Claims:1. A method for fabricating a cranial plate, comprising:
receiving, data related to the defect area from a patient or a surgeon;
creating, a virtual model and a suitable guide model of required part in three-dimension;
sending, the said virtual model to the surgeon;
printing, the cranial plate pattern along with the host model in three-dimension by using thermoplastic on acceptance from the surgeon;
comparing, the said printed cranial plate with approved virtual design for fitment and anomalies;
fabricating, a custom mold using low cost gypsum powder by considering the said thermoplastic material as the master; and
injecting, a bio compatible medical grade PEEK into the fabricated mold with 100-200 bar through an appropriate gate system.

2. The method according to claim 1, wherein the custom mold made of hybrid gypsum material is fabricated custom size with reusable metal base.

3. The method according to claim 1, wherein the use of gypsum type IV material for investment molding of the pattern is dewaxed and finished that reduces the cost.

4. The method according to claim 1, wherein a metal casing made with two halves are suitable for preparing any types of cranium size and form factors with appropriate draft angle.

5. The method according to claim 1, wherein large holes are milled on both halves of the metal casing for ease of pouring investment material and divesting.

6. The method according to claim 1, wherein the injection molding based technique is used to ensure uniformity of material spread and strength.

7. The method according to claim 1, wherein the speed and force applied in the injection process is controlled by microprocessor.

8. The method according to claim 1, wherein the PEEK implants are more comfortable and material is less dense and light weight.
, Description:Technical Field of the Invention

[0001] Present invention relates to a method for fabricating a cranial plate. It relates to a method for fabricating a customized implant by 3-dimensional designing, printing and injection molding processes.

Background of the Invention

[0002] Cranioplasty is a surgical intervention to repair defects or deformity on human skull or bone that may be due to congenital abnormalities injuries or diseases. It involves surgical repair of defect or imperfection in the skull by implanting pre-designed and shaped biocompatible cranial implants. The major purpose of cranioplasty surgery is to improve the symmetry and shape the defected area and protect the inner bone tissues. From ancient days, several types of materials such as precious metals, Methyl methacrylate, Base metal alloys, titanium and other polymers were used for and gourds are used for cranioplasty.

[0003] Among the materials mentioned, PEEK has an edge over then others in terms of holding capacity, strength and its closeness to bone anatomy. It is a Bio-compatible thermoplastic polymer which matches the physical characteristics of Bone in terms of texture and density, hence will be the best material for customized cranial implants. Also, PEEK is radiolucent that eliminates the occurrence of artifacts during CT or MRI. PEEK is clearly advantageous over the other polymers in its holding capacity and strength.

[0004] Currently there are different number of manufacturing routes for fabricating PEEK cranial customized implants such as Thermo forming, CNC milling, Injection molding, 3D printing etc. Injection molding process is time tested in producing the cranial implants with high dimensional accuracy without shrinkage, the product is highly compacted, homogenous there by leading to desired physical properties consistently with high impact, compressive and the tensile strengths.

[0005] The 3D printing method is most cost-effective solution for accuracies up to 0.25mm, this works on an additive principle by laying down material in layers and a plastic filament or metal wire is unwound from a coil and supplies material to produce a part. The other available method is Selective Laser Sintering (SLS) 3D printing which is an additive manufacturing technique that uses a laser as the power source to sinter powdered material (typically metal), aiming the laser automatically at points in space defined by a 3D model and binding the material together to create a solid structure. The major problem of the technology is the fabricated parts can be porous, have a rough surface depending on the used materials and causes shrinking and warping.

[0006] The prior art U.S. Patent No. 2006094951 discloses a method a computer aided design method for producing an implant for a patient prior to operation. The method comprises of generating data that represent an area that will receive the implant, designing the implant and fabricating the implant. This invention mainly focuses on the fabrication of implant directly from a rapid prototyping technology but not from molds or 3D data of medical images.

[0007] Another prior art U.S. Patent No. 2011144752 discloses a method for manufacturing customized implant by using a computer-based imaging and rapid prototyping-based manufacturing technique. The customized implant is formed using a solid free-form fabrication method comprising sequential layers of polyether ketone powder. This prior art focuses on direct manufacturing of implants but not on manufacturing of molds for implants.

[0008] Thus, the above mentioned prior arts are not capable of producing implants by using mold/patterns from biocompatible plate. Therefore, a need raises to produce an implant formed by a mold with desired shape by using injection molding process that ensure uniformity of material spread and strength in a lesser time and cost.

Brief Summary of the Invention

[0009] The present invention recognizes the limitations of the prior art and the need for systems and methods that can aid users in a manner that overcomes these limitations.

[0010] The principal object of the present invention is to develop a method to fabricate cranial plate for cranioplasty.
[0011] According to a first aspect of the present invention, a method for fabricating a cranial plate is disclosed. The method comprises steps of receiving the 3D data related to the defect area, creating a virtual model and a suitable guide model of required part in three-dimension and then the created model is crosschecked and confirmed with host model virtually.

[0012] In accordance with the first aspect of the present invention, further the method comprises steps of comparing the printed cranial plate with approved virtual design for fitment and anomalies. Fabricating a custom mold using low cost hybrid gypsum powder in metal casing, making a customized single shot split mold and injecting a bio compatible medical grade PEEK into the fabricated mold with suitable pressure through an appropriate gate system. The method employs the hot mold technique with long hold time allowing the material to form its semi crystalline structure to obtain full physical, chemical and thermal properties.

[0013] In accordance with the first aspect of the present invention, in the disclosed method the custom mold is created by using low cost hybrid gypsum material that is fabricated in a custom sized reusable metal base.

[0014] In accordance with the first aspect of the present invention, the reusable metal base holder gives as much as needed speed for this procedure and the use of gypsum type IV material for investment molding of the pattern that is de-waxed and finished reduces the cost to a great extent.

[0015] In accordance with the first aspect of the present invention, wherein the injection molding based technique is used to ensure uniformity of material spread and strength.

[0016] In accordance with the first aspect of the present invention, wherein the use of PEEK implants is more comfortable due to the material dense and light weight.

[0017] In accordance with the first aspect of the present invention, wherein reuse of reusable metal base helps in quick turnaround time and lower cost of manufacturing.

[0018] In accordance with the first aspect of the present invention, wherein use of GYPSUM powder will help in easily accessible base material and a lower cost due to replacing a metal core with GYPSUM powder for the corresponding load.

Brief Description of the Drawings

[0019] Various objects and advantages of the present invention will become apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments, in conjunction with the accompanying drawings, wherein like reference numerals have been used to designate like elements, and wherein

FIG. 1 illustrates a process flow depicting a method to fabricate cranial plate for cranioplasty according to the present invention.

FIG. 2a and 2b illustrates a perspective view of metal casing depicting the process of preparing the custom mold by using the metal casing according to the present invention.

FIG. 3 illustrates a block diagram depicting the injection process according to the present invention.
Detailed Description of the Invention

[0020] The present invention is directed towards a method of fabricating cranial plate. Referring to the drawings, wherein like reference numerals designate identical or corresponding systems, preferred embodiments of the present invention are described.

[0021] In accordance with the preferred embodiment of the present invention, the method for fabricating cranial plate in cranioplasty process is disclosed. The process of fabricating cranial plate involves multiple steps like reconstructing the virtual design of defect area by using 3D, once virtual design is accepted the cranial plate pattern is printed in thermoplastics, custom mold making by using hybrid gypsum materials and reusable metal casing and injecting the bio compatible medical grade PEEK in to the mold.

[0022] This injection molding process requires the use of an injection molding machine, raw plastic material, and a mold. The plastic is melted in the injection molding machine and then injected into the mold where it cools and solidifies into the final part. Bio compatible medical grade Polyetheretherketone (PEEK) is a semi-crystalline polymer that is radiolucent, chemically inert and can be sterilized by steam or gamma irradiation. It resembles titanium in its perfect intraoperative fitting and its resistance to aggressive sterilization procedures (heat and ionizing radiation). The elasticity and energy-absorbing properties of PEEK match closer to bone than the mechanical properties of titanium.

[0023] The above-mentioned process will shorten time, improve quality and reduce cost of custom implants for non-load deformities especially in cranioplasty.

[0024] Referring to the drawings, FIG. 1 illustrates a process flow 100 depicting a method to fabricate cranial plate for cranioplasty according to the present invention. A method to fabricate cranial plate for cranioplasty comprises the following process, at the start the data like MRI or CT scan, etc related to the defect area is received 102. The collected data is in Dicom files that are used to select the area of interest and a surface is generated upon that surface the defected part is reconstructed virtually 104 then the virtually design plan is sent to the surgeon for approval.

[0025] Once the virtual design is accepted, the cranial plate pattern along with the host model is first 3D printed 106 in thermoplastic and checked for fitment and compared with approved virtual design for anomalies. After this process, the thermoplastic material is taken as the final piece of the implant model. This final design is used as final pattern to create PEEK injection molded implant using custom split mold hot mold injection technique 108. A custom split mold 108 is created using low cost gypsum powder that is set on a custom sized reusable metal casing as shown in Fig. 2. The reusable metal casing gives as much as needed speed to this procedure and the use of gypsum type IV material for investment molding of the pattern that is de-waxed and finished reduces the cost.

[0026] The prepared mold 108 is heated to 400 degrees centigrade and held for long enough sinking time that is appropriate for the material. The Peek material is loaded in the Aluminum cartridge and inserted into the heating chamber in injection molding machine 110. The heating is set for 400 degrees and adequate holding time as per pre- calculated measure, is given for homogenous melting of material. The mold is shifted from furnace to the injection-molding machine and clamped securely. The injection process is initiated to inject molten PEEK in Al cartridge into the mold with 10 to 12 bar pressures. The speed and force of the injection is controlled by microprocessors as shown in Fig. 3. The injection pressure is maintained for long enough time, allowing PEEK to attain its semi crystalline structure.

[0027] FIG. 2a and 2b illustrates a perspective view 200a & 200b of metal casing depicting the process of preparing the custom mold according to the present invention. A metal casing 200a is made of two halves 202a & 204a that is milled out of metal block in the dimensions that are suitable for preparing any types of cranium size and form factors with appropriate draft angle. The orientation mechanism is created to align both the halves 202a & 204a with fixating screws 206a in all the four corners as shown in Fig. 2a.

[0028] The mould box as shown in Fig. 2b is provided with an injecting gate of 8 to 10 mm that is created in the center of one half of the casing 202a or 204a. A large cavity 208b is milled on both halves of the metal casing 202a & 204a for ease of pouring investing material and divesting. When the final thermo plastic pattern is attached with a spur in the center of convex pattern and aligned to the gate in one half of the metal casing cavity 202a or 204a. The casing cavity 202a or 204a is filled with Type IV gypsum material with care to avoid air trapping under gentle vibration.

[0029] FIG. 3 illustrates a block diagram 300 depicting the injection process according to the present invention. In this process the final thermoplastic pattern is attached with spure in the center of the convex pattern 302 and aligned to the gate in one half of the metal casing cavity. The casing cavity 304 is filled with Type IV gypsum material with care to avoid air trapping under gentle vibration. After the investment material is set the surface is coated with separate media like cold mould seal or Vaseline. The second half of the metal casing 304 is aligned with the first half using orientation pins and fixation screws for tightening.

[0030] After filing the casing 304, the metal mold is heated in boiling water for three minutes and then the fixation screws of the both halves are removed to separate the metal casing 304. The thermoplastic pattern is removed and the mold cavity is cleaned with hot water to remove the entire residue. Then the mold cavity is inspected for any defects and corrected if necessary. After this the two halves were reassembled to create custom mold for injecting PEEK 306. The custom mold is heated in a furnace 308 up to 400 degrees centigrade and kept for long enough sinking time appropriate for the material.

[0031] In the meantime, the PEEK material is loaded in the Aluminum cartridge 310 and inserted into the heating chamber 308 in injection molding machine 306. The mold 312 is then shifted from furnace 308 to the injection molding machine 306 and clamped securely by using clamping unit 314. The injection process is then initiated to inject molten PEEK in Aluminum cartridge into the mold by using 10 to 12 bar pressures. The speed and force of the injection process is controlled by microprocessor 316. The injection pressure is maintained for long enough time, allowing he PEEK to attain its semi crystalline structure.

[0032] After the mold is cooled the fixation screws were unscrewed and both the halves of the casing were separated. Then the investment material is removed from the casing using the divesting holes, the final molded PEEK Implants is separated from the sprue and sandblasted with aluminum oxide under sufficient pressure, to clean from investment material.

[0033] In one embodiment, the usage of PEEK implants is more comfortable due to its dense molding and lighter weight. The PEEK implants do not create artifacts on CT or MRI because they are translucent to x-rays and are nonmagnetic. They do not conduct temperature and does not have negative ramifications on the brain.

[0034] The embodiments of the present invention have been shown and described, it will be apparent those skilled in the art that changes and modifications may be made therein without departing from the invention in its broader aspects. The aim of the appended claims, therefore, is to cover all such changes and modifications that fall within the true spirit and scope of the invention.