresorbable copolymers prepared from l-lactide, 1, 3-trimethylene carbonate, and glycolide for cardiovascular applications

PLLA-TMC-GA terpolymer was prepared by ring-opening polymerization of l-lactide, 1, 3-trimethylene carbonate (TMC), and glycolide (GA). The biocompatibility of terpolymer was evaluated in comparison with PLLA and PLLA-TMC with the aim of assessing their potential in the development of bioresorbable cardiovascular stents. Various aspects of in vitro biocompatibility were considered, including MTT assay, hemolytic test, dynamic clotting time, platelet adhesion, platelet activation, protein adsorption, plasma recalcification time and release of cytokines. The results revealed that the terpolymer presents good cytocompatibility and hemocompatibility. Moreover, no significant increase in the release of cytokines was detected. It is thus concluded that these polymers, in particular PLLA-TMC-GA terpolymer present good biocompatibility for cardiovascular applications.

Enzyme-Catalyzed Degradation of Biodegradable Polymers Derived from Trimethylene Carbonate and Glycolide by Lipases from Candida Antarctica and Hog Pancreas

Abstract Enzyme-catalyzed degradation of poly(trimethylene carbonate) homo-polymer (PTMC) and poly(trimethylene carbonate-co-glycolide) co-polymer (PTGA) was investigated in the presence of lipases from Candida antarctica and Hog pancreas. Degradation was monitored by gravimetry, size-exclusion chromatography (SEC), nuclear magnetic resonance (NMR), tensiometry and environmental scanning electron microscopy (ESEM). PTMC can be rapidly degraded by Candida antarctica lipase with 98% mass loss after 9 days, while degradation by Hog pancreas lipase leads to 27% mass loss. Introduction of 16% glycolide units in PTMC chains strongly affects the enzymatic degradation. Hog pancreas lipase becomes more effective to PTGA co-polymer with a mass loss of 58% after 9 days, while Candida antarctica lipase seems not able to degrade PTGA. Bimodal molecular weight distributions are observed during enzymatic degradation of both PTMC and PTGA, which can be assigned to the fact that the surface is largely degraded while the internal part remains intact. The composition of the PTGA co-polymer remains constant, and ESEM shows that the polymers are homogeneously eroded during enzymatic degradation. Contact angle measurements confirm the enzymatic degradation mechanism, i.e., enzyme adsorption on the polymer surface followed by enzyme-catalyzed chain cleavage.

Enhanced bone regeneration composite scaffolds of PLLA/β-TCP matrix grafted with gelatin and HAp

The composite polylactide PLLA/β-TCP scaffolds were fabricated by solution casting and were coated with gelatin/hydroxyapatite (Gel/HAp) to improve the biological properties of the composite scaffolds. The Gel/HAp mixture was prepared using an in situ reaction, and a grafting-coating method was used to increase the efficiency of coating the PLLA/β-TCP matrix with Gel/HAp. First, free amino groups were introduced by 1,6-hexanediamine to aminolyze the PLLA/β-TCP matrix surface. Second, glutaraldehyde was coupled to Gel/HAp as a crosslinking agent. The structure and properties of Gel/HAp-modified PLLA/β-TCP films were characterized by Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and water contact angle measurements (WCA). The experimental results show that 23 wt% HAp was uniformly dispersed in the gelatin coating by in situ synthesis. The Gel/HAp composite coating was successfully immobilized on the aminolyzed PLLA/β-TCP surface via a chemical grafting method, which promoted a lower degradation rate and was more hydrophilic than a physical grafting method. The Gel/HAp composite coating adhered tightly and homogeneously to the hydrophobic PLLA/β-TCP surface. Moreover, mouse embryo osteoblast precursor (MC3T3-E1) cells grown on the scaffolds were behaviorally and morphologically characterized. The results indicated that the Gel/HAp composite coating was favorable for the attachment and proliferation of preosteoblasts and that Gel/HAp-NH-PLLA/β-TCP would be a candidate scaffold for bone repair.

Improved cell adhesion and osteogenesis using a PLTGA (poly L-lactide, 1,3-trimethylene carbonate, and glycolide) terpolymer by gelatin-assisted hydroxyapatite immobilization for bone regeneration

A PLTGA (poly l-lactide, trimethylene carbonate, glycolide) terpolymer possesses great potential for orthopedic applications due to its excellent biocompatibility and controllable biodegradability. However, the unfavorable surface conditions of bare PLTGA such as its poor hydrophilicity and smooth morphology impede its clinical applications, highlighting the need for tailored surface modifications to improve its cytological behavior and osteogenic capacity. We herein develop a facile and effective strategy to deposit a gelatin/hydroxyapatite (GEL/HAP) hybrid coating onto the surface of PLTGA that involves consecutive chemical grafting and in situ reaction steps. Following the surface modification treatment, the resultant PLTGA scaffold with the GEL/HAP coating exhibited drastically improved hydrophilicity (79.1°vs. 48.2° in water contact angle) and increased surface roughness (18.4 vs. 267.9 nm, more than 14-fold, in root-mean-square roughness), respectively. In addition, preosteoblast (MC3T3-E1) cells were seeded onto the bare/modified PLTGA scaffold to evaluate biological performance, including cell adhesion, proliferation, mineralization and osteogenic differentiation. Based on these results, the GEL/HAP hybrid coating can endow the PLTGA terpolymer substrate with enhanced cell adhesion, proliferation and osteogenic functionality. Overall, post-treatment of PLTGA with the GEL/HAP hybrid coating may be a promising methodology in bone regeneration applications.

Composites of poly(L-lactide-trimethylene carbonate-glycolide) and surface modified calcium carbonate whiskers as a potential bone substitute material

Calcium carbonate whisker (CCW) particles were surface modified by grafting of poly(L-lactide) (PLLA) chains in order to improve their affinity to a poly(L-lactide-trimethylene carbonate-glycolide) (PLTG) terpolymer matrix. Composites of the PLTG matrix with CCW and PLLA-g-CCW of various contents were prepared by mixing in solution followed by solvent evaporation. The structure and properties of pure CCW, surface modified PLLA-g-CCW and PLTG/PLLA-g-CCW composites were investigated using Fourier transfer-infrared spectrometry (FT-IR), mechanical testing, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), contact angle measurement, thermal gravity analysis (TGA) and differential scanning calorimetry (DSC). Data show that PLLA chains were successfully grafted on the CCW surface. The PLTG/PLLA-g-CCW composites exhibit a higher tensile strength and elongation at break than neat PLTG. Optimal values are obtained with a PLLA-g-CCW content of 2 wt%. It is assumed that PLLA-g-CCW particles present both reinforcing and toughening effects on the PLTG matrix. The cytocompatibility of the materials was evaluated from cell morphology and MTT assay using the L929 mouse fibroblast cell line. The results indicate that the composite presents very low cytotoxicity. Therefore, PLTG/PLLA-g-CCW composites with improved mechanical properties and good cytocompatibility could be promising as a potential bone substitute material.

The accelerating effect of the star-shaped poly(D-lactide)-block-poly(L-lactide) stereoblock copolymer on PLLA melt crystallization

A star-shaped poly(D-lactide)-block-poly(L-lactide) (PDLA-PLLA) stereoblock copolymer was introduced into a poly(L-lactide) (PLLA) matrix. The impacts of the PDLA-PLLA copolymer on PLLA melt crystallization, mechanical properties and rheological properties were investigated. The research results indicated that the PDLA-PLLA copolymer could significantly accelerate the crystallization rate of PLLA. The non-isothermal crystallization results showed that the crystallization temperature shifted to a higher temperature with the increase in the addition of the PDLA-PLLA copolymer. The crystallization temperature increased to about 25 °C with the addition of 10 wt% PDLA-PLLA copolymer. The isothermal crystallization results showed that the half-time of crystallization (t0.5) decreased from 10 min to 2.5 min at 120 °C as the PDLA-PLLA copolymer fraction increased from 0 to 10 wt%. Nucleation efficiency (NE) was used to describe the nucleation efficiency of the PDLA-PLLA copolymer. The highest NE of 65% was obtained for PLLA samples with a PDLA-PLLA copolymer content of 10 wt%. As polarized optical microscopy revealed, this accelerating effect resulted from the good nucleation ability of the PDLA-PLLA copolymer. Moreover, dynamic mechanical analysis results indicated that the addition of the PDLA-PLLA copolymer enhanced the storage modulus of PLLA in the glass state. Rheological properties of nucleated PLLA showed the existence of a network structure of a stereocomplex crystallite (sc-crystallite) above 5 wt% addition of the PDLA-PLLA copolymer.

Biodegradable PTLGA Terpolymers versus Collagen Implants Used as an Adjuvant in Trabeculectomy in Rabbit Eye

Purpose. To evaluate the effectiveness and safety of three biodegradable terpolymers prepared from L-lactide, trimethylene carbonate, and glycolide (PTLGA) as an aid for trabeculectomy compared with the Ologen (OLO). Methods. Trabeculectomy was carried out on rabbits with implantation made from OLO or three PTLGA terpolymers. Intraocular pressure (IOP) was recorded 1, 2, 3, and 6 months postoperatively and bleb evaluations were performed using ultrasound biomicroscopy (UBM) 3 months after surgery, optical coherence tomography (OCT) every month, and transmission electron microscopy (TEM) six months after surgery followed by histological examination 1, 2, 3, and 6 months postoperatively. Result. IOP was significantly reduced in all groups after surgery. There were no significant differences in the IOL between groups at any time after implantation. There was no significant difference between the groups examined by OCT, UBM, and TEM. Exposure of the implant was observed in one eye from the OLO group and one eye in the P1. Subconjunctiva hyperblastosis was observed in one eye from group P3 and two eyes from the OLO group. Conclusions. Subconjunctival implantation of filtering devices made from PTLGA may present a safe and effective additional surgical tool for the treatment of filtering surgery. Fewer complications were observed in the group with P2 implants compared to other groups.

Bioinspired Modification of Poly(L-lactic acid)/Nano-Sized β-Tricalcium Phosphate Composites with Gelatin/Hydroxyapatite Coating for Enhanced Osteointegration and Osteogenesis

Compared to pure poly(L-lactic acid) (PLLA), PLLA/nano-sized β-tricalcium phosphate (PLLA/nβ-TCP) composites show both superior interfacial compatibility and osteoinductive, and consequently hold great potential for bone defect repair applications. However, their dismal osteointegration limits their further development in bone regeneration, adding the need for tailored modification. In this study, a bioinspired modification approach was proposed to construct gelatinhydroxyapatite (GEL/HAP) coating onto PLLA/nβ-TCP composites by combining chemical grafting with in situ reaction methods. The incorporation of the biomimetic GEL/HAP coating substantially improved MC3T3-E1 cell adhesion, proliferation and osteogenic differentiation, as demonstrated by morphological observation. Cell Counting Kit-8 (CCK-8) assay, alkaline phosphate activity test (ALP), and quantitative real-time polymerase chain reaction (qRT-PCR) analysis. Furthermore, GEL/HAP-PLLA/nβ-TCP composites and their control counterparts (i.e., bare PLLA/nβ-TCP) were synchronously implanted into femoral condylar defects of an identical rabbit. Characterizations including microcomputed tomography (micro-CT), histological analysis and the push-out test revealed that the biomimetic coating not only improved osteointegration but also significantly promoted bone regeneration. Overall, for the first time, bioinspired surface modification of the PLLA/nβ-TCP composite with GEL/HAP coating was demonstrated to be an efficient strategy for enhancing the osteointegration and osteogenesis functions of bone implants.