Biomechanical study of the edge outgrowth phenomenon of encapsulated chondrocytic isogenous groups in the surface layer of hydrogel scaffolds for cartilage tissue engineering

In cartilage tissue engineering, hydrogel is widely used as the scaffold for hosting and culturing chondrocyte suspension during neo-tissue formation. In order to develop cultured chondrocytes into a functional cartilage equivalent, the hydrogel must provide an ideal microenvironment for the rapidly proliferating chondrocytes. At the same time, the essential functions of chondrocytes, such as the secretion of type II collagen and glycosaminoglycans, must be maintained. In these studies, we quantitatively characterize the mechanobiology underlying a newly discovered “edge flourish” phenomenon of cultured chondrocytes within a three-dimensional agarose hydrogel, which may ultimately nurture scaffold-free cartilaginous tissue regeneration. First, real-time microscopy was used to track the spatiotemporal distributions of chondrocytes at different focal planes. The chondrocytes were observed to exhibit abundant neo-tissue outgrowth and significant cartilaginous phenotype at the edge of the hydrogel compared to those inside the hydrogel bulk. Secondly, the hydrogel surface stresses induced by the encapsulated chondrocytes were characterized quantitatively in real time using the finite-element method. Finally, the real-time three-dimensional matrix deformations of agarose hydrogel under the influence of chondrocytes were measured using a multiple-particle tracking assay. Our results indicate that the mechanism of the “edge flourish” phenomenon is induced by the oriented outgrowth of chondrocytic isogenous groups located at the edge of hydrogel. These isogenous groups exhibit directed outgrowth towards the surface of the hydrogel and eventually generate substantial surface tension on the interface of hydrogel and medium. Ultimately, the encapsulated chondrocytes closest to the hydrogel/medium interface will spontaneously sprout out of the hydrogel and form a layer of rich proliferative and chondrocytic extracellular matrix secreting chondrocytes at the surface of the hydrogel.     

聚乙烯醇/羟基磷灰石复合水凝胶修复膝关节软骨缺损的组织相容性

背景：将羟基磷灰石与聚乙烯醇水凝胶复合之后应用于软骨缺损修复中,可在软骨连接部位产生良好的生物活性,有效促进骨细胞的生长,提高植入材料的稳定性和生物活性。 目的：观察聚乙烯醇/羟基磷灰石复合水凝胶修复兔膝关节软骨缺损的组织相容性。 方法：取20只新西兰大白兔,随机分为空白对照组(n=6)与实验组(n=14),构建单侧膝关节软骨缺损模型,空白对照组不予以修复,实验组予以聚乙烯醇/羟基磷灰石复合水凝胶修复。术后4,8,12周获取膝关节标本进行大体观察及组织学观察。 结果与结论：空白对照组关节软骨面在术后12周内始终未得到修复,软骨下缺损存在肉芽组织充填现象,组织学也未见明显修复。实验组术后4周可见聚乙烯醇/羟基磷灰石复合水凝胶填充于缺损处,与周围软骨组织之间连接紧密,且存在清晰的界限,未出现细胞长入情况;至12周时,聚乙烯醇/羟基磷灰石复合水凝胶呈白色、半透明状,表面平坦,与周围软骨组织之间存在清晰界限,两者交界面存在软骨细胞大量增殖现象,与周围组织发生紧密结合,二者之间无间隙,底部与软骨下骨紧密连接,并存在骨样组织长入。表明聚乙烯醇羟基磷灰石复合水凝胶修复兔膝关节软骨缺损具有良好的组织相容性。 中国组织工程研究杂志出版内容重点：生物材料;骨生物材料; 口腔生物材料; 纳米材料; 缓释材料; 材料相容性;组织工程     

The use of covalently immobilized stem cell factor to selectively affect hematopoietic stem cell activity within a gelatin hydrogel

Hematopoietic stem cells (HSCs) are a rare stem cell population found primarily in the bone marrow and responsible for the production of the body's full complement of blood and immune cells. Used clinically to treat a range of hematopoietic disorders, there is a significant need to identify approaches to selectively expand their numbers ex vivo. Here we describe a methacrylamide-functionalized gelatin (GelMA) hydrogel for in vitro culture of primary murine HSCs. Stem cell factor (SCF) is a critical biomolecular component of native HSC niches in vivo and is used in large dosages in cell culture media for HSC expansion in vitro. We report a photochemistry based approach to covalently immobilize SCF within GelMA hydrogels via acrylate-functionalized polyethylene glycol (PEG) tethers. PEG-functionalized SCF retains the native bioactivity of SCF but can be stably incorporated and retained within the GelMA hydrogel over 7 days. Freshly-isolated murine HSCs cultured in GelMA hydrogels containing covalently-immobilized SCF showed reduced proliferation and improved selectivity for maintaining primitive HSCs. Comparatively, soluble SCF within the GelMA hydrogel network induced increased proliferation of differentiating hematopoietic cells. We used a microfluidic templating approach to create GelMA hydrogels containing gradients of immobilized SCF that locally direct HSC response. Together, we report a biomaterial platform to examine the effect of the local presentation of soluble vs. matrix-immobilized biomolecular signals on HSC expansion and lineage specification. This approach may be a critical component of a biomaterial-based artificial bone marrow to provide the correct sequence of niche signals to grow HSCs in the laboratory.