Biomaterials in Tissue Engineering: Autografts and Allografts in Spinal Fusion Surgery

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Contents
CHAPTER 1: INTRODUCTION........................................................................................................................3
Background of the study..........................................................................................................................3
Introduction.............................................................................................................................................4
CHAPTER 2: LITERATURE REVIEW................................................................................................................7
Autografts................................................................................................................................................7
Advantages, disadvantages and Considerations of autograft..............................................................7
Allograft Bone in Cervical Spinal Fusion Surgery......................................................................................8
Uses of Allograft Bone.......................................................................................................................10
Considerations for Allograft...............................................................................................................10
Bioactive glass.......................................................................................................................................12
Features and Benefits of Bioactive glass............................................................................................15
Bone Morphogenetic Protein................................................................................................................16
Demineralized Bone Matrix...................................................................................................................17
Hydroxyapatite......................................................................................................................................18
Calcium Phosphate/Calcium triphosphate............................................................................................20
Surgeons opinion about different materials and how much materials are surgeon using per surgery. 23
CHAPTER 3: RESEARCH METHODLOGY......................................................................................................25
Data collection Method.........................................................................................................................25
CHAPTER 4: RESULTS AND DISCUSSION.....................................................................................................26
Cost Comparisons of the Various Biomaterials......................................................................................26
Autograft versus allograft......................................................................................................................26
Discussion..............................................................................................................................................29
References.................................................................................................................................................31

CHAPTER 1: INTRODUCTION
Background of the study
A surgical repair or replacement is necessitated by trauma, diseases or degeneration.
When an individual experiences pain in the joints, the main focus tends to relief of the pain
restoration of the health of the individual to a not only healthy but functional lifestyle. This
normally comes with the replacement of some of the skeletal parts including hips, finger joints,
elbows, teeth, knees, vertebrae or even repair of the mandibles. The value of biomedical
materials globally currently stands at approximately $24,000M with dental and orthopedic
applications accounting for about 55% of the total market for biomaterials. In the year 2000, the
value of orthopedic products in the market was more than $13 billion and an expansion in such
trends expected to continue citing a number of factors among them the ageing population,
advancements and improvements in technology and lifestyle, an increased taste and preference
by the younger to middle aged population to undertake surgery, desire for better function,
enhanced aesthetics as well as better comprehension of the functionality of the body.
The use and requirements for biomaterials in tissue engineering is strictly defined with
biocompatibility being the top of the agenda for the choice of any material for use for their
orthopedic or diagnostic purposes. For the case of biocompatibility, the scaffolds and bioreactors
have to attain qualities among them tissue friendly so as not to invoke an immune-response. At
best, biomaterials should be supportive of the cellular and tissue functions among the adhesion,
proliferation and differentiation through its special surface in chemistry. Another important
requirement for scaffolds is porosity which is supposed to be at least 90% so as to allow cells to
seed evenly and promote vascular growth after implantation. Controlled biodegradation gains
concern especially under circumstance that implanted materials are replaced by healthy tissues

and then biomaterial slowly degrades in the body of the host. Biomaterials are either natural or
synthetic.
Introduction
The science of biomaterials was in place more than a century ago when artificial devices
and objects were enhanced to the point where they could replace different components of the
human body. A biomaterial is a substance that can has been tailored to interact with the systems
of biology for the purposes of medical practice. These composites have the ability to be in
contact with the fluids of the body and tissues from relatively long periods of time without
invoking any significant if any adverse reactions with the body systems. Biomedical materials
are used either of therapeutic i.e. treatment, replacement or repair of a tissue that functions in the
body or they can be used for diagnostic purposes (Bandyopadhyay, 2013). They are non-viable
materials that have the capability to be implanted to replace or repair a tissue that is missing or
worn out. Biomaterial can either be synthesized in the laboratory or be of natural origin.
Biomaterials traces its roots as far back as the ancient Phoenicia during which gold wires
were used in binding together loose teeth by tying artificial teeth to the neighboring natural teeth.
Implementation of bone plates was successful in stabilization of bone fractures and thus
accelerating the process of healing in the 1900s. Artificial hip joints and heart valves were under
development and replacement of blood vessels was undergoing clinical trials in the 1950s and
60’s (Black, 2014).
Biomaterials are categorized into metals, ceramics, polymers and natural biomaterials.
Metals are the group of biomaterials that is most commonly used due to the ability to bear loads.
This load bearing ability makes metals ideal for such practices as knee implants and total hip
replacements. These metallic implants comes in various ranges of shapes and sizes and do vary

from modest wires to screw to plates for fixation of fractures and to as complicated as total joint
prostheses. artificial joint implantation have been successful on joints including ankles, shoulder,
hops and knees with different metals currently being used in various medical applications to
meet different surgical needs. Cobalt-base alloys, stainless steel, titanium alloys and pure
titanium are among the most commonly used metals as biomaterials (Dobke, 2013).
A good biomaterial of metallic nature should have the same values of Young’s modulus
as the bone or the tissues for which it is replacing. The surrounding tissues may degenerate as a
result of lack of mechanical loading in cases where the biomaterial is carrying too much loading.
On the other hand, a biomaterial that cannot carry adequate load cannot make an adequate
replacement (DiMasi, 2014).
Ceramics and composites: these biomaterials are mostly used on dental applications
including fillings, crowns and dentures. The application and utilization of ceramics is limited to
the cats that they have poor toughness to fracture due to their brittle property. Ceramics cannot
be applied in implantations that required high tolerance of loads. Despite the shortcomings,
calcium phosphates have been applied in augmentation and bone repair while alumina and
zirconia have formed fundamental materials in joint replacement (Black, 2014).
Composites widely find their applications in dentistry. PMMA-glass filter and BIS-
GMA-quartz-silica filler are the two most commonly used composites and are mostly used for
dental filling and restoration. Other applications of composts include prostheses which are
favored by heir light weight and high loading capability.
Polymers are grouped as one of the most versatile biomaterials and have the widest range
of applications from scaffolds used in tissue engineering to the PLGA that is used in drug

delivery. It is possible to mold polymers into any desirable shapes or size. Collagen or synthetic
fibre is used in making scaffolds that are used in tissue engineering (Bronzino, 2016). Scaffolds
are very important as they offer both the molecular and physical cues that control development
of the donor cells. The extra cellular matrix is normally used in the provision of these cues.
Nevertheless, the polymers also have the capability to provide protection to the donor cells from
the different immune systems that are available as a result of the transplant. Lastly, the three
dimensional space offers a convenient way of package to the cells thereby prompting growth
after transplantation has been done. It is possible to design the pores in the polymers in such a
way that they are large enough to allow the growth of endothelial cells and blood vessels into the
scaffold.

CHAPTER 2: LITERATURE REVIEW
Autografts
Autograft, also known as autologous bone or autogenous bone graft is harvesting of the bone
from a patient and transferring it to the part of the spine that is to be fused. A separate spinal
fusion procedure is carried out during spinal fusion surgery to extract a bone from another part of
the body of the patent and place it in the region of the spine that is to undergo fusion. This is a
surgical process and is termed as harvesting of the bone graft (Bronzino, 2016). The procedure is
normally carried out through a separate incision on anterior fusions and through a same incision
in the posterior fusions.
Harvesting of the bone is normally done from one of the bones of the patient in the iliac
crest also known as the pelvis. Under other circumstances, this can also be extracted from the rib
or another region of the spine. Very few spine procedures include autograft harvesting. This is
attributed to the morbid nature of the bone graft harvest procedure as well as an ever increasing
number of better and more reasonable alternatives to autograft.
Advantages, disadvantages and Considerations of autograft
As a result of bearing all the features that are required for a solid bridge to grown, autograft is
perceived to be the gold standard in the achievement of a successful and solid spine fusion.
Among those characteristics include:
 It is composed of osteophytes which are the bone growing cells as well as bone-growing
portions also called bone morphogenic proteins which are all used in facilitating the
growth of new bone in the patient.
 It offers the spinal fusion with calcium scaffolding which forms a base on to which the
new bone grows (Williams, 2014)

There are two main benefits or advantages that are associated with autograft:
 There is no risk of transmission of disease
 There are higher chances of success of fusion versus allograft (cadaver bone) as well as
some types of substitutes for bone graft
Risks and chances of complications that are associated with carrying out any surgical
procedure is the main disadvantage of autograft. Among such risks include bleeding, injury to
the nerves as well as surgical wound problems for example infection (Guda, 2017).
Still, there is a risk of chronic pain associated with autograft procedures at the site of harvest
of the bone. The incidence of ongoing pain is a factor of the technique adopted in the harvesting
for the case of posterior incisions. The incidences of such pain are usually very low in actual
practice. Research has established that site pain of ongoing graft is relatively higher in separate
incision rather than using the same incision. The pain is worse in cases where the graft requires
three cortical surfaces for example a structural bone graft that is to be use on an interbody fusion
(Gunzburg, 2012).
Limitation in the supply of this type of bone graft is as well a disadvantage. Under some
circumstances, bone graft may need to be supplemented with some bone graft substitute form in
order to meet the required expectations.
Allograft Bone in Cervical Spinal Fusion Surgery
Allograft is a bone that has been extracted from a cadaver by a tissue bank for the purposes of
medical procedures. Allograft can be prepared in a number of various forms among them chips
for use in a spine fusion. In as much as allograft bone only offers a calcium scaffolding, has not
any bone growing cells or proteins that grow bones needed to ignite growth of a new bone and