Functional bone tissue engineering has arisen to address the need for implantable bone tissue in cases of trauma or disease. Some challenges to generating functional bone tissue have included the need to identify biocompatible substrates with appropriate mechanical properties, as well as a suitable cell source. Subsequently, human adipose-derived adult stem cells (hASCs) have been used in an assortment of tissue engineering applications in recent years. They are attractive cells for use in clinical applications due to their multi-lineage potential, relative abundance, and ease of harvest relative to other cell lines. The pluripotency of hASCs isolated from adipose tissue and used in the various studies described here has been tested by inducing both osteogenic and adipogenic differentiation pathways. These hASCs were then seeded on three different types of three-dimensional scaffolds. In the first study, hASC viability and proliferation were compared between custom-designed titanium implants and commercially available implants of the same composition. In the second study, viability and proliferation of hASCs were assessed for cell-seeded collagen-PCL sheath-core electrospun scaffolds. Osteogenic differentiation of hASCs on these scaffolds was also quantified. In the final study, islands-in-the-sea nanoporous fibers were designed and fabricated for bone tissue engineering applications. Initial cell viability was examined over a 4 week time period for hASCs seeded on the novel scaffolds.
Titanium implants are commonly used in medical procedures such as hip replacements. There is a need however, to design patient specific titanium scaffolds. An important factor in scaffold acceptance by the body is osseointegration, or bone ingrowth. Micromotion between the implant and surrounding tissue can hinder osseointegration, and ultimately lead to implant failure. Using computed tomography (CT) data, micromotion can be minimized by designing patient-specific implants. Implants from these designs can then be fabricated by electron beam melting (EBM) using titanium powder, built layer by layer to the appropriate specifications. In this study, hASCs were used to validate the effects of EBM processing when compared to commercially available medical-grade titanium implants. Results suggest EBM fabricated porous scaffolds promote hASC proliferation and do not adversely affect biocompatibility.
Natural polymers have also been investigated for bone tissue engineering applications. This study describes the design of electrospun fibers, which are on a similar size scale to the native collagen fibrils found in human bone tissue. Polycaprolactone (PCL) electrospun fibers were coated with type I collagen, a natural component of bone, during a co-axial electrospinning process, generating a sheath-core fiber morphology. Human ASCs seeded on the scaffolds were differentiated down the osteogenic lineage, and calcium deposition was compared to that of hASCs seeded on uncoated PCL scaffolds. The results indicated the collagen coating increased cell spreading and osteogenic differentiation of hASCs seeded on the sheath-core electrospun scaffolds.
Nanoporous fibers are also desirable for bone tissue applications, as the micropores should enhance nutrient delivery and waste removal. In the final study, melt spun islands-in-the-sea fibers were extruded with a polylactic acid (PLA) sea matrix and islands comprised of EastONE, a water-dispersible sulfopolyester. The EastONE polymer was also added to the sea matrix in various concentrations, yielding micropores within the PLA sea after washing. These fibers were then knitted into three-dimensional fabrics, and the physical properties characterized. Microscopic observations revealed the presence of micropores throughout the fiber structure. Removal of the EastONE additive was also confirmed by weight loss measurements obtained before and after washing. Human ASCs were cultured on these three-dimensional fabrics for four weeks in vitro, and examined for cell viability. Confocal images confirmed the presence of viable hASCs throughout the four week culture period on both solid and porous scaffolds.
|Zuk PA, Zhu M, Mizuno H, Huang J, Futrell JW, Katz AJ, Benhaim P, Lorenz HP, Hedrick MH. Multilineage cells from human adipose tissue: implications for cell-based therapies. Tissue Eng. April 2001;7(2):211-228.
|Lewis G. Properties of acrylic bone cement: state of the art review. J Biomed Mater Res. Summer, 1997;38(2):155-182.
|Karageorgiou V, Kaplan D. Porosity of 3D biomaterial scaffolds and osteogenesis. Biomaterials. September 2005;26(27):5474-5491.
|Rezwan K, Chen QZ, Blaker JJ, Boccaccini AR. Biodegradable and bioactive porous polymer/inorganic composite scaffolds for bone tissue engineering. Biomaterials. June 2006;27(18):3413-3431.
|Sachlos E, Czernuszka JT. Making tissue engineering scaffolds work: review on the application of solid freeform fabrication technology to the production of tissue engineering scaffolds. Eur Cell Mater. 2003;5:29-40.
|Yang S, Leong K-F, Du Z, Chua C-K. The design of scaffolds for use in tissue engineering, I: traditional factors. Tissue Eng. December 2001;7(6):679-689.
|Yoshimoto H, Shin YM, Terai H, Vacanti JP. A biodegradable nanofiber scaffold by electrospinning and its potential for bone tissue engineering. Biomaterials. May 2003;24(12):2077-2082.