Xueli Mao

Amphiphilic Triblock copolymers of Methoxy-poly(ethylene glycol)-b-poly(L-lactide)-b-poly(L-lysine) for enhancement of Osteoblast attachment and growth

Amphiphilic triblock copolymers of methoxy-poly(ethylene glycol)-poly(L-lactide)-poly(L-lysine) (MPEG-b-PLLA-b-PLL) (Mn=8540-22 240) were synthesized through the ring-opening polymerization of Nepsilon-(Z)-lysine-N-carboxyanhydrides (N(epsilon)-(Z)-Lys-NCA) using MPEG-b-PLLA-NH2 as a macroinitiator. The triblock copolymers and diblock precursors were characterized by 1H NMR, ATR-FTIR, and GPC. The chain lengths of each block could be controlled by varying the feed ratios of the monomers. The surface properties of films of PLLA modified by blending with the triblock copolymers were investigated by XPS and AFM and demonstrated an enrichment of PLL blocks on the surface of the PLLA film. No cytotoxicity was detected on a range of modified PLLA films arising from the incorporation of the triblock copolymers. The triblock copolymers MPEG-b-PLLA-b-PLL showed better surface properties in promoting osteoblast adhesion and proliferation compared with pure PLLA and PLLA modified with MPEG-b-PLLA diblock copolymers. This study demonstrated that the triblock copolymers containing free amino groups, which self-segregate on the surface of biodegradable polyesters, have potential for applications in cell delivery and tissue engineering.

Enhanced human bone marrow stromal cell affinity for modified poly(L-lactide) surfaces by the upregulation of adhesion molecular genes

To enhance and regulate cell affinity for poly (L-lactic acid) (PLLA) based materials, two hydrophilic ligands, poly (ethylene glycol) (PEG) and poly (L-lysine) (PLL), were used to develop triblock copolymers: methoxy-terminated poly (ethylene glycol)-block-poly (L-lactide)-block-poly (L-lysine) (MPEG-b-PLLA-b-PLL) in order to regulate protein absorption and cell adhesion. Bone marrow stromal cells (BMSCs) were cultured on different composition of MPEG-b-PLLA-b-PLL copolymer films to determine the effect of modified polymer surfaces on BMSC attachment. To understand the molecular mechanism governing the initial cell adhesion on difference polymer surfaces, the mRNA expression of 84 human extracellular matrix (ECM) and adhesion molecules was analysed using quantitative reverse transcriptase polymerase chain reaction (qRT-PCR). It was found that down regulation of adhesion molecules was responsible for the impaired BMSC attachment on PLLA surface. MPEG-b-PLLA-b-PLL copolymer films improved significantly the cell adhesion and cytoskeleton expression by upregulation of relevant molecule genes significantly. Six adhesion genes (CDH1, ITGL, NCAM1, SGCE, COL16A1, and LAMA3) were most significantly influenced by the modified PLLA surfaces. In summary, polymer surfaces altered adhesion molecule gene expression of BMSCs, which consequently regulated cell initial attachment on modified PLLA surfaces.

A novel xylene substitute for histotechnology and histochemistry.

Abstract Propylene glycol methyl ether (PGME) exhibits excellent solvent and coupling properties. A toxicity database provided evidence suggesting that PGME might be a useful substitute for xylene in histotechnology and histochemistry applications. Tissue specimens were fixed, cleared in either PGME or xylene, embedded in paraffin wax, then dewaxed in either PGME or xylene. Sections were treated with the following stains: hematoxylin & eosin (H & E), three special stains of the Gordon/Sweet silver staining method, PAS, and Massons trichrome, and immunostains including actin, CD3, CD34, CK, CK7/CK9, Ki-67, and ER/PR. The sections were mounted in a resinous medium consisting of PGME and pinene copolymer, then examined under a microscope. Variables such as water tolerance, dimension change, organic solvency, and anti-fading efficacy also were assessed. Depending on the application, PGME performance was equal to or exceeded that of xylene. PGME provided better optical clarity and nuclear detail, did not harden the tissue samples, conserved tissue antigenicity, and was amenable to resinous mounting. Tissues not dehydrated with absolute ethanol also were processed properly. Tissues treated with PGME did not warp or contract compared to those treated with xylene (p < 0.0001). PGME, however, exhibited less organic solvency than xylene. There was no discernible change in the colors of stains in sections processed with PGME even after storage for two years. These results suggest that PGME is a novel xylene substitute for applications in histotechnology and histochemistry.

Methoxy-Poly(ethylene glycol) Modified Poly(L-lactide) Enhanced Cell Affinity of Human Bone Marrow Stromal Cells by the Upregulation of 1-Cadherin and Delta-2-catenin

Poly(l-lactide) (PLLA), a versatile biodegradable polymer, is one of the most commonly-used materials for tissue engineering applications. To improve cell affinity for PLLA, poly(ethylene glycol) (PEG) was used to develop diblock copolymers. Human bone marrow stromal cells (hBMSCs) were cultured on MPEG-b-PLLA copolymer films to determine the effects of modification on the attachment and proliferation of hBMSC. The mRNA expression of 84 human extracellular matrix (ECM) and adhesion molecules was analyzed using RT-qPCR to understand the underlying mechanisms. It was found that MPEG-b-PLLA copolymer films significantly improved cell adhesion, extension, and proliferation. This was found to be related to the significant upregulation of two adhesion genes, CDH1 and CTNND2, which encode 1-cadherin and delta-2-catenin, respectively, two key components for the cadherin-catenin complex. In summary, MPEG-b-PLLA copolymer surfaces improved initial cell adhesion by stimulation of adhesion molecule gene expression.

Novel Synthetic Bio-Mimic Polymers for Cell Delivery

Cell-based therapy is one of the major potential therapeutic strategies for cardiovascular, neuronal and degenerative diseases in recent years. The aims of this study is to develop a novel biomimic polymeric materials which will facilitate the delivery cells, control cell bioactivities and enhance the focal integration of graft cells with host tissues. We synthesized a novel tri-block copolymer, methoxy-terminated poly (ethylene glycol) (MPEG)-polyL-lactide (PLLA)-polylysine (PLL) via sequential polymerization of PLLA onto MPEG, followed by ring opening polymerization of PLL onto the functionalized chain end. The triblock copolymer (5%) was then mixed with high molecular weight PLLA (95%) to form cell-delivery membranes. The spectra of copolymers were determined by NMR and ATR-FTIR spectroscopy. Human osteoblasts were used for testing biocompatibility and initial cellular reaction. It was noted that no cytotoxicity was detectable in our synthesized copolymers. Compared with pure PLLA and diblock copolymers, the triblock copolymers showed significantly better cell adhesion and proliferation. Interestingly we identified that cellular activity (attachment, proliferation and differentiation) could be regulated by the molecular weight and composition of the triblock copolymers. In conclusion controllable synthetic copolymers can be designed and synthesized to modulate cellular function in facilitating tissue repair and regeneration.