Biomedical Engineering Reference
In-Depth Information
synthetic nanotubes, nanoparticles, molecular engines, and also the study of cellular nano-
structures such as pores, envelopes, chromosomes (DNA), etc.
Health and lifestyle improvements have caused a progressive increase in old age groups
around the world [2]. As a result, the body and its organs can suffer disease or damage and
these global changes cause pressure to discover new methods for replacement of organs,
joints, etc., to support the aging population. It is further clear that the numbers of allograft
transplants are not sufficient and the adverse immune reactions with transplanted organs
leading to the need for immunosuppressive drugs coupled to limitations in donors make
regeneration of organs and/or engineered replacements very attractive [3].
Manipulation of cellular fates is one of the most important aspects of the biologists'
interests in developing new materials for tissue engineering. Use of these methods in cell
therapy and replacement of body tissues or organs using the multipotent stem cells taken
from the same patient is a particular focus. This scope of such innovation is constantly
expanding as more is discovered about the usefulness of these adult stem cells. Engineering
the tissues and making new organs are major drivers in regenerative medicine [4-6]. Making
bone tissue [7, 8], joint [9-11], tendon [11], heart [12-14], bladder [15], pancreatic island
cells, liver and hepatobilliary system [16, 17], kidney [18, 19], eyelayers [20], brain, and neural
tissues [21], and many other tissues, are under research and at various stages of success/
clinical usage [22].
Mesenchymal Stem Cells
Stem cells are capable of making one or several tissues and organs according to body needs,
based on complex messages at different developmental and regenerative stages. The other
characteristic aspect of stem cells is their ability to replicate, making a cell similar to them-
selves (self-renewal) and another daughter cell that will also be a stem cell (symmetrical
self-renewal) or a specialized, progenitor cell (asymmetrical self-renewal). As well as pluripo-
tent embryonic stem cells, there are multipotent adult stem cells throughout the body, residing
in niches in many tissues and organs. They are supported by special microenvironments
(lacuna or niches) surrounded by blood vessels, neurons, supportive cells, and soft tissue. This
environment works to control quiescence, a way of preserving stem-cell numbers without
DNA damage and self-renewal/differentiation based on tissue demand [23, 24]. It is hoped
that their potential can be tapped to aid with transplantation, organ donation and rejection,
malfunctioning organs and limbs, genetic diseases, cancer treatment, threatening infectious
diseases, and many other medical issues.
Mesenchymal stem cells (MSCs) are a type of adult stem cell, residing since early neonatal
(cellular) phase, in special niches close to the red bone marrow and surrounded by neural,
vascular, and bone tissue. The laboratory characteristics of MSCs are: (i) adherence to tissue
plastic culture dishes under standard culture conditions; (ii) cell surface characterization
(e.g., positive for CD73, CD90, and CD105, and negative for CD11b or CD14, CD34, CD45,
CD79α or CD19, HLA-DR); and (iii)
in vitro
mesodermal differentiation [25, 26]. They are
typically considered capable of differentiation to fibroblasts, osteoblasts, chondrocytes, and
adipocytes [27, 28].
It has been shown that there is a strong correlation between changes in focal adhesion
(FA) complex (larger, mature, highest in number) and MSC differentiation toward, for
example osteoblasts and adipocytes, with MSCs with very few, small adhesions forming
fat and MSCs with supermature (>5 μm in length) adhesions forming bone [29-33], as will
be discussed later. This information on adhesions linked to differentiation potential of the
MSCs could be used for tissue engineering, especially for bone, cartilage, and tendon tissue
