Research On Construction Of Diced Cartilage Grafts In Customized Shapes

?Background?Cartilage is a kind of commonly used transplantation material in plastic surgery,especially in total nasal reconstruction,auricular reconstruction and other skin organ reconstruction,in which is indispensable.In the traditional autologous cartilage transplantation,solid cartilage has to be carved and combined according to the desired shape after it is obtained.Solid cartilage has a problem of warping,which often results in retrimming surgery,thus affects the final surgical outcomes.To avoid warping,diced cartilage,a kind of cartilage finely diced in pieces 0.5-2 mm,was introduced into clinic use.Diced cartilage was reported early more than 60 years ago,which was effective in skull defect repair,maxillofacial filling,even auricular reconstruction and femoral head reconstruction by means of hollow metal molds.However diced cartilage was soon replaced by synthetic materials,such as silicon,polyethylene and polytetrafluoroethylene.Synthetic materials once were widely used because of several advantages,but they also had some problems,such as infection,rejection and extrusion.In recent 10 years,diced cartilage has been widely used again.Besides being injected for filling,more commonly,diced cartilage are wrapped in oxidized cellulose,autologous fascia or accelular dermal matrix(AlloDerm),or combined by fibrin glue,that make diced cartilage facilitating transplantation.Diced cartilage is one sort of near-perfect graft material,of which there are several advantages,such as diverse donor sources,easily preparation,malleability and less liability of warping when was compared with solid cartilage.Diced cartilage also has advantages of autolo gous origin,no rejection,and low infection and extrusion rate,when was compared with synthetic materials.Nevertheless,there are still quite some problems following diced cartilage graft before it's widely used: 1,Whether the mechanical strength of diced cartilage can meet the clinical requirements? There have been no published studies on the strength of diced cartilage grafts yet.2,The metal mold has been abandoned for high price and infection rate while synthetic materials bring more options.Can synthetic materials be used for hollow mold to construct diced cartilage grafts in customized shapes? 3,The current rib cartilage obtaining procedure will result in relative large injury and the diced cartilage preparing procedure of hand cutting cartilage with surgical blade is highly time consuming.?Objective?Establish a rabbit costal cartilage anatomical and biomechanical model.Constructing diced cartilage grafts in customized shapes by using polymer hollow molds.The mechanical properties of mold formed diced cartilage grafts were examined.The differences of diced cartilage grafts' mechanical properties between different timings postoperation and different mold materials are observed.Moreover,for minimizing the chest scar caused by current rib cartilage obtaining procedure,a method of obtaining cartilage chips via minimal invasive incision is investigated.?Methods?(1)For establishing a rabbit costal cartilage model,8 New Zealand white rabbits were included in this study.The structure and permutation of thoracic ribs and costal cartilages were observed.Length and transverse diameter of each rib cartilage was measured,tensile and compressive test was taken on the 4th to 7th rib cartilage.(2)Electrospinning technology was used for PLGA absorbable mold preparation,and hot pressing technology was used for HDPE nonabsorbable mold preparation.24 male New Zealand rabbits were divided into tensile test group and compressive test group.Cartilage was harvested from the 6th,7th and 8th rib.Four ca rtilage segments was prepared from the 7th rib,one for mechanical test and the other transplanted to abdominal subcutaneous pockets as well as nonabsorbable mold formed diced cartilage(NDC)and absorbable mold formed diced cartilage(ADC)grafts.At 1 month,3 months and 6 months after operation,each type of graft was harvested and sent to take tensile and compress test.(3)After imitating and comparing with the existing rotary cutting instruments,a digital model of rotatory cutter head was built up in AutoCAD.Then the rotatory cutter head was made by means of metal 3D printing technology.With combinations with cutter main parts,cannula and power system,an electric cartilage rotatory cutter device was assembled.Experimental operation by using the invented rotatory cutter in cadaver and swine is assigned to test the possibility of the device.Cartilage product from this rotatory cutter device was sent for chondrocyte isolation and Dead/Live cell counting.With trypan blue staining,dead cell would be stain to blue and the live cell would not.?Results?(1)Most rabbits have 12 pairs of ribs as well as human;about 12.5% of the rabbit have 13 pairs of ribs.The 1st to 7th rib cartilage directly connected to the sternum,called True Rib;the 8th to 10 th rib cartilage are not directly connected with the sternum,but point to the xiphoid with ligaments connecting at the medial part,called False Rib;The 11 th to 13 th rib are free in the abdominal wall,known as the Floating Rib.The length of rib cartilage gradually increased from 1th to 7th rib,and declined from 8th to 13 th.AS come to the transverse diameter of each costal cartilage,True Rib is thicker than False Rib and Floating Rib.The compressive strength of rabbit rib cartilage is 12.73 ±1.06 MPa on average,the modulus of elasticity 27.64 ±1.88 MPa,and ultimate strain 63.77%±2.67%.The tensile strength is 3.78 ± 0.48 MPa on average,the elastic modulus 25.94 ± 4.09 Mpa,ultimate strain 19.79%±2.38%.(2)Successfully constructed diced cartilage grafts by previously made PLGA and HDPE molds.The individual cartilage pieces would become a solid after be transplanted.All types of cartilage grafts had weight gain postoperation,especially,the weight gain of diced cartilage were more higher.The PLGA molds significantly swelled at the first month,of which weight more than doubled.In the compressive test group,the modulus of elasticity of ADC at the 1st,3rd and 6th month postoperation were 6.63±1.20 MPa,8.00±1.94 MPa,10.50±1.82 MPa respectively,while those of NDC were 5.07±1.00 MPa,10.61±1.80 MPa,13.11±2.59 MPa respectively.There is no significant difference between ADC and NDC at the same time(p>0.05).The modulus of elasticity of solid cartilage segment was 28.14±1.96 MPa before operation,and 29.11±3.00 MPa,32.45±2.79 MPa,32.70±2.56 MPa at the 1st,3rd and 6th month postoperation respectively.In the tensile test group,the ultimate tensile stress of ADC at the 1st,3rd and 6th month postoperation were 0.41±0.06 Mpa,0.91±0.25 MPa,1.24±0.11 MPa respectively,and those of NDC were 0.15±0.05 MPa,0.85±0.18 MPa,.09±0.10 MP.There was significant difference between ultimate tensile stress of ADC and that of NDC at the 6th month postoperation.Histological examination showed that diced cartilage was encapsulated by fibrous tissue,and the collagen content was decreased when time prolonged.Compared with the solid cartilage graft,diced cartilage grafts showed more inflammation.(3)The most effective rotatory cutter head was chosen from five options,and then a rib rotatory cutter device was invented,which can directly cut cartilage pieces from rib cartilage via minimal invasion while be drove by electromotor or hand.This device has been applied for invention patent,the application number is 201510023304.4.As to the viability of chondrocytes,there was no significant difference between the cartilage cutted by rotatory cutter and that by surgical blade.?Conclusion?First established a rib cartilage anatomical and biomechanical model in rabbit.Constructed diced cartilage graft by absorbable mold and nonabsorbable mold.The strength of diced cartilage graft was low at the early stage after operation,but increased when time prolonged.The compressive strength of diced cartilage is better than tensile strength.It suggested that diced cartilage be used in where high strength is not needed,for instance,reconstruction of tissue defects.AutoCAD and 3d printing were used to make rotatory cutter device.This device can easily harvest cartilage pieces from cadaver and swine,which approved the method of rotatory cutting cartilage via minimal invasive incision.