Stephenson School of Biomedical Engineering, University of Oklahoma, Norman, OK 73019, USA.
Chemistry and biochemistry University of Oklahoma, Norman, OK 73019, USA.
Acta Biomater. 2019 Sep 1;95:176-187. doi: 10.1016/j.actbio.2019.01.041. Epub 2019 Jan 19.
Bioprinting technologies have tremendous potential for advancing regenerative medicine due to the precise spatial control over depositing a printable biomaterial, or bioink. Despite the growing interest in bioprinting, the field is challenged with developing biomaterials for extrusion-based bioprinting. The paradigm of contemporary bioink studies relies on trial-and-error methods for discovering printable biomaterials, which has little practical use for others who endeavor to develop bioinks. There is pressing need to follow the precedent set by a few pioneering studies that have attempted to standardize bioink characterizations for determining the properties that define printability. Here, we developed a pentenoate-functionalized hyaluronic acid hydrogel (PHA) into a printable bioink and used three recommended, quantitative rheological assessments to characterize the printability: 1) yield stress, 2) viscosity, and 3) storage modulus recovery. The most important characteristic is the yield stress; we found a yield stress upper limit of ∼1000 Pa for PHA. Measuring the viscosity was advantageous for determining shear-thinning behavior, which aided in extruding highly viscous PHA through a nozzle. Post-printing recovery is required to maintain shape fidelity and we found storage modulus recoveries above ∼85% were sufficient for PHA. Two formulations had superior printability (i.e., 1.5 MDa PHA - 4 wt%, and 1 MDa PHA - 8 wt%), and increasing cell concentrations in PHA up to 9 × 10 cells/mL had minimal effects on the printability. Even so, other factors such as sterilization and peptide modifications to enhance bioactivity may influence printability, highlighting the need for investigators to consider such factors when developing new bioinks. STATEMENT OF SIGNIFICANCE: Bioprinting has potential for regenerating damaged tissues; however, there are a limited number of printable biomaterials, and developing new bioinks is challenging because the required material physical properties for extrusion-based printing are not yet known. Most new bioinks are developed by trial-and-error, which is neither efficient nor comparable across materials. There is a need for the field to begin utilizing standard methods proposed by a few pioneering studies to characterize new bioinks. Therefore, we have developed the printability of a hyaluronic acid based-hydrogel and characterized the material with three quantitative rheological tests. The current work impacts the bioprinting field by demonstrating and encouraging the use of universal bioink characterizations and by providing printability windows to advance new bioink development.
生物打印技术在再生医学领域具有巨大的潜力，因为它可以精确控制可打印生物材料（或生物墨水）的空间沉积。尽管人们对生物打印技术越来越感兴趣，但该领域仍面临着为基于挤出的生物打印开发生物材料的挑战。当代生物墨水研究的范例依赖于反复试验的方法来发现可打印的生物材料，这对于其他试图开发生物墨水的人来说几乎没有实际用途。迫切需要遵循少数先驱性研究设定的先例，这些研究试图为确定可打印性定义的特性对生物墨水进行特征描述标准化。在这里，我们将戊烯酸官能化透明质酸水凝胶（PHA）开发成一种可打印的生物墨水，并使用三种推荐的定量流变学评估来对其可打印性进行特征描述：1）屈服应力，2）粘度和 3）储能模量恢复。最重要的特性是屈服应力；我们发现 PHA 的屈服应力上限约为 1000 Pa。测量粘度有利于确定剪切稀化行为，这有助于通过喷嘴挤出高粘度的 PHA。需要进行后打印恢复以保持形状保真度，我们发现储能模量恢复超过 85%就足以满足 PHA 的要求。两种配方具有更好的可打印性（即 1.5 MDa PHA-4wt%和 1 MDa PHA-8wt%），并且将 PHA 中的细胞浓度增加到 9×10 个细胞/mL 对可打印性的影响很小。即便如此，其他因素，如灭菌和肽修饰以增强生物活性，也可能影响可打印性，这凸显了研究人员在开发新生物墨水时需要考虑这些因素。 意义声明：生物打印具有再生受损组织的潜力；然而，可打印的生物材料数量有限，并且开发新的生物墨水具有挑战性，因为基于挤出的打印所需的材料物理特性尚不清楚。大多数新的生物墨水是通过反复试验开发的，这种方法既不高效也不具有材料间的可比性。该领域需要开始利用少数开创性研究提出的标准方法来对新的生物墨水进行特征描述。因此，我们已经开发了基于透明质酸的水凝胶的可打印性，并使用三种定量流变学测试对该材料进行了特征描述。目前的工作通过展示和鼓励使用通用的生物墨水特征描述以及提供推进新生物墨水开发的可打印性窗口来影响生物打印领域。
