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SPECIALIZED BIO IMPLANTS

3.5.1 TOTAL AND PARTIAL KNEE REPLACEMENT

Among the knee replacement procedures, about 90% is the total knee replacement. During TKR procedure, the repair of the knee joint is by covering the thighbone with metal and encasing the shinbone with a plastic frame. The procedure makes replacement of the rough and irregular surface of the worn bone with a smooth surface. The undersurface of the kneecap will be replaced with a plastic surface to decrease the pain and provide a smooth functional joint. The process is to remove some of the parts of bones and cartilage. In case of a partial knee replacement, only the part of the knee that’s damaged or arthritic will be replaced. It requires only smaller operation procedure and involves less bone and blood loss and also produces less pain. These are the advantages to this approach. Partial knee replacement patients will get a faster recovery time compared to TKR procedures. The disadvantage of the process is that there can be arthritis developed which needs another surgeiy in the parts of the knee that are not replaced [70, 71].

3.5.2 HIP JOINT REPLACEMENT

Joints in any parts of the body are important components of the skeletal system. It is positioned at bone joints for the transmission of loads from bone to bone by muscular action; also, there can be some relative motion of the component bones. Tissue of a bone is complex in nature and the composite consisting of soft and strong protein collagen and brittle hydroxyapatite. Bone is an anisotropic material with mechanical properties that differ in the longitudinal (axial) and transverse (radial) directions. The cartilage is a coating on each connecting surface, which consists of body fluids that lubricate and provide an interface with a very low coefficient of friction that provides the bone sliding movement. The human hip joint occurs at the junction between the pelvis and the upper leg (thigh) bone, or femur. Large rotary motion is allowable at the hip by a ball-and-socket type of joint. The top of the femur terminates in a ball-shaped head that fits into a cuplike cavity within the pelvis.

There are national and international standards on which the orthopedic community is taking guidelines. For better mechanical properties of medical-grade UHMWPE is preferred, medical-grade UHMWPE is as per the standard ASTM F-648 and ISO 5834. It contains the specifications of the unconsolidated resin powder and consolidated stock material. Processing to be done in various stages to produce highly crosslinked polyethylene for hip and knee bearings. These steps are to promote crosslinking by an irradiation process. Residual stresses are removed by thermal irradiation after the processing step which will increase the level of crosslinking. There will be also a sterilization step given to those implants. The properties of UHMWPE are less influenced by processes of irradiation, thermal processing, and sterilization [72, 73].

3.5.3 POLYMERS IN DENTAL IMPLANTS

There are methods to replace a missing tooth by the use of many materials as an implant. Great advancements occurred in the field of science and technology related to the materials for dental implants [74]. There are many types of polymers like ultrahigh molecular weight pu, polyamide, polymethylmethacrylate, polytetrafluoroethylene, and pu used as materials for dental implants. There is a great amount of researches and advancements in the field of biomaterials available for dental implants. Newer materials came up like zirconia, roxolid, and surface-modified titanium implants. These materials have the satisfactory functional requirements and also esthetically pleasing. The earlier material, methyl methacrylate resin implants became failures in many cases [74—76]. In 1969, Hodosh reported that polymers were biologically useful substances [77]. Polymethacrylate based tooth-replica implants was the polymer dental implant developed by Milton Hodosh. When natural tooth replacing polymers are found to be the ideal material for the restoration of function and appearance [78].

Polymers were selected for many reasons [78]. The physical properties of the polymers can be easily altered and compositions may be changed easily depending upon the applications. Polymers can be changed into porous or softer form, polymers can be processed can have larger productivity. They do not generate microwaves or electrolytic currents as in the case of metals. It shows fibrous connective tissue attachment, it can be easily analyzed compared with metals and give better esthetics. Disadvantages are like inferior mechanical properties and poor adhesion to living tissues.

3.5.4 NEURAL IMPLANTS

Electrical circuitry is implanted into the nerve cells to activate the parts and structures of the nervous system are called neural implants. Many experiments in the 1960s, material sciences, and the progress in medical and neuroscience lead to advancements in therapies of neurological diseases. This will lead to repair and rehabilitation of lost functions of human systems [80, 81]. Neuromodulation is the process of stimulation of the central nervous system (CNS). These structures which will be modulating the nerve excitability and neurotransmitters release [80]. Patients suffering from Parkinson’s disease (PD) will be cured by suppressing tremor and movement disorders by deep brain stimulation. Similarly, treatment for epilepsy and other psychiatric diseases like depression and obsessive- compulsive disorder are done with the help of vagal nerve stimulation [82, 83]. These treatments are now expanded to psychiatric diseases and many more applications. Some of them are in the development stages in preclinical and clinical trials.

Motor implants to restore grasping [85] stance and gait [86, 87] as well as ventilation [88] by the electrical stimulation of the diaphragm have been developed and introduced into preclinical studies or even as commercial products to the market. Lower number of patients benefit from this system due to some technical issues. There is a limited number of studies about the performance of the implants in patients due lack of availability. Genitally deaf children and adults who have lost their hearing at a later point in life [88] have been implanted and were able to hear and to communicate with these implants. Developed implants can connect to the brain stem [89] and midbrain auditory structures [91] when tumors have destroyed the pathways from the ear to the cortex, will restore sound perception.

The retinal process to restore vision using implantation of complex electrical stimulators into the eyes of blind people is one of the modem technological progresses. This gives as a miniaturization technology helps the development such implants [80, 92]. Benefits and demerits have to be studied clearly and carefully in any medical and surgical treatment. It is also important that the patient should give the final consent for implantation. All neural implants approved as a medical device have to fulfill general requirements. They should make any hann to the body and should stay stable and functional over a certain period of time as decades. Proper design of any neurotechnical interface is the major key challenge for the creation of any neural implant. Many electrical sites have to give proper close contact with neural tissue to activate the nerve cells. Nerves are very delicate and soft tissue gets damaged by hard materials when forces due to movements of the implants. Polymers are found as the optimal material class. Because there is no response to implantation, gives long-tenn stability in any hostile environment, low material stiffness, and good electrical insulation compared to metallic conductors [93-98].

3.5.5 IMPLANTS HELPS IN CONTROLLED DRUG RELEASE

Biodegradable polymers can work for shorter times and slowly degrade if there are desirable conditions under the controlled mechanism, into products which are easily eliminated in the body’s metabolic pathways [97]. Biodegradable polymers are more popular than no degradable delivery system, as they are eventually absorbed or metabolized and removed from the body by excretion. This method totally eliminates the need for surgeiy for the removal of the implant after the completion of the therapy.

The major advantage of this system include administration of a therapeutic drug in a controlled mamier at the required delivery rate, maintaining the concentration of drug within the optimum therapeutic range for a prolonged treatment duration, minimum side effects and needs of frequent dosage is minimized. Controlled drug delivery systems are effectively used to control of hypercholesterolemia [100]. LDL cholesterol biosynthesis can be controlled by slow release of Simvastatin for a prolonged period of time which also gives prevention of coronary heart disease.

Anticancer drugs have poor performance against solid tumors in which drug penetration into the tumor is prevented. Toxicity is a limiting factor for the dose to be increased. Polymeric biodegradable poly-L-lactic acid (PLA) and poly(L-lactic acid-co-glycolic acid) (PLGA) copolymer can be administrated locally as an implant carrying an anticancer drug may a suitable method of concentrating the drug near the tumor site. S. O. Adeosun et al. studied that PLA can degrade hydrolytically and suitable fillers can be incorporated in the implants to reduce the cost [101]. There is a large difference in elastic modulus between the metal fixture and the bone. This can cause residual stress in the screw holes and also give adverse effect of rigid plates on bones and get the stress on the implants. PLA like biopolymers can solve these issues and can replace metals.

METHODS FOR MAKING BIO IMPLANTS

3.6.1 3D PRINTING

Shortage of donor organs remains as a major concern in the medical [102] field and researchers are continuously searching for new methods to mimic or even replicate organs [103]. In such circumstances one of the best solution found out by researchers are the use of Bio-implants. A bio-implant is an implant with a biological component that is placed in a cavity of the human body for 30 days or more [104]. It can restore, support, or enhance the functions of the human tissues. It can also maintain the compatibility and conformity with the tissues along with the acceptability by the body. It gives the strength to the materials and the intactness of the implant. Biological materials such as cells, protein, etc., using bioprinting are prepared from biological implants. 3D printing of implants can be considered as organ printing. It uses ideally autologous cells to reduce the chances of rejection by the body. This can also reduce the waiting time for the replacement organ.

Two components are needed for making biological implants. A bioprinter containing materials such as living cells which predetermine the 3D foim for creating the organ and biochemical reactor in which the manufactured organ can mature in vitro. Organ printing is defined as a computer-aided processing which cells or cell-laden biomaterials are placed in the form of aggregates, which then serve as building blocks and are further assembled into a 3D functional organ. Solid objects with complex shapes are manufactured by additive manufacturing methods and referred as 3D printing. This is a method used to manufacture objects by making layers of material arranged one over the other to get the finished article. Fused deposition modeling (FDM) is an additive manufacturing method. Thin strands of molten thermoplastics materials are laid down on each other using a print-head controlled by a computer-aided design (CAD) software. The printed object will form when the material gets solidified over the print surface.

Acrylonitrile-butadiene-styrene (ABS) resin can be used in FDM printers and personal desktop printers with ABS but now shifted to PL A due to its bio-compostability, pleasant smell as well as low shrinkage and good print- ability. PLA based materials used in FDM printers are not perfect. Printing fine details could be very much challenging due to melting and flowing is affected by temperature and viscosity of the melt. PLA based materials has the drawback as it weak in temperature resistance, which can cause deformation of printed objects under elevated temperatures may be during storage and shipping or usage.

  • 3D bone structure requires porosity, for the flow of nutrients, blood, oxygen, and mineral. Production of such structure remains a problem using conventional methods. Blends made up of PLA and poly-e-caprolactone (PCL) is a suitable material that gives properties required. Bone grafting method is used for the repair of bones that are severely damaged or lost completely. Arthritis, traumatic injury, and surgery for bone tumor are veiy common in the senior people. New researches for the design of new materials for the wide application are veiy much necessaiy. There can be permanent or temporary bone replacement depending on the properties of the material. A permanent bone replacement can use when a bone is missing due to some conditions. A temporary implant is used when the implant could be removed when the treatment is completed [101]. The selection will be depending on various factors, the purpose clinical application, defect area size, mechanical, and strength properties, material availability, and required bioactivity, material handling, cost aspects, and ethical concepts [105,106].
  • 3.6.2 ELECTROSPINNING

Electrospinning is one of the nanotechnologies with the largest diversity of applications. This can be used for the processing of a wide range of basic materials and the production of a diversity of electrospun nanofibers assembly organization. It helps in making of ID to 3D products and diversity of forms with different arrangements [i07—111]. The nano fibers obtained by electrospinning can be of polymeric, ceramic, or composite nature. Each of these groups has a wide portfolio of applications (Table 3.2) [113-115]. Biomedical applications of the polymeric nanofibers obtained through electrospinning are multiple [116, 117].

TABLE 3.2 Classification of Electro Spun Products

Electrospun

Nanofibers

Polymeric

Biomedical

Regenerative medicine, tooth implants, bone, blood vessel implants, neural tissue engineering, structural tissues, such as cartilages, muscles, ligaments, dressings, meshes, medial prostheses.

Structures for controlled drug release, cosmetics, drug delivery, and nanofibrous drug delivery system, polymer-drug blend fiber system, hemostatic devices.

Polymeric

Industrial

Filtering mediums, separating membranes, nanosensors

Ceramics

Biomedical/

Industrial

Biomechanical devices, biosensors, bone reconstruction, catalysts, biosensors, membranes, storage batteries.

Aerospatiale products, finishing treatments by chemical, storage devices for information

Composites

Regenerative

Medicine

Implants

The most common technique of electrospinning is by using the electrostatic production method of nanofibers. Electric power is used to make polymer fibers with diameters 2 nm to several micrometers. Preparation is done from polymer solutions or melts. It is a versatile method to produce continuous fibers on a scale of nanometers. It is difficult to achieve using any other standard spinning techniques. It is a very simple way of preparing nanofibers. There are several parameters that will influence the formation and structure of nanofibers prepared using electro spinning [118].

 
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